Study On Dry Sludge Incineration And Pollutant Discharge

With the rapid development of society,the output of sewage is getting larger and larger,resulting in the increase of sludge production after treatment.Sludge incineration has the advantages of reduction,stabilization and resource utilization,but in the process of incineration,various pollutants(NOx,SO2,heavy metals)will be produced,and direct discharge will cause serious harm to the environment.Therefore,it is of practical significance to study the characteristics of sludge incineration and pollutant discharge.In this paper,the combustion of dry municipal sludge in fluidized bed and the emission of pollutants are simulated and analyzed,and the mechanism of NO oxidation and reduction in the combustion process is analyzed.Firstly,the geometric model of the furnace is built and the mathematical model to be used is introduced.The furnace model is meshed and checked,and the results of 286900 meshes satisfy the requirement of irrelevance.By comparing the calculated results with the actual parameters,the error of the furnace outlet temperature is 3.98%,and the outlet NO concentration error is 8.27%,which verifies the rationality of the selected model.The combustion simulation of fluidized bed boiler was carried out.The concentration field distribution of the two working conditions was similar.The temperature of the furnace designed to fuel was higher than that of urban sludge.The NO emission of urban sludge was 17.3% higher than that of designed fuel.Then,the effects of different primary wind speeds,different sludge particle average diameters,different combustion atmospheres and mixed coal blending factors on the combustion characteristics and NO emission of municipal sludge in fluidized bed boilers were analyzed.The distributions of velocity field,temperature field and concentration field in the furnace under different factors and the effects of different parameters on NO emission under different working conditions are obtained.The results under different calculation conditions are compared,and the optimal operating parameters of the boiler during combustion are obtained.Finally,using density functional theory(DFT),the mechanism of migration and transformation of NO from coke nitrogen in sludge combustion process was studied at the molecular level.The reaction mechanism of heat-induced HCN produced by the armchair nitrogen-containing coke model was studied.The reaction mechanism of NO in the hetero-phase oxidation of the armchair nitrogen-containing coke model was studied.NO was heterogeneously reduced at the edge of the armchair coke.And the activation energy of each reaction process is calculated.By comparing the magnitude of activation energy,the difficulty of the reaction is explained.