Abstract: A method for increasing the hydrogen sulfide concentration in a gas stream, particularly a stream to be fed to a Claus unit, is disclosed. The method is characterized by the measurement of the flow of the gas stream to an absorption system, and in response to such measurement, separation of a portion of the acid gas leaving the regenerator of the system, and selective absorption of the H.sub.2 S in the portion, with passage of the loaded absorbent to the regenerator.

Abstract: In a process for recovery of sulfur by the Claus process from hydrogen sulfide-containing gases, in which process residual sulfur compounds in the Claus off-gas are reduced to hydrogen sulfide which is selectively absorbed, recovered and recycled to the Claus reaction, the process is adapted for conversion of feed gas which is high in CO.sub.2 and which also contains significant amounts of COS and/or organic sulfur compounds by having such fresh feed gas bypass the Claus reactor and combining it with the Claus off gas ahead of the reduction step.