Process Control and Dynamics - Universiti Teknologi...
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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
Transcript of Process Control and Dynamics - Universiti Teknologi...
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
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Outline of this lectureOutline of this lecture
1 Typical Control Variables
2 Common Unit Operations
3 Classification of Variables
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Chemical process variables.
TYPICAL CONTROL VARIABLES
Chemical process variables.
Typical control variables.
TYPICAL CONTROL VARIABLES
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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)
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Measured: values are known by directly measuring them (V and T)Unmeasured: cannot be measured directly
Exercise: Typical control variables for l liSolvent Splitter.
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Exercise: Typical control variables for l i iPolymerization Reactor.
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Some typical continuous processes.
COMMON UNIT OPERATIONS
Some typical continuous processes.
Some typical noncontinuous processes.
COMMON UNIT OPERATIONS
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Some typical continuous processes.Some typical continuous processes.
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Some typical noncontinuous processes.Some typical noncontinuous processes.
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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
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Chemical process variables.Chemical process variables.
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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
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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)
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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
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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
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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
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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.
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MIMO controller.MIMO controller.
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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)
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Feedback Control for TemperatureFeedback Control for Temperature
Ti, Fi = constant
Thermocouple
T
h
Thermocouple
Set point
T -
F, T
Condensate
Ts +e
Fst
Controller
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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
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Feedforward Controller for TemperatureFeedforward Controller for Temperature
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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
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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
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