Heat Exchanger Control Systems

Some Types of Heat Exchangers

• Sensible Heat Cooling and Heating• Change of Phase Boilers and Condensers• Partial Condensing or Partial Vaporization • Wiped Film Units for Viscous Fluids

Basic Model

• Simple Heater Loop

• Actual loop on P&ID

Riggs & Karim, Chemical and Bio-Process Control, 2006, p. 12

Control Loop Options

• Feedback has some lag time

• Feedforward based on steady state process

Perry, Chemical Engineers Handbook, 7th Ed., p. 8-17

Alternate Methods

• Bypass Control Options

• Combined Feedback & FeedForward

Marlin, Process Control Designing Processes and Control Systems for Dynamic Performance, 2000, p.784

Riggs & Karim, Chemical and Bio-Process Control, 2006 p. 401

Physical Installation • Cascade control

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/control-applications/pressure-control-applications.asp

Change of Phase HX

• Condenser on Distillation Column

http://eweb.chemeng.ed.ac.uk/courses/control/restricted/course/fourth/course/module3-1.html

Change of Phase HX

• Partial Condenser on Distillation Column

http://eweb.chemeng.ed.ac.uk/courses/control/restricted/course/fourth/course/module3-1.html

Change of Phase HX

• Reboiler on Distillation Column

http://eweb.chemeng.ed.ac.uk/courses/control/restricted/course/answers/fourth/answer2.html

Condenser Pressure ControlTowler & Sinnott, Chemical Engineering Design Principles, Practice and Economics of Process Design, 2008, p. 279

Steam Boiler Control

• Steam Pressure is used to control fuel feed rates

• Can be linked to consumer

http://www.powermag.com/issues/features/Drum-pressure-the-key-to-managing-boiler-stored-energy_300.html

Actual Boiler Control Systems

• Allow for capacitance in system

http://www.powermag.com/issues/features/Drum-pressure-the-key-to-managing-boiler-stored-energy_300.html

Boiler Drum Level Control

• Can use feedback, feedforward & combination

Riggs & Karim, Chemical and Bio-Process Control, 2006, p. 12

Partial Condenser Options

• Can control reflux rate

William L. Luyben, Alternative Control Structures for Distillation Columns with PartialCondensers, Ind. Eng. Chem. Res. 2004, 43, 6416-6429

Partial Condenser Options

• Can control condenser cooling rate

William L. Luyben, Alternative Control Structures for Distillation Columns with PartialCondensers, Ind. Eng. Chem. Res. 2004, 43, 6416-6429

Partial Condenser Options

• Can control reflux ratio

William L. Luyben, Alternative Control Structures for Distillation Columns with PartialCondensers, Ind. Eng. Chem. Res. 2004, 43, 6416-6429

Wiped Film Evaporator• Control product feed rate

http://www.artisanind.com/ps/docs/rototherm.pdf