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

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.

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

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

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

Sample Problem Solving Exercise #1

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

Sample Problem Solving Exercise #2

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

Sketch of a three-way valve

PC-Education Tutorial Question 15.1

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.

PC-Education Tutorial Question 15.2

PC-Education Tutorial Question 15.2

PC-Education Tutorial Question 15.2

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

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