Page 28 - Compression Machinery for Oil and Gas

18 SECTION I Fundamentals of Compression

gas-phase compression of CO 2 range from 1.7 to 15.27MPa versus CO 2 liq-
uefaction at 1.7MPa and pumping that liquid CO 2 to 15.27MPa.
8. Distribution: After natural gas has been produced and cleaned, it must be
pumped/compressed and stored for consumption by a multitude of residen-
tial, commercial and industrial users primarily for residential heat and
industrial processes. To maximize capacity and deliverability to midstream
and transmission pipelines feeding lower pressure gas distribution systems,
gas is typically compressed to higher pressures ranging 3.4–10MPa. The
required boosting compression function power is delivered using a mix
of reciprocating engines, turbines, and electric motors. The prime power
devices are used to drive a mix of reciprocating piston, centrifugal, and
screw compressors.

Factors to Consider When Selecting Compression Equipment
Selecting the ideal compressor for a given application should include consider-
ation for a wide variety of complex factors. Many of these key considerations
are presented in the following.

Flow Rates and Absolute Pressures
The maximum flow of a reciprocating compressor is limited by the cylinder size
(bore and stroke), the number of compressor cylinders, and the operating speed.
The maximum flow of a centrifugal compressor is typically limited by driver
power or some choke point internal to the compressor where the flow velocity
nears the speed of sound of the fluid.
Both reciprocating and centrifugal compressors can reach maximum dis-
charge pressures in the range of 70–100MPa. However, discharge pressures
of approximately 10MPa or less are most common. Special “hyper” reciprocat-
ing compressors, often used in low-density polyethylene production, can reach
discharge pressures up to 340MPa.
Fig. 2.3 provides an overview comparison of typical ranges of flow rates and
discharge pressures that can be attained with different types of compressors.
These criteria are a good starting point for selecting a compressor type. How-
ever, when multiple compressor types overlap for a given application, the fol-
lowing factors should be considered.

Compression Ratio and Maximum Temperatures

For a single-stage reciprocating compressor, the compression ratio typically
varies from 1.1 up to 4.0. The maximum compression ratio is usually limited
by a goal of preventing discharge temperatures from reaching no more than
approximately 296.33 °F. However, multistage reciprocating compressors with