Oil and gas production handbook An introduction to oil ... - ABB Group

Heat exchangers of various forms are used to cool the gas. Plate heat
exchangers (upper picture) consist of a number of plates where the gas and
cooling medium pass between alternating plates in opposing directions.
Tube and shell exchangers (next picture) place tubes inside a shell filled with
cooling fluid. The cooling fluid is often pure water with corrosion inhibitors.
When designing the
process, it is important to
plan the thermal energy
balance. Heat should be
conserved, e.g., by using
the cooling fluid from the
gas train to reheat oil in the
oil train. Excess heat is
dispersed, e.g., by
seawater cooling.
However, hot seawater is
extremely corrosive, so
materials with high
resistance to corrosion,
such as titanium must be
used. Photo: SEC Shell and
Tube Heat Exchanges
4.3.2 Scrubbers and reboilers
The separated gas may contain mist and other liquid droplets. Drops of
water and hydrocarbons also form when the gas is cooled in the heat
exchanger, and must be removed before it reaches the compressor. If liquid
droplets enter the compressor, they will erode the fast rotating blades. A
scrubber is designed to remove small fractions of liquid from the gas.
There are various types of gas-drying equipment available, but the most
common suction (compressor) scrubber is based on dehydration by
absorption in triethylene glycol (TEG). The scrubber consists of many levels
of glycol layers.
A large number of gas traps (enlarged detail) force the gas to bubble up
through each glycol layer as it flows from the bottom to the top of each
section.
Processed glycol is pumped in at the top from the holding tank. It flows from
level to level against the gas flow as it spills over the edge of each trap.
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