Experimental Study On The Removal Of N₂O With Biomass Gas Reburing In A Coal-fired CFB

Circulating fluidized-bed (CFB) bed has developed rapidly these years in China due to its good fuel adaptability, high load regulation capability and high combustion efficiency, where high desulfurization efficiency using limestone can be achieved. However, emissions of another greenhouse gas (N2O) in CFB are higher than those in other combustion systems. While using CFB technique, appropriate technical measures should be applied to reduce N2O emissions. In CFB, biomass gas contains large amounts of CH4, H2, CO and CnHm and high temperature combustion of biomass gas is exothermic, which promote the thermal decomposition of N2O. Hence, based on CFB, agriculture and forestry waste can be reused and the amount of coal for burning can be decreased.In this work, CFB and a fixed bed biomass gasification system have been developed. In CFB, simulated biomass gas and gas from fixed bed biomass gasification system were mixed with pulverized coal for combustion experiment repectively. Results show that effective removal of N2O could be realized for the simulated biomass gas and gas from fixed bed biomass gasification system. While CO as a reburn gas passed into the furnace from different gas nozzle, the highest N2O removal rate (88%) could be achieved at C nozzle, where the ration of the height between C nozzle and air distribution plate and the diameter of reaction tube of CFB is 8.3. While simulated biomass gas passed into CFB from C nozzle, N2O removal rate increased with the increase of the amount of biomass gas; and when the heat ratio of biomass gas to caol in the furnace is 10.5%, the N2O removal rate reached 99%. Then, while real biomass gas from fixed bed biomass gasification system passed into CFB through different nozzle, biomass gas present to be effective for N2O removal and C nozzle showed the highest removal rate of 99%, which corresponded to the experimental results. Results of these experiments implied that C nozzle with its high ratio of height to diameter (8.3) is the best inlet for the CFB system. In addition, biomass gas is also efficient for NO removal and the highest removal rate can reach 55%.