Transformation and Migration of Mercury during Chemical-Looping Gasification of Coal

Transformation and migration of mercury during coal chemical-looping gasification (CLG) of lignite were studied in a batch-fluidized bed with magnetic CuFe2O4 as the oxygen carrier. The results showed that mercury distribution in CLG was similar to that in conventional coal gasification. Compared to conventional coal gasification, the CuFe2O4 oxygen carrier promoted transformation of Hg(g) to particle-bound mercury (Hg-P) and elemental mercury (Hg-0) to gaseous oxidized mercury (Hg2+). X-ray photoelectron spectroscopy results indicated the CuFe2O4 oxygen carrier can promote the Hg(g) transformation into Hg-P because of the adsorption and oxidation of mercury on their surface. Thermodynamic calculations showed that the oxygen carrier can affect the concentration of oxidizing gases (e.g., Cl-2, SO2, or NO2); this indirectly affected the transformation of Hg-0 to Hg2+. In addition, 10 reducing-oxidizing cycles were investigated, and the reduced CuFe2O4 oxygen carriers were regenerated in an air reactor. The ability of the CuFe2O4 oxygen carrier to retain mercury increased slightly after 10 regeneration cycles.