Investigation On Co-thermal Charateristic Of Textile Dying Sludge And Waste Tea And The Migration And Transformation Behavior Of Heavy Metals

The composition of textile dyeing sludge（TDS）is more complex,more pollutants,and more cost to deal with it.Combustion technology can quickly and thoroughly reduce the capacity and amount of sludge,and also recover energy,which can use for power generation and heating.This treatment has gradually become one of the best treatment methods with great development potential and prospects.The characteristics of textile dyeing sludge is high moisture content,low calorific value and high ash content,which leads to its unstable burning process,incomplete reaction and lar ge amount of energy consumption.Waste tea（WT）has the characteristics of high volatile content,high calorific value,low ash content and large output,and it can improve the combustion performance of TDS.At the same time,a large number of heavy metals and other toxic and harmful substances will be discharg ed in the process of incineration,which restricts the use of combustion technology.This paper investigates the co-combustion characteristics of textile dyeing sludge and waste tea,and the transfer and transformation of heavy metals in the combustion process.（1）Thermogravimetric analysis（TGA）was used to investigate the combustion characteristics of WT at different heating rates and different combustion atmospheres.The results show that the combustion process of WT in N₂/O₂ and CO₂/O₂ atmosphere consists of three stages,and the temperature of the main stage is 200～600°C.With the increase of the heating rate,the combustion parameters of tea leaves T_i,T_p,T_b,-R_pC_i,C_b,D_v and S increase obviously.The combustion parameters of WT in N₂/O₂atmosphere are larger than that in CO₂/O₂ atmosphere.The activation energy of combustion of WT in N₂/O₂ atmosphere is higher than that in CO₂/O₂atmosphere.H₂O,CH₄,CO,CO₂,NH₃,HCN are the main gases released during combustion process.（2）Thermogravimetric-Fourier transform infrared spectrometry（TG-FTIR）and pyrolysis gas chromatography-mass spectrometry（Py-GC/MS）were used to analyze the thermal decomposition kinetics and products of WT at N₂ atmosphere.The results show that the pyrolysis process of tea leaves can be divided into three stages.The average E values of the three sub-stages were 161.81,193.19 and 224.99 k J/mol,respectively.The decomposition mechanism of three sub-stages corresponding modelThe content of main gaseous products during pyrolysis as flowing:CO₂>C=O>Phenol>CH₄>C-O>NH₃>H₂O>CO.According to the Py-GC/MS,the products released during the rapid pyrolysis process include olefin,acid,benzene,furan,ketone,phenol,nitride,alcohol,aldehyde,alkane and ester.（3）Thermogravimetric mass spectrometry（TG-MS）,principal component analysis（PCA）and interaction are using to study the co-combustion characteristic of TDS and WT at different blending ratio.The results show that the main stages of mass loss increased from 36.66%to 63.41%with the increase of the blending ratio.Accoding to the comprehensive combustion performance parameters（CCI）,adding WT can promote the TDS burning.The average E value of the blends reached the minimum（154.82 k J/mol）when add 40%WT.The micro-morphology of the ash of the blands is larger,coarser and looser than that TDS.During the combustion process,the emission of NH₃,HCN,NO,CO₂,NO₂ and SO₂ is mainly between 200°C and600°C co-combustion can inhibit and reduce SO₂ emissions.（4）The migration and transformation of heavy metals at different blends ratio and different temperatures was investigated by tubular furnace experiment and thermodynamic simulation calculation.The results showed that the residual rate of Cu increased slightly with the increase of the ratio.The residual rates of Zn,Ni and Cr increased first and then decreased with the increase of the rati o of WT.The addition of WT can inhibit the volatilization of heavy metal As but promote the volatilization of Cd.With the increase of the proportion of WT,the proportion of the acids extractable state,the reducible state and the oxidizable state of Cu decreased.For Zn,Ni and Cr,the chemical form in the bottom ash is basically the residue state.For Mn,co-combustion will make the stability of chemical morphology of Mn in bottom slag worse,however,will promote the transformation of As and Cd from in stability to stable chemical morphology.The results of thermodynamic simulation show that with the increase of the blends ratio,the Zn,Cu,Mn and As have little influence,and the Cd and Pb gradually changes into the gaseous form.The heavy metals residual rate of Cu,Zn,Ni and Cr did not change significantly with temperature increasing.With the temperature increasing,Cr,Pb and As volatilize to fly ash or flue gas.The main forms of Cu,Ni,Cr and Pb are oxidizable states,which gradually change to stable residue state with the increase of temperature.The main forms of Zn,Mn and Cd are acid extractable states,whi ch are relatively harmful to the environment.As the temperature rises,they gradually change to stable residue states.For As,the temperature rise will lead to the transformation of As in the ash into unstable chemical form,which will gradually increase the harm to the environment.Thermodynamic equilibrium simulation show that the existence forms of Cu,Zn,Mn and As did not change,while the stability of Ni and Cr decreased slightly with the increase of temperature.Temperature has the greatest effect on Cd and Pb residual rates.