An example of a process using O2 to oxidize H2S is the Stretford® process, which is licensed by the British Gas Corporation. In this process the gas stream is washed with an aqueous solution of sodium carbonate, sodium vanadate, and anthraquinone disulfonic acid. Figure 7-9 shows a simplified process diagram of the process.
Oxidized solution is delivered from the pumping tank to the top of the absorber tower, where it contacts the gas stream in a counter-current flow. The reduced solution flows from the contactor to the solution flash drum. Hydrocarbon gases that have been dissolved in the solution are flashed and the solution flows to the base of the oxidizer vessel. Air is blown into the oxidizer, and the solution, now re-oxidized, flows to the pumping tank.
The sulfur is carried to the top of the oxidizer by a froth created by the aeration of the solution and passes into the thickener. The function of the thickener is to increase the weight percent of sulfur, which is pumped to one of the alternate sulfur recovery methods.