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CHAPTER 2 : CONTROL OBJECTIVES

AND BENEFITS

When I complete this chapter, I want to be

able to do the following.

Recognize examples of the seven (7)control objectives in chemical processes

Calculate indicators of variability in a

process variable

Be able to calculate the economic impact

of variability

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Outline of the lesson.

Seven (7) Control Objectives

1. Safety

2. Environmental protection

3. Equipment protection4. Smooth operation

5. Product quality

6. Profit

7. Monitoring and diagnosis

Variability measures

Economic impact of variability

Workshop

CHAPTER 2 : CONTROL OBJECTIVES

AND BENEFITS

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EXAMPLE PROCESS: FLASH SEPARATION

Feed

Methane

Ethane (LK)

Propane

Butane

Pentane

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

Lets discuss

this process

P 1000 kPa

T 298 K

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 PC

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

High pressure

in drum is

dangerous

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Never release

hydrocarbons

to atmosphere

To flare

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

LC

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

No flow could

damage the

pump

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

FC

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Always keep

the production

rate smooth

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

AC

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Achieve L.Key

by adjusting

the heating

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

AC

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Use the least

costly heating

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Give example

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

Calculate & plot

key parameters,

e.g., UA.

time

UA

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Feed

Vapor

product

Liquid

productProcessfluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

1. Safety

2. Environmental

Protection

3. Equipment

protection

4. Smooth operation

production rate

5. Product quality

6. High profit

7. Monitoring &

diagnosis

SEVEN CONTROL OBJECTIVES

All seven must be achieved. Failure to do so

will lead to operation that is

unprofitable or worse, unsafe.

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BENEFITS FROM PROCESS CONTROL

When we control a process, we reduce the variability of

key variables to achieve the seven objectives.

Without feedback control

0 50 100 150 200 250 300 350 400 450 5002

3

4

5

6

time (min)

outletconcen

tration

0 50 100 150 200 250 300 350 400 450 50049

49.5

50

50.5

51

time (min)

valveposition(%o

pe

n)

Composition (% H. Key)

Reflux valve

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BENEFITS FROM PROCESS CONTROL

When we control a process, we reduce the variability ofkey variables to achieve the seven objectives.

With feedback control

0 50 100 150 200 250 300 350 400 450 5002.5

3

3.5

time (min)

outletconcentration

0 50 100 150 200 250 300 350 400 450 50020

40

60

80

100

time (min)

valveposition

(%o

pen)

Composition (% H. Key)

Reflux valve

Variability is moved from controlled to manipulated variable!

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BENEFITS FROM PROCESS CONTROL

When we control a process, we reduce the variability of

key variables to achieve the seven objectives.

What statistics

can we calculate

from this data?

How do we relate

variability toprocess performance?

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BENEFITS FROM PROCESS CONTROL

Calculate the process

performance using the

distribution, not theaverage value of the key

variable!

Process performance =

efficiency, yield, production

rate, etc. It measuresperformance for a control

objective.

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Example of Benefits of reduced

variability for chemical reactor

Goal: Maximize conversion of

feed ethane but do not exceed

864C

Which operation, A or B, is better

and explain why.

A

B

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Example of Benefits of reduced

variability for chemical reactor

Goal: Maximize efficiency and

prevent fuel-rich flue gas

Which operation, A or B, is better

and explain why.

A

B

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CHAPTER 2: GOALS AND BENEFITS WORKSHOP 1

Determine one example for each of the seven control objective categories.

FT

1

FT

2

PT

1

PIC

1

AT

1

TI

1

TI

2

TI

3

TI

4

PI

2

PI

3

PI

4

TI

5

TI

6

TI

7

TI

8

TI

9

FI

3

TI

10

TI

11

PI

5

PI

6

air

feed

fuel

product

The feed flows

through a pipe andis heated by the

combustion of fuel

Flue

gas

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CHAPTER 2: GOALS AND BENEFITS WORKSHOP 2

Two process examples show the benefit of reduced variability,

the fired heater reactor and the boiler. Discuss the difference

between the two examples. Can you think of another example

that shows the principle of each?

0

0.1

0.2

0.3

0.4

frequency

of

occur

rence

-3 -2 -1 0 1 2 3

deviation from mean

Squeeze down the variability

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Feed

Vapor

product

Liquid

productProcess

fluid

Steam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

A1

L. Key

CHAPTER 2: GOALS AND BENEFITS WORKSHOP 3

In both the flash drum and the fired heater examples,

temperature measurement is very important. Describe

several methods for measuring temperature and recommendthe most appropriate for the flash drum example.

How hot is it?

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CHAPTER 2 : CONTROL OBJECTIVES & BENEFITS

When I complete this chapter, I want to be

able to do the following.

Recognize examples of the seven (7)control objectives in chemical processes

Calculate indicators of variability in a

process variable

Be able to calculate the economic impact

of variability

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 2: LEARNING RESOURCES

SITE PC-EDUCATION WEB

- Instrumentation Notes

- Interactive Learning Module (Chapter 2)

- Tutorials (Chapter 1/2)

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CHAPTER 2:

SUGGESTIONS FOR SELF-STUDY

1. Discuss the importance of consistent quality in your

decisions to purchase food, clothing, etc.

2. A P&I drawing of a distillation process is given in

Woods*. Determine at least one example of each of the

seven control objectives for this process. Evaluate thecontrol designs given; do they achieve your objectives?

3. Find process examples in your previous textbooks and

determine the advantage for reduced variability in each.

Can you provide quantitative values for the economic

benefit?

* Woods, D.Process Design and Engineering Practice, Prentice-Hall, 1995 (page 2-65).