Desulfurization Characteristics of Carbide Slag during Circulating Fluidized Bed Coal Combustion

At low loads, the desulfurization efficiency of circulatingfluidizedbed (CFB) boilers tends to decrease due to the deviation of low bedtemperature from the optimal temperature required for limestone desulfurization.However, carbide slag, a waste product rich in Ca-(OH)(2) andpossessing a low decomposition temperature, can be an economicallyviable alternative to limestone. In this study, the desulfurizationcharacteristics during coal combustion with carbide slag additionwere studied both in a fixed-bed reactor and a 30 kW CFB reactor.The effect of different reaction conditions on the desulfurizationperformance was evaluated. Results showed that the addition of carbideslag decreased SO2 emission effectively. A higher oxygencontent prompted the improvement of the desulfurization efficiency.The carbide slag showed the highest desulfurization efficiency atabout 800 degrees C. The desulfurization performance deteriorated whenthe temperature was beyond 800 degrees C. To explain this phenomenon,the micromorphology of carbide slag raw particle, calcined particle,and sulfated particle was observed by scanning electron microscopy.More holes formed on the surface of the particles after calcination.Besides, the outer surface of the holes formed more crystal grainswith the increasing temperature. CaSO4 products coveredthe outer surface of the crystal grains after desulfurization. Thecrystal grain gaps on the surface of carbide slag were easily blockedat high temperatures, which resulted in the low desulfurization efficiency.