Chap_01_Marlin_2013.ppt

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Process Control: Designing Process and ControlSystems for Dynamic Performance

Chapter 1. Introduction to Process Control

Copyright Thomas Marlin 2013

The copyright holder provides a royalty-free license for use of this material at non-profiteducational institutions

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CHAPTER 1 : INTRODUCTION TOPROCESS CONTROL

When I complete this chapter, I want to beable to do the following.

Explain the feedback concept applied tocontrol

Explain and identify the three elements in

a feedback loop Be able to apply feedback manually to

many chemical process examples

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CHAPTER 1 : INTRODUCTION TOPROCESS CONTROL

Outline of the lesson.

Why Process Control and Why Now? Basic Questions about Control

- What does a feedback system do?- Why is control necessary?- Why is control possible?- Where is control done?- How is control documented?

Workshop

Self-Study Guides

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When I run a kinetics experiment, how do Imaintain the temperature and level at desiredvalues?

How do I manufacture products with consistentlyhigh quality when raw material propertieschange?

How much time do I have to respond to a

dangerous situation?

WHY HAVE A PROCESS CONTROL COURSE ?

Every engineer needs basic knowledge about control.Many exciting career opportunities exist for a

technical specialist.

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We started with steady-state analysis because it iseasier and important.

We are building expertise in fundamentals (fluids,heat transfer, thermo, etc.) and process units(distillation, CSTR, etc.). Now we have examplesthat need control!

We need to master control before integrating our

knowledge in process design?

WHY NOW FOR THE CONTROL COURSE?

Its a perfect time to learn how to drive the chemical process. With this insight, we will be able to design plants

that can be controlled safely and produce high quality products.

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WHAT DOES A FEEDBACK SYSTEM DO?

Lets look at a few examples first. Then, we willdevelop a general concept.

Describe your methodfor driving a car.

Could you drive a carwithout looking outthe windshield?

What must beprovided by the cardesigner?

Can a good designeliminate the need tosteer?

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Lets look at a few examples first. Then, we willdevelop a general concept.

Describe how homeheating works.

Describe the dynamicbehavior of T.

What must beprovided by the housedesigner?

Can a good designeliminate the need tochange the heating?

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Why does the temperature cycle?

Is this good enough for all variables in a chemicalprocess? Hint: if yes, the course is over!

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The control systems appear to have three basic elements.

PROCESS

Inputs Outputs

FINALELEMENT

CONTROLLER

SENSOR

Desired value

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PROCESS

Inputs Outputs

FINALELEMENT

CONTROLLER

SENSOR

Desired value


What is a typical final element forchemical processes?

How do we select the sensorlocation?

What is the meaningof the arrows?

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PROCESS

Inputs Outputs

FINALELEMENT

CONTROLLER

SENSOR

Desired value


FEEDBACK CONTROL makes use of an output of a systemto influence an input to the same system.

CONTROL (verb): To maintain desired conditions in aphysical system by adjusting selected variables in the system.

input = cause output = effect

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Caution : Common misunderstanding in terminology!

Common vernacular

Negative feedback: You arean idiot!

Positive feedback: That wasa good idea. Thank you!

Engineering & Science

Positive feedback: Action toincrease the error from

desired.

Negative feedback: Actionto reduce the error fromdesired.

Good!

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WHY IS CONTROL NECESSARY?

T

AC B

v1

v2

One word: DISTURBANCES ! Give someexamples in the CSTR in the figure.

We want to achieve thefollowing:1. Safety2. Environmental Protect.3. Equipment protect.

4. Smooth operation5. Product quality6. Profit7. Monitoring and diagnosis

Chapter 2

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WHY IS CONTROL NECESSARY?

One word:DISTURBANCES !

Give some examplesin the distillation

tower in the figure.

F R

F V

xB

xD

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WHY IS CONTROL POSSIBLE?

T

A

C B

v1

v2

Control is possible only if the engineer providesthe required equipment during process design .

Part 1: Control equipment

Final element

Finalelement

Sensors Computingand interfacefor person

Communication

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WHY IS CONTROL POSSIBLE?

Control is possible only if the engineer providesthe required equipment during process design .

Part 2: Process equipment

How do we determine

the heat transfer area?

T

A

C B

v1

v2

How do we

determinethe reactorvolume?

