Study On Heavy Metals Migration Behaviors Of Municipal Solid Waste Typical Components Under Oxy-fuel Combustion

The harmless,volume reduction and resource disposal of municipal solid waste have always been an important part of the construction of ecological civilization.The 14th Five-Year Plan shows that China is striving to achieve carbon neutral by 2060.Combine the incineration of municipal solid waste with oxy-fuel combustion technical advantages can achieve large-scale carbon emission reductions.Oxy-fuel combustion technology uses high-purity oxygen instead of combustion-supporting air,and at the same time assists with the combustion technology of flue gas circulation,it can obtain up to 80%of the volume concentration of CO₂ flue gas,which is one of the very promising carbon dioxide capture technology and get attention by research scholars.In view of the complex composition of municipal solid waste and the unusually complex behavior of heavy metals of municipal solid waste incineration,the goal is to explore the migration and transformation of heavy metals in the oxy-fuel combustion of municipal solid waste,and to find efficient heavy metal control methods of this process.Research on the migration and transformation of heavy metals under combustion,and at the same time study the control methods of heavy metals applicable to the process.First,select the largest component of municipal solid waste food waste and organic chlorine source PVC as research object,study the volatilization of heavy metals of food waste under air atmosphere and O₂/CO₂ combustion conditions,and compare the effects of different combustion conditions in air atmosphere and O₂/CO₂ atmosphere on the volatilization of heavy metals in food waste,and find that the content of heavy metals in food waste is Cr>Zn>Cd,and the order in PVC is Zn>Cr>Cd.The higher the burning temperature of food waste and PVC,the higher the volatilization rate of Cd,Cr and Zn.The volatilization of Zn in PVC is affected by temperature higher than that of food waste.Using CO₂/O₂ atmosphere instead of N₂/O₂atmosphere can reduce the volatilization rate of Cd and Cr to a certain extent,but on the contrary increase the volatilization rate of Zn.Combustion temperature and PVC addition have significant effects on volatilization of Cd,Cr and Zn.With the increase of PVC added to the food waste,the content of Zn in the combustion ash decreases;the addition of 5%PVC in the food waste reduces the volatilization rate of Cr,but the addition of 15%PVC leads to higher volatile.The volatilization of Cr and Zn is highly affected by the ratio of CO₂/O₂,while the volatilization of Cd is not significantly affected by the ratio of CO₂/O₂.The volatilization rate of Zn in 70CO₂/30O₂ atmosphere is much lower than in 85CO₂/15O₂ and 80CO₂/20O₂atmosphere.Secondly,the modified and unmodified calcium-based adsorbents were used to conduct experiments on the adsorption of heavy metals in food waste combustion under O₂/CO₂atmosphere to explore the heavy metal adsorption performance of different calcium-based adsorbents in air and oxygen-enriched combustion atmospheres.The element content of the combustion bottom ash is Al>Cr>Zn.Increasing the furnace temperature is conducive to the fixation of Al in the bottom ash,but it increases the volatilization of zinc.The adsorption capacity of adsorbents for heavy metals is mainly affected by the type of metal.Natural and modified CaO has better adsorption performance for aluminum,while CaCO₃ has poor adsorption performance for aluminum,the content of Al in combustion ash of adding 5wt%CaO-10%Na₂CO₃ and CaCO₃-10%Na₂CO₃ sorbent were 158.309 and 76.4548?g/g,respectively.Neither CaCO₃ nor CaO can be used as adsorbents for Cr.The CO₂/O₂ ratio has a greater impact on the adsorption of Cr and Zn,but has a smaller impact on the adsorption of Al.Lowering the CO₂/O₂ ratio is beneficial to the adsorption of Cr and Zn.Then,calcium oxide was used as a conditioning agent to study the distribution of heavy metals in the oxy-fuel combustion of food waste.In the tube furnace,the calcium oxide conditioning agent,the addition amount of the conditioning agent,the combustion temperature,and the ratio of oxy-fuel combustion CO₂/O₂ were explored.The influence of oxy-fuel combustion on the form of heavy metals.Zn in the bottom ash after the burning of food waste samples mainly exists in an unstable state.The addition of CaO conditioner reduces the weak acid extraction state and the reducible state presents an upward trend.The addition of CaO conditioner reduces the weak acid extraction state of Al in the combustion bottom ash,but at the same time increases the reducible state and the oxidizable state.The addition of CaO conditioner reduces the weak acid extraction state and reducible state of Cr.Changing the combustion atmosphere from 80N₂/20O₂ to 80 CO₂/20O₂ can convert the reducible state of Al in the bottom ash to an oxidizable state,greatly reducing the weak acid extraction state of Cr in the bottom ash,but the effect on Zn is not obvious.The increase of the O₂ ratio in the CO₂/O₂atmosphere is not conducive to the conversion of the heavy metal elements in the bottom ash of food waste combustion by the CaO conditioner to a stable state.Finally,study the thermal weight loss characteristics of food waste and food waste blended with HTC pretreatment and dechlorination of PVC,and its combustion process.The evolution characteristics and evolution behavior of gas products.The food waste combustion process is divided into three stages,and there are five stages in the PVC combustion process of food waste mixed with HTC treatment.The first stage of food waste combustion(50?-423.2?)is the thermal decomposition of the protein,polysaccharides and most of the lipids,cellulose,hemicellulose and lignin contained in the food waste.The second stage(423.2?-558.5?)comes from the decomposition and combustion of fats and bones that are difficult to burn in food waste.The third stage(558.5?-1000?)is the decomposition of hard-to-decompose shellfish in food waste.PVC treated by HTC reduces its ignition temperature and apparent activation energy,but also reduces its comprehensive combustion index,which shows that HTC pretreatment will reduce the combustion performance of PVC.The order of absorption peak intensity from high to low is FW combustion,FW-PVC260,FW-PVC200,FW-PVC,FW pyrolysis.Compared with FW-PVC and FW-PVC200,FW-PVC260 has the highest C-H,C=O,C=C absorption peak,the highest CO and the lowest HCl emission.The research results contributes to the understanding of the migration and transformation of heavy metals in the process of oxy-fuel combustion of municipal solid waste,and provide effective information for the control of heavy metals during waste incineration in the future,especially for the control of heavy metals in the process of co-combustion of food waste and PVC and provide a new idea for the harmless treatment of municipal solid waste and carbon emission reduction.