空气分级对旋风锅炉燃烧及NO_(x)释放的影响规律

Effect of Air Stagging on Combustion and NO_(x) Emission of Cyclone Boiler

针对纯高碱煤在旋风液态排渣锅炉实际燃烧过程中存在的局部温度高及NO_(x)排放超标等问题,采用数值模拟的方法研究了燃尽风的布置及风量配比等因素对炉内温度场、组分分布特性和NO_(x)排放的影响规律。研究结果显示:燃尽风喷口的布置形成了良好的空气分级燃烧效果,炉内温度整体降低。不同燃尽风工况下,炉内各组分分布规律一致,w(O_(2))质量分数高于无燃尽风的工况,w(CO)和w(CO_(2))低于无燃尽风的工况。确定了旋风锅炉纯燃高碱煤时最佳的主燃区过量空气系数为0.9,且总过量空气系数相同时,增大第一层燃尽风速可达到最佳低氮排放效果,炉膛出口NO_(x)浓度可降至398.3 mg/m^(3),炉膛出口烟气温度最低为900.4 K。

Aiming at the problems of slagging,high local temperature and NO_(x) emission in the actual combustion process of pure high alkali coal in the cyclone boiler.By means of numerical simulation,the excess air coefficient,distribution of over-fire air and air ratio in the main combustion zone were analyzed for temperature field,component distribution and NO_(x) release characteristics in the boiler.The results show that the arrangement of over-fire air nozzle has formed a good effect of air staged combustion and the temperature in the furnace decreases as a whole.Under different over-fire air conditions,the distribution of components in the furnace is consistent,the mass fraction of O_(2) is higher than that of non-over-fire air,and the mass fraction of CO and CO_(2) is lower than that of non-over-fire air.When the total excess air coefficient is the same,the best excess air coefficient in the main combustion zone is determined to be 0.9,the best low nitrogen emission effect can be achieved by increasing the first layer over-fire airspeed,and the maximum NO_(x) concentration at furnace outlet can be reduced to 398.3 mg/m^(3),and the lowest flue gas temperature at the furnace outlet is 900.4 K.