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WHERE IS CONTROL DONE?

Sensors, localindicators, andvalves in the process

Displays of variables,calculations, and commandsto valves are in thecentralized control center.

Shows an older-style

control panel

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Creative Commons License, see http://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_- _Center_and_Left_Panels.jpg

http://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://upload.wikimedia.org/wikipedia/commons/a/aa/Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpghttp://en.wikipedia.org/wiki/File:Nuclear_Ship_Savannah_-_Reactor_Control_Room_-_Center_and_Left_Panels.jpg

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Sensors, localindicators, andvalves in the process

Displays of variables,calculations, and commandsto valves are in thecentralized control center.

Shows a modern, computer-

based control panel

Central control room

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Photo courtesy of Worsley Alumina and Honeywell

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HOW IS CONTROL DESIGN DOCUMENTED?

LC

FC

TC

A

Piping and instrumentation (P&I) drawings providedocumentation.

The system is too complex to describe in text.

We must use standard symbols.

F = flow

L = level

P = pressure

T = temperature

..

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CHAPTER 1: INTRODUCTION - WORKSHOP 1

You are implementingcontrol manually.

a. Explain the principlefor a typical flowsensor

b. Explain how the finalelement affects the

controlled variable.c. Explain the correct

action if you want toincrease the controlled

variable

pump valve

sensor

Flow Control

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You are implementingcontrol manually.

a. Explain the principlefor a typical liquidlevel sensor

b. Explain how the finalelement affects thecontrolled variable.

c. Explain the correctaction if you want toincrease the controlled

variable

Level Control

pump valve

sensor

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You are selling a gas to a customer based on the volumetricflow at standard conditions. You decide to use an orificemeter to measure the flow rate.

You have learned that the gas flow density may change by-10% from its design (expected) value. What do you do?

compressor valve

Orifice meter

CustomerOurplant

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The next page contains a Piping and Instrumentation drawing (P&ID) for asolvent storage tank. First, refer to the following references.

Marlin (200) Appendix A Sample chapter of Design textbook by Turton et.al.

http://www.pearson.ch/download/media/9780130647924.pdf

Answer the following questions.

Determine the flow of fluid in and out of the process Find examples of measurements displayed locally, in a local control

room and a centralized control room. Evaluate these choices. Identify different types of signal transmission. Identify different kinds of valves and evaluate the choices. Identify examples of safety and equipment protection. Suggest additions to improve this design.

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Source: Tony R. Kuphaldt, CC License, http://www.openbookproject.net/books/socratic/sinst/output/realistic_diagrams.pdf

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CHAPTER 1 : INTRO. TO PROCESS CONTROL

How are we doing?

Explain the feedback concept applied tocontrol

Explain and identify the three elements ina feedback loop

Be able to apply feedback manually tomany chemical process examples

Lots of improvement , but we need some more study! Read the textbook Review the notes, especially learning goals and workshop Try out the self-study suggestions Naturally, well have an assignment!

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CHAPTER 1: LEARNING RESOURCES

SITE PC-EDUCATION WEB

- Instrumentation Notes

- Interactive Learning Module (Chapter 1)

- Tutorials (Chapter 1/2)

Textbook Appendix A on drawing symbols

- See references for much more detail or symbols

- See following general reference book by Tony R.Kuphaldt on instrumentation and control

http://www.openbookproject.net/books/socratic/sinst/

www.pc-education.mcmaster.ca/
http://www.openbookproject.net/books/socratic/sinst/http://www.pc-education.mcmaster.ca/http://www.pc-education.mcmaster.ca/http://www.pc-education.mcmaster.ca/http://www.pc-education.mcmaster.ca/http://www.openbookproject.net/books/socratic/sinst/

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CHAPTER 1:SUGGESTIONS FOR SELF-STUDY

1. Write down the rules (algorithm) that you use when youdrive an automobile or bicycle.

2. Formulate questions with answers and trade with

members of your study group.

3. Find a P&I drawing in one of the textbook references (orrecent volume of Chemical Engineer ing Progress ),explain the strategy, and prepare questions for yourinstructor on aspects that you do not understand.

4. Find examples of control systems in your house. (Hint:look at the heating, air conditioning, toilet tank, and themost highly automated room, the kitchen.)

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Chap_01_Marlin_2013.ppt