富氧燃烧对投运混煤锅炉低负荷稳燃性的影响

Influence of Oxygen Enriched Combustion on Low Load Combustion Stability of Mixed Coal Boiler

针对某650 MW超超临界燃煤锅炉在深度调峰过程中燃用大同烟煤时无法稳定燃烧的情况开展研究,就如何提高锅炉在低负荷运行中稳燃性的问题,对原煤种进行掺混改良,改变不同富氧燃烧配风方式,利用计算流体力学模拟软件模拟了不同工况的炉内燃烧情况。模拟结果表明:由于锅炉降低负荷运行增加了原煤种的着火难度,固定碳含量低且挥发分高的煤种可以较好适应锅炉运行调整;富氧燃烧可以提高锅炉低负荷运行时的出口烟温,能满足后续脱硝处理的要求;随着富氧燃烧程度的增大,煤粉燃烧耗氧量增加,每秒燃烧的煤粉颗粒数增加,加剧了炉内的燃烧,使燃烧更稳定;当富氧浓度大于27%时,不能高效提高炉内温度,NOx排放量增多;当富氧浓度为27%时,炉膛出口NOx排放量按6%O2折算为负增长的最小值,是该锅炉低负荷投运较为理想的工况。

Aiming at the situation that Datong bituminous coal cannot be burned in a 650 MW ultra-supercritical coal-fired boiler stably during deep peak shaving,this paper studied how to improve the combustion stability of the boiler during low load operation.The raw coal is mixed and improved,and the air distribution mode of different oxygen-enriched combustion is changed.The combustion in the furnace under different conditions is simulated by using computational fluid dynamics simulation software.The simulation results show that the ignition difficulty of raw coal is increased due to the reduced load operation of the boiler,and the coal with low fixed carbon content and high volatile content can better adapt to the boiler operation adjustment;oxygen-enriched combustion can improve the outlet flue gas temperature of boiler under low load operation,and can meet the requirements of subsequent denitration treatment;as the degree of oxygen-enriched combustion increases,the oxygen consumption of pulverized coal combustion increases,and the number of pulverized coal particles burned per second increases,which intensifies the combustion in the furnace and makes the combustion more stable;when the oxygen-enriched concentration is greater than 27%,the temperature in the furnace cannot be effectively raised,and the NO_x emission increases;when the oxygen-enriched concentration is 27%,the NO_x emission at the furnace outlet(6%O_2)is the minimum value of negative growth,which is an ideal condition for the boiler to be put into operation at low load.