Abstract:

Due to the rapid surface reaction and strong exothermic properties of CO methanation, the fluidized bed methanation technology using small particle catalysts has obvious technical advantages in terms of reactivity and catalyst stability compared to fixed bed. The latest developments in the development of fluidized bed methanation technology are summarized from the aspects of high attrition-resistant catalyst, fluidized bed reactor and its innovation and shortened two-stage methanation technology. The primary particles with high skeleton strength and homogeneity is prepared by optimizing the preparation methodology of the precursor and the composition, and then the attrition-resistant catalyst spheres with relatively uniform size distribution are obtained by spray granulation of the precursor with binder addition under the optimized operation parameters. However, the catalytic activity at low temperatures decreased for the resulting catalyst because the binders block the active sites. Another technical method for preparing a fluidized bed methanation Ni-based catalyst having a high activity and an abrasion index of less than 1.5 has been developed by modifying spherical particles such as Al₂O₃ and FCC catalysts and further supporting the active components. The experimental results of bubbling fluidized bed methanation reveal that the reaction rate is very fast so methanation reaction completes at first few millimeters from distributor. The CO conversion and catalyst stability in fluidized bed reactor is better than that in fixed bed, because of the quick surface refreshment and good reaction uniformity (especially temperature) in the bed.The raising active surface of the catalyst particles by loosen the particles contact resulted from the higher bed voidage ensures the fluidized bed methanation endure higher space velocity and superficial gas velocity. Transport bed, which is unlimited by operation velocity, is easy to be scaled up for the high-capacity system producing synthetic natural gas (SNG). Most importantly, the catalyst particles with high heat capacity are used as the main heat carrier in the transport bed methanation, so the heat transfer rate compared with gas is improved. The long-time operation of the demonstrations that established for the utilization of biowaste and coke oven gas methanation respectively, identify the technical feasibility for a simple two-stage methanation process with fluidized bed.

Key words: methanation, fluidized bed, syngas, attrition-resistance, catalyst, synthetic natural gas

摘要：

由于CO甲烷化的快速表面反应、强放热特性，相比固定床，采用小颗粒催化剂的流化床甲烷化技术在反应活性和催化剂稳定性方面具有明显的技术优势。从高耐磨催化剂、流化床反应器及其创新、短流程两段甲烷化技术构建及其验证等方面总结了流化床甲烷化技术开发的最新进展。优化催化剂前体制备方法、调变催化剂组成可获得具有较高骨架强度和均匀性的催化剂一次微粒，进而通过优化的喷雾造粒工艺和填充黏结剂，制备出具有可调变粒度分布、高强度和高球形度的流化床用粉末催化剂，但其黏结剂的添加明显影响催化剂的低温活性。通过改性如Al₂O₃和FCC催化剂的球形颗粒，进而负载活性组分，开发了制备高活性、磨损指数小于1.5的流化床甲烷化Ni基催化剂的另一种技术方法。实验室研究证实了流化床甲烷化反应速率极快，在分布板上数毫米处即可实现可能的最高转化率，且在转化率和催化剂稳定性方面明显优于固定床，不仅由于流态化催化剂床层温度均匀，而且催化剂在床层内不停循环，加快了颗粒表面的更新。增大空速和表观气速，流化床的催化剂床层膨胀，反应气体与催化剂颗粒表面间的有效接触面积增加，使得流化床甲烷化对空速和表观气速的可调范围大。操作在更高气速条件的输送床甲烷化避免了操作气速的上限限制，可大幅降低反应器尺寸，有效提高单位截面的原料气负荷能力。输送床甲烷化可采用高热导率的催化剂颗粒传递反应热，相对于气体移热效率高、能力大。流化床甲烷化已在生物废弃物利用和焦炉煤气甲烷化方面开展了侧线示范，形成了相对多段绝热固定床工艺更简单的短流程两段甲烷化新工艺。

关键词: 甲烷化, 流化床, 合成气, 耐磨, 催化剂, 合成天然气