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)