75 t/h双速CFB锅炉炉膛结构优化数值模拟

Numerical simulation on furnace structure optimization for a 75 t/h double-speed CFB boiler

由于结构特殊,高低双速循环流化床(CFB)锅炉炉膛内部气固两相流密相区和稀相区颗粒质量浓度的变化增强了受热面处对流换热,但同时也加剧了对金属受热面的冲击磨蚀。为解决二者间的矛盾,本文采用欧拉-拉格朗日方法对某燃用高比例煤泥的75 t/h高低双速CFB锅炉炉膛内气固两相流进行冷态数值模拟,通过仿真计算得出了该炉膛结构内部气体与固体颗粒的流动速度和质量浓度的变化规律,在相同边界条件下研究炉膛稀相区和密相区的截面比对炉膛壁面磨损与对流换热的影响,得到了优化后的炉膛结构参数。结果表明,炉膛壁面的磨损量比值和对流换热系数均随炉膛截面比的增大而降低,综合考虑后,建议该炉膛截面比选择在82.5%～92.5%较为合适。将该建议值应用于实际电厂锅炉炉膛结构技术改造后,锅炉运行情况良好。

Due to the special structure,in furnace of a two-speed fluidized bed boiler,rapid change of mass concentration of particles in air-solid two phase flow between the dense-phase region and rare-phase region enhances the heat transfer intensity on the surface of heat exchangers,but it also aggravates the erosion of the metal heating surface.In order to resolve this contradictory,cold state numerical simulation on air-solid two-phase flow in a75t/h two-speed circulating fluidized bed boiler firing fuels with high proportion of coal slime is carried out,through using the Euler-Lagrangian algorithm.The flow velocity and mass concentration of the air and solid particles in the furnace are calculated by simulation.Moreover,the influence of cross section ratio of the rare-phase region area to that of the dense-phase region area in the furnace on wall erosion and convective heat transfer is investigated,under the same boundary conditions,and the optimal furnace structural parameters are obtained.The results show that,both the wear ratio and convective heat transfer coefficient decreases with the increasing furnace cross section ratio.Considering the combined effects of furnace wall surface wear and convective heat transfer,the suggestion that the furnace cross section ratio should be within the range of82.5%to92.5%is presented.Additionally,this suggestion is applied in boiler structure optimization of a power plant,and after the retrofitting,the boiler runs well.