Study On Collaborative Optimization Of Unburned Carbon And NO_x Emission Of Coal Blends Combustion

Application of coal blends has becoming increasingly common in pulverized fuel power plant of our country, for blending different types of coal is a n effective mean for power plant to extend the range of acceptable coals. However, un-rational utilization of coal blends may cause low combustion efficiency, the excess emission of pollutants et al. This paper study on unburned carbon and NOx emissions characteristics of different blending methods, through numerical simulation, theory analysis, and test validation means, to obtain optimization strategy of unburned carbon and NOx emission in the process of coal blends combustion.In this paper, 2 pilot scale furnaces were designed for coal blends combustion study. Results showed that:(1) With regard to unburned carbon, utilization of in- furnace blending method, optimizing the air distribution mode, prolonging residence time of low volatile coal, all of these means above can improve the performance of unburned carbon;(2) With regard to NOx, high volatile coal can release a large amount of HCN during devolatilization process, coupled with the reducing atmosphere, can lead NOx reduction. The field test also showed that the results of numerical simulation can predict the trend in furnace effectively.Study of coal blends combustion were also carried out on a 660 MW tangentially coal-fired power plant boiler. Results showed that:(1) With regard to unburned carbon, combined influence of various factor, such as coal blending method, air distribution mode(regional oxygen supply), residence time et al, all of these can influence the unburned carbon level of coal blends. It also found that in the process of coal blends combustion in this power plant boiler, the oxygen supply to low volatile coal with a low combustibility during its combustion process in furnace play the most significant influence on unburned carbon of coal blends.(2) With regard to NOx, the low NOx emissions performance are often occur in those in- furnace blending method cases which injecting high volatile coal at downstream(upper-stage burner) of entire flow field inside the boiler. Considering all the optimization information above, we found that the in-furnace blending method case with reasonable combustion condition setting, compared with out- furnace blending methods, can reduce by 34% in the carbon content of fly ash, while reduce by 11% NOx emissions at the outlet, namely collaborative optimization of unburned carbon and NOx emission. Field test at this boiler demonstrate the reliability of the conclusions conclude from numerical simulation study in this paper, it can provide theoretical guidance for practical industrial applications.