劣质煤低负荷稳燃技术数值计算研究及应用

Numerical study and application of steady combustion under low load for inferior coal

电厂煤粉锅炉在深度调峰低负荷运行状况下,燃煤输入热量大幅减小,炉内整体温度下降,导致煤粉燃烧稳定性下降,锅炉易发生灭火,维持燃烧的稳定性难度非常大,如果燃用劣质煤则稳燃难度将进一步增大。为提升对冲燃煤锅炉低负荷运行工况下燃用劣质煤时的稳燃能力,研发一种更加经济高效的超低负荷稳燃技术,运用fluent软件对3种对冲燃煤锅炉低负荷稳燃燃烧器方案进行数值模拟分析研究,对比各方案中燃烧温度、氧量、CO等分布情况。结果表明:采用新型带外置分离式煤粉燃烧器后,整个炉膛内燃烧组织更好、燃烧温度更高,炉膛火焰充满度好,可有效增强煤粉着火和稳燃能力;提升一次风温对低负荷稳燃有利,在低负荷运行工况下,可在燃烧器入口增设一次风加热系统,尽可能提高一次风的运行温度;采用外置式分离技术或提升一次风温度均可减少锅炉侧墙水冷壁附近的CO浓度,使煤粉在主燃烧区域燃烧更充分,进而提高低负荷状态下的燃烧效率。在某600 MW锅炉项目上得到应用,取得了良好的低负荷稳燃效果,为实际工程设计及运行提供借鉴。

Under the condition of deep peak shaving and low load operation of pulverized coal fired boilers in power plants,the input heat of coal is greatly reduced,the overall temperature in the boiler is reduced,resulting in the decline of pulverized coal combustion stability,and the boiler is prone to fire extinguishing.It is very difficult to maintain the combustion stability,and the difficulty of stable combustion will further increase if inferior coal is burned.In order to improve the stable combustion ability of the coal-fired boiler when burning low-quality coal under low load operating conditions,a more economical and efficient ultra-low load stable combustion technology is developed.The numerical simulation analysis of three low load stable combustion burner schemes of the coal-fired boiler is carried out by using FLUENT software,and the distribution of combustion temperature,oxygen content,CO,etc.in each scheme is compared and analyzed.The results show that after adopting the new type of pulverized coal burner with external separation,the combustion organization in the whole furnace is better,the combustion temperature is higher,and the furnace flame fullness is better,which can effectively enhance the ability of pulverized coal ignition and stable combustion;Increasing the primary air temperature is beneficial to low load stable combustion,under low load operating conditions,a primary air heating system can be added at the burner inlet to increase the primary air operating temperature as much as possible;using external separation technology or increasing the primary air temperature can reduce the CO concentration near the water wall of the boiler side wall,making the pulverized coal burn more fully in the main combustion area,thus improving the combustion efficiency under low load.The research results provide ideas and references for practical engineering design and operation,and have been applied in a 600 MW boiler project,and achieved good low load stable combustion effect.