G06 Aryclic Production

FINAL REPORT 6 May 2009

70000 metric ton Acrylic Acid Production Plant

Prepared by: Jackson Toh Lee Sin Wei Lee Yu Wee Lim Yee Chiat Mohd Izham bin Ibrahim

KEK 050019 KEK 050035 KEK 050036 KEK 050039 KEK 050042

Department of Chemical Engineering University of Malaya 50603 Kuala Lumpur

TABLE OF CONTENT Content Chapter 1:

Pages

Introduction

1.1

Biodiesel Production

1-1

1.2

Glycerol Produced from Biodiesel Plant

1-1

1.3

Potential Product of Glycerol 1.3.1 Process Route 1.3.1.1 Acrylic Acid via Acrolein 1.3.1.2 Propylene Glycol 1.3.1.3 Hydrogen 1.3.1.4 Epichlorohydrin 1.3.2 Comparison of the Products

1.4

1-2 1-2 1-2 1-3 1-3

Introduction of Acrylic Acid 1.4.1 Description 1.4.2 Chemical Identification 1.4.3 Potential Usage of Acrylic Acid 1.4.4 Physical Properties of Acrylic Acid

1.5 References Chapter 2:

1-4 1-4 1-4 1-5 1-6

Process Description of Acrylic Acid Production

2.1

Process Principle

2-1

2.2

Unit Operation Description 2.2.1 Reactor 1, CRV-100 2.2.2 Separator, V-100 2.2.3 Reactor 2, CRV-101 2.2.4 Quenching Tower, T-100 2.2.5 Extractive Distillation Column, T-101 2.2.6 Decanter, X-100 2.2.7 Solvent Recovery Distillation Column, T-102

2-1 2-2 2-2 2-2 2-3 2-3 2-3

2.3

Process Description

2-3

2.4

Process Flow Diagram 2.4.1 Flow Description

2-6 2-7

2.5

References

2-10 i

TABLE OF CONTENT Content Chapter 3: 3.1

Plant Economic & Feasibility Study

Market Analysis 3.1.1 Global Demand 3.1.2 Local Demand 3.1.3 Forecasted Future Demand 3.1.4 Production of Acrylic Acid 3.1.5 Major Manufacturer of Acrylic Acid

3.2

3.3

3.4

3.5

Pages

3-1 3-2 3-2 3-2 3-3

Location of Acrylic Acid Plant 3.2.1 Site Selection 3.2.2 Plant location

3-3 3-5

Government Policy-Taxation 3.3.1 Company Tax 3.3.2 Real Property Gain Tax 3.3.3 Sales Tax 3.3.4 Import Tax

3-6 3-7 3-7 3-7

Economic Evaluation

3-7

3.4.1 Purchased Equipment 3.4.2 Total Capital Investment 3.4.3 Total Product Cost 3.4.4 Profitable Analysis

3-8 3-9 3-10 3-11

References

3-13

ii

TABLE OF CONTENT Content

Pages

Chapter 4: Environmental, Safety and Health 4.1

4.2

Environment 4.1.1 Law and Regulation 4.1.2 Waste Water Treatment 4.1.3. Gas Emmision and Treatment

4-1 4-1 4-3

Health 4.2.1 Effect to Human 4.2.1.1 Acetic Acid 4.2.1.1.1 Health Hazard

4-5

4.2.1.1.2. Exposure Limits

4-5

4.2.1.2 Acetol 4.2.1.2.1 Health Hazard

4-5

4.2.1.2.2 Exposure Limits

4-5

4.2.1.3 Acrolein 4.2.1.3.1 Health Hazard

4-5


4-6

4.2.1.4 Acrylic Acid 4.2.1.4.1 Health Hazard

4-6


4-6

4.2.1.5 Carbon Dioxide 4.2.1.5.1 Health Hazard

4-6


4-7

4.1.1.6 Glycerol 4.2.1.6.1 Health Hazard

4-7


4-7

iii


Pages

Chapter 4: Environmental, Safety and Health 4.2.2 Effect to Environment

4.3

4.2.2.1 Acetic Acid

4-7

4.2.2.2 Acrolein

4-7

4.2.2.3 Acrylic Acid

4-7

4.2.2.4 Glycerol

4-8

Safety 4.3.1 Hazard Introduction

4-8

4.3.2 Handling and Storage of Hazardous Chemical

4.4

4.3.2.1 Acetic acid

4-9

4.3.2.2 Acetol

4-9

4.3.2.3 Acrolein

4-9

4.3.2.4 Acrylic Acid

4-10

4.3.2.5 Glycerol

4-10

4.3.2.6 Isopropyl Acetate

4-10

4.3.2.7 Thermal Oil

4-11

References

4-11

iv


Pages

Chapter 5: Mass and Energy Balances 5.1

Introduction

5-1

5.2

Comparison between Manual Calculations and HYSIS Result 5.2.1 Approach of Manual Calculation 5.2.2 Approach to HYSIS Simulation

5-1 5-1

Mass Balance Results 5.3.1 Feed rate calculation 5.3.2 Mixture of Stream 4 and 16 5.3.3 CRV-100 5.3.4 V-100 5.3.5 Purge Stream from Stream 10 5.3.6 Mixture of Stream 14, 15 and 16 5.3.7 Mixture of Stream 20, 21 and 22 5.3.8 CRV-101 5.3.9 Mixture of Stream 26 and 34 5.3.10 T-100 5.3.11 MIX-100 5.3.12 T-101 5.3.13 X-100 5.3.14 T-103

5-1 5-2 5-2 5-2 5-3 5-4 5-4 5-4 5-5 5-5 5-5 5-6 5-6 5-7

5.3

5.4

Comparison of Mass Balance Results between Hand Calculations with HYSIS 5-7

5.5

Energy Balance Results

5.6

Comparison Energy Balance Result between Hand Calculation and HYSIS

5-8

5-9

v


Pages

Chapter 6: Packed Bed Reactor 1

6.1

CHEMICAL ENGINEERING DESIGN

6.1.1 Introduction

6-1

6.1.2

6-2

Type of Catalyst

6.1.3 Type of Reactor 6-2 6.1.3.1 Packed Bed Reactor 6-2 6.1.3.1.1 Type of Heat Transfer Fluid 6-3 6.1.3.1.2 Packed Bed Reactor Dimension 6-4 6.1.3.1.3 Equation Involved in Packed Bed Reactor Design 6-5 6.1.3.1.3.1 Rate Law 6-5 6.1.3.1.3.2 Mole Balance 6-6 6.1.3.1.3.3 Ergun Equation for Pressure Drop 6-6 6.1.3.1.3.4 Simultaneous Ordinary Differential Equations 6-7 6.1.3.1.4 Packed Bed Reactor Optimization 6-8 6.1.3.1.4.1 Shell Diameter Analysis 6-9 6.1.3.1.4.2 Pressure Analysis 6-10 6.1.3.1.4.3 Temperature Analysis 6-12 6.1.3.1.4.4 Result of Packed Bed Reactor Optimization Analysis 6-12 6.1.3.2 Fluidized Bed Reactor 6-13 6.1.3.2.1 Equation Involved in Fluidized Bed Reactor Design 6-14 6.1.3.2.1.1 Conversion of Glycerol in Fluidized Bed Reactor 6-14 6.1.3.2.2 Fluidized Bed Reactor Optimization 6-15 6.1.3.2.2.1 Temperature Analysis 6-15 6.1.3.2.2.2 Reactor Diameter Analysis 6-16 6.1.3.2.2.3 Result of Fluidized Bed Reactor Optimization Analysis 6-17 6.1.3.3 Comparison of Packed Bed and Fluidized Bed Reactor 6-17 6.1.4 Heat Duty of Heating Jacket

6-18

vi


Pages

Chapter 6: Packed Bed Reactor 1 6.1.5

Clean Overall Heat Transfer Coefficient 6.1.5.1 Tube-side Film Coefficient, hio 6.1.5.2 Shell-side Film Coefficient, ho

6-19 6-19 6-19

6.1.6

Fouling Factor

6-20

6.1.7 Summary of Specification of Reactor 1

6-21

6.2

MECHANICAL ENGINEERING DESIGN

6.2.1

Design Pressure

6-22

6.2.2

Design Temperature

6-22

6.2.3

Material of Construction

6-22

6.2.4

Design Stress

6-22

6.2.5

Welded Joint Efficiency

6-23

6.2.6

Corrosion Allowance

6-23

6.2.7

Minimum Practical Wall Thickness

6-23

6.2.8 Head and Closure

6-24

6.2.9

6-24

Connection

6.2.10 Manhole

6-24

6.2.11 Compensation for Openings

6-25 vii


Pages

Chapter 6: Packed Bed Reactor 1 6.2.11.1 Compensate Opening for Feed 6.2.11.2 Compensate Opening for Molten Salt (Heater)

6-25 6-25

6.2.12 Dead Weight Load 6.2.12.1 Cylindrical Vessel 6.2.12.2 Tubes 6.2.12.3 Catalyst 6.2.12.4 Baffles 6.2.12.5 Feed 6.2.12.6 Molten Salt 6.2.12.7 Insulation 6.2.12.8 Total Dead Weight

6-26 6-26 6-27 6-27 6-27 6-28 6-28 6-28 6-29

6.2.13 Winds Load

6-29

6.2.14 Analysis Stress 6.2.14.1 Pressure Stress 6.2.14.2 Dead Weight Stress 6.2.14.3 Bending Stress 6.2.14.4 Resultant Longitudinal Stresses

6-29 6-29 6-30 6-30 6-30

6.2.15 Vessel Support 6.2.15.1 Skirt Supports 6.2.15.2 Total Weight 6.2.15.3 Bending Stress 6.2.15.4 Dead Weight Stress 6.2.15.5 Tensile Stress 6.2.15.6 Compressive Stress

6-31 6-31 6-31 6-31 6-32 6-32 6-32

6.2.16 Criteria for Design

6-32

6.2.17 Summary of Mechanical Design of Reactor 1

6-33

viii


Pages


6.3

SAFETY AND PROCESS CONTROL

6.3.1

Safety Consideration 6.3.1.1 Safety Review 6.3.1.2 Reactor Potential Hazards 6.3.1.3 Reactor Safety Practices

6-36 6-36 6-37 6-37

6.3.2

Hazard and Operability Studies (HAZOP) Analysis 6.3.2.1 Objectives of HAZOP 6.3.2.2 HAZOP Procedures

6-38 6-38 6-38

6.3.3

Process Control and Instrumentation 6.3.3.1 Description of Instruments 6.3.3.2 Description of Control System 6.3.3.2.1 Inlet Feed Temperature Control 6.3.3.2.2 Inlet Feed Flow and Pressure Control 6.3.3.2.3 Molten Salt (Heating Stream) Temperature Control

6-45 6-45 6-45 6-45 6-48 6-48

6.4

Reference

6-48

ix


Pages


7.1.0. CHEMICAL ENGINEERING DESIGN 7.1.0.1． Vapour Phase Oxidation of Propylene and Acrolein 7.1.0.2． Objective 7.1.0.3． Reactor Selection

7-1 7-1 7-1

7.1.1. Process Description 7.1.1.1. Feed Stream Condition 7.1.1.2. Properties of Feed Stream and Cooling Stream 7.1.1.3. Properties of Catalyst

7-2 7-2 7-3

7.1.2. Process Principle 7.1.2.1. Proposed Reaction Scheme for Oxidation of Acrylic Acid

7-4

7.1.3. Chemical Design 7.1.3.1. Kinetic Parameter 7.1.3.2. Assumptions 7.1.3.3. Catalyst Weight and Pressure Drop 7.1.3.4. Reactor Sizes 7.1.3.5. Tube Size Selection 7.1.3.6. Number of Tubes 7.1.3.7. Number of Tubes Passes 7.1.3.8. Tube Pitch and Buddle Diameter 7.1.3.9. Shell Inside Diameter 7.1.3.10. Baffles

7-4 7-5 7-5 7-7 7-7 7-7 7-8 7-8 7-8 7-8

7.1.4. Cooling Stream Requirement 7.1.4.1.Log Mean Temperature Difference 7.1.4.2.Cooling Water Flow 7.1.4.3.Tube Side Heat Transfer Coefficient 7.1.4.4.Shell Side Heat Transfer Coefficient 7.1.4.5.Overall Heat Transfer Coefficient 7.1.4.6.Heat Transfer Area Required

7-9 7-9 7-10 7-10 7-11 7-12

x

Content

Pages


7.1.5. Pressure Drop 7.1.5.1. Tube Side Pressure Drop 7.1.5.2. Shell Side Pressure Drop

7-12 7-12

7.1.6. Fluidized Bed Reactor 7.6.1.1.Minimum Fluidization Superficial Velocity, vsfm 7.6.1.2.Minimum Bubbling Velocity, vmb 7.6.1.3.Terminal Velocity, ut 7.6.1.4.Superficial velocity, vsf 7.6.1.5.Actual Velocity, v 7.6.1.6.Diameter of reactor, D 7.6.1.7.Minimum Reactor Wall Thickness, tm 7.6.1.8.Outer Diameter, OD 7.6.1.9.Bubble Velocity, vB 7.6.1.10. Slugging Problem & Reactor Height at Minimum Fluidization, Hmf 7.6.1.11. Reactor Height 7.6.1.12. Pressure Drop 7.6.1.13. Comparison between FBR and PBR

7-13 7-13 7-14 7-14 7-14 7-14 7-15 7-15 7-15 7-16 7-16 7-17 7-18

7.1.7. Summary of Chemical Engineering Design

7-19

7.1.8. Cost Analysis

7-20

7.1.9. Comparison of the Conversion

7-20

7.1.10. Comparison of the Molar Flow of the Components in Reactor Product Stream 7-21 7.1.11. Case study 7.1.11.1. Optimization of Temperature 7.1.11.2. Optimization of Pressure 7.1.11.3. Summary Optimization Analysis

7-22 7-22 7-23

xi

Content

Pages


7.2.0. MECHANICAL ENGINEERING DESIGN 7.2.0.1. Codes and Standards 7.2.1. General Design Considerations 7.2.1.1. Design Pressure 7.2.1.2. Design Temperature 7.2.1.3. Material of Construction 7.2.1.4. Design Stress (Nominal Design Strength) 7.2.1.5.Welded Joint Efficiency and Construction Categories 7.2.1.6.Corrosion Allowance

7-24

7-24 7-24 7-25 7-25 7-26 7-26

7.2.2. Shell and Tube Wall Thickness Design 7.2.2.1.Shell Wall Thickness and Outer Diameter 7.2.2.2.Tube Wall Thickness 7.2.2.3.Head and Closure 7.2.2.4.Tube Sheet Thickness

7-26 7-27 7-27 7-27

7.2.3. Design Loads 7.2.3.1.Dead Weight Load 7.2.3.2.Weight of Vessel 7.2.3.3. Total Dead Weight 7.2.3.4. Wind Load

7-28 7-28 7-30 7-30

7.2.4. Stress Analysis

7-31

7.2.5. Vessel Support 7.2.5.1.Design of Skirt Support 7.2.5.2.Pipe Sizing for Nozzles and Flanges 7.2.5.3.Manholes 7.2.5.4.Base Ring and Anchor Bolt

7-32 7-33 7-34 7-35

7.2.6. Summary of Mechanical Engineering Design

7-36

xii

Content

Pages


7.3.0. SAFETY, CONTROL AND INSTRUMENTATION 7.3.1. The Importance of Safety 7.3.1.1. Safety Considerations 7.3.1.1.1. Pressure Relief Systems 7.3.1.1.2. Effects of Fouling 7.3.1.1.3. Corrosion Failure 7.3.1.1.4. Stress Failure

7-38 7-39 7-39 7-39 7-39

7.3.2. Process Safety Design

7-40

7.3.3. Process Hazard Analysis (HAZOP Analysis)

7-40

7.3.4. The Importance of Control System

7-46

7.3.4.1. Types of Controller 7.3.4.1.1. Temperature Control 7.3.4.1.2. Pressure Control 7.3.4.1.3. Level Control 7.3.4.1.4. Feed Flow Control 7.3.4.1.5. Feed Composition Control 7.3.4.2. Control System Loop 7.3.4.2.1. Feed Flow Control (Control System Loop 1) 7.3.4.2.2. Reactor Pressure Control (Control System Loop 2) 7.3.4.2.3. Cooling Stream and Reactor Temperature Control (Control System Loop 3)

7-46 7-47 7-47 7-47 7-47

7-48 7-48 7-48

xiii


Pages

Chapter 8: Quenching Tower

8.1

CHEMICAL ENGINEERING DESIGN

8.1.1 Objective

8-1

8.1.2

Introduction 8.1.2.1 The Mechanism of Absorption

8-1 8-1

8.1.3

General Design Decisions

8.1.4

8.1.3.1 Choices of Solvent

8-3

8.1.3.2 Determination of Operating Pressure and Temperature

8-3

8.1.3.3 Selection of the Type of Quenching Tower

8-4

8.1.3.4 Simulation of Design Problem

8-4

8.1.3.5 Physical Properties Data

8-5

8.1.3.6 Prediction of Overall Column Efficiency

8-6

8.1.3.7 Number of Stage

8-7

Plate Specifications and Configurations 8.1.4.1 Plate Contactors

8-8

8.1.4.2 Choice of Plate Type

8-9

8.1.4.3 Plate Design Algorithm

8-10

8.1.4.4 Physical Properties

8-12

8.1.4.5 Plate Spacing

8-12

8.1.4.6 Column Diameter

8-13

8.1.4.7 Flow Arrangements

8-14

8.1.4.8 Provisional Plate Design

8-15

8.1.4.9 Weep Point

8-17

8.1.4.10 Pressure Drop

8-19

8.1.4.10.1 Column Pressure Drop Estimation

8-20 xiv


Pages

Chapter 8: Quenching Tower 8.1.4.10.2 Dry Plate Drop

8-20

8.1.4.10.3 Residual Head

8-22

8.1.4.11 Downcomer Liquid Back-up

8-22

8.1.4.12 Residence Time

8-24

8.1.4.13 Entrainment

8-24

8.1.4.14 Trial Layout

8-25

8.1.4.14.1 Perforated Area

8-26

8.1.4.15 Hole Pitch

8-27

8.1.4.16 Height of Column

8-29

8.1.5

Summary of Chemical Design Parameter

8-30

8.2

MECHANICAL ENGINEERING DESIGN

8.2.1

Introduction

8-31

8.2.2

Vessel Function

8-31

8.2.3

Operating Design Pressure and Temperature 8.2.3.1 Design Pressure 8.2.3.2 Design Temperature

8-31 8-31 8-31

8.2.4

Material of Construction

8-32

8.2.5

Maximum Allowable Stress Value

8-32

8.2.6

Welded Joint Efficiency

8-33

8.2.7

Corrosion Allowance

8-33

8.2.8

Design of Thin Walled Vessel

8-33

8.2.9

Torispherical Head Design

8-34

xv


Pages

Chapter 8: Quenching Tower 8.2.10 Design of Vessel Subject to Combined Loading Dead Weight of Vessel 8.2.10.1 8.2.10.1.1 Shell 8.2.10.1.2 Plates 8.2.10.1.3 Insulation 8.2.10.2 Wind Loading 8.2.10.3 Analysis of Stress 8.2.10.1.3.1 Pressure Stresses 8.2.10.1.3.2 Longitudinal and Circumferential Stresses due to Pressure 8.2.10.1.3.3 Dead Weight Stress 8.2.10.1.3.4 Bending Stress 8.2.10.1.3.5 Check Elastic Stability (Bucking)

8-35 8-35 8-35 8-35 8-36 8-36 8-37 8-37 8-37 8-37 8-37 8-38

8.2.11 Design of Skirt Support 8.2.11.1 Operating Weight 8.2.11.1.1 Weight of Full Liquid 8.2.11.1.2 Weight of Skirt 8.2.11.2 Thickness of Skirt

8-39 8-39 8-39 8-40 8-40

8.2.12 Opening

8-41

8.2.13 Design of Manhole

8-42

8.2.14 Design of Anchor Bolt 8.2.14.1 Design Anchor Bolt 8.2.14.2 Checking Stress in Anchor Bolt

8-43 8-43 8-44

8.2.15 Design of Base Ring 8.2.15.1 Design Base Ring 8.2.15.2 Checking Stress

8-44 8-44 8-45

8.2.16 Design Parameters

8-46

xvi


Pages

Chapter 8: Quenching Tower

8.3 SAFETY, CONTROL & INSTRUMENTATION 8.3.1 Safety Analysis 8.3.1.1 Introduction 8.3.1.2 Hazardous and Operability Study 8.3.1.3 Conclusion

8-48 8-48 8-48 8-49

8.3.2

Control and Instrumentation 8.3.2.1 Introduction 8.3.2.2 Control of Quenching Tower 8.3.2.3 Control Variable and Parameter

8-50 8-50 8-50 8-51

8.4

Nomenclatures

8-53

8.5

References

8-57

xvii


Pages

Chapter 9: Extractive Distillation Column

9.1.0. CHEMICAL ENGINEERING DESIGN 9.1.1．Introduction

9-1

9.1.2． Objective

9-1

9.1.3． Process Description

9-2

9.1.4. Selection of Column 9.1.4.1. Selection of Internal Column 9.1.4.2. Packing Selection 9.1.4.3. Random Packing selection

9-3 9-3 9-3 9-3

9.1.5

9-4 9-4 9-4 9-5 9-5 9-6 9-6 9-8 9-8 9-9 9-9

Packed Column Design 9.1.5.1. Selection of solvent 9.1.5.2. Composition and condition of feed stream, distillate and bottom 9.1.5.3. Number of theoretical stages 9.1.5.4. Optimum Feed Location 9.1.5.5. Optimum reflux ratio 9.1.5.6. Column Diameter 9.1.5.7. Height of Packed Zone 9.1.5.8. Wetting rate 9.1.5.9. Liquid Hold-up 9.1.5.10. Operating Void Space

9.2.0. MECHANICAL ENGINEERING DESIGN 9.2.1．Introduction

9-11

9.2.2． Material of Construction 9.2.2.1. Design Pressure 9.2.2.2. Design temperature 9.2.2.3. Material of construction 9.2.2.4. Material of construction 9.2.2.5. Welded joint factor 9.2.2.6. Corrosion Allowance

9-11 9-11 9-11 9-11 9-11 9-12

9.2.3． Internal Fitting 9.2.3.1. Packing support

9-12 9-12 xviii

Content

Pages

Chapter 9: Extractive Distillation Column

9.2.4

9.2.3.2. Vapor distributor 9.2.3.3. Hold down plate 9.2.3.4. Liquid distributors 9.2.3.5. Liquid redistributors 9.2.3.6. Mist eliminator (Demister) 9.2.3.7. Support ledges 9.2.3.8. Manhole

9-12 9-12 9-12 9-13 9-13 9-13 9-13

Column Design 9.2.4.1. Cylindrical Shell Thickness 9.2.4.2. Vessel Head 9.2.4.3. Vessel Height 9.2.4.4. Flange 9.2.4.5. Load Analysis 9.2.4.5.1. Dead Weight loads 9.2.4.5.2. Wind load 9.2.4.6. Stress analysis 9.2.4.7. Support 9.2.4.8. Pipe Sizing for Nozzles 9.2.4.9. Reinforcement of Openings

9-14 9-14 9-14 9-14 9-15 9-15 9-15 9-15 9-15 9-15 9-16 9-16

9.3.0. SAFETY, CONTROL AND INSTRUMENTATION 9.3.1.Introduction

9-17

9.3.2． Control

9-17

9.3.3． Safety 9.3.3.1. HAZOP analysis

9-19 9-19

xix


Pages

Chapter 10: Distillation Column

10.1. CHEMICAL ENGINEERING DESIGN 10.1.1. Introduction

10-1

10.1.2. Distillation Column Design 10.1.2.1. Schematic Diagram of T-102 10.1.2.2. Type of Column of T-102

10-1 10-2 10-3

10.1.3. Key Components

10-3

10.1.4. Number of Stages 10.1.4.1. Relative Volatility 10.1.4.2. Number of Stages and Operating Reflux Ratio 10.1.4.2.1. Minimum Number of Stages 10.1.4.2.2. Minimum Operating Reflux Ratio 10.1.4.3. Number of Theoretical Stages 10.1.4.4. Overall Column Efficiency 10.1.4.5. Actual Number of Stages

10-3 10-3 10-4 10-4 10-4 10-5 10-6 10-7

10.1.5. Feed Point Location

10-7

10.1.6. Plate Specification 10.1.6.1. Plate Spacing 10.1.6.2. Types of Plate 10.1.6.3. Liquid and Vapour Flow in a Plate Colum

10-7 10-7 10-8 10-8

10.1.7. Plate Design Procedure 10.1.7.1. Vapour and Liquid Flow Rates 10.1.7.2. Physical Properties 10.1.7.3. Column Diameter 10.1.7.3.1. Liquid Vapour Flow Factor 10.1.7.3.2. Flooding Velocity 10.1.7.3.3. Maximum Velocity Flow Rate 10.1.7.4. Liquid Flow Pattern

10-9 10-10 10-11 10-11 10-11 10-12 10-12 10-13 xx


Pages

Chapter 10: Distillation Column 10.1.7.5. Provisional Plate Design 10.1.7.6. Check Weeping 10.1.7.6.1. Weir Liquid Crest 10.1.7.7. Plate Pressure Drop 10.1.7.7.1. Dry Plate Drop 10.1.7.7.2. Residual Head 10.1.7.7.3. Total Pressure Drop 10.1.7.8. Check Entrainment

10-14 10-14 10-15 10-16 10-16 10-17 10-17 10-17

10.1.8. Trial Layout

10-18

10.1.9. Perforated Area 10.1.9.1. Number of Holes

10-18 10-19

10.1.10. Column Height

10-19

10.1.11. Simulation by HYSYS 10.1.11.1. Approach by Manual Calculation 10.1.11.2. Approach by HYSYS

10-20 10-20 10-20

10.1 MECHANICAL ENGINEERING DESIGN 10.2.1. Introduction

10-21

10.2.2. General Design Consideration of Pressure Vessel 10.2.2.1. Design Pressure 10.2.2.2. Design Pressure 10.2.2.3. Materials of Construction 10.2.2.4. Design Stress 10.2.2.5. Welded Joint Efficiency 10.2.2.6. Corrosion Allowance

10-21 10-22 10-22 10-23 10-23 10-23 10-24

xxi


Pages

Chapter 10: Distillation Column 10.2.3 Design Column 10.2.3.1 Wall Thickness 10.2.3.2 Design of Vessel Head 10.2.0.3.2.1 Choice of Closure 10.2.0.3.2.2 Design of Torispherical Head

10-24 10-24 10-25 10-25 10-25

10.2.4 Design of Vessel Loads 10.2.4.1 Weight Loads 10.2.4.2 Vessel Weight 10.2.4.3 Plate Weight 10.2.4.4 Cage Ladder Weight 10.2.4.5 Platform Stells Weight 10.2.4.6 Total Load Weight

10-26 10-26 10-26 10-27 10-27 10-27 10-27

10.2.5 Wind Loads 10.2.5.1 Load per Unit Length 10.2.5.2 Bending Moment at Colum Height

10-28 10-28 10-28

10.2.6 Analysis of Stress 10.2.6.1 Pressure Stress 10.2.6.2 Dead Weight Stress 10.2.6.3 Bending Stress 10.2.6.4 Principal Stress 10.2.6.5 Critical Buckling Stress

10-28 10-28 10-28 10-29 10-29 10-30

10.2.7 Vessel Support 10.2.7.1 Skirt Thickness 10.2.7.2 Bending Moment at Base of Skirt 10.2.7.3 Design Criteria

10-30 10-30 10-31 10-31

10.2.8 Manhole

10-32

10.2.9 Summary

10-33

xxii


Pages

Chapter 10: Distillation Column

10.3 SAFETY, CONTROL AND INSTRUMENTATION 10.3.1 Introduction 10.3.1.1 Safety 10.3.1.2 Environment Protection 10.3.1.3 Equipment Protection 10.3.1.4 Smooth Plant Operation 10.3.1.5 Product Quality 10.3.1.6 Profit 10.3.1.7 Monitoring and Diagnosis

10-35 10-35 10-35 10-36 10-36 10-36 10-36 10-36

10.3.2 Distillation Control Objective

10-37

10.3.3 Column Control 10.3.3.1 Feed Stream Control 10.3.3.2 Product Quality Control 10.3. 3.3 Top Stream Control 10.3. 3.4 Bottom Stream Control

10-38 10-39 10-39 10-39 10-40

10.3.4 Instruments Notation

10-40

10.3.5 Instrumentations 10.3.5.1 Pressure Measurements 10.3.5.2 Flow Measurements 10.3.5.3 Level Measurements 10.3.5.4 Temperature Measurements

10-41 10-41 10-41 10-41 10-41

10.3.6 Hazards and Operability Study

10-43

xxiii

LIST OF TABLES Table 1.1: Comparison the Economic for Different Products of Glycerol

1-3

Table 1.2: Physical Properties of Acrylic Acid

1-5

Table 3.1: Forecasted Global Growth of the Usage of Acrylic Acid up to Year 2011

3-2

Table 3.2: Forecasted Annual Production of Acrylic Acid up to Year 2011

3-2

Table 3.3: Major Manufacturer of Acrylic Acid

3-3

Table 3.4: Price of Acrylic Acid at Asia and USA

3-3

Table 3.5: Petrochemical Plant in Gebeng

3-6

Table 3.6: Estimation of Equipment Cost

3-8

Table 3.7: Estimation of Total Capital Investment

3-9

Table 3.8: Estimation of Total Product Cost

3-10

Table 3.9: Estimation of Payback Period

3-11

Table 4.1: Waste Water Composition

4-1

Table 4.2: Waste Water Discharge Target

4-3

Table 4.3: Gas Emission Target

4-4

Table 5.1: Molar Flow Rate at Stream 5 and its Comparison with HYSIS

5-2

Table 5.2: Molar Flow Rate of Stream 6 at CRV-100 and its Comparison with HYSIS

5-2

Table 5.3: Molar Flow Rate of Stream 10 at V-100 and its Comparison with HYSIS

5-2

Table 5.4: Molar Flow Rate of Stream 20 at V-100 and its Comparison with HYSIS

5-3

Table 5.5: Molar Flow Rate of Stream 11 of and its Comparison with HYSIS

5-3

Table 5.6: Molar Flow Rate of Stream 12 and its Comparison with HYSIS

5-3


5-4


5-4

Table 5.9: Molar Flow Rate of Stream 24 at CRV-101 and its Comparison with HYSIS

5-4


5-5

Table 5.11: Molar Flow Rate of Stream 28 at T-100 and its Comparison with HYSIS

5-5


5-5

Table 5.13: Molar Flow Rate of Stream 31 at MIX-100 and its Comparison with HYSIS 5-5 Table 5.14: Molar Flow Rate of Stream 33 at T-101 and its Comparison with HYSIS

5-6


5-6

LIST OF TABLES Table 5.16: Molar Flow Rate of Stream 34 at X-100 and its Comparison with HYSIS

5-6

Table 5.17: Molar Flow Rate of Stream 35 at X-100 and its Comparison with HYSIS

5-6


5-7


5-7

Table 5.20: Summary of Energy Balance and the Comparison

5-8

Table 6.1: Property of Catalyst

6-2

Table 6.2: Property of Hot Molten Salt (HITEC)

6-4

Table 6.3: Dimension of Packed Bed Reactor

6-4

Table 6.4: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Number of Tube per Reactor

6-10

Table 6.5: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Pressure, Po

6-11

Table 6.6: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Temperature, To

6-13

Table 6.7: Results of Packed Bed Reactor Optimization Analysis

6-13

Table 6.8: Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Temperature, To

6-16

Table 6.9: Length of Reactor, L and Ratio of Length to Diameter, L/D for Different Shell Diameter, IDs

6-17

Table 6.10: Results of Packed Bed Reactor Optimization Analysis

6-17

Table 6.11: Variables to Calculate Heat Duty

6-18

Table 6.12: Variables to Tube-side Film Coefficient

6-19

Table 6.13: Variables to Shell-side Film Coefficient

6-19

Table 6.14: Variables to Calculate Fouling Factor

6-20

Table 6.15: Summary of Specification of Reactor 1

6-21

Table 6.16: Variables to Calculate Optimum Diameter in Feed Opening

6-25

Table 6.17: Variables to Calculate Optimum Diameter in Molten Salt Opening

6-26

Table 6.18: Variables to Calculate Total Weight of Shell

6-26

Table 6.19: Variables to Calculate Total Weight of Tube

6-27

LIST OF TABLES Table 6.20: Variables to Calculate Total Weight of Baffles

6-27

Table 6.21: Variables to Calculate Total Weight of Feed

6-28

Table 6.22: Variables to Calculate Total Weight of Molten Salt

6-28

Table 6.23: Variables to Calculate Total Weight of Insulation

6-29

Table 6.24: Criteria for Design

6-32

Table 6.25: Summary of Mechanical Design of Reactor 1

6-33

Table 6.26: HAZOP Analysis on Packed Bed Reactor 1 – Streamline 5

6-39

Table 6.27: HAZOP Analysis on Packed Bed Reactor 1 – Streamline 6

6-41

Table 6.28: HAZOP Analysis on Packed Bed Reactor 1 – Streamline H_1

6-42


6-43

Table 6.30: Description of Instrument

6-45

Table 6.31: Description of Inlet Feed Temperature Control

6-45

Table 6.32: Description of Inlet Feed Flow and Temperature Control

6-46

Table 6.33: Description of Molten Salt Temperature Control

6-46

Table 7.1: Initial Condition of Feed Stream Reactant

7-2

Table 7.2: Properties of Feed Stream and Cooling Stream

7-3

Table 7.3: Properties of Catalyst

7-3

Table 7.4: Kinetic Parameter for Oxidation of Acrolein

7-5

Table 7.5: Determination of Catalyst Weight and Pressure Drop

7-6

Table 7.6: Determination of Reactor Sizes

7-7

Table 7.7: Properties of Pipe

7-7

Table 7.8: Specifications of Baffles

7-9

Table 7.9: Determination of Tube Side Heat Transfer Coefficient

7-10

Table 7.10: Determination of Shell Side Heat Transfer Coefficient

7-10

Table 7.11: Determination of Overall Heat Transfer Coefficient

7-11

Table 7.12: Inner Diameter of Reactor for Various

vsf vsfm

Ratios

7-15

Table 7.13: Determination of Height of Reactor

7-17

Table 7.14: Comparison between FBR and PBR

7-18

LIST OF TABLES Table 7.15: Summary of Chemical Engineering Design of Reactor

7-19

Table 7.16: Comparison of the Conversion Value with the HYSYS Simulation

7-20

Table 7.17: Comparison of the Component Molar Flow with the HYSYS Simulation

7-21

Table 7.18: Design Pressure for Tube Side and Shell Side

7-24

Table 7.19: Design Temperature for Tube Side and Shell Side

7-25

Table 7.20: Design Stress for Tube Side and Shell Side

7-25

Table 7.21: Optimum Diameter for Inlet Streams and Outlet Streams

7-34

Table 7.22: HAZOP Analysis on Feed Stream of the Reactor

7-41

Table 7.23: HAZOP Analysis on Outlet Stream of Reactor

7-43

Table 7.24: HAZOP Analysis on Cooling Water Supply of Reactor

7-44

Table 7.25: Control Variables for Packed Bed Reactor

7-50

Table 8.1: Comparison between Different Trays

8‐9

Table 8.2: Summary of Chemical Design Parameter for the Quenching Tower

8‐31

Table 8.3: Piping System

8‐43

Table 8.4: Mechanical Design Parameter for Quenching Tower

8‐47

Table 8.5: Control Variable and Parameter

8‐51

Table 9.1: Comparison between Plate Column and Packed Column

9-3

Table 9.2: Comparison between Random Packing and Structured Packing

9-3

Table 9.3: Molar Flow Rate of the Inlet Streams and Outlet Streams of Extractive Distillation

Column

9-4

Table 9.4: Operating Condition of the Inlet Streams and Outlet Streams of Extractive Distillation Column

9-4

Table 9.5: Equilibrium Data for Raffinate Phase

9-5

Table 9.6: Equilibrium Data for Extracted Phase

9-5

Table 9.7: Purify of Product with vary Reflux Ratio

9-6

Table 9.8: Extractive Distillation Column Design Summary

9-10

Table 9.9: Control System for Extractive Distillation Column

9-18

Table 9.10: HAZOP Analysis

9-19

10-2

Table 10.1: Stream Description for Distillation Column T-102

LIST OF TABLES Table 10.2: Stage Requirement at Different Reflux Ratio

10-6

Table 10.3: Vapor and Liquid Flow Rates

10-10

Table 10.4: Physical Properties

10-11

Table 10.5: Provisional Design

10-15

Table 10.6: Molar Flow Rate of Feed Stream and its Comparison with Hysys

10-21

Table 10.7: Molar flow rate of Top stream and its Comparison with Hysys

10-21

Table 10.8: Molar flow rate of Bottom Stream and its Comparison with Hysys

10-21

Table 10.9: Summary of Chemical Engineering Design

10-34

LIST OF FIGURES Figure 4.1: Schematic of Water Treatment System

4-2

Figure 4.2: Schematic of Gas Treatment System

4-3

Figure 6.1: Schematic Diagram of Reactor 1

6-1

Figure 6.2: Shell-and-tube Packed-bed Reactor with Co-current Heating

6-3

Figure 6.3: Plot of Conversion and Pressure Ratio Obtained from Matlab

6-8

Figure 6.4: Data of Conversion and Pressure Ratio Obtained from Matlab

6-9

Figure 6.5: Schematic Diagram of Fluidized Bed Reactor

6-14

Figure 6.6: Ellipsoidal Head

6-24

Figure 6.7: Schematic Diagram of Opening

6-25

Figure 6.8: Mechanical Drawing of Reactor 1

6-34

Figure 6.9: Detail A of Mechanical Drawing

6-35

Figure 6.10: Process and Instrumentation Diagram (PID) of Reactor 1

6-47

Figure 7.1: Fluidized Bed Reactor

7-13

Figure 7.2: Ratio of Length and Diameter, L/D vs. Inlet Temperature, To

7-22

Figure 7.3: Ratio of Length and Diameter, L/D vs. Inlet Pressure, Po

7-23

Figure 7.4: Control System for Packed Bed Reactor

7-49

Figure 8.1 Schematic Diagram of Quenching Tower

8-5

Figure 8.2: Absorber Column Efficiency

8-6

Figure8.3: Typical Cross Flow Plate (Sieve)

8-8

Figure 8.4: Column Operation Regimes

8-8

Figure 8.5: Plate Design Algorithm

8-11

Figure 8.6: Flooding Velocity, Sieve Plate

8-13

Figure 8.7: Selection of Liquid Flow Arrangement

8-15

Figure 8.8: Relationship between the Weir Length and Downcomer Area

8-17

Figure 8.9: Weep Point Correlation

8-20

Figure 8.10: Discharge Coefficient, Sieve Plates (Liebson et al., 1957)

8-22

Figure 8.11: Entrainment Correlation for Sieve Plates

8-26

Figure 8.12: Trial Layout of the Plate Design

8-27

Figure 8.13: Relation between Downcomer Area and Weir Length

8-28

LIST OF FIGURES Figure 8.14: Relation between Hole Area and Pitch

8-30

Figure 8.15: Torispherical Head

8-36

Figure 8.16: Analysis of Stresses

8-39

Figure 8.18: Feedback Control Loop in Quenching Tower

8-53

Figure 8.19: Ratio Control Loop in Absorbed

8-53

Figure 9.1: Flow Diagram for Extractive Distillation Column

9-2

Figure 9.2: Flooding and Pressure Drop in Packed Column

9-6

Figure 9.3: Table Constant for TETP Correlation

9-8

Figure 9.4: Flow Diagram with Controller

9-17

Figure 10.1: Schematic Diagram of Distillation Column T-102

10-2

Figure 10.2: Flow of Vapor and Liquid across Each Plate

10-9

Figure 10.3: Trial Plate Layout

10-18

Figure 10.4: Complete Process Control and Instrumentation Diagram of Distillation Column 10-43

KKEK 4281 Design Project Chapter 1: Introduction

Group 6 Acrylic Acid Project

CHAPTER 1: INTRODUCTION 1.1 Biodiesel Production Biodiesel can be produced from vegetable oil, animal oil/fats, tallow and waste oils. There are three basic routes for biodiesel production from oils and fats. •

Base catalyzed transesterification of the oil

•

Direct acid catalyzed transesterification of the oil

•

Conversion of the oil to its fatty acids and then to biodiesel.

Almost all biodiesel is produced by base catalyzed transesterification as it is the most economical process requiring only low temperatures and pressures and producing a 98% conversion yield.[1] The production of biodiesel by using oil and fats and shown below.

The oil or fats is reacted with alcohol under proper catalyst and condition will produce biodiesel as main product and glycerol as by product for process. For every 1 tonne of biodiesel that is manufactured, 100 kg of glycerol are produced. [2] After neutralization treatment, crude Glycerol with 80-88% purity containing water and catalyst residual can be obtained. [1]

1.2 Glycerol Produced from Biodiesel Plant In year 1999 biodiesel glycerol accounted for just 7% of the glycerol market and in year 2004 that figure had grown to 19%. This has lead to oversupply in the market and new investments in oleochemical as well as biodiesel industries are expected to make the situation worse in the next couple of years. 450 million gallons of biodiesel were produced in 2007, which left with 45 million gallons of glycerol. Considering that the National Biodiesel Board is expecting 60 new plants with a production capacity of 1.2 billion gallons of biodiesel to come online by 2010, over 100 million gallons of glycerol is expected to be produced annually.[3] Due to the overcapacity of glycerol, the price

1-1



decreased drastically over recent years. Hence researches have been made to develop technologies to utilize the glycerol produced from biodiesel plant.

1.3 Potential Product of Glycerol By research there are several useful products that can be manufactured by using glycerol. •

Acrylic acid via acrolein

•

Propylene glycol

•

Hydrogen

•

Epichlorohydrin

1.3.1 Process Route 1.3.1.1 Acrylic Acid via Acrolein The production of acrylic acid is by two reaction routes. Glycerol (C3H8O3) is dehydrated to form acrolein (C3H4O), which acts as an intermediate (refer to Equation 1.1). Then the acrolein is oxidized to form acrylic acid (C3H4O2). (refer to Equation 1.2).

C3 H 8O3 ⎯⎯ → C3 H 4O + 2 H 2O

(Equation 1.1)

1 C3 H 4O + O2 ⎯⎯ → C3 H 4O2 2

(Equation 1.2)

1.3.1.2 Propylene Glycol

The production of propylene glycol is by dehydration of glycerol (C3H8O3) to produce an intermediate product, acetol (C3H6O2) (refer to Equation 1.3). Then it is further hydrogenated to produce propylene glycol (C3H8O2) (refer to Equation 1.4). C3 H 8O3 ⎯⎯ → C3 H 6O2 + H 2O

(Equation 1.3)

C3 H 6O2 + H 2 ⎯⎯ → C3 H 8O2

(Equation 1.4)

1.3.1.3 Hydrogen

The production of hydrogen from glycerol is by steam reforming (refer to Equation 1.5), followed by the water-gas shift reaction (refer to Equation 1.6). The overall reaction is summarized in Equation 1.7.

