Â Performance and capacity of sulfur recovery unit (SRU) are greatly affected by the H2S:CO2 ratio of the acid gas stream. The acid gases in Iran contain around 35 mol% H2S and 60 mol% CO2. This low concentration of H2S calls for more complex sulfur plant, larger equipments, and higher costs. Acid gas enrichment processes (AGE) is run to upgrade low quality acid gas collected from gas treating units in to higher quality Claus plant feed stream. Using specially formulated solvents or modifications of the existing gas treating units are the most popular approaches for efficient acid gas enrichment. Â Three different enrichment schemes are considered and simulated for Khangiran refinery acid gas stream. The results are then compared with each others to select the optimal AGE scheme, which can maximize the H2S content of SRU feed stream while minimizes H2S emission to atmosphere. In the first scheme, part of the acid gas leaving the GTU regenerator overhead is recycled back to the main contactor. In the other two, a separate enrichment tower is utilized between the amine flash drum and regenerator. In the second scheme, the enrichment tower pressure is set between regenerator pressure and ambient pressure, while in the third scheme, the enrichment tower pressure is fixed between amine flash drum pressure and regenerator pressure. The simulation results revealed that the SRU feed stream can be significantly enriched from its original value of 33.5 mol% H2S to about 70 mol%, by applying to the third scheme.