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 OxyCFBC has the advantages of fuel flexibility, in-situ desulfurization and NOx emission reduction. In this study, domestic limestone samples with a particle size range of 0-1 mm (0-75 mu m, 75-106 mu m, 106-212 mu m, 212-300 mu m and 500-1000 mu m) 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.