Ing. Mecanico

World Academy of Science, Engineering and Technology 34 2007

Industrial Compressor Anti-Surge Computer
Control
Ventzas Dimitrios, and Petropoulos George

Keywords—Anti-surge, control, compressor, PID control, safety,
fault tolerance, start-up, ESD.

The input signals are the suction flow differential pressure,
suction pressure and discharge pressure, see Fig. 2. A
temperaturemeasurement corrects flow and speed at the
compressor suction.
Surge detection devices are static and dynamic ones. The
pressure transmitter monitors the pressure and controls the
blow-off valve to avoid stall and surge. Surge cycles occur
fast and can even go undetected if the applied instrumentation
and controls are too slow.

I. INTRODUCTION

III. COMPRESSOR SURGE

Abstract—The paperpresents a compressor anti-surge control
system, that results in maximizing compressor throughput with
pressure standard deviation reduction, increased safety margin
between design point and surge limit line and avoiding possible
machine surge. Alternative control strategies are presented.

T

HE compressor is a multi-stage type; the incoming air is
compressed in the first stage and then passedthrough a
heat exchanger to be cooled off before being injected into the
next stage, see Fig. 1.
Anti-surge control system design practices encompass the
proper sizing, selection, and location of piping of the recycle
loops, the recycle valves, volumes of vessels in the recycle
path, check valves, etc..

Compressor surge occurs when the developed compressor
head (H) drops below thenetwork resistance (discharge
pressure). Surge is a fluctuation of flow and pressure and it
causes overheating and damages; it may be violent enough to
damage a compressor in a few cycles. Surging gives cyclic
flow, back-flow, high vibrations, pressure shocks and rapid
temperature increase. Process design minimizes the piping
volume in the recycle and forward path [1].

Fig. 1 Compressordetails

II. INSTRUMENTATION AND ACTUATORS

Fig. 3 Momentary flow reversal
Fig. 2 Required input signals

An increase in pressure across the compressor, results in a
momentary flow reversal, see Fig. 3. This surge cycle goes
until a change is made in the process conditions. The
controller operates a surge valve to maintain sufficient

Ventzas Dimitrios is with Department of Informatics &Communications,
TEI of Larissa, Larissa 41 100, Greece (e-mail: dventzas@uth.gr).
Petropoulos George, Associate Professor is with Department of
Mechanical Engineering, University of Thessaly, Greece (e-mail:
gpetrop@uth.gr).

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World Academy of Science, Engineering and Technology 34 2007

forward flow to prevent surge, see Fig. 4; the external causeseffects are:
bad machine design,system damage
improper assembly, mispositioned rotor
restriction in suction or discharge
internal plugging of flow passages (fouling)
process conditions upsets, sudden load change
inadvertent loss of speed
changes pressure,temperature,gas composition
instrument or control malfunction
hardware malfunction (variable inlet vanes)
de-tuned controller
operator error
the inability of the coldrecycle valve to quickly and
effectively de-pressurise the large volume in the cold
recycle flow loop, etc
Surge is detected by
1. the boundary layer reversal
2. the compressor 2nd harmonic excitation
The model features are inlet flow, gas parameters, molecular
weight, pressure and temperature, compression ratio, shaft
power in steady-state and transient conditions.

Fig. 5 Anti-surgecontroller

Fig. 6a Pressure oriented anti-surge control system

Fig. 6b Flow oriented anti-surge control system

In the surge control map the compressor flow set point is
provided by the control line positioned to the right of the
surge line which provides a safety margin for the surge PI
controller output to the surge valve to prevent the flow from
decreasing below the control line,...