Page 190 - Compression Machinery for Oil and Gas

Reciprocating Compressors Chapter 5 179

Steel couplings with leaf springs and oil circulation are available and widely
used in medium to high HP applications, and they are available up to the max-
imum kiloWatt ratings of modern engines and compressors. The oil supply usu-
ally comes through the crankshaft either from the engine, gear box, or
compressor. The stiffness is accurate and independent of temperature. The
damping capacity is high, relatively constant, and predictable over the coupling
life. These couplings are selected when damping is required, for example, for
variable speed applications using a motor VFD, turbine gear drive, or when cou-
pling a large engine to a compressor. The TNF can be set below 1 (when using
a gearbox) or near a higher harmonic where the damping will effectively reduce
the resonant stresses.

Engineering Scope
Packaged Units vs. Block-Mounted Units
Oil and gas industry reciprocating compressors can be packaged or block
mounted. Upstream and midstream applications typically use a packaged unit
while the downstream (refining and petrochemical) industry uses block mount
but is moving toward packaged units for lower powers, say less than 3700kW.
A packaged unit has the compressor with its driver and coupling mounted on
structural steel skid. For compressors up to 1500kW the skid is the foundation.
Higher powers may require the skid be attached to a concrete pad to provide
additional foundation mass. The fundamental idea of a package is to have a por-
table compressor that can be moved from well to well, as an example. A pack-
age is completely self-contained unit. The only required connections are
compressed gas suction (in) and discharge (out) and the package is ready to
be used.
A block-mounted compressor is typical for the refining industry and has the
compressor system built at site rather than in a shop as in the case of a packaged
unit. The compressor, driver, and all the auxiliaries are shipped to site where
they are assembled into the gas compression system. The compressor is
mounted on a large concrete block (hence the term “block mounted”) that is
the compressor foundation.
In either case the compressor, driver, coupling, and all of the auxiliary sys-
tems are engineered specifically for the gas compression application.

Importance of Pulsation Studies
The fundamental idea of a pulsation study is to ensure the process gas piping
system will not fail due to stresses caused by pulsation (pressure fluctuations).
Failure can lead to a release of process gas. Therefore, a pulsation study is an
extremely important piece of the engineering design of the overall compression
system.