铁基化学链燃烧载氧体特性试验

论文总字数：29041字

摘 要

本文以Fe₂O₃为活性载氧体，在小型单流化床反应器上开展了不同惰性载体对化学链制氢性能的影响研究。利用机械混合法制备了基于Al₂O₃、SiO₂、MgAl₂O₄、ZrO₂和YSZ等五种载体的铁基载氧体，其中惰性载体占比为40wt%；在900℃下进行了CO还原、水蒸气氧化及空气氧化10次循环实验，并对反应前后的载氧体进行了SEM、XRD表征分析。实验结果表明：惰性载体的抗烧结性能及其化学反应活性会严重影响载氧体的反应活性和稳定性；以MgAl₂O₄和YSZ为惰性载体时，其反应活性先增加随后趋于稳定，而以ZrO₂、Al₂O₃和SiO₂为惰性载体时，其反应活性逐渐降低并趋于稳定。经过四次循环，各载氧体活性达到相对稳定状态，此时其反应活性由大到小排序为MgAl₂O₄gt; ZrO₂gt; YSZgt; Al₂O₃gt; SiO₂。SEM及XRD表征结果显示：10次循环后，MgAl₂O₄为惰性载体的铁基载氧体仍保持较好的孔隙结构，且Fe₂O₃与惰性载体之间没有发生化学反应；而以SiO₂为惰性载体的铁基载氧体出现了严重的烧结，增加了反应气体的内扩散阻力，造成反应活性的下降，且在反应后的载氧体中发现了FeSiO₃，使得活性氧化物减少，载氧体活性进一步降低。

此外，本文还探究了不同的载氧体制备工艺对化学链制氢性能的影响。分别采用机械混合法、共沉淀法及浸渍法，制取了基于Al₂O₃惰性载体的铁基载氧体，并在900℃下进行了7次循环实验。实验结果表明：相比机械混合法，共沉淀法制得的物料在反应后出现了严重烧结，使得反应活性迅速下降；机械混合法较共沉淀法具有更好的反应活性和稳定性。浸渍法得到的载氧体在循环后也出现了烧结现象，但出现了大孔结构，反应气体易扩散至载氧体表层的Fe₂O₃中，使得浸渍法得到的载氧体活性较稳定，但基于浸渍法本身的特征，其不适于负载大量活性载体，载氧能力较小，限制了其广泛应用。

关键词：化学链制氢；载氧体；铁氧化物；制备方法；流化床

Investigation of Characteristics of Iron-based Oxygen Carrier for

Chemical Looping Hydrogen Generation

ABSTRACT

In this paper, experiments were carried out to study the impacts of inert supports on the characteristics of Fe₂O₃ based oxygen carriers for chemical looping hydrogen generation in a batch-scaled fluidized bed reactor. Five kinds of oxygen carriers, supported by Al₂O₃, SiO₂, MgAl₂O₄, ZrO₂ and YSZ, were prepared by mechanical mixing, and the inert supports in each were accounted for 40wt%. At 900℃, experiments for 10 cycles were conducted and each contained three steps: CO reduction, steam oxidation and air oxidation. Oxygen carriers before and after each experiment were characterized by XRD and SEM. Experimental results show that anti-sintering properties and chemical reactivity of inert supports will seriously affect the reactivity and stability of oxygen carriers. The reactivity of the oxygen carriers supported by MgAl₂O₄ and YSZ increases first and then stabilized with the increasing number of cycles. However, the reactivity of the oxygen carriers supported by ZrO₂, Al₂O₃ and SiO₂ decreases first and then stabilizes. After four cycles, the reactivity of each oxygen carrier reaches a relatively stable state. Finally, the descending order of their reactivity is MgAl₂O₄gt; ZrO₂gt; YSZgt; Al₂O₃gt; SiO₂. SEM and XRD results show that, after 10-cycles experiment, iron-based oxygen carrier supported by MgAl₂O₄ maintains good pore structure and there is no reaction between Fe₂O₃ and the inert support. However, iron-based oxygen carrier supported by SiO₂ presents serious sintering, leads to the increasing of the internal diffusion resistance for reaction gas and causes the loss of reactivity. FeSiO₃ is found in the oxygen carrier after the reaction, which reduces the content of reactive oxygen species and the reactivity of the oxygen carrier.

In addition, the effects of different methods for synthesizing oxygen carriers on the performance of the oxygen carriers were also explored. Three kinds of iron-based oxygen carriers supported by Al₂O₃ are prepared by mechanical mixing, co-precipitation and impregnation methods respectively, and experiments are carried out at 900℃ for 7 cycles. The results show that the oxygen carrier prepared by co-precipitation method presents serious sintering, causing loss of reactivity. So the oxygen carrier prepared by mechanical mixing method has better reactivity and stability than that prepared by co-precipitation. The oxygen carrier synthesized by impregnation method presents sintering after reaction. However, macroporous structure emerges which facilitates the spreading of the reactant gas in the surface of the oxygen carrier, leading to the stability of reactivity. However, due to the characteristics of impregnation method, it is not suitable for loading too much active metal oxide which limits its wide application.

KEY WORDS: chemical-looping hydrogen generation(CLHG); oxygen carrier; iron oxide; synthesis method; fluidized bed

目录

摘要 I

ABSTRACT II

第一章 绪论 1

1.1 课题的研究背景及意义 1

1.1.1 温室气体排放与全球变暖 1

1.1.2 氢能 2

1.2含碳能源制氢的主要研究现状 2

1.2.1 天然气蒸汽重整制氢法 2

1.2.2 生物质制氢 3

1.2.3 煤气化制氢 3

1.3 化学链燃烧的国内外研究现状 4

1.3.1 化学链燃烧 4

1.3.2 化学链制氢 5

1.4 本文的研究目标和内容 6

1.4.1 本文研究目标 6

1.4.2 本文研究内容 6

第二章 实验装置及载氧体制备 7

2.1实验装置 7

2.1.1小型流化床反应器 7

2.1.2扫描电子显微镜（SEM） 7

2.1.3 X射线衍射仪(XRD) 7

2.2 载氧体的制备 8

2.3.1机械混合法 8

2.3.2共沉淀法 9

2.3.3浸渍法 9

2.3 实验过程 9

2.4数据处理方法 9

2.5 本章小结 11

第三章 基于不同惰性载体的铁基载氧体化学链制氢实验 12

3.1 引言 12

3.2 实验装置及实验步骤 12

3.3 不同惰性载体的铁基载氧体制氢特性对比分析 12

3.4铁基载氧体的表征 14

3.4.1 基于惰性载体的铁基载氧体 14

3.4.2 基于惰性载体的铁基载氧体 17

3.5 本章小结 19

第四章 制备方法对Fe₂O₃/Al₂O₃载氧体制氢性能的影响 21

剩余内容已隐藏，请支付后下载全文，论文总字数：29041字