Page 440 - Compression Machinery for Oil and Gas

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Summary
The growth of the LNG industry has resulted in the use of very complex and
high-technology compressors for refrigeration service. The propane compressor
represents one of the most challenging designs. From the perspective of com-
pressor selection, design, and testing, close designer-user interaction and good
communication are important to derive a robust compressor solution that will
operate under varied operating conditions. Imposition of simple and rigid rules
of thumb and specifications by the user that do not recognize that design com-
promises are inherent in compressor design will often result in nonoptimal
designs. Recognition should exist that turbocompressor aeromechanical design
is a complex area where several advanced tools are available to optimize design.
The design of LNG turbomachinery must be considered in an integrated manner
so that all components including auxiliaries work well.

Fuel Gas Compression (FGC)
The fuel gas system is the life blood of a combustion turbine or reciprocating
engine power plant, and there several factors that should be considered when
specifying a system that meets the requirements for a project.
The fuel gas system generally includes one or all three of the following
major components:

1. Fuel gas compression (FGC), if the gas pressure at the site boundary is lower
than what is required for the turbine or engine.
2. Gas filtration, to remove liquids (could be residual oil from upstream com-
pression, water, and/or condensed hydrocarbons).
3. Pressure regulation, if the gas pressure at the site boundary is higher than
what is required for the turbine or engine.
Many times the entity providing fuel gas to a power plant will have a wide range
of gas pressures. Contractually, they may be required to supply a minimum gas
pressure to a site, and this is the suction gas pressure needed for the FGC selec-
tion and system design. But the specifying engineer also needs to determine the
actual historical gas pressure available, which is typically much higher and
often varies seasonally based on local demand due to high usage for heating
and/or electrical production. The range could be wide enough that at times
gas compression is required to increase pressure, and at other times pressure
regulation is required to reduce gas pressure and the compression system is
bypassed.
Fuel gas requirements are specific to the turbine/engine size and manufac-
turer, and even the same model may have slightly different fuel gas flow and
pressures needs, depending on the project and conditions. For example, for a
Solar Taurus 60 turbine on a recent project the flow/pressure at 20°F ambient
was 1300scfm/250psig, but at 100°F reduced to 1050scfm/210psig. It is best to