Compressor Modeling Using Aspen HYSYS Dynamics Glenn Dissinger, Director of Product Management Martyn Blanchard, Global Practice Director
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April 2013: Modeling Solids Dryers and Granulators with Aspen Plus V8
April 2013: Optimize Specialty Chemical Processes with aspenONE Engineering
March 2013: The New Aspen HYSYS for Refining
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Compressor Modeling Using Aspen HYSYS Dynamics Glenn Dissinger, Director of Product Management Martyn Blanchard, Global Practice Director
Disclaimer
Aspen Technology may provide information regarding possible future product developments including new products, product features, product interfaces, integration, design, architecture, etc. that may be represented as “product roadmaps.” Any such information is for discussion purposes only and does not constitute a commitment by Aspen Technology to do or deliver anything in these product roadmaps or otherwise. Any such commitment must be explicitly set forth in a written contract between the customer and Aspen Technology, executed by an authorized officer of each company.
Outline
Overview of HYSYS V8
Compressor Overview – Types – What’s Important to Consider – Surge
Modeling Compressors in HYSYS – Overview – Demo
Compressor Trip Case Studies – Best Practices – Customer Examples – AspenTech Global Services & Capabilities
Wrap-Up and Q&A
New Aspen HYSYS: Easier to Use Faster to Learn
Easier to Learn
Streamlined Workflow & Easier Access New Aspen HYSYS
Multiple Views
Environments Interactive Analysis
Workflow Oriented Ribbon -> Left to Right
Navigation Pane to Easily Browse Objects
Add Pure or Hypothetical Components from the Same Form
Properties Environment
Home Ribbon
Units of Measure
Simulation Options
Summary and Reports Solver
Simulation Environment
Analysis Tools
Easy Navigation Pane
Status Icons
One Dockable Model Palette
Stream Analysis Button in Ribbon
One Click to Analyze
Case Study Button in Ribbon
Drag &inDrop Variables Results Table and Plots
Outline
Overview of HYSYS V8
Compressor Overview – Types – What’s Important to Consider – Surge
Modeling Compressors in HYSYS – Overview – Demo
Compressor Trip Case Studies – Best Practices – Customer Examples – AspenTech Global Services & Capabilities
Wrap-Up and Q&A
Poll Question
Compressors – Three Typical Types Compressors are mechanical devices commonly used to increase the pressure of a gas and transport it through a pipeline
Centrifugal Most common compressor used in industry
105
•
104
Discharge Pressure (psia)
Reciprocating Piston Used for very high pressures and low flow rates
103
•
Centrifugal 102
Axial Flow
Axial Special compressor used for very high flow rates and low pressures •
10
Reciprocating
1 1 0
10
10
10
10
10
2
3
4
5
6
Inlet Flow (acfm) Reference Compressor Handbook for the Hydrocarbon Industries, Gulf Publishing Co., 1979 –
Compressors – Why Worry? From both a design and controllability / operability point of view, compressors provide unique issues and challenges
Design Issues Expensive equipment Often customized with long lead times to replace • •
Operability Issues Very fast dynamics Compressor trips are costly Compressor surge is very hazardous Specialized anti-surge control systems are common • •
•
•
What is Surge and Why is it Such a Problem? Surge is the point where a centrifugal compressor cannot add enough energy to overcome the system backpressure
Results •
Rapid flow reversals (e.g., surge)
•
Rapid changes in axial thrust
•
High vibration
•
•
Potential damage to rotor seals and bearings Catastrophic equipment failures and release of gases to atmosphere
Outline
Overview of HYSYS V8
Compressor Overview – Types – What’s Important to Consider – Surge
Modeling Compressors in HYSYS – Overview – Demo
Compressor Trip Case Studies – Best Practices – Customer Examples – AspenTech Global Services & Capabilities
Wrap-Up and Q&A
Two Operating Modes – Centrifugal & Reciprocating
Operating Mode
Theory - Efficiencies • Isentropic Efficiency = ratio of isentropic (ideal) power required for compression to the actual power required
Centrifugal
Efficiency(%) = (Power Requiredisentropic) / (Power Requiredactual) x 100%
• Polytropic Efficiency = Work for a mechanically reversible (polytropic) process W = V dP
where W = work V = volume dP = pressure difference
For a polytropic compression of a gas from P 1 to P 2 W = F 1 ( MW ) (n/ (n-1)) CF (P 1/r1) ( P 2/ P 1)((n-1 )/n) - 1]
Reciprocating
Flow (ACFM)
Polytropic Efficiency (%)
2000
69
5000
72
10,000
73
20,000
74
50,000
75
100,000
76
Pressure Ratio
