二次风对CFB锅炉NO_x排放的影响

The Influence on NO_x Emission of Secondary-air in CFB Boiler

为准确掌握和评价二次风对早期投运的燃烧福建无烟煤CFB锅炉NOx排放浓度的影响,在1台75 t/h中温分离CFB锅炉上进行工业热态试验。试验表明：（1）NOx排放浓度随着空气过量系数λ增加呈现明显增加的趋势,并且增加速率逐渐减小;保持省煤器出口处的空气过量系数1.15≤λ≤1.25可以取得控制飞灰含碳量和NOx排放量的良好效果;（2）随着二次风率β的增加,NOx排放浓度明显下降,降低速率逐渐减小;保持二次风率β在40%~50%之间,NOx排放浓度较低;（3）随着上二次风率k的增加,NOx排放浓度呈现先明显下降再逐渐减小至平缓最后略微上升的趋势,表明燃烧福建无烟煤的中温分离CFB锅炉存在有一个最佳的上二次风率k,使NOx排放浓度最小;根据本试验结果,在过量空气系数λ=1.2、二次风率β=45%的情况下,最佳的上二次风率k在55%~65%之间。

Industrial thermal experiments were carried out on the circulating fluidized bed boiler using medium temperature separation, in order to accurately grasp and evaluate the effect of secondary air on NOxemission concentration from the early launched 75 t/h circulating fluidized bed boiler burning fujian anthracite. The results show that, the NOxemission concentration increases obviously with the increase of excess air coefficient, used as λ, While, the increasing trend becomes slow down. When keeping the air excess coefficient of the exit of economizer between 1.15 and 1.25, good effect of the control of fly ash carbon content and NOxemission can be obtained. With the increase of secondary air ratio, used as β, NOxemission concentration decreases obviously, the rate gradually reducing. The NOxemission concentration is lower as the secondary air of between 40% and 50%. With the increase of upper secondary air ratio, used as k, the NOxemission concentration firstly decreases significantly and then reduces slightly to a flat, at last it has gentle upward trend, which means that there is an optimal upper secondary air ratio for the circulating fluidized bed boiler using medium temperature separation and burning fujian anthracite to minimize the NOxemission concentration. In the case of the excess air coefficient of 1.2 and the secondary air ratio of 45%, the best upper secondary air ratio is between 55% and 65%.