| Grate-type waste incinerators are widely used in waste-to-energy(WTE)power plants in China,and the capacity accounts for 85%of the domestic WTE market share,and is expected to expand until 2030.The WTE industry in China has exploided in last twenty years,and the existing grate-type waste incinerator technologies are mainly imported and digested from abroad.These incinerators are composed of two parts,the moving-grate and the furnace.The differences in the structure of the grates and the furnaces lead to obvious variations in the combustion performances especially when MSW(Municipal Solid Waste)with different calorific values are used.In order to comprehensively investigate the relationship between the furnace structure and the calorific value of waste in the combustion process,this paper uses a new gas-solid two-fluid based CFD model of waste incineration and focus on the combustion process of the lower furnace of the waste incinerator.The computations are realized on ANSYS FLUENT platform.A series of simulations are performed with direct coupling of the solid-phase combustion of the solid bed and the over-bed gas-phase combustion of the furnace.The results are summarized as follows:1.Using an efficient gas-solid two fluid CFD model,a 750 t/d Hitachi furnace operating at MCR conditions were simulated,the gas and solid temperature distributions,the velocity distributions,he gas-solid phase compositions and the pollutant emission characteristics were obtained.The simulated results of the temperature in the first flue duct and the gas compositions of the flue gas at the exit are compared with the measured data of the incinerator to verify the accuracy of the model method.2.Using the verified CFD model,the effects of MSW residence time,primary air temperature,primary air patition and the excess air coefficient on combustion of the incinerator were simulated,and the Morris method was used to analyze the sensitivity of each parameter.Simulation analysis of Hitachi furnaces with changes in furnace structure parameters were performed.The results show that if the residence time of MSW on the grate is too long,the combustion zone will be shifted forward,and the phenomenon of high temperature sticking to the wall will appear in the flue duct.When the primary air temperature reaches 453 K,increases in the air temperature t will instead cause a substantial increase in the NOx content at the flue gas outlet.When the primary air patition ratios are 0.3/0.54/0.16,the temperature distribution in the furnace is reasonable,he degree of MSW burning is better.In order to ensure that the MS W in the furnace is fully burned and the flue gas meets the emission standard,the excess air coefficient should be kept between 1.55 and 1.65.When the inclined angle of the front arch is reduced from 25° to 20°,the release of volatile matter is more uniform,and the combustion position is more reasonable,which is beneficial to improve the high temperature sticking to the wall in the flue gas.When the rear arch angle increases from 42° to 46° the carbon residual of the slag increases from 0.57%to 1.84%.3.Simulation and analysis of the combustion performance of three widely used typical grate-type waste incinerators burning with different calorific values MSW are performed.The results show that when the Hitachi furnace and the Martin furnace are burning low calorific value MSW,the ignition position will lag,and fuel oil is need to support the wastes combustion;when the Sity-2000 furnace burns high calorific value MSW,the temperature of the front arch wall is high,and the MSW residence time,the primary air temperature and primary air patition ratios are adjusted to 1h,368K,0.05/0.25/0.5/0.2,respectively,which can effectively reduce the wall temperature of the front arch. |
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