多流程循环流化床气固流动和燃烧的计算颗粒流体力学数值模拟

Simulation on the gas-solid flows and combustion in a multi-pass circulating fluidized bed based on computational particle fluid dynamics method

多流程循环流化床与传统流化床相比,能有效降低炉膛高度,实现小型化。以多流程循环流化床锅炉为研究对象,基于计算颗粒流体力学,对气固流动和燃烧过程进行了数值模拟,计算结果与中试装置结果吻合较好。结果表明:炉膛内颗粒相浓度由高到低依次为主燃烧室、副燃烧室、燃尽室,炉内颗粒分布呈现“环-核”结构;炉膛温度范围为1 000~1 200 K,主燃烧室的温度大于副燃烧室,副燃烧室的温度大于燃尽室与旋风分离器;增大一、二次风的配比使炉膛密相区的氧气含量增大,加剧了燃烧,使床温升高;由副燃烧室进行分级给料,有利于焦炭还原NO,使出口NO浓度明显下降,有利于减少氮氧化物的排放。

The furnace temperature of a multi-pass circulating fluidized bed(CFD)is higher than that of a traditional CFD,which advances the miniaturization of CFDs.The gas-olid flows and combustion of a multi-pass CFD were numerically stimulated by computational particle fluid dynamics method.The simulation results fitted well with the results of the pilotscale experiment.The results indicate that volume fractions of particle phase show core-annulus structure,ranking from high to low in the main combustion chamber,auxiliary combustion chamber,and burnout chamber.The furnace temperature is from 1000 to 1200 K.The temperature of the main chamber is higher larger than that of the auxiliary chamber,and the temperature of the auxiliary chamber is higher than that of the burnout chamber and the cyclone separator.Increasing the oxygen content in the dense phase zone of the furnace by enlarging the proportion of primary air to secondary air can intensify the combustion and increase the bed temperature.Pre-classification of fuel at the secondary chamber inlet is beneficial for coke reduction reactions,which is favorable to the reductions of NO concentration and nitrogen oxide emissions.