Quiz on CSTR Case Study
 |  |  |  |
|---|
1. What are some of the challenging temperature control aspects of the case study as a continuously stirred tank reactor (CSTR) with an exothermic reaction. Select all that apply.
A. Linear response to cooling jacket temperature
- Incorrect. The response is highly nonlinear with the possibility of temperature run-away. It is not linear because of the heat generated by the reaction.
B. Nonlinear response to cooling jacket temperature
- Correct. The response is highly nonlinear with the possibility of temperature run-away. It is not linear because of the heat generated by the reaction.
C. It is very challenging to meet the objectives of this assignment with a PID controller because the reactor verges on the edge of stability.
- Correct. You don’t necessarily need to achieve the target final concentration without temperature run-away. However, you should show methods to attempt this challenging problem.
D. Using the IMC or ITAE tuning correlations achieves acceptable control.
- Incorrect. The IMC or ITAE suggested tuning values give acceptable performance. You will need to “tune” the parameters by adjusting them to get better performance after you get the initial recommended values.
2. What role does the FOPDT parameter regression and the doublet test play in designing a PID controller?
A. Gives insight on the nonlinearity of the process
- Incorrect. Answer D
B. Quantifies the response of the system to step changes
- Incorrect. Answer D
C. Produces parameters that directly correlate with the PID tuning parameters
- Incorrect. Answer D
D. All of the above
- Correct.
3. Which of these options is not a good control approach for dealing with a system that shows a high degree of nonlinearity?
A. Step up or ramp up the set point
- Incorrect. Small set point changes allow the controller to make smaller changes that don’t initiate a reactor run-away.
B. Gain scheduling
- Incorrect. Gain scheduling is one possible approach. A nonlinear system behaves differently in different ranges of step values. Gain scheduling changes the parameters in these different ranges to better fit the reactor response.
C. Using disturbance rejection correlations
- Correct. This is not a good approach. Disturbance rejection tuning correlations are more aggressive than servo control correlations. An overly aggressive controller can lead to reactor run-away in the case of the CSTR.
D. Each of the above is a good approach
- Incorrect. Option C is not a good approach to control systems with high nonlinearity
