Introduction_2014-15.pdf

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Process Dynamics and Control

(B.Tech. 6thSemester ChE & PE)

Dr. U D Dwivedi

Assistant Professor (Electrical Engineering)Room No. 202, Rajiv Gandhi Institute of Petroleum

Technology, Ratapur Chowk,

Rae Bareli -229316 INDIA


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Course Introduction: Control System

a core subject

extreme importance in process industry,

space-vehicle, missile-guidance systems,

robotics, and the like

integralpart of modern manufacturing and

industrial processes

essentialin industrial operations such as

controlling pressure, temperature, humidity,

viscosity, and flow in the process industries.2U D Dwivedi12/29/2014


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Objective of Control System

The primary objective of process control is to

maintain a process at desired operating

condition, safelyand efficiently

(economically), while satisfying environmental

and product quality.

The subject of process control is concerned

with how to achieve this goal.

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Course Objectives:

To familiarize you with the basics of dynamical

system theory and practices,

To equip you with the tools necessary for

control system modeling, analysis, simulation

and design.

The emphasis will be on a model-based

approach to control system simulation, design

and analysis.



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Class Time Table

Hours per Week:

3 Lectures, 1 Tutorial, 1 Matlab based Lab

Session of 2 hours work

Days and Room:

As per institutes semester time table (see noticeboard)



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Syllabus & Lectures Plan



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Syllabus & Lectures Plan



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SIMULATION LAB:



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SIMULATION LAB:



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Textbooks:

1. Lecture Notes and Study Material Provided inthe class.

2. Seborg D.E., T.F. Edgar, and D.A. Mellichamp,

Process Dynamics and Control, 2nd Ed., JohnWiley & Sons Inc., New York, NY (2004)

3. Ogata.Kafsutuko, Modern Control

Engineering, 4th

Ed., Prentice Hall of India,New Delhi, 2002.

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Reference Book:

1. Stephanopoulus, G., Chemical Process Control: An Introduction toTheory and Practice, Prentice Hall of India, New Delhi, 1997.

2. Ogunnaike, B. A., and Ray, W. H., Process Dynamics, Modeling and

Control, Oxford University Press, New York, 1994.

3. Perry, R.H. and Green, D.W., Perry's Chemical Engineers'

Handbook, 8th Ed., McGraw Hill, New York, 2007.

4. Eckman D. P.,Industrial Instrumentation, Wiley, New York, 1990.

5. B. Wayne Bequette , Process Control: Modeling, Design, andSimulation, Prentice Hall, 2003.

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Performance Evaluation/Course Grade

1stMid-term Exam: 20 %

2ndMid-term Exam: 20%

Final Exam: 35%

Home Work/ Term Paper: 5%Quizzes : 10 %

Laboratory Work: 10%

Attendance : *

TOTAL 100%

* As per Institutes Policy 0-10 marks12U D Dwivedi12/29/2014


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Class and Lab participation will be considered

for borderline grades. Students may be calledupon for discussion questions.

Attendance policy: As per Institutes Policy

Late homework/Lab work report will beaccepted with a penalty of 20% for each day

late.

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a) Definitions & Control Terminology

b) An Everyday Example of Process Control

c) prototype system-blending tankd) feedback control

e) implementation of control

f) justification of control

Chapter1

Introduction to Process

Control


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Plant:A plant may be a piece of equipment,

perhaps just a set of machine parts functioningtogether, the purpose of which is to perform a

particular operation.

Any physical object to be controlled is called

plant.

Ex: a mechanical device, drilling machine, electrical drive,

a heating furnace, a chemical reactor, or a spacecraft.

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Processes:

Dictionary Definition: a natural, or an artificial,

progressively continuing operation that consists of aseries of controlled actions systematically directed

toward a particular result or end.

Chemical Process: The conversion of feed materials to

products using chemical or physical operations.

We will call any operation or equipment to be controlled

a process.

Examples are chemical, electrical, economic, and

biological processes.

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Disturbance:

A disturbance is an input or a change in theinput that tends to adversely affect the value of

the output of a system.

Can be internally generated or generated

outside.

Can be known or unknown.

Measured or unmeasured

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Process Control meanscontrol of a process by process engineer

manually or through automatic controller in

order to have the process occurring in thedesired way.

A process may involve

Heat transfer, Mass transfer, Chemical reaction,Speed control, Position control, Inflation (Price)Control, etc.

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Most courses in Engineering Design involve Steady State(ss.)

In fact, no process will ever operate at a true ss.

For instance:

1) Start up of a new plant

2) Shut down for maintenance

3) Some process variable can not be controlled to ss.

(raw material from other processes and material fromthe environment (cooling water)) Disturbance

4) Change of product specification Set-point

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Why do you need process control?

Safety

Pressure

Temperature

Product quality specifications and production rate

Maintain specifications of product (no oscillation)

Environmental Regulations Flow rates of effluents from plants must be within

allowable limits

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Why do we need process control?

