Kinetics of CaO-H{sub 2}S reaction at high temperature under pressurized conditions

Kinetic study of H{sub 2} absorption with calcined limestone was performed under pressurized conditions (up to 20 atm) by means of a self-made pressurized thermobalance mainly consisting of a quartz spring balance and a pressure vessel. The adsorption of 200--4,200 ppm (mainly 1000 ppm) of H{sub 2}S was carried out with calcined limestone (710--1,000 {micro}m) at 1,023--1,223 K and 1--20 atm. The effect of pressure on the kinetics of H{sub 2}S adsorption was investigated. The film resistance of mass transfer was negligible when the total gas velocity was 0.53 m/s (10 SLM). The rate of H{sub 2}S adsorption decreased with increasing total pressure (H{sub 2}S pressure was kept at 0.004 atm). The level of conversion of CaO to CaS was 87% at 1 atm and 38% at 20 atm after 5 h of reaction. The used limestone samples were characterized with SEM and EDAX. Based on the SEM and EDAX observations on the cross section of limestone particles, a CaS layer was clearly developed from the surface to the interior in the progress of sulfidation in all cases. Although the authors applied the conventional shrinking-core models with different rate-determining steps for analyzing the H{sub 2}S adsorption kinetics, these SCM modelsmore » failed to explain the sulfidation behavior in the early stage of sulfidation at higher pressures. Thus, they developed empirical equations to express the sulfidation behavior in the wide ranges of the solid conversion and the total pressure. Equations developed in this study can predict the sulfidation kinetics at higher pressure well.« less