Document Text Contents
Page 1
71
Saudi Aramco EDP 2004
Compressors 71
A Model of Surge
Surge Definition
Surge is self-oscillations of pressure and flow, including a flow
reversal. The surge flow reversal is the only point of the curve
when pressure and flow drop simultaneously.
Characteristic Curve of a Typical Centrifugal Compressor
– B to C in 20 to 50 mSec
– Cycle B to B at 0.33 to 3 Hertz
Page 11
81
Saudi Aramco EDP 2004
Compressors 81
Compressor
Inlet
Gas
FT PT PT
UIC
FT I/P FV
Recycle
∆Pc
Discharge
Gas
Simple Antisurge System
Flow measured in suction
(∆Po)
Suction and discharge
pressure transmitters for
pressure differential
calculation
Control strategy is
proportional plus integral
control to manipulate
recycle valve
Increase flow through
compressor and reduce
discharge resistance when
required to prevent surge
In a simple antisurge system, flow and pressure measurements on the suction and
pressure measurements on the discharge are sent to the antisurge controller, UIC.
The UIC controls the recycle valve which is normally closed. If surge is
approached, the UIC opens the recycle valve.
71
Saudi Aramco EDP 2004
Compressors 71
A Model of Surge
Surge Definition
Surge is self-oscillations of pressure and flow, including a flow
reversal. The surge flow reversal is the only point of the curve
when pressure and flow drop simultaneously.
Characteristic Curve of a Typical Centrifugal Compressor
– B to C in 20 to 50 mSec
– Cycle B to B at 0.33 to 3 Hertz
Page 11
81
Saudi Aramco EDP 2004
Compressors 81
Compressor
Inlet
Gas
FT PT PT
UIC
FT I/P FV
Recycle
∆Pc
Discharge
Gas
Simple Antisurge System
Flow measured in suction
(∆Po)
Suction and discharge
pressure transmitters for
pressure differential
calculation
Control strategy is
proportional plus integral
control to manipulate
recycle valve
Increase flow through
compressor and reduce
discharge resistance when
required to prevent surge
In a simple antisurge system, flow and pressure measurements on the suction and
pressure measurements on the discharge are sent to the antisurge controller, UIC.
The UIC controls the recycle valve which is normally closed. If surge is
approached, the UIC opens the recycle valve.
