在一台600 MW的北京巴威W型(B&W)火焰锅炉上采用了新型燃烧系统,在原始燃烧系统的基础上调整了二次风配比并且引入了燃尽(SOFA)风,该系统在大幅降低NOx排放的同时能保证飞灰含碳量不会明显增加。研究目标是通过数值模拟的方法评估新型燃烧系统在不同SOFA风率和不同SOFA位置时的整体燃烧性能。为了更加准确的计算飞灰含碳量,采用了CBK焦炭燃烧模型。结果表明当SOFA风率从15%上升到20%时,氮氧化物由823 mg/m3骤降至738 mg/m3,飞灰含碳量仅增加了0.264%;而当SOFA风率从20%上升到25%时,氮氧化物仅降低了32 mg/m3,飞灰含碳量却增加了0.41%。因此综合考虑NOx排放和飞灰含碳量,SOFA风率取20%最为合理。对于SOFA风位置而言,从拱上3.0 m增加到6.0 m,NOx排放略微减少,与此同时飞灰含碳量小幅增加。综合考虑经济性和NOx排放,最优的SOFA布置位置在拱上5 m处。

A novel combustion system has been applied to a 600 MW Babcock & Wilcox (B & W) down-fired boiler to reduce NOx emissions without obvious increasing of the carbon content in fly ash. The modification mainly includes rearranging secondary air,and introducing separated over-fire air ( SOFA). The aim of this work is to evaluate the overall performance of the novel combustion system with different SOFA ratios (e. g. ,15% ,20% ,and 25% ) and dif- ferent SOFA locations in the upper furnace (e. g. ,3. 0,4. 0,5. 0,and 6. 0 m above the arches) using numerical simu- lations. In order to calculate the carbon content of fly ash more accurately, this paper used CBK coke combustion mode. Results showed that not only the NOx emissions were greatly reduced from 823 mg / m3 to 738 mg / m3 ,but also the carbon content in the fly ash decreased slightly in 0. 264% with increasing the SOFA ratio from 15% to 20% . When the SOFA ratio increased from 20% to 25% ,NOx emissions only decreased 32 mg / m3 ,but the combustible con- tent in the fly ash increased obviously in 0. 41% . Considering the NOx emissions and combustible content in the fly ash,an SOFA ratio of 20% was advisable. With increasing the height of SOFA from 3. 0 to 6. 0 m above the arches,the carbon content in the fly ash somewhat increased while NOx emissions decreased. Taking economic efficiency and NOx emissions into account,the location (5. 0 m above the arches) was the optimal SOFA location.