Simulation of Heat and Mass Transfer in a Moving Bed Part-Fluidized Boiler

Moving bed part-fluidized boiler is a new type of furnace. The new combustion method in the furnace has attracted a lot of attention and shown attractive prospects. Two-dimensional computational fluid dynamic (CFD) simulations were performed for a 116 MW moving bed part-fluidized boiler to investigate the different combustion patterns of coal particles of different particle sizes inside the furnace chamber. A low-NO_X combustion method based on the combination of laminar combustion and fluidized combustion is proposed. By comparing the effects of different air distributions on the fluidization state of coal particles, the air distribution values required for optimal fluidized combustion were obtained. The temperature field and pollutant distribution in the furnace chamber for the conventional combustion method and the new combustion method were also simulated. The results show that the combustion technology combining laminar combustion and fluidization of a moving bed part-fluidized boiler can significantly improve the combustion rate and reduce the NO_X concentration at the furnace exit. When the secondary air speed is up to 15 m/s, the coal particles smaller than 5 mm are fully fluidized and burned in the whole furnace chamber. The coal particles larger than 5 mm are burned on the bed. The pollutant emission of the boiler can reach the best condition. The new type of boiler can reach a super clean emission in which the NO_X emission value is below 47 mg/m³, and the SO₂ emission value is reduced to 0.15 mg/m³.