Sulfur transfers from pyrolysis and gasification of direct liquefaction residue of Shenhua coal

The sulfur transformation during pyrolysis and gasification of Shenhua direct liquefaction residue was studied and the release of H2S and COS during the process was examined. For comparison, the sulfur transfer of Shenhua coal during pyrolysis and that of pyrolyzed char during gasification were also studied. The residue was pyrolyzed at 10 °C /min to 950 °C. During pyrolysis about 33.6% of sulfur was removed from the residue, among which 32.1% was formed H2S in gas and 1.5% was transferred into tar, 66.4% of the sulfur was remained in residue char. Compared with coal, the residue has generated more H2S due to presence of Fe1−xS which was enriched in residue during liquefaction process. There is a few COS produced at 400–500 °C during pyrolysis of coal, but it was not detected form pyrolysis of the residue. During CO2 gasification, compared with pyrolysis and steam gasification, there are more COS and less H2S formation, because CO could react with sulfide to form COS. During steam gasification only H2S was produced and no COS detected, because H2 has stronger reducibility to form H2S than CO. After steam gasification no sulfur was detected in the gasification residue. The XRD patterns show after steam gasification, only Fe3O4 is remained in the gasification residue. This indicates that the catalyst added during the liquefaction of coal completely reacted with steam, resulting in the formation of H2 and Fe3O4.