Influence of secondary air distribution on the gas-solid mixing and combustion condition in a CFB (circulating fluidized bed) boiler furnace

For a CFB (circulating fluidized bed) boiler, its total air quantity is usually divided into a primary air flow and a secondary one to facilitate the control of combustion process, while for a large-sized CFB boiler, the secondary air flow is further divided into several layers along the furnace height and distributed on the four sidewalk of the furnace to strengthen combustion process control. First, the authors have described the role played by a transverse secondary-air jet flow in promoting the gas-solid mixing and coal combustion in the CFB boiler. Then, through an experiment performed on a CFB boiler burning low volatile coals, the influence of in-furnace flow field on the secondary air distribution in the furnace of the boiler under various air supply modes was analyzed. On this basis, the influence of different air distribution modes of the secondary air on the coal burn-off and in-furnace temperature field was also investigated. The test results show that through an optimization of the secondary air, the in-furnace gas-solid mixing can be strengthened, and the diffusion of gas and fuel, promoted, thus enhancing the combustion efficiency of the CFB boiler burning low-volatile coals.