ABSORPTION GAS CLEANING
ABSORPTION GAS CLEANING (RU: абсорбционная очистка газа) is the removal of the admixtures of H2S, CO2, organic sulfur compounds, and other compounds from the natural and oil gases (gas mixtures), using the liquid absorbents. Is carried out mainly at the gas processing plants for the prevention of the air basin pollution (in the areas with the industrial and other objects, which are processing or consuming the gas), the protection of the gas transmission systems against the corrosion, the separation of the impurities as the raw material for the production of the sulfur and mercaptans. In the USSR, it was used for the first time in the middle 50's of the 20th century, and is used on the large scale (15% of the total volume of the produced gas) since the early 70s.
A typical scheme of the absorption gas cleaning includes the continuous circulation between the absorbent device, in which the gas cleaning is occuring, and the regenerator, where the absorbing capacity of the solution is restored. There may be conventionally distinguished the 4 groups of the absorption gas cleaning processes.
1. The first group includes the processes, which are based mainly on the chemical interaction of the acidic components (mono-, di-, triethanolamine, di-isopropanolamine, diglycolamine, or the alkaline salts of the amino acids, carbonic acid, phosphoric acid, etc.) with the absorbent. The apparatuses, in which the processes of this group are implemented, are compact, may be used in the wide range of the loads and pressures; the main drawback is the relatively low absorption capacity of the absorbent.
2. The second group includes the processes, which involve the physical absorbers, such as the methylpyrrolidone, propylene carbonate, tributyl phosphate, methanol, etc. The main advantage is the increase of the economic efficiency of the absorption gas cleaning together with the increase of the content of the acid components in the gas which is cleaned.
3. The third group includes the processes, where the absorption is carried out due to the dissolution and the chemical reactions. This group of the processes allows to perform the comprehensive cleaning of the gas.
4. The fourth group of the absorption gas cleaning is based on the oxidation of the absorbed H2S to the elemental sulfur (the absorbers are the sodium salt of the naphthoquinone sulfonic acid, the cobalt phthalocyanine, the iron hydroxide, etc.). The main advantage of the absorption gas cleaning in this way is the fine cleaning, and the drawback is the relatively low productivity.
The choice of the cleaning methods is determined by the composition of the gas. The processes of the first group are used for the processing of the gas with the small concentrations of the acidic components (up to 5% by the volume) in the absence of the COS and CS2. The physical solvents are used for the very high concentrations of the acidic components. The sulphonol process is expedient for the low content of the heavy hydrocarbons (C5 about 1%, by the volume) and the high content (over 5%) of the acid components, as well as in the absence of the aromatic hydrocarbons in the gas.
The oxidation processes are used for the low productivity by the sulfur, the low H2S content, and the high SO2/H2S ratio (more than 10% by the volume) in the feed gas. The multi-stage processes are used sometimes in order to improve the efficiency of the absorption gas cleaning, including the processing of the gas by the various absorbents, or by the same absorber with the varying rates of the regeneration.
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