Operational constraints

Tanks must not overflow or go dry

Distillation columns must not be flooded

Economics

Economical utilization of raw materials, energy,

capital, human labor

Economic benefit(ex. increased production level,reduced raw material costs or enhanced

production quality)

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Control Terminology

Controlled Variables - these are the variables whichquantify the performance or quality of the final

product, which are also called output variables.

Manipulated Variables - these input variables are

adjusted dynamically to keep the controlled variablesat their set-points.

Disturbance Variables - these are also called "load"

variables and represent input variables that can

cause the controlled variables to deviate from theirrespective set points.

Chapt

er1

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Set-point change - implementing a change in theoperating conditions. The set-point signal is

changed and the manipulated variable is adjusted

appropriately to achieve the new operating

conditions. Also called servomechanism (or "servo")control.

Disturbance change - the process transient

behavior when a disturbance enters, also called

regulatory control or load change. A control systemshould be able to return each controlled variable

back to its set-point.

Control Terminology(2)

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Driving a Car: An Everyday Example of Process

Control

Control Objective (Set point):

Maintain car in proper lane

Controlled variable:

Location on the road

Manipulated variable:

Orientation of the front wheels Actuator or final control element:

Drivers steering wheel

Sensor:

Drivers eyes

Controller:

Driver

Disturbance:

Curve in road

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Schematic of Feedback Loop

General diagram

Actuator

Sensor

Process

Controlled

Variable

Disturbance

uController

cSetpoint+

-

e

Manipulated

variable

Controlledvariable

Error

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Chapt

er1

Home Heating Control System

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Chapt

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Chapt

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Chapte

r1

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Heat Exchanger Control:

TT

TC

Condensate

Steam

Feed

ProductStream

Pneumatic signal (solid line) and electronic signal (dash line)

TT:Temparature Transmitter ; TC: Temparature Controller

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Heat Exchanger Control

Controlled variable

Outlet temperature ofproduct stream

Manipulated variable

Steam flow

Actuator Control valve on steam

line

Sensor

Thermocouple on productstream

Disturbance

Changes in the inlet feed

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Illustrative Examples

Continuous stirred-tank heater

Question ; Assume that inlet temperature changes with

time. How can we ensure that T remains at or near the

desired (set point) temperature T=TR?

Continuous stirred-tank heater.

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Possible Strategies

1.Measure T and adjust Q .

2.Measure Tiand adjust Q.

3.Measure T and adjust w.

4.Measure Tiand adjust w.

Objective :T=TR

5.Measure T and Tiand adjust Q.

6.Measure T and Tiand adjust w.7.Place a heat exchanger on the inlet stream.

8.Use a large tank.

Classification

1 & 3; Feedbackcontrol

2 & 4; Feedfowardcontrol

5 & 6; Feedfoward-Feedbackcontrol

7 & 8; Design change34U D Dwivedi12/29/2014


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Illustrative Example: Blending system

Notation:

w1, w2and w are mass flow rates

x1,x2andxare mass fractions of component A

Chapt

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Assumptions:


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Assumptions:

1. w1is constant

2. x2

= constant = 1 (stream 2 is pure A)

3. Perfect mixing in the tank

Control Objective:

Keepxat a desired value (or set point)xsp, despite variations inx1(t). Flow rate w2can be adjusted for this purpose.

Terminology:

Controlled variable (or output variable):x

Manipulated variable (or input variable): w2

Disturbance variable (or load variable):x1

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D i Q i Wh l f i i d h


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Design Question. What value of is required to have2w

?SPx x=

Overall balance:

Component A balance:

1 20 (1-1)w w w= +

1 1 2 2 0 (1-2)w x w x wx+ =

(The overbars denote nominal steady-state design values.)

At the design conditions, . Substitute Eq. 1-2, and, then solve Eq. 1-2 for :

SPx x= SPx x=2 1x = 2w

12 1 (1-3)

1

SP

SP

x xw w

x

=

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Equation 1-3 is the design equation for the blending

system.

If our assumptions are correct, then this value of will keep

at . But what if conditions change?

x

SPx

Control Question. Suppose that the inlet concentration x1

changes with time. How can we ensure that x remains at or near

the set point ?As a specific example, if and , thenx>xSP.

SPx

1 1x x> 2 2w w=

Some Possible Control Strategies:

Method 1.Measure x and adjust w2.

Intuitively, ifxis too high, we should reduce w2;

2

w

Chapt

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Manual control vs. automatic control

Proportional feedback control law,

1. where Kcis called the controller gain.

2. w2(t) andx(t) denote variables that change with time t.

3. The change in the flow rate, is proportional to

the deviation from the set point,xSPx(t).

( ) ( )2 2 (1-4)c SPw t w K x x t = +

( )2 2 ,w t w

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Chapt

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M th d 2 M d dj t


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Method 2.Measure x1and adjust w2.

Thus, if x1is greater than , we would decrease w2so that

One approach: Consider Eq. (1-3) and replace and with

x1(t) and w2(t) to get a control law:

1x

2 2;w w

Introduction_2014-15.pdf

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