DESIGN OF SODA ASH PRODUCTION PLANT Comprehensive Design Project Department of Chemical and Process Engineering University of Moratuwa Supervised by Dr.Padma Amarasinghe
Group members Danushka D.G.
050069L
Gunasekara D.T.
050137U
Jayakody J.R.U.C. 050166G Madurika B.N.
050254B
Weerasinghe D.T. 050472P
COMPREHENSIVE DESIGN PROJECT
PREFACE This report gives a narrative of our final year comprehensive design project, which is the production of Soda ash from the sea water and lime stone mines exist in number of places in the country. The project is the part of curriculum of the final year B.Sc. Engineering Degree program of the University of Moratuwa and in essence it consists of basic description of such attempt made by five undergraduate students of Chemical and process Engineering Department, University of Moratuwa. The content of this report are outlined here.
Chapter 1 gives a brief introduction to the report and the finding from literature survey is given in chapter 2. This was conducted to study about the soda ash production. It gives general information about soda ash, how it began, history of the production, the types of production, uses in industrial sectors, etc.
Designing of compatible, large scale industry in a developing country like Sri Lanka is a big task. Especially with matching technology and feasibility to the project in such situation is a heavy work. Chapter 3 consists of the evaluation of the complete feasibility study under technical economical, market….sectors.
Under chapter 4, we discussed the how we select most appropriate process for the Sri Lanka through the various operate processes in the world considering the pros and cons of several models. Chapter 5 is focused on the process description. It begins with the feed selection; and mainly this chapter contents based on each and every unit operation of the selected process. Equipment layout is enlightened at the end of this chapter.
The site selection and the plant layout are given in chapter 6. Chapter 7 contains the particulars of the environmental impact assessment. This contains the major environmental impact from the sodium bicarbonate process plant and the how to carry out processes of the effluent management.
Full details of the safety measures intended for the plant is given on chapter 8. After that the safety aspects considering equipment is expressed in detail.
Material balance and energy/ heat balance done on behalf of each unit operation selected is discussed in next two episodes chapter 9, 10. The overall material and energy flow sheets arranged for
i
COMPREHENSIVE DESIGN PROJECT
the plant is summarized within too. The detailed calculations as well as the assumptions made have been appended.
The final chapter is presenting the conclusion of this report a summing up of the whole project with the benefits of the selected process and technologies are imparted in this chapter, as well how it helped us improve our skill and knowledge. A list of abbreviations and the list of references are appended at the end of the report. 28/10/2008
ii
COMPREHENSIVE DESIGN PROJECT
ACKNOWLEDGEMENT When doing our Final year Comprehensive Design Project, we had to face many hardships and challenges. It was with the help of many people that we were able to complete this project. We would like to express our heartiest gratitude to all those people. First of all we would like to grant our heartiest gratitude to our project coordinator, Dr. Padma Amarasinghe, (lecturer- Chemical & Process Engineering department, University of Moratuwa) for all the valuable advice, guidance, support and encouragement given through out the time. Dear Madam, Thank you very much for spending your precious time to share your priceless knowledge with us, we owe you a lot. Then we express our gratitude to the department of Chemical and Process Engineering , all the staff members of Chemical & Process Engineering department, including Dr. Jagath Premachandra (head of the department), for all the assistance and big hearted support given toward while doing many activities of this project and for including a design project in the final year syllabus. Thereby providing us with a valuable opportunity to improve our knowledge and experience on doing a project, this will come very useful when we go out to the industry as Chemical and Process Engineers. We appreciate the support given by all the non academic staff of the Department of Chemical and Process Engineering, especially the people who were in charge of the department of CAPD center, for keeping it open at all hours so we could continue our work without interruption. Then we would like to thank the staff of the Ceylon Glass Limited and the Holcim Lanka limited for giving us permission to visit the glass plant and provide us necessary experience and relevant data regarding this project. Finally we thank all our colleagues of the department of Chemical and Process Engineering for their help stimulating suggestions and encouragement. Thanking You. Group Members Danushka D.G.
: 050069L
Gunasekara D.T
: 050137U
Jayakody J.R.U.C
: 050166G
Madurika B.N.
: 050254B
Weerasinghe.D.T.
: 050472P
iii
COMPREHENSIVE DESIGN PROJECT
CONTENTS PREFACE
i
ACKNOWLEDGEMENT
iii
CONTENTS
iv
CHAPTER 1: INTRODUCTION
1
CHAPTER 2: LITERATURE SURVEY 2.1. General Information
4 5
2.1.1. Other Names for Sodium Carbonate
5
2.1.2. Physical Properties of Sodium Carbonate
5
2.1.3. Hydrates of Sodium Carbonate
5
2.1.4. Chemical Properties of Sodium Carbonate
6
2.1.5. Grades and Specification of the Soda Ash
6
2.2. Uses of Na 2 CO 3 in Industrial Sectors
7
2.2.1. Glass Industry
7
2.2.2. Detergent Industry
8
2.2.3. Metals and Mining
8
2.2.4. Steel Industry
8
2.2.5. Paper and Pulp
9
2.2.6. Textiles
9
2.2.7. Non-ferrous metallurgy industry
9
2.2.8. Chemical industry
9
2.2.9. Other Applications
9
2.3. Uses of NaHCO3 in Industrial Sectors
10
2.4. History of the Production
10
2.5. Overview about Type of Production
12
2.5.1. Le Blanc process
12
2.5.2. Solvay Process
14
2.5.3. Hou's Process
15
2.5.4. Dual process
15
2.6. Sodium Carbonate Minerals
15
2.6.1. Trona Based Process
16
2.6.1.1.
Trona Products
17
2.6.1.2.
Monohydrate Process
18
2.6.1.3.
Sesquicarbonate Process
19
2.6.1.4.
Alkali Extraction Process
20
2.6.2. Nahcolite based process
22 iv
COMPREHENSIVE DESIGN PROJECT
2.7. International Scenario
22
2.8. Structure and Status of Indian Industry
23
CHAPTER 3: FEASIBILITY STUDY 3.1. Preliminary Study
24 25
3.2. Economical Feasibility
27
3.3. Market Feasibility
30
3.4. Technical Feasibility
31
3.5. Social Feasibility
33
CHAPTER 4: PROCESS SELECTION 4.1. Introduction 4.2. Comparison of Solvay process with Others Methods of Production 4.3. Process Selection Conclusions
35 36 37 40
CHAPTER 5: PROCESS DESCRIPTION
41
5.1. Main Chemical Reactions in Solvay process
42
5.2. Process Steps
44
5.2.1. Brine purification
44
5.2.2. Calcinations of limestone in kilns and the production of CO2 and milk of lime
45
5.2.3. Absorption of ammonia into purified brine
46
5.2.4. Carbonation of the ammoniated brine with CO2 to produce sodium bicarbonate
46
5.2.5. Separation of Sodium Bicarbonate from Mother Liquid
47
5.2.6. Recovery of the Ammonia using Milk of Lime
48
5.2.7. Calcinations of Sodium Bicarbonate to form Sodium Carbonate (light ash)
49
5.2.8. Densification of Sodium Carbonate to form Dense ash
49
5.3. Product (Soda Ash) Storage and Handling
50
5.4. Raw Materials
50
5.4.1. Brine
50
5.4.2. Limestone
51
5.4.3. Carbon for the Lime Kiln
51
5.4.4. Ammonia
52
5.4.5. Various additives
52
5.5. Utilities
53
5.5.1. Steam
53
5.5.2. Process water
53
5.5.3. Cooling waters
53
5.5.4. Electricity
54
5.6. Energy saving in the process
54 v
COMPREHENSIVE DESIGN PROJECT
5.6.1. Heat recovery
55
5.6.2. Energy Minimization
55
5.7. Process Flow Diagram
57
5.8. P & I Diagram
58
CHAPTER 6: SITE SELECTION & PLANT LAYOUT 6.1. Introduction 6.2. Site Selection Considerations
60
6.3. Plant layout
65
CHAPTER 7: ENVIRONMENTAL IMPACT ASSESSMENT 7.1. Gaseous Effluents
66 67
7.1.1. Particulate Dust
67
7.1.2. Carbon dioxide and monoxide
67
7.1.3. Nitrogen oxides
68
7.1.4. Sulfur oxides
68
7.1.5. Ammonia
68
7.1.6. Hydrogen sulfide
69
7.2. Gaseous Effluents Management
69
7.2.1. Calcinations of Limestone
69
7.2.2. Precipitation of Crude Sodium Bicarbonate
70
7.2.3. Filtration of the Bicarbonate
70
7.2.4. Conveying and Storage of Soda Ash
70
7.3. Liquid Effluents
71
7.3.1. Wastewater from Distillation
71
7.3.2. Wastewater from Brine Purification
72
7.4. Liquid Effluent Management
73
7.4.1. Liquid Effluent Treatments
73
7.4.1.1.
Total Dispersion
74
7.4.1.2.
Separation of the Suspended Solids and Liquid Dispersion
74
7.4.2. Liquid Effluent Discharge Management
75
7.5. Solid Effluents
76
7.6. Solid Materials Management
76
7.6.1. Limestone Fines
76
7.6.2. Grits from slaker
76
7.7. By-Products Recovery and Reuse
59 60
77 vi
COMPREHENSIVE DESIGN PROJECT
7.7.1. Calcium Chloride
77
CHAPTER 8: SAFETY MEASURES
78
8.1. Plant Safety
79
8.2. General Plant Safety
79
8.3. Personal Safety
80
8.4. Safety Aspects of Equipments
81
8.4.1. Lime Kiln
81
8.4.2. NH3 Absorbing Unit
82
8.4.3. Carbonator Unit
82
8.4.4. NH3 Recovery Unit
82
8.4.5. Drier
83
8.4.6. Storage Vessels
84
8.4.6.1.
Ammonia
84
8.4.6.2.
Soda ash
84
8.4.6.3.
Baking soda
84
8.4.6.4.
Calcium Carbonate and Calcium Oxide
84
8.4.7. Pipelines
85
8.5. Safety Aspects of Chemical
85
8.5.1. Carbon Dioxide (CO 2 )
85
8.5.2. Ammonia (NH 3 )
86
8.5.3. Sodium Carbonate (Na 2 CO 3 )
88
CHAPTER 9: MATERIAL BALANCE
91
9.1. Product specification
92
9.2. Components in Purified brine
92
9.3. Calculations for NH 3 Absorption Unit
93
9.4. Air Mixture
95
9.5. Gas Washing Tower with Purified Brine
96
9.6. Carbonator Unit
97
9.7. Filter
99
9.7.1. Calculation for residue solid
100
9.7.2. Calculation for permeate
100
9.8. Lime Kiln
101
9.9. Slaker of lime
103
9.10.
104
Ammonia Recovery Unit
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COMPREHENSIVE DESIGN PROJECT
9.11.
Gas Cooler
107
9.12.
Air Mixture (Before the Gas Cooler)
108
9.13.
Dryer
109
9.14.
Material Flow Sheet
111
CHAPTER 10:
ENERGY BALANCE
112
10.1.
Kiln Energy Balance
113
10.2.
Energy Balance for Air Preheated
115
10.3.
Calcinations of Crude Bicarbonate
116
10.4.
CaCO3 Preheated
119
10.5.
Air Mixer Energy Balance
120
10.6.
Heat Balance for Gas Cooler
122
10.7.
Slaking of Lime
123
10.8.
Recovery of Ammonia Column Energy Balance
126
10.8.1. Find Outlet Temperature of the Cool Gas
127
10.8.2. Fine Quantity of Steam Consumption
128
10.9.
Carbonation of Ammoniated Brine Column
CHAPTER 11:
CONCLUSION
133
REFERENCE
135
CD CONTENTS Excel Spreadsheets Soft Copy Of Report
130
viii
COMPREHENSIVE DESIGN PROJECT
Table & Figure Table2.1: Market specifications of dense soda ash
7
Table2.2 : Worldwide capacity of soda ash manufacture
11
Table 2.3: Natural soda minerals occurred worldwide
16
Table 2.4: products of Trona
17
Table 4.1 a comparison of the Solvey and dual processes
40
Table5.1: Raw and purified brines (typical composition ranges)
51
Table 5.2: Typical compositions for coke to the lime kiln
52
Table 5.3: Soda ash process major Input/output levels
56
Table 7.1: Rough concentrations of the waste water from the distillation column
71
Table 7.2: Typical concentration wastewater from brine purification
72
Table 9.1- Soda ash specification
92
Table 9.2- Purified brine specification
92
Table 9.3- Residue solid composition
99
Table 10.1- a,b,c constant
113
Table 10.2- kiln inlet enthalpy
114
Table 10.3- kiln outlet enthalpy
114
Table 10.4- Air enthalpy change
115
Table 10.5- CaO enthalpy change
116
Table 10.6- flue gas enthalpy change
119
Table 10.7- Soda ash specification
123
Table 10.8- a, b, c constant for CaO
124
Figure 2.1: Distribution of soda ash by end use
7
Figure 2.2: Flow diagram of monohydrate process
18
ix
COMPREHENSIVE DESIGN PROJECT
Figure2.3: Flow diagram of sesquicarbonate process
19
Figure 2.4: Flow diagram of alkali extraction process
21
Figure 3.1: Soda ash imports (2006)
25
Figure 3.2: Variation in soda ash imports
26
Figure5.1: Block diagram of the soda ash production plant
42
Figure5.2: Vertical shaft kiln for lime stone
46
Figure5.3: Process flow diagram
57
Figure5.4: P&I diagram Figure 6.1- Mineral Map of Sri Lanka
63
Figure 6.2- Geographical map of proposed land
64
Figure 6.3- Plant layout
65
Figure 9.1- NH 3 Absorption Unit
93
Figure 9.2- Air mixture before NH3 Absorption Unit
95
Figure 9.3- Gas washing tower with purified brine
96
Figure 9.4- Carbonator Unit
97
Figure 9.5- Filter
99
Figure 9.6- Lime Kiln
101
Figure 9.7- Slaker of lime
103
Figure 9.8- Ammonia Recovery Unit
104
Figure 9.9- Gas Cooler
107
Figure 9.10- Air mixture before gas cooler
108
Figure 9.11- Dryer
109
Figure 10.1- kiln
113
Figure 10.2- Air preheated
115
Figure 10.3- Dryer
117
Figure 10.4- Cyclone
119
Figure 10.5- Air mixture before gas cooler
120
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COMPREHENSIVE DESIGN PROJECT
Figure 10.6- Gas cooler
122
Figure 10.7- Slaker
124
Figure 10.8- NH3 Recovery column
126
Figure 10.9- Carbonation column
130
xi
Chapter 1
INTRODUCTION
CHAPTER 01
INTRODUCTION
Sodium carbonate or soda ash is used in many process industries such as in glass manufacturing, Detergents & soaps, Metals and mining, Paper and pulp and Textiles industries. Raw materials for the manufacturing of sodium carbonate are readily available and inexpensive. Raw materials for the Sodium carbonate can be obtained from sea water and lime stone mines exist in number of places in the country……
1
Chapter 1
INTRODUCTION
In developed areas of the world mainly in the western European countries and in North America the annual dollar value of industrial mineral production has surpassed that for metals and continues to grow rapidly. This is due to the fact of high income levels per capita consumption of industrial mineral products in developed Countries exceeds that in developing countries. While in developed countries industrial minerals and rocks provide inputs in many industrial processes, in some developing countries with little industrial infrastructure significant portions of their foreign exchange derive from exports of industrial minerals like Sri Lanka. Thus, industrial minerals are of great economic value to developed and developing economies alike. When we consider the Sri Lankan perspective as one of the developing countries the scenario mentioned above applies without much deviation. Sri Lanka is a country which is rich in minerals and natural resources, but these have not been utilized to an extent where they will contribute to the country production and hence to its development. Sri Lanka as a county can capitalize on its exports if it were to manufacture value added products from the existing resources instead of an economy based on export of raw materials to industries in other countries. Soda ash, the common name for sodium carbonate (Na 2 CO 3 ), has significant economic importance because of its applications in manufacturing glass, chemicals, detergents metals and mining, paper and pulp, textiles industries and many other products. There are many evidences to show that people have been using soda ash extracted from earth in crude form, in glass manufacturing industries since ancient times. But the production of soda ash as an industry itself, emerged only during the late 18th century. Raw materials for the manufacturing of sodium carbonate are readily available and inexpensive. Main raw materials can be obtained from sea water and lime stone mines exist in number of places in Sri Lanka. So the purpose of our final year comprehensive design project is production of sodium carbonate from brine and lime stone. The comprehensive design project is done as per the requirement for the award of the B.Sc. (Honors) Engineering degree. The literature survey that was conducted as part of the project included a thorough study on several soda ash consuming and lime stone consuming industries in Sri Lanka. Since the Holcim Cement plant in Palavi will have a considerable amount of relation to the proposed plant, as explained in later chapters a brief study on its operations was also carried out. The results of the design project for the commercial production of soda ash are presented. The project has been performed in two stages. The first part concerns the feasibility of the project, literature survey and the second part presents the detailed material and energy balances.
2
Chapter 1
INTRODUCTION
From the investigation into project feasibility, it is proposed to construct a plant using the Solvay process for the production of soda ash and will deliver 50 tons per day of 99.5(wt) Na 2 CO 3 . It is envisaged that this soda ash production facility will be located in Karadipuval near Puttalam. The process has been tailor-made and designed to utilize limestone available locally at the North-Western area of the country. Saturated brine from the adjacent lagoon is the other raw material utilized for the proposed soda ash plant. Coke for the combustion of limestone in order to produce CO 2 for the process will have to be imported. It is hoped that this project makes a contribution to further the cause of national development by provision of a viable, cost-effective, and environmental friendly solution.
3
Chapter 2
LITRETURE SURVEY
CHAPTER 02
LITRETURE SURVEY
Soda ash has a number of diversified uses that touch our lives every day. Glass manufacturing is the largest application for soda ash whether it is in the production of containers, fiberglass insulation, or flat glass for the housing, commercial building etc. As environmental concerns grow, demand increases for soda ash used in the removal of sulfur dioxide and hydrochloric acid from stack gases. Chemical producers use soda ash as an intermediate to manufacture products that sweeten soft drinks, relieve physical discomfort and improve foods and toiletries, Household detergents and paper products are a few other common examples of readily identifiable products using soda ash………
4
Chapter 2
LITRETURE SURVEY
2.1 General Information 2.1.1 Other Names for Sodium Carbonate
Soda ash
Carbonate acid.
Disodium salt
Dry alkali
Molecular formula:
Na 2 CO 3
2.1.2 Physical Properties of Sodium Carbonate
Specific Gravity
: 2.53
Solubility in water(22°C) : 22g/100ml
Melting Point
: 851.0°C
Boiling Point
: Decomposes before melting
pH (1% aq. solution.)
: 11.5
Sodium carbonate is an odorless, opaque white, crystalline or granular solid. It is soluble in water and insoluble in alcohol, acetone, and ether. Sodium carbonate reacts exothermically with strong acids evolving carbon dioxide. It corrodes aluminium, lead and iron.
2.1.3 Hydrates of Sodium Carbonate The three known hydrates exist in addition to anhydrous sodium carbonate. Sodium carbonate monohydrate ( Na 2 CO 3 .H 2 O )
This contains 85.48 % Na 2 CO 3 and 14.52 % water of crystallization. It separates as small crystals from saturated aqueous solutions above 35.4 °C, or it may be formed simply by wetting soda ash with the calculated quantity of water at or above this temperature. It loses water on heating, and its solubility decreases slightly with increasing temperature. In contact with its saturated solution it is converted to Na 2 CO 3 at 109 °C.
5
Chapter 2
LITRETURE SURVEY
Sodium carbonate heptahydrate ( Na 2 CO 3 .7H 2 O ),
This contains 45.7 % Na 2 CO 3 and 54.3 % water of crystallization. It is of no commercial interest because of its narrow range of stability, which extends from 32 °C to 35.4 °C.
Sodium carbonate decahydrate ( Na 2 CO 3 .10H 2 O ),
Commonly called sal soda or washing soda which usually forms large transparent crystals containing 37.06 % Na 2 CO 3 and 62.94 % water. It may be crystallized from saturated aqueous solutions below 32.0 °C and above -2.1°C or by wetting soda ash with the calculated quantity of water in this temperature range. The crystals readily effloresce in dry air, forming a residue of lower hydrates, principally the monohydrate.
2.1.4 Chemical Properties of Sodium Carbonate Sodium carbonate is hygroscopic. In air at 96 % R.H. (relative humidity) its weight can increase by 1.5 % within 30 minutes. If sodium carbonate is stored under moist conditions, its alkalinity decreases due to absorption of moisture and carbon dioxide from the atmosphere. Water vapor reacts with sodium carbonate above 400 °C to form sodium hydroxide and carbon dioxide. Sodium carbonate is readily soluble in water and the resulting solutions are alkaline, as expected a salt formed from a strong base and weak acid. At 25 °C the pH of 1, 5 and 10 wt % solutions are 11.37, 11.58 and 11.70 respectively. Sodium carbonate reacts exothermically with chlorine above 150 °C to form NaCl, CO2, O2 and NaClO4. 2.1.5 Grades and Specification of the Soda Ash Soda ash is produced in two principal grades, known as light soda ash and dense soda ash. These grades differ only in physical characteristics such as bulk density and size and shape of particles, which influence flow characteristics and angle of repose. Dense soda ash has a bulk density of 950 to 1100 kg/m3, may command a slightly higher price than the light variety, and is preferred for glass manufacture because the lighter variety leads to frothing in the glass melt. Light soda ash having a bulk density at 520 to 600 kg/m3, is the normal production item direct from the calcining furnace and is preferred by the chemical and detergent industries. Other physical properties, as well as chemical properties and properties of solutions, are common to both grades of soda ash. All commercial grades are chemically similar. As density differences are the main distinguishing feature, Table 2.1 shows the typical market specifications of dense soda ash.
6
Chapter 2
LITRETURE SURVEY
Chemical composition Sodium Carbonate (Na2CO3)
≥
99.8 %
Sodium Oxide (Na2O)
≥
58.4 %
Sodium Sulfate (Na2SO4)
≤
0.10 %
Sodium Chlorite (NaCl)
≤
0.03 %
Iron (Fe)
≤
0.0005% ( 5 ppm)
Bulk density
(0.96-1.04 g/cm3)
Particle size
75 micron - 850 micron Table2.1: Market specifications of dense soda ash
2.2 Uses of Na 2 CO 3 in Industrial Sectors
Figure 2.1: Distribution of soda ash by end use
The distribution of soda ash by end use in 2007 was glass, 49%; chemicals, 27%; soap and detergents, 10%; distributors, 5%; miscellaneous uses, 4%; flue gas desulfurization and pulp and paper, 2% each; and water treatment, 1%. 2.2.1 Glass Industry Soda ash is used in the manufacturing of flat and container glass. When mixed in proportion with sand and calcium carbonate, heated to the right temperature and then cooled quickly, the end result will be a glass that has an excellent level of durability and clarity. Na2CO3 as a network modifier or fluxing agent, it allows lowering the melting temperature of sand and therefore reduces the energy consumption.
7
Chapter 2
LITRETURE SURVEY
Soda ash reduces the viscosity and acts as a fluxing agent in glass melting [soda-lime glass (flat and container glass), fiber-glass, specialty glass (e.g. borosilicate glass)].
