1. Chemical Engineering 3P04
Process Control
Tutorial # 10
Learning goals
Trouble shooting – A quick introduction
Feedforward – Questions 15.1, 15.2, 15.5, 15.6

2. TROUBLE SHOOTING IN THE PROCESS INDUSTRIES
A “bread and butter” skill for all chemical engineers!
Uses systematic TS method and builds technical knowledge through experience.
No systematic method. No way to focus technical knowledge.

3. Trouble Shooting is a Key Component of Chem. Eng. 4N04
Why introduce it here (briefly)?
A new way to learn and apply control principles
Begin to analyze process operations (vs. process design)
What will we do?
Review the (short-cut) Trouble Shooting method
Do exercises on the distillation towers

4. Trouble Shooting Worksheet
PS method tailored to
Trouble Shooting.
Trouble Shooting Worksheet
1. Engage
2. Define
Current, desired,deviation
Desired final state: SMARTS
The problem IS/IS NOT
3. Explore
a. Fundamentals
b. Relevant Changes
c. Experience factors
d. Data consistency
e. Bounds on behavior
4. Plan Solution, Perform Actions, Find Root Cause
5. Do it : based on root
cause
a. Operation or equipment
b. Short / Long term solutions
c. Continue to trouble shoot
d. Clear communication, plan,
and documentation
6. Evaluate: Check & Create
a Lookback
a. Predictions vs. results
b. Extra benefits
c. Potential problems
d. Prevent reoccurrence
e. Experience factors
f. Improved plant monitoring
Explain each diagnostic action here
Don’t memorize. We
will have a worksheet.
Full method taught and used in 4N04

5. Short-cut Trouble Shooting Procedure
Brainstorm many potential causes for the initial evidence – rely on principles
Eliminate candidates that are not consistent with initial information
3. Plan actions that would collect more information to reduce candidates (to one true root cause). Select order of implementation to:
a. Collect information fast
b. Incur low cost
c. Remove several candidates with one action
d. Achieve highest likelihood of success

6. Sample Problem Solving Exercise #1

7. Time = measured variable = controller set point
TIC-12 tray temperature
4 min.
Time

8. Sample Problem Solving Exercise #2

9. PC-Education Tutorial Question 15.1
Is feedforward recommended to improve control performance for the outlet temperature?

10. Sketch of a three-way valve

11. PC-Education Tutorial Question 15.1

12. PC-Education Tutorial Question 15.1
Because the feedback dynamics are very fast, we expect the feedback performance to be very good. We would not recommend feedforward compensation for this process.

13. PC-Education Tutorial Question 15.2

14. PC-Education Tutorial Question 15.2

15. PC-Education Tutorial Question 15.2

16. 15.4 For feedforward control (used in conjunction with feedback), the sensor for the disturbance variable should provide good
 accuracy
 reproducibility
 noise moderation

17. 15.5 After feedforward control has been implemented, what changes should we make to the feedback controller tuning?
 make more aggressive because the controlled variable will stay in a narrow range
 make less aggressive because feedforward will “do most of the work”
 make no change