Attrition and morphological analysis of CaCO₃ corresponding to oxy-fuel circulating fluidized bed conditions

The specific surface area of CaCO₃ has always been an essential parameter for various oxy-fuel combustion processes and chemical looping processes. However, the circulating of bed material through the furnace, cyclone and loop-seal in an oxy-fuel circulating fluidized bed (CFB) reactor may trigger the particle size changes as a result of rapid collisions among particles and friction with the inner refractory wall. Rather than considering only the effect of initial particle size, it is significantly important to emphasize on the change in limestone particle size due to in-reactor attrition. In addition, the changes are further enhanced with calcination reaction that occurred under high-temperature conditions. Herein an investigative account of limestone in a lab-scale CFB process was presented by using two types of fluidizing media (Air, CO₂) to determine its attrition and morphological changes under simulated operating conditions for riser and loop-seal. A significant difference in attrition index was observed as calcination of limestone occurred at high temperature under air atmosphere which was not observed under CO₂ condition. With similar cross-sectional area observed for both the tested (CO₂ condition) and re-carbonated limestone, it was concluded that re-carbonation of calcined lime at high CO₂ concentration in the loop-seal resulted in a comparable abrasion resistance that further improved desulfurization performance by reducing the amount of ultra-fine particles generated from limestone.