ChE-411
INSTRUMENTATION AND PROCESS CONTROL (Th)
Fall 2017 Credit Hours: 03
Engr. Amir Muhammad
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Marks Distribution
• Final Term= 50 %
• Mid Term= 25%
• Quiz + Assignment+ Presentation= 20 %
• Attendance + CP= 5 %
( There will be 03 Quizzes, 03 Assignments
and 02 Presentations)
Text and References
Text
• G. Stephanopoulos. Chemical Process Control: An introduction to theory
and practice. Prentice Hall, New Jersey.
• Donald R. Coughanowr. Process System analysis and Control. 3rd Ed.
McGraw Hill Inc. 1999.
• DOE Fundamentals Handbook: Instrumentation and Control. Vol 1 & 2.
US Dep. Of Energy.
References
• D.E. Seborg, T.F. Edgar. Process dynamics and Control. 2nd Ed.,
• M. A. Tahir. Process Control: Application in Chemical Industry. 2009.
• Bela G. Leptak. Process measurement and analysis In Instrument
Engineer’s Handook. Vol 1 4th Ed. CRC Press, 2003.
• Luyben W. L., “Process Modeling, Simulation and Control for Chemical
Engineers,” McGraw-Hill, New York, 2nd Ed., 1990
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At Completion of this Course, students will be able...
1. To understand the significance and practical application of Process control and
instrumentation in chemical industry
2. To be able to model first and second order systems to assess process dynamics.
3. To be able to understand the use of block diagrams & the mathematical basis for
the design of control systems.
4. To be able to use appropriate software tools (e.g. Matlab Control Toolbox &
Simulink) for the modelling of plant dynamics and the design of well tuned control
loops
5. To be able to understand the importance and application of good instrumentation
for the efficient design of process control loops for process engineering plants.
6. Draw a PID (Process & Instrumentation Diagram) & devise simple but effective plant
wide control strategies using appropriate heuristics.
7. Stability studies, frequency response analysis.
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Contents of the Lecture
1. Introduction to Process Control.
2. Incentives for chemical process control
3. Design aspects of a process control system
4. Hardware for a process control system
5. Solved problems
6. Assignment
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Chemical Engineering
• Aimed towards design of processes that
change materials from one form to another
more useful (and so more valuable) form,
economically, safely and in an
environmentally acceptable way.
• Application of basic sciences (math,
chemistry, physics & biology) and
engineering principles to the development,
design, operation & maintenance of
processes to convert raw materials to
useful products and improve the human
environment.
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Chemical Engineering
• ChE involves specifying equipment,
operating conditions, instrumentation and
process control for all these changes.
Chemistry
Air Mathematics
Natural Gas
Coal
Economics
Minerals
Energy
Physics
Biology
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Introduction to Process Control
• Process
– Changing or refining of raw materials that pass
through or remain in a liquid, gaseous or slurry
state to create end products.
• Control
– The regulations of all aspects of the process.
Process control
- the methods that are used to control
process variables when manufacturing a
product.
Process industries include the chemical industry, the oil and gas industry, the food and beverage industry, the pharmaceutical
industry, the water treatment industry, and the power industry.
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Introduction to process control
Process variable is a condition that can change
the process in some way.
Common process variables are
• Pressure
• Level
• Temperature
• Density
• Ph (acidity or alkalinity)
• Mass (concentration)
• conductivity 9
Incentives for chemical process control
1. Safety
2. Production specifications
3. Environmental regulations
4. Operational constraints
5. Economics
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Overview of Control System Design
General Requirements
1. Safety. It is imperative that industrial plants operate safely
so as to promote the well-being of people and equipment
Chapter 10
within the plant and in the nearby communities. Thus, plant
safety is always the most important control objective.
2. Environmental Regulations. Industrial plants must comply
with environmental regulations concerning the discharge of
gases, liquids, and solids beyond the plant boundaries.
3. Product Specifications and Production Rate. In order to be
profitable, a plant must make products that meet
specifications concerning product quality and production
rate.
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4. Stable Plant Operation. The control system should facilitate
smooth, stable plant operation without excessive oscillation in
key process variables. Thus, it is desirable to have smooth,
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rapid set-point changes and rapid recovery from plant
disturbances such as changes in feed composition.
5. Economic Plant Operation. It is an economic reality that the
plant operation over long periods of time must be profitable.
Thus, the control objectives must be consistent with the
economic objectives.