Polytropic Efficiency (%)
1.5
73
2.0
79
3.0
83
5.0
85
Centrifugal Compressor Performance Curves
Typically available from the manufacturer as plots of efficiency and head vs. flow capacity of a centrifugal compressor for one or more operating speeds (e.g., RPM) Head vs. Flow Capacity
Decreasing Speed
Input for Multiple Head and Efficiency Curves The Enable Curves checkbox must be clicked One curve per speed All curves must use the same efficiency definition (Adiabatic or Polytropic) Individual curves may be activated or deactivated Remove any input value for efficiency on the Parameters page
Input for Multiple Head and Efficiency Curves Able to Add Additional Curves for Other MW Gases Compressor performance impacted by significant shifts in gas molecular weight, particularly for low pressure compressors Able to add performance curves for the different molecular weights
Centrifugal Compressor Performance Limits
Surge Limit – Lower Flow Capacity Limit – Occurs at the upper end of head vs. flow curve (for a given speed) where the performance curve’s tangent becomes zero
Stonewall Limit – Upper Flow Capacity Limit – Maximum flow rate for a given speed due to the approach of sonic flow of the gas within the compressor – Occurs at the lower end of head vs. flow curve (for a given speed) – Important for capacity control, but not as critical as surge control
Surge and Stonewall Curves
Handling Inertia of Compressor Impeller & Shaft Used to account for frictional energy loss associated with the impeller and the energy required to accelerate the rotational speed of the shaft Key Equations I = MR2 EI = I IωI dω /dt Ef = f fric I ω IωI I = rotational inertia EI = power to accelerate impeller Ef = frictional work ω = rotational speed M = mass of impeller and rotating shaft R = radius of gyration
Surge Controller
Surge controller attempts to maintain a minimum flowrate through the compressor Surge controller takes more aggressive action if compressor is close to surging Parameters for surge controller set on Surge Control page on the Parameters tab
Modeling Linked Compressors & Expanders Used to model compressors and expanders that are physically connected to the same shaft • Operate at the same speed or a specified gear ratio • Total Power Loss can be specified Notion of upstream and downstream links is arbitrary and determined by the user
Demonstration
Outline
Overview of HYSYS V8
Compressor Overview – Types – What’s Important to Consider – Surge
Modeling Compressors in HYSYS – Overview – Demo
Compressor Best Practice & Case Studies – Best Practices – Customer Examples – AspenTech Global Services & Capabilities
Wrap-Up and Q&A
Centrifugal & Axial Compressors – What’s Important
What power will it absorb and what mechanical design does it have? – – – –
What driver does it have? – – –
Gas Turbine Steam Turbine Electric Motor – variable speed or fixed speed
What arrangement are you looking at: – – – –
Back to back casing designs have particular issues Axial compressors are not very rugged Single small wheel high pressure compressors have less issues than multi-wheel ones Surging a 5MW compressor is very different to surging a 40MW one
Stages in parallel, series Multiple drivers per train or only one? How is it controlled? What protection is there for high or low pressures, low flows
What range of operating conditions will it be expected to cope with? – – – –
Differing gas molecular weights Differing ambient temperatures (gas turbine driver) Continuous recycle? Special start-up conditions (nitrogen, de-frost gas)
Best Practices for Modelling Compressors What is Needed in a Dynamic Model
Compressor dynamics – Accurate modelling of speed lines to at least minimum governed speed (don’t just assume the fan laws apply) – Inertia of all items on the string, must be related to the same speed (watch the units used) – Driver power decay rate
Accurate capacities/holdups in all pipelines to/from compressor – Return location of the recycle or hot gas bypass line – Piping details of the recycle line, both up and down stream in case choking occurs – Discharge volume up to the NRV after the compressor and the hot gas bypass or recycle take-off
Valve dynamics – Size, speed of operation and characteristics of the recycle or hot gas bypass valve – Relative timings and delays if these can be assessed
Valid Boundary Conditions
Best Practices for Modelling Compressors Compressor Trip Tests on the Dynamic Model
Discuss the basis for the trip tests. Possible scenarios are:
Trip from design? Trip from the surge line just out of recycle ? Trip at maximum power?
