Study On Mechanism Of Ash Regulating Oxygen Carrier Structure To Improve Attrition Resistance

Chemical looping combustion technology has the advantage of capturing carbon dioxide at low cost.It is an important means to effectively deal with global warming and achieve the goal of"2030 carbon peak and 2060 carbon neutralization".Oxygen carrier is the key of chemical looping combustion technology.Due to the fluidization cycle in fuel reactor and oxidation reactor,oxygen carrier is impacted by mechanical,thermal and chemical stress,causes serious attrition phenomenon.This working condition causes the problems of short service life and poor oxygen release performance for oxygen carriers in long cycle,which limits the popularization and application of chemical looping combustion technology.Poor toughness is the root cause of oxygen carrier attrition.Enhancing structural toughness is the key to improve attrition resistance.Biomass ash contains inert components and a small amount of alkali metals,which interact with oxygen carrier,and has the potential to enhance the structure of oxygen carriers by combine.The effects of three kinds of ash on the properties of red mud oxygen carrier were studied in this thesis.Through fluidized bed and thermogravimetric experiments,combined with particle characterization analysis,the effects of corn straw,rape straw and bagasse ash on the attrition characteristics and reaction activity of oxygen carriers were studied.The phenomenon of fiber reinforced skeleton was found,and the formation mechanism was discussed.Finally,the method of using biomass ash to enhance the structural toughness of oxygen carrier is proposed,which is described as follows:Firstly,three kinds of biomass ash are selected,which are rich in K and Si alone or together,with significant component differences.The effects of ash type,binding temperature and ash content on the red mud oxygen carrier were studied.According to the actual temperature difference between the two reactors,exploring the bonding temperatures at 800℃,850℃,900℃and 950℃.The effect of ash content on the modified oxygen carrier for ash rich in Si and K was studied,and the group distribution ratio was optimized.The combination of ash and oxygen carrier was identified by FESEM-EDS to verify the effectiveness of the sample.Secondly,through the fluidized bed experiment,15 chemical looping cycle reactions are simulated,the ash-modified oxygen carrier is tested.Base on the flue gas analyzing online,fluidization reactivity for the oxygen carrier is evaluated.It is found that the activity of oxygen carriers is generally improved by modifying from K-rich ash,and the Si component was deposited into a stable inert structure and inhibits the reaction.K.Si synergism makes the oxygen carrier more sensitive to ash content and bonding temperature.CSA-800 and CSA-900-2.5%activity remained good.The fluidization reaction samples were collected to characterize the particle properties to evaluate the attrition characteristics.It is found that the modified oxygen carrier rich in Si and K ash has low attrition rate,good particle size retention and high hardness,appears good macro attrition resistance.The structural stability of oxygen carriers prepared by directly adding K-rich or Si rich ash is poor,indicating that the improvement effect may come from the synergistic effect of Si and K.Then,the reactivity of the oxygen carrier was tested by fixed bed thermogravimetric analysis,to analyzed the reason that the poor fluidization reaction from the oxygen carrier.It is found that there is activity inhibition in the initial stage of fresh ash-modified oxygen carrier,which proves the ash deposition.The initial inhibition of K-rich ash modified oxygen carrier disappears rapidly,reflecting the poor stability of the sedimentary layer.Si rich ash causes stable attenuation of performance and remains after 15 fluidization reactions.It is speculated that a stable inert structure is formed.Finally,the skeleton characteristics were obtained by XRF,FESEM-EDS and XRD to identify the binding region between ash and oxygen carrier.After the reaction,it is found that there are plastic tearing edges in the oxygen carrier modified by K-rich ash,and the Si rich ash forms a stable and dense layer.In particular,there are fibers structure in the oxygen carrier modified by Si and K ash,and the morphology of fiber bridging and crack closure was observed,which is a typical fiber toughening phenomenon.Based on the comprehensive characterization results,it is speculated that the fiber is related to the structure of KNa₃（Al Si O₄）₄,which reduces the research scope to construct oxygen carrier fiber skeleton with ash.