2.2.2 Detergent Industry Soda ash is used in a large number of prepared domestic products: soaps, scouring powders, soaking and washing powders containing varying proportions of sodium carbonate, where the soda ash acts primarily as a builder or water softener. The addition of the soda ash prevents hard water from bonding with the detergent, allowing for a more even distribution of the cleaning agent during the washing cycle. In addition, soda ash has demonstrated an ability to help remove alcohol and grease stains from clothing. Sodium carbonate is a major raw material in the manufacture of sodium phosphates and sodium silicates which are important components of domestic and industrial cleaners. Sodium carbonate is also added to these detergents to produce formulations for heavy duty laundering and other specialized detergents manufacture. Sodium carbonate may also be used for neutralizing fatty acids in the production of soap.
2.2.3 Metals and Mining Sodium carbonate is used for the production of metals in both the refining and smelting stages. It is often used for producing a metal carbonate which can later be converted to the oxide prior to smelting.
2.2.4 Steel Industry Soda ash is used as a flux, a desulfurizer, dephosphorizer and denitrider. Aqueous soda ash solutions are used to remove sulfur dioxide from combustion gases in steel desulfurization, flue gas desulfurization (FGD) systems, forming sodium sulfite and sodium bicarbonate. Na 2 CO 3 + SO 2
Na 2 SO 3 + CO 2
CO 2 + Na 2 CO 3 + H 2 O
2NaHCO 3
2Na 2 CO 3 + SO 2 + H 2 O
Na 2 SO 3 + 2NaHCO 3
8
Chapter 2
LITRETURE SURVEY
2.2.5 Paper and Pulp Sodium carbonate solution is used for the production of sodium sulphite or bisulphite for the manufacture of paper pulp by various sulphite processes. 2.2.6 Textiles Sodium carbonate is widely used in the preparation of fibers and textiles. In wool processing it is used during scouring and carbonizing to remove grease and dirt from wool. It is also used as a neutralizer after treatment with acids. 2.2.7 Non-ferrous metallurgy industry
Treatment of uranium ores.
Oxidizing calcination of chrome ore.
Lead recycling from discarded batteries.
Recycling of zinc, aluminium.
2.2.8 Chemical industry Soda ash is used in a large number of chemical reactions to produce organic or inorganic compounds used in very different applications. It is used to manufacture many sodium-base inorganic chemicals, including sodium bicarbonate, sodium chromates, sodium phosphates, and sodium silicates.
2.2.9 Other Applications
Production of various chemical fertilizers
Production of artificial sodium bentonites or activated bentonites
Manufacture of synthetic detergents
Organic and inorganic coloring industry
enameling industry
Petroleum industry
Fats, glue and gelatine industry, etc.
9
Chapter 2
LITRETURE SURVEY
2.3 Uses of NaHCO 3 in Industrial Sectors Sodium bicarbonate can also be manufactured by Solvay process.
Animal feeds to balance their diets to compensate for seasonal variations and meet specific biological and rearing needs
Paper industry for paper sizing
Plastic foaming
Water treatment
Leather treatment
Flue gas treatment, especially in incinerators
Detergent and cleaning products such as washing powders and liquids, dishwashing products, etc…
Drilling mud to improve fluidity
Fire extinguisher powder
Human food products and domestic uses: baking soda, effervescent drinks, toothpaste, fruit cleaning, personal hygiene, etc.
Pharmaceutical applications: effervescent tablets, etc.
2.4 History of the Production Before the advent of industrial processes, sodium carbonate, often-called soda ash, came from natural sources, either vegetable or mineral. Soda made from ashes of certain plants or seaweed has been known since antiquity. At the end of the 18th century, available production was far below the growing demand due to the soap and glass market. The French Academy of Science offered an award for the invention of a practical process to manufacture soda ash. Nicolas Leblanc proposed a process starting from common salt and obtained a patent in 1791. The so-called Leblanc or black ash process was developed in the period 1825 till 1890. The major drawback of this process was its environmental impact with the emission of large quantities of HCl gas and the production of calcium sulfide solid waste which not only lost valuable sulfur but also produced poisonous gases. In 1861, Ernest Solvay rediscovered and perfected the process based on common salt, limestone and ammonia.
10
Chapter 2
LITRETURE SURVEY
Competition between both processes lasted many years, but relative simplicity, reduced operating costs and, above all, reduced environmental impact of the Solvay process ensured its success. From 1885 on, Leblanc production took a downward curve as did soda ash price and by the First World War, Leblanc soda ash production practically disappeared. Since then, the only production process used in Western Europe as well as in main part of the world is the Solvay process. In the meantime and mainly since the twenties, several deposits of minerals containing sodium carbonate or bicarbonate have been discovered. Nevertheless the ore purity and the location of these deposits, as well as the mining conditions of these minerals, have limited the effective number of plants put into operation. Worldwide capacity of soda ash manufacture
Table2.2 Worldwide capacity of soda ash manufacture
11
Chapter 2
LITRETURE SURVEY
2.5 Overview about Type of Production Geographical location and site characteristics such as environmental matters, specific energy resources, distribution methods, and trade barriers are key elements in a selection of processing method. Soda ash is readily produced from either natural deposits or trona or by synthetic pathways. Soda ash production methods are given below in historical sequence.
Le Blanc Process (synthetic soda ash)
Solvey Process (synthetic soda ash)
Dual and NA Processes (synthetic soda ash)
Monohydrate Process
Sesquicarbonate Process
Carbonation Process
Alkali Extraction Process
2.5.1 Le Blanc process This process was invented by Nicolas Le Blanc, a French man, who in 1775, among several others submitted an outline of a process for making soda ash from common salt, in response to an offer of reward by the French academy in Paris. Le Blanc proposal was accepted and workable on a commercial scale. Reactions 2NaCl + H 2 SO 4C
+
NaSO 4
Na 2 S + CaCO 3
Na2SO4 + 2HCL NaS + 4CO Na 2 CO 3 + CaS
A mixture of equivalent quantities of salt and concentrated sulphuric acid is heated in cast iron salt cake furnance. Hydrochloric acid gas is given off and sodium hydrogen sulphate is formed. The gas is dissolved in water and the mixture is raked and transferred to the muffle bed reverbratory furnance where it is subjected to stronger heat. Here sodium sulphate called salt cake is formed. The cake is broken, mixed with coke and limestone and charged into black ash furnace. The mass is heated and a porous grey mass know as black ash is withdrawn.
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The black ash is cursed and leached with water in the absence of air in a series of tanks. The extract containing sodium carbonate, sodium hydroxide and many other impurities, is sprayed from the top of a tower counter current to the flow of hot gases from the black-ash furnace. This converts sodium hydroxide, aluminate, silicate, cyanate to sodium carbonate. The liquor is concentrated in open pans until the solution is concentrated in open pans until the solution is concentrated enough to precipitate sodium carbonate on cooling. The product is calcined to get crude soda ash which is purified by recrystallisation. The liquor remaining after removal of first crop of soda crystals is purified to remove iron and causticised with lime to produce caustic soda. The mud remaining in the leaching tanks containing calcium sulphide is suspended in water and lime kiln gas is passed through it. The following reaction occurs. CaS + H 2 O + CO 2
CaCO 3 + H 2 S
The lean gas containing hydrogen sulphide is passed through another tank containing suspension of calcium sulphide. CaS + H 2 S
Ca(SH) 2
This solution is again treated with lime kiln gas liberating a gas rich in hydrogen sulphide. Ca(SH) 2 + CO 2 + H 2 O
CaCO 3 + 2H 2 S
The hydrogen sulphide is burnt in limited supply of air in a special furnace in presence of hydrated iron oxide as a catalyst to obtain sulphur. H 2 S + 1/2O 2
H2O + S
This sulphur is sublimed and collected.The hydrochloric acid produced by the Leblanc process was a major source of air pollution, and the calcium sulfide byproduct also presented waste disposal issues. However, it remained the major production method for sodium carbonate until the late 1880s.
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2.5.2 Solvay Process In 1861, the Belgian industrial chemist Ernest Solvay developed a method to convert sodium chloride to sodium carbonate using ammonia. The Solvay process centered on a large hollow tower. At the bottom, calcium carbonate (limestone) was heated to release carbon dioxide: CaCO 3 → CaO + CO 2 At the top, a concentrated solution of sodium chloride and ammonia entered the tower. As the carbon dioxide bubbled up through it, sodium bicarbonate precipitated: NaCl + NH 3 + CO 2 + H 2 O → NaHCO 3 + NH 4 Cl The sodium bicarbonate was then converted to sodium carbonate by heating it, releasing water and carbon dioxide: 2 NaHCO 3 → Na 2 CO 3 + H 2 O + CO 2 Meanwhile, the ammonia was regenerated from the ammonium chloride byproduct by treating it with the lime (calcium hydroxide) left over from carbon dioxide generation: CaO + H 2 O → Ca(OH) 2 Ca(OH) 2 + 2 NH 4 Cl → CaCl 2 + 2 NH 3 + 2 H 2 O Because the Solvay process recycled its ammonia, it consumed only brine and limestone, and had calcium chloride as its only waste product. This made it substantially more economical than the Leblanc process, and it soon came to dominate world sodium carbonate production.
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2.5.3 Hou's Process This process is developed by a Chinese chemist Hou Debang in 1930s. It is the same as the Solvay process in the first few steps. But, instead of treating the remaining solution with lime, carbon dioxide and ammonia is pumped into the solution, and sodium chloride is added until it is saturated at 40 °C. Then the solution is cooled down to 10 °C. Ammonium chloride precipitates and is removed by filtration, the solution is recycled to produce more sodium bicarbonate. Hou's Process eliminates the production of calcium chloride and the byproduct ammonium chloride can be used as a fertilizer.
2.5.4 Dual process In this process ammonium chloride is produced as a co product in equivalent quantities and differs from conventional, Solvay process and it does not recycle ammonia. The mother liquor from the carbonating system, containing ammonium chloride, unreacted salt and traces of carbonate is ammoniated in ammonia absorber. The ammoniated mother liquor is passed through a bed of salt in a salt dissolver. Exit liquor from the dissolver, saturated with salt, is gradually 0
0
cooled from 40 C to 10 C by evaporation under vacuum to separate ammonium chloride. The slurry containing ammonium chloride is centrifuged and dried. The product is 98% pure and is marked as ammonium chloride fertilizer with nitrogen content of 25%. The mother liquor obtained after the separation of ammonium chloride crystals is recycled to the carbonation vessels placed in series. Carbon dioxide obtained from ammonia plant and the calciner section of soda ash plant is injected in the carbonation vessels. There is provision of cooling coils in the lower carbonation vessels. Sodium bicarbonate is formed. The growth of crystals, of sodium bicarbonate is controlled by the supply of cooling water to cooling water to cooling coils in carbonation vessels. Sodium bicarbonate is thickened in a thickener and centrifuged. The sodium bi carbonate is calcined to soda ash.
2.6 Sodium Carbonate Minerals Whereas the production of sodium carbonate from the ashes of plants in salty soil near the sea is only of historical interest, extraction from soda-containing minerals, especially trona, is of increasing importance. The natural soda minerals occurred in the world is given in the following table.
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Types of Natural soda minerals occurred worldwide Mineral
Chemical Name
Chemical Composition
Trona
Na 2 CO 3 .NaHCO 3 .2H 2 O
Nahcolite Bredeyit
Natural sodium sesquicarbonate Natural sodium bicarbonate Natural sodium bicarbonate
Gaylusitte
% Na 2 CO 3 content 70.3
NaHCO 3
63.1 47.1
Natural sodium bicarbonate
Na 2 CO 3 .CaCO 3 .5H 2 O
35.8
Pirrsonite
Natural sodium bicarbonate
Na 2 CO 3 .CaCO 3 .2H 2 O
43.8
Thermonatrite
Na 2 CO 3 .H 2 O
85.5
Na 2 CO 3 .10H 2 O
37.1
Burkeit
Sodium carbonate monohydrate Sodium carbonate decahydrate -
Na 2 CO 3 .2Na 2 SO 4
27.2
Dawsonit
-
NaAl(CO 3 )(OH)
35.8
Hankcite
-
Na 2 CO 3 .9Na 2 SO 4 .KCl
13.5
Sortite
-
Na 2 CO 3 .2CaCO 3
34.6
Natron
2
Table 2.3: Natural soda minerals occurred worldwide
Only Trona and Nahcolite are the minerals those commercial interest. These Na 2 CO 3 containing minerals were formed from the original rock by the erosive action of, air, water, heat, and pressure, followed by chemical changes caused by the action of atmospheric carbon dioxide. The carbonate containing salts formed were leached by water and then concentrated and crystallized by evaporation.
2.6.1 Trona Based Process The production of sodium carbonate from the ashes of plants in salty soil near the sea is only of historical interest, extraction from soda-containing minerals, is of increasing importance. Trona, hydrated sodium bicarbonate carbonate (Na 2 CO 3 .NaHCO 3 .2H 2 O), is mined in several areas of the world.
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This underground dry Trona processing consists in several steps:
First Trona has to be mined by the room and pillar or long wall method mechanically.
As Trona is an impure sodium sesquicarbonate mineral (Na 2 CO 3 ·NaHCO 3 ·2H 2 O), it has to be calcined to produce a soda ash still containing all the impurities from the ore.
Next, calcined Trona is dissolved, the solution is settled and filtered to remove impurities (insoluble and organics), and the purified liquor is sent to evaporators where sodium monohydrate crystals precipitate.
The monohydrate slurry is concentrated in centrifuges before drying and transformation into dense soda ash.
Deposits from Trona lakes and solution mined Trona are processed as follows:
Dissolving Trona in wells
Carbonation of the solution in order to precipitate sodium bicarbonate filtration of the slurry and Calcination of the bicarbonate to get light soda ash , recycling of the carbon dioxide to the carbonation
Light soda ash transformation into dense by the monohydrate method
Carbon dioxide make-up produced by burner off-gas enrichment
2.6.1.1 Trona Products Various Forms of Sodium
Formula
Carbonate Anhydrous sodium carbonate
Na2CO3
Sodium carbonate monohydrate
Na2CO3. H2O
Sodium carbonate heptahydrate
Na2CO3 .7H2O
Sodium carbonate decahydrate
Na2CO3 .10H2O
Caustic Soda
( NaOH )
Sodium Bicarbonate
( NaHCO3)
Sodium Derivatives
Table 2.4: products of Trona
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2.6.1.2 Monohydrate Process Soda ash is generally produced from trona by monohydrate process that produces only dense soda ash. The first FMC Wyoming Corporation plant using this process went into operation in late 1972. In this process, the trona ore is first converted to crude soda ash by calcination and all subsequent operations are performed on the resulting carbonate solution, as given in following figure.
Figure 2.2: Flow diagram of monohydrate process
Crushed Trona is calcined in a rotary kiln to dissociate the ore and drive off the carbon dioxide and water by the following reaction: 2 (Na 2 CO 3. NaHCO 3 .2H 2 O) (s) .
3 Na 2 CO 3 (s) + 5 H 2 O + CO 2
The calcined material is combined with water to dissolve the soda ash and to allow separating and discarding of the insoluble material such as shale or shortite by settling and /or filtration. The resulting clear liquid is concentrated as necessary by triple-effect evaporators, and the dissolved soda ash precipitates as crystals of sodium carbonate monohydrate, Na 2 CO 3 .H 2 O. Other dissolved impurities, such as sodium chloride or sodium sulfate, remain in solution. The crystals and liquor are separated by centrifugation. The sodium carbonate monohydrate crystals are calcined a second time to remove water of crystallization. The resultant finished product is cooled, screened.
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2.6.1.3 Sesquicarbonate Process An alternate method of soda ash production from trona is the sesquicarbonate process. This is the original process, developed by FMC Wyoming Corporation and put in operation in 1953, for producing pure soda ash from Wyoming trona. Trona ore is leached in recycled mother liquor at as high a temperature as possible to maximize the amount dissolved. The solution is then clarified, filtered and sent to a series of evaporative cooling crystallizers where sodium sesquicarbonate (Na 2 CO 3 .NaHCO 3 .2H 2 O) is crystallized. Carbon is added to the filters to control any crystal modifying organics. The purified sesquicarbonate crystals may be calcined to produce a light soda ash product. Simplified flow diagram of sesquicarbonate process is shown in following figure. The mother liquor is recycled to the dissolvers. In a variation of the process, trona ore is dissolved in hot water and the centrate is returned to the evaporator crystallizer (Haynes, 1997). This produced soda is the light soda ash. Densities similar to the monohydrate soda ash may be achieved by subsequently heating the material to about 350 °C. Alternatively, soda ash can be converted to the monohydrate and then calcined.
Figure2.3: Flow diagram of sesquicarbonate process
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2.6.1.4 Alkali Extraction Process Alkali extraction process is mainly to dissolve crude trona in an aqueous sodium hydroxide solution. In this process, trona is dissolved in an aqueous sodium hydroxide to obtain pregnant sodium carbonate solution. This method is generally used for bicarbonate content that dissolves to be an incongruent consisted in trona. The diluted solution has a composition of 2-7 % caustic soda. Dissolution reaction is given as follows: Na 2 CO 3 .NaHCO 3 .2H 2 O + NaOH
2 Na 2 CO 3 + 3 H 2 O
The solution at 30 °C was filtered and the pregnant carbonate solution is heated, sufficient water is evaporated to form slurry of sodium carbonate monohydrate crystals and aqueous sodium carbonate. The slurry was filtered and the mother liquor was recycled to dissolve raw mineral. The regeneration was done by adding sodium hydroxide to the mother liquor.
The monohydrate crystals were dried and calcined. The most important parameters in alkaline extraction process are; the dissolution temperature, concentration of sodium hydroxide and evaporative crystallization temperature. The appropriate temperatures for the dissolution and evaporative crystallization are 30 °C and 100 °C respectively. The flow diagram of alkali extraction process is shown in following figure.
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Figure 2.4: Flow diagram of alkali extraction process
In a trona bed, the effect of water on the solubility of sodium carbonate will decrease due to the precipitated bicarbonate. In the conventional mining technique, bicarbonate can be converted to carbonate with a pre-calcination stage. The problem associated with the presence of sodium bicarbonate in trona deposits can be solved by applying of sodium hydroxide solution. The required amount of sodium hydroxide is the stochiometric amount that is necessary to convert all of the bicarbonate to carbonate. The aqueous sodium hydroxide solvent preferably contains 1-15 wt% NaOH. Using an excess of sodium hydroxide causes unreacted NaOH to remain in the solution and this effect decreases the solubility of sodium carbonate.
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2.6.2 Nahcolite based process A Nahcolite deposit has been found in several places in the world. Nahcolite is processed as follows:
By solution mining (wells, with injection of hot mother liquor returned from the surface facilities), Nahcolite is separated.
As nahcolite is an impure sodium bicarbonate mineral (NaHCO 3 ), it must be treated.
The hot solution is decarbonated by heating. Then the solution is sent to settling and filtration.
Next, the purified liquor is sent to evaporators where sodium monohydrate precipitates.
The slurry is concentrated by centrifugation and the monohydrate crystals transformed to soda ash by drying. The mother liquor is sent back to the solution mining
2.7 International Scenario The present global capacity of soda ash is 37.0 million tones per annum and the long term growth rate is 1.5-2%. The major technology suppliers for the soda ash plant are:
Solvay and Cie SA, Belgium
AKZO-ZOUT Chemie BV, Netherlands
Asahi Chemical Industry, Japan
Polimex Cheepok, Poland
Technology Exports Divn, DSTA, China
The basic process for the manufacturer of soda ash has not undergone much change since last 130 years. Developments however are taking place in the following areas:
Process technology
Operation technology
Improvement of quality
New product from waste
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2.8 Structure and Status of Indian Industry The manufacture of soda ash in India started in 1932 at in Gujarat with an installed capacity of 50 tons per day. This was followed by the entry of another Chemicals manufacturing plant at Mithapur in Gujarat in 1894 with an installed capacity of 100 tons per day. In a span of 50 years it has grown to be the biggest soda ash unit in the country with daily capacity of 2000 tones. In the same region in Gujarat, two more soda ash plants came up after-wards. First one was commissioned in 1959 with a capacity of 200 tons per day which has been expanded to 800 tons per day. Second one was commissioned in 1988 with a capacity of 1200 tons per day. All these four units in Saurashtra in Gujarat are based on Solvay process. Three units are operating on the modified Solvay process (Dual Process) in which ammonium chloride is the co-product. The first plant based on this technology was set up in 1959 at Varansai, with an installed capacity of 120 tons per day. The two other units operating on Dual process are at a capacity of 200 tons per day. The present installed capacity of six soda ash manufacturing units is 17.09 lakh tones.
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CHAPTER 03
FEASIBILITY STUDY
The feasibility analysis is a preliminary study undertaken to determine a project's viability or the discipline of planning, organizing, and managing resources to bring about the successful completion of specific project goals and objectives. The results of this study are used to make a decision whether or not to proceed with the project. In the case of the soda ash plant an analysis of possible alternative solutions and scenarios that has an impact on the proposed was done and recommendations have been made on the best alternative.
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3.1 Preliminary Study As a preliminary study of the prospective soda ash plant a simple feasibility analysis has been summarized in this chapter. The main objective of this feasibility is to explore the economical aspects of the process and other concerns like environmental, technical, social issues that may arise as a result. It can be said that the necessity of the plant is primarily based on final out come of the plant and the market availability for its products. The bulk of the soda ash imported into the country is primarily for the consumption of the glass industry. The main player in the present glass industry in Sri Lanka is ‘Ceylon Glass’ with a daily consumption of almost 20 Metric Tones per day. A considerable growth in the consumption of Soda ash can be seen within this single entity itself. SODA ASH IMPORTS (2006) Quantity Kg
Country Bulgaria China India India Iran Japan Kenya Malaysia Pakistan Romania Singapore Taiwan Turkey U.K. Ukraine Total Avg price of 1kg of imported Na 2 CO 3 (Rs) Average consumption per day
Value Rs.
619000 975407 4089598 83284 1 792000 1 100000 440000 725350 78 36000 469 175000 8,036,188
17120020 28721920 9342 101802615 2643973 4282 15948728 9510 3496878 13901583 19914608 26244 960489 824657 3573407 208958256
26.00 22016.95342 22.01695342
kg MT
Figure 3.1: Soda ash imports (2006)
When we consider the total soda consumption based on the amount imported to the country it can be clearly seen from the above graph (figure 3.1)that an average of almost 40 MT (2008)is consumed daily. Also a considerable increase in the amount demanded per year is depicted in the figure 3.2. Therefore a daily production capacity of 50 MT on a continuous basis is justifiable.
