Effect of particle size on in-situ desulfurization for oxy-fuel CFBC

Oxy-fuel circulating fluidized bed combustion (Oxy-CFBC) has been widely recognized as an economically promising way to capture carbon dioxide by injecting pure O₂ and recycling CO₂ from the flue gas because Oxy-CFBC has the advantages of fuel flexibility, in-situ desulfurization and NO_x emission reduction. In this study, domestic limestone samples with a particle size range of 0–1 mm (0–75 μm, 75–106 μm, 106–212 μm, 212–300 μm and 500–1000 μm) were reacted in a thermogravimetric analyzer (TGA) under 60% CO₂/40% O₂ and 80% CO₂/20% O₂ at 1073 K and 1123 K for a direct desulfurization reaction. The surface and cross-section of limestone and CaSO₄ samples with different conversion ratios were analyzed using a field emission scanning electron microscope (FE-SEM) and an energy dispersive spectrometry (EDS). FE-SEM images and EDS analysis of limestone and CaSO₄ showed that direct desulfurization reaction starts from surface and progresses to center of particles, and the layer of CaSO₄ expands into the whole particle. Since the experimental conditions of all particles were the same, the difference in CaSO₄ conversion ratio by particle size confirmed through the TGA results depends only on the specific surface area. Also, the CaSO₄ layer was formed at a uniform thickness regardless of the particle size.