循环流化床锅炉低氮燃烧的CPFD数值模拟

CPFD Simulation of Low Nitrogen Combustion in Circulating Fluidized Bed Boilers

针对某75 t/h循环流化床锅炉炉膛出口NOx排放超标问题进行分析探讨,以合理的低氮燃烧控制技术为主,辅以SNCR烟气脱硝技术,争取达到NO x超净排放要求。采用CPFD计算方法对循环流化床锅炉炉膛内的气固流动和燃烧特性进行数值模拟,运用低过量空气燃烧法和空气分级技术对锅炉进行低氮燃烧控制,研究一、二次风配比、二次风射流、过量空气系数、循环倍率和颗粒粒径等因素对炉内燃烧及NO x排放的影响。结果表明:通过低氮燃烧控制后,炉内速度场和温度场分布均匀,炉膛出口处烟气流速增加,炉膛平均烟温和出口氧浓度降低,还原性气体CO浓度和优化前基本相同,炉膛出口NOx浓度降低,减排效果显著,为以后的锅炉运行提供实际指导经验。

The problem of NOx emission exceeding the standard at the furnace outlet of a 75t/h circulating fluidized bed boiler is analyzed and discussed.Reasonable low nitrogen combustion control technology and SNCR flue gas denitrification technology are mainly used in order to meet the requirements of ultra-net NOx emission.In this paper,the numerical simulation of gas-solid flow and combustion characteristics in CFB boiler furnace is carried out by using CPFD calculation method.Low excess air combustion method and air classification technology are used to control low nitrogen combustion of the boiler,and the primary and secondary air mix ratio is studied,and the gas-solid flow and combustion characteristics in the furnace of CFB boiler are simulated.The effects of secondary air jet,excess air coefficient,circulation ratio and particle size on combustion and NOx emission in the furnace were studied.The results show that under the control of low nitrogen combustion,the distribution of velocity field and temperature field in the furnace is uniform,the velocity of flue gas at the furnace outlet increases,the average flue gas temperature and outlet oxygen concentration decrease,and the CO concentration of reductive gas is basically the same as that before optimization.The NOx concentration at furnace outlet is reduced,the emission reduction effect is remarkable,and provides practical experience for boiler operation in the future.