PROPOSAL FOR A REGENERATIVE HIGH-TEMPERATURE PROCESS FOR COAL-GAS CLEANUP WITH CALCINED LIMESTONE

This paper deals with a new regenerative, high-temperature process for coal gas desulfurization using calcined limestone (CaO) as a sorbent. The process includes three steps. First H2S reacts with CaO toward Ca S (sulfidation), which is then partly oxidized with SO2 in a second st ep to obtain CaSO4 and elemental sulfur. Finally, in a third step (reg eneration) the solid mixture of CaS and CaSO4 remaining after the oxid ation step is decomposed to produce CaO and SO2 which are both reused in the first and second steps, respectively. The proposed process thus yields elemental sulfur as the final product. Several sulfidation-oxi dation-regeneration cycles (up to nine) were carried out in a thermogr avimetric analyzer (TGA) using various calcined limestones. The result s are promising, showing a constant absorption capacity of 30-50% from two cycles on. On the basis of kinetic experiments and thermodynamic considerations, the optimum temperatures were determined at 815-845 de grees C for the desulfurization of Shell coal applicability of calcine d limestone for nonregenerative HCl removal was examined. The reaction between CaO and HCl was found to proceed fast enough to enable practi cal application. The limestone utilization was found to vary from 8% a t 200 degrees C to 80% at 600 degrees C.