unique applications for embedded model predictive control ... · embedded model predictive control...
TRANSCRIPT
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Unique Applications for Embedded Model Predictive
Control Technology Paper 137a
James Beall
Principal Control Consultant
Emerson Automation Solutions
April 2, 2019
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Speaker –James Beall
• Principal Process Control Consultant with Emerson Automation Solutions since 2001
• 37+ Years experience with Petrochemical Process Automation
• Specialist in advanced regulatory control and multivariable control
• Eastman Chemical Company, Texas Operations (1981-2001)
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Introduction
•What is MPC?
•What is Embedded MPC?
•Example Uses of Embedded MPC
•Questions
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“MPC”: Multivariable, Model Predictive Controller
Uses the Past to
Predict the Future
Past Present Future
Modeled
Relationship
Process Input
Process Output
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“MPC”: Multivariable, Model Predictive Controller
Energy Flow
(manipulated)
Lime Mud Flow
(optimized and
disturbance)
ID Fan Speed
(manipulated)
Hot-end Temperature
(controlled)
Cold-end Temperature
(controlled)
Excess Oxygen
(controlled and constraint)
Hood Draft Pressure
(constraint)
Kiln Stack Emissions
(constraint)
Lime Kiln Process
Manipulated
Con
tro
lle
d
FC 1-3
Reboil Rate
AT 2-2
A btms comp
TC 1-2
Top Temp
AT 1-2
A ovhd comp
Con
str
ain
t
FC 1-2
Reflux rate
TT 1-4
Reflux temp
TT 1-5
Tower A temp
Disturbance
PT 1-3
Steam PressureFC 1-1
Feed Rate
DP 1-1
Delta P
FEED TGT
A ovhd comp
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What is Embedded MPC?
Embedded MPC:
• NO extra databases
• NO database synchronization issues
• NO watchdog timers
• NO fail/shed logic design
• NO custom DCS programming
• NO interface programming
• NO operator interface development
Traditional APC Embedded MPC:
• Can run in DCS controllers/stations
• Redundant and fast (e.g. 1/sec)
• Integrated operator user interface
• Configuration through standard configuration tools
• Automated step testing and Model ID
• Off-line simulation and testing
• Implementation by plant control engineers
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Traditional and Embedded MPC
•Traditional MPC• Well developed, full featured
technology
• Higher “minimum” project cost
• Medium to larger req’d for ROI
•Embedded MPC• Less features to “fit” in DCS
• Lower implementation cost
• ROI for smaller
MPC SizeLarge
Medium
Small
Traditional
MPC
Embedded
MPC
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Examples of Unique Applications
• “Big Valve, Little Valve”
•Dead time dominant SISO
•Feed Forward and Override
•Waste heat steam generator
•Waste heat recovery – steam export
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“Big Valve, Little Valve”
•PID Considerations• Large PV disturbances can
saturate Small valve – loss of control
• ZC should have “gap” control to eliminate potential Large valve limit cycles
Neutralizer
AC
1-1
AC
1-1
AT
1-1
PID Controller
Large
(Coarse)
Small
(Fine)
ZC
1-1
ZC
1-1
Integral only Controller
(CV is Implied Fine
Control Valve Position)
Reagent
CV
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“Big Valve, Little Valve”•MPC Considerations
• Large PV disturbances handled by moving both Large and Small valves
• Use constraint control on small valve position to eliminate large valve limit cycles
Neutralizer
AC
1-1
AC
1-1
AT
1-1
MPC Controller
Large(Coarse)
Small(Fine)
Reagent
MPC Design
CV1 Tank Discharge pH
MV1 Small Valve
MV2 Large Valve
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“Big Valve, Little Valve”
Successive Load Upsets Set Point Change Trim Valve SP Change
Critical Process Variable
Coarse Valve
Trim Valve
MPC Performance
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Deadtime Dominant Loops
Tau
Dead time >= 4*Tau (definition varies)
~4*Tau
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Deadtime Dominant Loop
• Reactor coolant supply temperature
• “Mixing” temperature response fast (~15 sec Tau)
• Step test revealed 80 seconds of dead time!
TC
MPC Variables
CV1 Coolant Temperature
MV1 3-Way Valve
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Feed Forward with MPC
• Temperature of cooling water impacts outlet temp
• Typically implemented as feedforward to PID (calculate FFWD Gain, dead time, lead-lag
• Use TI-2 as a Disturbance Variable with MPC-simple model
TC-1
TI-2
MPC Variables
CV1 Coolant Temperature
MV1 3-Way Valve
DV1 Cooling Water Temp
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Override/Constraint with MPC
• Suppose there is a minimum flow through exchanger tubes, FI-3, to avoid fouling
• Typically done with 2 PID’s and a hi/lo selector
• Implement as a Constraint Variable (LV) with MPC
TC-1
FI-3
TI-2
MPC Variables
CV1 Coolant Temperature
CV2 Minimum Tube Flow
MV1 3-Way Valve
DV1 Cooling Water Temp
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Optimize Small Applications
TCJC
Fractionator
PA
Steam
BFW
TC
Debutanizer
Duty
BTU/hr
Goal is to maximize steam production while ensuring sufficient heat for
debutanizer reboiler. Also, handle limited BFW supply.
FI
PI
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Optimize Small Applications
Objective: Maximize steam production
Implementation time: 2 days
Benefit: $120K/year
Steam
BFW
MPC
MV
JCDuty
BTU/hr
CV
PI
FI
CV
FI
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Heat Recovery
Steam
Steam Drum
Condensate Drum
Primary
Secondary
Fin-Fan Cooler
350 PSIG Steam Header
150 PSIG Steam Header
150 PSIG
Steam Users
Steam Export
SIC SIC
Reactive Distillation
Column
BFW
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Heat Recovery
150
PSIG
Steam
Users
Steam
Steam Drum
Condensate
Drum
Primary
Secondary
Fin-Fan Cooler
350 PSIG Steam Header
150 PSIG Steam Header
Steam Export
SIC SIC
Reactive
Distillation
Column
BFW
MPC Variables
CV1 Steam Drum Pressure
CV2 Cond. Drum Pressure
CV3 Steam Export Pressure
CV4 350-150 PRV Position
MV1 Steam Export Valve
MV2 Steam Valves to Cooler
MV3 Total Fan Speed
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Heat Recovery• Plant personnel learned about MPC application selection,
MPC design and commissioning
• Identified a steam valve that had excessive leakage at shutoff
• Increase average steam export ~3000 lb/hr = $240K/year, repair of leaking steam valve $200K/yr benefit
• Benefit• Implementation time – 2 weeks• Benefit – $440K/yr• Payback period – 3 weeks
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Summary• Traditional MPC is well developed, full function technology but
requires a high minimum investment requiring larger projects to provide ROI
• Embedded MPC has less features but is easy to implement, low implementation cost and executes fast resulting in smaller projects to provide ROI
• Each technology has a “best fit”, so utilize each technology where they provide the best ROI
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Questions