Page 427 - Compression Machinery for Oil and Gas

406 SECTION III Applications

FIG. 10.4 Large barrel-type LNG compressor.

large horizontally split compressor casings and may exceed the supplier’s cas-
ing joint bolting experience. These off-design process conditions should be
reviewed with the compressor designer. Higher pressure refrigeration services
are accomplished in a radially split (barrel compressor), which has less stringent
limitations as regards MAWP. A large barrel compressor is shown in Fig. 10.4.

Horizontally Split and Barrel Designs
Propane (precooling) refrigeration service is usually accommodated in one or
two horizontally split compressor casings. The propane compressor is the most
challenging machine in terms of flow coefficient and inlet relative Mach num-
ber. The low inlet temperature and high molecular weight (mole weight of 44
for propane) combined with large side streams flow require a precise fluid
dynamic design of the gas path and particular attention to rotordynamics.
Mixed refrigerant service, which handles large capacities at low tempera-
tures, requires the solution to many technical manufacturing and assembly
issues. Mixed refrigerant service is typically implemented at two or three
pressure levels in two or three compressors (horizontally split and barrel).
Other refrigeration services are often facilitated by one compressor casing in
a back to back or compound arrangement. Particular attention has to be paid to
rotordynamics, due to the high-pressure ratio and consequent large number of
impellers (and long rotor length) generally associated with this.
For refrigeration services, required to develop a very high-pressure ratio
is generally obtained utilizing a three casing solution. The last casing is a
barrel-type compressor while the first and second are horizontally split.