循环流化床二次风射流相关影响因素的数值模拟研究

Numerical Simulation of Influencing Factors for Secondary Air Penetration Depth in Circulating Fluidized Bed Boiler

采用欧拉-欧拉双流体模型,对某大型循环流化床锅炉炉膛内二次风射流的流动进行数值模拟,研究二次风动量、床内颗粒浓度、温度、颗粒物性等因素对二次风穿透性和气固两相混合的影响。结果表明,穿透深度与射流动量成正比,与颗粒浓度、颗粒密度和直径成反比。射流温度对射流深度也有影响。在正常工况下,该CFB锅炉的射流深度不足以穿透至炉膛中心,不能完全满足中心需氧量。因此,在二次风量一定的情况下,为保证二次风对炉内燃烧的混合效果,可以降低下二次风的比例来保证上二次风,在一次风完全可以满足流化要求的情况下,甚至可以考虑取消下二次风。解决大容量CFB锅炉炉膛设计的主要途径可以在适当增加炉膛宽度的同时通过加大炉膛深度来满足进行放大。模拟结果可以为大型循环流化床锅炉的设计和运行提供理论参考。

A three-dimensional numerical simulation was is conducted for a 300 MW circulating fluidized bed boiler by CFD software,as a multi-fluid Eulerian–Eulerian model is adopted.The influence of following factors on secondary air penetration and gas-solid mixture were studied,such as secondary air momentum,particle concentration,temperature,particulate characteristics.Results show that the secondary air momentum which is decided by the nozzle diameter and jet velocity is the most important influencing factor for secondary air penetration depth.The secondary air penetration depth is proportional to jet velocity and nozzle diameter,inversely proportional to particle concentration,particle density and particle size.Besides,the temperature also has effects on secondary air jet penetration.In normal conditions,the secondary air jet can not reach the center of the boiler to completely meet oxygen demand.Because of the limited air volume,it should lower the lower-second-air ratio to ensure penetration and mixing effect.In the condition that primary air can completely satisfy the fluidization requirements,lower-second-air can even be scrapped.The way to satisfy the area expanding needs in large-scale CFB boiler is not through increasing chamber width,but through increasing Chamber depth.Simulation results can provide theoretical reference for large-scale CFB boiler＇s design and operation.