【作者】 张曦；

【导师】 刘方；

【作者基本信息】 中国矿业大学 ， 动力工程及工程热物理， 2022， 硕士

【摘要】 化学链燃烧技术具有低成本捕集二氧化碳的优势,是有效应对全球气候变暖,实现“2030碳达峰、2060碳中和”目标的重要手段。载氧体是化学链燃烧技术的关键,由于流态化循环于燃料反应器和氧化反应器,受到机械、热、化学应力冲击,存在严重的磨损现象,造成寿命短、长周期释氧性能差的问题,限制了化学链燃烧技术的推广应用。韧性差是载氧体磨损的根源,增强结构韧性是提升耐磨性的关键。生物灰含有惰性组分及少量碱金属,存在与载氧体相互作用的现象,具有形成载氧体增强结构的潜力。通过流化床、热重等实验,结合颗粒表征分析,研究了玉米秸秆灰、油菜秸秆灰、甘蔗渣灰对载氧体磨损特性和反应活性的影响,发现了纤维生成增韧骨架的现象,并讨论了形成机理,提出了利用生物质灰增强载氧体结构韧性的方法,分述如下:首先,选取3种生物质灰,单独或同时富含K和Si,具有显著的组分差异。通过机械混合煅烧,制备灰改性载氧体,研究灰类型、结合温度、灰负载量对赤泥载氧体的影响。根据实际双反应器的温差情况,研究800℃、850℃、900℃、950℃温度对结合的影响。讨论负载量对富Si、K灰改性载氧体的影响,优化组分配比。联用FESEM-EDS表征手段,鉴定灰与载氧体结合,验证了样品有效性。其次,通过流化床实验,模拟15次化学链循环反应,测试灰改性载氧体,在线分析烟气,评价流态化反应活性。发现富K灰改性载氧体活性普遍提升,Si组分沉积为稳定惰性结构并抑制反应进行。K、Si协同作用导致载氧体对灰负载量与结合温度更敏感。CSA-800和CSA-900-2.5%活性保持良好。收集流态化反应样品,表征颗粒结构物性,评价磨损特性。发现富Si、K灰改性载氧体磨损率较低、粒度保持较好、硬度较高,具有良好的宏观耐磨表现。直接添加富K或Si灰制备载氧体,结构稳定性较差,表明提升效果可能来自Si、K协同作用。然后,通过固定床热重分析,测试载氧体本身的反应活性,分析载氧体流化反应差的原因。发现新鲜灰改性载氧体初期均存在活性抑制,证明了灰沉积。富K灰改性载氧体的初期抑制快速消失,反映出沉积层的稳定性较差。富Si灰造成性能稳定衰减,15次流态化反应后仍保持,推测形成稳定的惰性结构。最后,通过XRF、FESEM-EDS、XRD测试,获得骨架特征,聚类并鉴定灰与载氧体的结合区域。反应后,发现富K灰改性载氧体存在塑性撕裂棱,富Si灰形成稳定致密层。特别地,发现富Si、K灰改性载氧体存在的纤维结构,观测到纤维联桥、裂纹闭合的形貌,是典型的纤维增韧现象。综合表征结果,推测纤维与KNa₃（Al Si O₄）₄结构相关,缩小了灰构建载氧体纤维骨架的研究范围。更多还原

【Abstract】 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.更多还原