Study On Synergistic Thermal Treatment Characteristics And Cl/S Transformation Mechanism Of Textile Dyeing Sludge And Spent Mushroom Substrate

Textile dyeing sludge（TDS）usually contains large amount of hazardous components,such as heavy metals and organic substances,and it urgently needs to be treated in a safe and effective way.The synergistic thermal treatment method of sludge and biomass is one of the effective ways to achieve the recycling and harmlessness of sludge.The physicochemical characteristics of biomass and thermal treatment technique will directly affect the treatment efficiency of sludge.As a kind of abundant agricultural biomass waste,spent mushroom substrate（SMS）contains a large amount of organic substances,such as cellulose,hemicellulose and lignin,indicated its high potential in thermal treatment.This paper mainly investigated the thermal decomposition characteristics and the transformation characteristics of Cl/S during co-combustion/co-pyrolysis of TDS and SMS.The results may provide guideline for their practical industrial application.The main research contents are as follows:（1）Thermogravimetric analysis（TGA）was used to study the thermal decomposition characteristics of SMS under different heating rates and reaction atmospheres（air,N₂,and CO₂）.The results showed that the release and combustion of voatiles was the main decomposition stage during the combustion of SMS in air atmosphere,in which 54.53%of mass loss occurred.The increasing heating rate promoted the combustion process of SMS to the higher-temperature region,and it significantly increased the weight loss rate,ignition,burnout,flammability,and comprehensive combustion characteristic index.The maximum weight loss rates in air,N₂,and CO₂were 12.68,13.0,and 12.6%/min at 20℃/min,respectively.At low temperature region,the thermal decomposition performance was similar in N₂ and CO₂.The weight loss rate in CO₂ atmosphere increased significantly at above750℃ due to the gasification reaction of SMS.Multiple model-free methods were used to evaluate the kinetic behaviors of SMS during the combustion or pyrolysis process.Taking the Flynn-Wall-Ozawa（FWO）method as an example,the average activation energy in air,N₂,and CO₂ atmospheres were 171.49,214.30,and 211.64 k J/mol,respectively.The results showed that the average activation energy of combustion was lower than that of pyrolysis.thermogravimetric/mass spectrometry（TG-MS）and thermogravimetric/Fourier transform infrared spectrometry（TG-FTIR）were used to monitor the generation of gaseous products during the combustion process of SMS.The results showed that most of air pollutants generated in devolatlization and fixed carbon combustion stage.The order of the emission intensity of nitrogen compounds was:NH₃>NO>NO₂.Only a small amount of SO₂ was released.The results of pyrolysis–gas chromatography/mass spectrometry（Py-GC/MS）experiments indicated that aliphatic hydrocarbons,aromatic hydrocarbons,phenols and some nitrogen-containing compounds were the major components of pyrolytic oil at 800℃.（2）The effects of blending ratio and temperature on combustion performance,interaction effect and flue gas emission during the co-combustion of TDS and SMS were studied by TGA and TG-MS experiments.The results showed that the the increasing blending ratio of SMS improved the ignition,burnout and comprehensive combustion characteristics index of the mixtures,and the significant interaction occurred between350-600℃.The average activation energy reached the lowest value with 40%SMS added.The three-dimensional diffusion model could best describe the kinetic behavior of TDS,SMS and their blend during devolatilization stage.When TDS was co-combusted with SMS,the emissions of NH₃ and NO₂ increased slightly,while SO₂dropped significantly.（3）Co-pyrolysis characteristics and the interactions between TDS and SMS were studied by TGA.The results showed that the maximum weight loss rates of TDS and SMS occurred at the inorganics decomposition and devolatilization stage,respectively.The promotion effect between TDS and SMS was more obvious in high temperature region.Biochar was obtained from tube furnace pyrolysis experiments.The effects of pyrolysis temperature and SMS on the surface characteristics of biochar were investigated by some surface analytical techniques,such as X-ray photoelectron spectroscopy（XPS）,Scanning electron microscopy（SEM）,and FTIR.The results showed that the addition of SMS improved the melting effect on biochar surface.High temperature promoted the formation of quaternary-N and the decomposition of sulfate on the biochar surface,while SMS promoted the formation of nitrogen oxides and the fixation of sulfur during co-pyrolysis,resulting in an increase in the relative content of sulfate on the surface.SMS promoted the generation of aromatic compounds and reduced the relative content of nitrogen compounds and acidic substances in pyrolysis oil.（4）TG-FTIR and tube furnance combustion experiments were conducted to study the migration and transformation characteristics of Cl and S during the co-combustion of TDS and SMS and CaO.The results showed that the release of HCl,SO₂,COS and H₂S mainly occurred at devolatilization stage.When temperature rose from 600 to 1000℃,the content of Cl and S in ash of TDS decreased from 0.27 to 0.09%and 3.95%to 0.10%,while the SO₂mass emission rose from 104.27 mg/g to 153.41 mg/g.The Cl content was bascically stable in ash at above 700℃.With the fraction of SMS increased from 0%to 50%,the Cl content in ash increased from 0.09%to 0.13%at 1000℃,while CaO had little effect on Cl distribution in ash.It indicated that the interaction between TDS and SMS promoted Cl volatilization at high temperature.The conversion rate and emissions of SO₂ in flue gas are inversely proportional to the blending ratio of SMS and CaO.The higher the addition ratio,the lower the conversion rate and emissions.When co-combusted with 50%SMS at 800℃,the SO₂ conversion rate reached the minimum value of 74.48%and the S fixation rate in ash was 21.22%.The S fixation rates were lower than 5%at above 900℃.The emission of SO₂reached the lowest value（48.05 mg/g）when TDS were co-combusted with 50%SMS at900℃.In TDS-CaO co-combustion system,SO₂ conversion rate increased with the increasing temperature.When temperature increased from 800 to 1000℃,the S content in ash dropped from 5.22%to 1.04%with 7%CaO added.Temperautre affected the S fixation efficiency of CaO critically.