Chapter 1 Introduction to Process Instrumentation and Control

Introduction to PIC

1. Introduction

2. Topics
▪Basic of process instrumentation and control
(PI&C).
▪Symbols identifications in piping and
instrumentation diagram (P&ID) drawing.
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3. Topic outcomes
▪Explain the basic instrumentation and process
control.
▪Construct a complete P&ID including alarm
system for a particular process or equipment.
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4. Process Control
4
Why
How
What
Where

5. What is control?
▪“measurement & adjustment”
▪Everyday example bounds
▫Room temperature (air conditioning)
▫measure room temperature
▫adjust thermostat
▫cruise control in car
▫measure speed of car
▫adjust gas flow rate to engine
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6. Example: Buffer tank
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h
Q
in
Q
out
H
How to keep the level at
desired value, H?
What happen if the level is too
high/low?
Overflow –may create safety and
environmental hazard
Too low –may effect the next process
equipment

7. Example:
The buffer tank has a relationship between flow and
level given by??????
??????��=??????ℎ. where h is in feet and K is
1.156 (gal/min) ft
1/2
. Suppose the input flow rate is 2
gal/min. At what value of h will the level when the
system stabilize at steady state condition?
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8. ▪The level will stabilize when Q
in= Q
out. Thus,
solve for h,
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9. Human Aided Control
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•The equipment has the
local gauge/ side tube
•Controlled variable-liquid
level
•Manipulated variable-Q
out
•What will cause the level
high/ low?
Q
in
h
Q
out
H

10. Automatic control
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•Machine, electronic, or
computer replace human
operation
h
Q
out
Controller
Actuator
Sensor
s
u
Q
in

11. Why control?
▪Steady operation (main reason)
▫consistent product despite disturbances
▪Optimal operation
▫minimise cost of production, use of
resources, increase throughput
▪Safety
▫protect people, environment, plants
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12. “
The primary objective of
process control is to
maintain the process at the
desired operating
conditions, safely,
efficiently, while satisfying
environmental, and product
quality requirements.
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13. Where is control done?
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14. Where is control done?
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15. DCS Main Competitors
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16. How is control design documented?
•Piping and Instrumentation Diagram (P & ID)
•Use standard symbol
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17. Control system elements
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Receives
information from
measuring devices
and decides what
action to be taken
Thermocouples,
flow meters, gas
chromatography
Implement the
decision taken by
the controller
Sensor Controller
Final
control
element

18. Control system elements
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Block diagram –shows the flow of information in the control system

19. Control terminology
▪Controlled/Process variables -these are the variables which
quantify the performance or quality of the final product, which
are also called output variables.
▪Manipulated variables -these input variables are adjusted
dynamicallyto keep the controlled variables at their set-points.
▪Disturbance variables -these are also called "load" variables and
represent input variables that can cause the controlled variables
to deviatefrom their respective set points.
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20. Piping and Instrumentation Diagram (P&ID)
•Process control employs a standard set of symbols and definitions
to represent a plant and its associated control systems.
•This standard was developed and approved by a collaboration
between the American National Standards Institute (ANSI) and the
Instrumentation, Systems and Automation (ISA) Society.
•The P&ID depicts the entire plant and associated control system.
•This includes plant operating units, product flow lines,
measurement and control signal lines, sensors, controllers and final
control elements.
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21. Piping and Instrumentation Diagram (P&ID)
•A complete control loop includes instrumentation for
measurement and control of a process variable.
•The complete loop includes:
▫Equipment i.e. reactor, column etc
▫Valves
▫Instrumentation i.eflow, temperature, pressure
sensor
▫Controllers
▫Piping i.e. process pipe, utilities (steam, water, fuel,
air etc) pipe
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22. The identification format
•Each loop on P&ID used ISA symbols to show the
particular devices that perform certain functions.
•The first letter of tag number is correspond to the
measured process variables.
•The succeeding letters in the tag number describe the
function of the elements in the loop such as T for
transmit, I for indicate, R for record, and or C for control.
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23. Instrumentation identification letters
Table A.1. Fraser (2001).Process measurement and
control
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24. Typical tag number
•TIC-103 Temperature Indicate Control (loop number) 103
•Where
▫TXX-103identifies the loop by first letter and number
and ICin place of XX identifies the functions by
succeeding letter.
▫Hyphens are optional
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25. Instrument line symbols
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Figure A.1. Fraser (2001).Process measurement and control

26. Example liquid flow and level control loops
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27. Example liquid flow and level control loops
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28. Example liquid flow and level control loops
•Flow loop F-212 includes both flow element and flow
transmitter.
•Level loop needs only the level transmitter.
•The P&ID shows all the instrument functions so that the
detailed drawings will reflect the complete loop and so
that any engineering cost estimates will be complete.
•The dotted line coming from the flow and level measuring
sensors to their controllers represent the electrical
feedback signal.
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29. General instruments or functions
•The ballons, rectangles, hexagons, and diamonds are
used to denote the instrumentation.
•A line through a symbol means it is accessible to an
operator, such as being in a panel in the control room.
•No lines means that the instrument is located in the field
and is not accessible to the operator in the control room.
•A dashed line means that the device is inaccessible by
virtue of being located within other equipment, such as
behind the panel of a control room.
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30. General instruments or functions
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31. Jigsaw Activities
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32. Exercise 1
You’re given a process that includes a chemical reactor, a flash
separator, heat exchangers, and associated piping. Propose one
control configuration for this process to control the following
variables:
a)Feed reactor temperature (T4)
b)Reactor liquid level
▪Draw the P& ID.
▪
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33. Exercise 1
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34. Exercise 1
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35. Exercise 2
Suggest a control configuration to satisfy the following
constraint. Draw the P&ID and justify your answer.
▪Case a: High pressure is dangerous.
▪Case b: No flow could damage the pump
▪Case c: High temperature may cause thermal loading in
the column
▪Case d: Quality of product at the bottom column is the
most critical
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36. Exercise 2
Flash separation
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37. 37
Thanks!