SO_2 emission characteristics of circulating fluidized bed boiler co-firing coal and petroleum coke
The combustion characteristics of a 410 t·h-1 circulating fluidized bed (CFB) boiler burning the fuels of bituminous coal (BC), 70% BC+30% petroleum coke (PC) and 50% anthracite (AN) +50% PC were studied.The effects of operation parameters, including bed temperature,molar ratio of Ca to S, excess air coefficient, fly ash recirculation rate and limestone microstructure on SO2 emission were investigated.Test results indicated that all the three kinds of fuels burned adequately in the boiler, and the bed temperature distribution was uniform.For different fuels, SO2 emission was correspondingly related to fuel sulfur content with the same operation parameters.With increasing bed temperature, SO2 concentration in the flue gas reduced first and then increased.There was an optimal desulfurization temperature.For burning BC only or 70% BC +30% PC, the optimal desulfurization temperature was about 850℃, while it was between 850-870℃ for burning 50% AN +50% PC, because of the different sulfur contents in the fuel.The SO2 concentration decreased with increasing Ca/S ratio, excess air coefficient and fly ash recirculation rate.The results also showed that the microstructures of limestones including specific surface area and specific pore volume had distinct impact on their SO2 retention.Larger specific surface area and higher specific pore volume could enhance their SO2 capture activities to a certain extent.The optimal temperatures, Ca/S ratios and excess air coefficients for different fuels were recommended for industrial application.