Advanced sulfur control concepts

Regenerable metal oxide sorbents, such as zinc titanate, are being developed to efficiently remove hydrogen sulfide (H{sub 2}S) from coal gas in advanced power systems. Dilute air regeneration of the sorbents produces a tailgas containing a few percent sulfur dioxide (SO{sub 2}). Catalytic reduction of the SO{sub 2} to elemental sulfur with a coal gas slipstream using the Direct Sulfur Recovery Process (DSRP) is a leading first-generation technology. Currently the DSRP is undergoing field testing at gasifier sites. The objective of this study is to develop second-generation processes that produce elemental sulfur without coal gas or with limited use. Novel approaches that were evaluated to produce elemental sulfur from sulfided sorbents include (1) sulfur dioxide (SO{sub 2}) regeneration, (2) substoichiometric (partial) oxidation, (3) steam regeneration followed by H{sub 2}S oxidation, and (4) steam-air regeneration. Preliminary assessment of these approaches indicated that developing SO{sub 2} regeneration faced the fewest technical and economic problems among the four process options. Elemental sulfur is the only likely product of SO{sub 2} regeneration and the SO{sub 2} required for the regeneration can be obtained by burning a portion of the sulfur produced. Experimental efforts have thus been concentrated on SO{sub 2}-based regeneration processes. Results from laboratory investigations are presented and discussed