Study On Co-combustion Technology Of Municipal Sewage Sludge And Municipal Solid Waste

Municipal sewage sludge（MSS）is a solid product produced in the process of wastewater treatment.It is one of the solid wastes that need to be disposed urgently due to its high annual output and great harm.In the construction of waste-free city,waste disposal adheres to the principle of"reduction,harmless and reutilization".The traditional treatment technologies of MSS such as sanitary landfill,land use and separate incineration disposal all have some disadvantages.It has been unable to meet the current demand for efficient resource treatment of waste,so the collaborative incineration（combustion）of MSS mixed with municipal solid waste（MSW）is more in line with the development trend of waste disposal at the present stage.For this reason,this paper takes MSS,MSW and their mixed samples as the research object,to explore the best process conditions of co-combustion of MSS and MSW through the comprehensive study of their physical and chemical properties,laboratory combustion experimental simulation and industrial tests.The specific research contents are as follows:（1）Based on the analysis of the physical and chemical properties of MSS and MSW,it is found that the nitrogen and sulfur content of MSS are higher than that of MSW,and the calorific value of mixed samples decreases with the increase of MSS moisture content and mixing ratio.when the mixing ratio of MSS is less than 30%,the calorific value of the mixed sample can meet the combustion limit condition（≥5000 k J/kg）..（2）The thermogravimetric analysis was used to analyze the thermal weight loss,combustion characteristics and synergistic effect of MSS,MSW and their mixtures.The results showed that the combustion of MSS,MSW and their mixtures can be divided into three stages:water precipitation（<180℃）,volatiles release and combustion（180-550℃）,inorganic matter and coke combustion（550-700℃）.The comprehensive combustion characteristic index of MSW is better than that of MSS.when a small percentage of MSS（the proportion is less than 10%）is mixed with MSW,the comprehensive combustion characteristic index is almost the same as that of MSW alone.There is a synergistic effect between the co-combustion of MSS and MSW,and the effect is most obvious when the mixing ratio is 90%MSW/10%MSS.The combustion kinetic parameters and reaction mechanism were explored by using four models KAS,OFW,Starink and FM.The results showed that the activation energy required by volatiles release and combustion stage decreased,with the increased of MSS mixing ratio,and that required by coke and inorganic combustion stage increased.The master diagram method was used to analyze the reaction mechanism,and it is found that the mechanism function is of[（1-α）^-2-1]/2 in the volatiles release and combustion stage of MSS combustion process,while the mechanism functionα^3/4 is appropriated of the burnt out stage of coke.In the volatiles release and combustion stage of MSW combustion process,the mechanism function is expressed as[（1-α）^-2-1]/2,and the burnout stage is1/（1-α）²,In the co-combustion process,the combustion mechanism function is the same as that of MSW combustion alone.（3）The combustion characteristics of MSS,MSW and their mixtures under different conditions were analyzed by the tube furnace built in laboratory.The results show that the yield of MSW combustion residue is lower than that of MSS under all combustion temperatures（750℃,800℃,850℃,900℃）.At a higher temperature combustion,the NO and SO₂ produced from MSS is lower,but at 900℃,the NO production of MSW is the highest.Meanwhile,when the moisture content of MSS is 10%,The emissions of pollutants（NO and SO₂）are lower under all MSS addition percentage（5%,10%,15%）.Therefore,considering low pollutant emissions,low energy consumption,and MSS reduction,it is preferred to select combustion temperature of 850℃,both moisture content and mixing ratio of 10%of MSS for co-combustion process.Moreover,the increase in air equivalent ratio makes the co-combustion more complete.（4）In order to explore the effects of different MSS mixing ratio and moisture content on the synergistic incineration process and pollutant emission characteristics,the industrial test was carried out by using a single-line 600t/d-scale MSW grate incinerator.The results show that co-combusion with mixing ratio of 6%and 8.6%of semi-dried MSS（30%-35%moisture content）has little effect on the evaporation,furnace temperature,slag thermal reduction rate and other operating parameters in the incineration system,which meets the requirements of environmental protection.Also,there is no significant change in the content of CO and NOx in flue gas,but the content of SO₂ increases,resulting in an increase in the amount of lime slurry.When the MSS mixing ratio is 8.6%,the content of SO₂ instantly rises to the critical value.Therefore,in the co-combusion process,the MSS mixing ratio should be controlled below 8.6%.In view of the analysis of economic and environmental benefits,when the moisture content of the MSS was 35%in the co-processing of MSS in MSW incineration power plants,and its mixing ratio can reach 8.6%.