焦炭气化反应对煤粉空气深度分级燃烧生成的影响 -

焦炭气化反应对空气深度分级工况下燃烧及污染物的生成具有重要影响。笔者采用滴管炉试验与数值计算相结合的方法,研究了主燃区过量空气系数SR1在1.2→0.6变化过程中,焦炭气化对空气深度分级工况下煤粉燃烧和NO_x排放特性的影响规律。通过对比滴管炉试验数据与传统模型和改进模型(考虑焦炭气化)结果可知,传统模型对空气分级燃烧的还原性气氛预测存在一定缺陷,改进模型与试验结果较吻合。滴管炉试验及改进模型计算结果表明,空气深度分级工况下,主燃区极度缺氧,燃烧过程由最初的挥发分着火(R1和R2)和焦炭不完全氧化(R4)过渡到以焦炭气化反应(R5和R6)为主导的燃烧状态,大量CO生成,高浓度CO_2逐渐被消耗,直至还原区段结束,随着燃尽风加入,O_2含量增加,CO被迅速消耗(以R2为主),CO_2生成。空气分级工况下NO_x排放特性表现为:燃烧器附近NO_x浓度高,伴随还原性气氛的形成,出现一定程度的下降后保持较低的NO_x水平,随着燃尽风的加入,出现一定程度的"反弹",这是因为还原区结束时,一部分未完全被还原的氮中间体在燃尽风加入后被迅速氧化造成的。 The gasification reactions of char have an important influence on combustion and pollutant formation under the condition of deep air-staging. In this paper,the influence of char gasification on the combustion and NO_xemission characteristics of pulverized coal under the condition of SR1 from 1.2 to 0.6 by the method of drop-tube furnace experiment and numerical calculation. Compared with the experimental data of the drop-tube furnace and the results of the traditional model and the improved model( considering char gasification),it can be seen that the traditional model has some defects in the prediction of reducing atmosphere of air-staged combustion,and the improved model is more consistent with the experimental results. The results of the experiment and the caculation of the improved model show that under the condition of deep air-staging,the main combustion zone is extremely anoxic,and the combustion process changes from the initial volatile ignition( R1 and R2) and incomplete char oxidation( R4) to the combustion state dominated by char gasification reaction( R5 and R6). At this time,a large amount of CO is generated,and the high concentration of CO_2 is consumed gradually until the end of reduction zone. With the addition of exhausted air,the oxygen content increases,CO is rapidly consumed( mainly R2),and CO_2 is gradually generated. The NO_xemission characteristics under the air classification condition are as follows: the NO_xconcentration near the burner is high; With the formation of reducing atmosphere,the NO_xlevel remains low after a certain degree of decline; And with the addition of burnout air,there is a certain degree of " rebound",which is caused by the rapid oxidation of some nitrogen intermediates that are not completely reduced after the addition of burnout air when the reduction zone is end