Process Instrumentation Diagram Student Copyaabi.uitm.edu.my/cpe562/slides/pidnotes.pdf · Process...

Process & Instrumentation Diagram (P&ID)

Purpose

1. To indicate the instruments or control devices attached to the process.

2. To indicate the control system architecture associated with the process.

How it is done?

Standard symbols and notations representing instruments or control devices are placed to the

pipings and vessels. Standard symbols and notations are available from ISA-5.1(1984) standard.

Methodology?

Process piping and sub-piping

A thick straight line represent main process piping

A thin straight line represent process sub-piping either

to instruments or by-pass process line.

PG

© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 1

Naming rule

1 2 3 4

Measurement Device Device / Condition Condition

P

T

L

F

A

Pressure

Temperature

Level

Flow

Analysis

C

T

R

I

A

S

G

Controller

Transmitter

Recorder

Indicator

Alarm

Switch / Safety

Gauge

C

T

R

H

L

V

Controller

Transmitter

Recorder

High

Low

Valve

H

L

High

Low

Complete guide on P&ID symbols & notations are available from ISA 5.1 (R1984)

Examples

No such

devices yet.

� �

PC

PIC

LG

FR

TAL

TALL

TAHL

Pressure Controller

Pressure Indicating Controller

Level Gauge

Flow Recorder

Temperature Alarm Low

Temperature Alarm Low Low

Temperature Alarm High Low

PCC

PTC

PTR

PIR

TRR

TRA

TAV

Complete guide on P&ID symbols & notations are available from ISA 5.1 (R1984)


Instruments / control devices:

A circle representing locally

mounted instrument

A circle with horizontal line

representing control room

panel mounted instrument.

A circle with horizontal line

inside a square representing

its function in DCS.

Symbols


Follow the standard published by the Instrument Society of America (ISA)

Instrument Line (Signal) Symbols


Final control elements

Control

valves =

Manual

valve= Not darkened � Always openOR

Manual

valve= Darkened � Always closedOR

NC

Solenoid

valve=

NCNO

NO � Normally open

NC � Normally closed


Current to pneumatic

transducerI/P

Devices (hardware) SymbolsDevice names

Pressure relief valve /

Pressure safety valvePSV PRV

Notations

I/P

Thyristor TY TY

Inverter VY VY


PG

Examples

= Pressure Gauge

PIC= Pressure Indicating Controller

FT = Flow Transmitter

TT

TE

= Temperature Transmitter

= Temperature Element (RTD/TC)


Can you read the following P&ID?

TT

product

Fuel

�

��

� Main process line

� Process instrument piping

� Temperature transmitter

� Temperature controller

� Flow controller

� Current to pnuematic transducer

Feed

TC�

FT

FCI/P TC SP

� �

�

��

�

�

�

Control valve

� Electrical signal

� Pneumatic signal

ASD

1112� Temperature controller DCS function

11 Automatic shut down PLC unit

12 Solenoid valve


Controller

Final

Control

Element

Process

Sensor

SP,

Set point

PV,

Controlled

Variable

PV,

Controlled Variable

© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011)

What is feedback control?

Outcome of an action is fed back to

the controller for corrective action.

Merit?

Simple design. Easy to tune (for linear, fast & short dead time

processes: flow, level & pressure).

Demerits?

Slow recovery for slow process upon load disturbance or change in

set point (such as temperature control). A process with long dead

time may exhibit oscillatory process response and with longer

settling time.

9

Controller

2

Final

Control

Element

Process 2SP,

Set point

PV,

Controlled

Variable

Process 1Controller

1

Sensor

2

PV,

Controlled Variable


Sensor

1

PV,

Controlled Variable

2

What is cascade control?

The inner loop controller obtains its set point

from the outer loop controller.

The purpose is to eliminate the effect of

disturbances.

Merit?

Faster recovery time as compared to SISO feedback

control.

Demerits?

Controllability will be worst than SISO if both

controllers were not properly tuned.

10

Feedforward

Controller

Final

Control

Element

SP,

Set point

PV,

Controlled

Variable

Feedback

Controller

Disturbance

Sensor

Process

D,

Disturbance


Sensor

PV,

Controlled Variable

What is feed forward control?

A method of control based on process

model: mass and energy balances.

Purpose

To compensate disturbances (D) before they

affect the controlled variable (PV).

Demerit

a) Fail to work if any of the sensor broke

down.

b) Poor process controllability due to

inaccurate process model.

11

TT

I/P

Steam in

Steam out

TC

Heated

product out

Product

in


Steam outin

12

TT

I/P

FT

FC

Steam in

Steam out

TC

Heated

product out

Product

in


Steam outin

13

TT

Σ X

L/L

I/P

FT

FC

FTTT

Steam in

Steam out

TC

Product

in

Heated

product out


Steam outin

14

X I/P

FT

FC

FT

Steam in

Steam out

Product

in

Heated

product out


Steam outin

15

Using correct P&ID symbols, draw the following

instruments to the reboiler as shown in figure

below.

(i) Steam pressure gauge

(ii) Reboiler vapor pressure gauge

(iii) Steam temperature gauge

(iv) Vessel over pressure relief valve

(v) Steam over pressure relief valve

(vi) Liquid level gauge at overflow

compartment

Reboiler vapor

Steam

compartment

(vii) Liquid level gauge at liquid boiling

compartment

(viii) Temperature gauge at liquid boiling

compartment.

Condensate

Bottom product

Tower bottoms

Install appropriate control systems for the

following tasks:

(i) Liquid level control at over flow

compartment

(ii) Reboiler vapor pressure control

(iii) Liquid temperature control

(iv) Reboiler vapor pressure alarm high

(v) Liquid temperature alarm high

(vi) Low and high level liquid alarm at

liquid over flow compartment

Reboiler vapor

Steam

liquid over flow compartment

(vii) Low liquid level alarm at boiling liquid

compartment

(viii) Steam flow cut upon low liquid level.

Condensate

Bottom product

Tower bottoms

Process Instrumentation Diagram Student Copyaabi.uitm.edu.my/cpe562/slides/pidnotes.pdf · Process...

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