Process for the high recovery efficiency of sulfur from an acid gas stream

A sulfur recovery process, comprising:

• passing an acid gas stream comprising hydrogen sulfide to a combustion zone defined by combustion means and providing for partially oxidizing the hydrogen sulfide in said acid gas stream with oxygen to form sulfur dioxide thereby providing a combustion gas stream comprising sulfur dioxide and hydrogen sulfide;
• controlling the amount of hydrogen sulfide oxidized in said combustion zone such that less than ⅓ (one third) of the hydrogen sulfide in said acid gas stream is oxidized to sulfur dioxide;
• passing said combustion gas stream to a Claus reaction zone operated under Claus conversion conditions to yield a reaction gas comprising sulfur;
• recovering sulfur from said reaction gas to yield a Claus tail gas comprising a concentration of hydrogen sulfide;
• passing said Claus tail gas to an absorption zone defined by absorber means for contacting said Claus tail gas with a lean caustic solution whereby hydrogen sulfide is recovered from said Claus tail gas and from which is yielded a sweet tail gas comprising less than 100 ppmv H2S and a rich caustic solution, wherein said lean caustic solution 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 caustic solution and which is selected from the genera of Beggiatoa, Thiothrix and Thiobacillus, and wherein said sweet tail gas comprises less than 100 ppmv hydrogen sulfide;
• and
• passing said rich caustic solution to a bioreaction zone defined by bioreactor means for the biological oxidation of the dissolved sulfide in said rich caustic solution by use of said sulfur bacteria to elemental sulfur, yielding from said bioreaction zone said lean caustic solution;
• passing a portion of said lean caustic solution to sulfur recovery means for recovering sulfur from a portion of said lean caustic solution and to yield a sulfur reduced lean caustic solution and sulfur;
• and
• returning said sulfur reduced lean caustic solution to said bioreaction zone.

A sulfur recovery process, comprising:

• reacting an acid gas steam with oxygen under such oxidation conditions to yield a combustion gas comprising relative amounts of hydrogen sulfide and sulfur dioxide so as to have a ratio of hydrogen sulfide to sulfur dioxide exceeding 2:1 but is less than 6:1;
• reacting said combustion gas under Claus reaction conditions to yield a reaction gas comprising sulfur;
• recovering sulfur from said reaction gas to yield a Claus tail gas comprising a concentration of hydrogen sulfide and less than 1000 ppmv sulfur dioxide;
• contacting said Claus tail gas with a lean absorbent thereby removing from said Claus tail gas a portion of the hydrogen sulfide contained therein and to yield a sweet gas, comprising less than 100 ppmv H2S, and a rich solvent comprising dissolved hydrogen sulfide;
• and
• biologically oxidizing the dissolved hydrogen sulfide of said rich solvent to elemental sulfur by contacting said rich solvent with a sulfur bacteria capable of biologically oxidizing the dissolved hydrogen sulfide of said rich solvent and which is selected from the genera of Beggiatoa, Thiothrix and Thiobacillus under biological oxidation conditions to yield a lean solvent containing said elemental sulfur, recovering said elemental sulfur from said lean solvent by use of sulfur recovery means for recovering sulfur from said lean solvent and to yield a sulfur product and a sulfur reduced lean solvent;
• and
• returning said sulfur reduced lean solvent to the bioreactor.