1-2



H 2O C3 H 8O3 ⎯⎯⎯ → 3CO + 4 H 2

(Equation 1.5)

CO + H 2O ⎯⎯ → CO2 + H 2

(Equation 1.6)

C3 H 8O3 + 3H 2O ⎯⎯ → 3CO2 + 7 H 2

(Equation 1.7)

1.3.1.4 Epichlorohydrin

Dichloropropanol

is

synthesized

from

glycerol

and

hydrochloric

acid.

Dehydrochlorination of the intermediates then produces epichlorohydrin.

1.3.2 Comparison of the Products Table 1.1: Comparison the economic for different products of glycerol [4, 5, 6, 7, 8, 9, 10, 11]

Acrylic acid

PG

Hydrogen

Epichlorohydrin

Annual Global

3.75 million

1.4 million ton/

675 billions

Demand

ton/ year

year

SCF/year

3.5

4.5

4.0

5.0

1650

1800

510.5

1650

Competition from

Propylene via

Propylene

Industries

Acrolein

Oxide

Methane

Propylene

1000

1410

122

1000

1.3 million ton/year

Forecasted Average Global Growth (%) Price per ton (USD)

Raw material’s price of competitor (USD/ton)

From the table above, all the potential products are considered profitable by using glycerol as raw material without consider the capital cost. However acrylic acid is chosen to be produced based on the following criteria: •

The annual global demand of acrylic acid is the highest.

•

The forecasted annual global growth is high that is 3.5%.

•

Price of glycerol is cheaper than the current raw material, propylene.

•

Storage and handling of acrylic acid is easier compared to hydrogen.

1-3



•

Acrylic acid is less toxic compared to epichlorohydrin.

•

The usage of acrylic acid is more and the potential market is wide.

1.4 Introduction of Acrylic Acid 1.4.1 Description

Acrylic acid or prop-2-enoic acid is a chemical compound that can be easily polymerized. Pure acrylic acid is a clear, colorless liquid with a characteristic acrid odor. It is miscible in water, alcohols, ethers and chloroform. Acrylic acid is used as monomer for acrylate resins and forms crystalline needle in solid state.

1.4.2 Chemical Identification

Structure formula:

H 2C = CHCOOH

Chemical structure:

H H OH | | | C=C–C=O | H

IUPAC name: Propenoic acid CAS number: [79-10-7] RTECS number: AS4375000 Synonyms: Ethylenecarboxylic acid, Propene acid, Propenoic acid, Vinylformic acid

1.4.3 Potential Usage of Acrylic Acid

Acrylic acid is most often been polymerize to form acrylic acid polymer. The most common product is superabsorbent polymers (SAP) that account for 32% of the global demand for acrylic acid. SAPs are cross-linked polyarcylates with the ability to absorb and retain more than 100 times their own weight in liquid. Acrylic acid also can be used to produce detergent polymer. It can be used with zeolites or phosphates in washing powder formulation. Besides that acrylic acid is also the raw material for various acrylic ester productions.

1-4



1.4.4 Physical Properties of Acrylic Acid

Important physical properties of acrylic acid are summarized in Table 1.2. Table 1.2: Physical properties of acrylic acid

Properties

Data

Molecular Weight

72.06 g/mol

Specific Gravity

1.050 (20/4 oC)

Melting Point

13 oC

Boiling Point (101.3 kPa)

141 oC

Flash Point

54 oC (Cleveland open cup)

Critical Temperature

380 oC

Critical Pressure

5.06 Mpa

Viscosity (25 oC)

1.149 mPa.s

Refractive Index (25 oC)

1.4185

Solubility

> 10g/L

Dissociation Constant (25 oC)

5.5 x 10 -5

pKa

4.26

Vapor Density (air =1)

2.5

Vapor Pressure (20 oC)

0.4133 kPa

Auto-ignition Temperature

360 oC

Explosive Limit

2.4 – 8.0 vol % in air

Heat of Vaporization (101.3 kPa)

45.6 kJ/mol

Heat of Combustion

1376 kJ/mol

Heat of Melting (13 oC)

11.1 kJ/mol

Heat of neutralization

58.2 kJ/mol

Heat of polymerization

77.5 kJ/mol

1-5



1.5 References 1. http://www.esru.strath.ac.uk/EandE/Web_sites/02-03/biofuels/what_biodiesel.htm 2. http://en.wikipedia.org/wiki/Biodiesel#Production 3. Frost & Sullivan - What is the Global Market Outlook for Glycerine in 2006, 19th Oct 2008. 4. http://www.alibaba.com/trade/search?Type=&ssk=y&year=&month=&industry= &location=&keyword=&SearchText=crude+glycerine&Country=MY&srchLocat ion=&srchYearMonth=&IndexArea=product_en&CatId=0 5. http://www.dow.com/productsafety/finder/prog.htm 6. http://www.icis.com/v2/chemicals/9076442/propylene-glycol/pricing.html 7. http://www.the-innovation-group.com/ChemProfiles/Propylene%20Glycol.htm 8. http://en.wikipedia.org/wiki/Ethanol#Production 9. http://www.the-innovation-group.com/ChemProfiles/Ethanol.htm 10. http://en.wikipedia.org/wiki/Hydrogen#Applications 11. http://www.the-innovation-group.com/ChemProfiles/Hydrogen.htm

1-6

KKEK 4281 Design Project Chapter 2: Process Description


CHAPTER 2: PROCESS DESCRIPTION OF ACRYLIC ACID PRODUCTION 2.1 Process Principle The raw material used is crude glycerol obtained from biodiesel plant. The purity of crude glycerol obtained is 88% purity. [1] The production of acrylic acid from glycerol is by two process routes. First, crude glycerol (C3H8O3) is dehydrated to acrolein (C3H4O) via acetol (C3H6O2) as intermediate (refer to Equation 2.1 and Equation 2.2) under heterogeneous catalytic reaction. The reaction is endothermic.

C3 H 8O3 ⎯⎯ → C3 H 6O2 + H 2O

(Equation 2.1)

C3 H 6O2 ⎯⎯ → C3 H 4O + H 2O

(Equation 2.2)

Acrolein is then oxidized to form acrylic acid in Reactor 2 (refer to Equation 2.3) via heterogeneous catalytic reaction. The reaction is exothermic. Acetic acid will form as the major by product for the process refer to Equation 2.4)

1 C3 H 4O + O2 ⎯⎯ → C3 H 4O2 2

3 C3 H 4O + O2 ⎯⎯ → C2 H 4O2 + CO2 2

(Equation 2.3)

(Equation 2.4)

2.2 Unit Operation Description 2.2.1 Reactor 1, CRV-100

In the first reactor, crude glycerol is dehydrated to acrolein via heterogeneous catalytic endothermic reaction. The catalyst used is aluminasilicates supported silicotungstic acid which by research gives a higher conversion of glycerol and higher yield of acrolein. The temperature of the reactor is maintained at 275oC by control the temperature of the inlet air-steam stream temperature. The pressure of the reactor is set at 1 atm. Under these conditions, the conversion of glycerol is 98.3% and selectivity of acrolein is 86.2%.[2, 3] Steam and air are added into Reactor 1 along with glycerol. The mass ratio of steam to glycerol is 4 to 1 while the proportion of oxygen to the total mass is 0.07. [3] Steam is added as inert gas to control the rate of the reaction. Air which consists of oxygen and nitrogen is added to increase the lifetime of the catalyst by reducing coke formation or

2-1



any undesired adsorption. [4] The gaseous phase products of this reaction consist of air, water vapour, acrolein, acetol, and some other minor by product. [3]

2.2.2 Separator, V-100

The separator separated the gaseous product stream from Reactor 1 to liquid stream and gas stream by an internal cooler. The cooling fluid used is cooling water. The purpose of the separation is to recycle back the huge quantity of water in the product stream to avoid wastage. The liquid stream which consists of major proportion of water and acetol will recycle back to Reactor 1 while gas stream consist of major proportion of acrolein and air will proceed to Reactor 2 for oxidation reaction.

2.2.3 Reactor 2, CRV-101

In the second reactor, acrolein is oxidized to form acrylic acid via heterogeneous catalytic exothermic reaction. The catalyst used is Mo10 W2 V3.5 Cu2 Sr

0.8. The

temperature of the

o

reactor is maintained at 260 C by using molten salt cooling jacket. The pressure of the reactor is set at 2 bar. The volume percentage of acrolein, oxygen, nitrogen and water vapour fed to Reactor 2 is 10%, 16%, 64% and 10% respectively. Under these conditions, the conversion of acrolein is 98% and yield of acrylic acid is 94.1%.[5] Steam is added as inert gas to control the rate of the reaction. Air is supplied to provide the oxygen required for the oxidation reaction. The nitrogen consists in air will act as an inert to control the reaction. The gaseous product stream consists of air, water vapour, acrylic acid and acetic acid which is a by product of the reaction, air and water vapour.

2.2.4 Quenching Tower, T-100

The product stream from Reactor 2 is fed into quenching tower to separate out the air and form aqueous solution. Water is fed from the top of the tower and the product stream from the bottom of the tower. Water will ‘wash’ the product stream in counter current flow. Air, water vapour and other minor component exited the tower at the top. Acrylic acid and acetic acid will dissolve in water and form aqueous solution.

2-2



2.2.5 Extractive Distillation Column, T-101

The aqueous acrylic acid and acetic acid solution is entering extractive distillation column. Due to close volatility between acrylic acid and acetic acid, the mixture cannot be separated by conventional distillation column. The solvent used for the extraction of acetic acid is the mixture of cyclohexane and isopropyl acetate. Polymer inhibitor, diphenylamine with benzoquinone and hydroquinone mono-methyl-ether is also fed to the column to prevent acrylic acid polymerization.

[6]

The solvent and polymer inhibitor

feed from the top while the mixture feed from bottom. The solvent extracted out acetic acid from the mixture and exit at the top of the column. The bottom exit stream consists of acrylic acid with purity 99.7% which is the process final product.

2.2.6 Decanter, X-100

Amount of water will exit along with the extracted stream from extractive distillation column and form two phase liquid, water phase and solvent phase. The water can be separated from the two phase liquid by using a decanter and is recycled back to quenching tower as solvent.

2.2.7 Solvent Recovery Distillation Column, T-102

After the water is separated, the extracted stream entered a distillation column to recover the solvent. The solvent with lower boiling point will exit as distillate while acetic acid and other residual with higher boiling point will exit as bottom product. The distillate solvent has the purity of 99.8% and is recycled back to extractive distillation column. The bottom stream is treated as residual and sent to waste water treatment plant.

2.3 Process Description Glycerol feed is preheated by E-100 and E-101 by heat exchanged with the product stream from Reactor 2, CRV-101 and molten salt from cooling jacket of CRV-101. The glycerol is then vaporized by using thermal oil in E-102. Steam feed is mix with the recycle stream and air feed from air compressor. The mixture is preheated by E-103 by heat exchanged with the product stream of Reactor 1, CRV-100. It is further heated by E104 by thermal oil to a temperature controlled by the temperature transmitter of CRV-

2-3



100 so that CRV-100 temperature always maintain at optimum reaction temperature of 275 oC.

Both gaseous glycerol and steam-air mixture is fed into CRV-100 by feed nozzle. The feeds undergo catalytic endothermic reaction under 1 atm absolute pressure at CRV-100. It produced acrolein, acetol and some other minor by-product. The product stream is compressed to 2.4 bar by a compressor, K-100 and cooled down by E-103 and E-105 by air-water mixture feed and recycled stream from separator, V-100 respectively.

The cooled acrolein stream is fed to V-100 and separated to liquid stream and gas stream. Liquid stream consist of higher proportion of water. A small portion of liquid stream is purged out to waste treatment plant. The remaining liquid stream’s pressure is reduced by a pressure relief valve to 1 atm and heated up by Reactor 1 product stream via E-105. It is then vaporized by E-106 by using molten salt from Reactor 2 cooling jacket. The vaporized stream is mixed with feed steam and recycled back to CRV-100.

The gas stream from V-100 consists of higher proportion of acrolein. It is fed into Reactor 2, CRV-101 along with make up air from air compressor and make up steam. The feeds undergo catalytic exothermic reaction under 2 bar to from gaseous acrylic Acid, acetic acid and some minor by-product. The reactor temperature is maintained at optimum reaction temperature, 260 oC by using molten salt cooling jacket. The hot molten salt is cooled down by heat exchange with glycerol feed and recycled liquid stream via E-101 and E-106. The acrylic acid product stream is cooled down at E-100 by heat exchanged with glycerol feed and fed into quenching tower, T-100.

In quenching tower water is fed from top stage and acrylic acid product stream is fed from bottom. Acrylic acid stream will cool by the water and exit as liquid stream at bottom while air and some volatile components are discharged as gaseous stream from the top of the tower. The gas stream will eventually treated at waste treatment plant before discharged.

2-4



The liquid stream consists of acrylic acid, acetic acid and water is fed into extractive distillation column T-101. The solvent used is a mixture of cyclohexane and isoprpyl acetate. Polymer inhibitor, diphenylamine with benzoquinone and hydroquinone monomethyl-ether is also added into T-101 to prevent acrylic acid polymerize in the column. The solvent and polymer inhibitor with higher density is fed from top while the liquid stream is fed from bottom. Under solvent extraction acetic acid will be extracted by the solvent and leave at the top of T-101 along with water. Acrylic acid discharged at the bottom of the column as raffinate is pure acrylic acid with 99.7% purity.

The solvent along with the extracted acetic acid and water is a two phases liquid with water phase and solvent phase. The mixture is fed into decanter, X-100 with water is separated and recycled back to quenching tower, T-100.

The solvent and acetic acid is then fed into solvent recovery distillation column, T-102. The bottom product will become residual of the process and sent to waste treatment plant. The solvent with 99.8% is recovered and recycle back to extraction distillation column, T-101.

2-5

KKEK 4281 Design Project Chapter 2


2.4 Process Flow Diagram

Figure 2.1: Process Flow Diagram

2-6


2.4.1 Flow Description Stream Unit Phase Pressure

1

2

3

4

5

6

7

8

9

10

L 160

L 140

L 120

G 101.3

G 101.3

G 101.3

G 240

G 220

G 200

L 200

25 135

157.1 135

230 135

300 135

135.00 0.00 0.00 0.00 0.00 0.00

135.00 0.00 0.00 0.00 0.00 0.00

135.00 0.00 0.00 0.00 0.00 0.00

Unit

11

12

13

14

15

atm

L 200

L 140

L 120

G 101.3

G 300

kPa

o C Temperature kmol/hr Mole Flow Component kmol/hr Glycerin Water Oxygen Nitrogen Acetol Acrolein

Stream Phase Pressure


o C Temperature kmol/hr Mole Flow Component kmol/hr Glycerin Water Oxygen Nitrogen Acetol

303.8 275 407.7 284.3 101.2 66 3932.41 4201.39 4201.39 4201.39 4201.39 2921.16

135.00 137.22 2.33 0.00 2780.90 3049.90 0.00 205.91 205.91 0.00 774.55 774.55 0.00 12.31 13.10 0.00 21.52 155.61

2.33 3049.90 205.91 774.55 13.10 155.61

2.33 3049.90 205.91 774.55 13.10 155.61

2.33 2.33 3049.90 2884.40 205.91 0.02 774.55 0.03 13.10 12.97 155.61 21.44

16

17

18

19

20

G 300

G 140

G 120

G 101.3

G 200

66 66 105 180 146.06 2775.11 2775.11 2775.11

133.6 50.95

25 144.3 295 304.5 66 980.40 3797.41 3797.41 3797.41 1280.23

0.12 2.21 2.21 2.21 144.22 2740.20 2740.20 2740.20 0.00 0.16 0.16 0.16 0.00 0.03 0.03 0.03 0.65 12.31 12.31 12.31

0.00 50.95 0.00 0.00 0.00

0.00 2.22 2.22 2.22 0.00 0.00 2780.90 2780.90 2780.90 165.52 205.89 205.91 205.91 205.91 205.89 774.52 774.55 774.55 774.55 774.52 0.00 12.31 12.31 12.31 0.13

2-7

KKEK 4281 Design Project Chapter 2 Acrolein Stream Phase Pressure


Unit

1.07 21

20.37 22

20.37 23

20.37 24

0.00 25

0.00 26

21.52 27

21.52 28

21.52 29

134.17 30

kPa

G 300

G 300

G 200

G 200

G 180

L 101.3

L 101.3

G 101.3

L 101.3

L 101.3

133.6 0.00

25 45.52

65.15 260 170 29 1325.75 1260.00 1260.00 245.90

42.17 69.07 72.88 400.00 1367.05 292.96

51.3 15.49

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00 9.52 36.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

165.52 215.41 810.52 0.13 134.17 0.00 0.00 0.00 0.00 0.00

400.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.18 15.44

o C Temperature kmol/hr Mole Flow Component kmol/hr Water Oxygen Nitrogen Acetol Acrolein Acrylic acid CO2 Acetic acid Cyclohexane I-P-acetate

165.52 144.42 810.52 0.14 2.69 126.25 5.23 5.23 0.00 0.00

165.52 144.42 810.52 0.14 2.69 126.25 5.23 5.23 0.00 0.00

245.90 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

402.94 144.43 810.51 0.00 2.54 0.58 5.23 0.81 0.00 0.00

162.58 0.15 0.01 0.13 0.14 125.67 0.00 4.42 0.00 0.00

2-8



Unit

31

32

33

34

35

36

37

38

39

40

kPa

L 101.3

L 15

L 15

L 15

L 101.3

L 15

L 15

L 15

L 101.3

L 101.3

32 425.51

87.97 124.70

35.68 593.80

53.97 154.50

63.2 154.50

31.87 439.30

45.66 29.28

31.26 410.00

31.34 410.00

240 619.16

0.19 0.32 0.00 0.00 191.25 233.75 0.00

0.15 124.36 0.06 0.13 0.00 0.00 0.00 0.00

162.62 1.32 4.69 0.00 0.14 191.25 233.75 0.00

154.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00

154.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00

8.13 1.32 4.69 0.00 0.14 191.25 233.75 0.00

8.00 1.32 4.38 0.00 0.00 0.17 15.42 0.00

0.14 0.00 0.30 0.00 0.14 191.08 218.33 0.00

0.14 0.00 0.30 0.00 0.14 191.08 218.33 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 619.16

Unit

41

42

43

44

45

46

47

kPa

L 101.3

L 101.3

L 101.3

L 101.3

L 101.3

L 101.3

L 101.3

236.14 619.16

330 558.66

300 558.66

330 65.70

300 65.70

236.14 619.16

200 619.16

619.16 0.00

0.00 558.66

0.00 558.66

0.00 65.70

0.00 65.70

0.00 619.16

0.00 619.16

o C Temperature kmol/hr Mole Flow Component kmol/hr Water Acrylic acid Acetic acid Acetol Acrolein Cyclohexane I-P-acetate Molten Salt



o C Temperature kmol/hr Mole Flow Component kmol/hr Molten Salt Thermal Oil

2-9



2.5 References 1. http://www.esru.strath.ac.uk/EandE/Web_sites/02-03/biofuels/what_biodiesel.htm 2. Hanan Atia, Udo Armbruster, Andreas Martin, Dehydration of glycerol in gas phase using heteropolyacid catalysts as active compounds, 29 May 2008 3. Eriko Tsukuda, Satoshi Sato, Ryoji Takahashi, Toshiaki Sodesawa, Production of acrolein from glycerol over silica-supported heteropoly acids, 27 July 2006 4. Jean-Luc Dubois, Millery (FR); Christophe Duquenne, Zickau (DE); Wolfgang Holderich, Frankenthal (DE), Process For Dehydrating Glycerol To Acrolein, Jul. 8, 2008 5. Won-Ho Lee, Kyung-Hwa Kang; Dong-Hyun Ko; Young-Chang Byun, Method Of Producing Acrylic Acid Using A Catalyst For Acrolein Oxidation, May 7, 2002 6. Otsuki et al., Polymerization Inhibition of Acrylic Acid, July 4, 1972

2-10

KKEK 4281 Design Project Chapter 3: Plant Economy and Feasibility Study


CHAPTER 3: PLANT ECONOMIC AND FEASIBILITY STUDY 3.1

Market Analysis

3.1.1 Global Demand The current global demand capacity for acrylic acid is about 7.5 billion pound/ year at year 2007 [1]

and global demand for raw acrylic acid is forecast to rise by 3.7% per annum in the coming 5

years (2007-2011). [2] The growth is especially high at Asia and China which shown amount of 8% annual growth.

[3]

This is partly due to demand competition for acrylic acid supply with

acrylic ester producers. Acrylic esters make the main product derived from acrylic acid and account for 55% of global demand. [2]

About half of the crude acrylic acid is processed to purified (glacial) acrylic acid, which is further processed both on-site (captive use) and by external downstream users. The other half of crude acrylic acid is transformed into various acrylate esters at the production sites. Identical to glacial acrylic acid, these acrylic esters serve as commercial products, which are further processed both on-site and by external downstream users. Glacial acrylic acid is used in the manufacture of superabsorbing polymers (SAP), which account for 32% of the global demand for acrylic acid. Acrylic acid and basic alkyl esters (methyl, ethyl, butyl and 2-ethylhexyl esters) are used for the manufacture of polymer dispersions, adhesives, super absorbent polymers, flocculants, detergents, varnishes, fibres and plastics as well as chemical intermediates. [4]

Besides, there are number of factors drive demand for acrylic acid. Typically, acrylic acid trends align with the economy; as the economy improves, so does demand for acrylic acid. Products made from acrylic acid have continued at their normal, constant growth rates in spite of economic slowdowns. There has not been a lot of additional acrylic acid capacity added in the recent years.

3-1

KKEK 4281 Design Project Chapter 3: Plant Economy and Feasibility Study 3.1.2


Local Demand

Malaysia has the demand of acrylic acid in producing polyacrylates and acrylic ester thus the local market of acrylic acid in different local sectors of industry has good prospect. Currently there is only one manufacturer of acrylic acid in Malaysia which is BASF Petronas Sdn Bhd located at Gebeng, Pahang. [5]

3.1.3

Forecasted Future Demand

The demand for Acrylic Acid to produce polyacylates and acrylic ester is increasing steadily. Table 3.1: Forecasted global growth of the usage of acrylic acid up to year 2011 [6]

3.1.4

Area

Growth (%)

United State

5

Europe

1.6

Asia (China)

8

Average Global Growth

3.5

Production of Acrylic Acid

Based on the average global growth of 3.7% and take the basis of year 2007 Acrylic Acid production, the future production of acrylic acid is forecasted. Table 3.2: Forecasted annual production of acrylic acid up to year 2011 [6], [9]

Year

Forecasted Demand (billion pound per year)

2007

7.50

2008

7.78

2009

8.07

2010

8.37

2011

8.68

3-2



Major Manufacturer of Acrylic Acid Table 3.3: Major manufacturer of acrylic acid [6]

Company

Based

Rohm and Haas

USA

BASF

Germany

Dow Chemical

USA

American Acryl

USA

LG Chemical

Korea

3.1.6 Price of Acrylic Acid The market price of Acrylic Acid at different area Table 3.4: Price of acrylic acid at Asia and USA [7]

3.2

Area

Price (per Metric Ton)

Asia

USD 1800 – 1850

USA

USD 1490

Location of Acrylic Acid Plant

Country – Malaysia Through the harnessing of its oil and gas reserves and the forging of smart partnerships with some of the world’s largest petroleum companies, Malaysia has established the ideal infrastructure to support a vibrant petrochemical industry. (i) Criteria of Chosen: [11] •

Strategic location in the heart of South-East Asia.

•

Gateway to ASEAN and AFTA.

•

(AFTA is a free trade zone in Southeast Asia where member countries include Malaysia, Singapore, Thailand, Philippines, Indonesia, Vietnam, Laos, Myanmar, Cambodia and Brunei. The AFTA agreement supports the effort to relax trade barriers amongst member countries in order to achieve direct trade benefits)

•

Rich reserves of natural gas.

3-3



•

Political and Economic stability.

•

Developed infrastructure.

•

Government’s commitment

•

Quantity of life.

•

World-class facilities.

•

Integrated infrastructure.

•

Availability of capable workforce and skilled technical manpower.

•

The fast development of China had become a net importer of petrochemical products; her entry into World Trade Organization will also open up new business opportunities for petrochemical manufacturers in Malaysia.

(ii) The GDP of Malaysia as shown as following: [12]

Year

Growth Rate %

2003

4.2

2004

5.2

2005

7.1

2006

5.2

2007

5.9

2008

5.7

(iii) Petrochemical industry in Malaysia The petrochemical industry is an important sector in Malaysia with investments totaling RM6.9 billion as at the end of 2007. [13] Malaysia is an exporter of major petrochemicals products such as ethylene oxides, glycols, oxo-alcohols, styrene monomers and so on. Petrochemical zones in Malaysia: [14] •

Kertih, Terengganu

•

Gebeng, Pahang

•

Pasir Gudang port

•

Tanjung Langsat port

3-4

KKEK 4281 Design Project Chapter 3: Plant Economy and Feasibility Study •


Bintulu, Sarawak

(iv) Export of Acrylic Acid Product With the full implementation of AFTA, petrochemical manufacturers in Malaysia will benefit from a single market. Manufacturers based in Malaysia will also benefit from the access to a much larger Asia Pacific market. With China being a net importer of petrochemicals, Malaysia's 'early harvest' Free Trade Agreement with China will open up new business opportunities for petrochemicals manufacturers in Malaysia. [14]

3.2.2

Plant location

Location: Gebeng, Pahang The development of petrochemicals zones where petrochemical plants are clustered together has created a value chain which ensures the progressive development of petrochemicals activities. Gebeng is another petrochemical hub for multinational players like BASF, Amoco, Kaneka, Eastman and Polyplastics.

[11]

The petrochemical zone provides an integrated environment that

meets specific needs of the petrochemical industry. (i) Factors: [11] •

Availability of land.

•

Strategic location for import of raw material and export of products.

•

Logistics gateway for the East Coast Economic Region (ECER) to the Asean and the Asia-Pacific regions

•

Eastern Corridor Incentives

•

Penisular Gas Utilisation (PGU) project which trans-peninsular gas transmission pipeline channels sales gas to industries around the country.

•

Centralised Utility Facilities (CUF) which provides sufficient supply of utilities such as power, industrial gases, water and steam.

•

Kuantan Port 9 Centralised tankage facilities. 9 Pipeline and piperack system connecting Gebeng to Kuantan Port. 9 Container and bulk liquid port.

3-5



9 Railway linking Kerteh, Gebeng and Kuantan Port. •

East Coast Highway.

•

Environment Technology Part which incorporating a training centre, a waste collection and processing centre as well as raw material management and storage facilities, maintenance and servicing facilities.

(ii) Petrochemical Plant in Gebeng Table 3.5: Petrochemical plant in Gebeng [11]

Petrochemical Plants

Products Acrylic Acid and Esters, Syngas, Butyl Acrylate, Oxo-alcohols, Phthalic Anhydride

BASF Petronas Chemical (M) Sdn Bhd

and Plasticizers, Butanediol, Tetrahydrofurane and Gamma-butyrolactone

Eastman Chemicals (M) Sdn Bhd

Polyester Copolymers

Amoco Chemicals (M) Sdn Bhd

Purified Terephthalic Acid

Kaneka Paste Polymers Sdn Bhd

Dispersion Polyvinyl Chloride

Kaneka Malaysia Sdn Bhd

Methyl Methacrylates Copolymers

Polypropylene (M) Sdn Bhd

Polypropylene

3.3

Government Policy-Taxation [16]

3.3.1

Company Tax

A company, whether resident or not, is assessable on income accrued in or derived from Malaysia. Income derived from sources outside Malaysia and remitted by a resident company is exempted from tax, except in the case of the banking and insurance business, and sea and air transport undertakings. A company is considered a resident in Malaysia if the control and management of its affairs are exercised in Malaysia. Effective from the year assessment of 2007, the company income tax rate be reduced to 27%, including for SMEs.

3-6



Real Property Gain Tax

Capital gains are generally not subject to tax in Malaysia. Real property gains tax is charged on gains arising from the disposal of real property situated in Malaysia or of interest, options or other rights in or over such land as well as the disposal of shares in real property companies. The tax rates for Malaysian citizens and permanent residents are as follows: Disposal within 2 years 30% Disposal in the 3rd year 20% Disposal in the 4th year 15% Disposal in the 5th year 5% Disposal in the 6th year and thereafter - Company 5% - Individual nil

Citizens and permanent residents also enjoy an exemption of RM5, 000 or 10% of the gains whichever is the greater, besides a one-time tax exemption on the gains arising from the disposal of one private residence. For non-citizens and non-permanent resident individuals, gains from the disposal of real property within five years are taxed at a flat rate of 30%, after which the tax rate will be 5%.

3.3.3

Sales Tax

Sales tax is generally at 10%. However, raw materials and machinery for use in the manufacture of taxable goods are eligible for exemption from the tax, while inputs for selected non-taxable products are also exempted.

3.3.4 Import Tax Malaysia is committed to the ASEAN Common Effective Preferential Tariffs (CEPT) scheme under which all industrial goods traded within ASEAN are imposed import duties of 0% to 5%.

3.4

Economic Evaluation

The main purpose of this study is to calculate the profit which could be generated if the product is selling at the current market value. With the profit, we can determine the period where the generated income can be compensate with the investment made throughout the project.

3-7



The cost measurement can be divided into few elements: I. Total Capital Investment II. Total Product Cost III. Profitability Analysis

3.4.1

Purchased Equipment Table 3.6: Estimation of equipment cost [17], [18]

No.

Equipment Type

Quantity

Unit Price

Total

1

Storage Tank 1

5

71521

357605

2

Storage Tank 2

5

77629

388145

3

Storage Tank 3

5

70781

353905

4

Distillation Column

2

408697

817394

5

Quenching Tower

1

123301

123301

6

Reactor 1

1

473200

473200

7

Reactor 2

1

139700

139700

8

E-101 & E-100

2

13346

26692

9

E-104

1

63000

63000

10

E105

1

50600

50600

11

E-103

1

81400

81400

12

Separator

1

27800

27800

13

Compressor

1

1900000

1900000

14

Pump

30

4500

135000

15

Cooling Tower

11

520100

5721100

16

Treatment Cost

1

2500000

1769500

17

Reboiler

3

947000

2841000

Total (USD)

15269342

Total (MYR)

50388828.6

Total Capital Cost (After Index Factor)

57415993.1

3-8



Total Capital Investment

Total capital investment can be defined as the sum of the fixed-capital investment and the working capital. Total capital investment is evaluated by using fraction of delivered equipment method. Table 3.7: Estimation of Total Capital Investment [19]

Fraction of Delivered

Cost (MYR)

Equipment Direct Cost Cost of Purchased Equipment, E'

60895750.00

Delivery, 10% E'

6089575.00

Subtotal: Delivery Equipment

66985325.00

Purchased Equipment Installation

0.47

31483102.75

Instrumentation & Controls (Installation)

0.36

24114717.00

Piping (Installed)

0.66

44210314.5

Electrical System (Installed)

0.11

7368385.75

Building (Including Services)

0.18

12057358.5

Yard Improvements

0.1

6698532.5

Service Facilities (Installed)

0.7

46889727.5

Land

0.06

4019119.5 176841258

Total Direct Cost, A

Indirect Cost Engineering and Supervision

0.33

22105157.25

Construction Expenses

0.41

27463983.25

Legal Expenses

0.04

2679413

Contractor's Fees

0.22

14736771.5

Contingency

0.44

29473543

Total Indirect Cost, B

96458868

3-9


Group 6 Acrylic Acid Project 273300126

Fixed Capital Investment (FCI) = A+B

3.4.3

Working Capital (15% of FCI), C

40995018.90

Total Capital Investment (TCI) = A+B+C

314295144.9

Total Product Cost

Product: Acrylic Acid Targeted Operating Time, day/ year: 330 day/ year Targeted Capacity, tonne/ day: 215.448 tonne/ day Table 3.8: Estimation of Total Product Cost [19]

Suggested Factor

Calculated Value

Manufacturing Cost A. Direct Production Cost Raw Material (Glycerol)

74652732.00

Catalyst

526694.00

Utilities

30585365.00

Opearating Labor

0.10 of TPC

26514140.00

Laboratory Charges

0.10 of OL

2651414.00

Operating Supervision

0.10 of OL

2651414.00

Maintenance and Repairs

0.05 of FCI

13665006.30

Operating Suppliers

0.10 of FCI

27330012.60

Insurance

0.01 of FCI

2733001.26

Local Taxes

0.02 of FCI

5466002.52

Financing

0.03 of TCI

9428854.35

C. Plant Overhead Cost

0.10 of TPC

26514140.00

B. Fixed Charges

General Expenses

3-10



Administrative Costs

0.03 of TPC

7954242.00

Distribution and Marketing Costs

0.08 of TPC

21211312.00

Research and Development Costs

0.05 of TPC

13257070.00

Total Product Cost

265141400.04

Revenue

410590026.00

Gross Profit (Before Tax)

145448625.96

Tax

0.28

Net Profit After Tax

104723010.69

Depreciation

0.05 of FCI

13665006.30 91058004.39

Annual Income (Including Depreciation)

3.4.4

40725615.27

Profitable Analysis

(i) Simple Payback Period Payback period is defined as the minimum length of time for the total return to equal the capital investment. Payback Period =

(ii) Compounded Payback Period Table 3.9: Estimation of payback period [19]

End

Cumulative PW

Present worth

Cumulative PW

at i=0%/year

of cash flow at

at MARR =

through year k

i=10%/year

10%/year

-314295144.9

-314295144.9

-314295144.9

-314295144.9

0.9091

91058004.39

-223237140.5

82780831.79

-231514313.1

2

0.8264

91058004.39

-132179136.1

75250334.83

-156263978.3

3

0.7513

91058004.39

-41121131.73

68411878.7

-87852099.58

4

0.683

91058004.39

49936872.66

62192617

-25659482.58

5

0.6209

91058004.39

140994877.1

56537914.93

30878432.34

Present Worth

Net cash

Factor (P/F)

flow

0

-314295144.9

1

of year

3-11



6

0.5645

91058004.39

232052881.4

51402243.48

82280675.82

7

0.5132

91058004.39

323110885.8

46730967.85

129011643.7

8

0.4665

91058004.39

414168890.2

42478559.05

171490202.7

9

0.4241

91058004.39

505226894.6

38617699.66

210107902.4

By using the compounded payback period, Payback Period =

(iii) Rate of Return Rate of Return = (Net Profit/ Total Investment) x 100 Rate of Return = 28.97%

(iv) Internal Rate of Return (IRR) Internal Rate of Return = 28.28%

3.5 Conclusion Since the Internal Rate of Return (IRR) is greater than the Minimum Attractive Rate of Return (MARR), the plant is worth to invest. Furthermore the payback period is around 4-5 years according to the calculation. Hence from the economic evaluation, it can be concluded that our project is economical feasible and relatively good future.

3-12



3.5 References 1. http://www.freedoniagroup.com/Acrylic-Acid-And-Derivatives.html 2. http://mcgroup.co.uk/researches/A/03/Acrylic%20Acid%20Market%20Research.html 3. http://www.icis.com/v2/chemicals/9074869/acrylic-acid/pricing.html 4. http://mcgroup.co.uk/researches/A/03/Acrylic%20Acid%20Market%20Research.html 5. http://www.chemicals-technology.com/projects/gebeng/ 6. http://www.icis.com/v2/chemicals/9074870/acrylic-acid/uses.html 7. http://www.icispricing.com/il_shared/Samples/SubPage219.asp 8. http://www.chemicals-technology.com/projects/gebeng/ 9. http://www.icis.com/v2/chemicals/9074870/acrylic-acid/uses.html 10. http://www.icispricing.com/il_shared/Samples/SubPage219.asp 11. http://www.mida.gov.my/beta/pdf/MIDA%20Petrochemical%202007.pdf 12. http://www.indexmundi.com/malaysia/gdp_real_growth_rate.html 13. http://www.aseansources.com/jsp/malaysia_petrochemical_polymer.jsp 14. http://www.mida.gov.my/en/view.php?cat=5&scat=9&pg=641 15. http://www.ktak.gov.my/template01.asp?contentid=306 16. http://e-directory.com.my/doc/taxation.htm 17. http://www.mhhe.com/engcs/chemical/peters/data/ce.html 18. www.matche.com 19. Peter, M. S., Timmerhaus, K. D.; Plant Design and Economics for Chemical Engineers, 5th Edition, McGraw-Hill Inc: New York, 2003.

3-13



3-14

KKEK 4281 Design Project Chapter 4: Safety, Health and Environment


CHAPTER 4: ENVIRONMENT, SAFETY AND HEALTH 4.1 Environment 4.1.1

Law and Regulation

In Malaysia, the environmental matter is handled by the Department of Environment (DOE), a department constituted under the Ministry of Science, Technology and Environment. The pollution control and strategy or remedial approach is implemented through the enforcement of the Environmental Quality Act, 1974. This act provides for the prevention, abatement, and control of pollution through licensing, and mandates the conducting of an Environmental Assessment Report.

The enforcement of this act and the accompanying 16 sets of Regulations and Orders have played a significant role in the management of the environment, and in particular, with respect to pollution control. Examples of the regulations have to be concern under Environment Quality Act, 1974 are: •

Environment Quality (Clean Air): Regulation 1978

•

Environmental Quality (Sewage and Industrial Effluents): Regulations 1979

•

Environmental Quality (Schedule wastes): Regulation 1989

4.1.2 Waste Water Treatment The waste water stream from production mainly contaminate by following contaminants. Table 4.1: Waste water composition

Mass flow

Mole flow

Concentration

Waste water

(kg/hr)

(kgmole /hr)

(ppm)

Glycerol

10.741

0.11663

3952.228846

Water

2599.2

144.28

-

Acetol

48.042

0.64853

17677.40231

Acrolein

59.724

1.0653

21975.87893

Total

2717.707

146.11046

4-1



1,2-Ethanedithiol Waste Water

meta-xylylenediamine

Flocculants

Flocculant tank Reactor

Reactor

Clarifier

Filter press

Sludge

halophilic bacteria

NaCl, Mg2+, K+, NH4+, PO43-

Discharge

Carbon Filter

Biological treatment system Membrane Bioreactor

Figure 4.1: Schematic of water treatment system

The flow rate of water is estimated 2717.7liter per hour. The waste water stream is stored in a stabilizer tank. The waste water stream is treated by chemical precipitation method as primary treatment and biological treatment as secondary treatment.

In primary treatment, the waste water stream is dosing with 1,2-Ethanedithiol and metaxylylenediamine in a reactor to remove acrolein and acetol. Dosing 1,2-Ethanedithiol at a pH of between 3.0 and 7.0 to form an acrolein derivative in a process stream to remove acrolein.[1] The polyamine interacts with or binds the carbonyl bearing impurities including acetol. Dosing meta-xylylenediamine can reduce the concentration of acetol. [2]

After the chemical precipitation process, the waste water then is dosing with flocculants for flocculation before flow into the clarifier. The bottom outlet is then pumped through

4-2



the filter press for dewatering process. Sludge generated is sent for disposal and the effluence water is pump to biological treatment system.

The biological treatment system used is membrane bioreactor. By adding halophilic bacteria into the solution and addition of ions NaCl, Mg2+, K+, NH4+, PO43- to enhance growth can remove the glycerol inside the waste water.

The treated water is filter by carbon filter to remove the remaining organic matter and reduce the COD before discharge out. The discharge waste water have following target. Table 4.2: Waste water discharge target

Concentration

After chemical

After biological

Waste stream

(ppm)

precipitation (ppm)

treatment

Glycerol

3952.228846

3952.228846

0

Acetol

17677.40231

0

0

Acrolein

21975.87893

0

0

The sludge / precipitate are then destroyed by controlled burning in an incinerator. 4.1.3 Gas Emmision and Treatment

Purge

Discharge

Scrubber System

Carbon Filter Figure 4.2: Schematic of gas treatment system

The gas emission from the plant mainly containing acrylic acid, acetic acid, acrolein and carbon dioxide.

4-3



Acrylic acid and acetic acid in gas phase can be neutralized by wet scrubber with caustic solution as scrubbing fluid.

[3]

Emissions of acrolein and other odorous components in

vents can be controlled with water scrubbers. [4]

Hence the purge gas is flow through scrubber system to remove the acrylic acid, acetic acid and acrolein. The concentration of carbon dioxide discharge is 0.6% which is insignificant which do not need addition treatment. Before the gas discharge to environment, the gas is flow through the carbon filter to filter out the remaining organic compounds. Removal of air pollutants by adsorption onto granules of activated carbon is an extremely effective technology for volatile organic compounds (VOCs) and other organic pollutants. [3]

The target of the gas treatment plant can simply in following table: Table 4.3: Gas emission target

Concentration

After Scubber

After Carbon

Waste stream

(ppm)

(ppm)

Filter(ppm)

Acrylic Acid

1022.686871

10

5

Acetic Acid

1282.029479

10

5

Acrolein

4059.200779

0.1

0.05

The water used for absorb the acrolein is sent to waste water treatment plant before discharge out. The granular activated carbon can be regenerated by controlled burning in the incinerator too. [5]

4-4



4.2 Health 4.2.1 Effect to Human 4.2.1.1 Acetic Acid 4.2.1.1.1 Health Hazard Glacial acetic acid is a highly corrosive liquid. Contact with the eyes can produce mild to moderate irritation in humans. Contact with the skin may produce burns. Ingestion of this acid may cause corrosion of the mouth and gastrointestinal tract. Death may occur from a high dose (20–30 mL), and toxic effects in humans may be felt from ingestion of 0.1–0.2 mL. An oral LD50 value in rats is 3530 mg/kg. Glacial acetic acid is toxic to humans and animals by inhalation and skin contact. In humans, exposure to 1000 ppm for a few minutes may cause eye and respiratory tract irritation. Rabbits died from 4-hour exposure to a concentration of 16,000 ppm in air.

4.2.1.1.2 Exposure Limits TLV-TWA 10 ppm (25 mg/m3) (ACGIH, OSHA, and MSHA); TLV-STEL 15 ppm (37.5 mg/m3) (ACGIH).

4.2.1.2 Acetol 4.2.1.2.1 Health Hazard Acetol is flammable liquid and vapor. It may cause eye and skin irritation. Ingestion of acetol may cause irritation of the digestive tract. Inhalation may cause respiratory tract irritation. Vapors may cause dizziness or suffocation. An oral LD50 value in rats is 2200 mg/kg.

4.2.1.2.2 Exposure Limits Not listed in ACGIH, OSHA and NIOSH.

4.2.1.3 Acrolein 4.2.1.3.1 Health Hazard Acrolein is one of the EPA Classified Acute Hazardous Waste. It is a highly toxic compound that can severely damage the eyes and respiratory system and burn the skin.

4-5



Ingestion can cause acute gastrointestinal pain with pulmonary congestion. An oral LD50 value in mice is 40 mg/kg.

Inhalation can result in severe irritation of the eyes and nose. A concentration of 0.5 ppm for 12 minutes can cause intolerable eye irritation in humans. In rats, exposure to a concentration of 16 ppm acrolein in air for 4 hours was lethal. Acrolein can be absorbed through the skin. The spillage of liquid can cause severe chemical burns. Skin contact may lead to chronic respiratory disease and produce delayed pulmonary edema. In a study on inhalation toxicity in rats, the exposure to 1 atm of acrolein vapors caused physical incapacitation. The animals lost the ability to walk and expired.

