Abstract
Previously we have reported that the presence of H_2S was indispensable for Hg^0 removal and the oxygen may play a very important role in the Hg^0 removal. Therefore, it was thought that iron oxide (Fe_2O_3) may react with H_2S to form FeS_x according to H_2S+Fe_2O_3→1/xFS_x+Fe_<2-1/x>O_2+H_2O (1), and some surface elemental sulfur (-S) species which may react with elemental mercury (Hg^0) to form HgS. Although the main purpose of this study is to develop a process for the removal of elemental Hg^0 using H_2S, it is also necessary to understand the reactions between the iron oxide sorbent with the other components of the fuel gas such as H_2S, CO, H_2, H_2O etc. We proposed that mercury removal unit should be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. Generally, COS produced during gasification of coal is converted to H_2S catalytically before entering the wet gas desulfurization unit, which is not effective for the absorption of COS. Therefore, if COS is produced during the removal of Hg^0 with H_2S in the presence of CO, this process cannot be put into practical use unless a COS converter is installed after the Hg^0 removal unit. In this study, the relation between sulfidation behavior, the mercury vapor capture performance of iron oxide, and catalytic formation of COS over sulfided iron oxide in the Hg^0 removal conditions was investigated.