– Depends on expected operation and possible consequences
Examine simulation results with a critical eye – First make sure you can trust them
If the trajectory isn’t very smooth or there seems to be any sign of instability, halve the sample time and repeat it. Continue to do this until there is no discernible difference between results. If you are inexperienced in dynamics you may want to do this in any case.
– Next gather the facts from the model
How long before it enters surge (if it does) What is the power at the time it enters? Does the model predict recovery within a very short period (1 second or so)
Best Practices for Modelling Compressors Modelling the Compressor under Surge Conditions
The only details you can rely on are the time and power of entry into surge – No commercially available dynamic compressor model accurately predicts behavior in surge
You may draw some tentative conclusions from the time spent in surge according to the model – Less than 0.5 seconds on a HYSYS Dynamics model is often unlikely to be real based on feedback from operations
Always discuss with the Compressor Vendor, in the end it is their decision on whether action needs to be taken Ideally surge should be totally prevented in all cases
Best Practices for Modelling Compressors Possible Design Changes to Avoid Surge
Minimize the discharge volume
Increase the recycle valve size (within the limits of controllability) Increase the speed of opening of the recycle valve
Consider a parallel cold gas bypass valve around the recycle valve Consider a hot gas bypass valve – Considerations such as leakage, vibration etc. often make this an unattractive option
Best Practices for Modelling Compressors Modelling the Anti-Surge Control System
Surge control systems are designed to detect the imminent start of surging, and prevent the compressor from reaching this operating condition Basic Strategy – Open a surge recycle valve that will allow outlet flow from the compressor to recycle back to the compressor inlet, thus providing a flow rate through the compressor above the minimum surge limit.