4.2.1.3.2 Exposure Limits TLV-TWA 0.25 mg/m3 (0.1 ppm) (ACGIH and OSHA); STEL 0.8 mg/m3 (0.3 ppm); IDLH 5 ppm (NIOSH).

4.2.1.4 Acrylic Acid 4.2.1.4.1 Health Hazard Acrylic acid is a corrosive liquid that can cause skin burns. Spill into the eyes can damage vision. The vapors are an irritant to the eyes. The inhalation hazard is of low order. An exposure to 4000 ppm for 4 hours was lethal to rats. The dermal LD50 value in rabbits is 280 mg/kg.

4.2.1.4.2 Exposure Limits TLV-TWA 10 ppm (30 mg/m3) (ACGIH).

4.2.1.5 Carbon Dioxide 4.2.1.5.1 Health Hazard Carbon dioxide is an asphyxiant. Exposure to about 9–10% concentration can cause unconsciousness in 5 minutes. Inhalation of 3% CO2 can produce weak narcotic effects. Exposure to 2% concentration for several hours can produce headache, increased blood pressure, and deep respiration.

4-6



4.2.1.5.2 Exposure Limits TLV-TWA 5000 ppm (9000 mg/m3) (ACGIH, MSHA, and OSHA); STEL 30,000 ppm (ACGIH).

4.1.1.6 Glycerol 4.2.1.6.1 Health Hazard Glycerol is a clear, colorless solution with a faint to slight odor. It may cause eye and skin irritation. Ingestion of large amounts may cause gastrointestinal irritation. It is low hazard for usual industrial handling. Inhalation of a mist of this material may cause respiratory tract irritation.

4.2.1.6.2 Exposure Limits TLV-TWA: 10 mg/m3 (ACGIH), 15mg/m3 (OSHA), TLV-STEL: 20mg/m3

4.2.2 Effect to Environment 4.2.2.1 Acetic Acid Environmental effects depend on the concentration and duration of exposure to acetic acid. In high concentrations it can be harmful to plants, animals and aquatic life. Acetic acid degrades rapidly to harmless substances in the environment.

4.2.2.2 Acrolein In view of the high toxicity of acrolein for aquatic organisms, it presents a risk to aquatic life at, or near, sites of industrial discharges or spills, and during biocidal use. Contamination of soil, water, and the atmosphere can be avoided by the use of proper methods of storage, transport, and waste disposal.

4.2.2.3 Acrylic Acid Acrylic acid emitted into the atmosphere will react with photochemically produced hydroxyl radicals and ozone, resulting in rapid degradation. There is no potential for long-range atmospheric transport of acrylic acid because it has an atmospheric lifetime of less than one month. When released into water, acrylic acid readily biodegrades. The fate

4-7



of acrylic acid in water depends on chemical and microbial degradation. When added to water acrylic acid is rapidly oxidized, and so it can potentially deplete oxygen if discharged in large quantities into a body of water. Acrylic acid has been shown to be degraded under both aerobic and anaerobic conditions. The toxicity of acrylic acid to bacteria and soil microorganisms is low.

4.2.2.4 Glycerol Acute toxicity of glycerol to fish, daphnia, algae and microorganisms has been test. The studies show that glycerol is of low acute toxicity to fish and aquatic invertebrates. LC/EC50 values are all in excess of 5000 mg/L.

4.3 Safety 4.3.1 Hazard Introduction The term hazardous properties may be broadly classified into two principal categories: namely toxicity, and flammability and explosivity.

The term toxicity refers to substances that produce poisoning or adverse health effects upon acute or chronic exposure. It includes mutagenicity and carcinogenic potential, teratogenicity and corrosivity or irritant actions.

Animal data on the median lethal dose (LD50) by various routes of administration is good indicator of the degree of toxicity of a substance. Substances that exhibit acute oral LD50 values of <100 mg/kg in rats or mice are termed highly toxic compounds. Those that have LD50 values of 100–500 mg/kg and >500 mg/kg are termed moderate and low toxicants, respectively.

The flammable properties of substances in air include their flash point, vapor pressure, autoignition temperatures, and flammability range. Liquids that have a flash point of <100°F (37.8°C) are termed flammable, whereas liquids that have a flash point of 100– 200°F (37.8–93.3°C) are termed combustible. A violent reaction that produces flame can cause an explosion under more severe conditions.

4-8



Hazardous substances can be disposed of in an approved landfill disposal site, although such disposal of highly toxic compounds can lead to groundwater contamination. Incineration in a chemical incinerator equipped with an afterburner and scrubber is a widely used practice for the destruction of toxic wastes. Biodegradation of toxic compounds to nontoxic products in soils, waters, treatment plants, and bioreactors has become treatment for toxic waste in recent years. Other processes that are used include treatment with molten metals, wet oxidation, ultraviolet (UV) light-catalyzed oxidation using hydrogen peroxide or ozone, and dechlorination or desulfurization.

4.3.2 Handling and Storage of Hazardous Chemical 4.3.2.1 Acetic acid Acetic acid is a combustible liquid and the vapor of acetic acid forms explosive mixtures with air. Acetic acid may react explosively with the fluorides of chlorine and bromine. When it reacts with metals, it will produce flammable hydrogen gas. The dilute acetic acid and dilute hydrogen also can undergo an exothermic reaction if heated, forming peracetic acid which is explosive at 110 °C. So it needed to be stored in a segregated and approved area and keep container in a cool, well-ventilated area.

Splash goggles, synthetic apron and vapor respirator is used as personal protective equipment when handling acetic acid since it is irritant and corrosive chemical.

4.3.2.2 Acetol Acetol is flammable liquid and incompatible with strong oxidizing agents. Safety glasses and adequate ventilation is used when handling the acetol. The storage area should keep away from any source of ignition. It also should protect from moisture or called as hygroscopic.

4.3.2.3 Acrolein Acrolein is highly flammable in presence of open flames and sparks, of heat. The vapors of acrolein may form explosive mixtures with air. When heated to decomposition it emits toxic fumes of carbon monoxide, peroxides. Hence it needed to be stored in a segregated

4-9



and approved area and keep container in a cool, well-ventilated area and do not store above 8°C (46.4°F).

Since acrolein is highly toxic, irritant and corrosive, eyewash stations and safety showers are ensure proximal to the work-station location. Personal protection such as vapor respirator, face shield, gloves and boots is put on when handling the chemical.

4.3.2.4 Acrylic Acid Acrylic acid is a flammable liquid. It’s extremely flammable in presence of open flames and sparks. The storage tank of acrylic acid should keep dry and the area keep locked up and dry. It should always keep away from all possible sources of ignition (spark or flame). The container should tightly close and sealed until ready for use. Hand gloves and vapor respirator is used when handling the chemical.

4.3.2.5 Glycerol Glycerol is slightly flammable to flammable in presence of open flames and sparks, of heat, of oxidizing materials. It is incompatible with strong oxidizers such as chromium trioxide, potassium chlorate, or potassium permanganate and may explode on contact with these compounds. Glycerol and chlorine may explode if heated and confined.

The container should keep container tightly closed and at cool, well-ventilated area. Safety glasses, lab coat, vapor respirator and hand gloves should be used when handling glycerol.

4.3.2.6 Isopropyl Acetate Isopropyl acetate is flammable liquid. It slightly flammable to flammable and explosive to explosive in presence of oxidizing materials, of acids, of alkalis. It should keep away from heat and ground all equipment containing material. Since it is flammable materials and should be stored in a separate safety storage cabinet or room. The container should keep away from sources of ignition and tightly closed. A refrigerated room would be preferable for materials with a flash point lower than 37.8°C

4-10



(100°F). Splash goggles, lab coat and vapor respirator is used when handling the chemical.

4.3.2.7 Thermal Oil When handling the thermal oil, avoid contact with eyes, skin and clothing. The container should always closed and avoid breathing vapour or mist. It use with adequate ventilation and wash thoroughly after handling. The heat transfer fluids are intended for indirect heating purposes only.

4.4 References 1. Gregory J. Ward, Process For Removal of Acrolein from Acrylonitrile Product Streams, 2003. 2. Zafarullah K. Cheema, Purification of Phenol, 1969. 3. Frank Woodard, Industrial Waste Treatment Handbook, 2001. 4. Van Nostrand Reinhold, Air and Waste Management Association, 1992. 5. Pradyot Patnaik, A Comprehensive Guide To The Hazardous Properties Of Chemical Substances, 2007.

4-11

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance


CHAPTER 5: MASS AND ENERGY BALANCE 5.1

Introduction

The objective of this project is to design a plant with production of 70,000 tonnes/year of acrylic acid from the dehydration of glycerol. In this chapter, mass and energy balance hand calculation was done based on the HYSIS simulation input values to calculate the output results in each unit operation. After that, the output results of HYSIS were compared with hand calculation and hence calculate the deviation between them.

5.2

Comparison between Manual Calculations and HYSIS Result

5.2.1

Approach of Manual Calculation

The manual calculation for this plant was calculated by making several assumptions for the purpose to simplify the equation. Since there is lack of literature values of date such as equilibrium constant, some of the thermodynamics data were obtained from HYSIS whenever it was necessary. In order to simplify the whole manual calculation, the input values of every unit operations are taken from the HYSIS results which the recycle streams were already considered. Assumption such as ideal mixing, and constant heat capacity with a wide range of pressure were made for the energy calculation.

5.2.2

Approach to HYSIS Simulation

Simulation was carried out using HYSIS 3.2 software. The package was used: NRTL for the acrylic acid production. Below are the tables that presented the mass and energy balance of each stream and its deviations with the HYSIS.

5.3

Mass Balance Results

5.3.1

Feed rate calculation

Acrylic Acid Rate Desire

= 70000ton/ year = 107.38kmol/h

Given:

Conversion rate for the reactor 2 is 98%, Yield is 94.1% 107.38 So, the acrolein fed to Reactor 2 = x 100 = 114.12kmol / h 94.1

Given:

Conversion rate for the reactor 1 is 98.3%, Selectivity is 86.2%

5-1

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance So, the glycerol fed to Reactor 1 =

Group 6 Acrylic Acid Project 114.12 x 100 = 134.68kmol / h ( 98.3x86.2 )

Given: In order to achieve high conversion and selectivity, we need to feed in water and oxygen together with the crude glycerol. From the sources that we found, the weight ratio of crude glycerol to water is 20:80. On the other hand, the oxygen needed for the mixture of glycerol and water is 0.07%. 5.3.2

Mixture of Stream 4 and 16 Table 5.1: Molar flow rate at stream 5 and its comparison with HYSIS

Component

Glycerin Water Oxygen Nitrogen Acetol Acrolein Total

Stream 5 HYSIS

Hand Calculation

% Deviation

137.22 2780.90 205.91 774.55 12.31 21.52 3932.41

137.22 2780.90 205.91 774.55 12.31 21.52 3932.41

0.0 0.0 0.0 0.0 0.0 0.0 0.0

5.3.3 CRV-100 Table 5.2: Molar flow rate of stream 6 at CRV-100 and its comparison with HYSIS

Component

Glycerin Water Oxygen Nitrogen Acetol Acrolein Total 5.3.4

Stream 6 HYSIS

Hand Calculation

% Deviation

2.33 3049.90 205.91 774.55 13.10 155.61 4201.39

2.33 3049.87 205.91 774.55 13.10 155.61 4201.37

0.0 0.0 0.0 0.0 0.0 0.0 0.0

V-100 Table 5.3: Molar flow rate of stream 10 at V-100 and its comparison with HYSIS

Component

Glycerin Water

Stream 10 HYSIS

Hand Calculation

% Deviation

2.33 2884.40

2.33 2904.95

0.0 1.9 5-2

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance Oxygen Nitrogen Acetol Acrolein Total

0.02 0.03 12.97 21.44 2921.16

Group 6 Acrylic Acid Project 0.16 0.03 12.98 120.63 3041.07

87.5 0.0 0.1 82.2 3.9

Table 5.4: Molar flow rate of stream 20 at V-100 and its comparison with HYSIS

Component

Glycerin Water Oxygen Nitrogen Acetol Acrolein Total 5.3.5

Stream 20 HYSIS

Hand Calculation

% Deviation

0.00 165.52 205.89 774.52 0.13 134.17 1280.23

0.00 144.95 205.04 774.52 0.12 34.98 1159.60

0.0 14.2 0.4 0.0 8.3 283.6 10.4

Purge Stream from Stream 10 Table 5.5: Molar flow rate of stream 11 of and its comparison with HYSIS

Component


Stream 11 HYSIS

Hand Calculation

% Deviation

0.12 144.22 0.00 0.00 0.65 1.07 146.06

0.12 144.22 0.01 0.00 0.65 1.07 146.06

0.0 0.0 100 0.0 0.0 0.0 0.0

Table 5.6: Molar flow rate of stream 12 and its comparison with HYSIS

Component


Stream 12 HYSIS

Hand Calculation

% Deviation

2.21 2740.2 0.16 0.03 12.31 20.37 2775.11

2.21 2740.18 0.15 0.03 12.33 20.37 2775.10

0.0 0.0 6.7 0.0 0.2 0 0.0

5-3

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance 5.3.6


Mixture of Stream 14, 15 and 16 Table 5.7: Molar flow rate of stream 17 and its comparison with HYSIS

Component


Stream 17 HYSIS

Hand Calculation

% Deviation

2.22 2780.90 205.91 774.55 12.31 21.52 3797.41

2.22 2780.90 205.91 774.55 12.31 21.52 3797.41

0.0 0.0 0.0 0.0 0.0 0.0 0.0

5.3.7 Mixture of Stream 20, 21 and 22 Table 5.8: Molar flow rate of stream 23 and its comparison with HYSIS

Component

Water Oxygen Nitrogen Acetol Acrolein Total

Stream 23 HYSIS

Hand Calculation

% Deviation

165.52 215.41 810.52 0.13 134.17 1325.75

165.52 215.41 810.53 0.13 134.17 1325.76

0.0 0.0 0.0 0.0 0.0 0.0

5.3.8 CRV-101 Table 5.9: Molar flow rate of stream 24 at CRV-101 and its comparison with HYSIS

Component

Water Oxygen Nitrogen Acetol Acrolein Acrylic acid Carbon dioxide Acetic acid Total

Stream 24 HYSIS

Hand Calculation

% Deviation

165.52 144.42 810.52 0.14 2.69 126.25 5.23 5.23 1260.00

165.52 144.43 810.52 0.13 2.69 126.25 5.23 5.23 1260.00

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

5-4

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance 5.3.9


Mixture of Stream 26 and 34 Table 5.10: Molar flow rate of stream 27 and its comparison with HYSIS

Component

Water

Stream 27 HYSIS

Hand Calculation

% Deviation

400.00

400.00

0.0

5.3.10 T-100 Table 5.11: Molar flow rate of stream 28 at T-100 and its comparison with HYSIS

Component

Water Oxygen Nitrogen Acrolein Acrylic acid CO2 Acetic acid Total

Stream 28 HYSIS

Hand Calculation

% Deviation

402.94 144.43 810.51 2.54 0.58 5.23 0.81 1367.05

405.52 144.43 810.52 2.69 0.00 5.23 0.00 1368.39

0.6 0.0 0.0 5.6 0.0 0.1

Table 5.12: Molar flow rate of stream 29 at T-100 and its comparison with HYSIS

Component

Water Oxygen Nitrogen Acetol Acrolein Acrylic acid CO2 Acetic acid Total

Stream 29 HYSIS

Hand Calculation

% Deviation

162.58 0.15 0.01 0.13 0.14 125.67 0.00 4.42 292.96

160.00 0.00 0.00 0.13 0.14 126.25 0.00 5.23 291.62

1.6 0.0 0.0 0.5 0 15.5 0.5

5.3.11 MIX-100 Table 5.13: Molar flow rate of stream 31 at MIX-100 and its comparison with HYSIS

Component

Water

Stream 31 HYSIS

Hand Calculation

% Deviation

0.19

0.19

0.0 5-5

KKEK 4281 Design Project Chapter 5: Mass and Energy Balance Acetic acid Acetol Acrolein Cyclohexane I-P-acetate Total

0.32 0.00 0.00 191.25 233.75 425.51

Group 6 Acrylic Acid Project 0.32 0.01 0.16 191.25 233.75 425.86

0.0 100.0 100.0 0.0 0.0 0.08


Component

Acrylic acid Others Total

Stream 33 HYSIS

Hand Calculation

% Deviation

1.32 592.45 593.77

1.26 593.81 595.07

4.8 0.2 0.2


Component

Acrylic acid Others Total

Stream 32 HYSIS

Hand Calculation

% Deviation

124.36 0.34 124.7

124.41 0.25 124.66

0.04 36.0 0.03

5.3.13 X-100 Table 5.16: Molar flow rate of stream 34 at X-100 and its comparison with HYSIS

Component

Water Total

Stream 34 HYSIS

Hand Calculation

% Deviation

154.49 154.49

154.49 154.49

0.0 0.0

Table 5.17: Molar flow rate of stream 35 at X-100 and its comparison with HYSIS

Component

Water Others Total

Stream 35 HYSIS

Hand Calculation

% Deviation

8.13 431.15 439.28

8.13 431.15 439.28

0.0 0.0 0.0

5-6




Component

Cyclohexane IP-acetate Others Total

Stream 36 HYSIS

Hand Calculation

% Deviation

0.17 15.42 13.69 29.28

7.65 9.35 14.28 31.28

97.7 64.9 4.1 6.4


Component

Cyclohexane IP-acetate Others Total 5.4

Stream 37 HYSIS

Hand Calculation

% Deviation

191.08 218.33 0.59 410.00

183.60 224.40 0.41 408.41

4.1 2.7 43.9 0.4

Comparison of mass balance results between Hand Calculations with HYSIS

In the mass balance, the deviations of results are mostly 0%. This is due to the formula and data we used in hand calculation are same with the HYSIS. Some of the small deviation results in HYSIS have fewer decimal points which also contribute to the deviation. However, high deviation of acetol and acrolein at MIX-103 is due to the value is relatively small. Thus a small change in amount of acetol or acrolein will cause a big deviation. This effect of the deviation also can be seen from others in Stream 32 and Stream 36. Besides that, the deviations in Stream 10, Stream 20 and Stream 37 are due to those assumptions made during manual calculation. This means the interaction between components, for example binary coefficient is neglected during hand calculation.

5-7


5.5


Energy Balance Results Table 5.20: Summary of Energy Balance and the Comparison

Hand

HYSIS

Calculation

Simulation

Temperature (K)

420.90

417.49

0.8

Mixer MIX-101

Temperature (K)

422.35

452.15

7.1

Mixer MIX-102

Temperature (K)

338.02

338.30

0.1

Mixer MIX-103

Temperature (K)

305.29

305.15

0.05

Mixer MIX-104

Temperature (K)

577.05

576.95

0.02

Mixer MIX-105

Temperature (K)

315.36

315.32

0.01

Heat Exchanger E-100

Temperature (K)

478.13

443.15

7.3

Heater E-101

Heat Flow (kJ/hr)

2.869x106

2.688x106

6.3

Heater E-102

Heat Flow (kJ/hr)

9.876 x 106

1.085x107

9.9

Heater E-103

Heat Flow (kJ/hr)

552.1

560.45

1.5

Heater E-104

Heat Flow (kJ/hr)

1.148 x 106

1.276x106

10.0

Heat Exchanger E-105

Temperature (K)

382.15

374.35

2.0

Heater E-106

Heat Flow (kJ/hr)

2.323x107

2.529x107

8.9

Reactor CRV-100

Heat Flow (kJ/hr)

-357.0

-323.8

9.3

Reactor CRV-101

Heat Flow (kJ/hr)

-2.91x x107

-2.809x107

3.5

Compressor K-100

Power (kW)

5767

5905

2.4

Pump P-100

Power (kW)

1.513

1.497

1.1

Pump P-101

Power (kW)

9.886

9.921

0.4

Separator V-100

Power (kW)

1.569x104

1.492x104

4.9

Quenching Tower T-100

Heat Flow (kJ/hr)

3.74x104

4.0x104

8.1

Condenser T-101

Heat Flow (kJ/hr)

8.74x107

8.85x107

1.3

Reboiler T-101

Heat Flow (kJ/hr)

8.80 x107

8.86x107

0.7

Separator X-100

Heat Flow (kJ/hr)

2.85x106

2.7x106

5.3

Condenser T-103

Heat Flow (kJ/hr)

5.79 x107

5.656x107

2.3

Reboiler T-103

Heat Flow (kJ/hr)

5.63 x107

5.657x107

0.5

Unit Operation

Parameters

Mixer MIX-100

% Deviation

5-8


5.6


Comparison Energy Balance Result between Hand Calculation and HYSIS

The discrepancies of results in energy balance were mainly due to those assumptions made in order to simplify the calculations such as negligible heat of dilution, negligible heat of mixing, negligible heat change due to pressure change, negligible heat loss to surrounding, negligible kinetic and potential energy and etc. Most of the mixer have small deviation with the HYSIS results compare with others unit operations maybe because mixing do not involve others heat such as heat of reaction and heat of formation. Beside that, sometime the assumptions such as the components in some stream are all change to vapor, or maybe the components all remain in liquid state are made when we do the hand calculation. In the other hand, the constant value such as heat capacity, heat of formation, heat of vaporization that we take from literature which the reference state are different with in the HYSIS make the deviation.

5-9

KKEK 4281 Design Project Chapter 6: Packed Bed Reactor 1


CHAPTER 6: PACKED BED REACTOR 1 6.1 Chemical Design of Reactor 1 6.1.1 Introduction In the first reactor, crude glycerol (C3H8O3) is dehydrated to acrolein(C3H4O) via heterogeneous catalytic endothermic reaction:

C3 H 8O3 ⎯⎯ → C3 H 4O + 2 H 2O

(Equation 1)

The raw material is crude glycerol obtained from biodiesel plant with purity of 88%. The catalyst used is aluminasilicates supported silicotungstic acid. The pressure and temperature of the reactor is maintained at 1 atm and 275oC. Under these conditions, the conversion of glycerol is 98.3% and the selectivity of the acrolein is 86.2%. The mass ratio of steam to glycerol is controlled to 4 to 1 while the proportion of oxygen to the total mass is controlled to 0.07. Steam is added as inert gas to control the rate of the reaction. Air which consists of oxygen and nitrogen is added to increase the lifetime of the catalyst by reducing coke formation or any undesired adsorption. The condition and composition of the reactor feed (Stream 5) and product (Stream 6) are shown below:

Conversion = 98.3% Selectivity = 86.2%

F5 = 3932.41 kmol/h Phase = Vapour FGly_5 = 137.22 kmol/h Fwater_5 = 2780.9 kmol/h FO2_5 = 205.91 kmol/h FN2_5 = 774.55 kmol/h FAce_5 = 12.31 kmol/h FAcro_5 = 21.52 kmol/h

65 = 4201.39 kmol/h Phase = Vapour FGly_6 = 2.33 kmol/h Fwater_6 = 3049.90 kmol/h FO2_6 = 205.91 kmol/h FN2_6 = 774.55 kmol/h FAce_6 = 13.10 kmol/h FAcro 6 = 21.52 kmol/h

Figure 6.1: Schematic Diagram of Reactor 1

6- 1



6.1.2 Type of Catalyst The catalyst used for the glycerol dehydration reaction is aluminosilicate supported silicotungstic acid. Some properties of the catalyst are shown in Table 1[1]. Assumption: (i) The catalyst is in spherical shape. (ii) The bed porosity = 0.7 Table 6.1: Property of catalyst

Parameter Catalyst used Shape BET surface area (m2/g) Diameter (µm) Surface density (µmol/m2)

Value aluminosilicate supported silicotungstic acid Porous spherical shape 309.2 315-500 0.197

Bed porosity, ø

0.7

Solid particle density, ρc (kg/m3)

885

6.1.3 Type of Reactor The dehydration of glycerol to acrolein is endothermic heterogeneous catalytic reaction with the feeds are in gaseous form and the catalyst used is in solid form. The reactors that can be used to handle this 2 phase reaction are either packed bed reactor and fluidized bed reactor. The dimension and performance of packed bed reactor and fluidized bed reactor are compared. The type of reactor which can achieve 98.3% of conversion of glycerol with a most economic design is chosen.

6.1.3.1 Packed Bed Reactor

Packed bed reactor is suitable to be used as reactor 1 as it provided higher conversion per unit weight of catalyst, low operating cost and can be run continuously. A packed-bed reactor is essentially a tubular reactor consists of one or more tubes packed with solid catalyst particles, in which the reactants and products flow through.

6- 2



Since the reaction is endothermic, extra heat has to be supplied to maintain the optimum temperature in the reactor. In the conceptual design, it is proposed that the feed itself served as the heating fluid. However in packed bed reactor, such heating method is not applicable as the temperature in reactor will become uneven. Hence a heating fluid is introduced into the reactor to maintain the reactor temperature. Since the reaction temperature is at 275oC, the heating fluid used is hot molten salt.

Figure 6.2: Shell-and-tube packed-bed reactor with co-current heating

6.1.3.1.1 Type of Heat Transfer Fluid

Hot molten salt is used as the heating medium to maintain the reactor 1 temperature at 275oC. We have decided to use HITEC Heat Transfer Salt supplied by Coastal Chemical Co. as the hot molten salt. HITEC is a white, granular solid; when melted, pale yellow. HITEC is an eutectic mixture of water-soluble, inorganic salts of potassium nitrate, sodium nitrite and sodium nitrate. We have decided to use HITEC Heat Transfer Salt supplied by Coastal Chemical Co. as the hot molten salt. HITEC is a white, granular solid; when melted, pale yellow. HITEC is a eutectic mixture of water-soluble, inorganic salts of potassium nitrate, sodium nitrite and sodium nitrate. It is a heat transfer medium for heating and cooling between 300-1100°F (149-538°C) and is suitable to be used as the heating fluid for reactor 1. HITEC is chosen because it has a low melting point (288°F, 142°C), high heat transfer coefficient, thermal stability, and low cost. It is nonfouling – a commonly recognized defect of 6- 3



many organic heat transfer media. HITEC is non-flammable, non-explosive and evolves no toxic vapours under recommended conditions of use. Besides, it has a low degree of corrosivity toward common materials of construction. Plain carbon steel, for example, can be used for installations that operate up to 850°F (454°C). The properties of HITEC are listed in Table 2[2]. The property is evaluated at 275°C and 1atm since the inlet temperature of hot molten salt is set to be 275°C. Table 6.2: Property of hot molten salt (HITEC)

Parameter

Value

Heat capacity, Cp_salt (J/kg•°C)

3420

Viscosity, μsalt (Pa•s)

2.1 x 10-3

Density, ρsalt (kg/m3)

1980

Thermal conductivity, ksalt (W/m•K)

0.57024

6.1.3.1.2 Packed Bed Reactor Dimension

Since the inlet flow rate is very high, 2 reactors which operate in parallel are used instead of one. Packed bed reactor with 1 shell pass and 1 tube pass is chosen because it easier to operate and control. The reactant (glycerol) and product (acrolein) are not corrosive in nature. However some of the by-product formed such as acrylic acid is corrosive. Hence tubes with BWF 40 are used to prevent tube leaking due to corrosiveness of the reactant and product. Triangular pitch is chosen to enhance the turbulence of molten salt (heating medium) in shell which resulting in higher heat transfer. Besides that more tubes can be placed in triangular pitch. Table 6.3: Dimension of Packed Bed Reactor [3]

Parameter Type No. of reactor operated in parallel Nominal tube size

Value 1 shell pass and 1 tube pass 2 1.5in tube of BWG 14

Outer diameter of tube, ODtube

1.5in.

Inner diameter of tube, IDtube

1.33in.

Tube pitch, PT

1.875in. triangular pitch

6- 4



Tube clearance, C’

0.375in.

Baffle spacing, B

0.1m

6.1.3.1.3 Equation Involved in Packed Bed Reactor Design 6.1.3.1.3.1 Rate law

Assumption: 1. The reaction is first order reaction. 2. The gas reactant and product obey ideal gas law. 3. Partial pressure of the reactant is calculated according to inlet pressure. 4. The reactor is assumed to be isothermal. 5. 80% of reactor is filled by catalyst. Rate Law: ⎛ mol Gly ⎞ − rGly ⎜ 3 ⎟ = k1 PGly ⎝ m catalyst ⋅ s ⎠ ⎛ mol Gly ⎞ 1 Hence, − rGly ⎜ k1 PGly ⎟= ⎝ kg catalyst ⋅ s ⎠ ρ c ⎛ ⎛ m3gas ⎞ 19 ⎜⎝ Where k1 ⎜ 3 ⎟ = 1.00 × 10 e ⎝ m catalyst ⋅ s ⎠

−248000 ⎞ ⎟ RT ⎠ [4]

For reaction with pressure drop: CGly =

CGlyo (1 − X ) ⎛ P ⎞ ⎛ To ⎞ ⎜ ⎟⎜ ⎟ 1 + ε X ⎝ Po ⎠ ⎝ T ⎠

From ideal gas law PGly = CGly RT Since it is assumed that the reactor is isothermal, T=To PGly =

PGlyo (1 − X ) ⎛ P ⎞ ⎛ To ⎞ ⎜ ⎟⎜ ⎟ 1 + 0.0698 X ⎝ Po ⎠ ⎝ T ⎠

6- 5



⎛ mol Gly ⎞ ⎛ 1 ∴−rGly ⎜ ⎟=⎜ ⎝ kg catalyst ⋅ s ⎠ ⎝ ρc

⎛ ⎞ 19 ⎜⎝ × 1.00 10 e ⎟ ⎠

−248000 ⎞ ⎟ RT ⎠

PGlyo (1 − X ) ⎛ P ⎜ 1 + 0.0698 X ⎝ Po

⎞ ⎛ To ⎞ ⎟⎜ ⎟ ⎠⎝ T ⎠

… (1)

6.1.3.1.3.2 Mole balance The design equation for packed-bed reactor is given as:

FGlyo

dX = −rGly dW

⎛ −248000 ⎞ PGlyo (1 − X ) ⎛ P ⎞ ⎛ To ⎞ dX ⎛ 1 ⎞ 19 ⎜⎝ RT ⎟⎠ 1.00 × 10 e =⎜ ⎟ ⎜ ⎟⎜ ⎟ dW ⎜⎝ ρ c FGlyo ⎟⎠ 1 + 0.0698 X ⎝ Po ⎠ ⎝ T ⎠

Let

Y=

P Po

dX ⎛ 1 =⎜ dW ⎜⎝ ρ c FGlyo

Z=

and

T To

⎛ −248000 ⎞ ⎞ CGlyo (1 − X ) ⎛ Y ⎞ 19 ⎜⎝ RT ⎟⎠ 1.00 10 e × ⎟⎟ ⎜ ⎟ 1 + 0.0698 X ⎝ Z ⎠ ⎠

… (2)

6.1.3.1.3.3 Ergun equation for pressure drop The gas-phase reaction is catalyzed by passing the reactant through a packed bed of catalyst

particles. The equation used most to calculate pressure drop in a packed bed is the Ergun equation. From Ergun equation, differential pressure drop across the tube is given as: ⎤ dP G ⎛ 1 − φ ⎞ ⎡150 (1 − φ ) μ =− + 1.75G ⎥ ⎜ 3 ⎟⎢ dz dP ρdP ⎝ φ ⎠ ⎣ ⎦

… (3)

Where z = length down the packed bed of tube At the entrance to the reactor: ⎛ P ⎞ ⎛ To ⎟⎜ ⎝ Po ⎠ ⎝ T

ρ = ρo ⎜

⎞ ⎛ FTo ⎞ ⎟ ⎟⎜ ⎠ ⎝ FT ⎠

… (4)

Substitute (4) into (3): dP ⎛ P ⎞⎛ T = −βo ⎜ o ⎟ ⎜ dz ⎝ P ⎠ ⎝ To

⎞ ⎛ FT ⎟ ⎜⎜ ⎠ ⎝ FTo

⎞ ⎟ ⎟ ⎠

… (5)

6- 6


βo =

Where


G (1 − φ ) ⎡150 (1 − φ ) μ ⎤ + 1.75G ⎥ 3 ⎢ ρ o d Pφ ⎣ dP ⎦

… (6)

Weight of catalyst, W = Volume of solid catalyst x Density of catalyst Weight of catalyst, W = Volume of reactor x (1 – bed porosity) x Density of catalyst W = (1 − φ ) Ac z × ρ c = ρb Ac z

ρb = ρ c (1 − φ )

Where

dz =

dW ρb Ac

… (7)

Substitute (7) into (5):

β ⎛ P ⎞⎛ T ⎞⎛ F dP = − o ⎜ o ⎟⎜ ⎟⎜ T dW ρb Ac ⎝ P ⎠ ⎝ To ⎠ ⎜⎝ FTo However,

⎞ ⎟ ⎟ ⎠

FT = 1+ ε X FTo ⎞⎛ T ⎞ ⎟ ⎜ ⎟ (1 + ε X ) ⎠ ⎝ To ⎠

∴

β ⎛P dP =− o ⎜ o dW ρb Ac ⎝ P

∴

βo ⎛ Z ⎞ dY =− (1 + 0.0698 X ) ρb Ac Po ⎜⎝ Y ⎟⎠ dW

… (9)

6.1.3.1.3.4 Simultaneous Ordinary Differential Equations

The conversion and pressure profiles for the packed-bed reactor are governed by 2 ODEs: 1)

⎛ −248000 ⎞ P 1− X ) ⎛ Y ⎞ dX ⎛ 1 ⎞ 19 ⎜⎝ RT ⎟⎠ Glyo ( e =⎜ × 1.00 10 ⎟ ⎜ ⎟ dW ⎝⎜ ρc FGlyo ⎠⎟ 1 + 0.0698 X ⎝ Z ⎠

2)

βo ⎛ Z ⎞ dY =− (1 + 0.0698 X ) ρb Ac Po ⎜⎝ Y ⎟⎠ dW

Since the reactor is assumed to be isothermal, Z=1. The ODEs are solved simultaneously by substituting all the relevant values, with the aid of MATLAB 7.0.

6- 7



6.1.3.1.4 Packed Bed Reactor Optimization

The reactor size and performances are analyzed by using different parameters such as pressure, temperature and the reactor shell diameter. The analysis is done by computing the variables with different pressure, temperature and flow area into the simultaneous equation. The result of weight of catalyst and the pressure ratio when the conversion, X=0.983[1] are obtained by solving the simultaneous equations using MATLAB software. The ratio of length and diameter of the reactor of different parameter are calculated. The reactor size and performance are optimized based on the following criteria: (i)

The ratio of length to diameter of the reactor (L/D) must be within the range of 510.[5]

(ii)

The pressure drop must be kept as low as possible or pressure ratio, Y as high as possible to prevent loss in pressure energy.

(iii)

The amount of catalyst should not be extremely high due to the economic consideration.

Example of the result of MATLAB by using P = 1 bar and T = 275oC. The result is shown in the plot obtained from MATLAB:

Figure 6.3: Plot of Conversion and Pressure Ratio Obtained from Matlab

Legend: Blue = Conversion

Green = Pressure Ratio

The accurate result is obtained from the “workplace” of MATLAB:

6- 8



Figure 6.4: Data of Conversion and Pressure Ratio Obtained from Matlab

6.1.3.1.4.1 Shell Diameter Analysis

Assume Pressure, P = 1.5 bar

Temperature, T = 275oC

The number of tubes that can be placed in the reactor is depends on the size of the shell of the reactor. Hence an analysis is done to study the performance of the reactor by using different size of shell. From the result of MATLAB, the weight of catalyst, W, pressure ratio, Y and the ratio of length and diameter of reactor, L/D are obtained and plotted against number of tubes.

6- 9



Table 6.4: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Number of Tube per Reactor [3]

Shell Diameter, IDs (m)

No. of Tubes per reactor, n

1.0 1.1 1.2 1.3 1.4 1.5

361 442 530 637 733 847

Flow Area, Ac (m2)

Weight of Catalyst, W (kg)

Pressure Ratio, Y

Length of Reactor, L (m)*

Ratio of Length to Diameter, L/D

4050 3820 3630 3510 3370 2980

0.872 0.898 0.917 0.932 0.9415 0.95

29.46 22.70 17.99 14.47 12.07 9.24

29.4609 20.6323 14.9882 11.1307 8.6238 6.1594

0.6472 0.7924 0.9502 1.1421 1.3142 1.5186 W * Length of reactor, L = ρb • Ac • 0.8 ρb = bed density (kg/m3) Ac = Total tubes flow area (m2) 0.8 means reactor is 80% filled by catalyst

From Table 4, it shows that the dimensions of reactor with shell diameter = 1.4 m and number of tube per reactor = 733 gives the result of length to diameter ratio = 8.6238 which is in the range of design criteria (5-10). Hence it is the most suitable dimension of the reactor to optimize the process.

6.1.3.1.4.2 Pressure Analysis

Set: Shell inner diameter = 1.4 m

Number of tube per reactor, n = 733

Assume: Temperature, T = 275oC

6- 10



From reference [1], the optimum pressure lies between 1 bar to 2 bar. From the result of MATLAB, the weight of catalyst, W, pressure ratio, Y and the ratio of length and diameter of reactor, L/D are obtained and plotted against inlet pressure.

Table 6.5: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Pressure, Po

Inlet Pressure, Po (bar)


Pressure Ratio, Y

Length of Reactor, L (m)


1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

2210 2440 2610 2850 3120 3370 3700 3800 3880 3970 4050

0.932 0.938 0.944 0.948 0.951 0.955 0.958 0.961 0.963 0.965 0.967

7.92 8.74 9.35 10.21 11.18 12.07 13.26 13.61 13.90 14.22 14.51

5.6552 6.2438 6.6788 7.2929 7.9838 8.6235 9.4680 9.7239 9.9286 10.1589 10.3636

6- 11



From Table 5, the length to diameter ratio at pressure 1 to 1.8 bars is within the design range, 510. However, operating under low pressure might causes the pressure driving force not sufficient to drive the reactant along the reactor. The situation become worse if there is clogging fouling that causing the pressure drop across reactor higher than expected. The outlet pressure might drop to less than 1 atm, which is vacuum condition under these situations. Hence it is better to have a safety margin to operate at higher pressure. Pressure of 1.4 bar is selected as the catalyst used is not too high and L/D ratio is still within 5-10. 6.1.3.1.4.3 Temperature Analysis

Set: Shell inner diameter = 1.4 m

Number of tube per reactor, n = 733

Pressure, P = 1.4 bar From reference [1], the optimum pressure lies between 260oC to 280oC. From the result of MATLAB, the weight of catalyst, W, pressure ratio, Y and the ratio of length and diameter of reactor, L/D are obtained and plotted against inlet temperature.

6- 12



Table 6.6: Weight of Catalyst, W, Pressure Ratio, Y, Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Temperature, To

Inlet Temperature, To (oC)


Pressure Ratio, Y

Length of Reactor (m)


260 265 270 275 280

8020 6500 5020 3120 1990

0.712 0.853 0.917 0.951 0.971

28.73 23.29 17.98 11.18 7.13

20.5225 16.6330 12.8458 7.9838 5.0922

From the Table 6, it is clearly show that 275oC is the best temperature to be operated because at 275oC, the ratio of length to diameter of reactor is 7.9838 which is in the range of design consideration, which is 5-10.

6.1.3.1.4.4 Result of Packed Bed Reactor Optimization Analysis Table 6.7: Results of Packed Bed Reactor Optimization Analysis

Parameter

Value


1.4


275

Number of Tubes per Reactor, n

733

Total Number of Tubes, N

1466


1.4


3120

Pressure Ratio, Y

0.951

Outlet Pressure, P=YPo

1.3314


11.18


7.9838

6.1.3.2 Fluidized Bed Reactor Fluidized bed reactor is operated by pumping in the inlet feed from the bottom of the reactor to

fluidize the catalyst particle in the reactor. The catalyst particle will fluidize if the inlet velocity is greater than minimum fluidization velocity. If not the reactor will only serve as a packed bed

6- 13



reactor. Fluidized bed reactor can produce uniform particle mixing and uniform temperature gradient which can provide a more uniform conversion along the reactor. Since the reaction is endothermic and additional heat has to be supplied to maintain the reactor temperature. The inlet feed itself will serve as the heating medium by feed into the reactor at a higher temperature to compensate the heat loss due to endothermic reaction. It is done by preheated inlet feed to desired temperature before feed into reactor.

Figure 6.5: Schematic Diagram of Fluidized Bed Reactor

6.1.3.2.1 Equation Involved in Fluidized Bed Reactor Design 6.1.3.2.1.1 Conversion of Glycerol in Fluidized Bed Reactor

Assumption: 1. 20% of the reactor volume is occupied by gas bubbles and 80% by catalyst particle. 2. Mass transfer coefficient, kmav = 0.60 s-1. 3. The reaction is first order reaction. From reference [6], conversion of glycerol in fluidized bed reactor is written as:

X = 1 − exp[−(

1 1 −1 L ) ] + ε d k ρc km av ub

εd = 0.80 (20% of reactor is filled by gas bubbles) ρc = catalyst density = 885 kg/m3

6- 14



kmav = mass transfer coefficient = 0.60 s-1 L = length of reactor ⎛ −248000 ⎞ 19 ⎜⎝ RT ⎟⎠

k = rate constant = 1.00 × 10 e ub= feed velocity = ∴ X = 1 − exp[−(

L=

−(

m π ( IDs ) 2 ρo

1 1 −1 L ) ] + 708k 0.6 ub

1 1 + ) 708k 0.6 ln(1 − X ) ub

6.1.3.2.2 Fluidized Bed Reactor Optimization

The fluidized bed reactor size and performance are analyzed by using different operating temperature and reactor diameter. The parameters to achieved conversion of glycerol = 0.983 [1] are obtained and the reactor size and performance are optimized based on the following criteria: (i)

The ratio of length to diameter of the reactor (L/D) must be within the range of 510.[5]

Since the inlet flow rate is very high, 5 reactors which operated in parallel are used in the process.

6.1.3.2.2.1 Temperature Analysis

Assume the reactor diameter = 1.5 m ub =

m = 2.515m / s π ( IDs ) 2 ρo

From reference [1], the optimum pressure lies between 260oC to 280oC.

6- 15



Table 1.8: Length of Reactor, L and Ratio of Length to Diameter, L/D at Different Inlet Temperature, To

Temperature

Rate Constant, k (s-1)



260 265 270 275 280

3.012E-05 4.983E-05 8.166E-05 0.0001326 0.0002136

78.6707 48.6250 30.7206 19.9513 13.4146

52.4471 32.4166 20.4804 13.3009 8.9431

From the Table 8, it is clearly show that 280oC is the best temperature to be operated because at 280oC, the ratio of length to diameter of reactor is 8.9431 which is in the range of design consideration, which is 5-10.

6.1.3.2.2.2 Reactor Diameter Analysis

Set temperature, T = 280oC k = 0.0002136 s-1

Table 6.9: Length of Reactor, L and Ratio of Length to Diameter, L/D for Different Shell Diameter, IDs

Shell Diameter, IDs (m) 1 1.1 1.2 1.3 1.4 1.5

Feed velocity, ub (ms-1) 5.6585 4.6764 3.9295 3.3482 2.8870 2.5149


5.9616 7.2136 8.5847 10.0751 11.6848 13.4136

Ratio of Length to Diameter, L/D 3.9744 4.8090 5.7232 6.7168 7.7899 8.9424

6- 16

KKEK 4281 Design Project Chapter 6: Packed Bed Reactor 1 1.6 1.7 1.8 1.9 2

Group 6 Acrylic Acid Project 2.2104 1.9580 1.7464 1.5675 1.4146

15.2617 17.2291 19.3156 21.5214 23.8465

10.1745 11.4861 12.8771 14.3476 15.8976

From Table 8, shell diameter of 1.4m is chosen because it gives a moderate value of length to diameter ratio, which is 7.7899.

