Experimental And Simulation On Flue Gas Cleaning And Temperature Based On MSW And Biomass Co-combustion

Co-combustion of municipal solid waste(MSW) and biomass can solve the problem of some MSW incineration plants which existing insufficient amount of MSW and low heating value. However, MSW and biomass co-combustion will impact on incinerator operation condition and flue gas pollutant concentration. In view of that, experimental studied on incinerator operation condition, flue gas pollutant concentration, flue gas cleaning effect after MSW and biomass co-combustion, and simulated on the characteristics of furnace temperature distribution and flue gas flow and the flue gas cooling process in reacting tower and cooling tower, which based on a MSW incineration plant in Jiangsu province in this thesis. The research results not only provide technical support of operation management of MSW and biomass co-combustion project, but also help to control the flue gas pollutants of this type projects.The effect of performance parameters and co-combustion on furnace temperature, the effect of co-combustion on furnace efficiency, and the effect of co-combustion and furnace temperature on flue gas pollutant concentration were studied based on in-situ tests. The significant effect of performance parameters on furnace temperature were the primary air temperature, the primary air rate and the excess air ratio, and it will rise with the increase of biomass adding amount. Through studied the affecting factors of furnace temperature was helpful to improve it condition which was affected by fluctuation of waste calorific value, and reduced the organic pollutants which generated from MSW combustion. The rated operation condition of incinerator was reached when the bamboo and rape blended ratio was15%and13%, thermal efficiency of furnace increased from69.7%to76.13%,76.37%. The increasing amplitude of boiler efficiency reached6.43%and6.67%,respectively, and reached the design efficiency. It was improved the energy efficiency greatly. Ecergy efficiency which analyzed energy efficiency from the perspective of energy quality. Ecergy efficiency of furnace was increased from28.95%to36.17%,35.93%, and the increasing amplitude of it reached7.22%and7.98%,respectively. The increasing amplitude of ecergy efficiency of furnace is greater than the thermal efficiency of furnace, indicating that co-combustion of biomass mainly to improve the energy quality of fuel. After co-combustion,except that the concentration of HCl, NOx was increasing caused by higher furnace temperature, the concentrations of CO, fly ash, SO2in flue gas were decreasing. With the increase of furnace temperature, the concentration of HCl would decrease at first and the increase afterwards, the concentrations of CO and SO2would decrease, the concentration of NOx would increase, and the concentration of fly ash had no significant relationship with it.The results showed that too high and too low of furnace temperature was not conductive to control pollutants generating.Temperature distribution and flue gas flow in furnace had significantly effect on heat transfer and pollutants controlling. In view of this, numerical simulated on flue gas flow and combustion in furnace by FLUENT. Drying process of waste on pusher was simulated by tracking moving-interfaces method, which gained the change characteristic of surface temperature of waste as boundary conditions. By simulated of moving and heat transfer processing of waste on grate, the characteristics of surface temperature, water evaporation and volatile element precipitation of it were gained as input value. The results showed that the flue gas temperature reached the highest value at furnace throat, and it was lower at front wall region ans higher at back wall region, and tended to uniform in the second passage. The highest flue gas temperature increased almost100℃after mixed combustion, and consistent with the actual situation. The flue gas flow in furnace was not uniform, and it was stronger at back wall region and weaker at front wall region. Due to the sudden shift of flue gas flow caused a bigger back flow, which made the flue gas flow weaker at front wall region and stronger at back wall region in second flow passage. The flue gas flow became more uneven after second air added, and it was bad for pollutants removal.At the bamboo and rape blended ratio was15%and13%, the effect of operation parameters of semi-dry circulating fluidized bed was researched, and found that the operation parameters had significantly effect on concentration of acid gas. The research results can guide controlling the concentration of acid gas and improving the utilization of hydrated lime. The effect of flue gas purification system on removing acids had achieved the optimum state when the furnace temperature is900℃～950℃, the Ca(OH)2feeding rate is160kg/h, the flue gas temperature is155℃～160℃, the flue gas flow rate is36000Nm3/h and the water spray flow rate is0.8t/h～1.0t/h.For flue gas purification process, the gas temperature uniformity had some impacted on the effect of acid gas removal and the operating condition of bag filter. The uneven distribution of flue gas temperature was not conductive to acid gas removal, and was prior to damage bag filter. In view of this, the flue gas cooling in reacting tower and cooling tower were researched by numerical simulation. The flue gas temperature in cooling tower varies from230℃,220℃,210℃,200℃to170℃respectively, and the flue gas temperature tended to stable at4.1m,5.8m,6.5m,8m high; The flue gas temperature in reacting tower varies from170℃,160℃to150℃respectively, and the flue gas temperature tended to stable at7.9m, 9m high. The research results showed that gas temperature tended to be uniform in two towers, and had not adversely effect on acid gas removal and bag filer's operation.The findings of this study is useful for application of MSW and biomass co-combustion and flue gas pollutant controllable.