Research On Chemical Looping Gasification Coupled With Pyrolysis Of Refuse Derived Fuel

With the development of society and the improvement of people’s living standards,the output of municipal solid waste is also increasing year by year.The disposal of solid waste is getting more and more attention.As a means of thermal disposal,gasification solves the problems of dioxins,nitrogen oxides and sulfides generated in the traditional incineration process,and is an important means of reducing the quantity of domestic waste and recycling resources.The traditional gasification process has the problems of low gasification efficiency and high maintenance cost.Chemical-looping gasification technology uses oxygen carrier as gasification medium,which avoids the reduction of calorific value of syngas caused by the introduction of a large amount of nitrogen,and also saves the maintenance cost of pure oxygen preparation equipment.At present,most of the research on chemical-looping gasification focuses on coal and biomass,while the research on chemical-looping gasification of MSW and its derived fuels is relatively scarce,the study on the reaction mechanism of chemical-looping gasification process is also insufficient.In view of the above deficiencies and the characteristics of complex components and uneven particle size of refuse derived fuel,a two-stage coupled pyrolysis and gasification chemical-looping gasification model was proposed in this paper.In order to understand the basic characteristics of chemical-looping gasification of refuse derived fuel and solve the problem of too high tar content,the reaction mechanism between tar and oxygen carrier was studied in depth,so as to provide a feasible reference way for clean and efficient treatment of MSW.In this paper,the basic characteristics of the chemical-looping gasification of refuse-derived fuel were studied by using a two-stage pyrolysis and gasification coupled chemical-looping gasification model with Fe₂O₃ as oxygen carrier and refuse-derived fuel as raw material.The effects of the amount of oxygen carrier,reaction temperature and mixing mode on chemical-looping gasification were investigated.The results show that the addition of oxygen carrier significantly improves the gas production rate of the gasification process,and the two-stage gasification method has a better gasification effect,which is about 32.8%higher than the uniform mixing and tiling method.The gas production rate increases with the increase of temperature,and the calorific value of syngas can reach 12.12 MJ/m³ at 850℃.When Fe₂O₃/C=0.15,the system has the best gas production rate.In the study,it is found that Fe₂O₃ as oxygen carrier has low gasification selectivity,high proportion of CO₂ in gas production,poor circulation,easy sintering and other problems.In view of these deficiencies,the Ca-Fe composite oxygen carrier Ca₂Fe₂O₅ was prepared by combustion method in this paper,and the reactivity and cycling performance of the composite oxygen carrier were tested.It is found that when Ca₂Fe₂O₅ is used as oxygen carrier,the CO₂ content in syngas is reduced due to CaO carbonation,and the presence of alkali earth metals can catalyze tar cracking to further improve the gas production rate.Using composite oxygen carrier,gasification efficiency and carbon conversion rate are increased to 70.3%and 89.5%,respectively.It was found that the Ca-Fe composite oxygen carrier maintained good circularity in the number of cycles by testing the cycling performance of the oxygen carrier.Finally,the reaction mechanism between tar and oxygen carrier was studied by using toluene as the model of tar.The pyrolysis of toluene mainly has two ways:one is to produce benzene free radical and methyl free radical,the second is to produce benzene methyl free radical and hydrogen free radical.Reaction with oxygen carriers can be divided into three main stages:lattice oxygen sufficient.What happens is complete oxidation,where only CO₂ is produced;When the lattice oxygen is insufficient,toluene can only be partially oxidized,and CO component appears in the product.When the metal is exposed,toluene dehydrogenates carbon on the metal surface,and H₂and CH₄ dominate the gas production at this stage.