KINETICS OF THE REACTIONS OF A ZINC FERRITE SORBENT IN HIGH-TEMPERATURE COAL-GAS DESULFURIZATION

The reduction, sulfidation, and regeneration kinetics of zinc ferrite extrudates were studied using a thermogravimetric reactor as a function of temperature, pressure, gas composition, and sorbent radius. Reduction causes the zinc ferrite to separate into the constituent oxides, and Fe2O3 is reduced to Fe3O4. Further reduction of FeO or even Fe, which may occur in highly reducing conditions, should be avoided. Sulfidation kinetics are a relatively strong function of H2S concentration, reaction pressure, and sorbent radius but are almost independent of temperature in the 500-700-degrees-C range. Regeneration kinetics are a strong function of temperature, pressure, and oxygen concentration. Zinc sulfate, which is formed during regeneration at certain conditions, may be decomposed by heating the sorbent to sufficiently high temperature. Sulfidation results are consistent with the unreacted core model in which the global kinetics are controlled by transport resistances.