铁基载氧体深度还原动力学及其微观反应机理研究

Chemical looping combustion has emerged as a promising technology for power generation and instinctive CO2 separation, which becomes important in energy and environment field, and attracts much attention in thermo-chemical treatment of solid waste. The oxygen carriers are vital to chemical looping combustion, and iron based oxygen carriers are extensively used in chemical looping combustion, especially chemical looping hydrogen generation, due to the high-reavtivity, low-cost and environmentally-friendly properties. The iron oxide goes through multiple reaction stages when reduced by syngas, however, the reduction of the iron based oxygen carrier in normal chemical looping combustion is limited to the first reaction stage, which leads to the low conversion of oxygen carriers, large oxygen carrier circulation mass and the larger reactor scale. The further study on deep reduction mechanism and process of iron based oxygen carriers is significant in both theoretical understanding and practical application. The apparent kinetics of iron based oxygen carriers with different porosity will be investigated by micro-structural characterization methods and kinetic analysis. The coupling mechanism of the gas diffusion and the lattice oxygen transfer in oxygen carriers will be verified by comparing the apparent kinetics with the gas diffusion and lattice oxygen transfer dynamics. Based on the coupling mechanism, the gas-solid reaction models will be obtained by weighted average of different elemental models. The kinetics of different reaction stage in deep reduction of iron based oxygen carriers will be analyzed by the modes and the results help to design the deep reduction process of iron based oxygen carrier.

化学链燃烧是一种高效清洁的新型能源转化技术，已成为能源环境领域重要的研究方向，近年来在固体废弃物热化学处理领域引起关注。载氧体是化学链燃烧技术的关键，铁基载氧体因其反应活性较高、成本低廉且环境友好，被广泛用于化学链燃烧技术，特别是化学链制氢技术。由于铁基载氧体还原过程需要经历多步反应，而常规的化学链燃烧工艺中铁基载氧体还原仅局限于第一步反应，导致载氧体转化率低，造成载氧体循环量和反应器尺寸过大。因此，铁基载氧体深度还原机理及工艺研究具有重要的理论意义和实用价值。利用微结构表征手段和动力学实验，深入研究不同孔隙度铁基载氧体的表观动力学，并与气体扩散和晶格氧传递动力学进行对比，揭示铁基载氧体中气体扩散与晶格氧传递耦合机理。基于耦合机理，采用加权平均的方式，由不同模型组合成气固反应动力学模型，并以此为基础对深度还原各反应阶段分别进行解析，获得相应动力学参数，为铁基载氧体深度还原工艺设计提供依据。

本研究在铁基载氧体深度还原的背景下，研究载氧体颗粒内部气体扩散与晶格氧传递耦合机理，探讨了在深度还原中Fe2O3在CO、H2和CO-H2中的还原动力学行为，Fe2O3→Fe3O4和Fe3O4→FeO均是相界面反应，而FeO→Fe是成核核增长反应和扩散反应交替控制。气固反应动力学机理模型及模型构建方式和铁基载氧体各反应阶段的解耦，三阶段Fe2O3→Fe3O4, Fe3O4→FeO和FeO→Fe的活化能分别为34.92±1.24, 70.13±0.88和44.12±1.44 kJ/mol。最终构建出各反应阶段的气固反应动力学模型，铁基载氧体在固定床内被还原时存在三个空间分离、独立移动的反应前沿，即Fe2O3-Fe3O4、Fe3O4-FeO、FeO-Fe，获得铁基载氧体深度还原各反应阶段的动力学数据，并发现了一个新的反应工程学基本参数—融合温度Tm，为铁基载氧体深度还原工艺中反应器的设计和分析提供保障。