NiFeAlO4载氧体制备及煤化学链燃烧反应特性

铁基载氧体是一种具有工业应用前景的载氧体,但存在氧利用率低、在高温下易烧结等问题。虽可通过制备双金属复合载氧体或添加惰性组分改进其性能,但均存在一定缺陷。若将活性组分和惰性材料融入到一个晶体结构制备尖晶石结构载氧体,则可实现利用双金属协同作用提高载氧体活性的同时,利用Al3+提高载氧体的稳定性。采用共沉淀法和溶胶凝胶法制备了具有尖晶石结构的NiFeAlO₄载氧体,考察了制备方法、载氧体与煤质量比对NiFeAlO₄载氧体化学链燃烧特性和循环稳定性的影响,并分析了载氧体对煤转化过程的作用。结果表明,溶胶凝胶法制备的NiFeAlO₄载氧体具有更好的反应性,载氧体与煤质量比为20∶1时,碳转化率为86.7%,远高于煤单独热解时的碳转化率(34%),此时CO₂体积分数为93.6%。对反应前后NiFeAlO₄载氧体晶相结构和形貌进行分析,表明循环过程中经“还原-氧化”后生成的NiO和载氧体颗粒团聚是导致载氧体活性下降的主要原因。相较于载热作用,NiFeAlO₄载氧体在煤化学链燃烧中主要起供氧作用,其不仅会促进挥发分向煤气的转化,且NiFeAlO₄载氧体与焦炭之间也存在固-固反应,利于更多CO₂的生成。

Synthesis of NiFeAlO4 oxygen carrier and its coal chemical looping combustion performance

Fe-based oxygen carrier is regarded as a promising industrial oxygen carrier,but there are some problems of low oxygen utiliza?tion rate and easy sintering at high temperatures.Although the performance of Fe-based oxygen carriers can be improved by preparing bi?metallic composite oxygen carriers or adding inert components,there are certain defects.If the active components and inert materials can be integrated into a crystal structure to prepare oxygen carrier with spinel structure,the synergistic effect of bimetal can be used to improve the activity performance of oxygen carrier while Al3+is employed to improve the stability of oxygen carrier.The NiFeAlO₄ oxygen carrier with spinel structure were synthesized via co-precipitation method and sol-gel method.The effects of preparation method and mass ratio(oxy?gen carrier to coal)on the coal chemical looping combustion reaction and cycling stability of the NiFeAlO₄ oxygen carrier were experimen?tally investigated.The function of oxygen carrier in coal conversion was also studied.The results show that NiFeAlO₄ oxygen carrier synthe?sized by sol-gel method possesses superior reactivity.When the mass ratio between oxygen carrier and coal was 20∶1,the carbon conver?sion is 86.7%,which is higher than that of coal pyrolysis(34%),and the CO₂ relative concentration is 93.6%.The analysis of the crystal structure and morphology of NiFeAlO₄ oxygen carrier before and after the reaction shows that the NiO detected after 10th redox cycle and the grain agglomeration are the main reason for the decrease of its cyclic stability.Compared to its heating supply function,NiFeAlO₄ oxy?gen carrier mainly plays the role of oxygen supply in coal chemical looping combustion,which not only promotes the conversion of vola?tile matter to coal gas,but also has solid-solid reaction between NiFeAlO₄ oxygen carrier and coke,and is conducive to the generation of more CO₂.