Research On Chemical Looping Hydrogen Generation Using Pyrolysis Gas Of Waste Plastics As Fuel

CO₂ produced from the combustion of fossil fuels is the main greenhouse gas,and its massive emission has caused global warming,which has caused widespread concern in the world.It is urgent to develop efficient CO₂ emission reduction technology.H₂ is a clean fuel with high calorific value,has a good application prospect.Chemical looping hydrogen generation technology combines iron-steam reaction with CO₂ capture,which has simple structure and can produce high-purity hydrogen without CO₂ separation process with high energy consumption,and has a good application prospect.At present,chemical looping hydrogen generation technology mostly uses coal as solid fuel,but ignores plastic.Oxygen carrier is the core of chemical looping hydrogen generation.Iron-based oxygen carrier is one of the most suitable oxygen carriers for chemical looping hydrogen generation.Red mud is aluminum smelting waste,mainly includes Fe₂O₃ and Al₂O₃,Si O₂,which can be used to prepare cheap and efficient iron-based oxygen carriers.In this paper,two kinds of red mud-based oxygen carriers were prepared using extrusion pelletizing method.The reactivity,oxygen transfer characteristics,stability and interaction of active components of oxygen carriers in chemical looping hydrogen generation were compared and investigated,and the process parameters were optimized under the condition of fixed bed.The main work and conclusions are as follows:The reduction reactivity of pure red mud（RM）and CuO modified red mud（RM＿CuO）was compared.The results show that the reduction reactivity of RM＿CuO with all three gaseous fuels was higher than that of RM.The addition of CuO improves the intrinsic activity of the surface lattice oxygen of the oxygen carrier,and improves the bulk lattice oxygen migration ability of the oxygen carrier.In the water splitting reaction,the oxygen yield of both the reduced RM and RM＿CuO in the range of 600℃-800℃increases with the increase of temperature.The oxygen gain of RM is higher than RM＿CuO.The redox stability of the two oxygen carriers in the chemical looping hydrogen production reaction was investigated.When H₂ was used as the reducing gas,with the circulation,the oxygen gain in the water splitting stage of RM decreases obviously.This is because in the reduction stage,the reduction degree of RM is deep.As the number of cycles increases,the Fe ions in RM migrate to the surface of oxygen carrier to form an oxide shell layer of Fe,which makes it difficult for the active component to be completely oxidized.The oxygen gain of RM＿CuO remaines stable in the water splitting stage.The active component Cu Fe₅O₈ of RM＿CuO was reduced to Fe,Fe Cu₄ in the reduction stage,and re-oxidized to Cu Fe₅O₈ in the water splitting and oxidation stage.The continuous precipitation and re-oxidation process inhibit the sintering of RM＿CuO.In the circulation process,part of Cu migrates to the surface of the oxygen carrier,which slows down the migration of Fe ions and lead to more iron substances react with steam in the water splitting stage,so the oxygen gain of RM＿CuO is stable in water splitting reaction.When C₂H₄ was used as the reducing gas,the degree of RM reduction is lower and the migration rate of Ca ions is higher than that of Fe ions,forming a shell of calcium-containing material on the surface of the oxygen carrier,which makes active component difficult to completely regenerate.RM＿CuO shows a slight migration of Cu ions during the cycling process,which slows down the migration of Ca ions and Fe.The effects of fuel,steam and regenerative oxygen concentration on the oxygen transfer characteristics of RM＿CuO were investigated.Increasing the gas concentration can significantly increase the reaction rate of the oxygen carrier.The decrease of regenerative oxygen concentration decreases the oxidation rate of RM＿CuO,reduces the tendency of oxygen carrier sintering,and improves the redox stability.The reaction characteristics of RM＿CuO under fixed-bed conditions were investigated,the results show that the reduction of weight hourly space velocity（WHSV）would slow down the reaction rate and have no effect on the conversion rate.The decrease in WHSV increases the oxygen supply of RM＿CuO,thus increasing the fuel conversion,and improving the CO₂selectivity and reducing the carbon deposition of oxygen carrier during the reaction of RM＿CuO with C₂H₄.