Study On Attrition Characteristics And Fragmentation Mechanism Of Iron-based Oxygen Carrier In Chemical Looping Process

Chemical looping combustion is a clean energy technology with the characteristics of CO₂ internal separation.The oxygen carrier is used as the carrier for the transfer of lattice oxygen and heat to achieve the purpose of capturing CO₂ with low energy consumption,which has broad application prospects and potential.However,the attrition behavior greatly shortens the operating life of the oxygen carrier particles,and the attrition phenomenon in the fluidized bed reactor cannot be avoided,which seriously hinders the commercial operation of the chemical looping combustion technology.In view of the attrition phenomenon of oxygen carriers,Fe₂O₃/Al₂O₃oxygen carriers were calcined at the temperature of 1300℃,1400℃and 1500℃and iron-based oxygen carriers calcined at the temperature of 1250℃with Al₂O₃ Fiber were manufactured by mechanical mixing method.The fluidization attrition test of oxygen carriers and iron-based oxygen carriers with Al₂O₃ Fiber were carried out in a fluidized bed reactor,and the fluidized attrition characteristics and attrition mechanism of Fe₂O₃/Al₂O₃ oxygen carrier in fluidized bed and the toughening mechanism of iron-based oxygen carrier with Al₂O₃ Fiber were studied.In the research on the fluidization attrition characteristics of oxygen carrier,the attrition law of fluidized oxygen carrier was deeply analyzed.The fluidized bed attrition experiments of cold,heat and reactive state were cleverly designed and carried out.It was found that the attrition rate of the same oxygen carrier obeyed the law of cold state<heat state<reactive state.After the 60^th cycle in the reactive state experiments,the attrition rates of oxygen carriers at calcination temperatures of 1300°C,1400°C and1500°C were 0.65wt.%/h,0.1 wt.%/h and 0.13 wt.%/h,respectively.Combined with the oxygen transport capacity,it can be seen that the oxygen carrier with the calcination temperature of 1400℃has the best comprehensive performance.Combined with the analysis of the fitting parameters of the Gwyn kinetic equation,the particle size distribution of the oxygen carriers before and after the reaction was studied.It was determined that the oxygen carrier in the cold and hot attrition experiments mainly suffered abrasion,while the attrition the oxygen carriers in the reactive experiments suffered from a mixed attrition mechanism dominated by bulk fracture.The contribution rate of mechanical stress,thermal stress and chemical reaction stress to the attrition of the oxygen carrier was quantitatively analyzed for the first time.It was found that in the early stage of the cycle reactions,the mechanical stress and thermal stress contributed more to its attrition rate,while in the middle and later stages of the cycle,the chemical stress gradually increased the proportion of particle attrition,and completely dominated in the later period.In the exploration of the attrition mechanism of oxygen carrier,the attrition mechanism and fragmentation process of the oxygen carrier in the reactive state were elucidated.Combined with the macroscopic attrition rate analysis of the oxygen carrier,the oxygen carriers in the reactive state were sampled and characterized in stages,and the relationship between the evolution of the mechanical strength and the attrition rate of the oxygen carrier during the reaction was analyzed.In most cases,it was found that the greater the mechanical strength of the oxygen carrier,the smaller the attrition rate,which had a certain correlation.It was found that the chemical reaction promotes the initiation and propagation of surface cracks on the oxygen carrier by means of Scanning Electron Microscopy,and makes its structure loose and porous.Combined with other characterization results,it can be concluded that under the synergistic effect of the pore-enlarging effect of the oxygen carriers in the reduction stage and the formation of an iron-rich layer on the surface during the oxidation process,and the mechanical collision of the oxygen carrier in the reactor,the internal support structure of oxygen carriers was severely damaged.In a word,In the combined action of chemical reaction as internal cause and mechanical collision as external cause,the oxygen carriers suffered from attrition and fragmentation.In the research on the toughening mechanism of Al₂O₃ fiber,a scheme of fiber toughening iron ore particles was proposed.The iron-based oxygen carrier and iron-based oxygen carrier with aluminum fiber were subjected to attrition experiments and mechanical strength tests,and it was found that aluminum fibers can significantly improve the mechanical strength and attrition resistance of the particles.Combined with the Scanning Electron Microscope observation,the cracks on the surface of the iron-based oxygen carrier with aluminum fibers appeared deflected,bifurcated and passivated.The expansion of cracks was hindered by fibers,which consumed the energy of expansion.Further research showed that aluminum fibers had a good toughening effect on iron ore particles.There are 62 figures,12 tables and 131 references in this thesis.