Numerical Simulation Research on Optimizing Blended- Anthracites Combustion in W-Shaped Flame Boiler With Direct-Fired Pulverizing System

Abstract

Two modes could be adopted such as pulverizing coal in different mills’ and ‘blending before furnace’. When blending different kind of coal, for “blending before furnace ’that means the different coals are blended previously before they are transported into Coal bunker and different mills pulverize same raw coal; on the other hand, Pulverizing coal in different mills’ means that different raw coals enter different mills, that is to say, different mills pulverize different raw coal. It is often held that it is unnecessary to optimize coal-blending mode since there are no essential difference of combustion characteristic etc. between anthracites. To determine the necessity of optimize mode when blending one anthracite with another anthracite, numerical simulation is carried out under different conditions using dual-mixture fraction/PDF approach. The calculated result shows that the furnace temperature field, oxygen distribution and velocity field are quite symmetrical under the ‘blending before furnace mode. But In contrast of that on the mode of pulverizing coal in different mills, the burn-off degree of powder coal and furnace outlet temperature are much lower. Even if using the same ‘pulverizing coal in different mills’ mode, if the mills running mode is changed, the efficiency of the boiler exist a gap from one to another. The simulation results prove that ‘pulverizing coal in different mills’ can enhance the combustion efficiency of boiler greatly even when one kind of anthracite is blended with another kind of anthracite. The operation mode of the coal-mills affect the furnace temperature field clearly and it could decrease coking tendency when the coal which is prone to be coked and so it is arranged far from the side wall of furnace.