Studies On Combustion Characteristics And Gaseous Pollutants Emission Of Municipal Sludge Co-conditioned By Fe²⁺/S₂O₈^2- And Furfural Residue

The treatment of municipal sewage sludge（MSS）is a particular challenge and can pose serious environmental risks due to its high levels of organic matter,heavy metal contaminants and toxin content.Sludge incineration,as a relatively environmentally friendly and efficient method for the treatment and disposal of municipal sewage sludge,can recover energy to a certain extent,but it needs conditioning to solve the problems of high moisture content and low calorific value of municipal sewage sludge.In this paper,ferrous ion activated persulfate(Fe²⁺/S₂O₈^2-)combined with furfural residue was used to conditioning municipal sludge.The effects of furfural residue mixture ratio and heating rate on the combustion characteristics and combustion dynamics of the mixed fuel were analyzed by thermogravimetry（TG）,and Design-Expert 12 was used to optimize the experimental parameters.The flue gas analyzer was used to monitor the emission of gaseous pollutants in the combustion process of mixed fuel in real time.The influences of furfural residue mixture ratio,combustion temperature and air flow rate on pollutant emission were analyzed,and the three influencing factors were fitted and optimized.The main weight loss of Fe²⁺/S₂O₈^2-combined furfural residue conditioning municipal sludge samples in the combustion process is concentrated in volatile combustion and fixed carbon combustion stage.When the proportion of furfural residue in the sample increases,the absolute value of DTG curve peak value increases first and then decreases,ignition temperature（T_i）increases,burnout temperature（T_b）decreases,and flammability index（C）and comprehensive combustion index（CCI）showed a trend of first increase and then decrease.As the heating rate increases,the ignition temperature（T_i）increases,the burnout temperature（T_b）decreases,and the flammability index（C）and composite combustion index（CCI）increase.The actual and theoretical weight loss difference（?TG）of Fe²⁺/S₂O₈^2-combined furfural residue conditioning sludge indicates that there is a certain interaction between furfural residue and Fe²⁺/S₂O₈^2-alone conditioning sludge,and it is relatively obvious in the high temperature region.The flammability index（C）and comprehensive combustion index（CCI）were used to evaluate the combustion performance of Fe²⁺/S₂O₈^2-alone conditioning sludge,furfural residue and Fe²⁺/S₂O₈^2-combined furfural residue conditioning municipal sludge samples,and the apparent activation energy（E_m）of the samples was calculated by coats-Redfern integral method.Furfural residues can significantly improve the flammability index and comprehensive combustion index of samples.The E_m of Fe²⁺/S₂O₈^2-combined with furfural residue conditioning municipal sludge was lower than that of furfural residue combustion alone.Design-expert 12 was used to optimize experimental parameters,and the optimized experimental parameters and experimental results are as follows:When the mixture ratio of furfural residues was 10%and the heating rate was 50K/min,the maximum flammability index（C）was 15.603×10^-5%?℃^-2?8)4)9)^-1.The maximum combustion index（CCI）was 51.868×10^-8%²?℃^-3?8)4)9)^-2,and the minimum apparent activation energy（E_m）was 27.884 k J/mol.In the combustion process of municipal sludge samples prepared by Fe²⁺/S₂O₈^2-combined with furfural residue,as the proportion of furfural residue increases,the NO_Xemission decreases slightly first and then increases.When the combustion temperature increases,the amount of NO_X produced also increases.As the air velocity increases,NO_Xemission increases rapidly at first and then flattens out.The emission characteristics of SO₂are as follows:when the proportion of furfural residue increases,SO₂ emission decreases;as the combustion temperature increases,part of the sulfate is decomposed at high temperature,and SO₂ emission increases;as the air flow rate increases,SO₂ emission increases at first and then flattens out.XRD analysis of the ash of the samples showed that the proportion of furfural residue increases,the sulfur mineral phase in ash decreased.When the incineration temperature rises,the sulfur compounds in the ash decompose and the characteristic peak of silicate increases.As the air flow increases,the main components in ash have little influence,while Na₆Ca₂Al₆Si₆O₂₄（SO₄）₂ decreases,and the peak intensity of Na Al Si₃O₈ increases.The optimum experimental conditions obtained by design-Expert 12 are as follows:furfural residue mixing ratio was 15.93%,combustion temperature was 800℃,air flow rate was 1L/min;The predicted minimum NO_X emission was 1.048mg/g,and the minimum SO₂ emission was 25.476mg/g.