Page 173 - Compression Machinery for Oil and Gas

Integrally Geared Compressors Chapter 4 161

leads to more complex instrumentation and control with fast actuators for valves
and guide vanes and preset values for the start-up procedure. One the most chal-
lenging application is fuel gas compression for gas turbine power plants, where
fast start-up and load sharing between multiple units has to be realized.
Steam turbines can drive big compressors with high-power demand and are
well suited for long uninterrupted operation. On the other hand, they need much
longer time for start-up due to their warm-up procedure at different speed steps.
They also need turning devices and are often limited in the maximum number of
starts per day. Electric motors are available in a wide power range and can be
used for long uninterrupted operation as well as for frequent starts and stops. In
the latter case, the thermal load due to frequent start-up current has to be con-
sidered. Depending on the required availability, multiple trains and hot standby
machines are used.

IGC Applications

IG turbomachinery are an important part of the oil and gas industry. They are
present in many different aspects of oil and gas plants, including air separation
units (ASUs), midstream petro-chemical processes, and power generation. In
recent years, IG machinery have become commonplace in midstream processes.

Air Separation
ASUapplicationshavereliedonIGmachinessincetheearly1970s.Powerranges
on individual units in ASU plants can be above 30MW. The air separation indus-
try is one of the most important customers for IGC manufacturers since they can
easily benefit from most of IGC advantages—like multispeed aero layouts, ease
of installing intercoolers between each stage, and relative simplicity to create
flexible and efficient compressor designs out of standardized and proven com-
ponents. This helps to improve both capital expenditures (development, etc.)
and operating expenditures (power consumption, maintenance, etc.).

Midstream

Liquefied natural gas (LNG) facilities are quite complex with unique demands
for the turbomachinery. For methane, BOG compressors are used to recover gas
that evaporates while offloading LNG from a carrier vessel to storage at the
facility terminal. Once the gas is reinjected back into the system, secondary
pumps raise the pressure of the fluid and transfer it to meet the demands of
the final application: power plant, city gas, etc. It is also possible to boost
the pressure after the BOG compressor with a higher-pressure compressor to
meet delivery needs. This is more commonly done with reciprocating compres-
sors, but advanced IGC designs can have the ability to meet the needs depending
upon flow and pressure requirements.