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• nokaraju

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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.

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

PG

1

Naming rule

P T L F A

1

2

3

4

Measurement

Device

Device / Condition

Condition

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
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

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



PCC PTC PTR PIR TRR TRA TAV

No such devices yet.

2

Symbols Instruments / control devices:

A circle representing locally mounted instrument

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

A circle with horizontal line representing control room panel mounted instrument.

A circle with horizontal line inside a square representing its function in DCS.

3

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

Instrument Line (Signal) Symbols

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

4

Final control elements

Control valves

=

Manual valve

=

OR

Not darkened
Always open

Manual valve

=

OR

Darkened
Always closed NC

Solenoid valve

NO
Normally open

=

NC
Normally closed NO

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

NC

5

Device names

Devices (hardware)

Current to pneumatic transducer

Pressure relief valve / Pressure safety valve

Symbols

Notations

I/P

I/P

PRV

PSV

Thyristor

TY

TY

Inverter

VY

VY

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

6

Examples

PG

= Pressure Gauge

PIC

= Pressure Indicating Controller

FT

= Flow Transmitter

TT

= Temperature Transmitter

TE

= Temperature Element (RTD/TC)

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

7

Can you read the following P&ID?

 Main process line  Process instrument piping  Temperature transmitter  Temperature controller

product Feed

 Flow controller

TT

 Current to pnuematic transducer

Control valve

Fuel



 Electrical signal Pneumatic signal  Temperature controller DCS function



 I/P





TC



 FC



TC

SP



FT

12

11 ASD

11 Automatic shut down PLC unit 12 Solenoid valve

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

8

SP, Set point

Controller

Final Control Element

Process

PV, Controlled Variable

PV, Controlled Variable Sensor

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.

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

9

SP, Set point

Controller 1

Controller 2

PV, Controlled Variable

PV, Controlled Variable

Final Control Element

Process 2

Process 1

Sensor 2

Sensor 1

What is cascade control? The inner loop controller obtains its set point from the outer loop controller.

Merit? Faster recovery time as compared to SISO feedback control.

The purpose is to eliminate the effect of disturbances.

Demerits? Controllability will be worst than SISO if both controllers were not properly tuned.

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

PV, Controlled Variable

10

D, Disturbance

SP, Set point

Feedforward

Disturbance

Controller

Sensor

Final Control Element

Feedback

Controller

Process

PV, Controlled Variable

PV, Controlled Variable Sensor

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).

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

Demerit a) Fail to work if any of the sensor broke down. b) Poor process controllability due to inaccurate process model.

11

TC

I/P

TT Heated product out

Product in

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

Steam in

Steam out

12

TC

FC

TT

FT

Heated product out

Product in

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

I/P

Steam in

Steam out

13

Σ

TC

X

TT

FC

I/P

FT L/L

Heated product out

TT Product in

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

Steam in

FT Steam out

14

X

FC

I/P

FT Steam in

Heated product out

FT Product in

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

Steam out

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

Reboiler vapor

(iii) Steam temperature gauge (iv) Vessel over pressure relief valve Steam

(v) Steam over pressure relief valve (vi) Liquid level gauge at overflow compartment (vii) Liquid level gauge at liquid boiling compartment

Condensate Bottom product

(viii) Temperature gauge at liquid boiling compartment. Tower bottoms

Install appropriate control systems for the following tasks: (i)

Liquid level control at over flow compartment Reboiler vapor

(ii) Reboiler vapor pressure control (iii) Liquid temperature control (iv) Reboiler vapor pressure alarm high (v) Liquid temperature alarm high

Steam

(vi) Low and high level liquid alarm at liquid over flow compartment (vii) Low liquid level alarm at boiling liquid compartment

Condensate

(viii) Steam flow cut upon low liquid level. Bottom product Tower bottoms