Development of iron oxide sorbents for Hg~0 removal from coal derived fuel gas: Sulfidation characteristics of iron oxide sorbents and activity for COS formation during Hg~0 removal

摘要

The aim of this study is to develop a process for the removal of Hg~0 using H_2S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H_2S, CO, H_2, H_2O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg~0 removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe_2O_3/TiO_2) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 ℃ (designated as Fe_2O_3-110) and calcined at 300 and 550 ℃ (Fe_2O_3-300 and Fe_2O_3-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg~0 removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg~0 removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg~0 removal experiments over Fe_2O_3-110. However, in the cases of calcined iron oxides (Fe_2O_3-300, Fe_2O_3-550) and 1 wt% Fe_2O_3/TiO_2, formation of COS was not observed but the Hg~0 removal activity of 1 wt% Fe_2O_3/TiO_2 was high. Both FeS and FeS_2 were active for Hg~0 removal in coal derived fuel gas without forming any COS.