四角切圆锅炉炉内煤粉燃烧过程数值模拟

NUMERICAL SIMULATION ON PULVERIZED COAL COMBUSTION PROCESS IN A TANGENTIAL FIRING FURNACE

利用计算流体动力学软件PHOENICS 3.5对一台200MW四角切圆水平浓淡燃烧煤粉炉进行数值模拟研究,采用多流体两相流动模型及煤粉燃烧综合模型,计算得出在垂直方向不同二次风风量分布的工况下,炉内各截面处的烟气温度、燃料浓度、燃烧产物组分浓度以及炉内辐射热流的分布。结果表明,在燃烧器出口处出现了高煤粉浓度和烟气高温区,并出现气固两相分离的现象,使得煤粉着火及时,燃烧器区域维持较高温度,并防止水冷壁结渣,炉内温度、炉膛出口氧量和飞灰可燃物的计算结果和试验结果相比,吻合较好。二次风分级配风工况下,下部燃烧器区烟气温度升高,但氧气推迟混入,相应位置飞灰可燃物有所增加。计算模型能够合理地模拟水平浓淡煤粉气流在大型锅炉炉膛内的燃烧过程,适用于运行工况的优化和炉内污染物的控制。

The computational fluid dynamics （CFD） code, PHOENICS 3.5, is employed to evaluate horizontal pulverized coal bias combustion process in a 200 MW tangential firing boiler. Multi-fluid two-phase model and coal comprehensive combustion model are integrated in the code. Gas temperature, particle distribution, gas species concentration and radiation heat flux at different sections of furnace are obtained from the numerical simulation at different secondary air （SA） vertical distribution. The calculation results show that a high particle concentration and high gas temperature zone exist, together with the separation of particle and gas downstream primary air （PA） nozzles, which ensure suitable ignition time, high temperature level of PA mixture and resistance to slag on the water-cooled walls. The calculated burnout of coal particles, O2 concentration at furnace exit and gas averaged temperature in furnace are compared with in situ measurement data, resulting in good agreement. The simulation results of staged SA distribution case show that gas temperature of down part of furnace increase and the final burnout of char is decreased for the postponing mixing between fuel and oxygen. Simulation results are also compared with in situ measurement data, resulting in good agreement with each other. Thus the comprehensive coal combustion model has reasonably simulated PF combustion process in large boiler furnace, which is benefit for optimizing unit operation conditions and reducing pollutants emission.