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Variation of Soda ash imports 45 40 35 MT/day
30 25 20 15 10 5 0 2004
2005
2006
2007
2008
year
Figure 3.2: Variation in soda ash imports
The present average imported price per kg of soda ash is `23`1. The cost incurred for the production of a single kg based on the raw material costs, maintenance and operation costs and other overheads will be far less than the importing price because of the availability of CaCO3 deposits in Sri Lanka at a considerable degree of purity, availability of skilled workers at considerably lower wage rates and mainly due to the avoidance of cost for freight services. But the lower price in itself doesn’t justify the high capital cost that has to be incurred for the implementation and construction of soda ash plant based on the Solvay process. A further in-depth analysis with considerations of strength of export market, pay back period, etc has to be taken into account. When we consider the importing scenario there are considerable fluctuations in the demand for soda ash and related products. It was noted that most of the soda ash imported to the country is in the form of high dense soda ash. This is because high dense soda ash is one of the main raw materials of the glass industry and most of the soda ash imported to the country is consumed by the same industry. A main factor for the increased price of the imported soda ash in to the country is because of the fact that different local companies import soda separately in small amounts and because of the cost incurred for the freight services. Also as mentioned above the unstructured importing from various suppliers and the unavailability of an agent to handle the soda import has led to higher prices. Another factor that would lead to higher prices when importing is because of levies and taxes that has been imposed on imported products and charges at the customs. Since soda is being imported to the country at a higher price the related industries face restrictions in implementation and expansion because they have a huge problem of the market share because of the high final cost.
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The main raw materials for the production of soda ash from the Solvay process are Brine and Calcium Carbonate. When we consider the availability of these raw materials in Sri Lanka, brine is present in the form of sea water all around the country and Calcium Carbonate can be obtained from sand stone or Dolomite reserves present throughout the country. Pure Miocene sand stone can be found in the land strip stretching from Puttalam to the Jaffna peninsula. Dolomite reserves are present to the middle of the country. Areas well known in this aspect is present in the Matale district. Also Calcium Carbonate can be found in the form of coral reefs in various parts of the costal belt in Sri Lanka though this is not an environmental friendly and feasible option. Also sea shells that is present in the costal areas is a good form of Calcium Carbonate but this is not a viable and secure raw material source for a soda ash production facility of the proposed scale. Therefore it can be concluded with confidence that a local soda ash production plant will be able to get the essential raw materials easily. Therefore based on this preliminary feasibility analysis it can be said that building a soda ash plant in Sri Lanka would be profitable. In addition to the facts highlighted and discussed above, the feasibility has been further divided and analyzed as economical, legal and administrative; market feasibility as part of the initial evaluations and technical, social and environmental feasibilities have been analyzed as a measure of viability when work is in progress.
3.2 Economical Feasibility •
Impact on local industry- Soda ash is one of the most important raw materials for the manufacturing as well as process industry. It can be used as a raw material for the production of glass, polymers, etc. Also it is extensively used in the process industry as a raw material in the production of various chemicals, fertilizers, etc. When soda ash is available locally at a lower price and most importantly in form of a continuous, secure supply there would be a considerable boom in the above mentioned industries. Also since the there would be developments in industries that are in parallel with this industry. For example saturated brine is required as a raw material in the Solvay process. Hence a salt production facility in the area can be utilized to provide saturated brine.
•
Impact on economy of area- As studied and evaluated under chapter 5 the location of the soda ash plant is designated as Karadipuval site in Puttalam. The Holcim Lanka cement plant and its quarry is located in the puttalam district. The Aruwakkaru Limestone Quarry site of Holcim Lanka Ltd is used to extract limestone to produce cement in Palavi plant of Holcim Lanka (pvt)
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ltd. This is the only quarry
in operation to extract limestone which is 150 km away from
capital city Colombo of Sri Lanka. Other than few industries the area presently can be considered as remote or rural. With the establishment of the soda ash plant and the completion of Norochcholai coal power plant the area will comprise of 3 main industries and would be similar to an industrial zone. The Norochcholai coal power plant already has many infrastructure developments which include the development of a port. The development of such industries will lead to considerable development of the facilities, economy and availability of jobs in the area.
•
Reduction of Imports- When we consider in a macro scale there will be considerable amount of savings when the production of Sri Lanka is increased. This in tern will benefit the country as a whole because of increase in GDP, reduction of unemployment, drop of inflation, increase of local currency.
•
Opportunity for export- There are several industries that consumes soda ash as a raw material. Also there is a high demand for soda ash in neighboring India and other south Asian countries. Though India is one of the major producers of soda ash in the world it utilizes the Dual purpose method to cater the fertilizer demand in the country and most of the plants are sited north of the country. Also the dual purpose method leads to higher cost for the soda ash because NH3 used in the process is of high cost. Therefore there would be considerable market for soda ash produced in Sri Lanka in the south Indian region. Also there would be considerable demand for end products like glass that is made from soda ash throughout the south Asian region.
•
Increase of production- The availability of locally produced soda ash will lead to a boom in the soda related industries. This would lead to the possibility of expanding local industries and emerging of new ones. Such an increase of production, production capacity and availability of raw materials would make Sri Lanka attractive to investors.
•
Production costs- As mentioned earlier the availability of raw materials locally for the production of soda ash in Sri Lanka itself will lead to reduction production cost. Also the availability of skilled workers and manpower at a relatively lower wage rates comparative to that of other soda ash producing European counterparts will lead to reduced cost. But it needs
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to be noted that the other overhead costs in Sri Lanka would be somewhat higher because of high electricity tariffs and condition of infrastructure. •
Incentives and levies imposed on the industry- Presently there are various levies and taxes imposed on imported goods. But Ceylon glass which is involved with importing most of the soda ash into the country for its production activities has a considerable concession as part of the agreement with the government when it was taken over by an Indian company. Even though this is the case if soda ash is produced locally the government would impose taxes on imported soda ash to promote the local producer.
•
Government support- Since a soda ash production plant is a huge production facility and it would be involved with providing jobs for considerable amount of people the government is likely to act in favor of the local soda ash producer. Government support at a considerable degree would be required because purchasing of land in the proposed area under Chapter 6, establishment of infrastructure support, environmental impact mitigations, obtaining quarrying rights for limestone, provision of security from terrorist threats etc would require government intervention and support.
•
Security- As discussed later in Chapter 5 the most suitable location for the proposed soda ash plant is at Karadipuval in Puttalam. Though more pure Miocene Limestone deposits are available in the Jaffna Peninsula, it will not be a likely option because of the terrorist activities present in the area and the on-going war effort. When we consider the site at Puttalam a secure security situation has been prevailing for several years. Also a tight security parameter presently has been set in the area which would be further strengthened once the Norochcholai coal power plant has been commissioned. Therefore it can be said that the security threat or risk is minimum.
•
Inflation and its impact- The present inflation rate of the country is very high. Therefore this would negatively impact on the project at the construction and maintenance phases because most of the equipment would have to be imported. But once the plant is running the soda produced and sold locally would not be severely affected. But the competitive edge of soda ash that is to be exported would be lost.
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•
Regional impact- A major administrative and management issue that would affect the functioning of the plant is the environmental concerns and waste management. When the plant has necessary control measure in-place, which is used successfully in other parts of the world, this threat can be avoided.
•
Impact from other main industries in the area (Holcim) - An administrative issue that the company involved will have to face is when obtaining quarrying rights to the limestone quarry. At present Holcim Lanka is involved with quarrying activities at Aruwakkaru. Since this site has already been reserved by the cement company obtaining quarrying rights and reserving of limestone deposits would be necessary.
When we consider the economical evaluation as a whole after considering lagal and administrative issues the implications are positive. But since this is a preliminary feasibility analysis of the project in-depth cost and benefit analysis are not possible. But when viewing the above facts and considering the economical parameters, it can be said with certainty that the expected outcome would be positive.
3.3 Market Feasibility •
Market trends – Presently there is considerable market trend towards the development of soda and salt related industries in Sri Lanka. This will result in a huge demand for soda ash which is being used as raw material. Also there is tremendous potential for the development of the glass industry. For instance Ceylon Glass moved from their conventional plant at Ratmalana and built a new one at Horana to cater the increasing demand. Therefore it can be said with confidence that there would be considerable demand for locally produced soda ash with the expected boost in industry.
•
Allowance for expansion- As mentioned in the economic feasibility and later on in the site layout selection there is considerable potential for expansion. The present demand for soda ash is about 40 MT/day. The proposed plant has a capacity of 50MT/day with an allowance of 10 MT/day. In the event of a huge increase in the market a new plant or an expansion of the plant itself would be required. The land selected under the latter chapter of site selection has allowance for such an expansion.
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•
Sales generation- As highlighted above the current market price for soda ash is around Rs 25. According to the present economic evaluation it can be said that a kg of soda ash can be produced from a cost of around Rs 8 which means that the gross profit is considerably high.
•
Pay back- As mentioned above the gross profit per kg of soda ash sold is high. Therefore it can be said that the payback would be less event though a thorough evaluation with a detailed financial statements would be required for in order to estimate the payback accurately.
•
Sales and marketing concerns- At present there won’t be any marketing concerns because there are no other players in this industry. The only competitor would be soda ash importers. But there are no big importers that have specialized in this business, currently in Sri Lanka. Also since the government is biased towards the development of the local industry there would be restrictions on imports once the plant has commenced production. Also since the no of consumers if Soda ash is less a highly costly marketing campaign would be meaningless.
•
Distribution network – As mentioned above since the consumers of soda ash is less the ideal distribution network would be a one-to-one system. For example when soda ash for the glass company can be sold to the Ceylon glass (pvt) ltd directly without the involvement of intermediates and complex sales networks. This would benefit the producer as well as the consumer because of simplicity and high profitability.
3.4 Technical Feasibility •
Infrastructure requirement- The proposed plant with a capacity of 50 MT/day would require considerable amount of infrastructure and utility processes. Normally Solvay process plants are considered to be some of the biggest plants in the world. The plant would require a road network, railroad or durable road to transport limestone from the quarry, uninterrupted electricity, basic water supply and process water, etc. The producers would have to build the internal road network as required. In the event of building a rail network for the transportation of limestone from the quarry the company would require the assistance of the governments. The case would-be the same if the plan to transport limestone from the quarry to the plant in Lorries and vehicles because a road with reinforced layer would be required. The plant could fulfill its power requirement by means of electricity from the National grid and power generated from steam/cogeneration at the plant. The plant can fulfill its domestic water
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requirement from the National water supply lines. But the process would require extensive amounts of process water. Since the use of treated and purified salt water for this purpose would not be feasible the need will have to be met by water from dug wells or stream/river.
•
Geological aspects- A process plant of this scale would require a strong foundation. Therefore the stability of the bedrock on which the plant is sited, is of importance. The land of Puttalam area consists of hard, moisture free soil. It has already been proved that the bedrock in the Puttalam area is one of the best to locate process plants by the survey done for the Norochcholai coal power plant. This is a positive aspect. But the soil in the area, especially in places near the lagoon and the salt production plants the soil consist of salts which might be harmful to the plant. By adopting necessary coatings on surfaces and having corrosion allowances this problem can be solved.
•
Availability of skilled workers and professionals for maintenance of plant- At present the district of Puttalm doesn’t comprise of a considerable skilled and professional workforce. Hence the human force requirement will have to be met by resident workers from other areas of the country. But it is possible to obtain unskilled laborers from the area for the plant construction activities and maintenance when the plant has been commissioned.
•
Availability of construction companies- At present Sri Lankan Process development companies doesn’t have the experience and capacity for the construction of a Solvay plant with a daily capacity of 50MT. Hence the assistance of process plant construction companies abroad with experience in similar construction activities will be required.
•
Availability of expert consultancy firms- At present there are companies that have extensive amounts of technical expertise regarding the Solvay process. Some of them are given below. Solvay and Cie SA, Belgium AKZO-ZOUT Chemie BV, Netherlands Asahi Chemical Industry, Japan Polimex Cheepok, Poland The technical assistance of such a consultancy provider will be required to oversee the construction activities and provide process consultancy when the plant has been commissioned.
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•
Fabrication concerns- Presently Sri Lanka has the capacity for fabricating most of the process vessels required for the plant. Other equipment that cannot be produced locally will have to be imported or fabricated and shipped to Sri Lanka.
•
Imported equipment transportation- The port that has been built at Norochcholai is to be used as a transportation channel for the imported equipment of the Norochcholai Coal Power Plant. The same port can be used when bringing Heavy process equipment or vessels for the proposed soda ash plant.
3.5 Social Feasibility •
Social condition of people- The living standard of an average resident in the area is low. Most of the population is farmers. The proposed plant will not have a huge impact on the residents of the area since not much farming is done or vegetation is present in the chosen area. It cannot be said that the plant will be involved to a great extent in uplifting the living standards of these people, but there are certain direct and indirect means related to the activities of the plant through which the local population can thrive and earn an extra income.
•
Resettlement and rehabilitation- This will not be a problem because the land chosen is a piece of bare land. Therefore no concern of this matter would be required. But in the event of placing rail lines from the existing one from the Holcim factory to the quarry, acquiring of certain land plots from the residents will be required. But even in this case resettlement or rehabilitation will not be a concern because this project will not need land from a process of nationalization.
•
Social resistance- The construction of the plant will definitely have to face public pressure and cultural resistance, as quite evident from other projects of this sort. The pressure would mainly be based on environmental issues, pollution and waste disposal. These resistances can be subdued to a certain degree by implementation of the best available pollution control techniques and waste management principles and increasing public awareness regarding them. This scenario as whole will not affect the decision of implementation of the plant.
•
Health and safety concerns- As mentioned above with the implementation of the best available practices and by designing process vessels according to standards the risk of a
33
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FEASIBILITY STUDY
disaster occurring due to failure can be avoided. By having a good training programme in-place and by recruiting skilled and experienced workers there would not be a risk of health and safety. Then it would not be a concern in the feasibility concern.
•
Employment- One of the positive implications of the plant on the surrounding community is the increase in job opportunities. These jobs can be in the form direct or indirect means. For instance with the start of construction activities of the plant many laborers (both skilled and unskilled), will be recruited from the area. Once the plant is complete and has been commissioned people across a diverse range will get job opportunities. In recruiting of recruiting such people the priority will be given to the locals in the area because the company will then not have to bear accommodation and transport costs. Also with the establishment of a new plant various businesses would come into being, whose activities are not directly related to the operation of the plant. For example many new shops and stores would be established by external people to cater the needs of the employees, suppliers, etc. This would result in the provision of employment as well as flow of money into the area. But on the plant’s perspective relying on employees from the adjacent areas alone, will not be sufficient because the lack of skilled workers and professionals in the area will affect the operations of the plant. Therefore the company will have to provide transport and accommodation to a certain degree to attract employees with the necessary traits from other parts of the country.
•
Local industry- At present in the Puttalam district, there are industries and commercial entities that will directly benefit from the proposed soda ash plant at Karadipuval. For instance the heavily spread saltern industries in the area discharge the Mother Liquor from the tanks after salt has crystallized. But since this mother liquor with saturated Sodium Chloride is a raw material for the soda ash industry the salterns can earn an income from their effluent. Also the Holcim cement factory can benefit immensely by leasing out their assets like the quarry, rail carriages, kiln for hazardous waste disposal, etc. Also the jetty/port that is being built in the area can benefit from the activities of the plant. Other than these industries small commercial entities like suppliers, caterers, transporters, etc also will get a new market onto which they can expand their business.
34
Chapter 4
PROCESS SELECTION
CHAPTER 04
PROCESS SELECTION
The selection of an appropriate process is an important decision, all the subsequent work depends upon this choice. Although the selection can be changed or modified at a latter stage, at least before the plant is built, such a decision results in a serious waste of time and money……….
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4.1 Introduction The stepping stone for the chemical revolution begun in Europe with the introduction of the Leblanc process for the production of Soda by Leblanc in 1790. This industry used as raw materials, salt, sulfur, limestone, saltpeter, coal, air, and water; its products were the alkalis, sodium carbonate and sodium hydroxide. Cheap alkalis brought to the ordinary citizen those luxuries which had formerly been enjoyed only by the rich and powerful: glass for bringing light into dark places, paper for bringing the printed word into proletarian homes, and soap for bringing sanitation into cities oppressed by filth and disease. A highlight of the developments in the soda ash industry was witnessed when the Belgian industrial chemist Ernest Solvay (in 1861), developed a method to convert sodium chloride to sodium carbonate using ammonia. Other than the Leblanc and Solvay process there have been various developments in the soda ash industry during the last 100 years. The processes that are present used for the production of soda ash are given below.
Leblanc Process
Solvay Process
Dual Process
Akzo Dry Lime Process
New Ashai ( NA) Process
Akzo Zoul Chemie Method
Nepheline syenite process
Carbonation of caustic soda
Also Trona and nahcolite based process are used in different countries but this is not an option in the Sri Lankan context because the island does not have soda ash reserves which can be mined and processed under these methods to yield soda ash for consumption. In other words Trona and Nahcolite processes are used for processing soda ash reserves to remove impurities within them. Also there are some plants operating under the ‘Nepheline syenite process’ and ‘Carbonation of caustic soda’ method. But it is not possible to obtain soda ash of good quality from the Nepheline syenite process and this would lead to additional cost for purification processes as demanded by soda ash consuming industries. Also carbonization of caustic soda is not feasible for Sri Lanka at present because it is dependent on imports to fulfill caustic soda requirements.
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4.2 Comparison of Solvay process with Others Methods of Production As mentioned above in the introduction, Leblanc process was the industrial process for the production of soda ash used throughout the 19th century. It involved two stages: Production of sodium sulfate from sodium chloride, followed by reaction of the sodium sulfate with coal and calcium carbonate to produce sodium carbonate. The Leblanc process was a batch process in which sodium chloride was subjected to a series of treatments, eventually producing sodium carbonate.It is also noteworthy that in addition to valuable alkalis, the Leblanc process produced two waste products, hydrogen chloride and calcium sulfide. Acidic hydrogen chloride gas was sent up the chimney, after which it decimated vegetation in the vicinity of an alkali works. Insoluble calcium sulfide was conveniently disposed of in heaps where the vegetation used to be. Unfortunately, when calcium sulfide reacts with rain water it farts out noxious hydrogen sulfide. Hence alkali manufacturers based on Leblanc process became popular targets for lawsuits and government regulations. The British Alkali Act of 1863, for example, required the absorption of 95% of the hydrogen chloride produced by the salt cake furnace. This was easily accomplished, hydrogen chloride being quite soluble in water; the waste gas was sent up through a stone tower filled with coke; water dribbling down through the tower absorbed the hydrogen chloride, producing aqueous hydrochloric acid. In addition to hydrogen chloride which can be presently considered as valuable product own its own account and after Henry Deacon in1868 introduced a process for turning waste hydrogen chloride into bleaching powder, which could be utilized in paper and textiles industry, calcium sulfide produced is a problem for soda manufacturers using the Leblanc process. This (calcium sulfide produced) became a persistent problem owing to the twin problems of stinking heaps of tank waste, and the loss of valuable sulfur. It is noteworthy at this point that pure source of Sulfur is not present in Sri Lanka. An alternative to sulfur is sulfur dioxide which was obtained during the latter stages of the soda industry from roasted from pyrites, which alternatively would have to be imported to Sri Lanka. Also whatever the source may be, it will eventually end up as calcium sulfide waste. The only positive solution for the disposal of calcium sulfide lies in the fact that it could be converted into sodium thiosulfate, used by photographers to fix photographs but this cannot be considered as a feasible option. Also at present there is a method of recovering sulfur from tank waste owing to the discoveries of Alexander Chance in 1887. But these slight improvements would adversely affect the efficiency of the overall process.
37
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PROCESS SELECTION
While the construction of a Solvay plant would be more expensive than a comparable Leblanc plant, it would require fewer raw materials; thus capital investment is higher but operating costs will be less. With lower operating costs, the Solvay process will be able to drop the price of soda produced. It can be said that the Solvay process is cleaner and more efficient where else Leblanc process is crippled by pollution and waste. Also the Solvay process has a distinct advantage over its Leblanc counterpart because of the continuous developments being carried on it, in other parts of the world where else soda production from Leblanc process is one of the diminishing technologies. It is evident from the fact that world production of soda in 1863 had been 150,000 tons, all produced in Leblanc plants. By 1902 world production of soda was at 1,760,000 tons, where over 90% of the amount was be produced using Solvay plants. A very recent development in the soda ash industry has enabled the co production of vinyl chloride monomer (for production of Poly Vinyl Chloride) and soda ash. Akzo Zoul Chemie Nederland has succeeded in producing (on a small scale) vinyl chloride with soda ash as a co-product. The process uses medium pressure steam and carbon-dioxide instead of more expensive electrical energy (for the electrolytic production of production of chlorine). The overall energy consumption of the new process is about one half that of the conventional method when caustic soda is the co-product. Here soda ash is produced from the reaction of salt with a concentrated aqueous trimethylamminecarbon doxide solution obtained downstream in the vinyl chloride process. Even though the advantages of the Akzo Zoul Chemie process are attractive, as evident from the above process description soda ash would be a by-product in this process. This would mean that the amount of soda- ash produced would be dependent on the demand for vinyl chloride monomer. That would imply that the soda ash output would be governed by the demand for PVC in the market. Also the capital cost that needs to be incurred for a plant involved with the cogeneration of both soda ash and PVC would be relatively higher than that for a plant involved with only the production of soda ash only. Also this is a relatively new technology which is still being developed and the rights for this plant are restricted by the patent company. Therefore additional administrative charges and royalty from the revenue needs to be bared. The Dual purpose plant came into being because of the concerns associated with the discharge of solid waste. The dual purpose is a modification of the existing Solvay process. It was developed by a Chinese chemist Hou Debang in 1930s. It is the same as the Solvay process in the first few steps. But, instead of treating the remaining solution with lime, carbon dioxide and ammonia is pumped into the solution, and sodium chloride is added until it is saturated at 40 °C. Then the solution is cooled down to 10 °C. Ammonium chloride precipitates and is removed by filtration, the solution is recycled
38
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to produce more sodium bicarbonate. Hou's Process eliminates the production of calcium chloride and the byproduct ammonium chloride can be used as a fertilizer. The constraints of Dual process are facts that it has to depend on the availability of carbon dioxide gas and ammonia from fertilizer unit and the production of soda ash will be restricted depending on the demand for ammonium chloride in the market. The New Asahi process in a relatively new modification of the Dual purpose process. This process came into being owing to the developments in the Japanese soda ash industry. The Japanese soda ash industry was based on high cost imported salt. Therefore this new NA process was developed which is essentially dual purpose process on a large scale. Many new modifications were made to incorporate a more efficient and less raw material utilizing process. These modifications include changes in the Carbonation section, cooling system used for cooling the mother liquor from centrifuges, adoption of Ammonium chloride distillation unit, system of raw salt crushing, etc. It also bears the same constraints of the conventional dual purpose process. In addition the initial investment is very high for New Asahi (NA) process. This is because the New Asahi process requires more investment to be made in the lime burning/lime slaking, ammonia recovery and ammonium chloride crystallization sections. It can be said that the effluent generation from Solvay plants is more compared to other process plants. Owing to the requirement of placing Solvay plants with proximity to the sea, the effluent from process are discharged into sea after some minor treatment which does not affect the ecological balance because the composition of effluent compares favorably with sea-body composition. Generally, a costal soda ash plant should go for the Solvay process whereas inland plant should opt for Dual process near a fertilizer unit. As discussed above the most likely option for the soda ash production plant is the conventional Solvay process and the Dual purpose method. A comparison of the two processes is given below. Solvay Process Uses Brine, limestone and coke as raw materials Uses small amounts of ammonia and carbon dioxide as makeup gases, while the bulk of the gases are recycled Soda ash is obtained as product
Dual Purpose Process Uses brine, ammonia, limestone and coke. Uses small amounts of and carbon dioxide as makeup gases, while the bulk of the gase is recycled Soda ash and Ammonium chloride(fertilizer) is obtained as co-products
Calcium chloride is obtained as a by product/waste. Therefore has a waste disposal No effluent disposal problem problem Ammonia has to be imported as a raw material Recovers most of the valuable ammonia if the process is stand alone plant (Not adjacent to a fertilizer production facility) Depend on availability of carbon dioxide and Production is not constrained ammonia from a fertilizer unit. But presently in Sri Lanka there is no such production facility
39
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PROCESS SELECTION
Completely close process when fertilizer unit is also present The production is solely dependent on the soda Production of soda ash is restricted by the ash demand in the market demand for ammonium chloride Efficiency is comparatively low Yield is slightly higher Investment and maintenance costs are Investment and maintenance costs are low comparatively high Many factors influence the placement of the plant. For example fertilizers produced is in Since the raw materials are present at the same demand at the agricultural zones near the location at Puttalam the plant can be easily Mahaweli, saturated brine is obtainable from sited there salterns, imported ammonia can be stored at a low cost near a port, etc. The technology of the Solvay process has This is relatively a new technology used mainly undergone several developments and is at a in China and India mature state Table 4.1 a comparison of the Solvey and dual processes Not a completely closed process
4. 3 Process Selection Conclusions The conventional solvay process appears to be preferred for a plant producing 50 tonne/day of light soda ash. The capital cost advantage of this process and the ability function independently surpasses the benefits of the high efficiency dual purpose process. Furthermore, the higher temperature (because of the availability of a kiln) and the favorable effect of pressure enable a greater recovery of energy from the process. This choice, made on both economic and operational grounds, can be said as being consistent when we consider the production capacity of soda ash, in the world throughout, from Solvay process over the Dual purpose method.
