A detailed numerical simulation study was conducted of the horizontal coal-fired boilers to burn biomass fuel combustion system with CFD. It simulates different spraying angles of secondary air, the different ratio of primary air and secondary air, and the distribution of flow field in the furnace of the boiler which is staggered the point of secondary air arrangement. As examples of DZL4-1.25-A II boiler of simulation, the result is studied carefully after simulation finished, when the angle of the nozzle is 30° at simulation calculation cond...