6.1.3.2.2.3 Result of Fluidized Bed Reactor Optimization Analysis Table 6.10: Results of Fluidized Bed Reactor Optimization Analysis

Parameter

Value


280


1.4


11.68 m


7.7899

6.1.3.3 Comparison of Packed Bed and Fluidized Bed Reactor

From the optimization analysis, it shows that the reactor dimension and operating condition to achieved glycerol conversion of 98.3% for both type of reactor are almost similar. However fluidized bed reactor system required 5 reactors to operate in series while packed bed reactor only requires 2. This is because fluidized bed reactor requires bigger vessel for fluidization of catalyst. Hence less feed will pump into each reactor and more reactors are required. This resulted in the higher initial capital cost for fluidized bed reactor compared to packed bed reactor. Besides that higher pumping effect is required for fluidized bed reactor to ensure fluidization of the catalyst. This result in higher operating cost compared to packed bed reactor. There is also a possibility that the solid catalyst particle will entrained out along with the product and contaminate the product. Furthermore severe agitation of catalyst will result in catalyst destruction and dust formation.

6- 17



6.1.4 Heat Duty of Heating Jacket Q = m(ΔH ) = msalt C p (Th,in − Th ,out ) = U d A(ΔTLMTD ) Table 6.11: Variables to Calculate Heat Duty

Symbol

Description

Value

Unit

m’

Mass flow rate of reactant per reactor

12.936

kg/s

ΔH

Heat of reaction

49000

J/kg

msalt

Mass flow rate of molten salt (heating medium)

15

kg/s

Cp

Specific heat capacity of molten salt

3420

J/kg.oC

ΔTh,in

Inlet temperature of heating stream

330

ΔTh ,out

Outlet temperature of heating medium

U

Overall heat capacity of the reaction

A

Heat transfer surface area, nπ(ID)L

ΔTLMTD

o

C

o

C

W/m2. oC 869.72

m2

Log mean temperature difference of reactant and heating stream

Q = (12.936)(49000) = 6.339 x 105 J/s Q = msalt C p (Th ,in − Th ,out ) Th ,out = Th ,in −

Q msalt C p

Th ,out = 305.3 oC

ΔTLMTD =

(Th ,in − T ) − (Th ,out − T ) T −T ln( h ,in ) Th ,out − T

ΔTLMTD = 41.43 Q = U d A(ΔTLMTD ) Ud = 182.92 W/m2. oC

6.1.5 Clean overall heat transfer coefficient 6.1.5.1 Tube-side film coefficient, hio Table 6.12: Variables to Tube-side Film Coefficient

Symbol Ac

Description

Tube side flow area

Value

Unit

1.3142

m2

6- 18

KKEK 4281 Design Project Chapter 6: Packed Bed Reactor 1 G Ret Prt


Tube side mass velocity, G =

9.843

m Ac

Tube side Reynolds Number, Ret = Tube-side Prandtl number, Prt =

n IDt Gt

kg/ m2

1.367x107

μ

Cp ⋅ μ

0.7526

kt

hi*

Convective heat transfer coefficient

6308.59

W/m2.oC

hio

⎛ ID ⎞ Tube-side film coefficient, hio = hi ⎜ t ⎟ ⎝ ODt ⎠

5593.61

W/m2.oC

*Since Ret >10000 and 0.7
Nut =

hi ⋅ IDt = 0.0243Ret 0.8 Prt 0.4 kt

⎛ k ⎞ hi = 0.0243Ret 0.8 Prt 0.4 ⎜ t ⎟ ⎝ IDt ⎠ hi = 202.87 W/m 2 ⋅ °C 6.1.5.2 Shell-side film coefficient, ho Table 6.13: Variables to Shell-side Film Coefficient

Symbol

Description

Value

Unit

0.1

m

B

Baffle Spacing

Pt

Tube pitch (square pitch)

1.875

in

C’

Tube clearance, C’=Pt - ODt

0.375

in

0.02800

m2

535.77

kg/s·m2

as

Gs

Shell-side flow area, as =

( IDshell ) ( C ' ⋅ B )

Shell-side mass velocity, Gs =

Pt msalt as

6- 19



De

⎛ ODt 2 ⎞ 4 ⎜ PT 2 − π ⎟ 4 ⎠ Equivalent diameter, De = ⎝ π ODt

0.0377

m

ho*

Shell-side film coefficient

201.34

W/m2·°C

*The shell film coefficient is given as: ho De ⎛DG ⎞ = 0.36 ⎜ e s ⎟ k ⎝ μ ⎠

0.55

⎛ Cμ ⎞ ⎜ ⎟ ⎝ k ⎠

0.55

⎛ C p _ salt μ salt ⎞ ⎜ ⎟ ⎝ ksalt ⎠

⎛DG ⎞ ∴ Shell-side film coefficient, ho = 0.36 ⎜ e s ⎟ ⎝ μ salt ⎠

0.33

0.33

⎛ k salt ⎞ ⎜ ⎟ ⎝ De ⎠

= 201.34 W/m2·°C

6.1.6 Fouling factor Table 6.14: Variables to Calculate Fouling Factor

Symbol

Description

Value

Unit

Uc

h ⋅h Clean overall heat transfer coefficient, U c = io o hio + ho

194.34

W/m2·°C

Ud

Actual heat transfer coefficient

182.92

W/m2·°C

Rd

Fouling factor, Rd =

1 1 − Ud Uc

0.00032

o

C/W

Fouling factor of 0.00032 m2•°C/W is sufficient to account for the flow across packed-bed of catalyst. Hence, the designed reactor dimension is acceptable.

6- 20



6.1.7 Summary of Specification of Reactor 1 Table 6.15: Summary of Specification of Reactor 1

Parameter

Description

Type of reactor

Shell-and-tube packed-bed reactor

Type of catalyst

aluminosilicate supported silicotungstic acid

Heating Medium Flow pattern Conversion, X No. of reactor operated in parallel

Molten Salt (HITEC) Co- current 0.983 2

No. of tubes per bank

733

Total no. of tubes, n

1466

Nominal tube size

1.5in. BWF 14

Outer diameter of tube, ODtube

1.50in.

Inner diameter of tube, IDtube

1.33in.

Tube pitch, PT

1.875in. triangular pitch

Tube clearance, C’ = PT - ODtube

0.375in.

Internal diameter of shell, IDshell

1.4m

Weight of catalyst

3120 kg

Length of reactor

11.18 m

Actual overall heat transfer coefficient, Ud

182 W/m2•°C

Mass flow rate of hot molten salt, msalt

15 kg/s

Temperature of inlet reactant, To

275°C

Temperature of outlet product, T

275°C

Inlet temperature of molten salt

330°C

Outlet temperature of molten salt

305.3°C

6- 21



Pressure at inlet of reactor

1.4bar

Pressure at outlet of reactor

1.3314bar

Heat transfer duty, Q

6.339 x 105 W

6.2 Mechanical Design of Reactor 1 6.2.1 Design Pressure The reactor must be designed to withstand the maximum pressure to which is it likely to be subjected in operation. For safety purpose, the design pressure normally is 5 to 10% above the operating pressure to avoid spurious operation during minor process upsets. The operating pressure of the packed bed reactor for dehydrogenation of glycerol is 1.4 bar. The reactor is designed to withstand the pressure 10% higher than the operating pressure. Design Pressure, PD = (1.4)(1.1) = 1.54 bar

6.2.2 Design Temperature The strength of metals decreases with increasing temperature so the maximum allowable design stress will depend on the material temperature. The design temperature at which the design stress is evaluated should be taken as the maximum working temperature of the material, with due allowance for any uncertainty involved in predicting vessel wall temperatures. Design Temperature, TD = 275oC

6.2.3 Material of Construction Since the reactant, glycerol and product, acrolein are not corrosive in nature, carbon steel should be used as the construction material for reactor. However oxygen is supplied into the column to oxidize the catalyst to elongate its lifetime. Carbon steel might be oxidized by the oxygen, resulting in the rust formation. Furthermore the formation of certain by-product such as acrylic acid is corrosive in nature. Hence Austenitic stainless steel type 304 is chosen for reactor fabrication due to its anti rust and corrosive natures while the cost is reasonable.

6.2.4 Design Stress According to reference [8], Tensile strength of Austenitic stainless steel type 304 = 510 N/mm2

6- 22



Design stress of Austenitic stainless steel type 304 at 275oC, f = 107.5 N/mm2 = 1.075 x 108 N/m2 Design stress is the maximum allowable stress that the Austenitic stainless steel type 304 could be expected to withstand without failure under standard test condition. It is noticed that the design pressure, PD = 1.54 x 105 N/m2 is much smaller than design stress, therefore it is safe and suitable to use Austenitic stainless steel type 304 as the material of construction.

6.2.5 Welded Joint Efficiency The value of the joint factor used in design will depend on the type of joint and amount of radiography required by the design code. Double-welded butt joint is chosen because it can withstand more stress and due to its high efficiency. In this design, welded joint efficiency, J is taken as 1.0 which implies that the join is equally as strong as the virgin plate. It is achieved by radiographing the complete weld length, and cutting out and remaking any defects. Welded Joint Efficiency, J =1.0

6.2.6 Corrosion Allowance Corrosion allowance is the additional thickness of metal added to allow for material losses by corrosion and erosion, or scaling. The allowance is generally based on the design experience. Normally, the value is range from 2.0mm to 4.0 mm. Since the reactant and product of the reactor is not corrosive, minimum corrosion allowance for alloy steels, which is 2mm is chosen.

Corrosion allowance, eallowance = 2.0mm

6.2.7 Minimum Practical Wall Thickness Minimum wall thickness is required to ensure that the reactor is sufficiently rigid to withstand its own weight and any identical loads. The packed bed reactor used is in cylindrical shape where the minimum thickness required to resists internal pressure is given by:

emin =

Po IDs 2 J f − Po

emin =

(1.4 x105 ) (1.4) = 0.025m 2(1.0) (1.075 x108 ) − 1.4 x105

where IDs = shell diameter

The wall thickness which includes corrosion allowance:

6- 23



ewall = emin + eallowance = 0.025 + 0.002 = 0.027 m Outer diameter of shell: ODS = IDS + 2ewall = 1.4 + 2(0.027) = 1.454m

6.2.8 Head and Closure An ellipsoidal head is selected as operating pressure above 15 bars and it proved to be the most economical closure. A commonly used ellipsoidal head has a ratio of base radius to depth of 2:1 (Fig. a). The shape can be approximated by a spherical radius of 0.9D and a knuckle radius of 0.17D (Fig. b). The thickness is obtained from the following equation:

ehead = ehead

Po IDs 2 J f − 0.2 Po

(1.4 x105 ) 1.4 = = 0.025m 2(1.0) (1.075 x108 ) − 0.2(1.4 x105 )

Thus, ehead _ new = ehead + eallowance = 0.025 + 0.002 = 0.027 m

Figure 6.6: Ellipsoidal Head [9]

6.2.9 Connection Nozzles are used for the reactor connections. It consists of a pipe stub welded into the vessel and terminating in a bolting flange.

6.2.10 Manhole Two manholes with a cover plate were designed to permit for access to the internal of the reactor during maintenance and inspection. One is located at the top and the other one is at the bottom.

6- 24



Both of the manholes are designed with the similar dimensions. According to BS 470, the minimum manhole diameter, Dmanhole and the minimum length of manhole, Lmanhole that can afford full rescue facilities with self-contained breathing apparatus shall be:

Dmanhole = 575 mm

Lmanhole = 500 mm.

6.2.11 Compensation for Openings The presence of an opening weakens the shell, and gives rise to stress concentrations. Thus, to compensate for the effect of an opening, sufficient reinforcement must be provided without significantly altering the general dilation pattern of the vessel at the opening by increasing the wall thickness in the region adjacent to the opening. The principal used to calculate the reinforcement needed is based on A1=A2 method, equal in cross sectional area to the area removed in forming the opening.

Figure 6.7: Schematic diagram of opening [8]

6.2.11.1 Compensate Opening for Feed Diameter optimum, dt_optimum in mm for the feed opening is calculated by:

dt _ optimum = 226 × m '0.5 × ρ o ( −0.35) Table 6.16: Variables to Calculate Optimum Diameter in Feed Opening

Symbol

Description

Value

Unit

m’

Mass flow rate of reactant

12.936

kg/s

ρo

Density of inlet feed

0.7276

kg/m3

dt _ optimum = 226 × (12.936)0.5 × (0.7276)( −0.35)

dt _ optimum = 251mm = 9.88in Hence nominal pipe size chosen = 10 in From reference [3], for stainless steel with schedule no 40 and nominal pipe size = 10 in,

6- 25



Outer diameter of inlet pipe = 10.75 in Inter diameter of inlet pipe = 10.02 in Thickness of compensate = 2.54 x (OD – ID) = 2.54 x (10.75-10.02) = 1.8542 in = 0.047 m Inlet flow rate and density of feed enter the reactor is the same as the product exit from reactor. Hence, both openings for inlet and outlet of reactor have the same ID and compensate thickness. 6.2.11.2 Compensate Opening for Molten Salt (Heater)

Diameter optimum, dt_optimum in mm for the molten salt opening is calculated by: dt _ optimum = 226 × msalt 0.5 × ρ salt ( −0.35) Table 6.17: Variables to Calculate Optimum Diameter in Molten Salt Opening

Symbol

msalt

ρo

Description

Mass flow rate of molten salt (heating medium) Density of molten salt

Value

Unit

15

kg/s

1980

kg/m3

dt _ optimum = 226 × (15)0.5 × (1980)( −0.35)

dt _ optimum = 61.42mm = 2.42in Hence nominal pipe size chosen = 2.5 in From reference [3], for stainless steel with schedule no 40 and nominal pipe size = 2.5 in, Outer diameter of inlet pipe = 2.88 in Inter diameter of inlet pipe = 2.469 in Thickness of compensate = 2.54 x (OD – ID) = 2.54 x (2.88-2.469) = 1.0439 in = 0.041 m It is assumed that the density of outlet molten salt does not change and the mass flow of outlet molten is the same as inlet flow. Hence, both openings for inlet and outlet of molten salt have the same ID and compensate thickness.

6.2.12 Dead Weight Load 6.2.12.1 Cylindrical Vessel

Total weight of shell, excluding internal fitting, is determined by:

Wv = 240Cv Dm ( L + 0.8 Dm )ewall Table 6.18: Variables to Calculate Total Weight of Shell

Symbol

Description

Value

Unit

6- 26



Cv

A factor to account for internal supports

1.80

kN/m2

Dm

Mean diameter of vessel, Dm = (IDs +ewall)

1.427

m

IDs

Inner diameter of shell

1.4

m

Length of reactor

11.18

m

Wall thickness

0.027

m

L ewall

Weight of shell, Wv = 205.09 kN

6.2.12.2 Tubes

Total weight of tubes is determined by:

Wt = n × m& t × L × g Table 6.19: Variables to Calculate Total Weight of Tube

Symbol

Description

Value

Unit

733

m

n

Total no. of tubes per reactor

L

Length of reactor

11.18

m

m& t

Specific mass per length of tube

5.45

kg/m

g

Gravitational acceleration

9.81

m/s2

Weight of tubes, Wt = 438.13 kN

6.2.12.3 Catalyst

Weight of catalyst, W = 3120 kg = 30.61 kN

6.2.12.4 Baffles

Total weight of baffles is determined by:

Wt = N B × AB × ρ B × 0.75 Table 6.20: Variables to Calculate Total Weight of Baffles

Symbol NB

AB

ρB

Description

Value

Total no. of baffles per reactor Flow area through shell, AB = Density of baffle

Unit

11

π IDS 2 4

− n(

π IDtube 2 4

)

1.538

m2

1120

N/m2

6- 27

KKEK 4281 Design Project Chapter 6: Packed Bed Reactor 1 0.75


25 % baffle cut

Weight of baffles, WB= 14.22 kN

6.2.12.5 Feed

Total weight of feed in reactor is determined by:

W f = Vt × φ × ρo × g Table 6.21: Variables to Calculate Total Weight of Feed

Symbol Vt

Description

Total volume of tube, Vt = n(

φ

Bed voidage

ρo

Density of inlet feed

π IDtube 2 4

)

Value

Unit

0.2259

m3

0.7

m2

0.7276

kg/m3

Weight of feed in the reactor, Wf = 1.13 kN

6.2.12.6 Molten Salt

Total weight of molten salt in reactor is determined by:

Wsalt = AB × L × ρ salt × g Table 6.22: Variables to Calculate Total Weight of Molten Salt

Symbol

AB L

ρ salt

Description

Value

Unit

1.538

m2

Length of reactor

11.18

m

Density of molten salt

1980

kg/m3

Flow area through shell, AB =

π IDS 2 4

− n(

π IDtube 2 4

)

Weight of molten salt in the reactor, Wsalt = 333.99 kN

6.2.12.7 Insulation

The material used for the insulation of reactor is mineral wood. Total weight of insulation of reactor is determined by:

Wi = Vi × ρi × g

6- 28



Table 6.23: Variables to Calculate Total Weight of Insulation

Symbol

Vi

Description

Volume of insulation, Vi = (

π ( IDS + ei )2 4

−

π IDS 2 4

)L

Value

Unit

1.893

m3

ei

Thickness of insulation

0.075

m

ρi

Density of mineral wood

130

kg/m3

Weight of insulation of the reactor, Wi = 2.41 kN

6.2.12.8 Total Dead Weight

Total Dead weight of the reactor, Wreactor = Wv + Wt + WB = 657.44 kN Total dead weight of load, Wload = Wv + Wt + W + WB + Wf + Wsalt + Wi = 1025.58 kN

6.2.13 Winds Load Wind speed of 160 km/h is used as the preliminary design study, which equivalent to wind pressure of 1280 N/m2. Dynamic wind pressure, Pw = 1280 N/m2 Mean diameter of reactor, Dm = 1.427 m Loading (per linear meter), Fw= Pw x Dm =1826.56 N/m Bending moment at bottom tangent line, M x =

Fw L2 = 1.14 × 105 Nm 2

6.2.14 Analysis Stress Reactor are subjected to various loads such as pressure, dead weight of vessel and contents, wind and external loads imposed by piping and attached equipment. Thus, it must be designed to withstand the worst combination of loading without failure. The primary stresses arising from these loads are calculated as following:

6.2.14.1 Pressure Stress

At bottom tangent line, the longitudinal and circumference stresses due to pressure (internal and external), given by: Longitudinal stresses, σ L =

Po ( IDs ) = 1.96 ×107 N / m 2 = 19.6 N / mm 2 4ewall

6- 29

KKEK 4281 Design Project Chapter 6: Packed Bed Reactor 1 Circumference stresses, σ h =


Po ( IDs ) = 3.92 ×107 N / m 2 = 39.2 N / mm 2 2ewall

6.2.14.2 Dead Weight Stress

The direct stress σw is due to the weight of the vessel, its contents, and any attachments. The stress will be tensile (positive) for point below the plane of the vessel supports and compressive (negative) for point above the supports.

σw =

Wload = 8.473 ×106 N / m 2 = 8.47 N / mm 2 π ( IDs + ewall )ewall

6.2.14.3 Bending Stress

The second moment of area of the vessel about the plane of bending, Iv:

Iv =

π 64

(ODs 4 − IDs 4 ) = 0.0308m 4 = 3.08 ×1010 mm 4

The bending stress will be compressive or tensile (σb), depending on location, and are given by:

σb =

M x IDs ( + ewall ) = 2.69 × 106 N / m 2 = 2.69 N / mm 2 Iv 2

6.2.14.4 Resultant Longitudinal Stresses

σ z = σ L +σw +σb σ z _ upwind = σ L + σ w + σ b = 30.76 N / mm 2 σ z _ downwind = σ L + σ w − σ b = 25.38 N / mm 2 As there is no torsional shear stress, the principal stress will be σz and σh. The radial stress is negligible. The greatest difference between the principle stresses will be on down-wind. Δσ = σ h + σ z _ downwind = 13.82 N / mm 2

which is smaller than design stress, f.

6.2.15 Vessel Support

6- 30



The method used to support a vessel will depend on the size, shape and weight of the vessel; design temperature and pressure; the vessel location and arrangement; and the internal and external fittings and attachments. Skirt supports are chosen as the supports for the reactor instead of saddle supports or bracket supports. This is because saddle supports are mainly for horizontal vessel while bracket supports are not recommended for tall, vertical vessel. Since the reactor is a tall (11.18m) vertical vessel, skirt supports is more suitable. This supports consist of a cylindrical shell.

6.2.15.1 Skirt Supports

A skirt support consists of a cylindrical or conical shell welded to the base of the vessel. A flange at the bottom of the skirt transmits the load to the foundations. It is recommended for vertical reactor as it does not impose concentrated loads on the reactor shell and they are particularly suitable for use with tall columns subjected to wind loading. The skirt may be welded to the bottom head of the vessel or welded flush with shell or welded to the outside of the vessel shell. The skirt welded flush with shell is usually preferred. Suggested skirt support height, Lsk = 0.1L=1.118 m (10% of total reactor height) Skirt thickness, esk = 10mm (the minimum thickness should not be less than 6mm) 6.2.15.2 Total Weight

The maximum dead load on the skirt is when the vessel is full of water, during the hydrostatic test. Therefore, approximately weight of vessel filled with water. Wapp =

π ( IDs ) 2 L ρ w g 4

= 168.83kN

Total dead weight, Wload = 1025.58kN Total weight, WT = Wload + Wapp = 1194.41kN

6.2.15.3 Bending Stress

Bending moment at base of the skirt, M s = Bending stress in skirt, σ bs =

Fw ( L + Lsk ) 2 = 138.13kN / m 2

4M s = 2.23 ×106 N / m 2 = 2.23N / mm 2 π ( IDs + esk )esk ( IDs )

6- 31



6.2.15.4 Dead Weight Stress

Dead weight stress in the skirt,

σ ws _ test =

WT = 2.70 ×107 N / m 2 = 27.0 N / mm 2 π ( IDs + esk )esk

σ ws _ operating =

Wload = 2.32 ×107 N / m 2 = 23.2 N / mm 2 π ( IDs + esk )esk

6.2.15.5 Tensile Stress

σ ws _ tensile = σ bs − σ ws _ operating = −20.97 N / mm 2 Tensile stress give a negative value because the bending moment obtained from wind loading calculation is very small compare to dead weight and total weight vessel.

6.2.15.6 Compressive Stress

σ s _ compressive = σ bs + σ ws _ test = 29.23 N / mm 2

6.2.16 Criteria for Design The skirt support is a straight cylindrical vessel (θs =90o) of plain carbon steel, design stress, f (107.5 N/mm2) and Modulus Young, E (200,000 N/mm2) at ambient temperature when Welded Joint Efficiency, J is 1. Table 6.24: Criteria For Design

Criteria 1 2

Criteria 2

σs_tensile = -20.97 N/mm f x J x sin (θs) = 107.5 N/mm2

σs_compressive =29.23 N/mm2 0.125E(esk / IDs)sin (θs) = 178.57 N/mm2

⇒σs_tensile < f x J x sin (θs)

⇒σs_compressive < 0.125E(esk / IDs)sin (θs)

∴Criteria 1 is satisfied

∴Criteria 2 is satisfied

Both design criteria are satisfied, adding the 2 mm corrosion allowance, the skirt thickness is taken as 12 mm.

6- 32



6.2.17 Summary of Mechanical Design of Reactor 1 Table 6.25: Summary of Mechanical Design of Reactor 1

Parameter

Value

Design pressure, PD

1.54 bar

Design temperature, TD

275oC

Material of construction

Austenitic stainless steel type 304

Design stress, f

107.5 N/mm2

Welded joint efficiency, J

1.0

Corrosion allowance, eallowance

2.0 mm

Wall thickness, ewall

0.027 m

Type of closure

Ellipsoidal head

Head thickness, ehead_new

0.027 m

Manhole Min diameter

575 mm

Max length

500 mm

Thickness of Compensation for Opening Feed

0.047 m

Molten salt (heating medium)

0.041 m

Dead Weight Load Shell, Wv

205.09 kN

Tube, Wt

438.13 kN

Catalyst, W

30.61 kN

Baffle, WB

14.22 kN

Feed, Wf

1.13 kN

Molten salt, Wsalt

333.99 kN

Insulation, Wi

2.41 kN

Total dead weight of reactor, Wreactor

657.44 kN

Total dead weight load, Wload

1025.58 kN

Wind loads

1.14 x 105 Nm

Skirt Supports Type

Cylindrical

Thickness of skirt

12 mm

Skirt support height

1.118 m

6- 33



Figure 6.9: Detail A of Mechanical Drawing

6- 35



6.3 Safety and Process Control of Reactor 1 6.3.1 Safety Consideration Results from a kinetic and process optimization study may indicate operating conditions that are unsafe from the view point of fire safety, equipment damage potential and operating sensitivity. The design of the plant should be such that the gas mixtures handled are always outside the explosive limit. The actual safe operating ranges are dependent on operating temperatures, pressures, equipment configurations, gas compositions, ignition sources present, and the dynamics of the catalyst, process and instrumentation system.

6.3.1.1 Safety Review The principle causes incidents which may occur in industry are: a. Scale-up Failure Failure to scale-up properly and to take appropriate precautions may lead to the loss of process control. Hence, runaway endothermic reaction and generation of toxic materials in the reactor can occur. These failures may lead to multiple fatalities, severe damage to property, environmental damage and business loss. Thus, the first and most critical step in the scale-up procedure is to undertake a risk assessment of the proposed chemical process at the concept stage which should include a study of thermo chemistry of the proposed reaction. b. Mechanical Impact (Stress Failure) Stress failure normally occurs due to the metals are subjected to repeated stress exceeding their limit. Excessive stresses can develop in vessels that are not free to expand and contracted with temperature changes. If the stresses are allowed to recur too frequently, eventually failure from fatigue can be expected. Hence, the maximum allowable stresses must be identified for a reactor design and all possibility sources of stress must take into account. Over-designing is not encouraged, but under design would lead to accident and fatality. c. Human Error Incorrect operating procedures conducted by the operators may cause severe damage and consequences to the plant properties. Reactor operated by non-technically qualified and inappropriately trained competent personnel is actually placing the plant into high disk

6- 36



condition. Wrong specification will not only affect the reaction output and decrease the overall yield but most importantly, it will cause fire and explosion if the equipment is not properly handled. The extra unknown or unforeseen hazards associated with the pilot plant should be compensated for by better instrumentation and technical control by the operators. d. Poor Maintenance of Safety Device Protective devices such as safety valves and any electronic devices which cause shutdown when the pressure, temperature, liquid or gas level exceed permissible limits fail to protect the equipment if they are not properly installed to the vessels, or pipe work according to the correct setting. Safety devices which are in poor condition are unable to give clear warning or signal to the operator either by sight or sound during emergency. Thus, prompt action cannot be taken by operator to overcome the situations. Improper functioning can result in disaster both to life and equipment. All safety devices should be tested regularly by an authorized person according to the schedule set.

6.3.1.2 Reactor Potential Hazards Reactor should be operating under its design condition. It may function outside its normal design limits and could cause certain potential hazards. Accident hazards for a reactor can be listed under fires, explosion, leakage, toxic release, mechanical impact and exposure to extremely hot corrosive materials. Reactor is a major source of hazard because it contains large amount of flammable material. There also could be some hot spots in the reactor and it occurs when heat exchanger does not functioning well due to dirt accumulation. This situation is likely to cause fire or explosion. Sudden releases of certain material such as acrolein which is toxic to human beings.

6.3.1.3 Reactor Safety Practices Precautions must be taken to prevent accident that may lead to injuries or fatalities. Before the operation is carried out, it is important to study the thermal effect of the reaction of the reactor, the catalyst behavior and materials handling procedures for safety operating limit and control. Safety devices can be installed on the vessel to reduce the temperature and pressure deviation

6- 37



from the reactor such as sensor, vent system, safety valve, bursting discs, alarm and indicator. Most importantly is to ensure that all the safety devices in are properly maintained.

6.3.2 Hazard and Operability Studies (HAZOP) Analysis HAZOP analysis is a set of formal hazard identification and elimination procedure designed to identify hazards to people, process plants and environment in a chemical process facility. It uses a systematic process to identify all possible deviations from normal operations and to ensure that appropriate safeguards are in place to help for preventing accidents. It is essentially a qualitative process.

6.3.2.1 Objectives of HAZOP HAZOP is carried out to ensure the overall safety of the reactor and to prevent the errors or problems that could occur as show at the previous part. HAZOP is done: a. To examine the inadequacies of the reactor by considering it as a fully integrated dynamic unit, rather than the ‘ad hoc’ design approach. b. To coordinate the various discipline involved in the design of the reactor and provide a mean for systematic analysis of the reactor system. c. To identify hazards or deficiency and operability problem that may occur in the reactor, which may lead to hazard such as fire, explosion, toxic release or reduce productivity. d. To prevent hazards in process plants that is growing in complexity with standards that are no longer adequate.

6.3.2.2 HAZOP Procedures The HAZOP is done by systematically examine the reactor design and asking questions using guide words representing deviations from the intended parameters of the process. A Process and Instrumentation Diagram (PID) is developed by referring to the HAZOP analysis which is shown in Figure 3.1.

6- 38


Group 6 Acrylic Acid Project Table 6.26: HAZOP Analysis on Packed Bed Reactor 1 – Streamline 5

HAZARD AND OPERABILITY STUDY ACTION REPORT Prepared by: Jackson Toh Equipment: Acrolein Packed Bed Reactor Line No: 5 Intention: Transfer of Glycerol feed at 275oC and 1.4 bar into the reactor Type of Guide Possible Causes Consequences Deviation Word Flow (A) (B) No 1.1 Major piping leakage and 2.1 No flow of feed into the reactor poor pipe connection 2.2 No reaction occur in the reactor 1.2 Piping blockage due to 2.3 High pressure in pipeline impurities 1.3 Feed (FIC 1) controller failure 1.4 Blockage of valve (V102)

Temperature

Less

(D) 1.1 Partial piping blockage 1.2 Minor pipe leakage

More

(G) 1.1 Shutdown system failure 1.2 Operator error - Incorrect specification and amount of process fluid charge

Less

(J)

(E) 2.1 Less flow of feed into the reactor 2.2 Reactor under filling 2.3 Runaway reaction may occur 2.4 Product yield decrease (H) 2.1 Reactor overfilling 2.2 Pipeline overpressure 2.3 High temperature in the reactor 2.4 As (E): 2.3 – 2.4 2.5 Rupture in the reactor 2.6 Potential fire and explosion hazard (K)

Actions (C) 3.1 Regularly inspection and maintenance for FIC1 and V-102 3.2 Check for piping connection 3.3 Install analyzers to detect leakage 3.4 Install no flow alarm 3.5 Install pressure safety valve (PRV) (F) 3.1 As for (C): 3.1 – 3.3 3.2 Install low flow alarm

(I) 3.1 Install flow indicator and controller (FIC1) 3.2 Install control valve (V-102) 3.4 Prepare a checklist for operator

(L)

6- 39


More

Pressure

Less

More

Contamination High


1.1 Heat loss 1.2 Temperature indicator (TIC1) is failure 1.3 Changes in ambient temperature 1.4 Input flow rate is too low 1.5 Heating system failure in the reactor (M) 1.1 High ambient temperature 1.2 Input flow rate is too high 1.3 External heat source 1.4 More heating medium inflow 1.5 Increase in pressure 1.6 Higher heat transfer in the reactor (P) 1.1 Pressure indicator (PIC1) failure 1.2 External cooling 1.3 Undetectable leakage

2.1 Decrease in reaction temperature 2.2 Incomplete reaction in the reactor 2.3 Decrease product yield 2.4 Phase change of substances 2.5 Poor heating effect in the reactor

3.1 Install low temperature alarm (TAH & TAL) 3.2 Install temperature indicator (TIC1)

(N) 2.1 Increase in reaction temperature 2.3 As for (H): 2.3 – 2.6

(S) 1.1 Under cooling in the reactor 1.2 Imbalance of input and output 1.3 Exposure to heat source 1.4 Thermal shock

(T) 2.1 Pipe surging 2.2 As for (H): 2.1 – 2.6

(V) 1.1 Feed source contaminated

(W) 2.1 Possible poisoning the catalyst

(O) 3.1 Isolation from external heat and ignition source 3.2 Install temperature indicator (TIC1) 3.3 Install high temperature alarm (TAH) 3.4 Regularly maintenance of the reactor (R) 3.1 Install low pressure alarm (PAL) 3.2 Install pressure indicator (PIC1) 3.3 As for (C): 3.1 – 3.3 (U) 3.1 Install high pressure alarm (PAH) 3.2 Install pressure gauge 3.3 Install fire alarm and explosion relief (FER) 3.4 As for (O): 3.1 3.5 As for (I): 3.4 (X) 3.1 As for (O): 3.3 – 3.4

(Q) 2.1 Poor heat transfer in the reactor 2.2 As for (E): 2.1 – 2.4

6- 40


Group 6 Acrylic Acid Project 2.2 Unexpected reaction 2.3 As for (H): 2.3 – 2.6 Table 6.27: HAZOP Analysis on Packed Bed Reactor 1 – Streamline 6

HAZARD AND OPERABILITY STUDY ACTION REPORT Prepared by: Jackson Toh Equipment: Acrolein Packed Bed Reactor Line No: 6 Intention: Transfer of acrolein product out from the reactor Type of Guide Possible Causes Consequences Deviation Word 1.1 As for (A): 1.1 – 1.2 2.1 Pipeline under pressure Flow No 1.2 Equipment and flange 2.2 No feed to collecting column failure 2.3 As for (H): 2.3 – 2.6 1.3 No flow to reactor 1.1 As for (D): 1.1 – 1.3 2.1 Collecting column under filling Less 2.2 Pipeline under pressure 2.3 As for (H): 2.3 – 2.6 1.2 As for (G): 1.2 – 1.3 2.1 Collecting column may rupture More 2.2 Pipeline overpressure 2.3 Vapor cloud explosion may occur 1.1 As for (J): 1.2 – 1.3 2.1 Change condition in collecting Temperature Less 1.2 Heating system failure in column the reactor 2.2 Phase change of substances - poor heat transfer 2.3 Poor heating effect in the reactor - heating medium failure 1.1 As for (M): 1.1 – 1.3 2.1 Over heating effect in the reactor More 1.2 Heating system failure in 2.2 Fouling the reactor 2.3 Injuries and fatalities - overheating from the molten 2.4 As for (H): 2.3 – 2.6 salt 1.1 As for (P): 1.1 – 1.3 2.1 Under filling in collecting column Pressure Less 1.2 Generation of vacuum 2.2 Additional pump is needed to

Actions 3.1 Install flow indicator (FI1) 3.2 As for C: 3.1 – 3.5

3.1 As for (F): 3.1 – 3.3

3.1 As for (I): 3.1 – 3.4

3.1 As for (L): 3.1 – 3.2 3.2 Provide accurate temperature monitoring in the reactor 3.3 Ensure the heating system function well 3.1 As for (O): 3.1 – 3.3 3.2 Regularly maintenance of the reactor heating system

3.1 As for (L): 3.1 – 3.2

6- 41



condition

More

1.1 Uncontrolled reaction in reactor 1.2 Pressure relief valve (PRV) failure 1.3 overfilling in the reactor 1.4 As for (S): 1.2 – 1.4

increase the pressure of product to collecting column 2.1 Pipe surging 2.2 Overfilling in collecting column 2.3 Overpressure in collecting system 2.2 As for (H): 2.3 – 2.6

3.1 As for (U): 3.1 – 3.4 3.2 Install pressure indicator (PI1)


HAZARD AND OPERABILITY STUDY ACTION REPORT Prepared by: Jackson Toh Equipment: Acrolein Packed Bed Reactor Line No: H_1 Intention: Transfer of hot molten salt into the reactor Type of Guide Possible Causes Consequences Deviation Word Flow 1.1 As for (A): 1.1 – 1.3 2.1 No hot molten salt flow into the No 1.2 Equipment and flange reactor failure 2.2 No heat transfer takes place 2.3 As for (K): 2.1-2.5

More

1.1 As for (D): 1.1 – 1.3 1.2 Fouling in the reactor 1.1 As for (G): 1.1 – 1.2

Temperature

Less

1.1 As for (J): 1.1 – 1.4

Pressure

More Less

1.1 As for (M): 1.1 – 1.3 1.1 Reverse heating flow 1.2 As for (P): 1.1 – 1.3

Less

Actions 3.1 As for (L): 3.1 – 3.2

2.1 As for (K): 2.1-2.5

3.1 As for (F): 3.1 – 3.3

2.1 Improper heating in the reactor 2.2 Pipeline overpressure 2.3 Possible runaway on heating 2.1 Poor heat transfer in the reactor 2.1 As for (N): 2.1 – 2.3 2.1 Reverse flow in the reactor 2.2 Accumulation of hot molten salt

3.1 As for (I): 3.1 – 3.4

3.1 As for (L): 3.1 – 3.2 3.1 As for (O): 3.1 – 3.3 3.1 As for (R): 3.1 – 3.3

6- 42


More


1.1 Overfilling of hot molten salt 1.2 Pressure relief valve failure

in the reactor 2.3 Fouling 2.4 Blockage 2.5 Poor heat transfer in the reactor 2.1 As for (T): 2.1 – 2.2

3.1 As for (U): 3.1 – 3.5


HAZARD AND OPERABILITY STUDY ACTION REPORT Prepared by: Jackson Toh Equipment: Acrolein Packed Bed Reactor Line No: H_1 Intention: Transfer of hot molten salt out from the reactor Type of Guide Possible Causes Consequences Deviation Word Flow 1.1 As for (A): 1.1 – 1.3 2.1 High pressure in the reactor No 1.2 No flow into pump P-108 2.1 As for (H): 2.3-2.6 Less

More

Temperature

Less More

1.1 As for (D): 1.1 – 1.3 1.2 Fouling in the reactor 1.3 Accumulation of hot molten salt in the reactor 1.1 Incorrect specification of hot molten salt charged

1.1 As for (J): 1.1 – 1.3 1.2 Poor heating effect 1.1 As for (M): 1.1 – 1.3 1.2 Fouling

Actions 3.1 As for (C): 3.1 – 3.5

2.1 As for (N): 2.1-2.3

3.1 As for (F): 3.1 – 3.3

2.1 Pipeline overpressure 2.3 Corrosion and erosion 2.3 Reverse flow due to incorrect pressure different 2.1 As for (H): 2.3 – 2.6

3.1 As for (I): 3.1 – 3.4

2.1 Overpressure in the reactor 2.2 Loss control of reaction rate in

3.1 As for (O): 3.1 – 3.3 3.2 Regularly maintenance of the

3.1 As for (L): 3.1 – 3.3

6- 43


Pressure

Less

More

1.3 Low reaction rate in the reactor 1.5 Low pressure in the reactor 1.1 Generation of vacuum condition 1.2 As for (P): 1.1 – 1.3 1.1 Overpressure in the reactor 1.2 Uncontrolled reaction in the reactor 1.3 Pressure relief valve failure 1.4 As for (S): 1.3 – 1.4

Group 6 Acrylic Acid Project the reactor 2.3 Effect the final productivity

reactor heating system

2.1 Poor heat transfer in the reactor

3.1 As for (R): 3.1 – 3.3

2.1 Overfilling of heating medium 2.2 As for (H): 2.2 – 2.6

3.1 As for (U): 3.1 – 3.5

6- 44



6.3.3 Process Control and Instrumentation A control system is designed for glycerol dehydration reactor to minimize down time, eliminating disturbance that tend to change operating conditions, compositions, and physical properties of the streams and also prevent quality loss and hazard in the process. The automatic control system is designed and all the data and signal are sent to control room for supervision.

6.3.3.1 Description of Instruments Table 6.30: Description of Instrument

Symbol FIC

Description Flow Indicator Controller Measure the flow rate of particular stream, send the data signal to control room and control valve for regulating the flow rate

PIC/TIC

Pressure/ Temperature Indicator Controller Measure the pressure/ temperature of particular stream or reactor, send the data signal to control room and control valve for regulating the flow rate

FT/PT/TT

Flow/ Pressure/ Temperature Transmitter Measure the flow rate/ pressure/ temperature of particular stream or reactor and send the data signal to controller for control action

FI

Flow/ Pressure/ Temperature Indicator Measure the flow rate/ pressure/ temperature of particular stream and send the data signal to control room

CV

Control Valve Control the flow rate of particular stream after receiving data signal from controller

PRV

Pressure Relief Valve Relief the pressure of reactor when the pressure of the reactor greater than the set pressure

6.3.3.2 Description of Control System 6.3.3.2.1 Inlet Feed Temperature Control Table 6.31: Description of Inlet Feed Temperature Control

Type of Control System

Feed back temperature control

Measured Variable

Inlet feed temperature

6- 45



Manipulated Variable

Inlet heating molten salt flow for heat exchanger E-107

Control Action

Control the molten salt flow rate by regulating control valve, CV101

Set Point

275oC If the temperature of the inlet feed appears to be +-10% of set point, temperature high/low alarm will be activated.

6.3.3.2.2 Inlet Feed Flow and Pressure Control Table 6.32: Description of Inlet Feed Flow and Temperature Control

Type of Control System Measured Variable Manipulated Variable Control Action

Set Point

Cascade pressure control Primary loop: Reactor pressure Secondary loop: Inlet feed flow rate Inlet feed flow rate Secondary loop: Flow controller Control the inlet feed flow rate by regulating control valve CV102 Primary loop: Pressure controller Maintain the reactor pressure by regulating the inlet feed flow rate 1.4 bar If the pressure of the reactor appears to be +-10% of set point, pressure high/low alarm will be activated.

6.3.3.2.3 Molten Salt (Heating Stream) Temperature Control Table 6.33: Description of Molten Salt Temperature Control

Type of Control System Measured Variable Manipulated Variable Control Action

Set Point

Cascade temperature control Primary loop: Reactor temperature Secondary loop: Molten salt flow rate Molten salt flow rate Secondary loop: Flow controller Control the molten salt flow rate by regulating control valve CV103 Primary loop: Temperature controller Maintain the reactor temperature by regulating the inlet flow rate of molten salt 275oC If the temperature of the reactor appears to be +-10% of set point, temperature high/low alarm will be activated.