40
Chapter 5
PROCESS DESCRIPTION
CHAPTER 05
PROCESS DESCRIPTION
Chemical and process Engineers are the leading characters in the process design and optimization. They put the desired target into a real world application by putting some unit processes together and interchange the possible unit operations along the process streams where it gives the best economic value. Under this section a thorough evaluation of the process selected is carried out. The process description of a particular process is expected to yield the parameters and restrictions that bind the process. Also an special emphasis on the process unit operations are considered under the process description
41
Chapter 5
PROCESS DESCRIPTION
5.1 Main Chemical Reactions in Solvay process
Figure5.1: Block diagram of the soda ash production plant
The Solvay process relative to the production of soda ash could be summarized by this equation involving the two main components: sodium chloride and calcium carbonate. 2 NaCl + CaCO 3 → Na 2 CO 3 + CaCl 2 In practice this direct way is not possible and it needs the participation of other substances and many different process steps to get the final product, soda ash. First reactions occur in salt solution (brine). First of all, ammonia is absorbed (equation 1) and then, the ammoniated brine is reacted with carbon dioxide to form successive intermediate compounds: ammonium carbonate (Equation 2) then ammonium bicarbonate (Equation 3). By continuing carbon dioxide injection and cooling the solution, precipitation of sodium bicarbonate is achieved and ammonium chloride is formed (equation 4).
Chemical reactions relative to different steps of the process. NaCl + H 2 O + NH 3 ↔ NaCl + NH 4 OH
---------------(1)
2 NH 4 OH + CO 2 ↔ (NH 4 ) 2 CO 3 + H 2 O
--------------- (2)
(NH 4 ) 2 CO 3 + CO 2 + H 2 O ↔ 2 NH 4 HCO 3
--------------- (3)
2 NH 4 HCO 3 + 2 NaCl ↔ 2 NaHCO 3 ↓ + 2 NH 4 Cl
--------------- (4)
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Chapter 5
PROCESS DESCRIPTION
Sodium bicarbonate crystals are separated from the mother liquor by filtration, then sodium bicarbonate is decomposed thermally into sodium carbonate, water and carbon dioxide (Equation 5). 2 NaHCO 3 → Na 2 CO 3 + H 2 O + CO 2
--------------- (5)
CO 2 is recovered in the carbonation step (Equations 2 and 3). Mother liquor is treated to recover ammonia. The ammonium chloride filtrate (Equation 4) is reacted with alkali, generally milk of lime (Equation 6), followed by steam stripping to recover free gaseous ammonia. 2 NH 4 Cl + Ca(OH) 2 → CaCl 2 + 2 NH 3 + 2 H 2 O
--------------- (6)
NH 3 is recycled to the absorption step (Equation 1). Carbon dioxide and calcium hydroxide originate from limestone calcination (Equation 7) followed by calcium oxide hydration (Equation 8). CaCO 3 → CaO + CO 2
--------------- (7)
CaO + H 2 O → Ca(OH) 2
--------------- (8)
Brine (NaCl) has to be treated before the input in the process to remove impurities like calcium and magnesium. If not removed they would react with alkali and carbon dioxide to produce insoluble salts contributing to scale formation inside equipment. Brine purification reactions are described in the following equations. 2+
2-
Ca + CO 3 → CaCO 3 ↓ 2+
--------------- (9)
-
Mg + 2 OH → Mg(OH) 2 ↓
--------------- (10)
Sodium carbonate formed (Equation 5) is called light soda ash because its bulk density is approximately 0.5 t/m3. A subsequent operation called densification enables this value to be doubled by crystallization into sodium monohydrate, by adding water (Equation 11) then followed by drying (equation 12). Final product is dense soda. Na 2 CO 3 + H 2 O → Na 2 CO 3 .H 2 O
--------------- (11)
Na 2 CO 3 .H 2 O → Na 2 CO 3 + H 2 O
--------------- (12)
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Chapter 5
PROCESS DESCRIPTION
5.2 Process Steps The manufacturing process consists of several discrete operations, each comprising a plant area:
Brine purification
Calcination of limestone in kilns and the production of CO 2 and milk of lime
Absorption of ammonia into purified brine
Carbonation of the ammoniated brine with CO 2 to produce sodium bicarbonate
Separation of sodium bicarbonate from mother liquid
Recovery of the ammonia using milk of lime
Calcination of sodium bicarbonate to form sodium carbonate (light ash)
Densification of sodium carbonate to form dense ash
5.2.1 Brine purification Crude brine received from the salt fields is treated to remove any impurities. Impurities such as calcium and magnesium have to be removed from brine. This operation is achieved in the brine purification area. Magnesium ions, are precipitated as insoluble magnesium hydroxide, Mg(OH) 2 , by the addition of an alkaline reagent. The most commonly used reagent is milk of lime as this is already produced in large quantity for ammonia recovery; another possibility consists of using sodium hydroxide (NaOH). Calcium ions are precipitated as insoluble calcium carbonate, CaCO 3 , by reaction with sodium carbonate. Depending upon the purification process used and to sulfate and magnesium contents, a certain amount of calcium can be precipitated as gypsum (CaSO 4 .2H 2 O). Addition of these two reagents is regulated in such a way as to reach the necessary reagent excesses for adequate purification. A sufficient reaction time of the suspension that contains suspended CaCO 3 and Mg(OH) 2 ensures a correct crystallization of the two components. Thereafter the separation of Mg(OH) 2 and CaCO 3 from the purified brine is usually achieved in a decanter or brine settler. The decanter has to be purged frequently. The purge can be treated or sent back to salt wells or cavities after treatment. A certain amount of CO 2 gas is sent in to the absorber at the same time with NH 3 but not enough to form (NH4) 2 CO 3 ,the calcium and the most of the Magnesium and all the iron salt precipitate and collect in the cone of the NH 3 absorber.
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5.2.2 Calcination of limestone in kilns and the production of CO 2 and milk of lime Theoretically, in the soda ash process, the CO 2 balance is stoichiometrically neutral. However, a CO 2 excess is needed to compensate the non complete absorption of CO 2 in the carbonation stage, in the different washers and losses in the treatment of the mother liquid in the distillation. This excess is generated by combustion of normally coke which provides an energy source used for limestone decomposition, as well as the additional CO 2. Burning of the limestone (natural form of CaCO 3 ) is carried out in a temperature range of 950 to 1100°C. The operating conditions for a lime kiln fitted to soda ash production are critically different from those used for lime production, because of the need to produce a gas with the maximum concentration of carbon dioxide for its subsequent use in the process. This is done to the detriment of produced lime purity, which will be less than that necessary in the lime industry. To improve particle sizing of limestone loaded in lime kiln, screening is carried out prior to kiln charging. In the case of soda ash plants, considering the quantities of limestone to be burned and the necessary CO 2 concentration, the energy contribution is generally provided by means of solid high carbon fuels such as coke, coal or lignite. Use of gaseous fuel leads to too low a CO 2 concentration in the gas produced making its subsequent use impossible without an expensive reconcentration unit. Raw burnt lime produced by lime kilns associated with a soda ash plant contains approximately 75 to 90% of CaO. Its direct use in the solid form is uncommon because of the difficulty in controlling an adequate feed rate of a material in which the active constituent, CaO, is not constant. By hydrating the CaO to milk of lime a better control of the alkali addition is achieved during the ammonia recovery step. Hydration of the raw lime is carried out in slakers (dissolvers) where raw lime and water flows are regulated to ensure that the alkali content of milk of lime produced is as constant as possible. This reaction is a highly exothermic. A part of the heat generated vaporizes some water which is released from the slaker vent. During the hydration, fine inert materials contained in limestone (sulfates, silica, clay, silico-alumina compounds, unburned limestone and others) can mainly be found in milk of lime. Larger particles are separated by screening, then washed and recycled or released out of the process. The unburned pieces of limestone are recycled.
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Figure5.2: Vertical shaft kiln for lime stone
5.2.3. Absorption of ammonia into purified brine Ammonia is recovered by recycling the outlet gas from the distillation plant to the absorption stage where it is absorbed in purified brine. This flow mainly contains recovered NH 3 and a quantity of CO 2 . This chemical operation is achieved in equipment that allows close gas liquid contact. Because this is an exothermic reaction, cooling of the liquid is necessary during the operation to maintain efficiency. The outlet solution, with a controlled ammonia concentration, is called ammoniacal brine. Any gas that is not absorbed is sent to washer contacted with purified brine to remove traces of ammonia before it is recycled or released to the atmosphere.
5.2.4 Carbonation of the ammoniated brine with CO 2 to produce sodium bicarbonate Ammoniacal brine is progressively CO 2 enriched (carbonated) with recycled carbon dioxide from sodium bicarbonate calcination and carbon dioxide originating from lime kilns. To ensure adequate CO 2 absorption and sodium bicarbonate precipitation, the ammoniacal brine is cooled with water. Suspension of crystals exiting from columns or carbonators is sent to the filters. Outlet gas from the carbonation towers is sent to a final washer, contacted with purified brine to absorb NH 3 traces still present in the gas before release to the atmosphere.
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There two sources of CO 2 . One is the lime stone kiln which furnishes gas containing 35 to 40 percent CO 2 the rest mainly Nitrogen, and other source is the furnace in which the sodium bicarbonate is calcined. it gets may be as high as 95 percent of CO 2 .This second portion of the gas maybe considered as circulating. In some plants these two gases are combined to in the pump house and no distinction is made. When separate flows are used at the first stage absorbs 40 vol% CO 2 gas from the kilns into the ammoniated brine stream from the absorbers, and proceeds to the point where most of the CO 2 in the solution exists as carbonate ions. Sodium Carbonate at the second stage of carbonation occurs in the Solvay towers. More kiln gas, and a recycled stream of up to 90 vol% CO 2 , are used to convert carbonate ions to bicarbonate ions. More heat is liberated, and cooling of the tower contents is necessary to assist absorption and to control crystallization of sodium bicarbonate. At the bottom of the Solvay towers, where the stronger CO2 stream enters, the pressure is approximately three atmospheres, giving maximum CO2 absorption.
5.2.5 Separation of Sodium Bicarbonate from Mother Liquid Separation of sodium bicarbonate crystals from mother liquor is achieved by means of centrifuges or vacuum filters. After washing of the cake to eliminate mother liquor chloride, it is sent to calcination. The liquid phase mother liquor is sent to the distillation sector for ammonia recovery. Where filters are used, air is pulled through the cake by means of vacuum pumps. Thereafter, this gas carrying ammonia and some CO 2 is cleaned by a washer fed with purified brine before exhausting to atmosphere. Crude sodium bicarbonate manufactured by the carbonation process is the primary output of the Solvay ammonia soda process. The bicarbonate produced in this way is the feed to the calcination stage for the conversion to the finished product solid soda ash. In some cases a small part of this crude bicarbonate, which although predominantly sodium bicarbonate also contains a mixture of different salts (ammonium bicarbonate, sodium carbonate and sodium chloride), may be extracted from the Solvay process cycle to be dried as crude bicarbonate product made without purification, by simple drying process. This crude product may find applications in some commercial outlets.
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5.2.6 Recovery of the Ammonia using Milk of Lime The filter liquor contains unreacted sodium chloride and substantially all the ammonia with which the brine was originally saturated, present as fixed and free ammonia. The fixed ammonia or ammonium chloride corresponds stoichiometrically to the sodium bicarbonate that had been precipitated. Free ammonia includes ammonium hydroxide, bicarbonate, carbonate, and the several possible carbon compounds of ammonia that decompose at moderate temperatures. Before preheating, sulfide solution may be added for corrosion protection. The sulfide is distilled for eventual absorption by the brine in the absorber. The filter liquor is preheated by indirect contact with the gases leaving the distiller. The warmed feed liquor then enters the main coke, or bubble cap filled sections of the distiller where heat decomposes free ammonium compounds and steam strips almost all of the free ammonia and carbon dioxide. The carbon dioxide free solution is usually treated with milk of lime in an external well agitated limiting tank called a prelimer. Here the ammonium chloride reacts with the milk of lime and evolved ammonia gas is vented back to the distiller. The resulting hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as distiller waste, contains calcium chloride, unreacted sodium chloride, and the excess lime, and is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains the inert of this solution. However, the waste liquors are usually pumped to settling basins where the suspended solids are deposited. The clear over flow contains dissolved salts, which are objectionable contaminants are locations where the quality of the receiving waters is materially affected.
Close control of the
distillation is required to thoroughly strip carbon dioxide to avoid waste o flame and achieve nearly 0
complete ammonia recovery. The hot (56 C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent to the absorber. One of the major achievements of the Solvay process is the high efficiency of the ammonia recycle loop. This loop circulates roughly 500 to 550 kg NH 3 /t soda ash from which the ammonia loss is less than 0.5 % of this flow rate. The purpose of this important process distillation is to recover ammonia from the ammonium chloride containing mother liquors recovered from the bicarbonate filters , centrifuges. After pre heating with outlet gas from the distiller, supported by the injection of steam at the bottom of the NH 3 stripping column, the mother liquor releases almost all its CO 2 content. Addition of
48
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alkali normally in the form of milk of lime decomposes NH 4 Cl into NH 3 which is stripped from the solution by injected low pressure steam at the bottom of the distillation column. The outlet solution contains calcium chloride together with all the residual solid materials. Ammonia recovery yield is controlled according to the permitted ammonia concentration in the released liquid. The lower the permitted value, the higher the quantity of stripping steam and therefore the global energy consumption, and the higher the cost of the ammonia recovery. This control can only be applied to a theoretical minimum ammonia level. After cooling and condensation of steam, the gaseous phase containing recovered CO 2 and NH 3 is returned to the absorption area for reuse.
5.2.7 Calcinations of Sodium Bicarbonate to form Sodium Carbonate (light ash) Sodium bicarbonate cake is heated (160 to 230°C) to achieve calcination into a solid phase light soda and a gaseous phase containing CO 2 , NH 3 and H 2 O. This gas is cooled to condense water and the condensates formed are sent to distillation for NH 3 recovery, either directly or via filter wash water. After cleaning, the gas (high CO 2 concentration) is compressed and sent back to the carbonation columns. Normally, energy needed for sodium bicarbonate calcination is provided by steam that condenses in a tubular heat exchanger which rotates through the sodium bicarbonate. The method consisting of heating externally by gas or fuel oil combustion in a rotating drum containing sodium bicarbonate is occasionally encountered. The kiln flue gas is also can be used.
5.2.8 Densification of Sodium Carbonate to form dense ash Sodium carbonate formed first is called light soda ash because its bulk density is approximately 0.5Mg/m3. A subsequent operation called densification enables this value to be doubled by crystallizations into sodium monohydrate, by first reacted with water and then gives sodium carbonate monohydrate crystals. These are then dehydrated by heating in a rotary drier or fluid bed drier.
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5.3 Product (Soda Ash) Storage and Handling Soda ash has to be stored in a dry place to avoid hydration, crusts formation or hardening. Precautions are taken to prevent contamination by other nearby stored products, and to prevent the release of soda ash dust during handling. Most of the time, sodium carbonate is stored in large capacity metallic or concrete silos. Because of high daily production in large production units ,the available total storage volume is normally less than a week production. Bulk handling of dense soda ash is easily achieved, for example, by belt conveyor. Necessary precautions have to be taken to avoid and control dust release. Handling methods are selected to minimize any particle size reduction of the product.
5.4 Raw Materials Because the production of sodium carbonate is a large-tonnage low cost operation, the plants have been historically situated close to some or all of the critical raw materials (limestone, brine, water) to reduce the transport cost.
5.4.1 Brine Sodium chloride (common salt) is extracted by evaporation of sea water. In several cases mother liquor from salt production process can be used as raw material to partially replace brine when the mother liquor has a suitable composition for the soda ash. So for our plant, we decided to brought brine or mother liquor from Puttalama soltern. In the Solvay process, the sodium chloride reacts in liquid phase (brine) which contains as much sodium chloride as possible (around 300 g NaCl/l) and is virtually saturated. This brine also contains impurities, mainly magnesium, calcium and sulfate.
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The raw and purified brine can be stored in open tanks made of mild steel, polymers, or in open lined reservoirs.
Table5.1: Raw and purified brines (typical composition ranges)
5.4.2 Limestone Basically, a high content of CaCO 3 in the limestone is an important parameter to avoid difficulties related to the limestone calcination and improves production efficiency. The cost to transport the inert part of the limestone from the quarry to the plant is also minimized. A limestone rich in CaCO 3 will not only reduce solid matters in the effluent of the distillation unit but will also, for those soda ash plants that have settling, reduce the volume of solids to be treated. Particle size distribution of the limestone from quarries is generally between 40 and 200 mm. The more homogeneous it is, the better the lime kiln will work but the greater the amount of limestone fine by-product produced at the quarry. We decided to take lime stone from Puttalam, Aruwakkalu, Eluwamkulam quarry. 5.4.3 Carbon for the Lime Kiln Coke, and rarely coal, is used in lime kilns for soda ash production due to the necessity to obtain the highest CO 2 concentration. Other type of fuels, natural gas or fuel oil, would result in a too low CO 2 concentration in the kiln gas. This is important because the kiln gas is used further in the
51
Chapter 5
PROCESS DESCRIPTION
process for its CO 2 contents. Higher CO 2 concentration enables reduction of the equipment size and ammonia losses. The particle size distribution of the solid fuel has to be appropriate in order to get a homogeneous distribution within the kiln. Constituents H 2 O [kg/t] Volatiles [kg/t] Fix carbon [kg/t] Ashes [kg/t] Net calorific value [GJ/t]
Coke 40 - 70 0 - 30 800 - 890 60 - 110 26.6 - 29.6
Table 5.2: Typical compositions for coke to the lime kiln
For the storage of coke requires no specific precaution other than normally adopted, that is open ground storage. 5.4.4 Ammonia The Solvay process for soda ash requires an input of ammonia to compensate for the inherent losses from the process. The input is generally carried out as aqueous ammonia solution (10 to 35%), or direct injection of anhydrous gaseous ammonia or by the use of an aqueous solution of ammonium bisulfide. Ammonia addition may also be achieved by the use of ammoniacal liquor from coal gas plants. Storage of the aqueous ammonia solution in achieved in steel tanks. Specific precautions have to be taken during works on the equipment, because some mixtures of air and NH3 are explosive when in contact with a heat source or flame. When liquefied NH3 is stored, additional specific preventive measures are required for safety. 5.4.5 Various additives In addition to the major raw materials there are a number of miscellaneous raw materials which may be added to the process for their various physical attributes: compounds to aid gas absorption, compounds to avoid scaling, corrosion inhibitors, settling aids. These all may have minor potential environmental
52
Chapter 5
PROCESS DESCRIPTION
5.5 Utilities 5.5.1 Steam Steam is an important energy vector in the manufacture of soda ash by the Solvay process both because of its mechanical capability (to drive a range of machinery including turbo generators, gas compressors, vacuum machines,etc…) and as a thermal energy carrier for distillation and drying. A range of pressures and temperatures are therefore required to meet the process needs and to maximize the energy efficiency of the process. LP steam is primarily used for ammonia distillation. The steam process consumptions lie in the range of: 1300 to 2400 kg/t soda ash for recovery of ammonia (depending of the applied process): The correctness of those values can be checked by material balance calculations.
5.5.2 Process water Basically, the main consumer of water (apart from brine) is the slaker where the lime coming from the lime kilns reacts with water to produce milk of lime. The quantity is in the range of 1.9 to 2.4 m3/t soda ash. The quality requirement for this water is not high. It is normally taken at the outlet of the cooling water system (warm water). Soda Ash Process other water needs, soda ash require higher purity (absence of Ca and Mg salts) for different uses as additional wash water to wash the sodium bicarbonate cake at the filter outlet. The above quoted process water needs exclude the water entering the process in the form of brine and steam condensate mainly partially condensing in the distillation tower.
5.5.3 Cooling waters Many unit operations of the soda ash process are exothermic. The cooling agent is normally cooling water in open or closed loop. The closed loop requires a cooling tower with special water treatment. The open loop is the once-trough system using for example river water. The total flow of cooling water required for,
53
Chapter 5
PROCESS DESCRIPTION
Lime kiln gas treatment
Carbonation towers
CO2 compression
Distillation
Absorption
Calcination
5.5.4 Electricity The gas compressors can be driven by either electrical motors or steam turbines, leading to a range of electrical consumption between 50 and 130 kWh/t soda ash. The necessary consumption for compression is also linked to CO2 concentration. Cooling water consumption is minimized by managing different cross flow heat exchangers.
5.6 Energy saving in the process Within the plant itself, reductions of energy losses are obtained by favouring energy transfer between flows at different thermal levels by the installation of heat exchangers and flash vessels for hot fluids, several possibilities to reduce the energy consumptions are possible as far as the technology and the economics allow. At the level of the use of primary energy, the initial design stages have to verify the interest of combined heat and power generation to improve the generation efficiency of electricity since the soda ash plant acts as the final stage condenser. Primary energy efficiency is outside the scope of this document. Energy savings are achieved at two levels, namely,
Heat recovery
Minimization of consumption.
54
Chapter 5
PROCESS DESCRIPTION
5.6.1 Heat recovery The recovery of heat has been gradually improved throughout the history of the process by optimizing energy fluxes of different thermal levels contained in gas and liquids flowing through the process. Heat generated from the system is used to preheat different streams such as,
Pre heat the air before enter in to the kiln by using the heated CaO to reduce the coke consumption.
Use kiln flue gas for calcinations of Sodium bicarbonate in the dryer, further the CaCO3 feed also pre heated by using this remaining heat flow.
