SULFATION OF HIGH-PURITY LIMESTONES UNDER SIMULATED PFBC CONDITIONS

The direct sulfation of three high purity limestones, all having more than 95% CaCO3 but differing in petrographic texture, was studied in a thermogravimetric analyzer under simulated PFBC (Pressurized Fluidize d-Bed Combustion) conditions, that is, in the presence of enough CO2 t o prevent decomposition of CaCO3. Experiments were carried out over a wide range of particle size (53-350 mum) at two temperatures (750 and 850-degrees-C), and two concentrations (1500 and 6000 mL/m3 (ppmv) SO2 ). The particle size and temperature had a strong influence on the var iation of the conversion with time. In contrast, the effect of concent ration was rather marginal over the whole duration of the process, and the analysis of the initial reaction rate data gave a reaction order of 0.4, with respect to SO2, for all solids. The measured reaction rat es were compared with those obtained in a past study for the sulfation of the calcines of the three solids under similar conditions. The ini tial rate of the calcine-SO2 reaction was found to be higher than that of the limestone-SO2 reaction, but since the former drops sharply as the pores at the external surface of the particles are filled with sol id product, higher conversions may be obtained in some cases during di rect sulfation for large reaction times.