Acid gas removal system

A bleed from the scmbbing system is sent to a sour slurry stripper. The water is then clarified and can be recycled to minimize the volume of effluent to be biotreated and discharged or evaporated. The acid gas from the acid gas removal system and from the sour slurry stripper is fed to a Claus plant, where salable elemental sulfur (qv) is produced. For maximum sulfur recovery and minimal sulfur emissions, the Shell Claus off-gas treating process (SCOT) is used. 

The physical solvent-based acid-gas removal systems do not rely upon the acidic properties of the acid gas. Rather, the polar acid gases have a much greater solubility in many oils and solvents, compared with fuel gas species. 

In many synfuel refinery flowsheets, the acid-gas partial pressure is borderline between obvious preferance for hot carbonate and physical solvent-based acid-gas removal systems. In these... 

Some acid-gas removal systems include mixed solvents - usually an amine in a physical solvent. This approach modifies the relative characteristics of the physical solvent by the amine and provides many of the advantages of each. Generally, only a moderate degree of selectivity can be achieved, but the total system appears to be improved. Typical in this area are the Sulfinol and Amisol processes. 

The direct-oxidation processes for recovery of sulfur from raw gases are also applicable on acid-gas streams. Usually, a direct oxidation process would be applied when a nonselective acid-gas removal system had been employed and the sulfur concentration in the acid gas is relatively low. At higher H2S concentrations, as achieved through selective acid-gas removal, the conventional Claus process appears to be more economic. 

The CALCOR process is similar to a conventional steam methane reformer with an amine acid gas removal system, except that the CO2 from the amine system is recycled to the reformer furnace. The reformer operates at a very low pressure to reduce reforming severity. The synthesis gas from the CO2 removal system is just above atmospheric pressure. It is saturated with water and residual CO2 and must be compressed before entering downstream separation equipment. The process features a very low methane slip below 500 ppm in the synthesis gas [11]. 

After the raw syngas is cooled it is routed to a high temperature shift reactor, if necessary, to make the proper Hj/CO ratio. It then enters an acid gas removal system to remove H2S and COj. Following the removal of acid gases, the syngas is delivered to the battery limits of the plant for downstream use. 

The effective design of optimal acid gas removal systems is a sophisticated field. The details of a well-designed acid gas removal system for any specific situation are beyond the scope appropriate for this overview. 

Tail-gas treating processes are generally unnecessary in coal gasification plants that require less than 95% overall sulfur recovery/reduction (26). A well-designed acid gas removal system can easily and effectively remove most of the sulfur from coal gas, and can readily attain this standard with a Claus plant. 

From an economic perspective, opportunity fuels also must be considered with particular attention to power plant or fuel user selection. Those utilities or process industries seeking to use petroleum coke, for example, must select boilers equipped with acid gas removal systems. Such systems may be scrubbers alternatively they may be fluidized bed boiler systems where limestone is added for sulfur capture. 

The basic equipment arrangement for an amine acid gas removal system is shown in Figure 3-3. It consists of an absorber in which cooled lean solvent flows downward in contact with the upwardly flowing gas to be treated. Before leaving the absorber, the purified gas may be washed with water to recover any vaporized MEA. The rich solvent at the bottom of the absorber is in contact with the entering gas stream, thus provid-... 

A different scheme is offered by C. F. Braun and Co., which takes the effluent vapor from the acid gas removal system and, after drying and cooling, feeds it to the depropanizer [15]. The overhead from this column is compressed to around 540 psia, hydrogenated to remove the dienes, and chilled to separate a hydrogen stream from the condensed hydrocarbons. Liquid condensates contain methane, plus the C-2 and C-3 hydrocarbons present in the feed to the depropanizer. These liquids are fed to the demethanizer, which strips the methane overhead. The demethanizer bottoms serve as feed to the deethanizer. The overhead from that column goes to the C-2 splitter, while the bottoms is the feed to the 03 splitter. The bottoms liquid from the original depropanizer is sent to the debutanizer for separation of the C-4 hydrocarbons from the aromatic gasoline fraction. 

More recent pilot plant data are available from the Coal Gasification/Gas Cleaning Test Facility at North Carolina State University (Ferrell et al., 1987). The acid gas removal system includes a gas absorption column, one or more flash tanks for intermediate pressure reduction, and a packed stripping column operated with a reboiler. Both of the columns are packed with 0.25-in. ceramic Intalox saddles. The project included the development of a system model and simulation program covering absorption, flashing, and stripping. 

Yosemite, 2012. SI 412C Wet Scrubber Plan Review, Lesson 9 Flue Gas Desulfurization (Acid Gas Removal) Systems. Retrieved from http //yosemite.epa.gov/oaqps/eogtrain. nsf/b81bacb527b016d785256e4a004c0393/d4ec501f07cOe03a85256b6c006caf64/ FlLE/ si412c lesson9.pdf (accessed 5.10.12). 

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