Numerical Study Of Combustion In Bed And NO Producing Characteristics Of Municipal Solid Waste

The combustion process of municipal solid waste and characteristics of NO release on the moving grate is studied and simulated by CFD codes. The results of simulation and experiments at the different primary air flow are compared and analyzed. Detailed combustion process and the law of the main gas produced are studied further. Afterwards the combustion process of municipal solid waste and characteristics of NO release at the different primary air temperature, particle size and waste composition are simulated and analyzed.In simulation, the drying process of MSW combustion is modeled by diffusion model. The separating out process from fuel for volatiles is modeled by one step reaction model. The char combustion is modeled by diffusion-kinetics model. In the NO formation process, only fuel NO is considered and modeled by overall reaction mechanism in which HCN is used as intermediate product, which is suggested by De'Soete. Dioxin formation process is modeled by a simplified model, which is proposed by Stanmore.Comparing the results of simulation and experiments, the combustion process of municipal solid waste is simulated accurately by the model. Evaporation of moisture, pyrolysis process, the oxidation of char particles and bun-ff happen successively in the combustion process of MSW. Due to the high water content, the time in the drying process is long, and evaporation of moisture mainly occurs in the bed temperature below 100℃. Char formation concentrates on the bed surface. In comparisons, waste combustion rate is increased first and then decreased as the primary air flow increasing, and the NO peak value reflects the same law.With waste particle size increasing, heat transfer in bed is strengthened and combustion rate is bigger, as a result, volatile release is accelerated, and volatile jet is becoming fine, and the more NO produced. Heating the primary air, the bed temperature increases, but NO formation is hardly influenced. Fuel NO is main source of NO in MSW combustion,and the N content is the key to NO formation.This thesis shows that the simulating model can describe layer combustion of MSW and NO emission characteristics in detail. The simulation results provide direction for design and optimization of the moving grate of MSW.