Abstract: A process for the recovery of sulfur from an acid gas stream is disclosed. The process includes a Claus sulfur recovery step in combination with a direct reduction step and a biological sulfur recovery step to provide a sweet gas stream having a very low concentration of hydrogen sulfide and sulfur dioxide. The process includes reacting an acid gas steam with oxygen under such oxidation conditions to yield a combustion gas comprising hydrogen sulfide and sulfur dioxide. The combustion gas is reacted under Claus reaction conditions to yield a reaction gas comprising sulfur. Sulfur is recovered from the reaction gas to yield a Claus tail gas comprising hydrogen sulfide and sulfur dioxide. The Claus tail gas is reacted under direct reduction reaction conditions to yield a direct reduction gas comprising sulfur. Sulfur is recovered from the direct reduction reaction gas to yield a tail gas comprising a concentration of hydrogen sulfide.

Abstract: A process for the recovery of sulfur from an acid gas stream is disclosed. The process includes a Claus sulfur recovery step in combination with a biological sulfur recovery step to provide a sweet gas stream having very low concentrations of hydrogen sulfide and sulfur dioxide. The process includes reacting an acid gas steam with oxygen under such oxidation conditions to yield a combustion gas comprising hydrogen sulfide and sulfur dioxide so as to have a ratio of hydrogen sulfide to sulfur dioxide exceeding 2:1, preferably from 2:1 to 30:1. The combustion gas is reacted under Claus reaction conditions to yield a reaction gas comprising sulfur. Sulfur is recovered from the reaction gas to yield a tail gas comprising a concentration of hydrogen sulfide and less than 1000 ppm sulfur dioxide. The tail gas is contacted with a lean absorbent thereby remove from the tail gas a portion of the hydrogen sulfide contained therein and to yield a sweet gas and a rich solvent comprising dissolved hydrogen sulfide.