Patent ID: 7351392

Claim:
A sulfur recovery process, comprising: charging an acid gas stream comprising hydrogen sulfide as a feed to a sulfur recovery system operated so as to yield a first sulfur product and a Claus tail gas comprising hydrogen sulfide and less than about 1000 ppmv sulfur dioxide; charging said Claus tail gas to a biological gas desulfurization system comprising absorber means for contacting said Claus tail gas with a lean solvent to yield a sweet gas and a rich solvent; bioreactor means for biologically oxidizing the dissolved hydrogen sulfide contained in said rich solvent and to yield a lean solvent containing sulfur; and sulfur recovery means for recovering sulfur from a portion of said lean solvent and to yield a second sulfur product and a sulfur reduced lean solvent and returning said sulfur reduced lean solvent to said bioreactor means; and operating said biological gas desulfurization system, wherein said lean solvent comprises an alkaline solution having a pH in the range of from 7.5 to 12 and sulfur bacteria capable of biologically oxidizing the dissolved hydrogen sulfide contained in said rich solvent and which is selected from the genera of Beggiatoa, Thiothrix and Thiobacillus to yield a second sulfur product and a sweet gas comprising less than 100 ppmv hydrogen sulfide.