Oil and gas production handbook An introduction to oil and gas production

type compressors 
with up to 15 wheels 
provide high volumes at 
a relatively low 
pressure differential 
(discharge pressure 3-5 
times inlet pressure), 
speeds of 5,000-8,000 
rpm, and inlet flows up 
to 200,000 m
3
/hour. 
Applications include air compressors and cooling compression in LNG 
plants. 
Axial rotor photo: Dresser Rand
 

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• Larger oil and gas 
installations use 
centrifugal compressors 
with 3-10 radial wheels, 
6,000–20,000 rpm 
(highest for small size), up 
to 80 MW load at 
discharge pressure of up 
to 50 bars and inlet 
volumes of up to 500,000 
m
3
/hour. Pressure 
differential up to 10. 
Photo: Dresser Rand
  
Most compressors will not 
cover the full pressure range 
efficiently. The lowest pressure is atmospheric, for gas to pipeline, some 3 to 
5 MPa (30-50 bar) pressure is used, while reservoir reinjection of gas will 
typically require 20 MPa (200 bar) and upwards, since there is no liquid in 
the tubing and the full reservoir pressure must be overcome. Therefore, 
compression is divided into several stages to improve maintenance and 
availability.  
Also due to single unit power limitations, compression is often divided in 
several parallel trains. This is not the case in this example, since gas is not 
exported and reinjection can be interrupted during maintenance periods. 
Compressors are driven by gas turbines or electrical motors (for lower power 
also reciprocating engines, steam turbines are sometimes used if thermal 
energy is available). Often, several stages in the same train are driven by the 
same motor or turbine.The main operating parameters for a compressor are 
the flow and pressure differentials. The product defines the total loading, so 
there is a ceiling set by the maximum design power. Furthermore, there is a 
maximum differential pressure (Max P
d
) and choke flow (Max Q), the 
maximum flow that can be achieved. At lower flow, there is a minimum 
pressure differential and flow before the compressor will "surge" if there is 
not enough gas to operate. 
 
If variations in flow are expected or differences between common shaft 
compressors occur, the situation will be handled with recirculation. A high 
flow, high pressure differential surge control valve will open to let gas from 
the discharge side back into the suction side. Since this gas is heated, it will 
also pass through the heat exchanger and scrubber so as not to become 
overheated by circulation. 
 

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