The inlet stream in to the kiln is heated by using exit stream from the striping column.
The heat absorbed cooling water is used for the shaking of the lime.
Mother liquor from the filtration to the recovery of ammonia by the distillation off gas.
5.6.2 Energy Minimization The following techniques may be used to minimize energy consumption.
Careful control of the burning of limestone and a good choice of the raw materials allow a reduction of the primary energy necessary for the operation.
Improvement of process control by the installation of distributed control systems.
Reduction of water content of the crude bicarbonate by centrifugation before calcination to minimize energy need for its decomposition.
Back-pressure evaporation for calcium chloride liquors.
Equipment lagging, steam trap control and elimination of energy losses.
55
Chapter 5
PROCESS DESCRIPTION
Soda ash process major Input/output levels
Table 5.3: Soda ash process major Input/output levels
56
5.7 Process Flow Diagram
Compressor
Purified brine
Waste gas CO2 from dissociation
Water
Flue gas
Gas Cooler Waste gas
C on d w en at s er ed
Recovered gas
Drier
Gas washing with purified brine Recovered gas
CaCO3
Cyclone
Brine
Preheated CaCO3
Ammonia recovery unit Makeup NH3
NH3 Absorption Unit
Lime Kiln
Coke
Carbonator Unit
End Product
Preheated Air
Air preheater
NaHCO3 Solution
Hot Air Cool Air
Pump Cooled CaO
Centrifugal fan
Waste water
Filter Ammoniated brine water Filtrate
pump
shaking of lime Vaporizes water
Figure 5.3: Process Flow Diagram
Excess water
5.8 P & I Diagram
Figure 5.4: Pipe and Instrumentation
Chapter 6
SITE SELECTION & PLANT LAYOUT
CHAPTER 06
SITE SELECTION & PLANT LAYOUT
Selecting a suitable site is the immediate step after process is selected. It’s a matter of mainly the raw materials, market, infra structure, water resources and impact on an adjacent ecologic systems. Process plants are complex facilities consisting of equipment, piping systems, instruments, electrical systems and control systems. The design, engineering and construction of process plants involve multidisciplinary team effort. Plant layout and design of piping systems constitute a major part of the design and engineering effort. The objective is to design safe and dependable processing facilities in a cost effective manner…….
Chapter 6
SITE SELECTION & PLANT LAYOUT
6.1 Introduction The basis for the site of the proposed soda ash plant, according to the feasibility study of Chapter 2 can be taken as availability of raw materials, geology, market, infrastructure, water resources, cultural /social impact, ease of waste discharge and the impact on the adjacent ecological systems. Also the process selected plays a major role in the location of the plant. The suitable location for the proposed plant has been selected as a piece of bare land in Karadipuval near Puttalam (Figure 6.2). The facts that had led to the selection of this particular site for the proposed soda ash plant are considered in the next section. 6.2 Site Selection Considerations •
The process has been selected as Solvay process which uses concentrated brine and limestone to produce soda ash. Therefore the availability of these raw materials is important in the site selection. Brine is present all around the country. Since saturated brine is required the ideal option is to place the plant close to a saltern. Presently salterns are present at Puttalam, Muturagawela and Hambantota. Makeup ammonia for the plant will have to be imported. CO2 can be generated onsite by burning limestone. Limestone is available in Sri Lanka in 4 forms. Miocene limestone is present in the land strip stretching from Puttalam to the Jaffna peninsula. Dolomite reserves are present to the middle of the country. Areas well known in this aspect is present in the Matale district. Also Calcium Carbonate can be found in the form of coral reefs in various parts of the costal belt in Sri Lanka though this is not an environmental friendly and feasible option. Also sea shells that is present in the coastal areas is a good form of Calcium Carbonate but this is not a viable and secure raw material source for a soda ash production facility of the proposed scale. The distribution of the limestone resources in Sri Lanka can be seen in Figure 6.1. Therefore according to the availability of raw materials placing the plant at Puttalam or Mutragawela is suitable. But Mutragawela is not an option because of the present security threat.
•
When we consider the market availability in the Puttalam area no huge demand exists for soda ash. But there is considerable potential that many industries will be built in the near future in this area because of land availability and climate.
•
The population density of the area is very low. This has its advantages as well as disadvantages. There amount of people affected by the plant would be less because of less population while there would be difficulties in finding manpower for the construction phase and the maintenance of the plant. But this problem can be dealt with by recruiting workforce from other areas and developing a residential workforce.
Chapter 6
SITE SELECTION & PLANT LAYOUT
•
The dry and sunny condition that is present throughout the year in this area is extremely suitable for a process plant because loss of heat by cooling of process due to rain is avoided. This also saves energy and makes it possible to obtain consistent product quality.
•
The geology and topology of the area has been assessed as being suitable for process plants because of the solid soil condition. From the feasibility study done to assess the feasibility of Norchcholai coal power plant it has shown that the area around Puttalam is one of the ideal areas to construct huge plants and factories.
•
The possibility of a natural disaster like an earthquake, flood, etc occurring in this area is very low. This is great advantage because the consequences of such an event will be very disastrous for the plant.
•
When we consider the site at Puttalam a secure security situation has been prevailing for several years. Also a tight security parameter presently has been set in the area because of the presence of the Palavi air force base, and the security would be further strengthened once the Norochcholai coal power plant has been commissioned. Therefore it can be said that the security threat or risk is minimum.
•
There is a considerable amount of infrastructure development in the area. The port that is been developed to assist the Norchcholai power plant will be of assistance in the process of constructing the soda ash plant at the proposed site.
•
There is a sound network of roads in the area. These roads have withstood the constant movement of container loads of cement and raw materials to and from the Holcim Cement plant, salt laden trucks and food containers moving to the North.
•
The Puttalam lagoon has been naturally sited to assist a network of salt water canals. Most of these canals lead to the salterns in the area. The white salt piles can be seen in close proximity to the proposed land in figure 6.2. Also a canal network has been highlighted in light blue in the diagram. The tanks with the mother liquor is just south of the proposed area.
•
Other infrastructure requirements like municipal water for general activities are available in the area. Once the Norochcholai coal power plant is complete high tension lines from the plant will
Chapter 6
SITE SELECTION & PLANT LAYOUT
pass near these areas and connect to the National grid. Hence the capital cost that has to be incurred in the event of power line erection in the construction phase will be less. •
The plant will require a constant supply of limestone from a quarry at the North. The most viable option would be to transport limestone via rail. Limestone for the Holcim cement factory is brought through by rail carriages through a network of railroads from its quarry at Aruwakkaru. Since the cement factory is present farther to the south of the proposed land as seen the figure 6.2, the rail line from the quarry can be used to transport limestone to the soda ash plant from a quarry at the north.
•
As mentioned in the technical feasibility the plant will require a source of process water. There are several water streams flowing through the area which can be utilized. But the proposed site has the option of using on-site water from the water pond that has been highlighted in figure 6.2 by a red circle.
•
Another great advantage of the selected site at Karadipuval is the availability of land for expansion. There are several pieces of bare land across the main road to the west and adjacent to the North and eastern boundaries of the proposed land. Also the availability of land can be used to aid in the establishment of an effective waste disposal system.
•
Because the area is gradually transforming into an industrial area rather than an attractive residential area the cost of land is low. Therefore the initial investment and cost for land in the event of an expansion is low.
•
The proposed land has a main road on the western perimeter while it has remote roads on the northern and the eastern boundaries. This is of great advantage because the access to the plant will not be restricted.
•
A positive aspect of the proposed site is that it is not situated close to vegetation or agricultural land. This is important because the impact on environment in the event of an unforeseen incident is low.
Chapter 6
SITE SELECTION & PLANT LAYOUT
Figure 6.1- Mineral Map of Sri Lanka
Chapter 6
SITE SELECTION & PLANT LAYOUT
Figure 6.2- Geographical map of proposed land
Chapter 6
SITE SELECTION & PLANT LAYOUT
6.3 Plant layout
Security Post
a
a
a
a
Office Area
Security Post NH4 Recovery Unit
NH4 Absorption Unit
Gas Cooler
Gas washing with brine
NH4 Storage
Brine purifying unit
Brine storage area Control Room
Filter
Carbonator Unit
Cooling Tower
Na2CO3 Storage Slaker of CaO
Product packing
Product Storage
Dryer
Boiler Room
CaCO3 Miller
Kiln CaCO3 Crusher Water Source
Crushed CaCO3 storage area
Security Post
Figure 6.3- Plant layout
CaCO3 Unload
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
CHAPTER 07
ENVIRONMENTAL IMPACT ASSESSMENT
Environmental impact assessment is the process of identifying, predicting, evaluating and mitigating the biophysical, social, and other relevant effects of development proposals prior to major decisions being taken and commitments made. This may include an assessment of both the short and long term effects on the physical environment, such as air, water and noise pollution; as well as effects on local services, living and health standards, and aesthetics.....
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.1 Gaseous Effluents 7.1.1 Particulate Dust Dust is emitted from the soda ash production in limited quantities, arising from the following steps:
handling of mineral raw materials (coke, limestone) as diffuse sources
limestone conversion in kilns, but in limited quantities or during abnormal operation since all the gas is collected to a washing cooling step and thereafter is used in the carbonation stage in a liquid solution
handling of soda ash and densification of light ash (hydration and dehydration) to produce dense ash
during the handling of these products
It is common to use bag filters or wet scrubbers which significantly reduce the levels of dust emitted to atmosphere. Roughly the dust emitted is around 0.10-0.15 kg of dust/t soda ash, and represents a typical quantity of 50-75 t/year. The composition of the dust reflects the composition of material handled, those are,
C from coke
CaCO 3 , Al 2 O 3 and SiO 2 from limestone, sand and clays
CaO from burnt lime
Na 2 CO 3 and NaHCO 3 from soda ash and sodium bicarbonate production and transport
The most stringent environmental regulations in western countries require limit values of 40 or 50 mg/Nm3 for atmospheric emission of dust.
7.1.2 Carbon dioxide and monoxide During the burning of CaCO3 to CaO inside the limekilns, CO and CO2 are produced from the combustion of coke and from the decomposition of limestone. A normal Solvay process needs an excess of CO2 above that which is stoichiometrically required. Some of the excess is required to compensate for non ideal absorption of CO2 in the carbonation towers. Carbonating towers also have an outlet for the discharge of gases that have not reacted in the process. This gas is cleaned with brine in a washer to recover NH3 and possibly H2S, if present, and to
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
reintroduce these components back into the process, while CO2, CO and other inert gases pass out to atmosphere. 7.1.3 Nitrogen oxides NOx are produced inside the kiln by oxidation of nitrogen during the combustion. Since the temperature inside the kiln are moderate (up to 1100°C), the formation of NO x is rather limited. Measurements in some plants indicate concentration after washing less than 500 mg NOx/m3. 7.1.4 Sulfur oxides SOx are produced by the oxidation of sulfur containing compounds in the limestone and coke. 7.1.5 Ammonia The soda ash production emissions of NH 3 represent only 0.2- 0.4 % of all emissions. The main atmospheric emissions containing ammonia originate from the bicarbonate precipitation and filtration stages of the process.
From precipitation of bicarbonate in carbonation tower after cleaning in a tower washers
From filtration of bicarbonate, after cleaning in filter washers
In addition they are a number of diffuse losses of ammonia from filters, bicarbonate conveyors and from the handling and processing of the distillation effluent.
The emissions fluctuate due to,
Performance of the stripping columns and operating parameters control (height, steam injection, temperature control, monitoring of outlet concentrations)
Disturbances in the mother liquor feed (flow rate, composition)
Normally the emitted gaseous load is on average of 0.55kg NH 3 /t soda ash but the spread can be very large, from 0.09 up to a typical range of 0.6 to 1.5 kgNH 3 /t soda ash from the production unit, representing a release into the environment of 30 to 750 t/year for a 500 kt/year soda ash unit. Considering the turnover in the process, the loss rate of ammonia in the process is therefore very low.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.1.6 Hydrogen sulfide In some plants H 2 S may be added as a corrosion inhibitor, in the form of sodium hydrogen sulfide. Emission sources are from the tower gas washers and H 2 S is typically controlled at maximal emission levels of 5 to 15 mg/Nm3.
7.2 Gaseous Effluents Management 7.2.1 Calcinations of Limestone The calcination of limestone produces CaO and CO 2 and is designed to maximize the CO 2 content by minimizing the presence of oxygen in the outlet gas. A conventional ammonia soda process produces about 30 % more CO 2 than theoretically needed and it is necessary to purge some of the CO 2 produced to the atmosphere.
Further excess CO 2 may be beneficially used in sodium bicarbonate production. Any surplus CO 2 is vented as kiln gas to atmosphere. If there is an associated sodium bicarbonate plant then this gas wasting can be reduced or avoided. But we haven’t such plant. So by optimizing the process we should reduce the amount of excess CO 2 .
CO gas is virtually inert through the process. All CO produced must therefore be vented to the atmosphere either at the kilns or through the carbonation tower after gas scrubbers.
Furthermore, provided the dispersion of CO and CO 2 is adequate and the stack construct according to the standard conditions, no local impact on the environment or health are expected or experienced.
Atmospheric emissions of SO 2 from the lime kilns are low. Because the concentration of sulfur in the fuel (coke) and the limestone employed is very low.
The formations of SO x are limited due to low sulfur content of fuels used and some auto purification reactions in the lime kilns. The small amount of SO 2 produced tends to be fixed by CaO and CaCO 3 as CaSO 4 furthermore ,SO x in the kiln gas sent to the process are absorbed.
Before discharge to the atmosphere, kiln gas may be cleaned and generally cooled at the same time by washing towers.
Considering the type of release the very low persistence of ammonia into the atmosphere due to its high solubility in rainwater and its rapid turnover into the ecosystems by biological nitrification/ denitrification mechanisms, the local or regional environmental impact trouble is to be considered as very low
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
Alternatively, gas cleaning systems (normally bag filters) can also be used to collect the dust as dry material. If dry cleaning is used, residual material is made of fine particulates containing limestone, lime, coke. This can be collected separately and may be disposed without further treatment. However this type of gas cleaning is difficult to operate because the lime kiln gas may be too hot for the filtering media.
7.2.2 Precipitation of Crude Sodium Bicarbonate Outlet gas from the carbonation columns is subjected to a cleaning process with brine in a packed or plate washer to recover NH 3 and possibly H 2 S and recycle them into the process via the feed brine. Washers may have an optional final water washing section to minimize emissions. This type of equipment has been designed to meet the specific needs of the process and to allow efficient recycle of valuable raw materials. Other way round the emissions to the atmosphere also is reduced.
7.2.3 Filtration of the Bicarbonate Air containing ammonia from the filtration step of crude sodium bicarbonate undergoes a cleaning process with brine in a washing tower to recover NH 3 and reintroduce it to the process.
7.2.4 Conveying and Storage of Soda Ash Storage of light and dense soda ash is achieved in large silos equipped with dedusting systems, which keep the products dry and isolated and prevent dust emission to the atmosphere. Because of the nature of conveyers, elevators, air lock valves, etc. the soda ash process typically uses a range of high efficiency bag filters to separate dust from vent gas streams.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.3 Liquid Effluents The sources of liquid effluent from the soda ash process are typically,
Wastewater from the distillation (after treatment).
Wastewater from the brine purification.
Cooling waters from lime kiln gas washers.
Cooling water in the CO 2 compression loop.
Cooling water of the absorption and distillation towers and calcinations.
7.3.1 Wastewater from Distillation Flow rates and concentrations for the major components present in the liquid outlet of distillation. These indicative ranges represent distiller effluent prior to any form of treatment and should not necessarily be considered as levels or concentrations emitted to the environment.
Table 7.1: Rough concentrations of the waste water from the distillation column
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
Some additional low quantities of calcium sulfate (CaSO4), calcium hydroxide (Ca(OH)2) and trace elements are also present. Traces of heavy metal originating naturally from raw materials are related to limestone, coke and salt composition; the process in itself does not add heavy metals. Given the alkaline nature of wastewater emissions, metals are in major part insoluble and are included as part of suspended solids. According to its composition, the suspended solids are classified as nonhazardous.
7.3.2 Wastewater from Brine Purification Brine purification wastewater is basically brine with suspended precipitated CaCO3 and Mg(OH)2 in variable proportions according to the nature of the salt deposits (calcium and magnesium ions coming naturally from the original sea water). These solids can be treated separately or can be disposed together with liquid effluent from the distillation unit for solid removal and treatment.
Table 7.2: Typical concentration wastewater from brine purification
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.4 Liquid Effluent Management Wastewater discharge treatment is the environmental aspect in which significant differences arise from one production plant to another. Apart from cooling water, aqueous emissions of soda ash production plants are characterized by a high concentration of suspended solids and dissolved salts. These solids and salts are unreacted lime stones and salts of natural origin. Suspended solids and dissolved salts originate from three different steps of the process.
Brine purification
Ammonia recovery
Cleaning of CO2 originating from calcination of limestone
In most soda ash production plants, brine purification effluent is discharged jointly with effluent originating from the distillation unit. The typical composition varies according to raw materials quality. However different treatment schemes have been developed according to geographical location of the production plants and the requirements of the local regulatory authorities.
Options available for treatment of these effluents are:
Direct discharge of raw effluent, with or without partial removal of some fraction of the solids, and with or without preliminary pH adjustment
Indirect discharge of waste water after removal of suspended solids and with or without preliminary pH adjustment
Further treatment to produce by-product such as CaCl 2
7.4.1 Liquid Effluent Treatments According to production plants location and raw materials deposits, two basic lines are established for the suspended solid treatment.
Total dispersion
Separation of the suspended solids and liquid dispersion.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.4.1.1 Total Dispersion Total dispersion is employed when production plant is close to the sea or high flow rivers. We decided to establish our plant close to the sea and we can use this method. This technique ensures that the solid material is incorporated with the natural sediments of similar composition. Chlorides and other soluble salts present in the liquid fraction are dispersed in a medium (in the sea). The environmental impact is minimal due to the similarity between the chemicals present in the receptor medium and in the discharged material (chloride, sodium, calcium as ions).
7.4.1.2 Separation of the Suspended Solids and Liquid Dispersion Separation of the suspended solids and liquid dispersion has generally been used where there is no suitable environmental medium to allow for total dispersion. This method involves the physical separation of liquid and solid phases. The liquid phase is then discharged to a local watercourse with or without pH adjustment as appropriate and solids are used to build up the settling basin itself. The underground deposition of the solids is carried out when salt deposits are found near production plants and when deposit characteristics and the salt extraction system enables it.
Settling ponds The clarification by liquid/solid separation large quantities of suspended solids in aqueous effluents is usually achieved in settling ponds. Fines of lime stones or solid particles settled in the basin can be used to build up the walls as the deposit in the basin accumulates The aqueous outfall is collected at several points through separators and drainage pipes to a secondary channel collecting all outfalls of drainage.
The location of settling ponds depends on several factors.
Area available for permanent long term land occupation
Distance between factory and final discharge point
Underground geological and hydro geological characteristics
Landscape impact.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.4.2 Liquid Effluent Discharge Management The impact of direct discharge of the liquid phase containing soluble salts in rivers is linked to the flow rate of the receiving rivers, the fluctuations of it and the inherent qualities of the water including its natural salinity.
Management of equalization basins The management of buffer equalization basins can be optimized by continuous monitoring of flow rate and chloride concentration in the receiving water, after complete mixing, controlling the daily discharge to be allowed.
Adjustment of pH The typical value of pH of raw effluent is higher than 11.5 due to the alkalinity of OH ions from Ca(OH)2. Theoretically the pH adjustment of such an effluent can be achieved by,
Mixing, in open channels or basins, with natural or raw waters containing dissolved bicarbonate.
Reacting with gas containing CO2 in pH adjustment columns.
Other pH adjustment mechanisms if acid solutions or acids wastewaters are available.
In practice, the pH adjustment of soda ash wastewater is usually achieved by mixing with natural water according to the following mechanism: Ca(OH) 2 + Ca(HCO3) 2 →
2 CaCO 3 .+ 2 H 2 O
Wastewater is mixed with available natural water (cooling waters after use or surface waters: river, channel, lake, sea or underground water,) in a typical ratio natural water/wastewater at 5 to 10:1. The formed CaCO3 particles are discharged or settled in ponds. Appropriate hydraulic retention time for settling in quiescent waters is usually 6 to 8 hours. Periodic removal of settled particles is achieved. This method offers numerous advantages: pH adjustment mechanism is efficient and reliable; no consumption of supplementary reactants is needed. The settled particles are inert.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.5 Solid Effluents The typical solid wastes produced by the soda ash process
Fines of limestone
None recycled stone grits at slaker
7.6 Solid Materials Management 7.6.1 Limestone Fines After crushing, the limestone is passed through a sieve in order to remove the fine gravel fraction which could be a cause of plugging and bad distribution of combustion air in the lime kiln. The fines composition is 85% to 97% CaCO 3 with impurities of sand, clays ( SiO 2 , Al 2 O 3 ) depending on the limestone composition in the deposit Since the composition of the limestone fines is the same as or close to raw limestone, this material can be used without any restriction for civil engineering works and filler material for roads, highway, and for cement manufacturing. Within the selected area of our plant the cement manufacturing plant (Holcim) has located and we can sell it to them. In some existing soda ash factories it is mainly used for internal purposes (walls of the dikes, roads in quarry operation). Higher specification would require a further separation of gravel and clay material by water washing.
7.6.2 Grits from slaker Some under burned stone, due to imperfect conversion reaction inside the kiln, are drawn with the lime to the slaker. The coarser unburned stone can be separated at the slaker and is sent back to the kiln. The smaller sizes of unburned stone are rejected and the very fine material is suspended in the milk of lime and simply passes through the distiller and out in the distiller waste liquid. The unburned stone contains most of the impurities and pieces of silica present in the limestone feeding the kiln. The composition of grits from slaking operation enables recycling of this product to the lime kiln, reuse of it as soil conditioner for pH correction or as filler for concrete. A milling step is required to adjust the particle size distribution, as fine as possible for soil conditioning or as regular as possible for concrete incorporation.
Chapter 7
ENVIRONMENTAL IMPACT ASSESSMENT
7.7 By-Products Recovery and Reuse By-products recovery and reuse can be done as an alternative of the total discharge method. The manufacturing of soda ash by the Solvay process enables two main co-products.
Calcium chloride
Sodium bicarbonate
7.7.1 Calcium Chloride Outlet liquor from the distillation unit contains primarily CaCl 2 in solution in quantity corresponding to sodium carbonate production. By treating this liquid by removing suspended solids and dissolved sodium chloride, a pure solution of calcium chloride can be obtained. By successive concentration steps in evaporators, the solution is concentrated from 11% to 40% and by further concentration up to around 78% CaCl 2 , to produce a white solid hydrated flake, which has to be dried, stored and it can be used for several applications. The recovery of CaCl 2 dissolved in wastewater from distillation requires a large amount of energy mainly in the form of steam to concentrate the diluted solution to solid CaCl 2 . Moreover, the market for CaCl 2 is also limited. So the CaCl 2 recovery units operating in soda ash plants has progressively decreased.
