超临界350MW机组W火焰锅炉多次引射分级燃烧三次风倾角数值优化

Numerical optimization of tertiary-air declination angle for a 350MW W-shaped supercritical boiler with multi-injection and staging combustion

针对某台新建的采用多次引射分级燃烧技术的超临界350 MW机组W火焰锅炉,采用数值计算研究了三次风倾角分别为0°、10°、20°、30°时对炉内流动和燃烧的影响。结果表明:三次风倾角为0°和10°时,炉内流场偏斜,下炉膛利用率偏低,炉膛出口烟气温度及NOx排放质量浓度较高;当三次风倾角增至20°后,炉内流场趋于对称,气流下射深度大,炉膛出口烟气温度及NOx排放质量浓度较佳;进一步加大三次风倾角至30°时,气流下冲过深,对冷灰斗产生明显的冲刷且冷灰斗内温度较高。综合考虑炉内流场对称性、炉膛出口烟气温度和NOx排放,三次风倾角取20°为宜。

For a newly built supercritical 350 MW unit with down-fired boiler applying multi-injection stag- ing combustion technology, the fluid flow and combustion characteristics inside the furnace were numerical- ly simulated,under conditions with the tertiary air declination angle of 0°, 10°, 20°, 30°. The results show that,with the tertiary air declination angle of 0° and 10°,a deflected flow field with low furnace room utili- zation efficiency was observed, accompanied by high levels of gas temperature and NO° emissions at the furnace outlet. As the tertiary air declination angle increased to 20°, the flow filed turned into a relatively symmetrical pattern with great flame penetration depth,and the aforementioned high NO. emission at the furnace outlet decreased apparently to acceptable levels. However, excessively increasing the tertiary air declination angle to 30° resulted in an excessively large downward flame penetration depth, with the down- ward coal/air flow washing over the hopper wall and high gas temperatures in the hopper zone. Compre- hensively considering the formation of symmetric combustion with low NO. emission and gas temperature at the furnace outlet,the optimal tertiary-air declination angle should be 20°.