6- 46

Acrylic Acid Production Plant Reactor 1

FI 1

TI 1

PI 1

PRODUCT

FI 2

Symbol

Description

FT

Flow Transmitter

TT

Temperature Transmitter

PT

Pressure Transmitter

FIC

Flow Indicator Control

TIC

Temperature Indicator Control

PIC

Pressure Indicator Control

FI

Flow Indicator

TI

Temperature Indicator

PI

Pressure Indicator

TAH

Temperature Alarm High

TAL

Temperature Alarm Low

PAH

Pressure Alarm High

PAL

Pressure Alarm Low

TI 2

MOLTEN SALT

TT 2

TAH TIC 2

TAL

PT 1

FT 2

PAH PIC 1

FIC2

TO STACK

TAH PAL TT 1

TIC 1

V-103 TAL

FIC 1

FT 1

SET 30 PSI

Reactor 1

P-101

HOT MOLTEN SALT

PRV

HOT MOLTEN SALT

MOLTEN SALT

V-101

V-102 E-107

PRV

GLYCEROL FEED

Pressure Relief Valve

Control Valve ACRYLIC ACID PRODUCTION PLANT GLYCEROL DEHYDRATION PLANT (REACTOR 1)

Drawn By

Dwg No

Jackson A138-112 Rev: 0

Figure 6.10: PID of Reactor 1

47 Chemical Engineering Department University of Malaya



6.4 Reference 1. Hanan Atia, Udo Armbruster, Andreas Martin, Dehydration of glycerol in gas phase using heteropolyacid catalysts as active compounds, 29 May 2008 2. http://www.coastalchem.com/PDFs/HITECSALT/HITEC%20Heat%20Transfer%20Salt. pdf 3. Kern, D.Q. (1986). Process Heat Transfer. (International Student Edition). USA: McGraw-Hill Ltd. 4. Masaru Watanabe, Toru Iida, Yuichi Aizawa, Taku M. Aida, Hiroshi Inomata, Acrolein synthesis from glycerol in hot-compressed water, 4 May 2006 5. Smith, J.M. (1981). Chemical Engineering Kinetics. (3rd Edition). McGraw-Hill Book Company. 6. Howard, J.R.(1989). Fluidized Bed Technology: Principle and Application. Adam Hilger. 7. Perry, R.H. & Green, D. (Ed.). (1997). Perry’s Chemical Engineers’ Handbook. (7th ed.). McGraw-Hill International edition. 8. Sinnott, R.K. (1999). Coulson & Richardson’s Chemical Engineering Design Volume 6. (3rd edition). Pergamon Press. 9. Farr, J.R. & Jawad, M.H. (1998). Guidebook For The Design of ASME Section VIII Pressure Vessel. ASME Press, New York. 10. Crowl, D.A. & Louvar, J.F. (1990). Chemical Process Safety – Fundamentals with Application. Prentice Hall. 11. Coughanowr, D.R. (1991). Process System Analysis and Control. (2nd edition). McGraw-Hill Inc.

6- 48



CHAPTER 7: PACKED BED REACTOR 2 7.1. Chemical Design of Reactor 2 7.1.0 Introduction 7.1.0.1 Vapour Phase Oxidation of Propylene and Acrolein From the earlier discoveries, during the late 1950’s, of effective solid catalysts for the vapour phase oxidation of acrolein to acrylic acid were probably incidental to study of catalysts intended for the oxidation of propylene to acrolein (Hancock). That is to say that acrylic acid was observed as a significant reaction product, and the natural assumption readily confirmed by experiment. Widespread interest was aroused, that the acrylic acid was derived from acrolein. 7.1.0.2 Objective The objective is to design the reactor for production of acrylic acid from acrolein. The plant produces 70,000 tonne of acrylic acid per year. It operates 24 hours for 330 days. Oxidation of acrolein in reactor will produce acrylic acid as main product where acetic acid as by product. The catalyst use is metallic salt components of the catalyst which including molybdate, vanadate and tungstate. It is dissolved in the water and is in solid phase. 7.1.0.3 Reactor Selection The reaction scheme defines the way that the reactants are converted to products, and additional rules can encode the related knowledge to produce synthetically feasible molecules. Good reactor performance is important in determining the economic viability of the overall design. Packed bed reactor is the first choice in economical production of large amount of product. It is tubular and is filled with solid catalyst particles, most often used to catalyzed gas reaction. It is preferred that the reactants flow upwards through the reactor as this provides good mixing.

[1]

Packed bed reactor used primarily in

heterogeneous gas phase reactions with catalyst as it promotes advantages of high conversion per unit mass of catalyst, lower operating cost, and continuous production. Both packed bed reactor and fluidized bed reactor are designed and better one is chosen. The oxidation reaction is an exothermic reaction. Thus, the packed bed reactor is 7-1



preferred constructed in shell and tubes, where the heat can easily be transferred to maintain the conversion. The Mo10 W2 V3.5 Cu2 Sr0.8 catalyst was packed inside the tubes side, where the cooling water is chosen as cooling fluid in shell side. (Refer to Chapter 1.6. for fluidized bed reactor design)

7.1.1 Process Description In the packed bed reactor, acrolein is oxidized to form acrylic acid via heterogeneous catalytic exothermic reaction. The catalyst used is Mo10 W2 V3.5 Cu2 Sr

0.8.

The

temperature of the reactor is maintained at 260oC by using cooling water. The pressure of the reactor is set at 2 bars. The volume percentage of acrolein, oxygen, nitrogen and water vapour fed to reactor is 10%, 16%, 64% and 10% respectively.[2] Steam is added as inert gas to control the rate of the reaction. Air is supplied to provide the oxygen required for the oxidation reaction. The nitrogen consists in air will act as an inert to control the reaction. The gaseous product stream consists of air, water vapour, acrylic acid and acetic acid which is a by product of the reaction, air and water vapour. 7.1.1.1 Feed Stream Condition Table 7.1: Initial Condition of Feed Stream Reactant

Reactants

Mole Flow (kmol/hr)

Mass Flow (kg/hr)

Acrolein Oxygen Nitrogen Water Acetol

134.17 215.41 810.52 165.52 0.1308

7522.2 6893.1 22705 2981.8 9.6937

The total volumetric flow rate, ν of the feed stream is 46.1218 m3/ hr. 7.1.1.2 Properties of Feed Stream and Cooling Stream Cooling water is chosen as the cooling stream because it is economical and available in large amount. All properties of the cooling water at 25°C and 1 atm is taken. Where, properties of the feed stream are taken from the Hysys simulation. The physical and chemical properties of both cooling and feed stream are important to determine the heat transfer coefficient (h) and pressure drop (ΔP). 7-2



Table 7.2: Properties of Feed Stream and Cooling Stream

Properties

Feed Stream

Cooling Water

Inlet Temperature (K)

533

298

Outlet Temperature (K)

533

323

Pressure (atm)

1.97

1.00

3

1.365

Density (kg/m )

2.557×10

Viscosity (Pa.s)

997.050 -5

8.909×10-4

Thermal conductivity (W/m.K)

0.040

0.610

Heat capacity (kJ/kg.K)

1.253

4.201

7.1.1.3 Properties of Catalyst The catalyst use is metallic salt components of the catalyst including molybdate, vanadate and tungstate are dissolved in the water and it is in solid phase, Mo10 W2 V3.5 Cu2 Sr 0.8. Table 7.3: Properties of Catalyst

Properties Catalyst density, ρp (kg/m3) Solid particle diameter, dp (m) Catalyst porosity, εp

5500 5×10-3 0.50

7.1.2 Process Principle The purity of crude glycerol obtained from biodiesel plant is 88% purity. [3] Production of acrylic acid from glycerol is by two process routes. First, crude glycerol (C3H8O3) is dehydrated to acrolein (C3H4O) via acetol (C3H6O2) as intermediate (under heterogeneous catalytic reaction. Acrolein is then oxidized to form acrylic acid in packed bed reactor (Equation 1.1) via heterogeneous catalytic reaction. The reaction is exothermic. Acetic acid will form as the major by product for the process (Equation 1.2). 7.1.2.1 Proposed Reaction Scheme for Oxidation of Acrylic Acid

7-3



Reaction 1: Formation of Acrylic Acid 1 O 2

C H O

C H O

Equation 7.1

Reaction 2: Formation of Acetic Acid 3 O 2

C H O

C H O

CO

Equation 7.2

Reaction rate: kCA CB

rA

.

Equation 7.3

Reactants concentration:

CA

CA

CB

CA

X

T

P

X

T

P

B

1

0.5X X

Equation 7.3.1

T T

P P

Equation 7.3.2

Where CA

W

AO F M .

.

D

AO

7.1.3 Chemical Design 7.1.3.1 Kinetic Parameter The rate constant can determined by using Arrhenius Law and the rate constant are expressed as k

A e

E RT

Equation 7.4

where the Ao is the pre exponential factor and E is the activation energy. [4]

Table 7.4: Kinetic Parameter for Oxidation of Acrolein

7-4


Group 6 Acrylic Acid Project Oxidation of Acrolein

Ao (mol/kg.hr.Pa3/2) E (J/mol) R (J/mol.K)

10.8 83678.51 8.314 6.80

k( .

10

.

7.1.3.2 Assumptions Assumptions are made for design of packed bed reactor.

Steady state condition.

No side reactions.

The reaction is an elementary reaction with the reaction-rate limiting step.

Conversion of the acrolein to acrylic acid is 98%.

The reactor contents are well mixed.

Isothermal operation since heat transfer limitations is negligible.

Physical and chemical properties are remaining constant.

Deactivation of the catalyst can be neglected under the reaction temperature.

7.1.3.3 Catalyst Weight and Pressure Drop Based on the packed bed reactor design equation, the catalyst weight, W required can be calculated: dFA dW FA

X W

rA

Equation 7.5

rA

Equation 7.5.1

By using MATLAB, both ordinary derivative of packed bed reactor design equation and Ergun equation are solved simultaneously. (Appendix Figure A-1) The catalyst weight and the pressure difference required for the reaction were obtained with X = 0.98. 7-5



Table 7.5: Determination of Catalyst Weight and Pressure Drop

dX dW

rA

k

yA P FA

Packed Bed Reactor Design Equation:

dX dW

Ergun Equation:

dy dx

G ρg D

dP dz

β

FA

dy dW

α 1 2y

y P

P

Ø

P T P TO

A 1

Pressure Drop:

PO

X 1

0.5X

B

εX

150 1 D

.

Ø µ

.

y

.

1.75G

FT FTO

Equation 7.5.2

Equation 7.6

Equation 7.6.1

P T Ø ρ P TO

FT FTO

εX

Equation 7.6.2

Equation 7.6.3

0.98

0.98 200kPa

∆P

1

Ø

β

38000 kg

1.5

1

dP dW

Weight of catalyst:

196 kPa

4kPa

7.1.3.4 Reactor Sizes Table 7.6: Determination of Reactor Sizes

7-6



Volume Volume of Catalyst

w

V

Equation 7.7

ρ

V

6.91 m

V

V Φ

V

13.80 m

V

V Φ

V

27.60 m

Total Volume of Tubes

Volume of Reactor

Equation 7.7.1

Equation 7.7.2

7.1.3.5 Tube Size Selection The stainless steel pipe with 2.5 in. normal pipe size (40S) 10 m length is selected. Table 7.7: Properties of Pipe

Unit SI 40S 2.500 in 2.880 in 0.203 in 2.469 in 4.788 in2

Schedule number Nominal pipe size Outside diameter, do Wall thickness, t Inside diameter, di Cross sectional area, Ac

0.0635 m 0.0732 m 0.0052 m 0.0627 m 0.0031 m2

7.1.3.6 Number of Tubes Number of Tubes Required

N

V A L

27.6 0.003089

10

895 tubes

7.1.3.7 Number of Tubes Passes 7-7



To provide good heat transfer of the tubes side, the flow condition of the tube should be maintained at turbulent flow. NR N

ρUd 1 µ 2100

ρVd NA 1

N 895

2100

µ

0.00309 1 1.365 4.147

0.5 2.557 0.0627

10

0.2092

Thus, minimum number of passes for turbulence flow is 1 pass.

7.1.3.8 Tube Pitch and Buddle Diameter The triangular pattern for the tubes arrangement is chosen because it allow higher heat transfer rate. It is essential in order to operate the reactor in isothermal condition. The recommended tube pitch (distance between tube centres) is 1.25 times the tube outside diameter. [5] Tube Pitch Bundle Diameter

P

1.25d 1.25 0.073152 0.091m N / 895 . d 0.073152 2.978 m D K 0.319 The dimensionless constant, K1 = 0.319 and n1 = 2.142 for a triangular pitch with single shell pass and 1 tube passes. (Appendix Figure A-3)

7.1.3.9 Shell Inside Diameter For a fixed tube heat exchanger with 2.978 m bundle diameter, bundle diameter clearance = 35.1745 mm. [5] Shell Inside Diameter

Ds = 2.978+ 0.0351745= 3.013 m

7.1.3.10 Baffles Baffles are used in the shell to direct the cooling fluid across the tubes, to increase the fluid velocity and improve the rate of transfer. Single segmented baffle is selected because it is the most commonly used type of baffle. The optimum baffle cut is 20% to 7-8



25%. The common baffle thickness, tb is 0.005 m. The optimum spacing, lB is usually between 0.3 to 0.5 times the shell diameters. [5] Table 7.8: Specifications of Baffles

Optimum Baffle Cut

20% to 25%

Baffle Thickness

0.005m

Spacing between Shell Diameter Optimum spacing usually between 0.3 to 0.5 times the shell diameter [5]. Thus, value of 0.5 is chosen. Baffle Spacing Number of Baffles Required

Actual Baffle Spacing

B

0.3 DS

0.3 3.013

NB

L B

10 0.904

lB

1 L

NB

1

10 11 1

1

0.904m 10.06

11

0.833m

7.1.4. Cooling stream requirement The tube-side heat transfer coefficient, ht, shell-side heat transfer coefficient, hs, and overall heat coefficient, Uo need to be determined to ensure effective the heat transfer between the catalyst bed and the cooling water at the shell-side. 7.1.4.1 Log Mean Temperature Difference Log Mean Temperature Difference LMTD

T

T T T

222.27K

7.1.4.2 Cooling Water Flow From the energy balance for the isothermal reactor, the heat released from the reactor, Q was found to be 3744 kJ/hr.

7-9


Group 6 Acrylic Acid Project m

Cooling Water Flow Rate

Q C ∆T

35.77kg/s

7.1.4.3 Tube Side Heat Transfer Coefficient In the tube side of the reactor, the reactants flow through the voidage of catalyst bed. Total flow area, Ac = 0.0031 m3. Table 7.9: Determination of Tube Side Heat Transfer Coefficient

Mass Velocity

G

Reynolds Number

Re

Prandtl Number

Heat Transfer Factor Heat Transfer Coefficient

Pr

4.030kg m .s

W NA

G. d µ 1 C

19769 turbulent flow

µ

,

0.0245

k

By taking account the ratio of L/D and Reynolds number of 19769, jh=0.0025 [Appendix Figure A-4] h

j . Re. Pr d

.

.k

9.181W. m . K

7.1.4.4 Shell Side Heat Transfer Coefficient Heat released from the reaction (exothermic reaction) is transferred by cooling water at the shell side. Table 7.10: Determination of Shell Side Heat Transfer Coefficient

Cross Flow Area

A

Mass Velocity

G

P

m A

d D . lB P

0.4923m

72.66kg. m . s

7-10

KKEK 4281 Design Project Chapter 7: Packed Bed Reactor 2 Equivalent D Diameter Reynolds Number

Re

Prandtl Number

Pr

1.10 P d D G µ


0.917d

0.0507m

4138 (Turbulent Flow)

C , .µ k

6.115

By taking account the 25 percent of baffle cuts and Reynolds number of 4138,

Heat Transfer Factor

jh=0.023 [Appendix Figure A-5]

Heat Transfer Coefficient

h

j . Re. Pr D

.

.k

2081.38W. m . K

7.1.4.5 Overall Heat Transfer Coefficient Table 7.11: Determination of Overall Heat Transfer Coefficient

Thermal Conductivity of Stainless Steel

21W.m-2.K-1

Fouling Coefficient : Rection mixture (heavy hydrocarbon) 2000W.m-2.K-1 6000W.m-2.K-1

Cooling water (tower) Overall Heat Transfer Coefficient: 1 h

d d 2k

d ln

1 U

1 h

U

513.61W. m . K

d 1 d h

d 1 d h

0.00195

7-11



7.1.4.6 Heat Transfer Area Required Required

.

Heat Transfer Area Available

A

Heat Transfer Area

N. π.

d 2

.L

37.62m

Heat transfer surface area available is larger than the heat transfer surface area required. Thus, cooling system is sufficient to meet the cooling requirement.

7.1.5. Pressure Drop 7.1.5.1 Tube Side Pressure Drop Ergun equation used to calculate pressure drop in a packed porous bed. dP dz

G ρg D

∆P

dP NL dz

1

Ø Ø

150 1 D

Ø µ

17565 1 10

Percentage of pressure drop

1.75G

17.565Pa/m

1.7565kPa 1.7565 200

100%

0.88%

7.1.6.7 Shell Side Pressure Drop By taking account the 25 percent of baffle cuts and Reynolds number of 4138, the friction number, jf =0.023 [Sinnott, 1986]. Shell Side Pressure Drop ∆P

8j

D

L

D

B

G

3.78kPa

7-12



7.1.6. fluidized bed reactor Refer to Figure A-2 for design procedures of fluidized bed reactor.

Figure 7.1: Fluidized Bed Reactor

7.1.6.1 Minimum Fluidization Superficial Velocity, vsfm Minimum v Fluidization Superficial v Velocity

33.7 2.557 10 0.005 1.365

1

3.6

10

5500

1.365 1.365 2.557 10

0.005

9.81

2.719m/s

7.1.6.2 Minimum Bubbling Velocity, vmb Applying Abrahamsen and Geldart correlation: v

2.07exp 0.716F

v

4.885m/s

Minimum Bubbling Velocity

d ρ µ .

.

7-13

.

1



vmb > vsfm, thus bubbles are constantly splitting and coalescing, and a maximum stable bubble size is achieved. This makes for good quality, smooth fluidization. 7.1.6.3 Terminal Velocity, ut To avoid excessive particle carryover, the fluidization operation must be conducted in such a way that: vsfm < vsf < ut. In practice, it has been observed that the ratio

ut is vsfm

between 10 (small particle) and 90 (large particle). Since the catalyst particle size is 500μm, which is intermediate size, thus ratio of 50 is chosen.

u

50

2.719

135.95m/s

7.1.6.4 Superficial velocity, vsf Operations are usually conducted with a superficial velocity, vsf 5 to 10 times higher than vsfm: 5

v v

10

7.1.6.5 Actual Velocity, v v

v

0.5

7.1.6.6 Diameter of reactor, D m

ρAv

ρπID v 4

4 11.1421 1.365

7-14



Table 7.12: Inner Diameter of Reactor for Various

vsf vsfm

vsfm

vsfm

Ratios

vsf (m/s)

v (m/s)

ID (m)

13.595 16.314 19.033 21.752 24.471 27.190

6.798 8.157 9.517 10.876 12.236 13.595

1.237 1.129 1.045 0.978 0.922 0.874

5 6 7 8 9 10 vsf

vsf

=10 is selected since the required inner diameter of reactor obtained is the smallest.

7.1.6.7 Minimum Reactor Wall Thickness, tm 2 2

Minimum Reactor Wall Thickness

1 64

0.2629

7.1.6.8 Outer Diameter, OD Outer Diameter

OD = ID + 2tm = 34.4248 + 2(0.2629) = 34.95 in = 0.8877 m

7.1.6.9 Bubble Velocity, vB For Group A particles, bubbles reach a maximum stable size which may be estimated from Geldart (1992) equation.

Bubble Diameter

dB

2v g

37.68m

Bubble velocity for Group A particles is given by Werther (1983) equation.

7-15

KKEK 4281 Design Project Chapter 7: Packed Bed Reactor 2 vB

Bubble Velocity

7.1.6.10

Group 6 Acrylic Acid Project .

ΦA gdB

48.07m/s

Slugging Problem & Reactor Height at Minimum Fluidization, Hmf

The higher the value of Hmf, the higher conversion can be achieved. But too high Hmf can cause slugging. Hence, optimum value of Hmf need to be determined. According to Yagi and Muchi (1952), slugging will not occur if criterion below is satisfied. 1.9 .

0.8744

Reactor Height at Minimum Fluidization

0.6147

7.1.6.11 Reactor Height By using Orcutt model, relation between conversions of fluidized reactor and height of reactor. 1

1

1

Conversion

1

where 13.595 2.719 13.595

0.8

0.6147

0.98

1

0.804

0.45

1 1 0.0301

0.804 0.5

1

0.804

7-16



Table 7.13: Determination of Height of Reactor

H mf (m)

χ

H (m)

0.6

1.150

51.34

0.5

1.159

52.85

0.3

1.365

52.94

0.1

1.522

54.56

0.05

1.683

57.26

From table above, observed that the higher value of H mf , the lower value of reactor height, H required to achieve 98% acrolein conversion. Thus, H mf = 0.6 m is selected which

give H = 51.34 m. 7.1.6.12. Pressure Drop Pressure drop can be determined by applying Ergun Equation.

Ergun Equation

∆P H ∆

Pressure Drop

∆

150

1

Ø µv Ø D

1.75

1

Ø ρv Ø D

30725.22

30725.22

17.97

5.52

10 Pa

7-17



7.1.6.13.Comparison Between FBR and PBR Both PBR and FBR reactors can be used to achieve high conversion of acrolein. However, by comparing the size of reactor required: Table 7.14: Comparison between FBR and PBR

Volume of reactor, V (m3)

Packed bed reactor

Fluidized bed reactor

27.6

173.5

As expected, volume required for FBR to achieve the same conversion (98%) as PBR is very large due to bed expansion. The volume required for FBR is about 6 times than that of PBR. Pressure drop across fluidized bed reactor also much higher in comparison to packed bed reactor. By considering economic aspect, PBR reactor is selected.

7-18



7.1.7 Summary of Chemical engineering Design Table 7.15: Summary of Chemical Engineering Design of Reactor

Catalyst Weight and Reactor Volume Catalyst weight

W

38000

kg

Reactor volume

V

27.6

m3

Tube Dimension Number of tube

N

Nominal pipe size

895 0.0635

m

Outside diameter

do

0.073152

m

Wall thickness

t

0.005162

m

Inside diameter

di

0.062713

m

Tube length

L

10

m

Triangular Tube Arrangement Number of passes

Npass

1

Tube pitch

Pt

0.09100

m

Bundle diameter

Db

2.97800

m

3.01300

m

Shell Dimemsion Shell inside diameter

Ds Baffle Dimension

Baffle thickness

w

0.005

m

Baffle spacing

lB

0.833

m

Number of baffles

NB

11

Baffle cut

25

%

Cooling Requirement Water flow rate

mw

35.77

kg/s

Tube side heat transfer coefficient

ht

9.18

W/m2.K

Tube side fouling coefficient

hid

2000

W/m2.K

Shell side heat transfer coefficient

hs

2081.38

W/m2.K

7-19



Shell side fouling coefficient

hod

6000

W/m2.K

Overall heat transfer coefficient

Uo

513.61

W/m2.K

Heat transfer area

A

37.62

m2

Pressure Drop Tube side pressure drop

∆Pt

1.76

kPa

Shell side pressure drop

∆Ps

3.78

kPa

7.1.8 Cost Analysis [12] Cost of Packed Bed Reactor = $10,000/m2 of heat transfer surface Heat transfer area, A = 37.62 m2 Thus, cost of packed bed reactor = $376,200 Year

1999

2009

Cost Index, I

3.954

4.675

Cost

of

Packed

Bed $376,200 = RM1,429,560

Reactor

$444,798 =RM1,690,236

Thus, cost of packed bed reactor is estimated to be RM1, 690,236.

7.1.9 Comparison of the conversion Table 7.16: Comparison of the Conversion Value with the HYSYS Simulation

Reaction

Assumed

HYSYS

Conversion (%)

Simulation

% difference

Conversion (%) Acrolein to acrylic acid

98

98

0

7-20



7.1.10 Comparison of the molar flow of the components in reactor product stream Table 7.17: Comparison of the Component Molar Flow with the HYSYS Simulation

Components

Hand Calculation

HYSYS Simulation

Mole flow (kmole/h)

Mole flow (kmole/h)

0

0

0.0000

Water

165.65

165.52

0.0811

Nitrogen

810.52

810.52

0.0000

Oxygen

145.17

144.43

0.5137

Acrolein

2.55

2.68

5.0000

Acetol

0.13

0.13

0.0000

Acetic Acid

4.03

5.23

23.0780

Acrylic Acid

127.46

126.26

0.9516

4.43

5.23

15.3857

Glycerol

Carbon Dioxide

% difference

From Table 2.2.1., the result of the percentage difference between hand calculation and HYSYS simulation for components such as acrolein and acrylic acid, are relatively small. This is because the HYSYS simulation is achieved the conversion of acrolein, which approximate to the conversion that used in hand calculation. The molar flow of glycerol, nitrogen and oxygen also show the small deviation because the oxidation reaction of acrolein is following the consecutive reaction mechanism. The percentage of deviation of acetic acid and carbon dioxide are slightly higher than other component because the conversion of the side reaction is slightly different with the conversion that used in hand calculation. Low conversions of side reaction are preferable in order to minimize side product or unwanted product. The amount of acrolein required is important in achieving a certain conversion.

7.1.11 Case Study The used of the case study tool is to monitor the steady state response of key process variables to changes in the process. 7-21

KKEK 4281 Design Project Chapter 7: Packed Bed Reactor 2 7.1.11.1


Optimization of Temperature

The reactor temperature was chosen as independent variable where the ratio of length and diameter of reactor, L/D are chosen as dependent variable in this case study. With varies the reactor temperature once at a time, and with each change, the ratio of length and diameter of reactor, L/D are calculated. (Refer Table A-1 in Appendix) Figure 7.2: Ratio of Length and Diameter, L/D vs. Inlet Temperature, To

Ratio of Length and Diameter, L/D vs. Inlet Temperature, To Ratio of Length and Diameter, 18 L/D 16 14 12 10 8 6 4 2 0 230

240

250

260

270

280

290

Inlet Temperature, To

The reactor temperature is set with the lower bound of 230°C to upper bound of 290°C. From the Figure 2.3.1.1., it is proved that 260oC is optimum temperature to be operated because the ratio of length to diameter of reactor is around 7.877 which is in the range of design consideration, which is 5 to 10 at that point. 7.1.11.2

Optimization of Pressure

The reactor operating pressure was chosen as independent variable where the ratio of length and diameter of reactor, L/D are chosen as dependent variable in this case study. With varies the reactor pressure once at a time, and with each change, the ratio of length and diameter of reactor, L/D are calculated. (Table A-2 in Appendix)

7-22



Figure 7.3: Ratio of Length and Diameter, L/D vs. Inlet Pressure, Po

Ratio of Length and Diameter, L/D vs. Inlet Pressure, Po

Ratio of Length and Diameter, 11 L/D 10 9 8 7 6 5

1.5

1.7

1.9

2.1

2.3

2.5

Inlet Pressure, Po

The reactor operating pressure is set with the lower bound of 1.5 bars to upper bound of 2.5 bars. From the Figure 2.3.2.1., pressures 1.6 to 2.4 are fulfilling the criteria of the length to diameter ratio to be 5 to 10. Optimum operating pressure is chosen among this value. Operating reactor under too low pressure might cause the pressure driving force not sufficient to drive the reactant along the reactor. Operating reactor under too high pressure might cause clogging fouling effect of reactor. Thus, pressure of 2 bars is selected as the catalyst used is not too high and L/D ratio is still within 5-10. 7.1.11.3 Summary Optimization Analysis Parameter

Value


2.00


260

Pressure Ratio, Y

0.980

Outlet Pressure, P (bar)

1.96


38000


7.985

7-23



7.2.0 Mechanical Engineering of Reactor 2 7.2.0.1 Codes and Standards The most of the conventional pressure vessels for use in the chemical and allied industries will invariably be designed and fabricated in accordance with the British Standard specification for fusion-welded pressure vessels, PD 5500; or the American Society of Mechanical Engineers code, Section VIII (the “ASME” code). In this mechanical design, British Standard specification for fusion-welded pressure vessel, PD 5500 will be followed. In addition, the TEMA standards will be used as reference because the packed bed reactor was constructed as tubular heat exchanger.

7.2.1 General Design Consideration 7.2.1.1 Design Pressure A vessel must be designed to withstand the maximum pressure to which it is likely to be subjected in operation. For vessel under internal pressure, the design pressure is normally taken as the pressure at which the pressure relief device is set. This will normally be 5 to 10% above the normal working pressure. [5] Table 7.18: Design Pressure for Tube Side and Shell Side

Design Pressure (kPa) Tube side

Pt = 200 kPa x 1.1 = 220 kPa

Shell side

Ps = 101.325 kPa x 1.1 = 111.46 kPa

7.2.1.2 Design Temperature The strength of the metals decreases with increasing temperature so the maximum allowable design stress will depend on the materials temperature. The design temperature at which the design stress is evaluated should be taken as the maximum working temperature. The 10% allowance is given to cope with any uncertainty involved in predicting vessel wall temperature. [5]

7-24



Table 7.19: Design Temperature for Tube Side and Shell Side

Design Temperature (°C) Tube side

Tt = 260°C x 1.1 = 286°C

Shell side

Ts = 25°C x 1.1 = 27.5°C

7.2.1.3 Material of Construction Selection of a suitable material must take into account the suitability of the material for fabrication (particularly welding) as well as the compatibility of the material with the process environment.

[5]

The reactant mixture contained most of acrolein is fed into the

tube side of the rector. Therefore the tube side was easily tend to exhibit corrosive behavior compared to the shell side, which only containing cooling water. Thus, tubes are selected to be made of Stainless steel 18Cr/8Ni Mo 2.5% (316). In order to easier the material construction of the rector, normally the shell is also selected to be made of same material of the tubes. 7.2.1.4 Design Stress (Nominal Design Strength) It is necessary to decide a value of the maximum allowable stress that can be accepted in the material of construction. This is determined by applying a suitable “design stress factor” (safety factor) to the maximum stress that the material could be expected to withstand without failure under standard test condition. (Refer FigureA-6 in Appendix) For materials not subject to high temperature the design stress is based on the yield stress (or proof stress), or the tensile strength (ultimate tensile stress) of the materials at the design temperature. [9] Table 7.20: Design Stress for Tube Side and Shell Side

Yield Stress

Tensile Strength 2

(N/mm )

Tube side

1.5

120

Shell side

1.5

175

Design Stress (N/mm2) f f

80.0MPa 116.7MPa

7-25



7.2.1.5 Welded Joint Efficiency and Construction Categories The possible lower strength of welded joint compared with the virgin plate is usually allowed for in design by multiplying the allowable design stress for the material by a “welded joint factor” J. The value of the joint factor used in the design will depend on the type of joint and amount of radiography required by the design code. The joint factor of 1.0 with 100% degree of radiography is chosen which implies that the joint is equally (double-welded butt) as strong as the virgin plate. This is achieved by radiographing the complete weld length, and cutting out and remaking any defects. Moreover, this construction category allows the use of all materials covered by the standard, with no restricted on the plate thickness. [5] 7.2.1.6 Corrosion Allowance The corrosion allowance is the additional thickness of metal for material lost by corrosion and erosion. The allowance should be based on experience with the material of construction under similar service conditions to those for the proposed design. However, most of the design and standards specify a minimum allowance of 1.0mm. [5]

7.2.2 Shell and Tube Wall Thickness Design 7.2.2.1 Shell Wall Thickness and Outer Diameter Cylindrical shell subjected to internal pressure, the minimum thickness, es,min can be calculated from the equation below: [5] Shell wall thickness

e

PD 2Jf P

1.4395mm

However, typical value for wall thickness for vessel diameter between 2.5 to 3.0 m should not be less than 10 mm, includes a corrosion allowance of 2 mm.[5] Thus, the shell thickness is taken to be 10 mm. Outer shell diameter

Do = Ds + 2e = 3033.00 mm

7-26



7.2.2.2 Tube Wall Thickness The minimum tube thickness can be calculated using the same equation as for shell. Tube Wall Thickness

e

PD 2Jf P

4.1496mm

The tube wall thickness selected according to schedule number of 40S is 5.16 mm, which is larger than es,min. Thus the tube wall thickness is acceptable. 7.2.2.3 Head and Closure Standard torispherical heads (ASME head) is chosen because it is most economical closure and most commonly used end closure. The domed head is shown (Refer Figure A-7 in Appendix). Besides, it is also ease of fabrication and required less space. The design configuration and the limitation for the torispherical head is shown as below: 0.002Do≤ e ≤ 0.12Do

Head thickness

6.066 mm ≤ e ≤ 363.96 mm Thus, the head thickness, e can be taken to be same as shell wall thickness. e =10mm Knuckle radius,Rk

Rk ≥ 0.06Do Rk ≥ 181.98 mm = 182 mm Rk should be larger than two time of the shell wall thickness. Thus, the knuckle radius is acceptable. Rc ≤ Do

Crown radius

Using the standard configuration, Rc = Ds = 3033.00 mm Outside height

head

h

R

R

D 2

R

D 2

.

2R

513.61mm

7.2.2.4 Tube Sheet Thickness The function of tube plate (tube-sheets) in tubular (shell and tube) packed bed reactor is to support the tubes, and separate the shell and tube side fluids. The plates must be designed to support the maximum differential pressure that is likely to occur in the shell 7-27



side and tube side. Tube plate is essentially a perforated plate with an unperforated rim, supported at its periphery.

[5]

The ligament efficiency of a perforated plate is calculated

with the hole pitch, Ph of 0.09144 m is shown as below: λ

P

d P

0.3142

The plates must be thick enough to resist the bending and shear stresses caused by the pressure load and any differential expansion of the shell and tube. Plate diameter must be bigger than shell outside diameter including the flange dimension. The minimum plate thickness to resist shear, t

0.155D ∆P′ λτ

4.060 mm

The typical value for plate thickness for tube outer diameter of 85 mm should not be less than 60 mm. So, the plate thickness is taken to be 60 mm. [5]

7.2.3

Design Loads

The reactor must be designed to resist gross plastic deformation and collapse under all the conditions of the loading, such as major and subsidiary loading. The main sources of loads which need to be considered are dead weight load and wind load. 7.2.3.1 Dead Weight Load The major sources of dead weight loads are the vessel shell, tubes, insulation, and catalyst in tubes, cooling water in shell side and reaction mixture in tube side. 7.2.3.2 Weight of Vessel Vessel

Total weight of a steel vessel, Wv with domed end and uniform wall thickness can be calculated as: W

240C D

H

0.8D

t

103.6127kN

7-28



where, Cv = a factor to account for the weight of nozzles, manways, internal supports, which can be taken as 1.15 (for vessel with support rings) Dm = Mean vessel diameter = Ds + e = 3.023 m Hv = Length of cylindrical section = 10+2(0.5136) = 11.0272 m t = wall thickness =0.01 m Tubes

Total weight of the tubes can be calculated as: W

1 Nρ gLπ d 4

d

765.9865kN

Where, ρt = density of tube (stainless steel) = 7832 kg/m3 Insulation

Insulation thickness, ti for high pressure with operating temperature between 150°C to 300°C of the vessel diameter larger than 8 inches should be 3.5 inches (8.89cm)

[6]

Fiberglass is the most common type of

the insulation, made from molten glass spun into microfibers with density of 100kg/m3. The weight of insulation can be calculated as: W

ρ gπD H t

7.8805kN

The weight of insulation is doubled up to allow for fittings. Thus, W Catalyst

15.761kN

The weight of catalyst can be calculated as: W

m

g

198.65kN

Fluid in tube Feed mixture occupied in the tubes side with the volume below, Vt = (1-εp)V = (1-0.5)(27.6) = 13.800 m3 Thus, the weight of feed mixture can be calculated as: Wr = ρfVtg = 1.365(13.800)(9.81) = 0.1848 kN 7-29



Fluid in shell Assuming that the shell side is fully occupied with cooling water. The volume of cooling water, Vw = πL(Ds2 – do2N)/4 = 33.6844 m3 Thus, the weight of cooling water can be calculated as: Wcw = ρwVwg = 330.444 kN

7.2.3.3 Total Dead Weight Total dead weight

WD=Wvessel + Wtubes + Winsulation + Wcatalyst + Wfeed mixture + Wcooling water = 1414.64 kN

7.2.3.4 Wind Load Wind loading will only be important on tall columns installed in the open. The load imposed on any structure by the action of the wind will depend on the shape of the structure and the wind velocity.

[5]

The local wind velocity in Gebeng area was found to

have an average value of 4.828 kph. Dynamic Wind Pressure

P

Mean Diameter

D

Wind Loading

F

Bending Moment at Bottom Tangential Line

M

0.05 μ D

2 t P

F D

D

H

1.165Pa t

3.4087 m 3.9711 m

159.2095 Nm

7.2.4 Stress Analysis 7-30



Pressure vessels are subjected to other loads in addition to pressure and must be designed to withstand the worst combination of loading without failure. Resultant stress from all load determined to ensure that the maximum allowable stress intensity is not exceeded at any point. The main sources of load to considered are pressure, wind, dead weight of vessel and content. [5] Longitudinal Stresses (referred to Figure A-9 in

σL

PD 4t

16.5715 N/mm

σ

PD 2t

33.1430 N/mm

Appendix) Circumferential Stresses (referred to Figure A-8 in Appendix) Direct Stresses (stresses due to dead weight

W

σ

π D

14.8956 N/mm

t t

loads) Bending Stresses

M l

σ

D 2

t

1.8302

10 N/mm

Where, Mx = total bending moment at the considered plane Iv

= the second moment of the area of the vessel

about

l

Resultant Longitudinal Stress

σ

the plane of bending. π D D 1.0849 64 σL

σ

σ upward σ downward Principal Stresses

∆σ

σ

σ

31.4671

10 mm

1.8302

10

31.4689 N/mm 31.4653 N/mm

σ downward

1.678 MPa 7-31



7.2.5 Vessel Support The methods used to support the vessel will depend on the size, shape, and weight of the vessel; the design temperature and pressure; the vessel location and arrangement; internal and external fittings and attachments. The support must be designed to carry the weight, content and wind loads of the vessel. Supports will impose localized loads on the vessel wall, and the design must be checked to ensure that the resulting stress concentrations are below the maximum allowable design stress. Support should be designed to allow easy access to the vessel and fittings for inspection and maintenance. [5] 7.2.5.1 Design of Skirt Support Skirt supports are used for all tall and vertical columns. A skirt support consists of a cylindrical or conical shell welded to the base of the vessel. A flange at the bottom of the skirt transmits the load. The openings are normally reinforced and must be provided in the skirt for access and for any connecting pipes. The skirt welded flush with the shell to the bottom head of the vessel is usually preferred.

[9, 15]

(Refer to Figure A-11 & Figure

A-12 in Appendix) Maximum Dead Weight Loads (Occur when the vessel is full with liquid)

W

Weight of Column Full of Liquid Bending Moment at Base of Skirt

WD′

π D H 4

ρ g

771.2984 kN

where, ρ w = water density,1000 kg/m3

M

WD F

W H

2185.9384 kN H

2

336.9636 Nm

where, Hs = skirt height = 2m

Bending Stress in the Skirt

σ

4M π D t t D

4.7103

10

N/mm

7-32



Where, Skirt inside diameter, Ds = Di = 3013.00 mm Skirt thickness, ts = t = 10 mm Dead Weight Stress in the Skirt

σ

,

Maximum Dead Weight Stress in the Skirt

σ

,

WD π D t t WD π D t t

14.8956 N/mm

23.0171 N/mm 23.0218 N/mm

Maximum Stresses in the Skirt

σ

,

σ

,

Design Criteria (2 criteria have to fulfil)

fs =135 N/mm2 (design stress for skirt)

σ σ

σ

σ

,

14.8909 N/mm

,

E = Modulus Young of skirt, 200000 N/mm2 θs = base angle of a conical skirt = 90˚ 1st criteria:

2nd criteria: σ

σ

,

f Jsinθ

σ

,

135 N/mm

σ

, ,

0.125E

t sinθ D

82.9738 N/mm

Both of the criteria have been fulfilled, so ts = 10mm is satisfactory with 2mm is added in skirt thickness for corrosion. 7.2.5.2 Pipe Sizing for Nozzles and Flanges In this design, there are four nozzles attached to the column as shown in the Appendix in which stainless steel pipe are used for nozzles attachment. For stainless steel pipe, the optimum diameter, dopt can be determined using the following expression: [5] d

260G

.

ρ

.

Where, dopt = optimum diameter (mm), G= fluid flow rate(kg/s), ρ = fluid density (kg/m3) Table 7.21: Optimum Diameter for Inlet Streams and Outlet Streams

7-33



Streams

G (kg/s)

ρ (kg/m3)

dopt (mm)

dopt (inch)

Inlet Feed

11.1422

1.365

760.9078

29.957

Outlet Feed

11.1422

1.365

760.9078

29.957

Cooling fluid

35.77

997.05

28.0819

1.1056

Cooling fluid

35.77

997.05

28.0819

1.1056

Table 7.2.5.2.2. Selected Pipe Sizes for Nozzles [7], [8]

Streams

dopt (in)

Schedul e No.

Nominal Pipe Size (in)

Wall thickness, (mm.)

30.0

Outer Diameter, (mm) 30.00

0.312

Internal Diameter, (mm) 29.38

Inlet Feed

29.957

10S

Outlet Feed

29.957

10S

30.0

30.00

0.312

29.38

Cooling

1.1056

40S

1.25

42.16

3.556

35.05

1.1056

40S

1.25

42.16

3.556

35.05

fluid Cooling fluid 7.2.5.3 Manholes Refer to BS 470: 1984 for the vessel with inside diameter more than 1.5 m, at least one manhole is required.[9] Hence, 3 manholes are provided which are located at the top, middle and bottom of column. The maximum length of a manhole is dependent on the diameter. (Refer to Figure A-13 and A-14 in Appendix). From BS470: 1984, the standard size of diameter and length is chosen as below:

Manhole

Diameter

Length

575mm

500mm

7-34



7.2.5.4 Base Ring and Anchor Bolt The loads carried by the skirt are transmitted to the foundation slab by the skirt base ring (bearing plate). The moment produced by wind and other lateral loads will tend to overturn the vessel; this will be opposed by the couple set up by the weight of the vessel and the tensile load in the anchor bolts.[5],[9],[10] By refer to the Figure A-15, A-16 & A-17 in the Appendix, the result of base ring and anchor bolt based on British Standard BS 470: 1984,BSI, 1984 are shown below: Bolt Size and Bolt Pitch

Bolt Diameter

Dbolt = 1.8m

Number of Bolt

Nb = 8 (minimum 8 bolts)

Bolt Size

M24

Root Area of Bolt

353mm2

Bolt Pitch

lB lB

π

D N

707 mm

600

Thus, the anchor bolts with diameter 1.8 is satisfactory. Total Compressive Load

F

4M

WD πD

πD

149.4976 kN/m

Base Ring Width

Minimum Width

l

F

21.3568 mm

Where fc = maximum allowable bearing pressure= 7N/mm2

Actual Width

l

L

t

50

136 mm

Where Lr = distance from the edge of the skirt to the outer edge of the ring = 76 mm

7-35


Actual Bearing Pressure

f

Group 6 Acrylic Acid Project F l

1.0992 N/mm

Minimum Base Ring Thickness

t

L

3f f

11.6640 mm

7.2.6 SUMMARY OF MECHANICAL ENGINEERING DESIGN Shell Design pressure

Ps

111.45

kPa

Design temperature

Ts

27.5

°C

Design stress

fs

116.667

N/mm2

Ds,o

2657.64

mm

es

10

mm

Corrosion allowance

1

mm

Construction material

Stainless steel (316)

Type of joint

Double-welded butt

Shell outer diameter Wall thickness

Tube Design pressure

Pt

220

kPa

Design temperature

Tt

286

°C

Design stress

ft

80

N/mm2

Wall thickness

et

4.1496

mm

Corrosion allowance

1.0

mm


Stainless steel (316) Head and Closure

Head thickness

eh

Corrosion allowance

10

mm

1.0

mm

Knuckle radius

Rk

182

mm

Crown radius

Rc

3033.00

mm

Head height

h

513.61

mm 7-36




Stainless steel (316)

Type of head

Torispherical Tube Sheet

Tube sheet thickness

tp

60

mm

Diameter

Dp

3043.00

mm

Skirt Support Skirt thickness

ts

10

mm

Skirt inner diameter

Ds

3033.00

mm

Design stress

fs

135

N/mm2

Modulus Young

E

200000

N/mm2

Base angle

θs

90

˚

Dbolt

1.8

mm

Nb

8

Base Ring and Anchor Bolt Bolt diameter Number of bolt Bolt size

M24

Root area of bolt

353

mm2

Bolt pitch

lB

707

mm

Total compressive load

FB

149.4976

kN/m

Minimum base ring width

lb

21.3568

Mm

Actual base ring width

la

136

Mm

Actual bearing pressure

f c'

1.0992

kN/mm2

tbase

11.6640

mm

Minimum base ring thickness

Manholes Diameter

Dm

575

Mm

Length

lm

500

mm

Pipe Sizing for Nozzles and Flanges Streams

Schedule No.

