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P180 Principles of Control

Session Objectives

Describe the relative response speeds of the control loops

for different process parameters (flow, pressure, level,

temperature etc.)

Apply single control loops in Process Flow Schemes

Discuss the use of multiple control loops

At the end of the session participants will be able to :

The lectured material will be applied in an engineering exercise

Principles of Control Session Objectives

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Principles of Control

Session Topics

Duty of Controllers Single Control Loops

Multiple Control Loops

Master/Slave Control (Cascade)

Ratio Control

Split Range Control Override (Selective) Control

Session Topics

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Principles of Control

Classification of Control Systems

Open Loop

e.g. Toaster, Brewing Coffee, etc.

Control action independent of output

Closed Loop

e.g. Furnace, Steam Generator, etc.

Control action dependent on output

Principles of Control

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Principles of Process Control

Objectives of Process Control:

Increase Productivity

Reduce Operating Costs

Maintain Quality

Maintain Quantity

Duty of a Controller:

Keep the Process running smoothly (at certain conditions)

Compensate for external changes (disturbances, weather, etc.)

Control is:

Measure Compare

Correct

Principles of Process Control

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LRC

100

MV

PV

SV

SV: Set Value (Desired Value )PV: Measured Value (Actual)

MV: Output to Final Element

The Controller

LT

The Controller

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Flow Control (Liquid or Gas)

FC

Flow is the Fastest Process Parameter

SV

PV

MV

Flow Control (Liquid or Gas)

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PC

Pressure Control (Liquid)

Similar response as Flow Control

SV

PV

MV

Pressure Control (Liquid)

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PC

Slower than Flow or Liquid Pressure

SV

PVMV

Pressure Control (Gas)

Pressure Control (Gas)

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PC

LC

Flow F

Gas Volume V

Fin

Fout

Gas Pressure Control

SV

PV

MV

Gas Pressure Control

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Vapour Pressure Control

to Boilers etc.

Gas

LNG

-160 oC

PC

Vapour Pressure Control

~Temperature Control

Vapor Pressure Control

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Level Control

LC Open

50 %

Closed

SV = 50 %

90 %

50 %10 %

outF

inF

Level Control

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Temperature Control

TC

Oil T1

T2

Fuel

Furnace

Air

Temperature Control

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Principles of Control(Multiple Loop Control)

Multi Loop Configurations

Master / Slave (Cascade)

Ratio

Split-Range

Selective (or Override)

Principles of Control (Multiple Loop Control)

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Level Control

LC

F

C-1

P1

C-2P2SV

PV

MV

Level Control

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Level Control

(Master/Slave)

LC

F

C-1C-2

P1

P2

FC

SVPV

MV

PV

SV

MV

Level Control (Master/Slave)

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Temperature Control

(Master/Slave)

TC

Oil T1

T2

Fuel

Furnace

Air

FC

Temperature Control

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P180 Control Principles17P180

Tank

Ratio Control

FT

QT

FC

X

Primary Flow (Uncontrolled)Mixing Coil

(Controlled)

Secondary Flow

Ratio Relay

Gain = K

x1

K.X1X2sv

Chemical Injection Skid

Ratio Control

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P180 Control Principles18P180

FT

X

FC

Fuel Gas

Combustion Air

Ratio Control

A/F Ratio 14:1

* 14

PV

SVMV

MV

PV

Ratio Control

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P180 Control Principles19P180

Gas

Liquid

Out

Out

Inlet

Split-Range Control (1)

LC

PC

Flare

Export

Split-Range Control (1)

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0% 50% 100%

Controller Output

Valve 1 Valve 2

0%

100%

SignaltoValves

Split-Range Control (1)

Split-Range Control (1)

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0% 50% 100%

Controller Output

Valve 1 Valve 2

0%

100%

SignaltoValves

Split-Range Control (2)

0% 50% 100%

Controller Output

Valve 1

0%

100%

SignaltoValves

Valve 2

PROCESS

PC

Gas InGas Out

0 - 50% 50 - 100%

Valve 1 Valve 2

Split-Range Control (2)

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Gas

Feed

Pipeline

Selective or Override Control

FC PC

SS

Gas

Processing

Plant

Selective or Override Control

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Compressor Control

Control Systems forReciprocating Compressors

Variable Speed

Inlet Throttling

Bypass (Recycle) Control

On/Off Control

Suction Valve Lifting

Symbol

Compressor Control

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PC

SC

Reciprocating Compressor Control

Reciprocating CompressorControl

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ASC

ASC

PC

SC

P1

P2

P3

P4

Discharge

Process

PC

Suction

Process

1 Stagest

1 Stagest

2 Stagend

2 Stage

nd

Suction

Drum

Interstage

Process

Compressor Control

Compressor Control