Reaction Characteristics Of Hyperaccumulator Processing By Chemical Looping Technology Using Lean Iron Ore As Oxygen Carrier

Chemical looping combustion（CLC）is a kind of efficient and clean energy conversion technology by using oxygen carriers transport lattice oxygen to fuels which fuel and air have no direct contact,not only can realize the gradient utilization of energy but can realize the capture of CO₂.Chemical looping gasification（CLG）is a kind of technology which controls the ratio of oxygen carriers and fuels to obtain the gasification products.With the wide application of phytoextraction for controlling soil heavy metal pollution,how to safely dispose hyperaccumulators has been an important issue.The rate of utilization of natural lean iron ore which has a low iron content is low due to the restrictions of technological level and smelting cost.In order to realize the resourceful utilization of lean iron ore and hyperaccumulators,the chemical looping technology was applied in the treatment of hyperaccumulators,which uses natural lean iron ore as oxygen carriers.The experimental results of the ryegrass in the thermogravimetric analyzer indicates that the ryegrass gasification process had three degradation peaks,the degradation peak at high temperature was due to the ryegrass char gasification in the presence of lean iron ore,supporting the feasibility of lean iron ore as oxygen carriers for chemical looping technology.Subsequently,experiment of chemical looping gasification with lean iron ore as oxygen carriers were carried out.The results indicated that the lean iron ore significantly promotes the gasification effect.Compared with SiO₂ as bed material,the application of lean iron ore significantly promotes the carbon conversion rate,heating value of syngas and gas production rate.The effects of gasification temperature,steam content and O/C molar ratio on gasification characteristics were investigated.The optimized conditions were presented as follows:the temperature was850℃,the water flow was 0.495g/min,the O/C molar ratio was 0.5.Under these conditions,it was found that the average concentration of H₂ was 52.04%and carbon conversion rate was51.40%.10 redox tests demonstrated that lean iron ore has a good cyclic stability.Volatilization rate of copper and zinc can increase with the rise of temperature,and the volatilization rate of zinc is higher that of copper.The purpose of treating ryegrass with chemical looping gasification is to obtain gasification products to realize the resourceful utilization of ryegrass,and the purpose of treating ryegrass by chemical looping combustion is to obtain high concentration of CO₂.The experiment of chemical looping combustion was carried out with lean iron ore as oxygen carriers.The effects of temperature and steam flow on the chemical looping combustion characteristics were investigated.The results show that the optimum reaction conditions were950℃,steam flow rate of 0.330g/min.Under the optimum reaction conditions,90.29%of CO₂concentration and 83.96%of carbon conversion rate were achieved.Moreover,lean iron ore had a good stability during the 10 redox tests,and the CO₂ concentration was above 80%.The increase of the reaction temperature promotes the volatilization rate of copper and zinc greatly,and the volatilization rate of copper and zinc at 950℃are 49.55%and 79.10%,respectively.Lean iron ore was decorated by alkali metal potassium to promote the reactivity of oxygen carriers through impregnation method.The experimental study on the chemical looping combustion of ryegrass was carried out,and the effects of alkali metal potassium,temperature and steam flow on the combustion characteristics of CLC were investigated.Compared with natural lean iron ore,the addition of potassium can significantly promote the reactivity of oxygen carrier.When the temperature was 950℃and the amount of water flow rate was0.330g/min,89.18%of CO₂ concentration and 90.72%of carbon conversion rate was achieved.The analysis of XRD and XRF shows that the alkali metal K react with lean iron ore to form stable K_xFe_yO_z,enhancing the reaction between fuel and iron ore,and there is no obvious loss of K of the decorated iron ore during cycles.The content of heavy metals in the residue after the reaction was measured.The results show that the increase of temperature promotes the volatilization rate of copper and zinc,resulting in more heavy metals volatilizing into the flue gases.The analysis of EDS shows that lean iron ore can adsorb a certain amount of zinc.