Simulation and Compressor Control Case Study
Transcript of Simulation and Compressor Control Case Study
Confidential Property of Schneider Electric
Turbomachinery Simulation and Compressor Control
Case Study
Presented by: Hector Buchelly
Compressor Components and Operational Safety
Dynamic Simulation
Case Study
Application of Dynamic Simulation
Agenda
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– Compressor
– Piping
– Heat exchangers
– Knockout drums
– Anti-surge valves
– Instrumentation
– Control system
F T
P
T
Elements are designed to maintain throughput and
keep the compressor at a safe operating point.
Compressor System Components
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Surge
Surge is a condition at which the
compressor cannot raise the pressure
any higher without causing a complete
breakdown of steady flow.
Choke (Stonewall)
Because the compressor operates at a
very high mass flow rate, flow through
the compressor cannot be increased
after sonic velocity is reached.
Compressor Operational Safety
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• Defining the Operating Point
• Locating the Surge Limit
• Surge Acceleration (Curve
Shape)
• Interacting with Control Loops
• Meeting Load-Sharing
Requirements
Surge Control Application
Challenges
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What is Surge?
A condition wherein the compressor is unable to
maintain a greater force than system resistance.
The Surge Cycle
1. System resistance
increases discharge
pressure required
(operating point moves
up the curve)
2. Operating point nears
the Surge Limit
3. Operating point goes
into the Surge Region Flow
4
Pressure
1
2 3
5
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The Surge Cycle
4. Flow reverses as
discharge pressure drops
5. Drop in discharge
pressure re-establishes
forward flow (Compressor
resumes full flow)
Since resistance has
not changed, surge will
continue until cycle is
broken
Flow
4
Pressure
1
2 3
5
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An operating point can move from stability
to surge in less than 100 milliseconds!
A complete surge cycle takes from ½ to 3 seconds,
depending on compressor size and piping volume.
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• The operator sees
process upset because
of flow reversals
• The machinery person
sees damage to seals
• The plant manager sees
catastrophic compressor
failure if surge is severe
Why is surge bad?
Several viewpoints:
How does simulation work across industries?
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Real Plane Virtual Plane
Real Plant Virtual Plant
How does simulation work in a plant?
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• Shows components and
thermodynamics
• Includes rigorous dynamic behavior
model of equipment and pipes
• Provides a high-fidelity rendering of
instruments and controls
• Enables testing of scenarios and
alarms
• Helps train operators
What is dynamic simulation?
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Safely study the integration of TMC equipment and controls
Boost system reliability
Avoid costly errors, thereby reducing expenses
Improve efficiency in real time
Reduce downtime during operation by debugging the system
Increase machinery availability
Why use simulation?
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Let’s consider a new field
unit consisting of:
• Elliot Steam Turbine
(1200 HP, 660# inlet
pressure)
• Atlas Copco Ethane
Kickback
Compressor (TP-
14/10)
Case Study
Control Hardware:
• Two-chassis Tricon System
• Bently Nevada BN3500
Control Software (Tristation 1131):
• Turbine – Compressor Start Stop Control
• Turbine Speed Control
• System Shutdowns
• Compressor Surge Control
• Decoupling
• Lube Oil Aux Pump Control
DCS: Suction Pressure Control in DCS (Guide Vanes)
Scope of Supply
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SimSci products:
• DynSim for the dynamic model
• TriSim to connect model to control program (PT2)
via Tristation Emulator
Modeling Software
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• Local Operator
Panel
• Wonderware HMI
• Honeywell DCS
(represented in
model)
Operator Interface
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Simulation Architecture
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System: Turbine and
Process
Control
System
Application
Human
Machine
Interface
Simulation: Dynsim Trisim Tristation
Emulator
Wonderware
Recycle valve critical flow
Motor torque curves
Shaft rotating inertia WK2
Piping and KO drum volumes for accurate
transients
Performance curves
Fluid feed composition
Intercoolers
Vapor-liquid equilibrium “flash”
Dynamic Simulation: Rigorous Model
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We start with the P&IDs, and then complete data input for each component.
Building the Model
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Process Design
Controls Configuration
Start Up
Plant Operation
Applying the Model
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Before completing the Front End Engineering
Design study or beginning commissioning,
verify elements of the compressor system:
• Compressor specifications
• Anti-surge valve sizing
• Compressor trips, driver failure, loss of instrument air, etc.