Chapter 8
SAFETY MEASURES
CHAPTER 08
SAFETY MEASURES
Safety first is a common set of words that you can see any where around. As far as the production industries are concerned, physical, chemical and operational safety are some the major issues which should be analyzed and monitored thoroughly for the whole plant and equipment wise well.....
Chapter 8
SAFETY MEASURES
8.1 Plant Safety Industrial processing plant may lead to accidents that unexpectedly interrupt the work process carry the potential for damage, injury - or even death. Hazardous conditions also can cause loss of material or property or decrease a company's production capability. But many of those accidents can be avoided all together by implementing proper safety program in the plant and following through with it. Safety program of our caustic soda plant should include general safety practices which are common to all kind of plants and unique safety practices due to its process, equipments and materials. Also safety program should include plans to fight accidents when it occurs.
8.2 General Plant Safety Plant location is important in safety point of view when considering the impact of the environment to the plant and its activities. Plant should be located at a place where inhabitants are interested in its success, the product can be sold profitably and production is in minimum cost. Selecting the location and reasons for the selection is described in detail in Chapter 6. Plant layout is a fundamental of every plant which strongly linked to safety aspects. Layout planning plays a key role in the inherent safety performance of process plants since this design feature controls the possibility of accidental chain-events and the magnitude of possible consequences. In order to obtain safe layout to the plant following points should be considered. Plant layout is described in detail in Chapter 6. •
Considering safety practices spaces between different areas and equipments need to be taken in to account when deciding the layout.
•
Proper interconnecting paths should be included in the layout.
•
Access points, walking ways and emergency exits need to be clearly indicated.
•
There should not be hard to access areas in the plant.
As lime kiln handle a temperature around 1000C it should be positioned away from the other equipments. Common safety measures for the plant are as following. Visual indicators should be used in appropriate places in order to express information, directions and warnings. Each equipment including vessels, pumps, heat exchangers, distillation columns, furnaces, valves ect. And sub components of those) should be labeled and coded in order to identify easily. There should be isolation valves for equipments in order to use in maintenance or
Chapter 8
SAFETY MEASURES
emergency and safety valves should be used so that accidents due to pressure increment can be avoided. Identified risky areas and hazarders areas should be isolated and indicated through standard indicators (warning signs). If any maintenance is going on or if there any special tests going on (ex: Xray test) those areas also need to be indicated with warning signs. In maintenance standard safety procedures should be followed. Rotating equipments and sharp edges should be covered appropriately in order to prevent accidents. Hot surfaces should be labeled with warning signs. All the parameters which related to safety (vibrations, noise, efficiency of equipment, and compositions of air, pressures in pipelines & vessels ect.) of the plant should be recorded as practical and analyzed to identify trends. Measuring instruments should be standardized time to time in order to maintain the accuracy. Measuring equipments should have proper positioning and lighting in order to get the reading easily and accurately. Rotating equipments and moving parts should get a special care. Those should be lubricated and tested regularly to make sure the long life of the equipment and safety. Inspections should be done time to time in order to identify material and energy leaks and should take corrective actions. Electrical wires should have a proper and full insulation. Automated alarm system should be implemented in the plant which activate out of the given safe region, so that it announce hazards situations when they occur, that may help to reduce the damage. Automated alarm system can be integrated with isolation valves and safety valves to assure more safety in the plant. Those equipments should be standardized time to time in order to keep the accuracy. Proper drainage system is important for safety in disposing materials. To avoid static electricity all electrical equipment and metal components should be earthed. Buildings, structures, supporters and equipments should have a proper strength to barer its load at work. High platforms, staircases and ladders should be in the standards and should be properly maintained. Highly toxic or flammable or radioactive materials should be stored in special areas. Special areas inside the plant should be separated by appropriate arrangement, if those areas need special authentication to enter, doors/gates and fences can be used. Whole plant or the land should be protected by appropriate fences and security system. Emergency showers and eye wash bottles should be provided. Instructions about personal protective equipments should be worn in each area should be displayed. Mobile phones, lighters and smoking will be prohibited in the plant area to reduce the risk of accident.
Chapter 8
SAFETY MEASURES
8.3 Personal Safety There employees should be trained and audited continuously about the proper use of personal safety equipments and safety practices. Employees should be promoted to behave safely. Commitment of top management and employees to the safety program is vital to its success. Personal Protective equipment (Safety glasses, safety helmet, Earplugs, gloves, overall, boots, safety shoes, safety belts) must be worn in the plant according to the job the employee involve and the area he/she work. Loose clothing or jewelry should not be worn when operating machinery. All guards provided must be in place before machine operation. Always machine should be turn off before adjusting, cleaning, lubricating or repairs. Aisles, doors, fire extinguishers or electrical power panels should not be blocked. Given instructions should be followed in disposing materials. No food or drink is permitted in the plant. Employee should not be drunk during the work hours. Seat belts must be worn by the driver and all passengers of company owned or leased vehicles.
8.4 Safety Aspects of Equipments 8.4.1
Lime Kiln
The Kiln handles high temperature and high amount of heat in its operation. Because of the high temperatures, firing a kiln also does release volatiles into the air, many of which are toxic. The kiln should have a proper insulation system which reduces heat transfer to the environment. It may help to improve the kiln efficiency and reduce the adverse effect on environment. Even when the kiln has more than adequate insulation, its outer surface can become hot enough to seriously burn someone if touched or brushed against with bare skin. •
Kiln mitts or gloves should be worn when handling any part of a kiln (other than a control panel) while it is firing or cooling. Even after power or fuel has been turned off, kilns will remain hot for hours. Do not open or touch until fully cooled.
•
Dark glasses from a safety supply house are recommended when looking into kiln spy holes. These protect your eyes from the radiant heat. (Please note that regular sunglasses are inadequate for this purpose and may actually melt.) Protective glasses may also allow you to see your cone packs more clearly. The kiln should properly vent to the outside. Every firing releases gases which will be irritating
to the body; they may also be toxic or even lethal if safety measures are not followed. •
Follow the kiln manufacturer's instructions and use a licensed heating, ventilation and airconditioning (HAC) contractor for proper installation.
Chapter 8
SAFETY MEASURES
•
HAC contractors have equipment to accurately test the adequacy of the system’s ventilation. Light a match in front of the kiln's hood. If the system is working properly, the hood draw should blow the match out.
•
Always turn on your kiln hood or vent prior to loading to prevent ceramic glaze dust exposure. Gases given off by kilns when firing can cause respiration problems. This is possibility is
heightened if it is a reduction or salt firing. Specific gases to be aware of are: •
Carbon dioxide is given off during any fuel-burning firing. Overexposure leads to blood oxygen levels falling, a decrease in hearing and pulse rate, and a rise in blood pressure.
•
Carbon monoxide is released during reduction firing. Exposure can lead to headache, dizziness, fatigue, and drowsiness. Carbon monoxide can be lethal.
•
Sulfur dioxide can be released when firing soluble metal salts; it is a strong lung irritant.
8.4.2
NH3 Absorbing Unit
As the ammonia absorbing tower handles brine ammonia and carbon dioxide, which create favorable condition to corrosion, the contact surfaces should have the property of corrosion resistant. Sprinklers and the tower should be able to withstand the load and safety valves should be fixed in order the act in pressure increment. There should be a proper drainage system to remove the liquid in order to empty the column. Column should be washed and purged with steam before entering for inspection or repair. Ammonia reacts corrosively with all body tissues so it is dangerous to allow contaminate air with ammonia. Even liquid output of the Ammonia absorption unit can release ammonia to the air when in expose to the environment. •
Before entering to the area gas tight chemical goggles or full-face piece respirator, gloves made of any suitable material should be worn.
•
Level C respiratory protection with full face piece or self-contained breathing apparatus should be available for emergency use. Air purifying respirators must be equipped with suitable cartridges. As ammonia has a flammable property the tower should be separated from high temperature
(especially kiln) to reduce fire risk.
Chapter 8
SAFETY MEASURES
8.4.3
Carbonator Unit
A safety aspect for the carbonator unit is much similar to the NH 3 absorbing unit because both units handle similar chemicals and similar operations. Carbonator unit has a cooling system which improves the efficiency of absorption. If the cooling water fails to supply the operation in the carbonator should be stopped in order to prevent over heating due to exothermic carbonization reaction. 8.4.4
NH3 Recovery Unit
Same as the NH 4 absorption unit and carbonator unit, the NH 4 recovery unit handles similar set of chemicals. Unlike absorption in NH 4 absorption unit desorption occur here. So the safety aspects for the units are also similar. NH 4 recovery unit has a heating unit which directly injects steam in to the column to provide required temperature to carry its operation. Safety steps should be followed in handling steam.
8.4.5
Drier
Dryer handles high temperature level (around 200C) in its operation which can lead to instant fire if supply oxygen level goes up. So oxygen level should be monitored and CO 2 purging should be fixed to use in an emergency. It will be very helpful if CO 2 purging is automated with oxygen set level. Air streams flow in the dryer is in high temperature and very low (theoretically zero) in oxygen so it is dangerous to directly contact the flow. Appropriate actions should be taken to prevent such situations. Workers should be trained to deal with dryer. Dryer room should have proper ventilation. Pressure protections should be there to withstand pressure fluctuations inside the dryer. As the dryer handles high temperature in its inside, so there should be a proper insulation system. But although there is insulation the outer surface will be hot, workers should be informed not to contact outer surface of dryer and bare skin.
Chapter 8
SAFETY MEASURES
8.4.6
Storage Vessels
8.4.6.1
Ammonia
If Ammonia store in insulated tanks those should be refrigerated and stored in low-pressure tanks. Generally structure should be fire resistant, separated from work areas. It is important to keep storage area dry and cool and away from steam pipes, heating devices, and tanks containing flammable liquids. If Ammonia stored outside in an uninsulated tank must be painted with reflective paint, which controls rust or corrosion, and helps keep the temperature and internal pressure lower during hot weather. 8.4.6.2
Soda ash
Bag Storage Soda ash tends to cake when exposed to moisture or the atmosphere for a long time. Dense soda ash does not cake as readily as lighter density products. Typically, the soda ash layer at the bag surface will begin to dissolve in a bag exposed to adverse conditions. Caking occurs because not enough water is present to dissolve the soda ash completely. Because caked soda ash has less surface area than the powdered product, the caked product does dissolve readily. Normal warehouse storage of soda ash seldom presents caking problems, especially if the oldest stock is used first. For best results, soda ash should not store in a damp or humid place or where there is excessive air circulation. Warehouse floors should be dry, smooth, free of breaks and able to support concentrated loads, especially when bags are tiered or handled with forklift trucks (nearly the entire weight of a loaded forklift falls on the two front wheels). Table 6-1 lists approximate floor areas, space requirements and floor loadings for warehousing soda ash in bags. 8.4.6.3
Baking soda
In between Carbonator and filter there is a NaHCO 3 storage tank. NaHCO 3 is in sludge state in the storage. When baking soda is stored as slurry, it may be convenient to store it in a tank. 8.4.6.4
Calcium Carbonate and Calcium Oxide
Calcium Carbonate and Calcium Oxide can be stored in dry sheltered open yards. But material should not be subjected to humidity or rain, especially Calcium Oxide (it react with water). if there is a risk of contaminating with water it is better to store I store rooms.
Chapter 8
SAFETY MEASURES
8.4.7
Pipelines
All the pipelines should be inspected continuously for leaks, damages ect. If any of these failures noticed proper actions should be taken to correct it. There should be a proper insulation to reduce energy loss to environment and avoid hot and cold surfaces. Dangerous surfaces should be indicated with slandered sign.
8.5 Safety Aspects of Chemical Similar to any processing plant this plant also involve with number of chemicals in its process and tastings. Those chemicals should be clearly labeled and details of the chemicals should be kept in order to refer any time. All the chemical should be stored according to their safety regulations. And safety regulations also should follow in transportation and usage. If there any spillage or contamination occurs recommended procedures should be followed in order to remove the adverse effect on health and environment. Employees should be trained to handle each chemical. 8.5.1
Carbon Dioxide (CO 2 )
Hazard Identification •
High concentrations may cause asphyxiation.
•
Slightly corrosive in the presence of moisture.
•
Solid carbon dioxide is white and when in direct contact with the skin will cause acute cold damage to skin – “cold burn”.
Health Effects &First Aid Measures Inhalation: •
Symptoms may include loss of mobility/consciousness. Victim may not be aware of asphyxiation. Low concentrations of CO2 cause increased respiration and headache. Remove victim to uncontaminated area wearing self-contained breathing apparatus. Keep victim warm and rested. Call a doctor. Apply artificial respiration if breathing stopped.
Skin/eye contact: •
Ingestion is not considered a potential route of exposure.
Ingestion: •
Ingestion is not considered a potential route of exposure.
Handling And Storage •
Below –30°C only use low temperature carbon steel, austenitic stainless steels, aluminum, copper and their alloys.
Chapter 8
SAFETY MEASURES
•
If carbon dioxide is dissolved in water, particularly at elevated pressures and in the presence of oxygen, use materials resistant to carbonic acid, e.g. stainless steel or Monel.
•
Keep container below 50°C in a well ventilated place.
Stability And Reactivity •
Stable under normal conditions.
Disposal Considerations •
Do not discharge into any place where its accumulation could be dangerous. Discharge to atmosphere in large quantities should be avoided.
Toxicological Information •
High concentrations cause rapid circulatory insufficiency.
•
Symptoms are headache, nausea and vomiting, which may lead to unconsciousness.
•
Carbon dioxide is mildly toxic, with no cumulative effects.
Permeable Exposure Limit •
TLV-ACGIH-5000 ppm TWA
•
TLV-ACGIH-30,000 ppm STEL
Personal Protective Equipments •
Safety goggles or glasses as appropriate for the job.
•
Protective gloves of any material appropriate for the job.
•
Positive pressure air line with full-face mask and escape bottle or self-contained breathing apparatus should be available for emergency use.
8.5.2
Ammonia (NH 3 )
Hazard Identification
•
Irritating or corrosive to exposed tissues.
•
Inhalation of vapors may result in pulmonary edema and chemical pneumonitis.
•
Slightly flammable.
Chapter 8
SAFETY MEASURES
Health Effects &First Aid Measures Inhalation: •
Corrosive and irritating to the upper respiratory system and all mucous type tissue. Depending on the concentration inhaled, it may cause burning sensations, coughing, wheezing, shortness of breath, headache, nausea, with eventual collapse.
•
Inhalation of excessive amounts affects the upper airway (larynx and bronchi) by causing caustic-like burning resulting in edema and chemical pneumonitis. If it enters the deep lung, pulmonary edema will result. Pulmonary edema and chemical pneumonitis are potentially fatal conditions.
•
Conscious persons should be assisted to an uncontaminated area and inhale fresh air. Quick removal from the contaminated area is most important. Unconscious persons should be moved to an uncontaminated area, given mouth-to-mouth resuscitation and supplemental oxygen. Keep victim warm and quiet. Assure that mucus or vomited material does not obstruct the airway by positional drainage.
Skin/eye contact: •
Mild concentrations of product will cause conjunctivitis. Contact with higher concentrations of product will cause swelling of the eyes and lesions with a possible loss of vision.
•
Mild concentrations of product will cause dermatitis or conjunctivitis. Contact with higher concentrations of product will cause caustic-like dermal burns and inflammation. Toxic level exposure may cause skin lesions resulting in early necrosis and scarring.
•
If contact eye(s) flush contaminated eye(s) with copious quantities of water. Part eyelids to assure complete flushing. Continue for a minimum of 15 minutes.
•
Remove contaminated clothing as rapidly as possible. Flush affected area with copious quantities of water. In cases of frostbite or cryogenic "burns" flush area with lukewarm water.
Ingestion: •
Ingestion is not considered a potential route of exposure.
Handling And Storage •
Use only in well-ventilated areas.
•
Do not drag, slide or roll cylinders. Use a suitable hand truck for cylinder movement.
•
Use a pressure regulator when connecting cylinder to lower pressure (<500 psig) piping or systems. Do not heat cylinder by any means to increase the discharge rate of product from the cylinder.
•
Store in cool, dry, well-ventilated area away from heavily trafficked areas and emergency exits.
•
Do not exceed temperature 125oF (52oC).
Chapter 8
SAFETY MEASURES
Stability And Reactivity •
Unstable
Disposal Considerations •
Do not attempt to dispose of residual waste or unused quantities.
Toxicological Information •
Genetic mutations observed in bacterial and mammalian test systems.
•
Toxic effects to the respiratory system, senses, liver, kidneys and bladder observed in mammalian species from prolonged inhalation exposures at above 100 ppm.
Permeable Exposure Limit •
TLV-ACGIH-25 ppm TWA
•
TLV-ACGIH- 35 ppm STEL
Personal Protective Equipments •
Gas tight chemical goggles or full-face piece respirator.
•
Protective gloves made of any suitable material.
•
Level C respiratory protection with full face piece or self-contained breathing apparatus should be available for emergency use. Air purifying respirators must be equipped with suitable cartridges.
8.5.3
Sodium Carbonate (Na 2 CO 3 )
Hazard Identification •
Hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of inhalation (lung irritant).
Health Effects &First Aid Measures Inhalation: •
Inhalation of excessive amounts affects the upper airway (larynx and bronchi) by causing caustic-like burning resulting in edema and chemical pneumonitis. If it enters the deep lung, pulmonary edema will result. Pulmonary edema and chemical pneumonitis are potentially fatal conditions.
•
Conscious persons should be assisted to an uncontaminated area and inhale fresh air. Quick removal from the contaminated area is most important. Unconscious persons should be moved
Chapter 8
SAFETY MEASURES
to an uncontaminated area, given mouth-to-mouth resuscitation and supplemental oxygen. Keep victim warm and quiet. Assure that mucus or vomited material does not obstruct the airway by positional drainage. Skin/eye contact: •
Skin contact cause irritant.
•
In case of contact, immediately flush skin with plenty of water. Cover the irritated skin with an emollient. Remove contaminated clothing and shoes. Cold water may be used. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention.
•
Eye(s) contact cause irritant.
•
Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Cold water may be used.
Ingestion: •
Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. Loosen tight clothing such as a collar, tie, belt or waistband. Get medical attention if symptoms appear.
Handling And Storage •
Do not ingest. Do not breathe dust. Wear suitable protective clothing. In case of insufficient ventilation, wear suitable respiratory equipment. If ingested, seek medical advice immediately and show the container or the label. Avoid contact with skin and eyes. Keep away from incompatibles such as acids.
•
Hygroscopic. Keep container tightly closed. Keep container in a cool, well-ventilated area. Do not store above 24°C (75.2°F). Hygroscopic
Stability And Reactivity •
The product is stable.
Disposal Considerations •
Waste must be disposed of in accordance with federal, state and local environmental control regulations.
Toxicological Information •
Routes of Entry: Inhalation. Ingestion.
•
Acute oral toxicity (LD50): 4090 mg/kg [Rat].
•
Acute toxicity of the dust (LC50): 1200 mg/m3 2 hours [Mouse].
•
Effects on Humans: May cause damage to the following organs: upper respiratory tract, skin, eyes. Hazardous in case of skin contact (irritant), of ingestion, of inhalation (lung irritant).
Chapter 8
SAFETY MEASURES
Permeable Exposure Limit •
LDL (Lowest Published Lethal Dose) [Man] - Route: Oral; Dose: 714 mg/kg
Personal Protective Equipments •
Splash goggles. Lab coat. Dust respirator. Be sure to use an approved/certified respirator or equivalent. Gloves.
•
Personal Protection in Case of a Large Spill: Splash goggles. Full suit. Dust respirator. Boots. Gloves. A self contained breathing apparatus should be used to avoid inhalation of the product. Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.
Chapter 9
MATERIAL BALANCE
CHAPTER 09
MATERIAL BALANCE
Material balances are based on the fundamental law of conservation of mass. In particular, chemical engineers are concerned with doing mass balances around chemical processes. Doing a ‘mass balance’ is similar in principle to accounting. In accounting, accountants do balances of what happens to a Company’s money. Chemical engineers do a mass balance to account for what happens to each of the chemicals that is used in a chemical process.....
Chapter 9
MATERIAL BALANCE
This chapter contains the material balance for the process we designed. There are number of assumptions and those are described in appropriate places. Some values are extracted from literature and those are mentioned in reference. This calculation based on 50Mg (tons) of product (Na 2 CO 3 ) output per day. All the rates are given in daily basis and haven’t mention in calculations. Most of the flow rates are calculated in mole. 9.1 Product Specification Ingredients Na 2 CO 3 Na 2 SO 3 Moisture and impurities
Percentage 99.5% 0.004% 0.495%
Table 9.1- Soda ash specification
Average molar weight of product
= (1063×0.995) + (183×0.005) + (14230.000042) = 105.566 g/mol
Production rate
= 50000kg/day
Production rate in kmol
=
/ .
/
= 473.6375kmol/day Note: We used Microsoft Excel in our calculation and its goal seek function was used to do the calculation targeting above calculated flow rate by varying total NH 3 input to the NH 3 Absorption Unit. Microsoft Excel worksheet was attached at the end of the chapter. 9.2 Components in Purified Brine NaCl Na 2 SO 4 Other Na/Ca/Mg salts H2O Salt (Total)
5.07 0.05 0.009 45.42 50.549
kmol/m3 kmol/m3 kmol/m3 kmol/m3 kmol/m3
Table 9.2- Purified brine specification
Density of brine
= 1122 kg/m3
By calculating we found that amount of NaCl we need for our process is 1477.31kmol. Using above concentrations the Flow rate of purified brine was calculated. Flow rate of purified brine
=
. .