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Needs that control system is called on to satisfy
a) Supressing the influence of external
disturbances
b) Ensuring the stability of a chemical process
c) Optimizing the performance of a chemical
process.
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a) Supressing the influence of external disturbances
Example 3.1 Controlling the operation of a
stirred tank reactor
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a)Supressing the influence of external disturbances
Example 3.1 Controlling the operation of a
stirred tank reactor
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a)Supressing the influence of external disturbances
Example 3.1 Controlling the operation of a
stirred tank reactor
Figure 1.3 Alternative level control schemes
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b) Ensure the stablity of a chemical process
Example 3.1 Controlling the operation of a
stirred tank reactor
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b) Ensure the stability of a chemical process
Example 1.2 Controlling the operation of a
unstable reactor
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b) Ensure the stability of a chemical process
Example 1.2 Controlling the operation of a unstable
reactor
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c) Optimizing the performance of a process
Example 1.3 optimizing the performance of a batch
reactor
A BC
Maximize profit = (revenue from the sales of poduct B )
–( cost of steam + cost of purchasing A)
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Design aspects of a process control system
Classification of the variables
• Input variables
denote the effect of the surroundings on the chemical process.
1. Manipulated variable (MV or Control variable)
Its value can be adjusted freely by the human operator or a control
mechanism.
Ex) In heated tank, the amount of heat added(Q) or mass
flow rate(w).
2. Disturbance variable(DV)
Its value is not the result of the adjustment by an operator or a
control system.
Ex) In heated tank, inlet temperature, because we can’t
usually control the temperature of inlet water.
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• Output variables
denote the effect of the process oh the surroundings.
1. Measured output variable or Controlled
variable(CV)
Its value is known by directly measuring it.
Ex) In heated tank, outlet temperature.
2. Unmeasured output variables
It is not or cannot be measured directly.
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Design elements of a control system
Control system design requirements:
• What are the operational objectives that a control system is
called upon to achieve?
• What variables should we measure in order to monitor the
operational performance of a plant?
• What are the manipulated variables to be used to control a
chemical process?
• What is the best control configuration for a given chemical
process control situation?
• How is the information, taken from the measurement, used to
adjust the values of the manipulated variables?
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Classification of Control Strategies (configurations)
• Feedforward Control
The disturbance variable is measured and the
measurement is used to manipulate MV.
Advantages
– If all sources of the disturbances are known and these
values can be measured accurately. Perfect Control !
Disadvantages
– No corrective action for unmeasured disturbances.
– In industrial applications, feedfoward control should be
used in combination with feedback control.
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• Feedback Control
The process variable to be controlled is measured and used to
adjust another process variable which can be manipulated.
Advantage
– Corrective action is taken regardless of the source of the
disturbance.
Disadvantage
– The controlled variable must be deviate from the set point
before corrective action is taken. Not Perfect Control!
Classification
– Negative feedback ; The desirable situation where the corrective
action taken by the controller tends to move the controlled variable
toward set point.
– Positive feedback ; The controller tends to make things worse by
forcing the controlled variable farther away from the set point.
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Expl: 2.10 Control system of a binary distillation column
Pentane (distillate) + Heptane (bottom
Figure. Feed back control system
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Expl: 2.10 Control system of a binary distillation column
Pentane (distillate) + Heptane (bottom)
Figure. Feedforward control system 30
Expl: 2.10 Control system of a binary distillation column
Pentane (distillate) + Heptane (bottom)
Figure. Inferential control system
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Control aspects of a complete chemical plant
Exp 2.13 A+B -C (endothermic)
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Control aspects of a complete chemical plant
Operational objectives
1. Product Specifications
2. Operational constraints
3. Economic considerations
Disturbances
Control system design
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Hardware elements of a control system
The chemical Process
The measuring instruments or sensors
Transducers
Transmission lines (transmitters)
The controller
The final control element (the relay switches, variable speed pumps)
The recording elements
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Harware elements of a control system
The Chemical Process
The measuring instruments or sensors
Thermocouples or resistance thermometers for measuring temperature
Venturi meters for measuring flowrates
Gas chromatograph for measuring composition of a stream
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Harware elements of a control system
Transducers
These convert measurement into physical quantities
Transmission lines (transmitters)
They are used to carry the measurment signal from the measuring
device to the controller
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Harware elements of a control system
The Controller
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Harware elements of a control system
The final control element (the relay switches, variable speed pumps)
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Harware elements of a control system
The recording elements
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Harware elements of a control system
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Thanks
UET Peshawar
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