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TRANSCRIPT
University of Al-Muthanna
Chemical engineering department
Fourth Year
PROCESS DYNAMICS AND CONTROL
By Asst. Lecturer: Forat Yasir Sharrad
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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University of Al-Muthanna
Chemical engineering department
Fourth Year
PROCESS DYNAMICS AND CONTROL
By
Asst. Lecturer
Forat Yasir Sharrad
2016
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
2
Introduction:
A chemical process plant is an integration of various
processing units (e.g. reactor, columns, exchangers,
pumps, etc.) placed in a systematic manner whose
objective is to convert a certain raw material into a useful
product in safe and economical manner.
Raw material PLANT Product
To meet the plant objective, we need to satisfy some
requirement:
1- Safety
2- Production specifications
3- Environmental requirements
4- Operational constrains
5- Economics
(will be explaining more in the class)
To keep all the above requirements, external intervention
is required and this is nothing but the control system.
Issues (Purpose of the control system):
Generally, there are three main issues could be dealt with
the control system as explain below:
1- The influence of external disturbances.
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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2- Stability of a chemical process.
3- The performance of a chemical process.
(will be explaining more in the class)
The objective of the control system, in this case, is to
maximize the profit of the process by trying to maximize
the desired product and minimize the undesired product
and hence increase the process performance. Therefore,
the control system should minimize the production cost,
losses, wastage, energy requirement and human labor.
Classification of variables:
Variables are generally divided into:
1- Input variables.
2- Output variables.
(will be explaining more in the class)
Control system design:
In order to design an active control system, the following
aspects should be clear to the design engineer:
1- Control objective.
2- Select measurements.
3- Select manipulated variables.
4- Select the control configuration.
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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5- The design of controller.
(will be explaining more in the class)
Laplace Transform:
The Laplace transform converts integral and differential
equations into:
algebraic equations, this is like phasors, but applies to:
- general signals, not just sinusoids
- handles a non-steady-state condition
Properties and formulas:
- Linearity
- The inverse Laplace transform
- Time scaling
- Exponential scaling
- Time delay
- Derivative
- Integral
- Multiplication by i
- Convolution
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Forcing functions:
They are the load disturbances affecting the process
and lead it to deviate from the steady state, and these
disturbances could be accidental or imposed. Actually,
there are infinite numbers of forcing functions, but in
practice, only a few forcing functions are exposed.
These are:
Step function.
1- Unit step.
2- Ramp function.
3- Pulse input.
4- Impulse function.
5- Sine wave forcing function.
6- Cosine wave forcing function.
(will be explaining more in the class)
Transfer function:
The transfer function of a linear system could be
defined as the ratio of Laplace transform of output
variable to the Laplace transform of input variable
setting all the initial conditions to be zero.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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First order system: (definition and classification)
First order systems are those systems described by a
first order differential equation that represents the
system dynamic behavior with time.
(will be explaining more in the class)
Modeling of chemical engineering processes:
To model any process, the following steps should be
applied:
1- Applied the material and energy balances in case of
the unsteady state.
2- Applied the material and energy balances in case of
the steady state.
3- Obtain the a differential equation in terms of
deviation variables.
4- Obtain the transfer function for the modeled
systems.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Response of Second order systems:
Study the responses for several types of forcing function
such as step change and ramp change.
Time response specification of second order system
(under-damped) practically, second order systems are
designed to be under-damped systems since these
systems tend to return to the steady state as soon as
possible. The following transient response
specifications should be understood.
(will be explaining more in the class)
Mathematical expressions of time response specifications:
Study the mathematical expression of:
1- Delay time.
2- Rise time.
3- Peak time.
4- Over shoot.
5- Setting time.
6- Decay ratio.
7- Period of oscillation.
8- The natural period of oscillation.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Steady state error analysis:
Study the steady state error for the following:
1- Steady state error for step input.
2- Steady state error for ramp input.
3- Steady state error for parabolic input.
(will be explaining more in the class)
Steady state error for type-0, type-1, type-2 systems:
Type of the system could be determined according to the
open loop transfer function G(s) H(s).
1- Steady state error for type-0 system.
2- Steady state error for type-1 system.
3- Steady state error for type-2 system.
There are advantages and disadvantages of static error
coefficients.
(will be explaining more in the class)
Block diagrams:
It is the pictorial representation of the relationship
between the input and output of the physical system.
Block diagrams consist of the following main parts:
1- Block.
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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2- Summing point.
3- Take off point.
4- Forward path.
5- Feedback path.
(will be explaining more in the class)
Techniques of block diagram reduction:
The techniques of block diagram could be explain as
below:
1- Blocks in series.
2- Blocks in parallel.
3- Moving a summing point after a block.
4- Moving a summing point before a block.
5- Moving a take-off point ahead of a block.
6- Moving a take-off point.
7- Eliminating a feedback loop.
8- Interchanging of two summing point.
9- Moving a take-off point ahead of a summing point.
10- Moving a take-off point after summing point.
There are a several steps that could be used to reduce the
block diagram.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Stability:
Stability is a very important characteristic of the
transient performance of a system as every system has
to pass through a transient stage for a small period
before reaching steady state study of stability is very
important to determine whether the system reaches its
steady state after passing through transient.
(will be explaining more in the class)
The Routh-Hurwits criterion of stability:
This creation tests the stability of a system by
converting its characteristics equation into an array
called "Routh array".
There are a specified steps that should be followed to
convert the characteristic equation of a system.
(will be explaining more in the class)
Frequency response analysis:
When a linear system is subjected to a sinusoidal input,
its response will appear in a characteristic equation
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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which its quantities could be obtained from the transfer
function as will be explaining more in the class.
Bode diagrams:
It is a convenient method to represent the frequency
response of a system. It consists of two parts to be
plotted.
(will be explaining more in the class)
Types of controllers:
In order to keep the output of a system at desired
value, the output of this system should be measured
and compared with desired value to determine how far
this output deviated from the desired value.
Basically, there are three types of controllers exists as
follows:
1- Proportional controller.
2- Proportional – integral controller.
3- Proportional – integral – derivative controller.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Nyquist plots:
It is an alternative way of representing the frequency
response characteristics. It uses Cartesian coordinate
in two dimensions whose ordinate represents the
imaginary axis and abscissa represents the real axis.
There are specified steps for Nyquis plot construction
depending on the overall transfer function of the
system that must be found at first.
(will be explaining more in the class)
Measuring devices (sensors):
The successful operation of any feedback control
system depends upon good measurement of the
controlled output and the uncorrupted transmission of
the measurement to the controlled.
1- Flow sensors.
2- Pressure sensors.
3- Temperature sensors.
4- Composition analyzers.
(will be explaining more in the class)
Al-Muthanna University/ College of Engineering/ Chemical Engineering department Fourth Year / Process Dynamics and Control Asst. Lect. Forat Yasir Sharrad
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Controllers tuning:
The choice of controllers parameters depends basically
on the nature of process model which adjusted the
controller parameters to attain a successful control.
Zieglar-Nichols tuning is an example of tuning
techniques which could be applied through specified
steps.
(will be explaining more in the class)