Direct sulfidation of half-calcined dolomite under pressurized conditions

There are pressurized gasification systems in which the desulfurization process is carried out with Ca-based sorbents at noncalcining conditions. At these conditions, the H2S reacts directly with CaCO3. The direct sulfidation reaction of a half calcined dolomite was analyzed under atmospheric and pressurized conditions (up to 1.0 MPa), temperatures between 923 and 1123 K, and with sorbent particle sizes between 0.4 and 2.0 mm. The half-calcined dolomite reacts quickly up to high conversions (> 85%), and it is an effective sorbent at noncalcining conditions. The sulfidation experiments were performed in an atmospheric thermogravimetric analyzer and a pressurized differential reactor. The effects of the reaction pressure and temperature, sorbent particle size, and H2S concentration were analyzed. The changing grain size model was used to predict the experimental results and to determine the kinetic parameters of the direct sulfidation reaction. The resistances to the global reaction considered in the model were the pore diffusion, diffusion through product layer, and chemical reaction. A. reaction order on H2S of 1 was obtained. The values of the activation energies were 267 kJ mol(-1) for the chemical reaction rate constant, k(S), and 25 kJ mol(-1) for the product layer diffusion coefficient, D-S. The sulfidation rate of the sorbents increased with total pressure, but less than expected. To predict the experimental data, an effective gas diffusivity in the pores and an effective diffusivity in the product layer varying with total pressure was used. In this way, good agreement between measured and predicted conversion-time curves was observed for any total pressure, temperature, particle size, and H2S concentration analyzed.