Page 63 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

5.1.1 Acid gas removal

Acid gases such as carbon dioxide and hydrogen sulfide form acids when
reacting with water, and must be removed to prevent corrosive damage to
equipment and pipelines. Hydrogen sulfide is also toxic and total sulfur
content is normally regulated.

The main removal process can be based on several principles:

Absorption allows
acidic gases to be
dissolved in a solvent,
to be released by
regeneration in a later
stage. Amine absorption
(as shown on the right)
is the most common
process for acid gas
removal.
Monoethanolamines
(MEA) dominate for
CO 2 removal. Solutions
with inorganic solvents
based on ammonia are
under development. Ill:
Wikipedia

A typical amine gas treating process (as shown in the flow diagram) consists
of an absorber unit, a regenerator unit and accessory equipment. In the
absorber, a "lean" amine solution absorbs H2S and CO2 from the upflowing
sour gas to produce a sweetened gas stream as a product. The "rich" amine
solution contains the absorbed acid gases and is routed into the regenerator
(a stripper with a reboiler). The stripped overhead gas from the regenerator
is concentrated H 2S and CO 2.

Adsorption relies on the molecules to bind to the surface of certain solids.
After a certain time the material must be regenerated to release the gas.
Principles used include Pressure Swing Adsorption (PSA), Temperature
Swing Adsorption (TSA) and Electric Swing Adsorption (ESA)

Cryogenic removal uses a turbo expander: A gas turbine is driven by the
expanding gas which then cools to below the dew point for the gas to be
removed.

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