For conceptual and FEED studies, use the HYSYS Anti-Surge controller
For detailed design, there may be a need to use a proprietary system: – CCC, Dresser Rand, Man-Turbo, Solar, Triconex etc
Most of these systems use multiple control lines, linking between serial and parallel units, surge protection by moving lines, various characterizers, algorithm selection etc. and can be quite complex to set up In some cases the Vendor will provide software (at a cost) or an emulator; in others just the algorithms are used and settings
PETRONAS – Malaysia LNG Dynamic Simulation for LNG Plant Revamp Challenge
Solution
Results
Liquefied Natural Gas (LNG) plant revamp design verification Ensure compressor anti-surge system will provide adequate protection from the risk of damage under all scenarios Verify controllability of the compressors during unit upsets, start-up, shutdown and normal operation scenarios Check the start-up and shutdown procedures for compressors Verify compressor systems and equipment design conditions Ref: Siti Rafidah Moslim, Petronas, Vikas Si ngh, AspenTech, aspenONE Global Conference, Boston, May 2010
PETRONAS – Malaysia LNG Dynamic Simulation for LNG Plant Revamp Challenge
Solution
Results
Aspen HYSYS Dynamics model to represent actual equipment, piping arrangements and controls – A high fidelity emulation of CCC controller to reproduce the precise behavior of anti-surge control – Torque and power characteristics of the gas turbines to reproduce precise conditions during start-up and shut down
Over 45 Scenarios were simulated and analyzed in an iterative process using HYSYS Event Scheduler Ref: Siti Rafidah Moslim, Petronas, Vikas Si ngh, AspenTech, aspenONE Global Conference, Boston, May 2010
PETRONAS – Malaysia LNG Dynamic Simulation for LNG Plant Revamp Challenge
•
•
•
Solution
Better sizing of recycle valves and bypass valves based on all failure scenarios compared to steady state
Results
Final Results (after implementing recommendations)
Relieving loads confirmed for various scenarios which form the basis for key relief valve sizing Start-up and shutdown procedures tested in advance of actual plant start-up
Safe Compressor Operating Points (outside surge line)
Ref: Siti Rafidah Moslim, Petronas, Vikas Si ngh, AspenTech, aspenONE Global Conference, Boston, May 2010
JGC – Ourhoud Algeria Gas Processing Facility Verification of Compressor Performance Challenge
Solution
Compressor operation and control critical to success of the overall gas processing project Customer determined that a dynamic simulation study was essential to verify the performance of the compressors and the associated control systems
Results
JGC – Ourhoud Algeria Gas Processing Facility Verification of Compressor Performance Challenge
AspenTech Global Services commissioned to develop a Aspen HYSYS Dynamics model to represent actual equipment, piping arrangements and controls – 5-stage compression train – Detailed vendor (Nuovo Pignone) compressor curves implemented – Production manifold & injection manifold modeled to match piping holdups
Solution
Many scenarios were simulated and analyzed covering trips, feed changes, start-ups etc. The project was completed to a fixed budget and was executed within 12 weeks. This met JGC's design and construction schedule and enabled equipment changes to be ordered.
Results
JGC – Ourhoud Algeria Gas Processing Facility Verification of Compressor Performance Challenge •
Solution
The study revealed many aspects that were significant to the operation and control of the compressors, one example below: •
In the original control scheme the recycle from the Lift Gas Compressor (LGC) was taken downstream of the cooler. With a large pressure drop a large Joule Thomson effect was observed so that the feed to the Booster Compressor (BC) cooled and the heavy components dropped out in the suction drum. In order to avoid this it was recommended that the recycle be taken upstream of the cooler with a smaller valve on temperature control to prevent the suction temperature increasing too much. This modification was subsequently agreed, implemented and proved to work well.
Results
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Outline
Overview of HYSYS V8
Compressor Overview – Types – What’s Important to Consider – Surge
Modeling Compressors in HYSYS – Overview – Demo
Compressor Trip Case Studies – Best Practices – Customer Examples – AspenTech Global Services & Capabilities
Wrap-Up and Q&A
aspenONE Engineering V8.0
The New HYSYS
Solids Modeling in Aspen Plus
Activated Economic Analysis
Activated Energy Analysis
Integrated Exchanger Design
Plant Data View
Easy To Adopt
aspenONE Engineering
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Inprocess
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Reliability of Dynamic Simulation to Reproduce Plant Dynamics
Refinery wide modeling with Aspen HYSYS
Jord International
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Optimization of a mixed refrigerant LNG process
Refinery energy reduction using Aspen HYSYS
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What Next?
Get more information now – Additional resources available at: http://www.aspentech.com/products/aspen-hysys.aspx http://www.aspentech.com/products/aspen-hysys-dynamics.aspx – Videos also available at: www.youtube.com/user/aspentechnologyinc
Contact info for today’s presenters and hosts – – – –
Glenn Dissinger
[email protected] Martyn Blanchard
[email protected] Luisa Herrmann
[email protected] Ron Beck
[email protected]
