宽负荷下切圆燃煤锅炉H_(2)S分布特性的数值模拟

Numerical simulation on H_(2)S distribution characteristics of tangentially coal-fired boiler under wide loads

锅炉采用空气分级燃烧降低NO_(x)排放的同时也提高了主燃区H_(2)S体积分数。炉墙壁面过高的H_(2)S体积分数是加剧水冷壁高温腐蚀的重要因素。为保障新能源并网发电,大型燃煤机组灵活调峰的需求增加,不同负荷下的水冷壁近壁面H_(2)S分布特性值得关注。通过正交试验分析了切圆燃煤锅炉运行参数对水冷壁近壁面H_(2)S体积分数分布的影响。选取一台超临界600 MW切圆燃煤锅炉建立数值模型,设计L_(16)(4^(5))正交工况,覆盖100%BMCR、75%THA,50%THA以及35%BMCR四种负荷。建立了自定义SO_(x)生成模型以确定燃料硫的析出和转化路径,模型包含多表面反应子模型以描述焦炭与O_(2)/CO_(2)/H_(2)O等3种气体的异相反应,并确定焦炭气化反应消耗量占总消耗量的比例,进而对炉膛H_(2)S空间分布进行了模拟计算。研究表明,近壁面高体积分数H_(2)S区域主要位于投运燃烧器层中最下层燃烧器以下以及最上层燃烧器以上至SOFA层之间,烟气切圆沿炉膛高度增加逐渐增大是造成后一区域H_(2)S体积分数较高的重要原因。35%BMCR负荷下水冷壁重点区域的H_(2)S平均体积分数为364μL/L,明显低于其他负荷。锅炉运行参数对重点区域H_(2)S体积分数影响程度的排序为:锅炉负荷>一次风率>主燃区空气过量系数>假想切圆直径>燃烧器竖直摆角。

Air staged combustion reduces NO_(x)emissions,but increases the H_(2)S concentration in primary combustion zone.The excessive H_(2)S concentration near the furnace wall is an important factor that aggravates the high-temperature corrosion of the water-cooled wall.With large-scale renewable power integrated into the grid,the demand for flexible peakshaving operation of traditional thermal power units has increased.The H_(2)S concentration distribution near the furnace wall under different boiler loads deserves attention.Hence,the influence of different operating parameters of tangentially coal-fired boiler on H_(2)S concentration distribution near the furnace wall was investigated by orthogonal test.A supercritical 600 MW tangentially coal-fired boiler was selected to establish a numerical model.The L_(16)(4^(5))orthogonal numerical conditions was designed to cover four boiler loads,including 100%BMCR,75%THA,50%THA and 35%BMCR.A userdefined SO_(x)generation model was employed to calculate the H_(2)S concentration distribution inside the furnace.The release of fuel sulfur and mutual transformation of sulfur components were considered.At the same time,the model included a multiple surface reaction model for describing the heterogeneous reaction between coke and O_(2)/CO_(2)/H_(2)O,and the ratio of the gasification rate to the consumption rate for char particle was calculated.The results show that the high H_(2)S concentration areas are mainly located below the bottom burner that on operation and between the top burner and SOFA nozzle.The main reason for the high H_(2)S concentration in the latter area is that the tangential circle of flue gas increases gradually along the furnace height.The orthogonal analysis indicates that the average H_(2)S concentration in the key area of the furnace wall under 35%BMCR load is 364μL/L,which is significantly lower than that under the other loads.In addition,the impact of operating parameters on the H_(2)S concentration in key areas follows the order of boiler load>primary air rate>excess air coefficient of main combustion zone>imaginary tangent circle diameter>vertical swing angle of burner.