Effect of pressure on the sulfidation of calcined calcium-based sorbents

The sulfidation process for two calcined limestones and a fully calcined dolomite was analyzed under pressurized conditions (up to 1.0 MPa), at temperatures of 723-1173 K, and with sorbent particle sizes of 0.25-2.0 mm. The sulfidation experiments were performed in a pressurized thermogravimetric analyzer and in a pressurized differential reactor. The effects of total pressure, temperature, sorbent particle size, and H2S Concentration were analyzed. The sulfidation rate of the sorbents increased with total pressure when the volume fraction of H2S was constant. However, the sulfidation rate decreased with total pressure when the partial pressure of H2S was constant. A reaction order on H2S of 1 was obtained at the different total pressures that were analyzed. In addition, the rate of H2S retention decreased as the sorbent particle size increased. The changing grain-size model, with the effective gas diffusivity in the pores and the effective diffusivity in the product layer varying with the total pressure, was used to obtain the kinetic parameters of the sulfidation reaction and to predict the experimental data. The values of the activation energies varied for the different calcium-based sorbents, from 29 kJ mol(-1) to 56 kJ mol(-1) for the chemical reaction rate constant (k(s)) and from 154 kJ mol(-1) to 217 kJ mol(-1) for the product layer diffusion coefficient (D-s). A good agreement between measured and predicted conversion versus time curves was observed for any total pressure, temperature, particle size, and H2S concentration analyzed.