• Valve opening time
Field Hardware Verification
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• Ascertain the best anti-surge &
performance control approaches
• Design and prove the value of Triconex
decoupling control algorithms
• Establish start-up and shut-down
sequencing
• Position the startup guide vane
• Position T&T valve
Control Strategy Definition
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Universal Surge Line
20 40 60 80 100 0
1
2
3
4
5
Pd
Surge Line
Ps
__
h Ps
__ %
Speed
Curves
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Setpoint Hover
20 40 60 80 100 0
1
2
3
4
5
Pd
Surge Line
Ps
__
h Ps
__ %
Control Line
Current Operating
Point
Setpoint Hover
Hover Setting
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Control Line Recalibration
20 40 60 80 100 0
1
2
3
4
5
Pd
Surge Line
Ps
__
h Ps
__ %
Control Line
Current
Operating
Point
Recalibrated
Control Line
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20 40 60 80 100 0
1
2
3
4
5
Pd
Control Line
Surge Line
Ps
h Ps
%
0%
100%
Valve Output
Surge
Override Line
Surge Override
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Decoupling Capacity Control
Breakpoint is stationary if Surge
Margin is between 1% and 3%:
• Speed is not reduced further, since
this would drive the compressor into
surge
• Further decrease in Process
Controller Output will immediately
open recycle valve
Breakpoint moves to right if Surge
Margin < 1%:
• Increases speed setpoint to speed
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Process Design
Controls Configuration
Start Up
Plant Operation
Applying the Model
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• Closed loop testing during
FAT
• Software testing independent
of hardware
• Loop tuning before
commissioning
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Testing
h/P1
Max
Gain
Normal
Gain
Min
Gain
Surge
Line
Control
Line
Adaptive Tuning
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Quickly responds to surge condition but doesn’t exceed response time of system
Fast Opening
Allows turbine speed controller/ process cascade controller to smoothly adjust to new process operating conditions
Slow Closing
Fast Opening, Slow Closing
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Manual Recycle Valve Control
• Operator can open the recycle valve only when above the surge controller demand
• Operator cannot close the recycle valve below the surge controller demand
Partial Authority
• Operator can close and open the recycle valve with no surge protection
• Useful to stroke test recycle valve prior to startup
• Useful in some fallback scenarios
Full Authority
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• Determine effectiveness of
controls
• Debug any control logic on the
system rather than on the
actual machine in field
• Establish initial controller
tuning
• Evaluate overrides that may
be necessary for particular
upsets
Pre-startup Controller Tuning
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Discovery:
• Speed couldn’t be
well controlled during
startup
Why?
• Design minimum stop
on IGV meant too little
mechanical load
Fix?
• Use model to find
optimum minimum
stop for IGV
Tune Speed Controller Pre-commissioning
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Process Design
Controls Configuration
Start Up
Plant Operation
Applying the Model
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Shorter
Commissioning
Schedule
Error-free
Startup
Operator
Training
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Benefits: Initial Startup Phase
• Final software
testing
• Controller tuning
using normal
field techniques
• Surge line
testing
Final Verification Pre-startup
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Discovered:
• Even though a full FAT
was performed,
simulation allowed us to
find and correct minor
logic errors. We also
made changes to the
HMI as requested by
operations.
Result:
• Saved time during
commissioning. Normal
schedule for a unit is 4–
5 days. Actual time
spent: less than 1 day.
Pre-commissioning Logic and HMI Checkout
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Process Design
Controls Configuration
Start Up
Plant Operation
Applying the Model
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Operator Training
Event Analysis
Process Modifications
Control Modifications
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Discussion:
How can we use the model when the system is online?
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Offline Test
With simulation, we are able to perform
multiple system upsets that would be
impossible to test in the field.
Results: we can tune the system
accurately and gain confidence in the
controls.
What concerns has simulation identified in actual situations?
• Recycle valve too small
• Recycle valve too slow
• One stage surges on shutdown
• EPC control strategy is “not optimum”
Before implementation, simulation can verify process
changes. Even with basic models, simulation enables more
effective closed loop software and HMI testing.
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Identifying Concerns Via Simulation
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KEY TAKEAWAYS
•Simulation saves money and time.
•It improves safety and increases availability.
•We have extensive experience with dynamic simulation modeling.
•Our model ties directly to the actual controls and HMI—a huge differentiator.