Nominal Pipe Size (in)

Wall thickness (mm.)

30.0

Outer Diameter (mm) 30.00

0.312

Internal Diameter (mm) 29.38

Feed stream

10S

Cooling fluid

40S

1.25

42.3164

3.556

35.052 7-37

ACRYLIC ACID PRODUCTION BY USING GLYCEROL 7.0: PACKED BED REACTOR TWO

7.3 Safety, Control and Instrumentation 7.3.1 The importance of safety Process safety has become important due to a number of serious accidents occurred in processing plant. Since the reactor is operating in high pressure and high temperature, safety should be put in the first place during equipment design. All engineers have a duty to use their best endeavors to ensure the plant is designed and operated under control. Not only treat safety as a legal duty, it should also be considered as a moral obligation. This duty is wide reaching and can be divided into a number of topics as follow:

Prevention of death or injury to workers

Prevention of death or injury to the general public

Prevention of damage to plant

Prevention of damage to third party property

Prevention of damage to the environment

7.3.1.1

Safety Considerations

One of the problems in reactor is generation of high-temperature portions referred to as hot spots in catalyst layer. The reactor involves with exothermic reaction, therefore some methods that can be used to avoid hot spots are:

Run heat transfer medium concurrently: The heat transfer medium which is cooling water enters at its lowest temperature. By matching this low temperature with the highest temperature zone in the packed bed reactor, the temperature gradient is the largest at the reactor entrance, providing more heat removal.

Use inert solid: by randomly packing the tubes with inert solid (no catalytic activity), the heat released per unit volume of packed bed reactor is reduced, thereby minimizing hot spots.

Use catalyst gradients in packed bed reactor: this is similar to above. Here, a larger fraction of inert solid is used where hot spots are anticipated. This minimizes hot spots.

7‐38


7.3.1.1.1 Pressure Relief Systems The installation of the pressure relief system is important to avoid an uncontrolled, azeotropic release of the contents or the destruction of the vessel. The relief valves are also known as safety valves are designed to operate under unsteady conditions. Usually, the safety valves on vessels or process lines that open automatically at a certain pressure. The designs of the safety valves are apparently important, as the worst case scenario must be considered. 7.3.1.1.2 Effects of Fouling The calculation of the overall heat transfer coefficient contains the terms to account for the thermal resistances of the fouling layers on the inside and outside heat transfer surfaces. These fouling layers are known to increase the thickness with the time as the reactor is operated. Fouling layers normally have s lower thermal conductivity than the fluids or the tube material, thereby increasing the overall thermal resistance. In order that the reactor shall have sufficient surface to maintain satisfactory performance in normal operation, with reasonable service time between cleanings, it is important in design to provide a fouling allowance appropriate to the expected operating and maintenance condition. 7.3.1.1.3 Corrosion Failure Most pressure vessel is subjected to deterioration by corrosion or erosion, or both especially when the substances are corrosive such as acrolein and acrylic acid. The effect of corrosion may be pitting or grooving over either localized or large areas that may cause a general reduction of the wall thickness. This will lead to cracking of vessel as well as contamination of the product. To overcome this problem the wall is designed for corrosion allowance to reduce the corrosion effect. For modern plant, weep holes are planted on the vessel for early stage detection of corrosion. 7.3.1.1.4 Stress Failure Excessive stresses can developing vessels that are not free to expand and contracted with temperature changes. If the stresses are allowed to often, eventually failure can be occurred. Hence, maximum allowable stresses must be identified for a reactor design and the possibility

7‐39


sources of stress must be considered. Over designing is not encouraged, but under design would lead to accident and fatality.

7.3.2 Process safety design Safety is a very precise and a very vague term. It is vague because, to some extent, safety is a value of judgment, but precise because in many cases, we can readily distinguish a safe design from an unsafe one. There are four criteria that must be fulfilling to aid ensure a safe design. First, a design must comply with the applicable law. Second, an acceptable design must meet the standard of accepted engineering practice. Third, an alternative designs that are potentially safer must be explored. Fourth, finished design must be rigorously tested. Moreover, the safety performance should improve through a practical and economical way. The design of an assessment of the safety programs such as safety and loss prevention activities, process safety management (OSHA related), risk management planning, process hazard analysis and risk awareness training are needed.

7.3.3 Process hazard analysis (HAZOP analysis) HAZOP is a systematic, highly structured assessment relying on HAZOP guide words. It is a modified brainstorming technique for identifying and resolving process hazards in order to generate a comprehensive review and ensure that appropriate safeguards against accidents are in place. It is considered is an important and common used method in identifying safety hazards and operability problems of continuous process system and in reviewing procedures and sequential operations. The Occupational Safety and Health Administration (OSHA) Process Safety Management regulation required that the actions assigned be taken in a timely manner. All process hazard analysis is updated at least every five years. For the oxidation reaction unit operation, HAZOP analysis is done on the inlet and outlet streams of the reactor and water cooling system. (Procedure refer to Figure A-18 in Appendix).

7‐40

ACRYLIC ACID PRODUCTION BY USING GLYCEROL 7.0: PACKED BED REACTOR TWO Table 7.22: HAZOP Analysis on Feed Stream of the Reactor

Guide word NO/ NONE

Deviation No flow

Causes Compressor failure Blockage in pipeline Large leakage in pipeline

Consequences No reaction occur in reactor Rate of reaction drop

Control valve fails

Action Install back up pump Install flow indicator Install low flow alarm Install back-up control valves Install manual bypass

and closed Controller fails and

valve Install back-up controller

valve closes

Check compressor/ pump MORE

More flow

Over pumping capacity Control valve fails and open Controller fails and valve opens

Reaction altered

Install high flow alarm

Resident time

Install back-up control

decrease Build up of reactant Runaway

valves Install manual bypass valve Install back-up controller

reaction LESS

Less flow

Defective pump

Reaction altered

Install flow indicator

Partial blockage in

Product yield


pipeline Small leakage in pipeline

decrease Loss of productivity

Abnormal opening


of valve REVERSE

Reverse

Pump reversed

Reaction altered

Install check valve

flow

Pump failure

Blockage of pipe


Reversed differential

Pipeline crack

Instruct operators on

pressure Incorrect operation

under high

procedure

pressure

Flooding of reactor

7‐41


MORE

More

Defective control

pressure

Compressor failure

Possible reactor fractured Over pressure of reactor or vessel

Perform scheduled maintenance Install high pressure alarm Install back-up controller Install high pressure emergency shutdown Install pressure relief valve

LESS

Less

Compressor failure

pressure

Partial blockage in

Reaction altered

Install back-up pump Install back-up controller Install pressure indicator

tube Leakage in tube

Instruct operators on

Abnormal opening

procedure

of valve Defective control MORE

More

More heating

temperature

Failed cooling system Defective control

High reactor temperature Runaway reaction Possible reactor fractured Production of side product

Install high temperature alarm to alert operator Perform scheduled maintenance Install back-up controller Install high temperature emergency shutdown Install flow rate controller for coolant

LESS

Less

Less heating

temperature

Failed cooling system Defective control

Rate of reaction drop

Perform scheduled maintenance Instruct operators on procedure Install flow rate controller for cooling system

7‐42

ACRYLIC ACID PRODUCTION BY USING GLYCEROL 7.0: PACKED BED REACTOR TWO Table 7.23: HAZOP Analysis on Outlet Stream of Reactor

Guide word NO

Deviation No flow

Possible causes

Consequences

Action

Pump failure

Product loss

Install back up pump

Blockage in pipeline

Downtime to


Large leakage in pipeline Control valve fails and closed

overall process Reaction altered Explosion hazard

Controller fails and

Install back-up control valves Install manual bypass valve Install back-up controller

valve closes MORE

More flow

Control valve fails and open Controller fails and valve opens

Reaction altered


Resident time


decrease Off-spec product


LESS

Less flow

Partial blockage in pipeline Small leakage in pipeline Abnormal opening

Reaction altered


Loss of


productivity Resident time increase

valve

Reverse

Pump reversed

Reaction altered

Install check valve

flow

Reversed differential

Product


pressure

reduction

Incorrect operation MORE

Install manual bypass Install back-up controller

of valve REVERSE

valves

More

Defective control

pressure

Pipe blockage

Instruct operators on procedure

Possible reactor fractured

Perform scheduled maintenance Install high pressure alarm to alert operator Install back-up controller Install high pressure emergency shutdown

7‐43


LESS

Less

Pump failure

pressure

Partial blockage in

Reaction altered

Install back-up pump Install back-up controller Instruct operators on

tube Leakage in tube

procedure

Abnormal opening of valve Defective control MORE

More

More heating

Runaway

Install high temperature

temperature

Failed cooling

reaction

alarm to alert operator

system Defective control

Possible reactor

Perform scheduled

fractured

maintenance

Production of

Install back-up controller

side product

Install high temperature emergency shutdown

LESS

Less

Less heating

temperature

Failed cooling

Reduce reaction

Perform scheduled

rate

maintenance Instruct operators on

system Defective control

procedure

Table 7.24: HAZOP Analysis on Cooling Water Supply of Reactor

Guide word NO

Deviation No flow

Possible causes Pump failure

Consequences

Blockage in pipeline

High temperature in reactor

Large leakage in pipeline

Possible thermal runaway

Action

Install low flow alarm

Install emergency shutdown

Control valve fails and closed

Install backup control valves

Controller fails and valve closes

Install manual by pass valve

Install backup cooling water source

Install high temperature alarm

7‐44

ACRYLIC ACID PRODUCTION BY USING GLYCEROL 7.0: PACKED BED REACTOR TWO MORE

More flow

Control valve fails and open Controller fails and valve opens

LESS

Less flow

Reaction altered


Reactor cools

Install back-up control valves

Install back-up controller

Low conversion Low reaction rate

Partial blockage in pipeline Small leakage in pipeline

Referred under

Referred under ‘NO’

‘NO’

Partial water source supply REVERSE

AS WELL AS

PART OF

Water source failure

Temperature rises

Reverse pressure differential

Possible runaway by improper cooling

Install high temperature alarm and check valve

Instruct operators on procedure

Reactor product in shell

leakage in tubes

Loss of productivity

Perform scheduled maintenance

Contamination of water

Continuous monitoring

Partial cooling

failure of the control valve

Reverse flow

reverse pressure differential

Partially plugged cooling water supply

Referred under

Referred under ‘NO’

‘NO’

Partial water source supply REVERSE

Reverse cooling water flow

Pump reversed

Improper cooling

Install check valve

Loss of cooling water pressure

Possible thermal runaway

Perform scheduled maintenance

Possible loss of cooling performance

Monitoring of cooling water source quality

Install filters to prevent contaminant from entering

Install check valve and high temperature alarm

Backward flow due to backpressure OTHER THAN

Other material

Water source contaminated Backflow from sewer Leakage from tube

possible reaction runaway

7‐45


7.3.4 The importance of control system A control system is critically important to maintain equipment performance within the bounds of safe operation. It is also used as protection to process equipment and environment. In addition, the control systems are becoming more critical to the profitable operation of process plant because of rising energy costs, limited availability of raw material, and tighter safety and environmental regulations. Objectives of control systems and instrumentation are: (a) Safety of plant operation Maintain the operating temperature at 260oC to avoid overheating or overcooling while the operating pressure at 200 kPa to avoid pressure build up and cause explosion hazard. (b) Production rate Achieve the desired product output which is 98% conversion of acrolein in reactor. (c) Product quality Produce acrylic acid with standard requirement and ensure the better product quality control

Since the reaction was carried out in the packed bed reactor at pressure of 200 kPa and temperature of 260°C, it is required of installation the temperature indicator as well as pressure indicator to measured the reactor condition for convenient the process monitoring. Beside, the high level alarm and low level alarm of temperature, pressure and flow is installed to alert operators in case of runaway in process condition. The gate valves are utilized as isolation valve and check valve to prevent the back flow. 7.3.4.1 Types of Controller 7.3.4.1.1 Temperature Control The primary control variable in most oxidation reaction is temperature. For a closer control, a cascade system is preferred for temperature control where cooling water is used to remove the exothermic heat of reaction. The control variable, reactor temperature which responds slowly to the change in heat transfer medium flow (cooling water as manipulated variable) is allowed to adjust the set point of temperature secondary loop which respond rapidly to the flow changes. 7‐46


The purpose of secondary loop is to correct the outside disturbances (i.e. temperature changes in heat transfer medium) without allowing them to affect the reaction temperature. If temperature exists more or less than 10% of set point, high or low temperature alarm will be activated. PID is chosen as it gives faster response, avoid lag time to system and eliminate the offset of the set point. [11] 7.3.4.1.2 Pressure Control When the pressure rises, that is the indication of excess gaseous reactant accumulation in the reactor. Thus, the pressure controller will reduce the gas flow. As the result, the gas consumption balance will re-establish. If the pressure exists more or less than 10% of the set point, high or low pressure alarm will be activated. PID controller is used to achieve effective control systems. [11] 7.3.4.1.3 Level Control Level is important in reactor and it should be maintained to achieve the desired conversion. If the inflow to the reactor varies, the easiest way to maintain the level is by manipulating reactor outflow. The ratio of volume to outflow is controlled by manipulating on the flow rate of the outlet stream from the reactor. Cascade control is used and PI controller is chosen because of its efficiency in controlling the level of reactor. 7.3.4.1.4 Feed Flow Control The objective of flow control is to maintain a constant production rate and make sure the amount of catalyst is sufficient enough for the occurrence of reaction. Flow transmitter (FT) is installed to detect the flow of the inlet stream to the reactor. Signal is then send to Flow Controller (FC) that will be controlling the limitation of feed flow rate at set point value by adjusting the final control element (control valve). For flow control system, feed forward control configuration is applied. If flow rate exist more or less than 10% of the set point, high or low flow alarm will be activated. PI controller is used since it is sufficient for controlling the feed flow. [11] 7.3.4.1.5 Feed Composition Control The molar ratio of reactant affects the conversion of the reaction and the composition of the product. Hence, to maintain these two output variable at desired set point, chemical composition 7‐47


analyzer is installed such as infrared analyzer, conductometric analysis ultraviolet or visible radiation analyzer to detect the concentration of the components. PI controller is selected because the integral action can eliminate the offset thereby establish precise ratio of streams. [11]

7.3.4.2 Control System Loop 7.3.4.2.1 Feed Flow Control (Control System Loop 1) This control system is used to control the reactor feed stream in a constant flow rate. The flow transmitter is utilized to detect the changes of the feed flow. A signal will be generated by the flow transmitter and send to the flow controller. The flow controller will convert the received signal and send to the flow control valve, which adjust the flow of the feed stream to the desired flow rate. 7.3.4.2.2 Reactor Pressure Control (Control System Loop 2) This control system is used to control the reactor pressure in a constant value. The pressure transmitter is utilized to measure the pressure of the reactor. When the reactor pressure is high than the set point value, the pressure transmitter send a signal to the pressure controller and the high pressure alarm will sounded to instruct the operators. The pressure controller and then will adjust the flow to maintain set point value. 7.3.4.2.3 Cooling Stream and Reactor Temperature Control (Control System Loop 3) This control system is used to control the cooling system to maintain reactor temperature. Heat transfer is necessary in the exothermic reaction to maintain the reactor in isothermal condition. Normally, heat transfer in the reactor is a slow process. Therefore, the reactor temperature can easily undergo a large deviation from the set point before control is again established. In order to have a better response to the temperature fluctuation, Cascade control is utilized rather than other control because can provide faster response of reactor temperature control to a disturbance in cooling water temperature. In this system, the output of primary controller becomes the set point of secondary controller which is used to control the flow rate of cooling water into the reactor. Under these conditions, the primary controller adjusts indirectly the flow rate of cooling water. 7‐48


The control and instrumentations of packed bed reactor is show as below:

Figure 7.4: Control System for Packed Bed Reactor

FC

Flow controller

TC

Temperature controller

PC

Pressure controller

FI

Flow indicator

TI

Temperature indicator

PI

Pressure indicator

FT

Flow transmitter

TT

Temperature transmitter

PT

Pressure transmitter

FAH

High flow alarm

TAH

High Temperature alarm

PAH

High Pressure alarm

FAL

Low flow alarm

TAL

Low Temperature alarm

PAL

Low Pressure alarm

7‐49

ACRYLIC ACID PRODUCTION BY USING GLYCEROL 7.0: PACKED BED REACTOR TWO Table 7.25: Control Variables for Packed Bed Reactor

Control Variables

Manipulated Disturbances Variables

Type of

Control

Control

Action

Set Point

Loop/ Controller Reactor

Cooling

temperature

water flow rate

Change in inlet

Cascade/

Control

PID

water

temperature.

cooling

Feed flow

flow rate

260oC ± 10%

rate. Change in reactor pressure. Reactor pressure

Gaseous inlet Acrolein flow flow rate

rate

Cascade/

Control

PID

gaseous

2 bar ± 10%

inlet flow rate Reactor

Flow rate of

Flow rate of

level

product

reactant

Cascade/ PI

Control

80% of reactor

product

height

stream flow rate Molar ratio of reactants

Acrolein feed

Control

Acrolein:O2:N2:H2O

rate from

feed flow

is 1:1.6:6.4:1

oxidation

rate

Feed flow

Cascade/ PI

reactor

7‐50

KKEK 4281 Design Project Chapter 8: Quenching Tower


CHAPTER 8: QUENCHING TOWER 8.1 Chemical Design of Quenching Tower (Absorber) 8.1.1 Objective The objectives of this project is the design a quenching tower, which is also called as an absorber, to separate the acrylic acid and acetic acid from the gas stream from reactor by using water as solvent.

8.1.2 Introduction The removal of one or more selected components from a mixture of gases by absorption into a suitable liquid is the second major operation of chemical engineering that is based on interphase mass transfer controlled largely by rate of diffusion. The product stream from Reactor 2 at 170oC and flow rate of 1260kmol/hr is fed into quenching tower counter-current to separate out the air and form aqueous solution. Water is fed from the top of the tower and the product stream from the bottom of the tower. Water will ‘wash’ the product stream in counter current flow. Air, water vapour and other minor component exited the tower at the top. Acrylic acid and acetic acid will dissolve in water and form aqueous solution. 8.1.2.1 The Mechanism of Absorption According to two film theory, material is transfer in the bulk of phases by convection currents, and concentration differences are regarded as negligible accepts in the vicinity if the interface between the phases [1]. On either sides of this interface it is supposed that the current die out and that there exists a thin film of fluid through which the transferred is affected solely by molecular diffusion. This film will be slightly thicker than the laminar sub layer because it offers the residence equivalent to that or the whole of the boundary layer. According to Fick’s Law, the rate of transfer by diffusion is proportional to the concentration gradient and to the area of interface over which the diffusion is occurring. Fick’s Law is limited to cases where the concentration of the absorbed component is low [3].

8-1



The direction of transfer of the material across the interface is not dependent solely on the concentration difference, but also in the equilibrium relationship. There is, therefore, a very big concentration gradient across the interface, but this is not the controlling factor in the mass transfer, as it generally assumed that there is no resistance at the interface itself, where equilibrium conditions will exist, the controlling factor will be the rate of diffusion through the two films where all the resistance is considered to lie.

8.1.3 General Design Decisions Before designing the quenching tower, some information below needs to be considered and determine: i.

Entering gas and liquid flow rate, composition, temperature, and pressure

ii.

Desired degree of recovery of one or more solutes

iii.

Choice of solvent

iv.

Operating pressure and temperature 8-2

KKEK 4281 Design Project Chapter 8: Quenching Tower v.


Minimum solvent flow rate and actual solvent flow rate as a multiple of the minimum rate needed to make the separation.

vi.

Number of equilibrium stages

vii.

Type of quenching tower

viii.

Height and diameter of quenching tower

8.1.3.1 Choices of solvent An important decision in the design process was which solvent to be used. The ideal solvent should: ¾

Have high solubility for solutes

¾

Have low volatility to reduce loss of solvent

¾

Be non-corrosive

¾

Have low viscosity to provide a low-pressure drop

¾

Be non-toxic

¾

Be available and not expensive

For our case, we chose water as our solvent to dissolve the acrylic acid and acetic acid since it fulfills all the requirements above. 8.1.3.2 Determination of operating pressure and temperature In general, operating pressure should be high and temperature low for quenching tower, to minimize stage requirement and/or solvent flow rate to lower the equipment volume required accommodating the gas flow. 8.1.3.3 Selection of the type of quenching tower The equipment used for contacting liquid and gas streams continuously may be a packed tower with regular or irregular solid packing material, a plate-type unit containing a number of bubble-cap or sieve plates, an empty tower wetted- wall column or a stirred or sparked vessel. Ordinarily, the gas and liquid stream are made to flow counter-currently pass each other through the equipment so that the greatest rate of absorption maybe obtained. A plate column is chosen in this design problem. This is based on some reason listed below: i. Plate column can handle a wider range of liquid and gas flow rates. 8-3



ii. The efficiency of plate can be predicted with more certainty than the equipment term for packing. iii. Plate column can be designed with more assurance than packed column. iv. It is easier to make provision for the withdraw of side stream form plate column rather than packed column where the dimension in the packed are calculated based on height and diameter only. v. Packing should always be considered for a small diameter column. vi. The total weight of a plate tower is usually less than that of the packed tower for the same duty. The limited cracking strength of many packing materials may make use of multiple packing support plate’s mandatory, to bear the weight of tall packed column. 8.1.3.4 Simulation of design problem Quenching tower is used to separate the acrylic acid and acetic acid from the gas stream. The schematic diagram of the quenching tower is given in the Figure 8.1 as an illustration of this design problem. The chemical engineering design of the quenching tower is based on the material and energy balance that is stimulated by HYSIS software. In order to dissolve as much as possible the acrylic acid and acetic acid in water, the pressure and temperature of the quenching tower is important to be controlled for not being too high.

Stream 27 Phase: Liquid Temperature: 42.17 oC Pressure: 101.3 kPa Mass Flow: 7206.0 kg/hr Mw = 18.02 kg/mole Density = 994.3 kg/m3 ......................................................... Water: 7206.0 kg/hr

Stream 25 Phase: Gas Temperature: 170oC Pressure: 180 kPa Mass Flow: 40111.85kg/hr Mw= 31.83 kg/mol Density= 1.556 kg/m3 ......................................................... Water: 2981.9kg/hr Oxygen: 4621.4kg/hr

Stream 28 Phase: Gas Temperature: 69.7oC Pressure: 101.3kPa Mass Flow: 35048.78kg/hr Mw = 25.64 kg/mol Density = 0.9128 kg/m3 ......................................................... Water: 7259.40kg/hr Oxygen: 4631.40kg/hr Nitrogen: 22705.00kg/hr Acrolein: 142.71kg/hr Acrylic Acid: 41.83kg/hr Carbon Dioxide: 230.13kg/hr Acetic Acid: 48.32kg/hr

8-4


Group 6 Acrylic Acid Project Stream 29 Phase: Liquid Temperature: 72.88oC Pressure: 101.3kPa Mass Flow: 12269.11kg/hr Mw = 41.88 kg/mol Density = 967.2 kg/m3 ................................................... Water: 2928.5kg/hr Oxygen: 0.044kg/hr Nitrogen: 0.103kg/hr Acetol: 10.371kg/hr Acrolein: 8.106kg/hr Acrylic Acid: 9056.2kg/hr Acetic Acid: 265.52kg/hr

Figure 8.1 Schematic diagram of quenching tower 8.1.3.5 Physical properties data There are several sets of physical properties that need to be calculated before the subsequent design can be calculated for each stream. Determination of these properties through the correlation involves a very complex step. Therefore, HYSIS software is used in generating most of property data. The values of the physical properties vary from top of top bottom of the absorber column. The physical properties need to be obtained in each stream for quenching tower design calculations include: i.

Density

ii.

Viscosity

iii.

Average molecular weight

iv.

Surface tension

8.1.3.6 Prediction of overall column efficiency For the overall efficiency of quenching tower, it is the same as the overall column efficiency of absorber. In O’Connell’s paper, the plate efficiency is correlated with a function involving Henry’s constant, the total pressure and the solvent viscosity at the

8-5



operating temperature. After convert the equation to SI unit, it is convenient to express this function in the following form [3]:

⎡ ρs ⎤ x = 0.062 ⎢ ⎥ ⎣ KM s μ s ⎦ Where: Ms= molecular weight of solvent= 18.02 μs = solvent viscosity, mNs/m2 = 0.6254 ρs = solvent density, kg/m3 = 994.3 K = equilibrium constant for the solute = 0.3762 Substitute the value given in equation above, ⎡ ρs ⎤ x = 0.062 ⎢ ⎥ ⎣ KM s μ s ⎦ 994.3 ⎡ ⎤ = 0.062 ⎢ ⎣ 0.3762 × 18.02 × 0.6254 ⎥⎦ = 14.54

With this value, use the graph from Figure 8.2 (from Figure 11.14 reference [2]) below to determine the quenching tower overall column efficiency. From the graph, the overall efficiency, Eo is around 63%

8-6



Figure 8.2: Absorber column efficiency [2] 8.1.2.7 Number of stage

In order to get the require mass flow rate for the liquid outlet flowrate and vapour outlet flowrate with desired mole fraction, we set up a model of quenching tower in HYSIS, by trial and error, the required number of stage to reach the target is 13. So, a quenching tower with 13 number of stage will be designed with all the specification as below.

8.1.4 Plate Specifications and Configurations 8.1.4.1 Plate contactors

Cross flow plates are the most common type of plate contactor and used in this quenching tower design. In a cross flow plate, the liquid flows across the plate and the vapour up through the plate. The following liquid is transferred from plate to plate through the vertical channels called downcomers. A pool of liquid is retained on the plate by an outlet weir.

8-7



Figure8.3: Typical cross flow plate (sieve) [2]

Figure 8.4: Column operation regimes Base on figure above, following information can be obtained: Column flooding: Occurs at a maximum vapour flow above which liquid back-up in the downcomer reaches the plate above, complete flooding leads to liquid leaving with the vapour steam.

8-8



Downcomer flooding: Liquid backup caused by too small downcomer areas, or too high liquid flows. As long as downcomer area is 10% or greater and tray spacing is 60cm or greater, this rarely occurs. Entrainment flooding: Excessive carry-over of one liquid by the gas to the tray above. The entrained liquid causes the liquid flowing down to increase exceeding the capacity of the downcomers and causing total flooding. Entrainment flooding normally limits operation and is the basis for column diameter estimation. Weeping: Liquid “weeps” through the perforations when the gas flow is too low. Excessive weeping reduces efficiency as the contact with the liquid phase is reduces. Turn-down ratio: The vapour rate at flooding to the minimum vapour rate. 8.1.4.2 Choice of plate type

There are three types of cross flow tray, which are bubble cap plate, sieve plate and valve plate. The principle factor to consider when comparing the performance of these three plates, cost, capacity, operating range, efficiency, and pressure drop. The comparisons are summarized in the table below: Table 8.1: Comparison between different trays Type of plate

Sieve

Bubble cap

Valve

Cost

Less expensive

Most expensive

Expensive

Capacity

Highest

Low

Moderate

Operating range

Satisfactory range 50% 120% of design capacity

At very low vapour rates

-

Efficiency

Same

Same

Same

Lowest Highest High Pressure drop From the table above, the sieve is chosen due to some considerations of many aspects. 8-9



8.1.4.3 Plate design algorithm

A trial and error approach is necessary in plate design starting with a rough plate layout, checking key performance factor and revising the design as necessary until a satisfactory design is achieved. The algorithm of the design is simplifies Figure 8.5 below.

8-10



Calculate maximum and minimum vapour and liquid flow rate from physical properties

Select trial spacing

Estimate column diameter based on flooding consideration

Describe flow arrangement

Make a trial layout

Check weeping rate

Check plate pressure drop

Check downcomer backup

Decide plate layout

Recalculate percentage flooding based on chosen diameter

Check entrainment

Recalculate percentage flooding based on chosen diameter

8-11


Group 6 Acrylic Acid Project Figure 8.5: Plate design algorithm

8.1.4.4 Physical properties

From the HYSIS results, some physical properties need to be obtained which are important before the subsequent design is calculated. Mass flow rate gas inlet, FGin

= 11.14kg/s = 1.56 kg/m3

Density of gas inlet, ρGin Mass flow rate of gas outlet, FGout

= 9.74 kg/s

Density of gas outlet, ρGout

= 0.92 kg/m3

Mass flow rate liquid inlet, FLin

= 2.00 kg/s = 994.30 kg/m3

Density of liquid inlet, ρLin Mass flow rate of liquid outlet, FLout

= 3.41 kg/s = 967.20 kg/m3

Density of liquid outlet, ρLout The liquid-vapour flow factor for bottom is given by: FLVbottom =

FLout FGin

ρ Gin ρ Lout

3.41 1.56 11.14 967.2 = 0.0123 =

8.1.4.5 Plate spacing

The overall height of the column will depend on the plate spacing. Plate spacing from 0.15m and 1.0m are normally used. The spacing will depend on the column diameter and operating conditions. Take plate spacing as 0.5m. Then from Figure 8.6 (from Figure 11.27 reference [2]) below, a value of K1 can be determined. Bottom, K1

= 0.09

8-12



Figure 8.6: Flooding velocity, sieve plate [2] 8.1.4.6 Column diameter

From the correlation given by Fair (1961), 1

⎡ ρ -ρ ⎤ 2 U f_bottom =K 2 ⎢ Lout Gin ⎥ ⎣ ρ Gin ⎦ 1

⎡ 967.20 − 1.56 ⎤ 2 = 0.09 ⎢ ⎥⎦ 1.56 ⎣ = 2.239m/s

Design 85% flooding at maximum rate,

U v_bottom = 0.85 × U f_bottom = 0.85 × 2.239 = 1.9m/s The maximum volumetric flow rate,

8-13


Group 6 Acrylic Acid Project υ bottom = =

FGin ρ Gin 1.9 =1.22m3 /s 1.56

Thus, the net area required, A n_bottom =

υbottom U v_bottom

1.22 1.9 =0.642m 2 =

For trial, the downcomer area as 12% of total column cross section area was chosen,

A c_bottom =

A n_bottom

100%-12% 0.642 = 100%-12% =0.73m 2

Therefore, the column diameter is calculated from the equation below, 1

Dc _ bottom

× 4⎤2 ⎡A = ⎢ c _ bottom ⎥ π ⎣ ⎦ 1

⎡ 0.73 × 4 ⎤ 2 =⎢ ⎣ π ⎥⎦ = 0.964m

Thus column diameter taken is 0.964m. Uf (bottom)

Where K1

= flooding velocity, m/s = constant obtained from Figure 8.5 [11.27]

Uv (bottom) = superficial vapour velocity υ (bottom) = volumetric flowrate An (bottom) = net area required Ac (bottom) = column area Dc (bottom) = column diameter

8-14



8.1.4.7 Flow arrangements

Cross flow trays are also classified according to number of liquid passes on the plate. The choice of liquid flow pattern is depends on the liquid flow rate and column diameter. υliq =

FLout ρ Lout 3.41 967.20 =3.536 ×10−3 m3 /s =

Base on Figure 8.7 (from Figure 11.28 reference [2]) below, when the column diameter is 0.964m, and liquid flow rate is 0.003536m3/s, the plate diameter outside range of the figure, but it is clear that a single pass plate can be used.

Figure 8.7: Selection of liquid flow arrangement [2] 8.1.4.8 Provisional Plate Design

Column diameter,

Dc = 0.964m

Column area,

A c = 0.73m 2

Downcomer area, 8-15



A d = 0.12 × A c = 0.12 × 0.73 = 0.088m 2 Net area,

A n = A c -A d = 0.73 − 0.088m 2 = 0.642m 2 Active area,

A a = A c − 2A d = 0.73 − 2(0.088) = 0.554m 2 Hole area,

A h = 0.10 × A a = 0.10 × 0.554 = 0.0554m 2 The relationship between the weir length and downcomer area is given in Figure 8.8 (from Figure 11.31 reference [2]). Ad 0.088 ×100% = × 100% Ac 0.73 = 12% From the Figure 8.8[2] below,

Lw = 0.76 Dc

8-16



Figure 8.8: Relationship between the weir length and downcomer area [2] Thus the weir length,

L w = 0.76 × Dc = 0.76 × 0.964 = 0.733m The height of weir determined the volume of liquid on the plate and is important f actor in determining the plate efficiency. A high weir will increase the plate pressure drop. For columns operating above atmospheric pressure, the weir height will normally between 40mm to 90mm. Take weir height,

h w = 50mm

Hole diameter,

d h = 5mm

Plate thickness,

t = 5mm

8.1.4.9 Weep point

The lower limit of the operating range occurs when it is known leakage through the plate excessive. This is known as the weep point. The vapour velocity at the weep point is the minimum value for stable operating. The hole area must be close so that at the lowest

8-17



operating rate the vapour flow velocity is still well above weep point. The one that is simplest to use and reliable is given by Chase (1967): ˆ = K 2 -0.9(25.4-d h ) U h ρ Gin 0.5

Where Ûh = minimum vapour velocity through the hole, m/s dh = hole diameter, mm K2 = constant, dependent on the depth of clear liquid on plate (from Figure 8.9[2]) It is important, to determine the maximum liquid rate that flows through the plates. Maxliq = FLout

Minimum liquid rate (at 70% turn-down), Min liq = 0.7 × Max liq = 0.7 × 3.41 = 2.387kg/s

The height of the liquid crest over the weir can be estimated using Francis weir formula. For a segmental downcomer this can be written as, 2

Maxh ow

⎡ Max liq ⎤ 3 = 750 ⎢ ⎥ ⎣ ρ Lout × L w ⎦ 2

3.41 ⎡ ⎤3 = 750 ⎢ ⎣ 967.2 × 0.733 ⎥⎦ = 21.37mm

8-18


Group 6 Acrylic Acid Project 2

Minh ow

⎡ Min liq ⎤ 3 = 750 ⎢ ⎥ ⎣ ρ Lout ×L w ⎦ 2

2.387 ⎡ ⎤3 = 750 ⎢ ⎣ 967.2 × 0.733 ⎥⎦ = 16.85mm Where how

= weir crest, mm liq

Lw

=weir length, m

At minimum rate,

h w +Minh ow = 50 + 16.859.63 = 66.85mm

Base on Figure 8.9 (from Figure 11.30 reference [2]), K2 = 30.6 Therefore, the minimum vapour velocity can be obtained. ˆ = K 2 -0.9(25.4-d h ) U h 0.5 ( ρGin ) 30.6-0.9(25.4-5) 1.560.5 = 9.08m/s =

Actual minimum vapour velocity through holes,

70%(υbottom ) ˆ U h_actual = Ah 0.7 ×1.22 0.066 = 12.94m/s =

So the minimum operating rate velocity will be above weep point.

8-19



Figure 8.9: Weep point correlation [2] 8.1.4.10

Pressure Drop

The pressure drop over the plates is an important design configuration. There are two main sources of pressure loss, that due to the vapour through the holes and due to the static head liquid on the plate. A simple additive model is normally used to predict the total pressure drop; the total is taken as the sum of the pressure calculated from the flow of vapour through the dry plate, the head of clear liquid on the plate, and terms account for other, minor, sources of pressure loss, the so-called residual loss. The residual loss is the different between the experimental pressure drop and the simple sum of the dry plate and the clear liquid height. It accounts for two effects, the energy to form the vapour bubbles, and the fact that an operating plate the liquid head will not be clear liquid but a head of aerated liquid froth and the froth density and height will be different from that of clear liquid. It is convenient to express the pressure drop in terms of mm of liquid. It is important to estimate the bottom pressure drop before calculate the dry plate pressure drop. 8.1.4.10.1

Column pressure drop estimation

Assume 100mm water, pressure drop per plate,

8-20



ΔP = 100 × 10−3 m × 1000

kg m × 9.81 2 × 13 3 m s

= 12753kg/ms 2 ( Pa )

Top pressure,

Ptop = 101334.6kg/ms2

So, estimated bottom pressure for the column,

Pbottom = Ptop + ΔP = 101334.6 + 12753 = 114087.6kg/ms 2 = 1.14bar

8.1.4.10.2

Dry plate drop

Maximum vapour velocity through hole, U h max =

υbottom Ah

1.22 0.0554 = 22.02m/s =

From Fig 8.10(from Figure 11.34 reference [2]) below, for thickness/hole diameter =1, Ah Ah = 0.1 Ap Aa Co = 0.84

8-21



Figure 8.10: Discharge coefficient, sieve plates (Liebson et al., 1957) [2] The pressure drop through the dry plate can be estimated using expression derived for flow through orifices. 2

⎡U ⎤ ρ h d = 51 ⎢ h max ⎥ Gin ⎣ Co ⎦ ρ Lout 2

⎡18.48 ⎤ 1.56 = 51 ⎢ ⎣ 0.84 ⎥⎦ 967.2 = 39.81mm

Where the orifices coefficients, Co is a function of the plate thickness, hole diameter, and the hole to perforated area ratio. Co can be obtained from Figure 8.11, which has been adapted from a similar figure by Liebson et.al (1957), Uh max is the maximum vapour velocity through the holes.

8.1.4.10.3

Residual head,

By using the equation Hunt (1955) 8-22


Group 6 Acrylic Acid Project 12.5 ×103 hr = ρ Lout 12500 967.20 = 12.92mm liquid =

8.1.4.10.4

Total plate pressure drop, h total = h d +h r +(h w +Maxh ow ) = 39.81 + 12.92 + 50 + 21.37 = 124.1mm liquid

Since 100 mm liquid was assumed to calculate the bottom pressure. Therefore, 124.1 mm liquid per plate is acceptable. 8.1.4.11

Downcomer Liquid Back-up

The downcomer area and plate spacing must be such that the level of the liquid and forth in the downcomer is well below the top of outlet weir on the plate above. If the level rises above the outlet weir the column will flood. The back-up of the liquid in the downcomer is caused by the pressure drop over the plate and the resistance to flow in the downcomer itself. In terms of liquid, the downcomer back-up is given by:

h b = h w +h ow +h total +h dc The main resistance to flow will be caused by the constriction at the downcomer outlet, and the head loss in the downcomer can be estimated using this equation;

⎡ Maxh ow ⎤ h dc = 166 ⎢ ⎥ ⎣ ρ Lout ×A m ⎦

2

h w = 50mm h ap = h w − 10 = 50 − 10 = 40mm

Where hb

= downcomer backup, measured from plate surface, mm

8-23

KKEK 4281 Design Project Chapter 8: Quenching Tower hdc


= head loss in the downcomer, mm

Maxhow = Liquid flowrate in downcomer, kg/s Am

=either the downcomer area, Ad or the clearance area under the downcomer, Aap, whichever is smaller, m2

The clearance under the downcomer area is given by, Aap = hap x Lw Where Downcomer pressure drop, hap = 40mm Thus, area under apron

, Aap = (40 ×10−3 ) × 0.733 = 0.02932m 2

Ap is less than Ad (0.088), by using equation for hd, ⎡ Max liq ⎤ h dc = 166 ⎢ ⎥ ⎣ ρ Lout ×A m ⎦

2

2

3.41 ⎡ ⎤ = 166 ⎢ ⎣ 967.2 × 0.02932 ⎥⎦ say 3mm = 2.4mm

Applying equation for hb,

h b = h w +h ow +h total +h dc = 3 + 50 + 21.37 + 124.1 = 198.47mm = 0.198m 1 1 × ( plate spacing + L w ) = × ( 0.05 + 0.733) 2 2 = 0.3915m

Standard design for hb design; hb < [0.5(plate spacing + weir height)] 8-24

KKEK 4281 Design Project Chapter 8: Quenching Tower 0.198 <


1 × ( plate spacing + L w ) = 0.3915 2

This tray spacing is acceptable. 8.1.4.12

Residence time

Sufficient residence time must be allowed in the downcomer for the entrained vapour to disengage from the liquid stream; to prevent heavily “aerated” liquid being carried under downcomer. A time of at least 3seconds is recommended. tr =

A d × h b × ρ Lout Max liq

0.088 × 0.198 × 967.2 3.41 = 16.85s > 3s

=

Where tr

= residence time, s

hb

= clear liquid backup, m

The residence time is more than 3s, considered satisfied. 8.1.4.13

Entrainment

Entrainment can be estimated from the correlation given by Fair (1961), Figure 8.12 (from Figure 11.29 reference [2]) which gives the fractional entrainment, ψ as the function of liquid vapour factor, FLV with the percentage approach to flooding as a parameter. Uv =

υbottom An

1.22 0.642 = 1.9m/s

=

The flooding percentage,

8-25


Group 6 Acrylic Acid Project % Flooding =

Uv U f_bottom

× 100

1.9 × 100 2.239 = 84.86% =

Base on Figure 8.11 (from Figure 11.29 reference [2]) below, with FLVbottom = 0.0123, ψ = 0.15, which is below 0.1, so it is satisfactory.

Figure 8.11: Entrainment correlation for sieve plates [2] Actual % flooding is less than 85% of estimated, thus the design is acceptable. 8.1.4.14

Trial Layout

8-26

KKEK 4281 Design Project Chapter 8: Quenching Tower Use cartridge-type construction.

Group 6 Acrylic Acid Project Allow 50mm unperforated strip round plate edge

50mm wide calming zones. Dc = 0.964m

Lw = 0.733

0.05m

0.964

0.733 m

m

0.05m Figure 8.12: Trial layout of the plate design 8.1.4.14.1

Perforated area From Figure 8.13 (from Figure 11.32 θ c = 98o

reference [2]), at

L w 0.733 = = 0.76 D c 0.964

8-27



Figure 8.13: Relation between downcomer area and weir length Angle subtended at plated by unperforated strip, θs = [180 − θ c ]o = 180 − 98

= 82o Mean length of unperforated edge strips

⎛θ ⎞ lmean = (Dc -0.05) × π × ⎜ s ⎟ ⎜ 180 ⎟ ⎝ ⎠ ⎛ 82 ⎞ = (0.964-0.05) × π × ⎜ ⎟ ⎝ 180 ⎠ = 1.31m Area of unperforated edge strips

Au = 0.05 × lmean = 0.05 ×1.31 = 0.066m 2 Mean length of calming zone (approximate),

8-28



⎛θ ⎞ lcz = (Dc -h w ) × sin ⎜ c ⎟ ⎜ 2 ⎟ ⎝ ⎠ ⎛ 98 ⎞ = (0.964-0.05) × sin ⎜ ⎟ ⎝ 2⎠ = 0.69m Area of calming zones

A cz = 2(lcz × h w ) = 2(0.69 × 0.05) = 0.069m 2 Total area available for perforation A p = A a -(A u + A cz ) = 0.554-(0.066 + 0.069) = 0.419m 2

8.1.4.15

Hole Pitch

The hole pitch (distance between the hole centre), lp should not be less than 2.0 hole diameters, and the normal range will be 2.5 to 4.0 diameters. Within this range, the pitch can be selected to gives the number of active hole required for the total area specified. The total hole area as a fraction of the perforated area, Ap is given by the following expression,

⎡d ⎤ Ah = 0.9 ⎢ h ⎥ Ap ⎣⎢ lp ⎦⎥

2

This equation is plotted in Figure 8.14 (from Figure 11.33 from reference [2]). From Figure 8.14, when

l A h 0.054 = = 0.129 p = 2.65 A p 0.419 , dh

It is satisfactory within 2.5 to 4.0.

