Page 43 - Compression Machinery for Oil and Gas

Centrifugal Compressors Chapter 3 35

FIG. 3.4 Blue-C hermetically sealed compressor.

to reduce windage, there is no possibility that gas from within a hermetically
sealed casing may escape to the environment since there are no shaft end seals.
For this reason, there are two primary uses for hermetically sealed units.
Common applications are subsea compression applications for gas gathering
or artificial lift. In this application, the hermetically sealed compressor is
located on the surface of the ocean floor. The blue-C compressor is one example
of the technology as pictured below. Hermetically sealed compressors also have
the potential to be used to compress gases that are toxic; however, this is less
common.

Overhung/Inline
Overhung inline compressors are the least common configuration seen in oil
and gas applications. These units are similar to an integrally geared compressor,
however, the gearbox is not located on the structure of the compressor, but is
instead driven by an external gearbox.

Multisection
So far, the flow through the casing has been described as passing from stage-to-
stage as the gas is compressed, ultimately leaving the compressor from the
discharge flange. This is true for a straight-through single-section compressor
as shown in Fig. 3.5 (top left). A two-section compressor, as shown in the other
windows in Fig. 3.5 have two distinct compressor sections, where gas passes
from one section to the next by leaving the compressor casing and entering
through a second inlet. This process allows for an intercooler to be used to