Study On Biomass Chemical Looping Technologies Using Fe-Based Material As Oxygen Carrier

Chemical looping combustion?CLC?is considered as an innovative breakthrough in solving energy and environmental problems due to the characteristics of the inherent separation of CO₂.Biomass energy is the potential new energy to replace fossil energy,because it is resourceful,widely distributed,low pollution,carbon-neutral and so on.Chemical looping technologies using biomass as fuel are promising to cut carbon emission.Compared with other oxygen carriers?OCs?,Fe-based oxygen carriers have the advantages of low cost,environment friendly and abundant resource.The cost of the chemical looping processes using Fe-based materials as an oxygen carrier is relative low.However,the low reactivity and low oxygen transport capacity of Fe-based oxygen carriers restrict their largescale applications.To solve the above problems,the biomass chemical looping technologies were studied using Fe-based materials as OCs.The main research contents and conclusions as follows:?1?The kinetic analysis of agriculture residue pyrolysis was performed in a TGA.Compared with the one-step reaction model,the combined kinetics three-parallel-reaction?CK-TPR?model fitted the agricultural residue pyrolysis experimental better.The pyrolysis mechanism of hemicellulose maybe the combined effect of the Nucleation and Diffusion mechanism.Nucleation was the mechanism of cellulose pyrolysis.The mechanism of lignin was quite complex and possibly rendered as the combine effects of Nucleation,Diffusion,Geometrical contraction,and Power law.Reaction mechanisms for pseudo hemicelluloses,pseudo cellulose,pseudo lignin in CK-TPR model were f???=?1-??^1.6244?^-0.3371[-ln?1-??]^-0.0515,f???=?1-??^1.0597?^-0.6909[-ln?1-??]^0.9026 and f???=?1-??^2.9577?^-4.7719,respectively.?2?Based on minimization of Gibbs free energy,thermodynamic simulation analysis of biomass chemical looping gasification using Fe-based OC was performed.The carbon conversion increased with the oxygen supply coefficient???under the same temperature.When the reaction temperature at 860°C,the maximum gasification efficiency,85.13%,was achieved at ? = 0.7.Moreover,the carbon conversion increased with the presence of steam and CO₂,used as gasification mediums.The SB= 0.2-0.4 was suitable to obtain syngas at ? = 0.7,at the same time,the reaction temperature has a range of 700-750°C.The ratio of H₂/CO increased with the increasing molar ratio of steam to biomass?S/B?,but its decreased sharply with the increasing molar ratio of CO₂ to biomass?C/B?.Additionally,an increase in the reaction pressure has a negative influence on syngas production.?3?Based on the results of TGA,the reduction of iron ore in the CO/CO₂ atmosphere was divided into two stages.In the first stage,namely the reduction from Fe₂O₃ to Fe₃O₄,reduction mechanism of iron ore met the Nucleation well,while the reduction mechanism of iron ore was Geometrical contraction in the second stages,namely the reduction from Fe3O₄ to Fe O.The reduction mechanism of iron ore were expressed as f???=3?1-??[-ln?1-??]^2/3 and f???=3?1-??^2/3,respectively.The activation energies in the first and second stages were 49.53 k J/mol and 80.05 k J/mol,while the pre-exponential factors were 5.28s^-1 and 27.82 s^-1,respectively.?4?The biomass chemical looping gasfication experiments were conducted in a fluidized bed reactor using iron ore as OC.When the temperature of fuel reactor?FR?was 850°C,the maximum value,78.53%,was reached at ? = 0.9 without steam.When the temperature of fuel reactor?FR?was 850°C and ? = 0.7,the maximum value,77.21%,was observed with S/B = 0.4.The presence of metal oxides increased the reactivity of iron ore.The XRD results indicated that the metal oxdies promoted the reduction of iron ore.The reactivity of modified OCs decreased in the following order: Ni-iron ore > Cu-iron ore> Ce-iron ore> iron ore > Ca-iron ore.The Ni-iron ore exhibited high cyclic performance,the carbon conversion and the gasification efficiency was 89.53% and 74.54% after 10 cycles,respectively.The iron ore,Cu-iron ore,Ce-iron ore and Ca-iron ore exhibited varying degrees of sintering phenomenon after 10 cycles.?5?Chemical looping hydrogen?CLH?tests were conducted in a fluidized bed reactor using modified iron ore as OCs.The model biomass syngas was used as fuel.The carbon capture efficiency increased with the temperature of FR,and it decreased with the increased reduction time in FR.The hydrogen yield increased with increasing temperature of FR or the rising reduction time in FR,however,the hydrogen purity had an opposite tendency.After comprehensive analysis,it is concluded that the Ni-iron ore exbited the optimal performance for hydrogen production when the reduction time was 40 min with the temperature of FR 900°C.At the same time,the carbon capture efficiency,the hydrogen yield and hydrogen purity of Ni-iron ore were 83.29%,8.89 mmol/g and 99.02%,respectively.After 10 cycles,both Ce-iron ore and Cu-iron ore exhibited sintering phenomenon to a certain extent.?6?The biomass chemical looping combustion?CLC?tests with carbon capture using MFe₂O₄?M = Cu,Ni and Co?as OCs were carried out in a fludized bed reactor.Both carbon conversion and carbon capture efficiency increased with the increasing temperature.When the temperature was 850°C,the values of carbon conversion and carbon capture efficiency were 95.66% and 95.88%,93.53% and 94.04%,and 95.17% and 94.04% for CuFe₂O₄,CoFe₂O₄ and NiFe₂O₄,respectively.The reactivity of three OCs increased in the following order: NiFe₂O₄ < CoFe₂O₄ < CuFe₂O₄.The NiFe₂O₄ had an excellent catalyst performance.Both CuFe₂O₄ and Co Fe₂O₄ had high thermal stability and cyclic performance while the cyclic performance of Ni Fe₂O₄ decreased with the number of cycle due to sintering.