Selective H2S Removal

There are numerous processes in with the objective to remove H₂S to ppm levels while allowing as much CO₂ as possible to rejected into the treated gas.  Examples are tail gas treaters (TGTUs) and Acid Gas Enrichment units (AGEs) where a perfect system would capture all the H₂S and reject all the CO₂.  Using a specialty solvent (piperazine promoted MDEA for example) is not the only way to do this.

There are ways to reduce the H₂S loading of the lean solvent, permitting removal of additional H₂S in the absorber.  One is to use a stripping promoter such as a HSS or a small amount of mineral acid to force more H₂S out of the lean solvent near the bottom of the regenerator.  An alternative is using HISULF technology to elevate the H₂S loading in the rich solvent feeding the regenerator.  There is also a method for improving the selectivity in the absorber.  This is done by forcing a trayed absorber to operate in the spray regime, and alter the tray's mass transfer characteristics in favor of H₂S removal and CO₂ rejection.