8-29



Figure 8.14: Relation between hole area and pitch 2] Area of one hole,

⎡d ⎤ A hole = π ⎢ h ⎥ ⎣2⎦

2

2

⎡ 0.005 ⎤ =π ⎢ ⎣ 2 ⎥⎦ = 1.963 ×10−5 m 2 Number of hole

n hole =

Ah A hole

0.054 1.963 ×10−5 = 2750.9

=

≈ 2751 Where Ahole

= area of one hole, m2

dh

= hole diameter, mm

nhole

= number of hole 8-30


Ad


= downcomer area, m2

8.1.4.16 Height of column

Once the tray plate or tray value is optimized, the height of column can be calculated using the following equation, H = (N x plate spacing) + Ho Where Nact

= number of stage

Ho

= skirt height, estimated = 1.5m

Therefore, H

= (0.5 x 13) + 1.5 = 8m

8.1.5 Summary of Chemical Design parameter Table 1.2: Summary of chemical design parameter for the quenching tower Column area

0.73m2

Column diameter

0.964m

Downcomer area

0.088m2

Active area

0.554m2

Hole area

0.0554m2

Weir height

0.733m

Hole diameter

0.005m

8-31


8.2


Plate thickness

0.05m

Plate pressure drop

124.1mm liquid

Residence time

16.58s

% Flooding

84.86%

Hole area

1.963 x 10-5

Number of hole

2751 hole

Column efficiency

62%

Column height

8m

Mechanical Engineering Design of Quenching Tower

8.2.1 Introduction The design of most structures states above is mainly based on “factor of safety” approach. The unknown items, such as extent of yielding and material behaviour, are consider to be provided for the use of working stresses that are admittedly below thise the member will fail. The design parameters, which required evaluation at this stage, are material of construction, insulation, vessel dimensions, wall thickness, ends (type, thickness) and support

8.2.2 Vessel Function

8-32



The vessel will be designed in accordance with the British Standard specifications for fusion welded pressure vessel. Pressure vessel component generally consists of a few basic parts, such as cylinder, opening and various shaped closure heads. The cylindrical part is selected at the vessel diameter is in the size range of procurable tabular products.

8.2.3 Operating Design Pressure and Temperature 8.2.3.1 Design pressure

A vessel must be designed to withstand the maximum pressure to which it is likely to be subjected in the operation. For vessels under internal pressure, the design pressure is recommended to take 10% above the working pressure. Design pressure

= (101325N/m2) x 1.1 =

0.1115N/mm2 8.2.3.2 Design Temperature

The strength of material decreases with temperature so that the maximum allowable design stress will depend on the material temperature. The design temperature at which the design stress is evaluated should be taken as the maximum working temperature of the material, with due allowance for any uncertainty involved in predicting vessel wall temperatures. Thus, the design temperature is taken as 10% above the highest temperature of the inlet. Therefore, T = (170 x 1.1) oC = 187 oC

8.2.4 Material of Construction Material of construction have an important bearing on the safe handling of chemical, Since acrylic acid and acetic acid are highly corrosive, so we had to chose stainless steel grade 316 as the material of construction. This is because stainless steel 316 is excellent in a range of atmospheric environments and many corrosive media, it generally more resistant than 304.

8-33



8.2.5 Maximum Allowable Stress Value In mechanical designing, it is necessary to decide the maximum allowable stress (nominal design strength) that can be accepted as in the material of construction (stainless steel grade 316). This is determined by applying suitable “design stress factor” (factor of safety) to maximum stress that the material could be expected to withstand without failure under standard test conditions. The design stress factor allows for any uncertainty in the design methods, the loading, the quality of materials and the workmanship. The approximate material standard should be consulted for particular grades and plate thickness. From reference [6] Design stress factor for SS316 = 1.5 Based on design temperature and material SS316, Typical design stress

= 125.19N/mm2

Practical design stress, f = 125.19/1.5 = 83.46N/mm2

8.2.6 Welded Joint Efficiency The strength of a welded joint will depend on the type of joint and the quality of the welding. The value of the joint factor used in design will depend on the type of joint and amount of radiography required by the design code. In this design, the welding joint factor is taken as 1 implies that the joint is equally as strong as the virgin plate. Thus, The NDT Examination = 100% Radiography So

Joint efficiency, J = 1.00

8.2.7 Corrosion Allowance The corrosion allowance is an additional thickness of metal to allow for material lost by of corrosion and erosion or scaling. The allowance used should be agreed between the customer and manufacturer. Corrosion is the complex phenomenon, and it is not possible to give specific rules for the estimation of the corrosion allowance required for all circumstances. The allowance should base on experience with the material of construction under similar service conditions to those for the proposed design. Nevertheless, 1-4 mm of allowance is used based on the different working conditions. In 8-34



this design, the recommended corrosion allowance for absorber is taken as 3mm for severe corrosion effect. Corrosion Allowance, C.A = 3mm

8.2.8 Design of Thin Walled Vessel 8.2.8.1.1

Minimum practical wall thickness

The minimum wall thickness must be calculated in order to ensure that the vessel can withstand its own weight.

PDi 2Jf- 0.2P (0.1115N/mm 2 )(964mm) e= 2 (1× 83.46N/mm 2 ) - 0.2(0.1115N/mm 2 ) e=

= 0.64mm Where Di

= inside diameter of cylindrical (mm)

P

= design pressure, N/mm2

J

= joint factor

f

= design stress, N/mm2

Adding corrosion allowance 3mm, the minimum practical wall thickness, e= 3.64mm But minimum thickness required for construction is 6 mm. So the minimum required thickness of the cover is taken as 6 mm.

8.2.9 Torispherical Head Design Torispherical head is chosen since it is most commonly used for vessel under internal pressure less than 15bar.

8-35



Figure 8.15: Torispherical head Most standard torispherical head are manufactures with a major and minor axis ratie of 2:1. For this ratio, following equation can be used to calculated the minimum thickness required. PDi 2Jf- 0.2P (0.1115N/mm 2 )(964mm) e= 2 (1× 83.46N/mm 2 ) - 0.2(0.1115N/mm 2 ) e=

= 0.64mm Adding corrosion allowance 3mm, the minimum practical wall thickness, e= 3.64mm But minimum thickness required for construction is 6 mm. So the minimum required thickness of the cover is taken as 6 mm.

8.2.10 Design of Vessel Subject to Combined Loading 8.2.10.1

8.2.10.1.1

Dead Weight of Vessel

Shell

The approximate weight of a cylindrical vessel with domed end and uniform wall thickness can be estimated from the following equation.

w v =Cvπρ m Dm g (H v + 0.8D)t ×10−3 Where wv

= total weight of shell excluding internal fittings, N Cv

= account factor =1.08

Hv

= height between tangent lines = 2.5m 8-36



g

= gravitation acceleration = 9.81m/s2

t

= wall thickness, 0.005m

ρm

= density of vessel material, 8000 kg/m3

Dm

= Di + e = 0.964+0.006= 0.97m

Therefore,

w v =Cvπρ m Dm g (H v + 0.8D)t ×10−3 = 2450N 8.2.10.1.2

Plates

Weight for a single plate,

w p =π ⋅ ρ m ⋅ g

Di 2 ⋅t 4

= 78N Total weight of plates, = 78N x 13 = 1014N 8.2.10.1.3

Insulation

Weight of insulation, Mineral wool density

=130kg/m3

Approximate volume of insulation, =π × D m × height × insulator thickness = 0.39m3

Weight of insulation

=130 x 0.39 x9.81 = 500N

Total stress due to dead weight, w

= shell + plate + insulation = 2450 + 1014+ 500 = 3964N

8.2.10.2

Wind Loading

8-37



Assuming maximum wind velocity 160km/hr Vw = 160km/hr Wind Pressure = 0.05 x Vw2

Pw

= 1280N/m2 Mean diameter including insulation =0.97 + 2(5 + 25) × 10−3 = 1.03m

Loading Fw = Pw x Mean diameter including insulation = 860N/m Bending moment at bottom tangent line, 860 × 2.52 2 = 2700Nm

M=

8.2.10.3

Analysis of Stress

8.2.10.3.1

Pressure stresses

8.2.10.3.2

P

= 65psi

Di

= 0.964m

t

= 0.05m

Longitudinal and circumferential stresses due to pressure PDi 4t = 13.4N/mm 2

σL =

PDi 2t = 26.8N/mm 2

σh =

8.2.10.3.3

Dead weight stress

8-38



σw =

W π (Di + t)t

= 0.4N/mm 2

8.2.10.3.4

Bending stress Do = 0.87m Iv =

π

(D o 4 -Di 4 )

64 = 4.6 × 108 mm 4

σb = ±

M ⎛ Di ⎞ + t⎟ ⎜ Iv ⎝ 2 ⎠

= 1.8N/mm 2

The resultant longitudinal stress is

σ x = σ L +σ w ±σb σ x is compressive and therefore negative

σ x (upwind) = σ L + σ w + σ b = 14.8N/mm 2

σ x (downwind) = σ L + σ w − σ b = 11.2N/mm 2 As there is no torsional shear stress, the principle stresses will be σ x and σ h . 18.9

7.1

26.8

28.8

Upwind

Downwind

Figure 8.16: Analysis of stresses

8-39



The greatest different between the principle stress will be on the downwind side 26.8-7.1 = 19.7 N/mm4 Maximum allowable design stress

= 12700psi

=86.4N/mm2

So, well below the maximum allowable design stress 8.2.10.3.5

Check Elastic Stability (Bucking)

Critical buckling stress ⎛ t ⎞ ⎟ ⎝ Do ⎠ 161.3N/mm 2

σ c = 2 ×104 ⎜

The maximum compressive stress will occur when the vessel is not under pressure = 0.4+1.8= 2.2N/mm2, so the design is satisfactory.

8.2.11 Design of Skirt Support Skirt is the most frequently used as support for vertical vessel. It is attached by continuous welding to the head and usually the required size of this welding determines the thickness of the skirt. Code UW-12 may be used. The minimum thickness for a skirt is 1/4 in (6.25mm). In the design, the butt weld joint is chosen. Outside diameter of skirt, Ds = 1.03m Butt weld joint factor, R 8.2.11.1

8.2.11.1.1

=0.6

Operating weight

Weight of Full Liquid

Column dimensions Di

= 0.964m Hv

=8m 8-40



Density of liquid

ρL

= 967.2kg/m3

Volume of shell,

π ( Di )

=

2

4 = 5.83m3

× Hv

From reference [5], the volume of 2 torispherical heads are: Vh

= 2 x 0.65 ft3 = 0.37m3

Volume of full liquid,

5.83 + 0.37 = 6.2m3 Weight of full liquid,

= 6.2 × ρ L × g = 5996.64N

8.2.11.1.2

Weight of skirt

Material of skirt = Carbon steel SA-283 Grade C Density of material

ρm

= 8000kg/m3

ts

= 6.25 mm

g

= 9.81mm

Minimum thickness of skirt

Gravitational constant

Height of skirt

hs

= 1.5m

Dm

= 0.97m

Mean of diameter

Weight of skirt

8-41



w s = πD m ρ m gt s h s = 2242.1N

Vessel weight,

wo

= shell + plate + insulation + skirt + full liquid

= 12202.74N 8.2.11.2

Thickness of Skirt

Wind pressure, Pw Wind load, Fw

= 1280N = 860N/m

Height from bottom, hb

= 8m

Bending moment at bottom tangent line 860 2 ×8 2 = 27520Nm

MT =

With

Do E

= 620mm = 0.62 Mt

= 27520Nm

Ro

= 310mm

Sr

= 86.4N/mm2

wo

= Operating weight

C.A

= 3mm

Required thickness of skirt, ts ts =

wo MT ×1000 + + C.A 2 R o π SrE Doπ SrE

= 6mm So the minimum thickness of skirt 6.25mm is acceptable.

8.2.12 Opening There are 4 nozzles attached to the column, 2 nozzles on the shell of column for gas stream and 2 nozzles for the liquid streams. An approximate of the economic pipe 8-42



diameter for normal pipe runs can be developed from an expression for stainless steel. d opt = 226G 0.5 ρ −0.35

Where dopt

= optimum pipe diameter

G

= mass flow rate, kg/s

ρ

= density, kg/m3

The equation above is carried to determine the piping size for the 4 streams. The calculation is summarized in the Table 8.6 below. Table 8.3: Piping system Gas In

Gas Out

Liquid In

Liquid Out

No of nozzles

1

1

1

1

Flow rates, G(kg/s)

9.74

11.14

2.00

3.41

Density, ρ (kg/m3)

994.3

1.55

0.92

967.2

Optimum diameter, dopt (mm)

62.89

647.05

329.08

37.63

Nominal pipe size(in)

2.5

30

14

1.5

Outer diameter, do (mm)

73.02

762

355.6

48.26

Inner diameter, di (mm)

65

750

350

40

Thickness, hi(mm)

5.156

9.53

9.53

3.683

Note that the nominal pipe size, OD and ID for each nozzle is obtained from Perry Chemical Engineering Handbook, Chapter 10[1].

8.2.13 Design of Manhole The requirements for provisions and dimensions of sight hole, handle, head hole and manhole opening into static and mobile pressure vessels are specified in BS470 Series. One manhole accordance with Table 8.7 BS470:1984 for vessel inner diameter over 1.5m, located on vessel shell and bottom of the column. The dimensions of manholes are selected based on BS 470 1984 the minimum size to afford full rescue facilities with selfcontained breathing apparatus shall inner diameter, Dim = 575mm and length =500mm.

8-43



Minimum thickness of manhole, PDim 2Jf- P

e=

(0.1115N/mm 2 )(575mm) 2 (1× 83.46N/mm 2 ) - 0.2(0.1115N/mm 2 )

=

= 0.38mm

Adding corrosion allowance 3mm, the minimum practical wall thickness, e= 3.38mm But minimum thickness required for construction is 6 mm. So the minimum required thickness of the cover is taken as 6 mm.

8.2.14 Design of Anchor Bolt 8.2.14.1 Design anchor bolt

A simplified method for the design anchor bolts is to assume the bolts being replaced by a continuous ring which diameter is equal to the bolt circle. The required area of bolts shall be calculated for empty condition of column. Empty weight of column Wm

= Operating weight – full liquid weight\ = 6206.1N

Maximum allowable stress Sm

= 15000psi = 102N/mm2

MT

= 27520Nm

Assume bolt circle = 625mm Area within the bolt circle, 6252 4 = 306800mm 2

As = π ×

Circumference of circle, 8-44


Group 6 Acrylic Acid Project Cb

= π x 625 = 1963mm

Number of anchor bolts N = 4 (for both circle 25 inch) Maximum Tension T=

1000MT Ws − AB CB

= 14.93N/mm Required area of one bolt BA =

T × Cs SB × N

= 71.8mm 2 (0.115in 2 )

From Table A in page 63 of reference [5] The root area of 0.5 in bolt size is 0.126 in2. Adding 0.125in for corrosion, use 4(5/8 in) size both. 8.2.14.2 Checking stress in anchor bolt

CB = 0.126 in2 (28.75mm2) SB =

T × Cs BA × N

= 93.04N/mm 2

Since the maximum allowable stress is 100 N/mm2, the selected number and size of bolts are satisfactory.

8.2.15 Design of Base Ring 8.2.15.1

Design base ring

Area of base ring

8-45



π ( d o 2 − d12 )

AR =

4 = 0.072m 2

Area within the skirt As =

π Do 2

4 = 0.302m 2

Circumference on O.D of skirt

Cs = π Do = 1948mm Safe bearing load on concrete

fb = 500psi(for design) = 3.45N/mm 2 Moment at the base due to wind MT = 27520N Operating weight wo =6206.06N Maximum compression Pc =

1000 × MT Wo + As Cs

= 24N/mm Approximate width of base ring l1 =

Pc fb

= 6.75mm But the minimum dimension for l1 = 38.55mm So take the greater l1 = 38.55mm Approximate thickness of base ring

t b = 0.31× l1 = 12.34mm 8-46



Use 0.5 in (12.5mm) thick base ring 8.2.15.2

Checking Stress

Bearing stress S1 =

Pc × C s AR

= 0.63N/mm 2

Bending stress S2 =

3 × S1 × l1 t B2

= 18.45N/mm 2

Use carbon steel SA-283 Grade C for base ring, allowable stress of 86.4N/mm2 can be taken for structural purposes. Thus the width and thickness of the base ring are satisfactory.

8.2.16 Design Parameters Table 8.4: Mechanical design parameter for quenching tower Designed Column Dimensions

Inside diameter

0.964m

Column height

8m

Shell thickness

0.005m

Corrosion allowance

0.003m

Dead Weight Load

Weight of shell

2450N

Weight of plates

1014N

Weight of insulation

500N

Weight of skirt

2242.1N

Skirt Support Design

Material of construction

Carbon steel SA-283 Grade C

8-47



Maximum allowable stress

86.4N/mm2

Skirt height

1.5m

Outer diameter

1.03m

Joint factor

0.6

Type of joint

Butt weld joint

Skirt thickness

0.00625m

Anchor Bolt Design

Material of anchor bolt



102N/mm2

Number of bolts

4

Bolts diameter

0.625in

Base Ring Design

Material of bolt ring



86.4N.m2

Base ring thickness

0.5in

Outer diameter

1.15m

Inner diameter

0.96m

8-48


8.3


Safety, Control & Instrumentation of Quenching Tower

8.3.1 Safety Analysis 8.3.1.1 Introduction

Hazard is always connected with accident. Hazard always present in a chemical plant. It is an advantage if we could identify in advance and take extra precaution step before hand. Unfortunately, it is difficult to identify hazard before accident occur, and this is very risky and costly. So it is essential to develop a mechanism in order to identify hazards that could threat the plant operation. There are several methods available for performing hazard identification and risk assessment. Four commonly practiced hazard identification methods are: 1. Process hazard checklist 2. Hazard surveys 3. Hazard and operability study (HAZOP) 4. Safety review 8.3.1.2 Hazardous and operability study

In assessing hazard in a unit operation, HAZOP is the most reliable method because: 9 It is very specific and objective but in the same time promotes the freedom flor of

thought. 9 It is considers various event and situation for the unit operation with prediction of

failure and action required. HAZOP study requires a committee with several experts in their field. The HAZOP procedures use the following steps to complete an analysis. i.

Break flow sheet into unit operation. In this case, a quenching tower.

ii.

Choose a study mode.

iii.

Pick a process parameter: flow, temperature, pressure, concentration. 8-49

KKEK 4281 Design Project Chapter 8: Quenching Tower iv.


Apply guide word to the parameter to suggest possible deviation (I.e. no, less, high, etc.) The usage of guide word varies with different parameter.

v.

Determine possible causes and note any protectable systems.

vi.

Evaluate the consequences (if any) and recommended action.

The full HAZOP study have been done and compiled at the appendix 8. With all the study node and parameter applied with the appropriate guide word. 8.3.1.3 Conclusion

Process specification resulting for the HAZOP studies are as the following: 1. Installation of controller valve in each stream 2. Installation of a backup controller valve to all steam in case of the controller valve failure. 3. Installation of High Pressure Alarm (PAH), Low Pressure Alarm (LAL), and High Level Alarm (LAH) to alert the operator in case of emergency or deviation in the process. 4. Installation of gas detector and alarm in case of any leakage or spill in order to let the operator aware. 5. Installation of check valve in every line to prevent reverse flow. 6. Installation of pressure indicator to line gas feed. 7. Ensure maintenance on equipment and pipeline are kept done often. 8. Installation of temperature indicator.

8-50



8.3.2 Control and Instrumentation 8.3.2.1 Introduction

Control system is the essential part of chemical engineering operation. In all processes, it is a must to keep all the parameters such as temperature and flow to be in a certain boundary in order to ensure a safe and compatible process. Automatic control is most desired because manual control (human operated) will definitely have a lot of down fall. Basically, process control is done by measuring the variable that we desired to control (variable), comparing the value with the desired set point, and adjusting a control variable which has a direct effect on the control variable. The objective of process control is to ensure safety in process, environmental protection, to meet the product specification, economics factor, and the final one, to overcome process limitation. 8.3.2.2 Control of quenching tower

Objectives: ¾ To ensure the liquid level (h) in the column base at desired value. ¾ To ensued the pressure (P) at desired balue. ¾ To keep the desired value of bottom product (B) 8.3.2.3 Control variable and parameter

Table 8.5: Control variable and parameter Control

Measured

Manipulated

Description

8-51

KKEK 4281 Design Project Chapter 8: Quenching Tower variable Flow rate of

variable Liquid inlet flow

variable Gas inlet flow

gas out

rate

rate

Group 6 Acrylic Acid Project ¾ Liquid flow rate can be measured directly

using sensor. ¾ Effect of this flow rate on gas out flow and

concentration is directly and fast Liquid level

Liquid level

Flow rate of

¾ Fast level control can be achieved by

existing liquid

measuring h and manipulating flow rate od

stream

existing liquid stream ¾ High level alarm (LAH) and low level alarm

(LAL) are installed as safety precautions. LAL and LAH enable immediate action taken by operator to control the level if the valve at the existing liquid stream is out of function. Temperature

Temperature

Flow rate of water

¾ Deviation in temperature will alter the

process

In this design procedure, two type of controller is used. Ration controller between two feed steam is used since the ratio of those twp parameter is known and can be set within the operation. Other streams are controlled by feedback controller. The ratio control and feedback control loop can be summarized as Figure 8.19 and Figure 8.20. Both controllers will ensure the operation condition operates as normal. Ratio controller was chosen because it is the simplest way to maintain the required ratio of inlet liquid and vapour. Since the required ratio between liquid and vapour is known.

Ratio controller operates by maintaining two flows by taking flow reading of one stream (wild stream) and controlling the other. Feedback control is use on other stream in order to retain the three parameters define above. The full control of quenching tower is shown is Figure 8.20.

8-52



+

+ GC

GF

GP

-

+ GM

Figure 8.18: Feedback control loop in quenching tower

GP + Gm1

Kr

GC

GV

1

+

+

+ Gm2

Figure 8.19: Ratio control loop in absorbed

8.4

NOMENCLATURES Dimension MLTθ

Aa

Active area

L2 8-53



Ac

Column area

L2

Ad

Downcomer area

L2

Ah

Hole area

L2

An

Net area

L2

Ap

Total area available for perforation

L2

As

Area of unperforated edge strip

L2

Av

Cross sectional area

L2

Az

Calming zone area

L2

Co

Constant

Dc

Actual column diameter

L

d

Column diameter

L

dh

Hole diameter

L

hb

Backup in downcomer

L

hd

Dry plate drop, head of liquid

L

ho

Weir height

L

ht

Total plate pressure drop, head of liquid

L

hap

Area under apron

L2

hdc

Head loss in downcomer

L

how1

Maximum height of liquid crest over the weir

L

how2

Minimum height of liquid crest over the weir

L

K1, K2

Constant

Lm

Minimum liquid rate

Ls

Molar flow rate of solute free liquid per unit cross section area

MT ML-2T-1

hw

Weir length

N

Number of holes

P

Operating pressure

T

Operating temperature

θ

t

Plate thickness

L

tr

Residence time

T

Ur

Velocity of feed

LT

L ML-1T-2

8-54



Uh

Maximum vapour velocity

LT

Uw

Gaseous flow rate

LT

Uac

Velocity at actual percentage of flooding

LT-1

Vs

Volume of gas in S.T.P

X

Mol of solute _ per mol of solvent in liquid phase

x

Mol fraction _ in liquid phase

Y

Mol solute _per mol inert gas without _ in gas phase

y

Mol fraction _ in gaseous phase

β

Constant

φ

Fractional entrainment

ρL

Density of liquid

ML-3

ρv

Density of vapour

ML-3

A1

Area of excess vessel

L2

A2

Area of excess nozzle

L2

A3

Area of inside extension of nozzle

L2

A4

Area of weld

L2

A5

Area of reinforcement pad

L2

AB

Area within the bolt circle

L2

AR

Area of base ring

L2

AS

Area within the skirt

L2

BA

Area of one bolt

L2

Cv

Account factor

C.A

Corrosion allowance

L

Cb

Bolt circle circumference

L

Cs

Outer skirt circumference

L

Di

Inner diameter of quenching tower

L

Inner diameter of pad

L

Dm

Mean diameter of quenching tower

L

Do

Outer diameter of quenching tower

L

Outer diameter of pad

L

Inner diameter of opening

L

Dipad

Dopad d

L3

8-55



di

Inner diameter of base ring

L

do

Outer diameter of base ring

L

E

Joint factor

Fw

Wind loading

MT2

f

Thinning factor

fb

Safe bearing load on concrete

g

Gravitational acceleration

Ht

Column height

L

Hv

Height between tangent lines

L

hb

Height from bottom

L

hs

Height of skirt

L

L

Inside radius of dish

L

M

Total bending moment

ML2T-2

Bending moment at base due to wind

ML2T-2

MT

LT-2

N

Number of anchor bolts

P

Design pressure

ML-1T-2

Pc

Maximum compression

ML-1T-2

Pw

Wind pressure

ML-1T-2

Ri

Inner radius of quenching tower

L

Inner radius of knuckle

L

r S1, S2

Bearing stress

ML-1T-2

Sa

Maximum allowable stress (base ring)

ML-1T-2

Sr

Maximum allowable stress (shell and head)

ML-1T-2

t

Thickness of wall less C.A

L

tb

Required thickness of base ring

L

ta

Thickness of pad less C.A

L

tn

Nominal thickness of shell and head

L

tr

Required thickness of shell and head less C.A

L

ta

Required thickness of skirt

L

trn

Required thickness of nozzle

L

Pad thickness

L

tpad

8-56


8.5


tmin

Minimum thickness

L

T

Design temperature

θ

Tt

Maximum tension

MT-2

Vh

Volume of torispherical head

Vw

Maximum wind speed

W

Total dead weight

MLT-2

Wa

Empty column weight

MLT-2

Wa

Operating weight

MLT-2

Wo

Weight of plates

MLT-2

Wv

Total weight of shell

MLT-2

ρm

Liquid density

ML-3

ρv

Vessel material density

ML-3

σb

Bending stress

ML-1T-2

σc

Critical buckling stress

ML-1T-2

σh

Circumferential stress due to pressure

ML-1T-2

σL

Longitudinal stress due to pressure

ML-1T-2

σw

Dead weight stress

ML-1T-2

σz

Resultant longitudinal stress

ML-1T-2

L3 LT-2

REFERENCES

1. R.E. Treybal, “Mass Transfer Operation”, 3rd Edition, McGraw Hill. 2. Coulson, J.M and Richardson, J.F, “An Introduction to Chemical Engineering Design”, Chemical Engineering Series, Vil 6 by Sinott R.K, Pergamon Press. 3. Perry, J.H and Chilton, C.H., “Chemical Engineers Handbook”, 5th Edition, McGraw Hill, 1973. 4. Stanley M. W., “Chemical Process Equipment: Selection and Design”, ButterworthHeinemann. 5. Eugene F. Megyesy, “Pressure Vessel Handbook”, Pressure Vessel Handbook Publishing Inc. 6. American Society of Mechanical Engineers (A.S.M.E. Codes)

8-57

KKEK 4281 Design Project Chapter 9: Extractive Distillation Column


CHAPTER 9: EXTRACTIVE DISTILLATION COLUMN 9.1: CHEMICAL ENGINEERING DESIGN 9.1.1 Introduction Distillation is the most widely used separation technique in the chemical process industries. Not all liquid mixtures can be separated by ordinary fractional distillation, however when the components to be separated of system have relative volatilities of close to 1.00 (i.e. close boiling mixture), separation becomes difficult and expensive because a large number of trays and a high reflux ratio are necessary.

In this case, extractive distillation is used. The extractive distillation column works because an heavy solvent is specially chosen to interact differently with the components of the original mixture, thereby altering their relative volatilities.

In our Acrylic Acid production plant, in order to produce acrylic acid which is our product purity up to 99.7%, we have decided to use extractive distillation column with the recovery of solvent system in our separation section.

9.1.2 Objective The objective of this design project is to design a extractive distillation column which can remove the impurities mainly are acetic acid and water from the acrylic acid with the highest purity of acrylic acid and lowest energy consumption.

9-1



9.1.3 Process Description

Figure 9.1: Flow Diagram for Extractive Distillation Column

The liquid stream consists of acrylic acid, acetic acid and water is fed into extractive distillation column. The solvent used is a mixture of cyclohexane and isopropyl acetate. The solvent and polymer inhibitor with higher density is fed from top while the liquid stream is fed from bottom. Under solvent extraction acetic acid will be extracted by the solvent and leave at the top along with water. Acrylic acid discharged at the bottom of the column as raffinate is pure acrylic acid with 99.7% purity. The solvent along with the extracted acetic acid and water is a two phases liquid with water phase and solvent phase. The mixture is fed into decanter with water is separated and recycle. The solvent and acetic acid is then fed into solvent recovery distillation column. The solvent with 99.8% is recovered and recycle back to extraction distillation column.

9-2



9.1.4 Selection of Column 9.1.4.1 Selection of Internal Column Table 9.1: Comparison between Plate Column and Packed Column

Plate Column

Packed Column

Wider range of liquid and gas flow rates

Lower liquid flow rates.

For higher column diameter

For small column diameter

Higher pressure drop

Lower pressure drop

Higher liquid hold up

Lower liquid hold up

Non-corrosive liquid

Corrosive liquid

Packed column is chosen because: •

The feed liquid is flammable liquid which required low liquid hold-up for safety reason.

•

More economical when the diameter of the column is low.

•

The pressure drop in packed column is lower which more suitable for low pressure system.

9.1.4.2 Packing Selection Table 9.2: Comparison between Random Packing and Structured Packing

Random Packing

Structured Packing

Easy separation which significant different Close boiling point separation between boiling point of the components. Low cost

High cost

Random packing is chosen because: •

More economically

•

Boiling point between the water, acrylic acid and acetic acid is significant.

9.1.4.3 Random Packing selection Basically random packing grouped into 2 groups, rings and saddles. Intalox saddle is chosen due to following reasons: •

It gives a better liquid distribution and larger free area.

•

Lower manufacture cost.

9-3



9.1.5 Packed Column Design 9.1.5.1 Selection of Solvent The solvent used is a mixture of cyclohexane (45%) and isopropyl acetate (55%) which is preferentially extracts the water and acetic acid from acrylic acid stream. Besides that it is noncorrosive and it has relatively low cost.

9.1.5.2 Composition and condition of feed stream, distillate and bottom Table 9. 3: Molar Flow Rate of the Inlet Streams and Outlet Streams of Extractive Distillation Column

Component

Make up solvent

From Quenching Tower

Top

Bottom

(kmol/hr)

(kmol/hr)

(kmol/hr)

(kmol/hr)

Acrylic acid

0.00

125.67

1.32

124.36

H2O

0.19

162.58

162.62

0.15

Acetol

0.00

0.13

0.00

0.13

Acetic Acid

0.32

4.43

4.69

0.06

Acrolein

0.00

0.14

0.14

0.00

Cyclohexane

191.25

0.00

191.25

0.00

i-p-Acetate

233.75

0.00

233.75

0.00

Table 9.4: Operating Condition of the Inlet Streams and Outlet Streams of Extractive Distillation Column

Parameter

Make up solvent

From Quenching Tower

Top

Bottom

32

72.88

35.68

87.87

101.3

101.3

15

15

Temperature (°C) Pressure (kPa)

9-4



9.1.5.3 Number of theoretical stages, N

Table 9.5: Equilibrium Data for Raffinate Phase

Extracted

Solvent

(water + acetic acid) %

(cyclohexane and isopropyl acetate) %

67.1

17.6

41.8

9.9

10.8

2.3

2.7

0.34

Table 9.6: Equilibrium Data for Extracted Phase

Extracted

Solvent

(water + acetic acid) %

(cyclohexane and isopropyl acetate)%

11.23

78.5

51.6

46.9

46.7

9.1

18.8

2.1

We can find the equilibrium data of the solvent and extract and plot equilibrium curve for the system. By using flow rate and composition of feed, solvent, extracted phase and raffinate phase, we can get number of stages from the equilibrium curve. The number of theoretical plate obtain is 10 stages.

9.1.5.4 Optimum Feed Location The stream from quenching tower is fed at the bottom stage of the extractive distillation column and the solvent is fed at the top stage of the extractive distillation column to achieve highest purity of acrylic acid. 9-5



9.1.5.5 Optimum reflux ratio Table 9.7: Purify of Product with vary Reflux Ratio

Reflux Ratio

Purify of Acrylic Acid

2.5

99.697%

3.0

99.725%

3.5

99.745%

With increasing of reflux ratio, the purify of Acrylic Acid can be increased. However the power required is increase which cost a lot. Therefore reflux ratio 3.0 is chosen since our product target is higher than 99.7% and it is more practicable by using reflux ratio as 3.0.

9.1.5.6 Column Diameter Flow parameter,

0.2

For distillation column, the pressure drop is between 40 to 80mm water/m of packed height. Thus, a pressure drop of 80mm H2O/m packed height was chosen in this design.

Figure 9.2: Flooding and Pressure Drop in Packed Column

9-6



K4 at pressure drop 80mm water/m = 1.5 K4 at flooding = 2.3 Percentage flooding =

1.5 ×100% = 80.7%(< 90%) -Acceptable 2.3

Packing diameter = 51mm Packing Factor = 130 ⎛ K 4 ρv ( ρ L − ρv ) ⎞ Flow rate per unit column cross-sectional area, Vw = ⎜ ⎜ 13.1× Fp ( μ L / ρ L )0.1 ⎟⎟ ⎝ ⎠

Required Area, A =

0.5

= 14.24kg / m 2 s

V = 0.844m 2 Vw

Column Diameter, D =

4A

π

= 1.03m

The calculated column diameter is acceptable to avoid poor liquid distribution as the value is higher than 0.9m for packing size of 51mm. Hence, the new column area = 0.85m2. Ratio of column diameter/packing diameter (Dc/dp ) = 20.6 > 15 (acceptable). For saddles, the ratio should be greater than 15 to ensure good liquid and gas distribution in the packing column.

9-7



9.1.5.7 Height of Packed Zone Norton’ correlation is used to predict the height of theoretical plate (HEPT) packed zone.

HEPT = n − 0.187 ln σ 0.213ln μ

Figure 9. 3: Table Constant for TETP Correlation

n = constant for HEPT correlation = 1.72330 Height of a Theoretical plate = 1.53 Column height = 15.3m 9.1.5.8 Wetting rate The minimum wetting rate for random packing should be larger than 2x10-5m2/s to have good contact between liquid. Minimum wetting rate=

B = 0.0147 m 2 s −1 (>2x10-5m2/s) ρ L AC

9-8



9.1.5.9 Liquid Hold-up

The void space in a packed bed is occupied by vapor and liquid during operation. A sufficient amount of holdup can represent an incipient flooding condition. There are two different types of liquid holdup in a packed bed which is static and operating. Static hold up represents that volume of liquid per volume of packing that remains in the bed after the gas and liquid flows stop and the bed has drained. hs = 2.79

C1μ C2 σ C3

ρl 0.37

where C1 =0.0055, C2 =0.04 and C3 =0.55 for saddles

Operating holdup is that volume of liquid per volume of packing that drains out of the bed after the gas and liquid flows to the column stop.

1/3

⎛ μu ⎞ ⎛μ 2 ho = 22 ⎜ L L 2 ⎟ + 1.8 ⎜ L ⎜ gρ d ⎟ ⎜ gd ⎝ L p ⎠ ⎝ p

1/2

⎞ ⎟⎟ ⎠

Where μ L = liquid superficial velocity g = gravitational constant = 9.81m/s2 dp = nominal packing size = 0.051 m hs = 0.009 ho = 0.08 Total liquid hold up is the sum of the static holdup and the operating hold up. ht = hs + h0 =0.089 9.1.5.10 Operating Void Space

The operating void space is the actual space that available for the gas to pass through the packed bed during the operation. Hence, the effective void space ε o = ε − ht = 0.69

9-9



Table 9.8: Extractive Distillation Column Design Summary

Column Diameter, Dc

1.03 m

Packed bed height, Z

15.3m

Flooding percentage

80.7 %

Wetting Rate

0.0147 m2/s

Total liquid hold-up

0.089 m3

9-10



9-1: MECHANICAL ENGINEERING DESIGN 9.2.1 Introduction Basically mechanical design of the column includes three main stages below: •

Material of construction including design pressure and temperature, construction materials, design stress, welded joint factor and corrosion allowance.

•

Fittings which including internal column fitting, manhole, pipe sizing, safe pressure and compensation for opening.

•

Column design which include cover thickness of cylindrical shell, vessel head, vessel height, dead load of vessel, wind load and analysis of stresses.

9.2.2 Material of construction 9.2.1.1 Design Pressure

The vessel must be designed withstand the maximum operating pressure, which is generally 1015% more than the maximum operating pressure. Design pressure = 101325Pa x 110% = 111457.5Pa

9.2.2.2 Design temperature

The strength of metals decreases with increasing temperature. Design temperature = 87.57 x 110% = 96.33°C

9.2.2.3 Material of construction

Stainless steel is the most suitable construction material for the extractive distillation column to provide better corrosion resistance. For the vessel support and piping, carbon steel is used because it easy to fabricate, ductility, cheap, high yield and tensile strength.

9.2.2.4 Design stress

The design stress is a value for the maximum allowable stress that can be accepted in the material of construction, so that the material could be withstand without failure under standard test conditions. A design stress factor of 1.5 is applied to the maximum stress. The design stress for the design temperature is 150N/mm2. 9-11

KKEK 4281 Design Project Chapter 9: Extractive Distillation Column The design stress f =


150 = 100 N / mm 2 1.5

9.2.2.5 Welded joint factor

The column requires 100% non-destructive testing of weld. The welded joint factor is taken as 1.0 by assuming the joint is quality and strong.

9.2.2.6 Corrosion Allowance

The corrosion allowance is the additional thickness of metal added to allow for material lost by corrosion and erosion, or scaling. According to Corrosion Data Survey by NACE, the tendency of pitting corrosion is 0.005in deep per year. Assuming the system is run for 10 years, the minimum corrosion allowance is 1.270mm. We take it as 2mm for the corrosion allowance.

9.2.3 Internal Fitting 9.2.3.1 Packing support

The primary function of the packing support plate is to serve as a physical support for the tower packing

9.2.3.2 Vapor distributor

In this packed columns need no vapor distribution devices.

9.2.3.3 Hold down plate

It also called bed limiter. It used to provide space to permit gas disengagement from the packed bed.

9.2.3.4 Liquid distributors

Liquid distributors is required at the location where liquid stream is introduced. It provide uniform liquid distribution pattern to the packed bed.

9.2.3.5 Liquid redistributors

9-12



Redistributors are used to collect liquid that has migrated to the column walls and redistribute it evenly over the packing. It should be installed for every 3m of packing to prevent channeling of liquid.

9.2.3.6 Mist eliminator (Demister)

It can be designed for up to 99% removal of liquid droplets and it is located at above of the liquid feed pipe. The pad height of the mesh droplet separators in most application lies between 100 and 150mm. it consists of coils or layers of knitted wire mesh. They are usually held together by top and bottom support grids.

9.2.3.7 Support ledges

The plates in the tower internal are designed to rest on a ledge. This ledge should be level and perpendicular to the tower’s vertical axis and flat to provide a uniform load-bearing surface.

9.2.3.8 Manhole

Three manholes are provided for cleaning, maintenance and inspection. The manholes with diameter 500mm are located at top, middle and bottom of the extractive distillation column.

9-13



9.2.4 Column Design 9.2.4.1 Cylindrical Shell Thickness

The minimum cylindrical shell wall thickness that sufficiently rigid to withstand its own weight. Temperature (°C) 20 150 87.97

Young Modulus E (N/mm2) 202000 192000 196800

Inner Diameter, Di = 1.03m Outer Diameter, Do = Di + 2t L’ = effective length between the ends = 0.4m Kc = collapse coefficient

Assume t = 4 mm Do/t = 155 L’/Do = 0.26 Kc = 25

Pc = K c E (

t 3 ) = 1.37N/mm2 (> design pressure) Do

By taking wall thickness of the column with corrosion allowance 2mm, the wall thickness will be 6mm.

9.2.4.2 Vessel Head A hemispherical head is the strongest shape, it capable of resisting about twice the pressure of a torispherical head of the same thickness but the cost is higher. A torispherical head of Korbbogen is

chosen as vessel head due to its economical factor since in this design is not high pressure system. The optimum thickness ratio is basically taken as 0.6. Thus, the head thickness is 0.6 x (shell thickness + corrosion allowance) = 5mm.

9.2.4.3 Vessel Height

The height of the column is determined by summing up height of packed zones as well as the internal fittings and vessel head.

9-14



9.2.4.4 Flange

Flange is a short cylindrical section between the cylinder body and the formed domed head. This ensures that the weld line is away from the point of discontinuity between the head and the cylindrical section of the vessel.

9.2.4.5 Load Analysis 9.2.4.5.1 Dead Weight loads

For loads Analysis, dead weight loads and wind loads is considered. The major sources of dead weight loads are vessel shell, internal and external fittings and insulation. In the design, the dead weight loads is 20.5 x 103N.

9.2.4.5.2 Wind load

The wind load imposed on any structure by the action will depend on the shape of the structure and the wind velocity. By using wind speed of 160 km/h (equivalent to wind pressure of 1280 N/m2) for preliminary study, the wind load per unit length of column estimated, Fw, is 371.456N/m.

9.2.4.6 Stress analysis

A number of stress conditions can occur simultaneously during the normal operation of the vessel. The standard procedure is to sum up all the stresses to determine the total stress on the pressure vessel. The total stress with the largest magnitude will be the expected stress applied to the vessel and this stress must not more than the maximum allowable stress. The type of stress including pressure stress, longitudinal stress, circumferential stress, dead weight stress and bending stress. The maximum compressive stress must be lower than critical bucking stress. In this design, the maximum compressive stress is 49.8N which is lower than the critical bucking stress, 349.18N.

9.2.4.7 Support The method used to support a vessel will depend on: •

Size, shape, and weight of the vessel

•

The design temperature and pressure

•

The vessel location and arrangement

9-15

KKEK 4281 Design Project Chapter 9: Extractive Distillation Column •


The internal and external fittings and attachments

Skirt support is used for the tall, vertical columns, as they do not impose concentrated loads on the vessel shell. Brackets support is chosen as vessel support since it is normally used to support short vertical vessel that is less than 20m height. It is more economical to use compare to the skirt support.

