Page 266 - Petroleum and Gas Field Processing

Figure 1 Operations involved in the treatment and processing of natural gas.

Natural gas field processing and the removal of various components from
it tend to involve the most complex and expensive processes. Natural gas
leaving the field can have several components which will require removal
before the gas can be sold to a pipeline gas transmission company. All of
the H 2 S and most of the water vapor, CO 2 , and N 2 must be removed
from the gas. Gas compression is often required during these various
processing steps. To illustrate this point, a sour gas leaving a gas–oil
separation plant (GOSP) might require first the use of an amine unit
(MEA) to remove the acidic gases, a glycol unit (TEG) to dehydrate it,
and a gas compressor to compress it before it can be sold.
It is also generally desirable to recover NGL present in the gas in
appreciable quantities. This normally includes the hydrocarbons known as
þ
C . In some cases, ethane C 2 could be separated and sold as a
3
petrochemical feed stock. NGL recovery is the first operation in stage II,
as explained earlier. To recover and separate NGL from a bulk of a
gas stream would require a change in phase; that is, a new phase has
to be developed for separation to take place by using one of the following:
1. An energy-separating agent; examples are refrigeration for
partial or total liquefaction and fractionation
2. A mass-separating agent; examples are adsorption and
absorption (using selective hydrocarbons, 100–180 molecular
weight).
The second operation in stage II is concerned with the fractionation of
NGL product into specific cuts such as LPG (C 3 /C 4 ) and natural
gasoline.
It should be pointed out that the fact that all of the field processes
do not occur at or in the vicinity of the production operation does not
change the plan of the system of gas processing and separation or its basic

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