THE DIRECT SULFUR RECOVERY PROCESS

The Research Triangle Institute under contract to the U.S. Department of Energy, Morgantown Energy Technology Center, is developing the Direct Sulfur Recovery Process (DSRP) for converting either reduced or oxidized sulfur gases directly to elemental sulfur. Laboratory tests were conducted to evaluate the effects of stoichiometry, pressure, temperature, space velocity and steam content. Pressure was found to be the most important variable. Increasing pressure from 1.5 atm to 20 atm quadrupled the sulfur recovery at equivalent space velocity. Sulfur recoveries from dilute SO2 streams were greater than 96% in tests simulating the first stage of reaction. In the first stage of reaction, SO2 is directly reduced to elemental sulfur by coal gas or other reducing gases at high temperature and high pressure. Under second-stage reaction conditions, recoveries ranged from 80 to 98% depending on operating conditions. Combined with a first-stage conversion of 96%, this translates into overall conversions of 99.2 to 99.9%. Preliminary economic comparisons with conventional processes that could be used for treating dilute SO2 tail gases showed a decisive cost advantage for the new catalytic process. The effectiveness of the high-pressure, high-temperature DSRP on H2S containing gases has also been demonstrated. Direct conversions of H2S to elemental sulfur ranged to 98% in a single stage of reaction using near stoichiometric amounts of air or oxygen. Bench-scale development is ongoing to investigate a variety of reactor types and configurations.