Chemical Engineering 3P04 Process Control Tutorial # 7 Learning goals 1.Experience with a single-loop controller 2.Answering some questions from PC-Education

An Introductory Experience with Feedback Control We use many feedback controllers for a typical process Each controller has one measurement and one manipulated variable Feed Methane Ethane (LK) Propane Butane Pentane Vapor product Liquid product Process fluid Steam FC-1 F2F3 T1 T2 T3 T5 TC-6PC-1 LC-1 AC-1 L. Key PAH LAL LAH

control display and computer A v1 v mA 3-15 psi T Heating medium Product composition An Introductory Experience with Feedback Control Let’s look at one example feedback loop

A v1 v psi T Heating medium Product composition An Introductory Experience with Feedback Control Our first task is to learn about the dynamics. We can apply the process reaction curve experiment.

% open Mole fraction minute An Introductory Experience with Feedback Control

Observations from the experiment. An increase in valve opening increases the concentration. The process gain is positive. Time to steady-state is about 25 minutes. Dead time is about 6 minutes and time constant is about 6 minutes. The process is stable and overdamped. The measurement has noise

A v1 v psi T Heating medium Product composition An Introductory Experience with Feedback Control The computer has a defined algorithm using the feedback measurement to determine the next value of the manipulated variable Calculations are done every 1/3 second The engineer enters the appropriate parameters

% open Mole fraction minute K C = 0 (Controller off) An Introductory Experience with Feedback Control Parameter sets the “aggressiveness” of the controller.

% open Mole fraction minute K C = 0.3 Parameter sets the “aggressiveness” of the controller. An Introductory Experience with Feedback Control

% open Mole fraction minute K C = 0.8 Parameter sets the “aggressiveness “ of the controller. An Introductory Experience with Feedback Control

% open Mole fraction minute K C = 1.2 Parameter sets the “aggressiveness“ of the controller. An Introductory Experience with Feedback Control

% open Mole fraction minute K C = 1.8 Parameter sets the “aggressiveness” of the controller. An Introductory Experience with Feedback Control

Observations from the samples of feedback performance. Feedback that is “too weak” takes a long time to compensate a disturbance Feedback that is “too strong” gives poor behavior and can result in instability Feedback can result in underdamped behavior for a process that is overdamped. The process dynamics have the dominant effect on control performance.

An Introductory Experience with Feedback Control Observations from the samples of feedback performance. Even the best behavior is “not perfect”. The process must be upset before feedback takes action. The valve must be moved to a different steady- state to compensate for a disturbance. We move the disturbance from the important controlled variable to the less important manipulated variable.

S_LOOP parameters for this example

Reinforcing PID Controller Concepts Let’s Perform the following exercises from PC-Education Interactive Learning Modules 8.5 – 8.9 and 8.13 Tutorial 8.5 (Problems with solutions – it doesn’t get any better than this!)