Page 48 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

flotation. The surface oil film is drained, and the produced water can be
discharged to sea. Recovered oil in the water treatment system is typically
recycled to the third stage separator.

4.3 Gas treatment and compression

The gas train
consists of several
stages, each taking
gas from a suitable
pressure level in the
production
separator's gas
outlet, and from the
previous stage.

A typical stage is
shown on the right.
Incoming gas (on
the right) is first
cooled in a heat
exchanger. It then
passes through the scrubber to remove liquids and goes into the
compressor. The anti surge loop (thin orange line) and the surge valve
(UV0121 23) allow the gas to recirculate. The components are described
below.

4.3.1 Heat exchangers
For the compressor to operate efficiently, gas temperature should be low.
The lower the
temperature, the less
energy will be used to
compress the gas for the
given final pressure and
temperature. However
both gas from separators
and compressed gas are
relatively hot. When gas is
compressed, it must
remain in thermodynamic
balance, which means
that the gas pressure

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