Study On Emission Characteristics Of Dioxins From Iron Ore Sintering Co-treating MSW Incineration Fly Ash

For decades,due to the rapid development of urban and rural areas,waste incineration power generation has gradually become the main way of waste treatment,and its by-product fly ash,as a kind of hazardous waste,contains dioxins and heavy metals.In2020,the output of fly ash in China exceeded 7 million tons.How to reduce and recycle municipal solid waste incineration fly ash（MSWI fly ash）has become a difficult problem at present.In this paper,the MSWI fly ash of a grate in Shanghai was taken as the research object,and the sintering process was simulated by high-temperature tube furnace and sinter pot in the laboratory to explore the possibility of the disposal of MSWI fly ash in high-temperature sintering process.The basic characteristics of materials,the influence of fly ash addition on dioxin emission characteristics,the evolution characteristics of dioxin fingerprint and the possible inhibition methods in the cooperative disposal process were systematically carried out,which provided some conclusions with practical guiding value for co-disposal of MSWI fly ash by sintering.The main contents and results of this study are shown below:（1）The basic physical and chemical characteristics and chemical composition of fly ash and sintered raw material used in the project are studied.The results show that the main component element of fly ash used in the experiment is Ca,accounting for more than 40%.The main crystal compositions in fly ash are Ca（OH）₂,Na Cl,Ca CO₃,KCl,etc.The main crystal compositions in washed fly ash are Ca CO₃,Ca SO₄,Ca（OH）₂.The morphology of fly ash and washed fly ash is irregular,and the particles of washed fly ash are finer.Leaching of Cu and Zn increased after washing,and the PH values of leaching solution were 11.84 and 11.28,respectively.The average particle size of mixed iron ore is 3.56mm,TFe content is 60.69%,Si O₂content is 4.37%,LOI is 4.93%.The concentration of dioxin in sintered raw material is 168.0 pg/g,and that in fly ash and washed fly ash is 1174.7 pg/g and 1156.2 pg/g,respectively.The concentration of dioxin in fly ash is much higher than that in sintered raw material.After conversion to toxic equivalent concentration,The toxic equivalent concentrations of sintered raw material,fly ash and washed fly ash were 66.9,114.5 and 124.2 pg I-TEQ/g,respectively.（2）The tube furnace was used to simulate the sintering process,and the influence of fly ash addition on dioxin emission was explored.As a whole,the toxic equivalent concentration of dioxin in tail flue gas shows an increasing trend with the increase of adding proportion.When the adding proportion of washing fly ash is 2%,the maximum value is 3.8 ng I-TEQ/Nm³.When the adding proportion of washing fly ash is 5%,the toxic equivalent concentration of dioxin shows a decreasing trend.OCDD,Hx CDF and Hp CDF were the three homolog with the highest proportion.The proportion of dioxins under heptachloride in PCDDs increased with the increase of the addition proportion of washing fly ash,and PCDFs were on the increase first,and then as the addition proportion of washing fly ash increased,PCDFs decreased accordingly.There was no obvious distinction in the distribution of dioxin homologues before and after water washing,and the proportion order of dioxin homologues was not changed by water washing,but only the concentration of dioxin homologues was changed.（3）The sintering pot was used to simulate the sintering process in a more realistic way to carry out experimental research on the cooperative disposal of waste incineration fly ash.The basic characteristics of sintering products were analyzed.The results show that when the proportion of washed fly ash is less than 2 wt.%,the indexes of sintered products will not be affected obviously,but when the proportion is 5 wt.%,the indexes of sintered products will decrease obviously.The generation data of 136 PCDD/Fs in 8 flue gas samples were analyzed,it was found that the addition of washed fly ash enhanced the chlorination effect onβpositions（2,3,7,8）,and the more the fly ash was added,the more the signal of highly chlorinated dioxins was enhanced.The evolution of the fingerprint characteristics of dioxins with the addition of washing fly ash was explored.In order to reveal the specific generation path of dioxins in the process of incineration of waste incineration in the cooperative disposal of sintering,special attention was paid to the path of pyrolytic recombination and polymerization of chlorophenol precursors to generate homologues.（4）A possible new dioxin inhibition method--adjusting sintering raw material ratio was tried to determine the best sintering raw material ratio and dioxin emission characteristics of tail smoke,and the theory of inhibition was discussed.The results showed that improved quicklime showed a better dioxin inhibition effect.Under the flux ratio of 5wt.%Ca O+3 wt.%Ca CO₃,the inhibition efficiency of dioxin reached 92.7%,and the inhibition efficiency of high-chlorinated dioxin was higher than that of low-chlorinated dioxin.