燃尽风对超超临界锅炉燃烧特性影响的数值模拟

Numerical simulation on effects of over fire air on the combustion characteristics in an ultra-supercritical boiler

对一台1000MW超超临界前后墙旋流对冲燃烧煤粉锅炉进行数值模拟,研究了燃尽风比例对燃烧、NOx排放及传热特性的影响.采用化学渗透脱挥发分模型替代经验方法,预测煤粉挥发分析出过程中氮的释放量以及挥发分氮转化为HCN与NH3的比例.模拟结果与试验测量值符合较好,随着燃尽风比例增加,飞灰含碳量增加,煤粉燃尽率降低,NOx排放量(浓度)下降;但下炉膛出口烟气温度增加,导致大屏过热器挂渣倾向增加,较优的燃尽风比例为25.7%.

The numerical simulations of combustion were carried out for a 1 000MW ultra-supercritical swirling opposed coal-fired utility boiler.The influence of the ratio of over fire air（OFA）on the characteristics of combustion,nitrogen oxides（NOx）emission and heat transfer in the furnace were investigated.The chemical percolation devolatilization（CPD）model,instead of an imperical method,was adapted to predict the mass fraction of nitrogen release during the devolatilization and the mass fractions of volatile nitrogen evoluing as HCN and NH3.The simulated results agree well with the measured values.The results show that the carbon content in the fly ash will increase when the ratio of OFA increases;the pulverized coal burnout decreaes and the NOxemission also reduces.However, the flue gas temperature at the exit of the lower furnace rises gradually,resulting in the increase of tendency of the ash deposit on the surfaces of the platen superheater.25.7%is an optimal ratio for OFA.