Study On Oxy-fuel Combustion Characteristics And Pollutant Emission Of Coal In Circulating Fluidized Bed

With fast development of global industrialization, the earth becomes warmer and warmer due to the excessive emission of greenhouse gas CO2, leading to serious environmental crisis. Oxy-fuel combustion technology is advanced, because zero CO2emission can be achieved. Compared with pulverized coal combustion, there are more advantages for oxy-fuel combustion in circulating fluidized beds. However, the research on oxy-fuel combustion in circulating fluidized beds (CFB) starts late, thus many items are still needed to be researched. In this dissertation, oxy-fuel combustion characteristics and pollutant emission of coal in circulating fluidized beds are investigated.Experiments were carried out in a23kW CFB combustion test rig with the overall oxygen concentration of about33%. The results show that coal could be combusted stably in the CFB with the overall oxygen concentration of33%and the local oxygen concentration of57.8%. Optimizaing the air distribution can help to reduce the emission of N2O and NO and improve the combustion efficiency. The combustion efficiency of Longkou coal could reach98.67%.0.15MW CFB combustion test system was constructed. Combustion could keep stable for a long time with the overall oxygen concentration of50%. The ignition, operation and shutdowns process of CFB was explored at50%oxygen concentration and banking fire could not be operated in the system. The system could only be started at oxy-fuel atmosphere.The influence of air distribution on combustion characteristics and pollutant emission was studied at50%oxygen concentration atmosphere. It was revealed that when the oxygen concentration of primary air was between45%and55%and the flow ratio of primary air ranged from50%to100%, the coal from Shenmu, Shigouyi and Datong could all be stably combusted. With the increase in the oxygen concentration of primary air, the combustion efficiency is improved, which could reach96.24%for Shenmu coal. Optimizaing the air distribution can effectively reduce the emission of CO, N2O and NO. However, it has no obvious effect on SO2emission.In the0.15MW CFB combustion test system, the effects of particle size and oxygen concentration on coal combustion were investigated, and the conversion rates of N and S were also studied. The results indicate that the impact of particle size distribution and thermal fragmentation of coal on combustion was amplified at high oxygen concentration atmosphere. The size of the Datong coal particles should be increased in order to keep stable operation of the CFB. Compared with combustion at the air atmosphere, both the conversion rates of N to N2O and to NO decrease19%-82%and32%-68%at50%overall oxygen concentration. However, increasing the overall oxygen concentration has no obvious effect on the conversion rate of S to SO2.