ANTI SURGE CONTROL

SYSTEM

BASIC CONCEPTS

ISSUES FOR DISCUSSION

• Introduction to compressor control• Surge Phenomenon, causes and remedy• Basic ASC system• Challenging Issues

– Algorithms– Control responses– Advance control strategies– Quick response of control valve– Elimination of dead time and lag time

• Surge limit line, Distance between SLL and operating point• Performance control• Non-integrated System• Interacting Performance controller and ASC• Integrated system• Selection criteria for FMD and AS Valve

PERFORMANCE CURVE OF COMPRESSOR

SURGE

• Surge : Very fast process

• Order of

milliseconds

• Potential to cause huge damage and losses

HOW SURGE DEVELOP ?

• Normal flow from higher pressure (P1) to lower pressure(P2)

• In Compressor gas flows from low suction pressure to high discharge pressure using external power.

• If discharge valve is closed discharge pressure (P2)increases. If P (P2 - P1 ) is more and power is not sufficient, flow will be reverse.

SURGE PHENOMENON

• • Fig shows... how surge develops using a model of an air compressor pumping into a closed tank.

• Machine shutdown : no flow, no pressure

• Machine start:

• High flow, less pressure (E)

• Start press. build up, decrease flow( E to D to A)

• Reversal of flow at A and again at C, causing flow & pressure oscillations

CAUSES FOR SURGE

• Discharge valve is closed• Suction flow decreases• Power increases• Change in gas composition

SURGE CONTROL METHODS

• Vent discharge pressure

– Wastage of power

– Loss of material

– Hazards

• Recycle from discharge to suction

– Wastage of power

ANTI-SURGE CONTROLLER

• KEY WORDS

– SURGE CONTROL LINE ( SCL )

– RECYCLE TRIP LINE ( RTL )

– SURGE LIMIT LINE ( SLL)

– SAFETY ON LINE ( SOL)

BASIC ANTI-SURGE CONTROL SYSTEM

• Anti surge controller protect the compressor against surge by opening the recycle valve

• opening the recycle valve lowers the resistance felt by compressor

• This takes compressor away from surge