US Patent 7811544 Sulfur recovery process

A method for recovering sulfur from a sulfur-bearing process gas stream in which a process gas stream comprising H2S and/or SO2 is contacted with a lean mixture of a lean UCSRP solution and a catalyst for promotion of a reaction between H2S and SO2 in anon-UCSRP vessel at a temperature below which H2S and SO2 react, whereby at least a portion of the H2S and/or SO2 is absorbed by the lean UCSRP solution, forming a rich mixture of a rich UCSRP solution and the catalyst. The rich mixture is introduced into a UCSRP vessel and heated to a reaction temperature greater than or equal to a melting temperature of sulfur, forming elemental sulfur and H2O.