Page 15 - Compression Machinery for Oil and Gas

4 SECTION I Fundamentals of Compression

The appropriate type of compressor for a particular application is a function
of the required flow rate and pressure ratio. A chart describing the approximate
operating envelopes of different compressor types has been provided by the
Natural Gas Processor Suppliers Association and is shown in Fig. 1.1. Although
the exact capabilities of a particular compressor type may deviate from these
conditions based on a specific design, the general trends are valid. In general,
there is significant overlap between the three compressor types, although recip-
rocating compressors uniquely cover low-flow applications with high pressures
and centrifugal compressors uniquely cover high-flow applications.

Basic Thermodynamics
The working principles of gas compressors can be understood by applying the
basic laws of physics. Using the first and second law of thermodynamics
together with basic laws of fluid dynamics, such as Bernoulli’s law and Euler’s
law allows us to explain the fundamental working principles, and by extension,
can increase the understanding of the operational behavior of gas compressors.
Most descriptions of compressors presented here are specifically geared
toward pipeline applications. They are usually also applicable to many other
gas compression applications. The general description of the thermodynamics
of gas compression applies to any type of compressor, independent of its
detailed working principles.

Discharge pressure vs. inlet flow
100,000

10,000
Discharge pressure (psig) 1000

100
Rotary-screw
Recip-single stage
10 Recip-multistage
Centrifugal-single stage
Centrifugal-multistage
1
1 10 100 1000 10,000 100,000 1,000,000
Inlet flow (acfm)
FIG. 1.1 Compressor types and application conditions. (Modified from NGPSA Engineering Data
Book, vol. 1, Revised tenth ed., 1994. Compiled and edited in cooperation with the Gas Processors
Association. Copyright 1987 Gas Processors Association.)