Study On Synergistic Thermal Treatment Characteristics And Typical Pollutant Fate Of Polyolefin Waste Plastics And Textile Dyeing Sludge

Textile dyeing sludge（TDS）is in urgent need of standardized treatment because of its toxic components such as dyes,additives and heavy metals.Thermochemical treatment including incineration,pyrolysis and other methods can quickly and thoroughly achieve waste volume reduction and energy recovery,has become the mainstream technology.However,the characteristics of low calorific value and high ash content of printing and dyeing sludge restrict the separate heat treatment process.Polyolefin waste plastics yield is huge,which has the characteristics of high volatile content,low ash content and high calorific value.Synergistic treatment can improve the heat treatment characteristics of sludge.In this thesis,TDS and polyene plastics were taken as the research object,and their thermal decomposition characteristics,interaction and typical pollution migration and transformation during heat treatment were studied under different atmosphere,which provided theoretical basis for pollution control of TDS and waste plastics co-disposal.The main conclusions are as follows:（1）The pyrolysis characteristics,pyrolysis products,reaction mechanism and pathway of two kinds of polyolefin plastics（syringe（SY）and medical bottle（MB））were analyzed by TG-FTIR and Py GC/MS under different heating rates in nitrogen atmosphere.The pyrolysis temperatures of SY and MB are 394.4 to 501℃and 417.9 to 517℃,respectively.The mean activation energies of SY and MB devolatilization are 246.5 and 268.51 K/mol,respectively.MB shows better pyrolysis performance,higher degradation rate and less residue.The most suitable reaction mechanism belongs to the geometric contraction model of SY pyrolysis（R2）and the nucleation and growth model of MB pyrolysis（A1.2）.The main pyrolysis products of SY are C4-C24 olefin and diolefin,and the main pyrolysis products of MB are C6-C41 alkanes and C8-C41 olefin,and the reaction pathways of the two plastics are analyzed.（2）The co-pyrolysis properties,synergistic mechanism and products of TDS,SY and MB were analyzed.The pyrolysis of polyolefin plastics with high calorific value and low ash content can make up for the poor pyrolysis performance of TDS.The synergistic mechanism mainly occurs in the range of 400-550℃.The best co pyrolysis performance and the lowest activation energy can be obtained by adding 10%SY or MB.CH4 and C-H emissions from pyrolysis increased,but CO2 emissions decreased.The interaction mechanism between them was obtained by the analysis of pyrolysis products.Co-pyrolysis produces more aliphatic hydrocarbons,alcohols and cyclic hydrocarbons,while reducing the yield of ether and furan.The addition of polyolefin plastics makes the micro surface particles of coke smaller and looser.（3）The（co-）combustion performance,gas emission and ash of TDS and two polyolefin plastics were quantified and characterized.The increase of PP and PE blending ratio improved the ignition,burnout and comprehensive combustion index.The two plastics have significant interaction with TDS in the range of 200-600℃.TDS pre ignites the combustion of plastics,which promotes the combustion of TDS.The CO combustion process leads to an increase in CO2 emissions,reducing the production of CH4,C-H and C=O.Calcium based minerals in plastics enhance sulfur fixation and reduce SO2 emission.When the addition of PE and PP increased from 10%to 50%,the activation energy of co-combustion decreased from 126.78 to 111.85 k J/mol and 133.71 to 79.91 k J/mol,respectively.The co-combustion reaction mechanism is well described by f（α）=（1-α）ⁿ model.With the addition of plastics,the reaction order decreases.The combustion synergy is optimized by artificial neural network,so as to jointly meet the multiple objectives of maximum energy production and minimum emission.（4）The effects of plastic type and temperature on the migration and transformation of heavy metals during the co-combustion/co-pyrolysis of TDS and SY and MB were investigated by tube furnace experiment and microwave digestion/ICP-OES experiment.The results showed that at 800℃,the addition of SY in air atmosphere reduced the residue rate of other heavy metals except Mn,and the addition of MB increased the residue rate of Cd.In N2 atmosphere,the addition of SY and MB led to the decrease of all heavy metal residue rates in varying degrees.Temperature has little effect on the residual rate of heavy metals Cr,Cu and Ni.The addition of plastics will have a small change on their residual rate.The residual rate of Cr,Cu and Ni remains at a high level,and most of Cr,Cu and Ni are still fixed in the bottom slag or coke.Driven by high temperature,the addition of SY increases the residual rate of Mn in the bottom slag.The increase of temperature leads to the decrease of Cd and Pb residual rates,and more volatilizes into fly ash and flue gas.The addition of plastic has little effect on the migration and transformation of Cd and Pb.However,the residual rates of Cd and Pb in nitrogen atmosphere are lower than those in air atmosphere,especially when the temperature exceeds800 With the increase of temperature,the residual rate of Zn decreases gradually,and the performance of nitrogen atmosphere is more obvious than that of air atmosphere.Under air condition,SY can transform Cd,Cu and Pb heavy metals into relatively stable states.Under the condition of nitrogen,MB can transform Cr,Mn and Zn into relatively stable states.SY can convert Cr,Mn,Pb and Zn to relatively stable states.