/
= 291.38m3 Flow rate of purified brine (mole)
= 291.38 m3 × 50.549 kmol/m3 = 14729.05kmol
Chapter 9
MATERIAL BALANCE
Now using the flow rate and above compositions of brine, = 291.38m3 × 0.05 kmol/m3
Flow rate of Na 2 SO 4 (mole)
= 14.57kmol Flow rate of Other Na/Ca/Mg salts (mole)
= 291.38m3 × 0.009kmol/m3 = 2.62kmol = 291.38m3 × 45.42kmol/m3
Flow rate of H 2 O (mole)
= 13234.56kmol
9.3 NH 3 Absorption Unit
NaCl Na 2 SO 4 Other Na/Ca/Mg salts H2O NH 3 OH
Brine
1477.31 14.57 2.62 13057.79 176.77
Waste gas
126.2654 29.67
kmole kmole
NH3 Absorption Unit
NH 3 CO 2
Makeup ammonia + Gas from ammonia recovery unit
H2O NH 3 OH NaCl Na 2 SO 4
13055.16 1136.389 1477.305 14.56909
kmole kmole kmole kmole
CO 2 NH 3
Ammoniated brine water
Figure 9.1- NH 3 Absorption Unit
32.28992 1085.883
kmol kmol
kmol kmol kmol kmol kmol
Chapter 9
MATERIAL BALANCE
Possible reactions inside the NH 3 Absorption Unit, NaCl (aq) + H 2 O (l) + NH 3(g) ↔ NaCl (aq) + NH 4 OH (aq) CO 2 (aq) + H 2 O (l) → CO 3 Ca
2+ (aq) 2+
Mg
+ CO 3
2(aq)
2(aq)
+ 2H
+
----------- (2)
(aq)
→ CaCO 3 ↓(s)
----------- (3)
-
(aq)
----------- (1)
+ 2 OH (aq) → Mg(OH) 2 ↓ (s)
----------- (4)
Gaseous streams at output of NH 3 Absorption Unit, NH 3 Total NH 3 (as ammonia gas and ammonium hydroxide) input to the NH 3 adsorption unit is 1262.654kmol. Gas stream of the output of NH3 Absorption Unit is assumed to have gas NH 3 . And the amount is equal to 10% of total NH 3 enter to the unit. NH 3 output of NH 3 Absorption Unit
= 1262.654 kmol × 10% = 126.25kmol
CO 2 Assume reacted amount of carbon dioxide with salt is equal (mostly salt contains Ca2+, Mg2+ which react 1:1 with CO 3 2+) to the salt amount (mole). Carbon dioxide output
= Input – Reacted with salt = 32.28992 kmol - 2.62kmol = 29.67kmol
Liquid streams at output of NH 3 Absorption Unit, NH 3 Ammonia exits as ammonium hydroxide in liquid stream from the system. As mentioned above input of total NH 3 is 1262.654kmol. Ammonium Hydroxide amount
= 1262.654 - 126.25 kmol = 1136.389 kmol
NaCl No reaction on NaCl, So Input is equal to output. Output
= 1477.31 kmol
Chapter 9
MATERIAL BALANCE
Na 2 SO 4 No reaction on Na 2 SO 4 , So Input is equal to output. Output
= 14.57 kmol
Other Na/Ca/Mg salts Here we assume 100% precipitation of salts of Na, Ca and Mg except Na 2 CO 3 and CaCO 3 . And equal amount of moles of water removes with the salt solid from the NH 3 Absorption Unit. This salt and water removes from the system at this unit. And it is assume that Na 2 SO 4 is 100% soluble in this condition. Salt precipitation
= 2.62kmol
H 2 O (Water) Water removed with the salt
= 2.62kmol (See Other Na/Ca/Mg salts)
Amount of water enter to the unit
= 13051.47kmol
Amount of water exit from the unit = Water enter to the unit - Water removed with the salt = 13048.85kmol
9.4 Air Mixture
Makeup Ammonia
NH 3
6.410432
CO 2 NH 3
CO 2 NH 3
kmol kmol
Air mixture To NH3 absorption unit
kmole
32.28992 1079.472
32.28992 1085.883
kmole kmole
Gas from ammonia recovery unit
Figure 9.2- Air mixture before NH 3 Absorption Unit
Air mixture has two input streams; both get mixed and go to the NH 3 Absorption Unit. CO 2 No two inputs of carbon dioxide and output stream equal to the input. 32.28992kmol. NH 4 Output Ammonia Amount
= From Ammonia recovery unit + Ammonia Makeup = 1079.472 + 6.410432 = 1085.883kmol
Chapter 9
MATERIAL BALANCE
9.5 Gas Washing Tower with Purified Brine
Purified brine
Waste gas
CO 2 N2 NH 3 NaCl Na2SO4 Other Na/Ca/Mg salts H2O
1477.31 14.57 2.62 13234.56
kmole kmole kmole kmole
423.78 1604.452 6.313271
kmole kmole kmole
NH 3 CO 2
56.81944 394.1129
kmole kmole
Waste gas from Carbonator unit
Gas washing with purified brine Brine
NaCl Na 2 SO 4 Other Na/Ca/Mg salts H2O NH 3 OH
1477.31 14.57 2.62 13057.79 176.77
Waste gas from NH3 adsorption unit
kmol kmol kmol kmol kmol
NH 3 CO 2
126.2654 29.67
Figure 9.3- Gas washing tower with purified brine
Output gas stream, CO 2 Assume carbon dioxide does not dissolve in brine. Output carbon dioxide amount
= From carbonator + From NH 3 Absorption Unit = 394.1129 + 29.67 = 423.78kmol
N2 Assume Nitrogen does not dissolve in brine. Output Nitrogen amount
= From carbonator + From NH 3 Absorption Unit = 1604.452 + 0 = 1604.452kmol
kmole kmole
Chapter 9
MATERIAL BALANCE
9.6 Carbonator Unit
NH 3 CO 2 N2
NH3 , CO2, N2 Mixture
57 394 1,604
kmole kmole kmole
Ammoniated brine
H2O NH 4 OH NaCl Na 2 SO 4
13054 1136 1477 15
kmole kmole kmole kmole
Carbonation tower
CO2, N2 mixture
Cooling System
H2O NaHCO 3 NaCl NH 4 Cl NH 4 HCO 3 Na 2 SO 4
13,359 1,047 430 1,047 32 15
1,604 1,474 305
N2 CO 2 H2O
kmole kmole kmole kmole kmole kmole
kmole kmole kmole
NaHCO3 Solution
Figure 9.4- Carbonator Unit
Possible reactions inside the Carbonator Unit, NH 4 OH (aq) ↔ NH 3(g) + H 2 O (l)
----------- (5)
2 NH 4 OH (aq) + CO 2(g) ↔ (NH 4 ) 2 CO 3(aq) + H 2 O (l)
----------- (6)
(NH 4 ) 2 CO 3(aq) + CO 2(g) + H 2 O (l) ↔ 2 NH 4 HCO 3(aq)
----------- (7)
2 NH 4 HCO 3(aq) + 2 NaCl (aq) ↔ 2 NaHCO 3(aq)
----------- (8)
↓
+ 2 NH 4 Cl (aq)
Gaseous streams at output of Carbonator Unit, NH 3 Ammonia occurs from decomposes of NH 4 OH in the carbonator column. We assumed the decomposed amount is equal to 5% of total NH 4 OH input to the Carbonator. NH 3 output of carbonator Unit
= NH 4 OH input × 5% = 1136 × 5% = 126.25kmol
Chapter 9
MATERIAL BALANCE
CO 2 Reacted amount (mole) of carbon dioxide in the column is equal to NaHCO 3 , NH 4 HCO 3 amount produce. Carbone dioxide enters only from the gas stream from the gas cooler. Carbon dioxide output
= Input – Reacted for NaHCO 3 - Reacted for NH 4 HCO 3 = 1473.68 kmol - 1047.182 kmol - 32.387kmol = 394.1129 kmol
Liquid streams at output of NH 3 Absorption Unit, NaHCO 3 The efficiency of the carbonator column was taken as 97% (generation of NaHCO 3 as a percentage to effective NH 4 OH input). Effective NH 4 OH amount (mole)
= NH 4 OH input – decomposes to NH 3 = 1136.388 kmol - 56.819 kmol = 1079.569kmol
Generation of NaHCO 3 amount (mole)
= Effective NH 4 OH amount × 97% = 1079.569kmol× 97% = 1047.182kmol
NH 4 HCO 3 This is an intermediate product in reaction chain and amount is inversely proportional to the efficiency. Generation of NaHCO 3 amount (mole)
= Effective NH 4 OH amount × 3% = 1079.569kmol× 3% = 32.387kmol
NaCl Sodium spent to generate NaHCO 3 . Sodium Chloride output from the carbonator
= Sodium Chloride input - NaHCO 3 output = 1477.305kmol - 1047.182kmol = 430.1231kmol
Chapter 9
MATERIAL BALANCE
NH 4 Cl Ammonium chloride generated in the reaction is equal to NaHCO 3 generated in the reaction. Ammonium chloride output
= 1047.182kmol
Na 2 SO 4 No reaction on Na 2 SO 4 , So Input is equal to output. Na 2 SO 4 output
= 14.57kmol
H 2 O (Water) Water amount exits from the unit is equal to the water enters to the system. = Water from NH 3 Adsorption unit + Gas Cooler
Water exits from the unit
= 13054.34kmol + 304.9075kmol = 13359.25kmol
9.7 Filter 13,359 1,047 430 1,047 32 15
kmole kmole kmole kmole kmole kmole
From Carbonator Unit
H2O NaHCO 3 NaCl NH 4 Cl NH 4 HCO 3 Na 2 SO 4
Residue solid
Filter
H2O NaCl NH 4 Cl NaHCO 3 NH 4 HCO 3 Na 2 SO 4
13,123.9 430.1 1,047.2 104.7 32.4 14.5
kmole kmole kmole kmole kmole kmole
Permeate
NaHCO 3 H2O Na 2 SO 4
942.464 235.3804 0.02
kmole kmole kmole
Figure 9.5- Filter
Product composition after the filter as follows, Component NaHCO 3 H2O Na 2 SO 4
Percentage 80% 19.98% 0.02%
Table 9.3- Residue solid composition
And the filter assumed to have 90% efficiency (based on NaHCO 3 ). As NaHCO 3 is our main product this calculation is based on NaHCO 3 .
Chapter 9
MATERIAL BALANCE
9.7.1.
Calculation for residue solid
NaHCO 3 NaHCO 3 in residue solid
= Input to the filter × 90% = 1047.182kmol × 90% = 942.464kmol
Other components are calculated according to the above composition. H2O Water in the residue solid (wet)
=
.
.
%
%
= 235.38kmol Na 2 SO 4 Although Na 2 SO 4 is not a solid in this condition, considering End Product composition it assumed some amount of Na 2 SO 4 remain in the residue solid. So Na 2 SO 4 amount remain in the residue solid equal to the Na 2 SO 4 in the End Product. Calculations are shown in dryer calculations. Na 2 SO 4 in the residue solid 9.7.2.
= 0.02kmol
Calculation for permeate
NaHCO 3 NaHCO 3 in permeate
= Input to the filter × 10% = 1047.182kmol × 10% = 104.7kmol
H2O Water in permeate
= Water input – Water in filtered solid = 13359.25 - 235.38 = 13,123.9kmol
Na 2 SO 4 Na 2 SO 4 in permeate
= 14.5kmol
NaCl It assumed that total NaCl amount is filtrate through the filter. So amount is equal to input of the filter. NaCl in permeate
= 430.1kmol
Chapter 9
MATERIAL BALANCE
NH 4 Cl It assumed that total NH 4 Cl amount is goes through the filter. So amount is equal to input of the filter. NH 4 Cl in permeate
= 1,047.2kmol
NH 4 HCO 3 It assumed that total NH 4 HCO 3 amount is goes through the filter. So amount is equal to input of the filter. NH 4 HCO 3 in permeate
= 32.4kmol
9.8 Lime Kiln
Hot Flue Gas
N2 CO 2
1604.45 1002.45
kmole kmole
Heated CaCO3 Coke
Coal
426.50
CaCO 3
kiln
kmole
575.95
kmole
Heated Ari
O2 N2
426.50 1604.45
kmole kmole
Figure 9.6- Lime Kiln
Calculation for the Lime Kiln has done considering material requirements (CO 2 , CaO) and energy requirements. Main base for the calculation was the CO 2 output from the Kiln.
Possible reactions inside the Carbonator Unit, CaCO 3(s) → CaO (s) + CO 2 (g)
----------- (9)
C (s) + O 2 (g) → CO 2 (g)
----------- (10)
Chapter 9
MATERIAL BALANCE
Gaseous products at outlet, CO 2 Considering above (9) and (10) reactions, Carbon dioxide output
= CaCO 3 reacted + C reacted = 575.95kmol + 426.50kmol = 1002.45kmol
N2 Before calculating N 2 , it needs to calculate air consumption for the kiln. In literature we found that the kiln is supplied no excess air. C reacted
= 426.50kmol
According to the Stoichiometric relation, amount of O 2 consumed. O 2 required
= 426.50kmol
Assuming composition of air is O 2 – 21%, N 2 – 79% N 2 comes with O 2
=
.
%
%
= 1604.45kmol Air amount
= O 2 required + N 2 comes with O 2 = 2030.95kmol
Solid products at outlet, It is assume that only solid product at outlet is CaO. Considering real situations it is possible to remain unreacted CaCO 3 in outlet but considering calculation complexity and effectiveness on the system we assumed it as 0kmol. Amount of CaO
= 575.95kmol
Chapter 9
MATERIAL BALANCE
9.9 Slaker of lime water coming from cooler CaO solid
17068 kmole/day
575.95 kmole/day
Hot water from cooler
Cold CaO
Excess water
extra water
Ca(OH)2 Solution
1417.2 kmole/day
Slaker
Ca(OH)2 H2O weight of solution Temperature
576kmole/day 13,418 kmole/day 284,135 kg/day 60 0C
Vaporizes water
evaporated water vapors 1657.4kmole/day Figure 9.7- Slaker of lime
Possible reactions inside the Slaker Unit, CaO (s) + H 2 O (l) → Ca(OH) 2(aq)
----------- (11)
Liquid products at outlet, Ca(OH) 2 Ca(OH) 2 amount
= Amount of CaO = 575.95kmol
H2O Water input amount
= Water from gas cooler - Excess water (remove) = 17068.07kmol - 1417.21kmol = 15650.85kmol
Water reacted with Ca(OH) 2
= 575.95kmol
Water vaporized amount
= 1657.4kmol
Excess water
= Water input - Water reacted - Water vaporized
(see energy balance)
= 15650.85kmol - 575.95kmol - 1657.4kmol = 13417.507kmol
Chapter 9
MATERIAL BALANCE
9.10
Ammonia Recovery Unit
CO 2 NH 3
Cool gas (NH3)
32.28992 kmole/day 1079.472 kmole/day
Cool NH4Cl Solution HE
Condensed water
H2O
1061.655 kmole/day
Hot NH3 ,H2O mixture
H2O NaCl NH 4 Cl NaHCO 3 NH 4 HCO 3 Na 2 SO4
H2O CO 2 NH 3
13,123.9 430.1 1,047.2 104.7 32.4 14.5
kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day
1061.655 kmole/day 32.28992 kmole/day 1079.472 kmole/day
Ammonia recovery unit
shaking of lime
Ca(OH) 2 H2O
575.95 kmole/day 13417.51 kmole/day
Steam
NaCl CaCl 2 NaHCO 3 NH 4 OH Ca(OH) 2 Na 2 SO 4 H2O
430.12 523.59 104.72 0.10 52.36 14.55 25,479.72
kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day
Waste water
Figure 9.8- Ammonia Recovery Unit
Possible reactions inside the Carbonator Unit, 2NH 4 Cl (aq) + Ca(OH) 2 → 2NH 3(g) + CaCl 2(aq) + H 2 O (l) NH 4 HCO 3(aq) → NH 3(g) + CO 2(aq) + H 2 O (l) (13)
----------- (12) -----------
Chapter 9
MATERIAL BALANCE
Gaseous products at outlet, CO 2 Considering 99.7% efficiency for (13) reaction, Carbon dioxide output
= NH 4 HCO 3 × 99.7% = 32.4kmol × 99.7% = 32.289kmol
NH 4 Considering 100% efficiency for (12) reaction and considering 99.7% efficiency for (13) reaction, Ammonia output
= NH 4 Cl × 100% + NH 4 HCO 3 × 99.7% = 1,047.2 × 100% + 32.4 × 99.7% = 1079.472kmol
Liquid products at outlet, NaCl NaCl involves with no reaction through the Ammonia recovery column. NaCl output
= 430.1kmol
NaHCO3 NaHCO3 involves with no reaction through the Ammonia recovery column. NaHCO3 output
= 104.72kmol
NH 4 HCO 3 Considering 99.7% efficiency for (13) reaction, NH 4 HCO 3 output
= NH 4 HCO 3 × 0.3% = 32.4kmol × 0.3% = 0.10kmol
Na 2 SO 4 Na 2 SO 4 involves with no reaction through the Ammonia recovery column. Na 2 SO 4 output
= 14.55kmol
Chapter 9
MATERIAL BALANCE
CaCl 2 According to the reaction (12). (Stoichiometric relation is 2:1) CaCl 2 at outlet
= NH 4 Cl × = 1,047.2 × = 523.59 kmol
Ca(OH) 2 Ca(OH) 2 amount is 110% of the actual Ca(OH) 2 requirement CaCO 3 to the kiln is back calculated from here. Ca(OH) 2 at the outlet
= Ca(OH) 2 × 10% = 523.59 × 10% = 52.36kmol
H2O Water involve no reaction in the Ammonia recovery column and it is assume that no water vapor in gaseous output. Water output amount
= Water from slaker + Water from filter = 13417.5 kmol + 13,123.9 kmol = 26,541.38 kmol
Chapter 9
MATERIAL BALANCE
9.11
Gas Cooler
N2 CO 2 H2O
(g)
1604.452381 kmole/day 1473.682222 kmole/day 304.9074568 kmole/day
Gas out
Water In
300 m3/day
H2O
Cooler
16669 Kmole/day
Gas mixer
H 2 O condense
N2 CO 2 H2O
(g)
1604.45238 kmole/day 1473.68222 kmole/day] 704.26438 kmole/day]
Hot Water Out
H2O
17068 Kmole/day
Figure 9.9- Gas Cooler
Gaseous products at outlet, CO 2 Carbon dioxide output
= Carbon dioxide input = 1473.68kmol
N2 Nitrogen output
= Nitrogen input = 1604.45kmol
H2O The gaseous outlet assumed to be saturated with water at its temperature. Water in gaseous outlet
= Dry air flow ×
= {(N2× 28) + (CO 2 × 44)} ×
.
= {(1604.45 × 28) + (1473.68× 44)} × = 304.90kmol
399kmole/day
.
Chapter 9
MATERIAL BALANCE
Liquid products at outlet, H2O Water in liquid outlet
= From air mixture + Additional injection – In gaseous outlet = 1326.26 + 6,623 – 304.90 = 7644.77kmol
9.12
Air Mixture (Before the Gas Cooler)
N2 CO 2 H2O
1604.452381 1473.682222 704.264384
Kmole/day Kmole/day Kmole/day
CO 2 H2O
471.232 704.264384
Kmole/day Kmole/day
Air Mixer
N2 CO 2
1604.452381 1002.450222
Kmole/day Kmole/day
Figure 9.10- Air mixture before gas cooler
Air mixture has two input streams; both get mixed and go to the Gas Cooler. CO 2 CO 2 in outlet
= From dryer + From CaCO 3 preheated = 471.232 + 1002.45 = 1473.68kmol
H2O Water in outlet
= From dryer + From CaCO 3 preheated = 704.26 + 0 = 704.26kmol
N2 Nitrogen output
= From dryer + From CaCO 3 preheated = 0 + 1604.45 = 1604.45kmol
Chapter 9
MATERIAL BALANCE
9.13
Dryer
CO2 H2O N2 CO2
1604.452381 1002.450222
Kmole/day Kmole/day
471.232 704.264384
Kmole/day Kmole/day
CO2, H2O Vapour
Flue gas out
NaCO3 Product NaHCO3 Solution
NaHCO3 H2O Na2SO4 Flow rate
942.464 235.3804 0.02 1177.844
Kmole/day Kmole/day Kmole/day kmole/day
N2 CO2
Calcinations NaHCO3
Flue gas in 1000 C
1604.45 1002.45
Na 2 CO3
471.232
Kmole/day
H2O Na2SO4 Total
2.348 0.02 473.6
Kmole/day Kmole/day Kmole/day
Kmole/day Kmole/day
Figure 9.11- Dryer
Possible reactions inside the Carbonator Unit, 2NaHCO 3 (s) → Na 2 CO 3 (s) + CO 2 (g) + H 2 O (g)
----------- (14)
Gaseous products at out let, Heat is supplies to the dryer through indirect contact of flue gas from the kiln. So composition of flue gas does not change by going through the dryer. In this calculation other gas outlet is considered. CO 2 CO 2 at outlet
= CO 2 generated by the reaction = NaHCO 3 amount reacted × = 471.232kmol
H2O H 2 O at outlet
= H 2 O generated by the reaction + H 2 O in inlet - H 2 O in product = 471.232 + 235.38 - 2.348 = 704.26kmol
Chapter 9
MATERIAL BALANCE
Solid products at out let, Na 2 CO 3 Na 2 CO 3 in product
= Na 2 CO 3 generated by the reaction = NaHCO 3 amount reacted × = 471.232kmol
Na 2 SO 4 Na 2 SO 4 amount in the product assume to be .02kmol. H2O H 2 O amount calculated assuming only material in the product is H 2 O except Na 2 CO 3 and Na 2 SO 4 .
Chapter 9
9.14
Material Flow Sheet
MATERIAL BALANCE
Chapter 10
ENERGY BALANCE
CHAPTER 10
ENERGY BALANCE
Energy is fundamental to the quality of our lives. Nowadays, we are totally dependent on an abundant and uninterrupted supply of energy for living and working. It is a key ingredient in all sectors of modern economies Energy supply must be sustainable and diverse. And energy needs to be used more efficiently........
Chapter 10
ENERGY BALANCE
10.1 Kiln Energy Balance N2 1604.45 CO 2 1002.45 Temperature 1000 C
Coal 426.50 Temperature 30 C
kmole/day kmole/day
CaCO 3 575.95 Temperature 566 C
kmole/day
O2 426.50 N2 1604.45 Temperature 900 C
kmole/day kmole/day
Figure 10.1- Kiln
Assumption •
Limestone is mixture of several components CaCO 3 =78% SiO 2 =18.5% Al 2 O 3 =3.5% mole Percentage Mixture Cp is 136 J/moleK
•
Heat loss from the kiln is considered as 15%
•
This calculation is down by using trial and error method using excel
Gas phase enthalpy change were calculated using following equation ΔH R 0 =
C p = Specific heat capacity
C p is changed with Temperature like following equation
C p = a + b T – c /T2 Component Co2 O2 N2 CaO
a 10.34 8.27 6.5 10
b 0.00274 0.000258 0.001 0.05
Table 10.1- a, b, c constant
c 195500 187700 0 108000
kmole/day
Chapter 10
ENERGY BALANCE
Object Fine the coke requirement for the kiln Energy balance Enthalpy of inlet material + Heat of combustion = Enthalpy of outlet material + Dissociation enthalpy of CaCO3 + Loss
Enthalpy of inlet material Component O2 N2 CaCO 3
Flow rate (kmole/day) Enthalpy @ 900 C (J/mole) 426.50 45,385.0 1604.45 28,837.0 575.95 136.0 Total Enthalpy of inlet material (kJ/Day)
Enthalpy(kJ/Day) 19,356,702.5 46,267,593.3 78,329.2 65,702,625.0
Table 10.2- kiln inlet enthalpy
Enthalpy of outlet material Component CO 2 N2 CaO
Flow rate (kmole/day) Enthalpy @ 1000 C (J/mole) 1002.45 51,060.0 1604.45 32,231.0 575.95 73.6 Total Enthalpy of outlet material (kJ/Day)
Table 10.3- kiln outlet enthalpy
Dissociation enthalpy of CaCO3 CaCO 3 supply rate per day =575.95 kmole/day CaCO 3s → CaO s + CO 2g
( H) =177 kJ/mole
Heat absorbed for reaction=101,943,189.33 kJ/Day Heat of combustion Calorific value of coke=32000 kJ/kg Assume kiln coke requirement is 426.5 kmole/day Coke supply rate per day =426.5 kmole/day Heat released due to combustion of coke=163776000 kJ/Day
Enthalpy(kJ/Day) 51,185,108.3 51,713,104.7 42,380.3 102,940,593.4
Chapter 10
ENERGY BALANCE
Heat loss to Environment 15% generated heat is Lost to the environment Heat loss = heat of combustion
percentage
=24566400 kJ/day
Substituting this value in to the energy balance equation satisfied both side. Coke requirement is satisfies 10.2 Energy Balance for Air Preheated CaO
575.95 kmole/day
Hot CaO 1000 C
Hot Air 900 C
Cool air 25 C
Air flow rate O2 N2
Cool CaO TC
2030.95 kmole /day 426.50 kmole/day 1604.45 kmole/day
Figure 10.2- Air preheated
Assumption • Pressure is constant inside unit. Enthalpy change can calculated as follows ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter • •
This calculation is done by using trial and error method Heat loss to the surrounding is 11% of the
Air enthalpy change Air mixture temperature is change from 25 C to 900 C Components N2 O2
Enthalpy Change (kJ/kmole) 26974.06 31969.88 Total Enthalpy
Flow rate kmole/day 1604.45 426.50
Table 10.4- Air enthalpy change
Enthalpy Change (kJ/day) 43278598.8 13635151.83 56,913,751
Chapter 10
ENERGY BALANCE
Enthalpy Change of CaO Hot CaO is cooled from 1000 C to 154 C Component CaO
Enthalpy Change (kJ/kmole) 111218.35
mole Flow rate(kmole/day) 575.95 Total Enthalpy
Enthalpy Change (kJ/day) 64056233.52 64,056,234
Table 10.5- CaO enthalpy change
Heat loss Heat loss to the environment is 11% of the heat gain by cooling of the CaO Heat loss to the surrounding
= 7,117,359.28 kJ/day
Enthalpy Change of CaO = Enthalpy Change of CaO + Heat loss
This equation is satisfies. So air is heated up to 900 C before feed to the kiln.
