Investigation Of Three-dimensional CFD Model Development For Full Furnace Of Moving Grate Incinerator And Its Engineering Application

Incineration,as an impactful way of municipal solid waste(MSW)disposal,is widely used in China.CFD simulation is an effective approach to optimize the design and operation of moving grate MSW incinerators.In this paper,a three-dimensional transient model is developed and applied to investigate the combustion process of a 750d/t industrial grate incinerator with real incinerator geometry.The gas-solid flow in the grate bed and the gas turbulent combustion were simulated in single scheme.Thermal conversion of wastes is characterized by the heterogeneous reactions of moisture evaporation,devolatilization,char-O2 combustion and the homogeneous reactions of hydrocarbons oxidation.The kinetic theory of granular flow(KTGF)is introduced to describe the rheological properties of waste particles,and the Ergun model is used for the gas-solid drag force.The simulation results show that the solid temperature in drying section is relatively low,and increases at the end of drying section.After passing the fall region,the bed solids starts to burn violently,and the temperature reaches about 1570K.The volatile is released and completely burnt in combustion section,and the solid temperature is around 900K in the last section.In addition to the primary air,the secondary air increases the oxygen content and enhances the gas disturbance,promotes the burnout of combustibles in the flue gas.The distributions of gas temperature,bed solid and gas component are predicted and validated by 9 temperature measurement points in the furnace.Two operating conditions of 60%and 110%loads are also simulated by the model,and the results are reasonable.An engineering approach is implimented to facilitate the application of CFD in industry,in which,the 3D unsteady simulation is replaced by 2D unsteady bed simulation and a 3D steady furnace simulation.The CPU hour is reduced sharply.The engineering method is validated by good agreement in results of the two methods.The effects of particle size,primary air distribution and the residence time of MSW in bed are investigated in the engineering model.The results verified that smaller sizes benefit the evaporation and char burnout;more air in dry section dvance ignition,and excessive air reduces the combustion intensity.A short residence time of MSW in bed will postpone the ignition,and reduce thermal efficiency,but an excessive residence time will make the combustion position unreasonable,and reduce the amount of waste incineration.