Experiments On Chemical-looping Gasification Of Corn Straw Based On Bimetal Oxygen Carrier

In recent decades,the non-renewable fossil energy consumption and the environmental problems caused by it,more and more research teams are devoted to the research of renewable energy.Among all alternative energy sources,biomass is recognized as an effective alternative energy source that can meet global energy needs.Biomass is mainly composed of elements of carbon,hydrogen and oxygen and has high energy.Biomass chemical looping gasification(CLG),as a relatively new gasification technology,uses lattice oxygen in the oxygen carrier to replace pure oxygen.It has the advantages of high economy and large development and utilization potential.It is the current research on biomass conversion and utilization.One of the key points is also an important direction for the development of renewable energy technologies.In this paper,corn straw are selected as the research object.Based on the kinetic reaction mechanism of the chemical looping gasification of corn straw,active metals are added to modify the iron-based composite oxygen carrier,which is combined into a bimetal oxygen carrier.The microscopic characterization of the experimental device and oxygen carrier is more suitable for metal ions combined with iron base,and reveals the gasification reaction characteristics of synthesis gas based on the chemical looping gasification of corn straw under the steam atmosphere of bimetal oxygen carrier.The chemical-looping gasification kinetics of corn straw with iron-based oxygen carrier to produce syngas were studied using thermogravimetric analysis.The main reactions of corn straw based on iron-based composite oxygen carrier is divided into three stages:the pyrolysis stage(200-500℃),the gas-solid reaction stage(500-700℃),and the solid-solid reaction stage(700-1100℃).The Coats-Redfern method and the Malek method were used to screen the thirty reactions.Through calculation and analysis,the activation energy and possible mechanism of the most suitable main reaction region are respectively to be 81.6 kJ/mol(Random nucleation and subsequent growth),117.5 kJ/mol(Chemical reaction),and 140.9 kJ/mol(Three-dimensional diffusion).The chemical-looping gasification of corn straw with Fe-based oxygen carrier involved multi-step reaction mechanismsAccording to the analysis results of the kinetic reaction mechanism,different metals(Ni,Cu,K,Mg,Zn)were added to the iron-based composite oxygen carrier to construct a bimetal oxygen carrier and investigate the effect on the chemical looping gasification of corn straw.It shows that the oxygen carrier(Fe-Ni),oxygen carrier(Fe-K)and biomass show better activity and lower residue on the thermogravimetric analyzer.Oxygen carrier(Fe-Ni)has a good performance in fixed bed reactor with other oxygen carriers.It is achieved under the condition that the reactant is corn straw and the reaction conditions are:temperature 850℃ and steam flow rate 0.75mL/min The hydrogen concentration is 46.48%,the gas production rate is 1.46L/g,H2/CO is 2.21,and the carbon conversion rate is 87.95%.Examining the microstructure of the surface of the oxygen carrier(Fe-Ni),it was found that the surface of the oxygen carrier(Fe-Ni)showed good spikes,which was beneficial to the lattice oxygen exchange with the reactantsFinally,the oxygen carrier(Fe-Ni)was used to investigate the gasification characteristics of syngas produced by chemical looping gasification of corn straw under steam atmosphere.Based on the analysis of the equation of gasification equilibrium reaction,the effects of factors such as the temperature of the gasification reactor,the flow rate of the gasified water vapor and the mass ratio of oxygen carrier to corn straw on the synthesis gas were investigated through a fixed bed experiment.The results show that there are multiple valence states during the reaction of Fe element.Fe3O4 tends to be generated during the reaction.Metal Ni can generate elemental Ni in a series of redox reactions.Higher temperature(900℃)is more conducive to syngas generation.At a water vapor flow rate of 1 mL/min,syngas exhibits better quality and carbon conversion.At a mass ratio of 1:1 and under optimal conditions(900℃,1 mL/min),the hydrogen concentration was 51.48%,the gas production rate was 1.71 L/g,the H2/CO was 2.72,and the carbon conversion rate was 93.61%.