10.3 Calcinations of Crude Bicarbonate Objective •
To determine the flue gas out T from the calcinations.
Assumption Pressure is constant inside unit. Enthalpy change can calculated as follows ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter •
10 % Heat is lost from indirect dryer which is supply from flue gas
•
Specific heat capacity of pure substance is get from parry hand book
•
NaHCO3
96kJ/kmole K
H2O
75.6kJ/kmole K
Na2CO3
121.38kJ/kmole K
Kiln internal pressure 1.5bar
Chapter 10
ENERGY BALANCE
N2 CO 2 Temperature
1604.452381 1002.450222 622
CO 2 H2O Temperature
kmole/day kmole/day C
471.232 704.264384 200
kmole/day kmole/day C
CO2, H2O Vapour
Flue gas out
NaCO3 Product NaHCO3 Solution
NaHCO 3 H2O Na 2 SO 4 Flow rate Temperature
942.464 235.3804 0.02 1177.844 30
Calcinations NaHCO3
kmole/day kmole/day kmole/day kmole/day C
Flue gas in 1000 C
N2 CO 2 Temparature
Na 2 CO 3 H2O Na 2 SO 4 Total Temperature
1604.45 1002.45 1000
471.232 2.348 0.02 473.6 200
kmole/day kmole/day kmole/day kmole/day C
kmole/day kmole/day C
Figure 10.3- Dryer
Inlet Enthalpy of the NaHCO 3 solution Heat Capacity of mixture of NaHCO 3
= Cp
mole fraction + C p
NaHCO3
fraction
H2O
mole
= 91.9 kJ/kmole = C p mixture Flow rate
Enthalpy of inlet mixture
= 32,806,204.21kJ/Day Outlet Enthalpy of the Na 2 CO 3 Enthalpy of Out let Material of Na 2 CO 3 = C p Na2CO3 Flow rate =27,190,673.66kJ/Day Outlet CO 2 , H 2 O mixture Enthalpy During thermal decomposition of the NaHCO 3 , H 2 O & CO 2 mixture is relished .Assume the temperature is 200 C H 2 O g enthalpy from steam table H 2 O g Total energy
= 2876kJ/kg = 2876 18 704.2 =36,455,025.6 kJ/kmole
Chapter 10
ENERGY BALANCE
CO 2 Enthalpy
=45.2kJ/kmole
Total energy CO 2
=45.2
kJ/day
=21,298.24 kJ/day Total Enthalpy of the Exit mixture
=36,479,658.89kJ/Day
Flue Gas Enthalpy Change Mixture of flue gas is cooled 1000 C to T C If Temperature of flue gas out is 622 C CO 2 enthalpy change = = 19,457,719.97 kJ/day
N 2 Enthalpy
= =24,535,963.06kJ/day
Total enthalpy change = 43,993,683.03 kJ/Day Decomposition NaHCO3 s Enthalpy Change NaHCO 3 s
Na 2 CO 3 s + H 2 O g + CO 2g ∆
Total energy absorb
.
= 9.24
/
kJ/day
= 8,708,367.36kJ/Day Heat loss Heat loss from indirect dryer 10 % supply from flue gas =4399368.303kJ/Day Energy equation Enthalpy change of flue gas = Hot product out (NaCO 3(s) ) + CO 2 , H 2 O mixture out + Reaction energy + heat loss to environment -Enthalpy of NaHCO 3 in Substituting the all calculated value to this equation is satisfies. This calculation is down by using trial and error method. So flue gas exit temperature is 622 C
Chapter 10
ENERGY BALANCE
10.4 CaCO 3 Preheated Objective • To determine the CaCO3 feed T Assumption •
Pressure is constant inside unit. Enthalpy change can calculated as follows
ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter •
10% heat loss during preheating
•
No Cp Change in limestone with increasing T @ Cp
136 J/mole
N2 CO 2
N2 CO 2
1604.452 kmole/day 1002.45 kmole/day
1604.452 kmole/day 1002.45 kmole/day
CaCO 3 Temperature
575.95 kmole/day 566 C
Figure 10.4- Cyclone
Energy Equation Heat IN = Heat Out + Loss Enthalpy Change of Flue Gas = Enthalpy Change CaCo3 + Losses Flue Gas Enthalpy Change mixture of flue gas is cooled 622C to 210 C CO 2 enthalpy N 2 Enthalpy Total enthalpy change
20,913,120.69 kJ/Day 26,177,959.30 kJ/Day 47,091,079.98 kJ/Day
Table 10.6- flue gas enthalpy change
Chapter 10
ENERGY BALANCE
Enthalpy Change Of CaCO3
42,376,113.55 kJ/Day
Heat loss 10% enthalpy change of the flue gas Loss of heat
4,709,108.00 kJ/Day
Energy balance equation is satisfied using these values. Using cyclone CaCO 3 is heated up to 566C. This Calculation is done by using trial and error method.
10.5 Air Mixer Energy Balance Objective • To fine the gas mixture temperature Assumption • Pressure is constant inside unit. Enthalpy change can calculated as follows ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter • • •
Nearly 4% of heat is lost to the environment Kiln internal pressure 1.5bar Air Mixture pressure is 1bar
N2 CO 2 H2O Temperature Stream 3
1604.452381 1473.682222 704.264384 T
kmole/day kmole/day kmole/day C
CO 2 H2O Temperature Stream 2
471.232 704.264384 200
Air Mixer
N2 CO 2 Temperature Stream 1
1604.452381 1002.450222 210
kmole/day kmole/day C
Figure 10.5- Air mixture before gas cooler
kmole/day kmole/day C
Chapter 10
ENERGY BALANCE
Stream 2 carrying energy is calculated in the calcinations energy balance section Stream 2 energy
= 36,479,658.89 kJ/day
Stream 1 energy
= CO 2 energy + N 2 energy
CO 2 energy change = N 2 energy change = Temperature of the mixture is 200 C Steam 1 energy = 92,634.44 kJ/kmole
Heat loss to the surrounding = (92,634.44+36,479,658.89) .4 =1,462,891.73 kJ/day Steam 3 energy calculation If out let temperature is 140 C, Water vapor enthalpy is = 2756.8 kJ/kg Energy of water vapor
=
kJ/day
= 34,947,288.97 kJ/day Gas carrying energy can calculated same as steam 1.if out let temperature is 140 C Gas carrying energy =110,493.69 kJ/day Total energy of steam 3 = 36,520,674.39 kJ/day Energy equation Stream 1 energy + Stream 2 energy = Stream 3 energy + loss Substituting values to the energy equation is satisfies so out let temperature is 140 C
Chapter 10
ENERGY BALANCE
10.6 Heat Balance for Gas Cooler Object •
To Find the Cooling water demand required for gas cooler.
Assumption •
Cooling water system used is ones through system having 30 0C temperature of inlet water.
•
Efficiency of the gas cooler is 95%.
•
Out let gas stream is saturated with water vapor and quantity of energy carries with the steam is neglected.
N2 CO 2 H2O g Temperature
1604.452381 kmole/day 1473.682222 kmole/day 304.9074568 kmole/day 40 0C
Gas out
H2O Temperature
N2 CO 2 H2O g Temperature
1604.45238 kmole/day 1473.68222 kmole/day] 704.26438 kmole/day] 140 0C
300 m3/day 16669 kmole/day 30 0C
Water In Cooler
Gas mixer
H 2 O condense Hot Water Out
H2O Temperature
17068 kmole/day 50 0C
Figure 10.6- Gas cooler
Heat given by the hot stream = Heat taken by the cold stream Enthalpy change ΔH R 0 =
Δ
C p = a + b T – c /T2 ΔH R 0 = a ΔT + b ΔT2– c /ΔT
399 kmole/day
Chapter 10
ENERGY BALANCE
Component CO 2 O2 N2
a b 10.34 0.00274 8.27 0.000258 6.5 0.001
c 195500 187700 0
Table 10.7- Soda ash specification
Total energy of the inlet gas mixture
= 35,057,783 kJ/day
Total energy of the out let gas mixture = 102,867 kJ/day Enthalpy change due to condensate of the of the water vapor = 9,751,817 kJ/day Total enthalpy change in gas stream = Total energy of the inlet gas mixture - Total energy of the out let gas mixture - Enthalpy change due to condensate of the of the water vapor = (35,057,783-102,867-9,751,817) kJ/day = 25203099 kJ/day Cooling water flow rate required = m kg Total enthalpy change in gas stream = m C water ΔT = 25203099 Cooling water flow rate required = m = 16669 kg/day = 300m3/day Condense water and heated cooling water is mixed and then supply hole quantity in to slaker to make Ca(OH) 2 solution.
10.7 Slaking of Lime Objective • Find the quantity of evaporated water vapor from the slaker. Assumption
•
15% brix, Ca(OH) 2 mixture is required for the process.
•
Heat loss to the surrounding is 10 %from the energy due to the reaction enthalpy.
Chapter 10
ENERGY BALANCE
CaO solid Temperature
water coming from cooler Temperature
575.95 kmole/day 154 0C
17068 kmole/day 50 0C
Hot water from cooler Cold CaO
Excess water
extra water temperature
Ca(OH)2 Solution
1417.2 kmole/day 50 0C
Slaker
Ca(OH) 2 H2O weight of solution Temperature
576 kmole/day 13,418 kmole/day 284,135 kg/day 60 0C
Vaporizes water
evaporated water vapors
1657.4kmole/day
Figure 10.7- Slaker
Energy with the inlet CaO stream
= m × Cp × T
Component CaO
a 10
b 0.05
c 108000
Table 10.8- a, b, c constant for CaO
C p = a + b T – c /T2
Energy with the inlet CaO stream = (10+0.05 × (154+273) ×108,000/(154+273) 2) ×4.2 × 575.95 =
74,402.4 kJ/day
Amount of the input energy of the water from the cooler
= m × C water ×ΔT = 15,650.9×18×4.2× (273+50) = 382,175,186 kJ/day
Total Heat in = Energy with the inlet CaO stream + Amount of the input energy of the water from the cooler
Total Heat in = 74,402.4 + 382,175,186 = 382,249,589 kJ/day
Chapter 10
ENERGY BALANCE
Reaction Enthalpy: CaO + H 2 O
Ca(OH) 2
ΔH= - 65 kJ/mole
Heat generated due to reaction = 65 × 1000 × 576 kJ/day Loss to surrounding
= 3,743,675 kJ/day
Cp of the Ca(OH) 2 mixture = 3.6183 kJ/kgK Heat out with Ca(OH) 2
= 3.6183 × 284135 × (273+60) = 342,353,062 kJ/day
Energy with water vapor = Heat in+ Heat generated due to reaction - Heat out with Ca(OH) 2 - loss.
Energy with water vapor
= 382,249,589 +37,436,750 - 342,353,062 - 3,743,675 = 73,589,615 kJ/day
Water vapor quantity
= 73,589,615/(4.2 × (100-50)+2256.7) = 29,833 kg/day =1,657.4 kmole/day
Chapter 10
ENERGY BALANCE
10.8 Recovery of Ammonia Column Energy Balance
CO 2 NH 3 Temperature
Boundary line
32.28992 1079.472 T
kmole/day kmole/day C
Cool gas (NH3)
H2O
1061.655
kmole/day HE
Condensed water
Cool NH4Cl Solution
H2O CO 2 NH 3 Temperature
1061.655 32.28992 1079.472 70
kmole/day kmole/day kmole/day C
Hot NH3 ,H2O mixture
H2O NaCl NH 4 Cl NaHCO 3 NH 4 HCO 3 Na 2 SO 4 Temperature Flow rate molecular weight
13,123.9 430.1 1,047.2 104.7 32.4 14.5 30 14,752.8 22.42532
kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day C kmole/day kg/kmole
Ammonia recovery unit
shaking of lime
Ca(OH) 2 H2O Temperature weight of solution Cp
575.95 13417.51 60 284135.4 3.6183
kmole/day kmole/day C Kg/day kJ/kgK
Steam
Bottom T low pressure steam
Waste water
NaCl CaCl 2 NaHCO 3 NH 4 OH Ca(OH) 2 Na 2 SO 4 H2O T Total Flow rate molecular weight
430.12 523.59 104.72 0.10 52.36 14.55 25,479.72 105 26,605.16 20.84993
kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day kmole/day C kmole/day kg/kmole
Figure 10.8- NH3 Recovery column
Objective • •
To fine Quantity of steam consumption Fine out let temperature of the cool gas
105 2
C bar
Chapter 10
ENERGY BALANCE
10.8.1 Find Outlet Temperature of the Cool Gas Assumption • 20 % Heat is lost to surrounding from HE • NH 4 Cl Solution is heated from 30C to 50C • Pressure is constant inside unit. Enthalpy change can calculated as follows ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter • Column Bottom And top Temperatures are got from literature Top Temperature 70 C Bottom Temperature 105C Energy equation Enthalpy change of cool steam + loss = Enthalpy change of hot stream Enthalpy change of hot stream Hot gas mixture is cooled up to T. Assume T is 40 C NH 3 & CO 2 mixture is cool from 70 C to 40 C this energy relies is = mole flow rate NH 3 & CO 2 mixture Energy = 1,837,568 kJ/day Steam Condense energy
= 1,061.55 2257 18 kJ/day = 43,130,800 kJ/day
Total Energy
= 44,968,368 kJ/day
Enthalpy change of cool steam Assume heat capacity of the NH 4 Cl mixture is same as water heat capacity because larger portion of mixture is include H 2 O. Energy grip by cool stream =
= =34,737,885 kJ/day
Chapter 10
ENERGY BALANCE
Heat loss to the surrounding
= total energy relies hot stream
0.2
= 8,993,674 kJ/day Substituting this value to the energy equation it satisfies. So assume temperature is Correct
10.8.2 Fine Quantity of Steam Consumption Assumption • Fully insulated the column no heat losses • NH4Cl solution feed stream line & waste stream from the column have more water compare with other substances. So Assume specific heat of solution is equal to the water specific heat • 2 bar saturated steam is used for column heating Apply energy balance for the system bounded by boundary line
Quantity of Energy supply to the column = Energy out from boundary- Energy in through boundary
Energy out from boundary Waste steam energy Waste steam is have column bottom T at 105 C, Cp same as water Waste steam energy = = 880,666,741.8 kJ/day Heat loss from HE = 8,993,674 kJ/day Heat carried from cool water =1061.655 175.2 18 =3,348,035.5 kJ/day Heat carried from cool NH 3 , CO 2 mixture = flow rate Cp
temperature
=12,696,681.8 kJ/day
Chapter 10
ENERGY BALANCE
Energy in through boundary Ca(OH) 2 mixture inlet energy
= =284135.4*3.6183*(60+273) =342,353,062 kJ/day
NH 4 Cl solution inlet energy = = 22.42 14752.8 4.2 (273+30) = 421,023,166 kJ/day
Quantity of Energy supply to the column using steam = 880,666,741.8 +8,993,674 +3,348,035.5 +12,696,681.8 - 342,353,062 - 421,023,166 kJ/day = 135,632,833.6 kJ/day 2 bar saturated steam enthalpy change = 2211.6 kJ/kg Steam consumption
=135,632,833.6/2211.6 =61,328 kg/day = 2.555330108 t/hour
Chapter 10
ENERGY BALANCE
10.9 Carbonation of Ammoniated Brine Column
NH 3 CO 2 N2
57 394 1,604
kmole kmole kmole
NH3 , CO2, N2 Mixture
H2O NH 4 OH NaCl Na 2 SO 4 Temperature flow rate mole weight
13054 1136 1477 15 36 15,683 23.0302373
kmole kmole kmole kmole C kmole/day kg/kmole
Ammoniated brine
N2 CO 2 H2O
Carbonation tower Cooling Water
Cooling water Flow rate
Out let temperature
22 1666.8
C m3/day
45
Cooling System
CO2, N2 mixture
C NaHCO3 Solution
Temperature H2O NaHCO 3 NaCl NH 4 Cl NH 4 HCO 3 Na 2 SO 4 flow rate mole weight
28 13,359 1,047 430 1,047 32 15 15,931 25.71239
C kmole kmole kmole kmole kmole kmole kmole/day kg/kmole
Figure 10.9- Carbonation column
1,604 1,474 305 40
kmole kmole kmole C
Chapter 10
ENERGY BALANCE
Objective • To Calculate Cooling water requirement Assumptions • Ammoniated brine water specific heat 3.85kJ/kg k , Density 1025kg/m3 • NaHCO 3 Solution has more water compare with other substances so assume water properties of the mixture • 10% heat loss to the surround from column • Pressure is constant inside unit. Enthalpy change can calculated as follows ΔH c 0 =
C p = a + b T – c /T2
a, b, c constants are gave in upper part of this chapter •
Cooling water is feed to the system at 22 C and heat up to 45 C
Reaction in the carbonation tower NH 4 OH (aq) + NaCl (aq) + CO 2 (g)
NaHCO 3
(s)
+ NH 4 Cl (aq)
Formation energy NH 4 OH (aq) -367.08 kJ/mole NaCl (aq)
-408.74 kJ/mole
CO 2 (g)
-395.0 kJ/mole
NaHCO 3
-949.2 kJ/mole
(s)
NH4Cl (aq) Reaction energy
-299.04 kJ/mole = =
-77.3976kJ/mole
Energy Equation for the unit Cooling water enthalpy change = energy out NaHCO 3 Solution + Energy out exit gases +reaction relies energy -energy input from ammoniated brine solution - energy input CO2 mixture - heat loss Energy out NaHCO 3 Solution = Mole flow rate heat capacity Average molecular weight = 517,836,893 kJ/day Energy out exit gases
= Flow Rate
Cp
T (this down as before section)
T
Chapter 10
ENERGY BALANCE
= 6,057,972 kJ/day Total Reaction relies energy = reacted mole
reaction relies energy
= 81,049,391 kJ/day Energy input from ammoniated brine solution = Mole flow rate heat capacity Avarage molecular weight
T = 429,670,827 kJ/day
Energy input CO 2 mixture = Flow Rate
Cp
T
=32,197,304 kJ/day Heat loss to the surrounding = (reaction energy relies + CO 2 mixture energy) 0.01 = 11,324,669 kJ/day From the above energy equation, substituting this value Cooling water enthalpy change = 131,751,455 kJ/day Cooling water quantity = 131,751,455/(4.2 =1,363,886.7 kg/day =1,363.9 m3/day
(45-22)) kg/day
Chapter 11
CONCLUSION
CHAPTER 11
CONCLUSION
The final outcome of the chemical process design is based on the process selection, material balance and the energy balance. These are some of the essential elements and preliminary stages of design that leads to a superior, cost-effective and technologically sound design. The final outcome of these components, presented in the form of a summary form the basis for the project conclusion.
•
This diagram shows the comparison of parameters calculated for the proposed plant with those obtained from literature for a plant of similar capacity. It can be clearly seen that the calculated values are very much similar to those obtained from existing plants. Data extracted from similar existing process plant
values obtained by our calculation
INPUT Main raw material
kg/t soda ash
1050 - 1600
Limestone Raw brine
NaCl (1530 - 1800) + water (4500 - 5200)
1476.8 6538.6
NH 3 make up
0.8 - 2.1
0.1
Water Process(1) Cooling
m3/t soda ash 6.0 27.8 GJ/t soda ash 3.3
2.5 - 3.6 50 -100 Energy
Fuels (lime kiln)
2.2 - 2.8
out put kg/t soda ash
Gaseous emissions CO 2
200 - 400
372.9
NH 3
< 1.5
1.9 kg/t soda ash
850 - 1100 340 - 400 160 - 220 1-11 0.3 - 2 90 - 700
1051 461 259 28 0.035 176
Liquid emissions -
Cl Ca2+ Na+ SO4-2 NH4+ Suspended solids
REFERENCE PERRY'S CHEMICAL ENGINEERING HANDBOOK, by ROBERT H. PERRY, DON W. GREEN RICHARDSON, J.F., HARKER, J.H., BACKHURST, J.R. “Coulson and Richardson’s CHEMICAL ENGINEERING VOLUME 2”. 5th ed. 2002. RICHARDSON, J.F., HARKER, J.H., BACKHURST, J.R. “Coulson and Richardson’s CHEMICAL ENGINEERING VOLUME 6”. 5th ed. 2002. RULE OF THUMB FOR CHEMICAL ENGINEERS A manual of quick, accurate solutions to every day process engineering problems. By CARL BRANAN. CHEMICAL ENGINEERING DESIGN PROJECT, A case study approach BY MARTYN S.RAY and DAVID W.JOHNSTON CHEMICAL ENGINEERING DESIGN PROJECT, A case study approach, Second edition By MARTYN S.RAY and MARTIN G. SNEESBY. A TEXT BOOK OF CHEMICAL TECHNOLOGY Volume 1 BY S.D. SHUKLA and G.N.PENDAY
Note: These references from internet were observed in July – October 2008
•
www.laxmi-group.com/kiln.html
•
www.amazon.co.uk/Small-scale-Vertical-Shaft-Lime-Kiln
•
www.massbalance.org/projects
•
http://minerals.usgs.gov/minerals/pubs/commodity/soda_ash/soda_myb05.pdf
•
http://www.webcitation.org/5WGM2f75m
•
http://www.webcitation.org/5W0IxdohY
•
http://www.cavemanchemistry.com/cavebook/chammonia.html
•
http://www.businessknowledgesource.com/manufacturing/daily_safety_measures_for_manufac turing_plants_025095.html
•
http://www.imec.org/imec.nsf/All/Solutions_Source_Implement_a_Safety_Plan?OpenDocume nt
•
http://pottery.about.com/od/safetyinceramics/tp/kilnsafe.htm
•
Msds sheets over the internet
135
Software Resources Microsoft Office Microsoft Office Visio Professional 2003 Google Earth Version 4.0.2737 Microsoft Paint Microsoft picture manager PhysProps Version 1.6.1
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