| The pore structure and reactivity changes occurring during the sulfidation of metal oxides sorbents used for the removal of {dollar}Hsb2S{dollar} from coal gas at high temperatures were examined. Two commercially available zinc oxides and calcines derived from three limestone precursors were reacted in a thermogravimetric apparatus using relatively broad ranges of particle size, temperature, and {dollar}Hsb2S{dollar} concentration. The ZnO samples were regenerated and subsequently sulfided to investigate the desulfurization performance of the regenerated solids. The pore structure of fresh, heat-treated, sulfided, and regenerated sorbents was analyzed by mercury porosimetry and nitrogen adsorption using samples prepared in a fluidized- and fixed-bed reactor under conditions similar to those used in the TGA system. Detailed mathematical models for reaction, diffusion, and structure evolution in chemically reacting media were used to analyze the experimental data, and very good agreement between theory and experiment was observed. Differences in the performance of sorbents of the same metal oxide were explained on the basis of differences in their pore structure (pore size distribution and pore structure connectivity). Desulfurization experiments were also carried out in a fixed-bed reactor using ZnO sorbents under various reaction conditions. It was found that the sorbent utilization in the bed is strongly influenced by the structure of the solid, the size of the particles, and the residence of the reactive gas in the reactor. The predictions of a mathematical model for fixed-bed desulfurizations were in excellent agreement with the experimental data, even though no adjustable parameters were used in the application of the model. |