9.2.4.8 Pipe Sizing for Nozzles For stainless steel pipe, the optimum diameter is given by equation:

dopt = 226G 0.5 ρ −0.35 Where dopt = optimum diameter in mm, G=fluid flow rate and ρ =density of the fluid. Streams

dopt (inch)

Feed Extracted Raffinate Solvent

0.1095 0.0703 0.0994 0.0923

Nominal pipe size (in) 0.125 0.125 0.125 0.125

do (in)

0.405 0.405 0.405 0.405

Wall Schedule thickness no. (in) 40ST,40S 0.068 40ST,40S 0.068 40ST,40S 0.068 40ST,40S 0.068

di (in)

0.269 0.269 0.269 0.269

do (mm)

di (mm)

10.287 10.287 10.287 10.287

6.8326 6.8326 6.8326 6.8326

9.2.4.9 Reinforcement of Openings

All the openings such as nozzle connections for piping and the openings for inspection above 2 in diameter are reinforced to compensate for the weakening effect of the openings.

Streams

do (mm)

di(mm)

hi(mm)

l(mm)

ho(mm)

t(mm)

All

10.2870

1.7272

6.8326

1.6891

2.8258

7.2232

9-16



9-3: SAFETY, CONTROL AND INSTRUMENTATION 9.3.1 Introduction Control system for the extractive distillation column is important to provide a safe and health environment to the operator. It also help to protect the environment from pollution since it can avoid spillage of toxic chemical.

9.3.2 Control Process control of the extractive distillation column is important to maintain the product quality and ensure stable operation. Proper control system also important to avoid overflow of chemical and flooding in the extractive distillation column.

Figure 9.4: Flow Diagram with Controller

9-17



Table 9.9: Control System for Extractive Distillation Column

Loop

1

Controlled

Manipulated

Objective

Controller

variables

variables

Liquid level

Feed flow

-

avoid overflow

-

Solenoid valve

in column

rate, Solvent

-

Avoid dry hole problem.

-

Flow transmitter

feed flow rate

-

Ensure column work in

-

Flow Controller

-

Pressure

flow rate required and maintain the composition of the bottom product (quality product). 2

Column

Feed flow

Pressure

rate, solvent

the column which may

flow rate

break the column.

-

-

Avoid excess pressure in

transmitter -

Ensure the purity of product since the

Pressure Controller

-

Safety valve

-

Temperature

composition of the outlet stream will vary with different pressure 3

Bottom

Steam flow

temperature

rate

-

To ensure efficient separation.

-

To maintain product

transmitter. -

quality

Temperature Controller

-

Flow transmitter

-

Flow controller

-

Solenoid valve

9-18



9.3.3 Safety

Safety analysis is important to ensure all people who operate the column are in safe condition and minimize the accident occur.

9.3.3.1 HAZOP analysis

A Hazop and Operability Study (HAZOP) is a set of formal hazard identification and elimination procedures designed to identify hazards to people, process plants, and the environment. It can predict all the potential accident.

Table 9.10: HAZOP Analysis

Guide

Deviation

word

No

Possible

Consequences

Actions

Causes

No Flow

Pipe

-

blockage

Pipe burst due to -

Install flow indicator and

overpressure in

alarm.

the pipeline. -

-

No product

Install pressure indicator and alarm

-

Perform regular checking on the pipe line

Failure

of -

solenoid

overpressure in

valve

the pipeline. -

More

More flow

Pipe burst due to -

Failure

of -

flow transmitter

-

Install manual bypass valve.

No product Purify

of -

Regular checking on the flow

product affected.

alarms.

Low efficiency -

Install high level alarm.

separation. More

Failure

Pressure

solenoid valve

of -

-

Purify

of -

Regular

checking

on the

product affected.

pressure alarms.

Low efficiency -

Install high pressure alarm.

9-19


Group 6 Acrylic Acid Project separation.

More

Pipe

-

temperature blockage -

Less

Less flow

Pipe leakage

-

Purify

of -

Regular

checking

product affected.

temperature alarms.

Low efficiency -

Install

separation.

alarm.

Product

spills -

Perform

high

on the

temperature

corrosion

out and bring

regularly.

dangerous

Install a flow indicator.

to -

test

operator. -

Product quality affected.

Less

Pipe leakage

pressure

Malfunction

-

Product quality -

Install low pressure alarm

affected.

of valve Reverse Reverse flow

Valve malfunction

-

Pressure

-

Install check valve

decrease in the column

9-20



References 1. Perry, R.H. and Green, D.W. (1997). Perry’s Chemical Engineers’ Handbook (7th Ed.). McGraw-Hill Co. 2. Janet K. Standard handbook of environmental science, health, and technology 3. Saint-Gobain NorPro (2007). “Packed tower internals guide”, retrieved 20th February 2009 from http://www.soint-gobain.com 4. Khoury.F.M (2005), Multistage Separation Processes. 5. Henry Z. Kister. Distillation Design 6. Lloyd, E.B. and Edwin, H.Y, (1959). Process Equipment Design. John Wiley & Sons. Inc, New York. 7. Thomas, E.M. (1995). Process Control: Designing Processes and Control Systems for Dynamic Performance. McGraw-Hill, United States of America.

9-21

KKEK 4281 Design Project Chapter 10: Distillation Column


CHAPTER 10: DISTILLATION COLUMN 10.1. CHEMICAL ENGINEERING DESIGN 10.1.1. Introduction Distillation is probably the most widely used separation process. It is a method used to separate the components of a liquid solution, which depends on the distribution of these various components between a vapor and liquid phase. All components are present in both phases. The vapor phase is created from the liquid phase by vaporization at the boiling point. The general principles of design of multi-component distillation column are the same in some aspects as those described for binary systems. But the calculations for multi-component distillation are much more complex than for binary systems. When the feed contains more than two components, it is not possible to specify the complete composition of the top and bottom products independently. One component may be more volatile than the average in one part of the column and less volatile than the average in another part, which leads to complex concentration profiles. The separation between the top and bottom products is specified by having two key components, between which it is desired to make the separation. Trial and error calculations will be needed to solve this problem. For a completely rigorous solution the compositions must be adjusted and the calculations repeated until a satisfactory solution is obtained. Clearly, the greater the number of components, the more complicated. In this chapter, chemical engineering design will be carried out based on the material and energy balance completed during the previous semester. The solvent and acetic acid is then fed into solvent recovery distillation column, T-102.The bottom product will become residual of the process and sent to waste treatment plant.The solvent with 99.8% is recovered and recycle back to extraction distillation column, T-101.

10.1.2. Distillation Column Design The algorithms for the design of distillation column are as follows: a) Establish preliminary compositions for the top and bottom products. 10-1



b) Determine column-operating conditions (temperature and pressure) at the top and c) Bottom of the column. d) Select type of contacting device – plates or packing e) Estimate the theoretical number of equilibrium stages f) Estimate the minimum reflux ratio g) Estimate reflux ratio and number of equilibrium stages and number of stages h) Estimate the feed-point location i) Determine the column diameter j) Specify column internals – plates, distributors, packing support k) Check for pressure drop, weeping and entrainment 10.1.2.1. Schematic Diagram of T-102

Figure 10.1: Schematic Diagram of Distillation Column T-102

Table 10.1: Stream Description for Distillation Column T-102

Stream

Feed

Top

Bottom

Phase

L

L

L

Pressure (kPa)

15

15

15

Temperature (C)

31.87

31.26

45.66

Mole Flow

439.30

410

29.28

8.13

0.14

8

Component (kmol/h) Water

10-2



Acrylic Acid

1.32

0

1.32

Acetic Acid

4.69

0.3

4.38

0

0

0

0.14

0.14

0

Cyclohexane

191.25

191.08

0.17

I-P-Acetate

233.75

218.33

15.42

Molten Salt

0

0

0

Acetol Acrolein

10.1.2.2. Type of Column of T-102 For large scale distillation, continuous distillation is the preferable choice. Comparing between plate or packed columns, plate column is chosen due to these factors : a) Plate columns can handle a wider range of liquid and gas flow-rates. b) A column with large diameter is not suitable for packing, as it would increases cost c) The process materials are not foaming, non-toxic, and inflammable. Thus the use of packed column is not considered.

10.1.3. Key Components Key components are components whose volatility that is its boiling point or vapor pressure characteristics relative to each other makes them adjacent in the listing of the component in the feed. Light key component, LK – the component that is desired to keep out of the bottom product. Heavy key component, HK – the component that is desired to keep out of the top product. In further calculation and discussion, the light key is the product.

10.1.4. Number of Stages 10.1.4.1. Relative Volatility The key to the separation is the relative volatility between the compounds to be separated. The higher the volatility, the easier the separation is and vice versa. If two components have very 10-3



similar vapor pressure characteristic, their relative volatility will be close to unity. This means that they have similar boiling points and therefore, it will be difficult to separate via distillation. For multi-component distillation, the relative volatility is calculated with respect to the heavy key.

10.1.4.2. Number of Stages and Operating Reflux Ratio 10.1.4.2.1. Minimum Number of Stages The Fenske equation (Fenske, 1932) can be used to estimate the minimum stages required at total reflux. Normally the separation required will be specified in terms of the key components, and given as:

Minimum number of stages,Nm = 36.63 stages

10.1.4.2.2. Minimum Operating Reflux Ratio Reflux ratio is the amount of flow from the top product that is returned into the column. The limiting conditions occur at minimum reflux ratio where the separation can only be achieved with an infinite umber of stages. Colburn (1941) and Underwood (1948) have derived equations for estimating the minimum reflux ratio for multi-component distillations. The equation can be stated in the form:

10-4



In the derivation of the equations above, the relative volatilities are taken to be constant. The geometric average of values estimated at the distillate and bottom temperatures should be used, in the same manner as described earlier. The value of θ is found by trial and error, and must lie between the values of the relative volatility of the light and heavy keys. By trial and error (using EXCEL),thus minimum operating reflux ratio,Rm = 4.343

10.1.4.3. Number of Theoretical Stages One of the most frequently used empirical method for estimating the stage requirements for multi-component distillations is the correlation published by Erbar and Maddox (1961). This correlation gives the ratio of number of stages required to the number at total reflux ratio, with the minimum reflux ratio as a parameter. From the correlation, it is observed that the stage requirement is reduced as reflux ratio is increased beyond the minimum reflux. This thus leads to reduction in the cost of column. However, a marked reduction is only achievable at values near Rm where further increment has a little effect on the number of stages, as shown in the table below. 10-5



Table 10.2: Stage Requirement at Different Reflux Ratio

R / Rm

1.1

1.2

1.3

1.4

1.5

1.6

1.7

R

4.776925

5.211191

5.645457

6.079723

6.513989

6.948255

7.382521

R /(R + 1)

0.826898

0.839

0.848752

0.849521

0.866915

0.874186

0.880704

Nm / N

0.375

0.483

0.56

0.625

0.67

0.67

0.7

N

97.66655

75.82067

65.40171

58.59993

54.66411

54.66411

52.32137

Practical values of reflux ratio are usually 1.1 -1.5 times the minimum, with much higher value being employed. Thus, R = 1.5Rm = 6.5 With theoretical number of stages, N = 54.66 stages 10.1.4.4. Overall Column Efficiency The concept of the stage efficiency is used to link the performance of practical contacting stages to the theoretical equilibrium stage. It is defined as:

The correlation by O’Connell (1946) to estimate the ove

rall column efficiency is expressed

by Eduljee (1958) in the form of an equation:

10-6



10.1.4.5. Actual Number of Stages

10.1.5. Feed Point Location A limitation of the Erbar-Maddox, and similar other empirical methods, is that they do not give the feed-point location. An estimate can be made by using the Fenske equation to calculate the number of stages in the rectifying and stripping sections separately, but this requires an estimate of the feed-point temperature. An alternative approach is to use the empirical equation given by Kirkbride (1944):

10-7



From the Kirkbride (1944) equation,Nr = 67.5 = 68.Thus the feed location is at 68th stage.

10.1.6. Plate Specification 10.1.6.1. Plate Spacing The overall height of the column depends on the plate spacing. For columns above 1 m in diameter, plate spacing of 0.3 to 0.6 m will normally be used. This plate spacing is selected to minimize entrainment. A larger spacing will be needed between certain plates to accommodate feed and side stream arrangement, and for manways.

10.1.6.2. Type of Plate In selecting the type of plates, several principal factors are to be considered: - Cost - Efficiency - Capacity - Operating pressure - Pressure drop Based on the above criteria, the sieve (perforated) tray is chosen; over the high-cost and high pressure drop bubble cap tray; and the valve trays.

10.1.6.3. Liquid and Vapor Flows in a Plate Column Each plate has 2 conduits, one on each side, called “downcomer”. Liquid falls through the downcomers by gravity from one plate to the one below it. The flow across each plate is shown in Figure 1.3. A weir on the plate ensures that there is always some liquid (backup) on the plate and is designed such that the holdup is at a suitable height. Being lighter, vapor flows up the column and is forced to pass through the liquid, via the openings on each plate. The area allowed for the passage of vapor on each tray is called the active plate area. At the hotter vapor passes through the liquid on the plate above, it transfers heat to the liquid. In 10-8



doing so, some of the vapor condenses adding to the liquid on the plate. The condensate, however, is richer in the less volatile components than it is in the vapor. Additionally, because of the heat input from the vapor, the liquid on the plate boils, generating more vapors. This vapor, which moves up to the next plate in the column, is richer in the more volatile components. This continuous contact between vapor and liquid occurs on each plate in the column and brings about the separation between low boiling point components and those with higher boiling points.

Figure 10.2: Flow of Vapor and Liquid Across Each Plate

10.1.7. Plate Design Procedure A trial-and-error approach is necessary in plate design: starting with a rough plate layout, checking key performance factors and revising the design, as necessary, until a satisfactory design is achieved. A typical design procedure is set out as below: 10-9



a) Calculate the maximum and minimum vapour and liquid flow rate for the turn down b) ratio required. c) Collect or estimate the system physical properties. d) Select trial plate spacing. e) Estimate the column diameter, based on flooding consideration. f) Decide the liquid flow arrangement. g) Make a trial plate layout: downcomer area, active area, hole area, hole size, weir h) height. i) Check the weeping rate. j) Check the plate pressure drop. k) Decide plate layout details (calming zones, unperforated areas). Check hole pitch. l) Recalculate the percentage flooding based on chosen column diameter. m) Check entrainment. n) Optimize design. o) Finalize design. 10.1.7.1. Vapor and Liquid Flow Rates Since the liquid and vapor flow rates and composition vary throughout the column, tray design should be made above and below the feed-point. Calculations for the molar flow rate are tabulated. Table 10.3: Vapor and Liquid Flow Rates

10-10



10.1.7.2. Physical Properties The physical properties at the bottom and top of the column are obtained for further calculation of the plate design.

Table 10.4: Physical Properties

10.1.7.3. Column Diameter 10.1.7.3.1. Liquid-Vapor Flow Factor The liquid-vapor flow factor to be used Figure 1A-2 is given by the equation

Therefore Top FLv = 0.01 and Bottom FLV = 0.07

10-11



10.1.7.3.2. Flooding Velocity The flooding condition fixes the upper limit of vapor velocity. The velocity will normally be between 70 to 90 percent of that which would cause flooding. For design, a value of 80 to 85 percent should be used. Flooding velocity is estimated from the correlation by Fair (1961):

With surface tension correction which is

Take tray spacing as 0.4 m. From Figure 1A-2, Top : K = 0.068 K ' = 0.093 Bottom : K = 0.069 K ' = 0.080 Flooding velocity Top : u f = 1.907 m / s Bottom : u f = 1.194 m / s Design for 85% flooding velocity at maximum flow rate, uv =0.85 u f Top : uv = 1.621 m / s Bottom : uv = 1.015 m / s

10-12



10.1.7.3.3 Maximum Volumetric Flow Rate V

88.082 m3 / s

X V

78.710 m3 / s

X

10.1.0.7.3.4. Column Diameter To estimate the column diameter, an estimate of the net area is required, Thus using this equation : Q

Top : An = 54.351 m2 Bottom : An = 77.581 The column cross-sectional area (taking the downcomer as 10 percent of total area), Therefore using this equation: A .

Therefore, the column diameter can be calculated as:

Top : Bottom :

= 8.768 m = 10.476

The diameter of the column is taken as

= 10.5 m , for the whole column, reducing the

perforated area for plates above the feed-point stage.

10-13



10.1.7.4. Liquid Flow Pattern The maximum volumetric liquid flow rate is calculated as

Although the value is out of range (refer to Figure 1A-3), it is clear that a double pass pattern flow plate should be used. Double pass plates are used for high liquid flow-rates and large diameter columns.

10.1.7.5 Provisional Plate Design Table 10.5: Provisional Design

10.1.7.6. Check Weeping Weeping is a phenomenon caused by low vapor flow. The pressure exerted by the vapor is insufficient to hold up the liquid on the plate. This causes the liquid to leak through the perforations. The vapor velocity at the weep point is the minimum value for stable operation. Thus the holes area must be chosen so that at the lowest operating rate the vapor velocity is still well above the weep point. 10-14



10.1.7.6.1. Weir Liquid Crest The height of the liquid crest over the weir can be estimated using the Francis weir formula. This can be written as:

Maximum liquid flow rate, 274.313

/s

Minimum liquid flow rate, at 65% turn down = 0.6 x 274.313 = 178.304 kg / s Therefore Maximum weir liquid crest, how = 97.242 mm liquid Minimum weir liquid crest, how = 72.968 mm liquid At minimum rate = 112.968 mm liquid , and from Figure 1A-5, K2 = 31.17 The minimum design vapor velocity, given by Eduljee (1959):

10-15



Actual minimum vapor velocity,

From the calculation,we know that the minimum operating rate is above weep point. 10.1.7.7. Plate Pressure Drop There are two main sources of pressure loss: that due to vapor flow through holes and that due to the static head of liquid on the plate. The total is taken as the sum of the pressure drop: a) The flow of vapor through the dry plate b) The head of clear liquid on the plate c) Residual loss which accounts for others; minor sources of pressure loss

10.1.7.7.1. Dry Plate Drop The pressure drop through the dry plate can be estimated using expressions derived for flow through orifices.

Maximum velocity through the holes,

10-16



Dry plate drop, 51

37.2

10.1.7.7.2. Residual Head The residual head can be estimated by equation proposed by Hunt et al. (1955). 12.5

10

16.083

10.1.7.7.3 Total Pressure Drop The total pressure drop,

The pressure drop is conveniently expressed in Pa with the following equation,

10.1.7.8. Check Entrainment Entrainment refers to the liquid carried by vapor up to the tray above and is again caused by high vapor flow rates. Entrainment can be estimated from the correlation given by Fair (1961), which gives the fractional entrainment ψ (kg/kg gross liquid flow) as a function of the liquid-vapor factor FLV, with the percentage approach to flooding as a parameter.

10-17



Percent flooding defined as,

Actual velocity,

Therefore, percentage flooding = 84.6%

10.1.8. Trial Layout

Figure 10.3: Trial Plate Layout

10-18



10.1.9. Perforated Area The area available for perforation will be reduced by the obstruction caused by structural members (the support rings and beams), and by the use of calming zones. Calming zones are unperforated strips of plate at the inlet and outlet sides of the plate. A strip of unperforated plate plate will be left around the edge of catridge-type trays to stiffen plate. Allow 50 mm of unperforated strip around plate edge. 1

8,

0.72

,

93

The angle subtended at plate edge by unperforated strip = 180 – 93 = 87 Mean length, unperforated edge strips,

Area of unperforated edge strips, Area of calming zone,

(Dc – 0.05)π = 15.14 m

0.05

= 2(0.05)[

- 2(0.05)] = 0.746

Thus, total area available for perforation, Therefore,

= 0.757

=

= 0.102,and from figure 1A-9.

-(

+

) = 67.78

- 2.883

This is accordingly to the normal range of 2.5 to 4.0 hole diameter, and of satisfactory value The hole pitch,

= 2.883 X

= 14.42 mm

10.1.0.1. Number of Holes Area of one hole,

=

= 1.964 x 10

Number of holes,

=

= 352841 holes

10.1.10. Column Height 10-19

KKEK 4281 Design Project Chapter 10: Distillation Column Height of 90 plates at 0.4 m spacing, and 6 mm thickness, Tower skirt height, Ratio of

Group 6 Acrylic Acid Project = 36.54 m

=7m

4.147 , thus the column is stable, having a ratio of 3 to 5.

10.1.11. Simulation by HYSYS To further prove the design that has been made is practical and achievable, simulation of the distillation column with the specification obtained is carried out. The simulation software used is HYSIS. 10.1.11.1 .Approach of Manual Calculation The manual calculation for this plant was calculated by making several assumptions for the purpose to simplify the equation. Since there is lack of literature values of date such as equilibrium constant, some of the thermodynamics data were obtained from HYSIS whenever it was necessary. In order to simplify the whole manual calculation, the input values of every unit operations are taken from the HYSIS results which the recycle streams were already considered. Assumption such as ideal mixing, and constant heat capacity with a wide range of pressure were made for the energy calculation. 10.1.11.2. Approach of HYSIS Simulation Simulation was carried out using HYSIS 3.2 software. The package was used: NRTL for the acrylic acid production. Below are the tables that presented the mass and energy balance of each stream and its deviations with the HYSIS.

10-20



Table 10.6: Molar Flow Rate of Feed Stream and its Comparison with Hysys

Table 10.7: Molar flow rate of Top stream and its comparison with Hysys

Table 10.8: Molar flow rate of Bottom Stream and its Comparison with Hysys

The discrepancies obtained mainly revolve around the fact that during simulation, calculation done on the composition of each and every tray is rigorous. Manual calculation for every single tray is possible but for 90 stages of distillation proves to be quite a burden. HYSIS is able to do a more rigorous computational calculation.

10-21



10.2 MECHANICAL DESIGN 10.2.1. Introduction The mechanical design of this chapter is to develop and specify the basic design information for the distillation column T-102. Basic data needed by the specialist designer to further design the column in detail will be: a) Vessel function b) Process material and services c) Operating and design temperature and pressure d) Materials of construction e) Vessel dimensions and orientation f) Type of vessel heads to be used g) Openings and connections required h) Specification of heating and cooling jacket or coils i) Type of agitator j) Specification of internal fittings

10.2.2. General Design Consideration of Pressure Vessel 10.2.2.1. Design Pressure, P A vessel must be designed to withstand the maximum pressure to which it is likely to be subjected in operation. For vessels under internal pressure, the design pressure is normally taken as the pressure at which the relief device is set, normally 5 to 10 percent above the normal working pressure. This is to avoid spurious operation during minor process upsets. Working pressure,15 kPa or 0.15 bar For a safety factor of 10 percent, design pressure,110% x 0.15bar = 0.17 bar

10-22



10.2.2.2 . Design Temperature, T The design temperature at which the design stress is evaluated should be taken as the maximum working temperature of the material, with 20 percent allowance for any uncertainty involved in predicting vessel wall temperatures. Maximum operating temperature = 45.66 C Design temperature, T = 120% X 45.66C = 54.79 C 10.2.2.3. Materials of Construction Selection of material must take into account the suitability of the material for fabrication (particularly welding) as well as compatibility of the material with the process environment. With the nature of the processed material not corrosive neither fouling, use of low-alloy steel is sufficient. Carbon steel being the most versatile metal used in the industry, with excellent ductility, and great ease of fabrication, is further improved with the existence of alloying agents. Such is carbon-manganese (AISI 4340) which contains 0.40 percent C, 0.70 percent Mn, 1.85 percent Ni, 0.80 percent Cr, and 0.25 percent Mo. 10.2.2.4. Design Stress It is necessary to decide a value for the maximum allowable stress that can be acceptable in the material construction. Maximum allowable stress a material can withstand without failure under operating conditions should be determined. This is done by applying a suitable “design stress factor” to the maximum stress. The design stress factor allows for any uncertainty in the design methods, the loading, the quality of the materials and workmanship. From Table 2A-1, Design stress factor = 1.5 At design temperature of 54.79°C, from Table 2A-2, Design stress = 120.3 Practical design stress,

⁄ =

. .

= 80.2

⁄

10-23



10.2.2.5 .Welded Joint Efficiency The strength of weld joint will depend on the type of joint and the quality of the welding. The soundness of welds is checked by visual inspection and by non-destructive testing (radiography). The value of the joint factor used in the design will depend on the type of joint and the amount of radiography required by the design code. Taking 100 percent degree of radiography implies that the joint is equally as strong as the virgin plate while the use of lower joint factors in design, though saving costs on radiography, will result in a thicker, heavier, vessel. There must be a balance in any cost savings on inspection and fabrication against the increased cost of material. From Table 2A-3, Maximum allowable joint efficiency for double-welded butt, J = 0.85 10.2.2.6. Corrosion Allowance The corrosion allowance is the additional thickness of metal added to allow for material lost by corrosion and erosion, or scaling. The allowance should be based on experience with the material of construction under similar service conditions to those for the purpose design. From Materials of Construction pg 28-29, Ref [2] carbon-manganese steel is frequently used in services with corrosion rates of 0.13 to 0.5 mm/y. For 20 years of operation, Minimum corrosion allowance = 0.13 x 20 = 2.66mm = 3mm

10.2.3. Design of Column 10.2.3.1. Wall Thickness certain wall thickness is required to ensure that any vessel in sufficiently rigid to withstand its own weight and any incidental loads, together with the internal pressure.

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Including the welded joint factor, minimum thickness required with, = 8.65mm

10.5

9

Therefore, wall thickness with corrosion allowance = 12 mm 10.2.3.2. Design of Vessel Heads 10.2.3.2.1. Choice of Closure The ends of a cylindrical vessel are closed by heads of various shapes. The principal types used are: a) Flat plates and formed flat heads b) Hemispherical heads c) Ellipsoidal heads d) Torispherical heads

Formed flat heads or “flange-only” ends are the cheapest but their use is limited to low-pressure and small-diameter vessels. As operation is carried out at 1.1 bar, the standard torispherical head is used due to its higher range of operating pressure and column size. Use of hemispherical head however, will lead to excessive cost at the same thickness, although it is the strongest shape. 10.2.3.2.2 .Design of Torispherical Head There are two junctions in a torispherical end closure: that between the cylindrical section and the head, and that at the junction of the crown and the knuckle radii. One approach taken is to use the basic equation for a hemisphere and to introduce a stress concentration, or shape factor to allow for the increased stress due to the discontinuity. The stress concentration factor is a function of the knuckle and crown radii.

10-25



To avoid buckling; 0.06

a) Ratio of the knuckle radii to crown radii: b) Crown radius: Stress concentration factor, with =

3

10.5

) = 1.7706

Minimum wall thickness, e =

.

12.7

13

Thus, thickness of the torispherical head with corrosion allowance

16 mm. For practical

purposes, the thickness of the whole column is taken as 16 mm.

10.2.4. Design of Vessel Loads Pressure vessels are subjected to other loads in addition to pressure and are designed to withstand the worst combination of loading without failure. The main sources of load to consider are: a) Pressure. b) Dead weight of vessel and contents. c) Wind. d) Earthquake (seismic). e) External loads imposed by piping and attached equipment.

10.2.4.1 .Weight Loads The major sources of dead weight loads are: a) The vessel shell b) The vessel fitting: man ways, nozzles c) Internal fittings: plates plus the fluid on the plates; heating and cooling coil d) External fitting: ladders, platforms, piping e) Auxiliary equipment which is not self supported: condenser, agitators 10-26



f) Insulation g) The weight of liquid to fill the vessel. The vessel will be filled with water for the h) hydraulic pressure test, and may fill with process liquid due to misoperation. 10.2.4.2. Vessel Weight, Wv 240

0.8

2087.55

Where Cv = a factor to account for the weight of nozzles, manways, internal support = 1.15 (for DC) = height of cylindrical section = 36.54 m t = wall thickness = 16 mm 2

Dm = mean diameter of vessel =

10.532

10.2.4.3. Plates Weight, Wp Plate area,

4

= 86.59 9351.7

Weight of a plate, Where

= contacting plates, steel, including typical liquid = 1.2 kN/m2 plate area N = number of plates = 90

10.2.4.4. Cage Ladder Weight, Wl 0.360

13.154

10.2.4.5. Platform Steels Weight, Wf 1.7

Weight of one platform steel, Using two platform steels,

2

147.2 294.4

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10.2.4.6. Total Load Weight, Wt

= 11.75 x 103 kN

10.2.5. Wind Loads For tall columns, the force that produces bending is a function of wind velocity and the shape of the column. Since the column is to be installed in the open, wind loading will be an important factor. Initially, the load imposed on the column structure by the action of wind (or named as wind pressure) is needed to be determined first. The maximum wind pressure should be used in the calculation of bending stress. The maximum wind pressure is considered as wind velocity of 160 km/hr, which is equivalent to wind pressure of 1280 N/m2. 10.2.5.1. Load per Unit Length, Fw 13.99

Where

= effective column diameter = mean diameter + allowance for attachment =

2

0.4

10.932

10.2.5.2. Bending Moment, Mx at Column Base

2

9341.5 10

= 9341.5 x 103 Kn/m

10-28



10.2.6. Analysis of Stresses 10.2.6.1 Pressure Stresses .

Longitudinal stress,

19.85 .

Circumferential stress,

39.7

⁄ ⁄

10.2.6.2. Dead Weight Stress The dead weight stress due to the weight of the column, its contents and attachment is given by: .

Dead weight stress,

2.22

⁄

10.2.6.3 .Bending Stress Bending stress resulting form the bending moments to which the vessel is subjected. The bending stresses will be compressive of tensile, depending on location, and are given by: (

6.73

⁄

Where Iv is the second moment of area of vessel about the plane of bending and is given by: (

–

) = 7.31 x 10

10.2.6.4. Principal Stress The resultant longitudinal stress is:

Where σw is compressive and therefore is a negative value.

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As there is torsional stress, the principal stresses will be σz and σh. The radial stress is negligible

= 0.0605 N/mm2

The greatest difference between the principle stresses will be on the down wind side, 48.81

⁄

Well below the maximum allowable design stress which is 120.3 N/mm2. 10.2.6.5. Critical Buckling Stress (Elastic Stability) A column design must be checked to ensure that the maximum value of the axial stress does not exceed the critical value at which buckling occurred. 2 104

Critical buckling stress,

0

The maximum compressive stress ( 2.22

6.73

11.43 N/mm2

must be below the critical buckling stress.

8.95 N/mm2

thus the design of the column is satisfactory.

10.2.7. Vessel Support The method used to support a vessel will depend on the size, shape, and weight of the vessel, the design temperature and pressure; the vessel location and arrangement; and the internal and external fittings and attachment. The support must be designed to carry the weight of the vessel and contents, and any superimposed loads, such as wind loads. Support will imposed localized loads on the vessel wall, and the design must be checked to ensure that the resulting stress concentrations are below the maximum allowable design stress. Supports should be designed to allow easy access to the vessel and fittings for inspection and maintenance. In this design, skirt support is used for tall, vertical columns. A skirt support consists of a cylindrical or conical shell welded to the base of the vessel. A flange at the bottom of the skirt transmits the loads of the foundations. 10-30



10.2.7.1 .Skirt Thickness The skirt must be able to withstand the dead weight loads and bending moments imposed on it by the columns. The maximum dead weight load on the skirt will occur when the vessel is full of water. 31038.88

Approximate weight, Where

= density of water = 1000 kg/m3

W=

42.79

10 Kn

10.2.7.2. Bending Moment at Base of Skirt, Ms

2

13260

Where Hs = skirt height = 7 m As a first trial, take the skirt thickness, ts as the same as the bottom section of the column, 16 mm. 10.2.0.7.2.1. Bending Stress in the Skirt =

9.556 N/mm2

10.2.7.2.2. Dead Weight Stress in the Skirt, ws Dead weight stress in the skirt for hydraulic test condition,

=

5.06 N/mm2

Dead weight stress under operating conditions, 10-31


=


3.949 N/mm2

10.2.7.3. Design Criteria The skirt thickness should be such that under the worst combination of wind and dead weight loading the following design criteria are not exceeded.

Both criteria are satisfied. Therefore, the skirt support of 7 m height, with an inside diameter of 10-32



10.5 m, and thickness of 16 mm is acceptable.

10.2.8. Manhole Manhole is an opening that permits a person entry and exit the vessel for inspection and vessel examination of the interior. BS 470 (1984) is used for manholes design. According to BS 470, the minimum number of manhole for column over 1500mm internal diameter is 1. Therefore, in this design, 5 manholes are provided, to cater for the 36 m high column. One of the manholes is located at the centre of the column, with the other 4 located at every 9 m of the column. The minimum size to afford rescue facilities with self-contained breathing apparatus is 575 mm diameter with length not restricted. Therefore, in this design, a size of 575 mm diameter is used with length 500 mm.

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10.2.9. Summary Table 10.9: Summary of Chemical Engineering Design

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10.3. Safety, Control and instrumentation 10.3.1. Introduction Control is one form or another is an essential part of any chemical engineering operation. In all process there arises the necessity of keeping flows, pressures, temperatures, composition, etc, within certain limits for reasons of safety or specification. Such control is most often accomplish simply by measuring the variable it is required to control (the controlled variable), comparing this measurement with the value at which it is desired to maintained the controlled variable (the desired value or set point) and adjusting some other variable (the manipulated variable) which has a direct effect on the controlled variable until the desired value is obtained. It can be seen that automatic operation is highly desirable, as manual control would accessitate continuous monitoring of the controlled variable by a human operator. The efficiency of observation of the operator would inevitably fall off with time. Furthermore, fluctuations in the controlled variable may be too rapid and frequent for manual adjustment to suffice. A chemical plant is an arrangement of processing units integrated with one another in a systematic and rational manner. The primary objectives when specifying instrumentation and control schemes are discussed in later sections. 10.3.1.1. Safety The safety of people in the plant and in the surrounding community is of paramount importance. Where no human activity is without risk, the typical goal is that working at an industrial plant should involve mush less risk than any other activity in a person’s life. Plants are designed safely at expected temperatures and pressures; however, improper operation can lead to equipment failure and release of potentially hazardous materials. Therefore, the process control strategies contribute to the overall plant safety by maintaining key variables, near their desired values. 10.3.1.2. Environment Protection Protection of the environment is critically important. The objective is mostly a process 10-35



design issue; that is, the process must have the capacity to convert potentially toxic components to design material. Again, control can contribute to the proper operation of these units, resulting in consistently low effluent concentrations. 10.3.1.3. Equipment Protection Much of the equipment in a plant is expensive and difficult to replace without costly delays. Therefore, operating conditions must be maintained within bounds to prevent damage. The types of control strategies for equipment protection are similar to those for personnel protection; that is, controls to maintain conditions near desired values and emergency controls to stop operation safely when the process reaches boundary. 10.3.1.4. Smooth Plant Operation A chemical plant includes a complex network of interacting processes; thus, the smooth operation of a process is desirable, because it results in few disturbances to all integrated unit. Naturally, key variables in streams leaving the process should be maintained. 10.3.1.5. Product Quality The final products from the plant must meet demanding quality specifications set by purchaser. Process control can maintain the optimum operation condition required for excellent product quality. 10.3.1.6. Profit To have a higher profit, the plant has designed to produce product at lowest cost. However, before achieving the profit-oriented goal, selected independent variables are adjusted to satisfy the first five higher priority control objectives. The control strategy must increase profit while satisfying all other objectives. 10.3.1.7. Monitoring and Diagnosis Complex chemical plants require monitoring and diagnosis by people as well as excellent automation. Since people cannot monitor all variables simultaneously, the control system 10-36



includes an alarm feature, which draws the operator’s attention to variables that are near limiting values selected to indicate serious maloperation. Good control design addresses a hierarchy of control objectives, ranging from safety to product quality and profit, which depend on the operating objectives for the plant. The control is an important factor in plant design. The plant design must included measurement element of plant output variables (or disturbance input) and final control element. The measurement element must respond rapidly so that the control action can be taken in real time. The final element in chemical process (in this process also) usually are the control valves that affect fluid flows.

10.3.2. Distillation Control Objective The philosophy of process control has a few objectives: a) Product quality control -Maintain either the overhead or bottoms composition at specified value. -Maintain the composition at the other end of the column as close as possible to a desired composition. b) Material balance control -Cause the average sum of distillate and tails streams to be exactly equal to average feed rate -The resulting adjustment in process flows must be smooth and gradual to avoid psetting either the column or downstream process equipment fed by the column -Column hold-up, and overhead and bottom inventories, should be maintained between maximum and minimum limits. c) Constraints -For safe, satisfactory operation of the column, certain constraints must be observed. For example:The column should not flood -Column pressure drop should be high enough to maintain effective column Operation. -The temperature difference in the reboiler should not exceed the critical 10-37



temperature difference d) Disturbances -The preceding objectives must be satisfied in the face of possible disturbances in -Feed flow rate -Feed composition -Feed thermal condition -Steam supply pressure -Cooling water supply temperature -Ambient temperature, such as that caused by rainstorms e) Special consideration If a column, its auxiliaries, and its controls are designed to accomplish the preceding objective, it may be shown that the consumption of utilities such as steam and cooling water is minimums, except in one instance. For any given feed composition and feed thermal condition, there will be an optimum feed tray location-optimum in the sense of requiring less reflux or boil-up and thereby less utilities, and n permitting the column to operate changes sufficiently, the column, control system, whether manual or automatic, should recognize this and select a new feed tray.

10.3.3. Column Control 10.3.3.1. Feed Stream Control A typical method to flow in the distillation column is using a feed forward system. Instead of temperature, flow is considering a critical parameter, since the temperature of the flow is controlled in the bottom line of previous column. At the same time, pressure is also maintained at indicated column pressure. Therefore it is assumed that accurate vapor liquid flow rate will be produced at accurate temperature and pressure of the expansion valve.

10-38



10.3.3.2. Product Quality Control The basic approach to composition control is to use feed forward from feed flow rate. This control maintains the reflux to feed ratio. The reflux ratio is “reset” by the overhead composition controller. In this configuration, wild stream is feed line. It is measured and manipulated by reflux line to desired reflux to feed ratio. Any disturbance to composition, composition control will send signal to ratio and indirectly adjust the reflux flow rate.

10.3.3.3. Top Stream Control Generally, top stream control system is more complicated than either feed stream of bottom stream control system. The control system must provide adequate coolant to condenser, the correct flow rate back to column and the distillate with the require composition. It also needs to satisfy all the operation condition. Pressure is the critical parameter to control compared to temperature or flow in the distillate. Any disturbance of pressure at the top column will disrupt the equilibrium of the components separation. The chief function of pressure control is to ensure that the rate of condensation is exactly equal, on the average, to the rate of vapor flow to the condenser. In this approach, the cooling water stream is manipulated to maintain the desired column pressure. Therefore, the pressure is controlled using a feedback loop by throttling the flow of the coolant entering the condenser. Any changes of top column pressure, a signal will be sent to the pressure controller to adjust the amount of coolant to the condenser in order to control the changes of pressure. The flow of product has adjusted by a level controller. A feedback level controller is fixed to the reflux drum. The main purpose of the level controller is to prevent the overflow of the receiver. The increase of level in the reflux will detect by the controller. The control valve will be adjusted to allow more distillate get out.

10.3.3.4. Bottom Stream Control The stream which enters reboiler must be controlled to provide desired flow to reboiler 10-39



without overload the reboiler. Feed forward flow controller controls this stream independently. The appropriate flow rate should be controlled so that the reboiler does not overflow and the circulation rate to reboiler can be maintained. In bottom section, temperature is the most critical parameter. High temperature will change the composition of the product. Thus, a feedback temperature controller is fixed. The bottom liquid hold-up is used by the controller as a basic to manipulate steam flow rate. The variation in temperature on bottom liquid hold-up will actuate the controller value in steam stream. Level controller is fixed to control the flow rate at line 3 (bottom product stream). This is because the level of liquid hold-up in the column will affect the flow. The disturbance in feed flow rate will change the product distribution of material balance in the column.

10.3.4. Instruments Notation Flow FC

Flow controller

FT

Flow transmitter

Level LT

Level transmitter

LC

Level controller

Pressure PC

Pressure controller

PT

Pressure transmitter

Temperature TC

Temperature controller

TT

Temperature transmitter

10-40



10.3.5. Instrumentation Instruments are provided to monitor the key process variables during plant operation. They may be used for the manual monitoring of the process unit operation or incorporated in automatic control loops. They may also be part of an automatic computer data logging system. Instruments while monitoring critical process variables will be fitted with automatic alarms to alert the operation is near or at hazards situations. 10.3.5.1. Pressure Measurement For the measurement of pressure, a Strain-Gauge Pressure Transducer is selected. It consists of elastic elements to which one or more strain-gauges have been attached to measure the deformation. The strain-gauges are bonded directly to the surface of the elastic elements whose strain is to be measured. The advantage of this type of pressure measurement gadget is that it has an extremely fast response time.

10.3.5.2. Flow Measurement Turbine meter is selected as the flow rate sensor. A turbine wheel is placed in a flowing fluid pipe and its rotary speed depends on the flow rate of the fluid. A turbine is designed whose speed varies linearly with flow rate. The speed can be measured accurately by counting the rate at which turbine blades pass a given point, suing magnetic pickup to produce voltage pulses. The flow rate can be measured by feeding these pulses to an electronic pulse-rate meter. The advantages are turbine meter are available at a wide scale of flow rate, has a low pressure drop and very accurate as its fluid/mechanical time constant is of the order of 210 msec.

10.3.5.3. Level Measurement Magnetic Coupled Devices is selected for the level measurement. Typical devices are magnetically operated level switched and magnetic-bond float gauges. A magnetic-bond float gauge consists of a hollow magnet-carrying float that rides along a vertical nonmagnetic guide tube. The follower magnet is connected and drives an indicating dial 10-41



similar to that on a conventional tape float gauge. The float and guide tube are in contact with the measured fluid tape gauge. The float and guide tube are in contact with the measured fluid and come in a variety of materials for resistance to corrosion and to withstand vacuum pressure.

10.3.5.4 .Temperature Measurement Thermocouple is selected as the temperature sensor for measuring the temperature of the distillation column and the streams. Temperature measurements using thermocouple is based on the discovery by Seedbeck that an electric flows in a continuous circuits of two different metallic wires if two junctions are at different temperatures. The advantages of this devices are the suitability for high and wide temperature range, great sensibility and economically cheap.

Figure 10.4: Complete Process Control and Instrumentation Diagram of Distillation Column

10-42



10.3.6. Hazards and Operability Study (HAZOP) Essentially the HAZOP procedure involves taking a full description of a process and systematically questioning every part of it to establish how deviations from the design intent can arise. Once identified, an assessment is made as to whether such deviations and their consequences can have a negative effect upon the safe and efficient operation of the plant. If considered necessary, action is then taken to remedy the situation. This critical analysis is applied in a structured way by the HAZOP team, and it relies upon them releasing theirimagination in an effort to discover credible causes of deviations. The great advantage of the technique is that it encourages the team to consider other less obvious ways inwhich a deviation may occur, however unlikely they may seem at first consideration. In this way the study becomes much more than a mechanistic check-list type of review. The result is that there is a good chance that potential failures and problems will be identified which had not previously been experienced in the type of plant being studied.An essential feature in this process of questioning and systematic analysis is the use of keywords to focus the attention of the team upon deviations and their possible causes. These keywords are divided into primary keywords and secondary keywords. Primary keywords which focus attention upon a particular aspect of the design intent or an associated process condition or parameter. The primary keywords using in this HAZOP analysis include temperature, pressure, flow and composition. Secondary Keywords which, when combined with a primary keyword, suggest possible deviations. The secondary keywords applied here included no, more, other, less, reverse and part of.

10-43

G06 Aryclic Production

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