2015-10-13
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Natural gas is not directly usable when it comes from the well. Often it is extremely rich in methane and contains heavy hydrocarbons; in addition, it contains varying proportions of nitrogen and carbon dioxide, hydrogen sulfide, mercaptans, and other sulfur compounds. The aim of gas processing is to make the gas conform to standards of use and to recover the liquid or solid components, which are often of greater commercial value than the gas itself.
After its arrival at the central plant, the gas must undergo the following series of treatments: 1) expansion at processing pressure, which causes the formation of condensates; these are removed, and the gas is then dehydrated by contact with glycol, which is regenerated; 2) sweetening, which removes the hydrogen sulfide and carbon dioxide by diethanolamine treatment, and fixes them in an absorber; 3) elimination of the mercaptans by soda fixation; 4) stripping (either by cooling or by absorption in an oil), which extracts the hydrocarbons with longer chains than methane and produces a gas conforming to commercial specifications. The rich absorption oil and the purified condensate are fractionated by distillation to produce propane, butane, stabilized gasoline, and residues. These successive operations are performed continuously and require an extremely sophisticated control system.
