洁净煤技术

2019, (04) 80-86

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燃尽风率对二次再热锅炉热量分配及NO_x的影响
Influence of over fire air ratio on heat absorption and NOx of a double reheated boiler

肖寒;蒙晨玮;吴玉新;冯乐乐;张海;张缦;
XIAO Han,MENG Chenwei,WU Yuxin,FENG Lele,ZHANG Hai,ZHANG Man

摘要(Abstract):

合理的燃尽风率对降低NO_x排放十分关键,也显著影响大容量锅炉炉膛内的燃烧和传热特性。针对1 000 MW超超临界二次再热塔式锅炉开展三维CFD数值模拟,研究燃尽风(OFA)率对于炉内NO_x生成及吸热量分配的影响规律。模型采用贴体六面体非结构网格,通过用户自定义函数(UDF)设置炉膛及各受热面的壁面温度;煤粉颗粒在炉内的运动及燃烧过程基于随机轨道法计算,采用Realizable k-ε模型模拟四角切圆炉内的湍流流动,采用离散坐标(discrete ordinates,DO)法计算炉内辐射传热;采用简化概率密度函数(probability density function,PDF)模型模拟湍流与化学反应的耦合特性。结果表明,燃尽风率对炉内的温度分布、炉膛的吸热比率以及污染物排放情况均存在显著影响。当燃尽风率在0~40%时,主燃区的平均温度随燃尽风含量的增大先升后降,而燃尽风区域的平均温度则随着燃尽风率升高显著上升。随着燃尽风率的升高,由于温度和氧含量变化等共同作用,原始NO_x排放量先降后升,燃尽风率在11%~25%时达到最低。随燃尽风率从0增至25%,锅炉炉膛吸热比率降低12%,过热器、再热器、省煤器等对流受热面的吸热比例相应增加。当燃尽风率大于25%时,炉膛吸热比例的降低趋势减缓。因此,建议在锅炉设计中应综合考虑OFA比例变化对炉膛吸热量以及污染物排放的影响。
Over Fire Air(OFA) ratio not only has strong influence on NOx emission,but also on heat flux and combustion inside the large capacity boilers.To investigate such effects,three-dimensional CFD numerical simulations were conducted for a 1 000 MW ultra-supercritical double reheated tower boiler.3D body fitted hexahedra meshes were adopted to discretize the simulation domain.Temperature of membrane wall and the tubes were identified through user defined functions(UDF).Stochastic particle tracking model was used to calculate dispersion of the pulverized coal particles.The turbulence information was calculated through Realizable k-ε model.Discrete-Ordinates model was used for the radiation heat transfer.The simplified PDF model was used to solve the coupling of turbulence and chemical reactions.The results show that OFA ratio has significant influence on the temperature,pollutant emission,and heat flux.When OFA ratio increases from 0 to 40%,the temperature of burner area will firstly increase and then drop down;the temperature of OFA area will increase,and the original NOx emission will decrease and reach the minimum value of 25% of OFA ratio.The heat absorption by the furnace membrane wall decreases by 12% with the increases of OFA ratio from 0 to 25%,then the heat absorption decreases slowly when OFA ratio increases.The heat absorption by the convection heat surfaces increases so that the total heat absorption doesn't change.Such trend shows the effect of OFA ratio on heat absorption of furnace has to be considered in the design of the large capacity boilers.

关键词(KeyWords): 燃尽风;二次再热锅炉;热量分配;NO_x;热流分布
over fire air;double reheated boiler;heat absorption;NOx;heat flux distribution

Abstract:

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作者(Author): 肖寒;蒙晨玮;吴玉新;冯乐乐;张海;张缦;
XIAO Han,MENG Chenwei,WU Yuxin,FENG Lele,ZHANG Hai,ZHANG Man

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