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Economic Plantwide Control usingCommercial Process Simulation Software

Name, title of the presentation

Adriana Reyes Lúa Supervisor: Sigurd SkogestadCo-supervisor: Vladimiros Minasidis

TKP4550 Specialization Project Fall 2013

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Plantwide Control

• “Control structure design for complete chemical plants”.

• Systematic procedure for the design of an economic plantwide control, based on steady state plant economics.

– Top down

– Bottom up

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Plantwide Control

1. Top-down

Step 1: Define operational objectives (economics) and constraints.

Step 2: Identify steady state degrees of freedom and determine steady state operation conditions.

Step 3: Identify candidate measurements y and select CV1 =Hy .

Step 4: Select the location of the throughput manipulator.

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Plantwide Control: The Challenge• To be accepted and used in industry, the procedure:

• must result in processes with near optimal operation • should not employ complex control technology.

• Proposed solution:• Develop an automated procedure. • Use of commercial process simulators?

Design mode vs. operation mode. Poor numerical properties. Not standardized.

Intuitive Widely used Pre-loaded information

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Objective

To explore the use of commercial process simulators to generate process models suitable for an

automated economic plantwide control procedure.

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Methanol Plant

• Reactor, a separator, and a recycle stream with purge

Scheme of a methanol plant (Løvik,2001)

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Methanol Plant

4 steady state degrees of freedom

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Methanol Plant Simulation

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”Operation Mode” Simulation

Reactor

Kinetics Sizing Ergun Δp

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”Operation Mode” Simulation

Circulationcompressor

Actual gas flow is limited by compressor curve.

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”Operation Mode” Simulation

Heat Exchangers

UA is fixed. Inlet temperatures

are given.

From recirculation

To Separator

To Reactor

From Reactor

Find Tc,out!

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Optimization Problem

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Plantwide Procedure: Step 1

Define operational objectives (economics) and constraints.

OK!

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Optimizing the Simulation

Hard constraints as inputs

Step 2

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Optimizing the Simulation

Matlab UniSim

• NLP Solver• fmincon • NLP Model

COM

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Plantwide Procedure: Step 2

Identify steady state degrees of freedom.

Identify important disturbances

Determine steady state operation conditions.

OK!

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Conclusion

• The use of commercial process simulators to generate process models suitable for an automated economic plantwide control procedure was explored.

• NLP model independent of NLP solver.

• The model for the methanol plant in ”operation mode” was generated.

• Recommendations for set-up of heat exchangers and compressors were given.

• Steps 1 and 2 of plantwide control procedure achieved.

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Thank you for your attention!