Combined calcination, sintering and sulfation model for CaCO3-SO2 reaction

A mathematical model developed accounts for the multiple rate processes inv olved in the reaction of solid CaCO3 or Ca(OH)(2) with SO2 at high temperat ures in the combustion environment. The model, based on the grain-subgrain concept, considers the concomitantly occurring calcination, sintering an su lfation reactions and their interactive effects on pore structure and react ion kinetics. It incorporates internal diffusion, reaction, and product lay er diffusion in simulating the calcination of the CaCO3 grain and subsequen t sintering and sulfation occurring on the CaO subgrains. It is the first s ulfation model to incorporate the true mechanism of diffusion through the s olid product phase: the solid-state ionic diffusion of Ca2+ and O2- ions in a coupled manner through the nonporous CaSO4 (Hsia et al., 1993, 1995). It s predictions are compared with the random pore model (Bhatia and Perlmutte r, 1981a) and the grain model (Szekely and Evans, 1971) using experimental CaO sulfation data from the literature as well as short-contact-time CaCO3 and Ca(OH)(2) sulfation data reported previously. Mahuli et al. (1997) disc ussed a high reactivity modified calcium carbonate synthesized by optimizin g the pore structural properties. This modified CaCO3 can convert 70-75% of sulfation within 0.5 s, which is substantially higher than any other sorbe nts reported for similar particle size and reaction conditions. The model i s used to pr edict the calcination and sulfation kinetics, as well as to si mulate the surface ar ea evolution of the modified CaCO3, which provides fu rther insights into its exceptional reactivity.