Direct desulfurization of limestones under oxy-circulating fluidized bed combustion conditions

We compared the direct desulfurization behavior of four different domestic limestone samples (CaO fraction 40–55%, average particle size 37.5 μm) using a thermogravimetric analyzer (TGA) for experiments conducted under oxy-circulating fluidized bed (CFB) combustion conditions (temperature 600–850 °C, CO₂ 60–95%). In addition, morphological variations of the limestones were analyzed during indirect and direct desulfurization using a scanning electron microscope (SEM). The data derived from the TGA experiments were applied to a gas–solid reaction rate model, and reaction kinetics at different temperature and carbon dioxide (CO₂) ratios were analyzed; we suggested the most suitable kinetic models for direct desulfurization. The direct desulfurization reactions of limestones increased in rate with increasing temperature. The activation energy of 50–120 kJ/mol was calculated using various gas–solid reaction models. By measuring the Brunauer-Emmett-Teller (BET) specific surface areas of the limestone samples, we explained the differences in the final conversion rates of the limestone samples.