Lecture 2 PDF
Lecture 2 PDF
Lecture 2 PDF
Mohd. Kamaruddin Abd. Hamid, PhD
kamaruddin@cheme.utm.my
www.cheme.utm.my/staff/kamaruddin
Learning Objectives
Learning Objectives
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Outline of this lecture
Outline of this lecture
3 Classification of Variables
3
Chemical process variables.
Chemical process variables.
Typical control variables.
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Chemical process variables.
Chemical process variables.
• Variables such as flow rates, temperatures,
pressures, volumes, pHs, viscosities and
concentrations can be divided in to two groups
– Input Variables: Effect of surroundings on the
chemical process
– Output Variables: Effect of chemical process on
the surroundings
the surroundings
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Exercise: Typical control variables for
Polymerization Reactor.
l i i
7
Some typical continuous processes.
Some typical continuous processes.
Some typical noncontinuous processes.
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Some typical continuous processes.
Some typical continuous processes.
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Some typical noncontinuous processes.
Some typical noncontinuous
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Chemical process variables.
Design elements of control system.
Selecting measurements.
Selecting manipulated variables.
Selecting manipulated variables.
Selecting controller configuration
CLASSIFICATION OF VARIABLES
CLASSIFICATION OF VARIABLES
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Chemical process variables.
Chemical process variables.
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Design elements of control system.
Design elements of control system.
Define control objectives
• 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 volume
p
– T = Ts
– V = Vs
– Where Ts and V
Where T and Vs are the desired values
are the desired values
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Selecting measurements.
Selecting measurements.
• Selecting measurement
– 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.
Selecting manipulated variables.
• What are the manipulated variables to be used to control a chemical
process?
– 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
Controller
e
hs
-
h
Level Meter
F, T
Condensate
Fst
Steam
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Selecting controller configuration
Selecting controller configuration
• Feedback control constitute two different
control configuration:
l fi i
– Same information flows to different
manipulated variables
– Same manipulated variables but different
S i l t d i bl b t diff t
measurement
• Control Structure
Control Structure
– Information structure that is used to
connect the available measurements to the
available manipulated variables
available manipulated variables
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Same information but different
manipulated variables.
i l d i bl
Controller
e
hs
-
h
Level Meter
F, T
Condensate
Fst
Steam
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Controller configuration.
Controller configuration.
• What is the best control configuration for a given process
control situation?
– The answer for this is very critical for the quality of the control system
we are to design
• Controller Configuration
– SISO
SISO – single input single output
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 Controller
Feedback 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 Temperature
Feedback Control for Temperature
Ti, Fi = constant
Thermocouple
T h
-
Set point
Ts +
F, T
e
Condensate
Controller
Fst
Steam
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Feedforward 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 Temperature
Feedforward Controller for Temperature
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Inferential Controller Configuration
Inferential 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:
• 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
Marlin, T. E. (2000). Process Control: Designing Processes and
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‐
0 3 86 9 0
01‐31286‐29‐0
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