chapter 2 : control objectives and · pdf filechapter 2 : control objectives and ... to...
TRANSCRIPT
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
Outline of the lesson.
• Seven (7) Control Objectives1. Safety 2. Environmental protection3. Equipment protection4. Smooth operation5. Product quality6. Profit7. Monitoring and diagnosis
• Variability measures
• Economic impact of variability
• Workshop
CHAPTER 2 : CONTROL OBJECTIVES AND BENEFITS
EXAMPLE PROCESS: FLASH SEPARATION
FeedMethaneEthane (LK)PropaneButanePentane
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
Let’s discuss this process
P ≈ 1000 kPa
T ≈ 298 K
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 PC
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
High pressurein drum isdangerous
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Never releasehydrocarbons to atmosphere
To flare
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
LC
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
No flow coulddamage the
pump
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
FC
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Always keepthe production
rate smooth
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
AC
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Achieve L.Keyby adjustingthe heating
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
AC
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Use the least costly heating
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Give example
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction rate
5. Product quality
6. High profit
7. Monitoring &diagnosis
SEVEN CONTROL OBJECTIVES
Calculate & plotkey parameters,
e.g., UA.
time
UA
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
1. Safety
2. EnvironmentalProtection
3. Equipmentprotection
4. Smooth operationproduction 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.
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)ou
tlet c
once
ntra
tion
0 50 100 150 200 250 300 350 400 450 50049
49.5
50
50.5
51
time (min)
valv
e po
sitio
n (%
ope
n)
Composition (% H. Key)
Reflux valve
BENEFITS FROM PROCESS CONTROLWhen we control a process, we reduce the variability of key 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)
outle
t con
cent
ratio
n
0 50 100 150 200 250 300 350 400 450 50020
40
60
80
100
time (min)
valv
e po
sitio
n (%
ope
n)
Composition (% H. Key)
Reflux valve
Variability is moved from controlled to manipulated variable!
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 to
process performance?
BENEFITS FROM PROCESS CONTROL
Calculate the process performance using the distribution, not the average value of the key variable!
Process performance = efficiency, yield, production rate, etc. It measures performance for a control objective.
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
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
CHAPTER 2: GOALS AND BENEFITS WORKSHOP 1
Determine one example for each of the seven control objective categories.
FT1
FT2
PT1
PIC1
AT1
TI1
TI2
TI3
TI4
PI2
PI3
PI4
TI5
TI6
TI7
TI8
TI9
FI3
TI10
TI11
PI5
PI6
air
feed
fuel
product
The feed flows through a pipe and is heated by the combustion of fuel
Flue gas
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 differencebetween the two examples. Can you think of another example that shows the principle of each?
0
0.1
0.2
0.3
0.4
freq
uenc
y of
occ
urre
nce
-3 -2 -1 0 1 2 3 deviation from mean
Squeeze down the variability
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
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 recommend the most appropriate for the flash drum example.
How hot is it?
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
Lot’s 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, we’ll have an assignment!
CHAPTER 2: LEARNING RESOURCES
• SITE PC-EDUCATION WEB
- Instrumentation Notes
- Interactive Learning Module (Chapter 2)
- Tutorials (Chapter 1/2)
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 the control 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).