CSE 425: Industrial Process Control 1

About the course Lect.TuTotal Semester work 80Final 125Total Grading Scheme Course webpage: Reference textbook Pao C. Chau, Process control a first course with Matlab, Cambridge University Press,

Topics to be covered: 1)Introduction 2)Mathematical modeling 3)Common dynamic systems 4)System structures 5)PID control 6)PID tuning 7)Frequency-response analysis 8)Lag compensator design 9)Cascade and ratio control 10)Multi-loop Systems 3

Introduction What is process control? What the procedure for control system design? How control design is documented? What are the guidelines for choosing controlled and manipulated variables. 4

What is process control? Process control is mainly concerned with the control of chemical and petrochemical process industries. In the processing industry, controllers play a crucial role in keeping our plants running virtually everything from simply filling up a storage tank to complex separation processes and chemical reactors. 5

Process example Consider the following bioreactor (fermenter). In order for the bioreactor to operate properly, we monitor and control variables such as: - temperature, - pH, - dissolved oxygen, - liquid level, - concentration of chemicals. 6

Process example For example, to control the pH, we use a pH electrode to measure its value and, with a transmitter, send the signal to a controller, which can be a little black box or a computer. The controller compares the pH value with the desired pH (the set point or the reference). If the values are not the same, there is an error, and the controller makes proper adjustments by manipulating the acid or the base pump – the actuator. This example is what we call a single-input single-output (SISO) system; the single input is the set point and the output is the pH value. 7

Why process control? One word: DISTURBANCES! We want to achieve the following: 1. Safety 2. Environmental Protection 3. Equipment protection 4. Product quality 5. Profit 8

Control system: design issues Identify the role of various variables: – what we need to control, – what we need to manipulate, – what the sources of disturbances are. State design objective and specifications: – servo or regulation, – the desired response of the system. Design the control system : – Select the proper control strategy and controller. – Select the proper sensors, transmitters, and actuators. – Tune the controller. 9

Control equipment 10 T A CBCB v1 v2 Final element Sensors Central control room Displays of variables, calculations, and commands to valves. Communication Cables potentially hundreds of meters long

LC FC TC A Piping and instrumentation (P&I) drawings provide documentation. We use standard symbols. F = flow L = level P = pressure T = temperature ….. How is control design documented? 11

WORKSHOP 1 You are implementing control “manually”. Explain the correct action if you want to increase the controlled variable pump valve sensor Flow Control 12

WORKSHOP 2 You are implementing control “manually”. Explain the correct action if you want to increase the controlled variable Level Control pumpvalve sensor 13

The sensor & actuator It important that the actuator and the sensor have a faster response than the process, otherwise, they will add extra time delay in the loop and consequently make the system less stable. 14

How Do We Choose the Controlled Variables? 15 CV to control? 1.those that affect process safety, product quality, etc. 2.those that are not self-regulating.

How Do We Choose the Manipulated Variables? MV to adjust ? 1.Causal relationship 2.Fast dynamics (those that have no dead time) 3.Good sensitivity (have a large steady-state gain) 4.Have no interaction with other control loops. 16

WORKSHOP C A0 CACA A  B Solvent Pure A vc T vAvA vSvS F V FCFC T Cin T Cout Suggest some possible pairs of controlled and manipulated variables for the following process. 17

Answer The following are possible controlled and corresponding manipulated variables: 18 MVCV Steam valve V C Temperature The valves V S and V A Concentration The valves V S, V A and the outlet valveLevel