Sour gas treatment
Nowadays the following methods are used to remove acidic components from natural gas:
- Absorption methods (which fall intro three groups, depending on the way the acidic components of the gas react with the active component of the absorbent)
Adsorption methods for gas purification are based on the selective removal of impurities by solid absorbents.
- Chemical absorption (chemisorption) is based on the chemical reactions of hydrogen sulfide and carbon dioxide with the active components of the absorbents. Among other chemical absorbents, alcanolamines are widely used in the industry: MEA (monoethanolamine), DEA (diethanolamine), TEA (triethanolamine), MDEA, DIPA (diisopropanolamine), as well as alkаline solutions, alkaline metal solutions (potassium carbonates, 25-30% К2СО3 or Na2CO3 solutions) and ferric hydroxide solution. Chemical absorption is highly selective in relation to acidic components and assures highdegrees of H2S and CO2 removal from the gas. If amines are used,
relatively minor quantities of sulfur-bearing organic compounds are removed. Fine removal of such compounds is achieved by the use of alkali.
- Physical adsorption involves the removal of acidic components and this is determined by the degree of solubility of the gas components in absorbents. Absorbents such as polyethylene glycol dimethyl ether (Selicsol®), methanol (Rectisol®), propylene carbonate (Fluor®), and various others are used. In contrast to chemisorption, physical absorption removes carbon oxysulfide, carbon bisulfide and mercaptans, as well as hydrogen sulfide and carbon dioxide.
- Physicochemical absorption uses composite absorbents, that is to say a mixture of chemical and physical absorbents. Such absorbents have an intermediate capacity to dissolve the acidic components of gases. These absorbents enable the fine removal of not only hydrogen sulfide and carbon dioxide, but also of organosulfurous compounds. The most widely used absorbent in the industry is Sulfinol, a mixture of diisopropanolamine (30-45%), sulfolane (tetrahydrothiophene dioxide) (40-60%), and water (5-15%). Also, lately, Ukarsol, a domestic analogue of Ecosorb, has become increasingly popular. This absorbent makes it possible to selectively remove H2S in the presence of СО2, while simultaneously removing organosulfurous compounds.
- high absorbing capacity;
- the conjunction of fine removal and deep dehydration (down to -70 0С).
Catalytic methods are used when the gas contains impurities (e.g. sulfides, disulfides, carbon oxide sulfide, carbon disulfide, thiophene) which cannot be efficiently removed by liquid absorbents or solid adsorbents. These are the following:
- relatively high operating costs;
- 50%-50% adsorbtion/desorbtion operation cycle.
- Hydrogenation into H2S or sulfur-free compounds by hydrogen or water steam. The catalysts used are cobaltous oxide, nickel oxide, molybdenum on aluminum oxide.
- H2S Oxidation into elemental sulfur on active aluminum oxide or (via the Merox process) into disulfides.
In choosing a certain method for removing acidic components at the design stage, Red Mountain Energy takes into account a number of factors, for example the ecological standards and requirements for the disposal of sulfurous compounds; the type and concentration of impurities in sour (untreated) gas; gas purity, sour gas temperature and pressure, purified gas temperature and pressure, plant capacity, gas composition, etc.