SKF 3143 Process Control and Dynamics: Process Control and Dynamics: Control of Chemical Processes Mohd. Kamaruddin Abd. Hamid, PhD [email protected] www.cheme.utm.my/staff/kamaruddin
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
SKF 3143
Process Control and Dynamics:Process Control and Dynamics: Control of Chemical Processes
Mohd. Kamaruddin Abd. Hamid, PhD
www.cheme.utm.my/staff/kamaruddin
Learning ObjectivesLearning Objectives
When I complete this chapter I want to be ableWhen I complete this chapter, I want to be able to do the following:
1. identify main control variables and their applicationapplication
2. classify type of variables in chemical processesp
2
Outline of this lectureOutline of this lecture
1 Typical Control Variables
2 Common Unit Operations
3 Classification of Variables
3
Chemical process variables.
TYPICAL CONTROL VARIABLES
Chemical process variables.
Typical control variables.
TYPICAL CONTROL VARIABLES
4
Chemical process variables.• Variables such as flow rates, temperatures,
pressures, volumes, pHs, viscosities and concentrations can be divided in to two groups
Chemical process variables.
– Input Variables: Effect of surroundings on the chemical process
– Output Variables: Effect of chemical process on the surroundingsthe surroundings
• Input Variables: Fi, Ti, Fst, (F)• Output Variables: F V or h T• Output Variables: F, V or h, TInput Variable
Manipulated: their values can be adjusted freely by control mechanism (Fst and F)Disturbances: values are not the result of adjustment by control mechanism (Fiand Ti)
Output VariableM d l k b di tl i th (V d T)
5
Measured: values are known by directly measuring them (V and T)Unmeasured: cannot be measured directly
Exercise: Typical control variables for l liSolvent Splitter.
6
Exercise: Typical control variables for l i iPolymerization Reactor.
7
Some typical continuous processes.
COMMON UNIT OPERATIONS
Some typical continuous processes.
Some typical noncontinuous processes.
COMMON UNIT OPERATIONS
8
Some typical continuous processes.Some typical continuous processes.
9
Some typical noncontinuous processes.Some typical noncontinuous processes.
10
Chemical process variables.
Design elements of control system.
Selecting measurements.
Selecting manipulated variables.
CLASSIFICATION OF VARIABLES
Selecting manipulated variables.
Selecting controller configuration
CLASSIFICATION OF VARIABLES
11
Chemical process variables.Chemical process variables.
12
Design elements of control system.
Define control objectives
Design elements of control system.
• What are the operational objectives that a control system is called upon to achieve– Ensuring the stability of the process
– Suppressing the external disturbances
– Optimising the economic performance of a plant
– A combination of the above
• For the example, the control objectives– To control the temperature and volumep
– T = Ts– V = Vs– Where Ts and Vs are the desired valuesWhere Ts and Vs are the desired values
13
Selecting measurements.
• Selecting measurement
Selecting measurements.
– We need some means to monitor the performance of the chemical process
– This is done by measuring the values of certain processing variables (temperature, pressures, concentration, flow rates, pH)
• What variables should we measure in order to monitor the operational performance of a plant?– For tank heating system our control objectives are to keep the volume
and temperature at desired value– Thus we have to measure
• Temperature (T) using thermocouple• Volume (V) using Differential Pressure Cell (DPC)
14
Selecting manipulated variables.• What are the manipulated variables to be used to control a chemical
process?
Selecting manipulated variables.
– Usually we have several options to choose (Fi or F)
– The selection is very crucial because it will affect the quality of the control action
Fi ,Ti = constant
Controller
Set point
hs
+
e
h
Level Meter
hs
h
-
F, T
Condensate
F
15
Steam
Fst
Selecting controller configuration
• Feedback control constitute two different l fi i
Selecting controller configuration
control configuration:– Same information flows to different
manipulated variables
S i l t d i bl b t diff t– Same manipulated variables but different measurement
• Control Structure• Control Structure– Information structure that is used to
connect the available measurements to the available manipulated variablesavailable manipulated variables
16
Same information but different i l d i blmanipulated variables.
Fi ,Ti = constant
Controller
Set point
hs
+
e
h
Level Meterh
-
F, T
Condensate
Steam
Fst
17
Controller configuration.
• What is the best control configuration for a given process
Controller configuration.
control situation?– The answer for this is very critical for the quality of the control system
we are to design
• Controller Configuration– SISO – single input single outputSISO single input single output– MIMO – multiple input multiple output
• For heated tank system• For heated tank system– If the control objectives is to keep the level at a desired value by
manipulating the effluent flow rate, we have a SISO system– If the control objectives are to control level and temperature we have– If the control objectives are to control level and temperature, we have
MIMO system.
18
MIMO controller.MIMO controller.
19
Feedback ControllerFeedback Controller• Uses direct measurements of the controlled variables to adjust the
values of the manipulated variables
• Objectives: to keep the controlled variables at desired levels (set points)
20
Feedback Control for TemperatureFeedback Control for Temperature
Ti, Fi = constant
Thermocouple
T
h
Thermocouple
Set point
T -
F, T
Condensate
Ts +e
Fst
Controller
21
Steam
Feedforward ControllerFeedforward Controller• Uses direct measurement of the disturbances to adjust manipulated
variables
• The objective here is to keep the values of the controlled output variables at desired levels
22
Feedforward Controller for TemperatureFeedforward Controller for Temperature
23
Inferential Controller ConfigurationInferential Controller Configuration• Uses secondary measurements to adjust the manipulated variables
because the controlled variables cannot be measured
• Control objective here is to keep the unmeasured controlled variables at desired levels
24
References:References:
• Seborg, D. E., Edgar, T. F., Mellinchamp, D. A. (2003). Process Dynamics and Control, 2nd. Edition. John Wiley, ISBN: 978‐04‐71000‐77‐8.
• Marlin T E (2000) Process Control: Designing Processes and• Marlin, T. E. (2000). Process Control: Designing Processes and Control System for Dynamic Performance, 2nd. Edition. McGraw Hill, ISBN: 978‐00‐70393‐62‐2.
• Stephanopoulos, G. (1984). Chemical Process Control. An Introduction to Theory and Practice. Prentice Hall, ISBN: 978‐01‐31286‐29‐00 3 86 9 0
25
Related Documents
