Abstract:

The reactivity of oxygen carriers is curial for biomass chemical looping gasification (CLG) process. Two kinds of manganese-iron composite oxygen carriers of MnFeO₃ and MnFe₂O₄ were synthesized by sol-gel combustion method. Though the in situ infrared, CLG experiments with straw were carried out. It indicated that the ferromanganese composite oxides accelerated the release rate of pyrolysis products and enhanced the yield of CO and CO₂, which promoted the carbon conversion efficiency. Further tests in fix-bed were to prove the feasibility of MnFeO₃ and MnFe₂O₄ and the influence by coupling with steam. It showed that components of H₂ and CO in syngas could be improved significantly by introducing steam and the gasification efficiency for MnFeO₃ and MnFe₂O₄ was 94.49% and 92.76% individually. The XRD analysis demonstrated that MnFeO₃ and MnFe₂O₄ transformed to a combination of (Fe, Mn)O during the reduction process and both of them exhibit recyclable crystalline phase variation. Moreover, multiple redox tests showed MnFe₂O₄ exhibited a decreasing tendency of gasification efficiency because of agglomeration, its typical surface morphology changed from scattered particles to blocky structure. However, MnFeO₃ formed a granular porous structure which helped to maintain a stable reactivity. Thus, MnFeO₃ was considered to have better applicability in CLG process.

Key words: biomass, gasification, syngas, ferromanganese composite oxygen carriers, chemical looping

摘要：

通过溶胶凝胶燃烧法合成了MnFeO₃和MnFe₂O₄两种锰铁复合氧载体。通过原位红外实验探究其与稻草的化学链气化过程，发现其加速了稻草热解产物的析出，并通过气化反应促进CO和CO₂的产生，提高了碳转化率。固定床实验结果表明MnFeO₃和MnFe₂O₄在与水蒸气耦合气化的条件下大幅提高了合成气中H₂和CO的产率，气化效率分别达到94.49%和92.76%。并通过XRD分析，发现MnFeO₃和MnFe₂O₄在气化过程主要还原为(Fe,Mn)O，且在氧化反应后能回到初始晶相。在固定床的10次循环实验以及SEM的结果表明，MnFeO₃在循环反应中逐渐形成的颗粒状多孔结构有利于维持稳定的气化效率，而MnFe₂O₄由于团聚和烧结作用形成了块状结构，气化效率呈缓慢下降趋势。因此，认为MnFeO₃在生物质化学链气化中具有更好的适用性。

关键词: 生物质, 气化, 合成气, 锰铁复合氧载体, 化学链