【作者】 王凯；

【导师】 王贲；

【作者基本信息】 华中科技大学 ， 动力工程， 2019， 硕士

【摘要】 生物质的燃烧过程能够实现具有生态意义的碳的零排放,是理想的替代煤炭等化石燃料的选择。在大型电站锅炉上进行生物质与煤粉的混燃是目前的研究热点之一。本文以一台670MW煤粉锅炉为研究对象,应用数值模拟计算的方法,研究了生物质及生物质气化气作为混合燃料耦合煤粉燃烧过程,考察了生物质燃料喷入位置、颗粒粒径、气体再燃等因素对于燃烧过程及氮氧化物的影响。本文首先采用数值模拟方法并结合锅炉实际运行数据,分析了锅炉的原始工况下的燃烧过程,发现存在着氮氧化物排放偏高以及水冷壁高温腐蚀等问题。不改变其余喷口负荷的前提下,进行掺烧比例为11%生物质燃料的模拟计算,对生物质喷入的位置和生物质粒径等参数变化的影响进行了深入研究。研究结果表明,生物质替换下层煤粉燃料后,炉膛下部整体温度下降,而且有降低NOx排放的作用,不过会导致燃尽位置的后移,可能引起过热器超温等问题。同时比较了生物质燃料分别替换第一层一次风喷口和第二层一次风喷口的煤粉燃料的情形,由于参与燃烧的时间更早,释放的挥发分等还原作用的成分会更早,因此第一层的工况降低NOx排放的效果会更好。接着研究生物质粒径的影响,考察了颗粒粒径分别为0.5mm、1mm、2mm的情形,生物质颗粒从2mm变化到1mm时,粒径变化的影响不大,但是从1mm变化到0.5mm后,氮氧化物排放有明显下降。为了对比生物质和生物质气化气的区别,将同种生物质气化后送入炉膛。研究表明更换气体燃料后,炉膛下部的整体温度下降更明显,NOx排放也有所降低。同样的,在对比了生物质气替换下层不同喷口煤粉燃料的数据后,结论与生物质的一样。最后,利用生物质气进行再燃的数值模拟研究。对比前面的模拟数据,生物质气再燃降低NOx排放效果非常明显,从原始的612 mg/Nm~3可以降低到402 mg/Nm~3,降幅约为34%,可以认为生物质气再燃是降低NOx排放效果最好的方案。本文的研究方法与结论对于大型燃煤锅炉生物质与煤混燃的研究和应用具有一定的现实参考意义。更多还原

【Abstract】 Biomass combustion process has ecologically significant zero carbon emissions,so it has always been an ideal alternative to fossil fuels such as coal.Co-firing of biomass and pulverized coal on large power plant boilers is one of the current research hotspots.In this paper,a 670MW four-corner tangential boiler is taken as the research object,with method of numerical simulation,which mainly considers the injection position,particle size,gas fuel reburning,and analyzes the influence of these factors on combustion and NOx emissions.In this paper,the numerical simulation method is combined with the actual operating data of the boiler,and the combustion process under the original working conditions of the boiler is analyzed.It is found that there are problems such as high nitrogen oxide emission and high temperature corrosion of water wal.and then the simulation calculation of 11%biomass co-firing is carried out,and the influence of the parameters such as the position of biomass injection and the particle size of biomass is deeply studied.The results show that after biomass replaces lower layer pulverized coal,the overall temperature of the lower part of the furnace decreases,and it has the effect of reducing NOx emissions,but it will lead to the backward movement of the burnout position,which may cause overheating of the superheater.At the same time,the situation that the biomass fuel replaces the pulverized coal fuel of the first layer primary air nozzle and the second layer primary air nozzle respectively is compared,since the time to participate in the combustion is earlier,and the release of volatiles and other components of the reduction will be earlier,it is better to replace the first layer of working conditions to reduce NOx emissions.Then,the influence of the particle size of the biomass was investigated.The particle size was 0.5mm,1mm,and 2mm.When the biomass particles changed from 2mm to 1mm,the particle size change had little effect,but after changing from 1mm to 0.5mm,NOx emissions have dropped significantly.After gasification of the same biomass,send gas into the furnace,then continue to study the effect of combustion.Studies have shown that after replacing the co-firing fuel,the overall temperature drop in the lower part of the furnace is more obvious,and NOx emissions are also reduced.Similarly,after comparing the data of biomass gas replacement of different nozzle pulverized coal fuels,the conclusion is the same as that of biomass.Finally,numerical simulation of reburning using biomass gas.Compared with the previous simulation data,the effect of biomass gas reburning to reduce NOx emissions is very obvious,from the original612 mg/Nm~3 can be reduced to 402mg/Nm~3,approximately 34%reduction,it can be considered that biomass gas reburning is the best solution to reduce NOx emissions.The research methods and conclusions of this paper have certain realistic reference significance for the research and application of biomass and coal blending utilization in large coal-fired boilers.更多还原