Combustion characteristics and numerical simulation of sludge coal water slurry fired by double cone combustor

In order to promote the utilization of municipal sludge,and further to solve the secondary pollution problem in sludge physical disposal and the high cost problem of sludge drying combustion in traditional way,a technical idea of preparing sludge-coal-water slurry by mixing sludge slurry with pulverized coal,and using the central reverse injection double cone burner with enhanced combustion function was proposed.The combustion characteristics of pulverized coal,coal water slurry and sludge coal water slurry were analyzed by thermogravimetric analysis experiments.The combustion characteristics of sludge coal water slurry in double-cone burner were studied by numerical simulation.The feasibility of sludge coal water slurry application in double-cone burner was studied by reducing secondary air,increasing secondary air swirl intensity and secondary air temperature. The comparison of basic combustion characteristics of sludge-coal-water slurry shows that the moisture content in sludge-coal-water slurry exceeds 35%,and the fuel calorific value,water evaporation and heat absorption are the key factors affecting the ignition and burnout of sludge-coal-water slurry combustion process.Due to the presence of water,the initial ignition temperature of CWS is 11.3 ℃ higher than that of coal powder,and the burnout temperature is 13.6 ℃ lower than that of pulverized coal.The maximum heat absorption rate is 0. 504 k W/kg,accounting for 56. 05% of the maximum heat release rate of CWS,and the total heat absorption is 1.917 MJ/kg,accounting for 9.94% of the combustion heat.When 20% sludge is mixed,the initial ignition temperature of sludge CWS is 12.3 ℃ higher than that of CWS,and the burnout temperature is 59.1 ℃ lower than that of CWS.The heat absorbed by water evaporation is 0.546 k W/kg,which is 8.4% higher than that of coal water slurry combustion,and the total heat released is 16.88 MJ/kg,which is 12.5% lower than that of coal water slurry combustion.In this paper,a double-DPM Discrete-Phase numerical simulation model is used to fully consider the influence of water evaporation during sludge CWS combustion,and the numerical simulation of sludge CWS combustion is closer to the actual results.The simulation results of sludge CWS combustion in 14 MW doublecone burner show that the existing double-cone burner can not achieve stable combustion of sludge CWS,only can burn sludge CWS with water concentration of ca.25%,which is not existed in actual form. When the concentration of water in sludge CWS increases from 0 to35%,the average temperature of burner outlet decreases by 7.95 ℃ and the average temperature of burner interior decreases by 7.69 ℃with the increase of 1% water concentration.The average temperature of burner interior decreases by 269 ℃ and the average temperature of burner outlet decreases by 278 ℃,when the concentration of water is 35%.The combustion of sludge CWS in a double cone burner can be realized by reducing secondary air flow,increasing secondary swirl intensity and increasing secondary air temperature.When the swirl intensity of secondary air changes from 1 to 2,the average temperature of burner outlet increases by 20 ℃.When the secondary air volume decreases to 0.6 of theoretical air,the average temperature of burner outlet increases by 203 ℃.The average temperature of burner outlet increases by 289 ℃,it is basically close to the burning condition when the burner burns pulverized coal.After comprehensive application,the double-cone combustor can realize the stable combustion of sludge CWS.