Simultaneous calcination and sulfidation of calcium-based sorbents

This work analyzes the simultaneous calcination and sulfidation of a dolomite and a limestone during the H2S retention under calcining conditions. The experiments have been carried out in a thermogravimetric analyzer at 0.1 MPa and in a pressurized differential reactor at 1 MPa using different CO2 partial pressures. The H2S retention process depended on the relative rate of the reactions of calcination, sulfidation of calcined sorbents, and direct sulfidation. A model considering the simultaneous calcination- sulfidation of the sorbents was developed to predict the experimental H2S retention data at different temperatures and pressures. For reaction temperatures far away from the calcination temperature, the sulfidation took place on the full calcined sorbent. Lower temperatures produced a lower calcination rate and a delay in the sulfidation process. The strong decrease in the calcination rate observed at temperatures near the calcination equilibrium produced different behaviors depending on the type of Ca-based sorbent. In the dolomite, the sulfidation took place on the CaCO3 when the calcination rate was lower than the direct sulfidation rate, even working at calcining conditions. In the limestone, the simultaneous presence of CO2 and H2S in some cases produced an inhibition of the calcination and sulfidation reactions. The model used in this work allowed definition of the application limits (temperature, pressure, and gas concentration) of the different particle reaction models (direct sulfidation, sulfidation of calcined sorbents, or simultaneous calcination- sulfidation) to be used in the design of desulfurization reactors.