反应器-催化剂颗粒双尺度分析费托合成的产物分布及其影响因素

The Analysis on Products Distribution and Influence Factors of Fischer-Tropsch Synthesis by Reactor-Catalyst Particle Double-Scale

在考虑产物液膜传质阻力的情况下,构建了反应器-催化剂颗粒双尺度费托合成产物分布的多场耦合数学模型,讨论了产物液膜及催化剂粒径对产物分布特性的影响。结果表明,产物碳原子选择性的计算结果符合费托合成经典的ASF分布。反应物浓度在催化剂颗粒表面处的浓度最高,沿着半径方向向中心处不断降低,而产物的浓度分布状态则正好相反。沿着流动方向,主体气流中反应物CO的浓度要高于催化剂内部平均值,产物C_(5+)浓度则与此相反;且浓度差异在反应器入口部分最为明显,随着反应不断进行,催化剂颗粒内外组分的浓度差异逐渐缩小。此外,催化剂粒径越大,颗粒内部组分的浓度差也越大,而减小粒径可以降低液态产物传质阻力,同时有效避免催化剂的"死区"现象,有利于提高其利用效率。

A multi-scale and multi-physics-coupled numerical model containing the momentum,mass transfer,as well as the chemical Fischer-Tropsch synthesis kinetic equations in both reactor and catalyst particle scales with the consideration of mass transfer resistance caused by liquid products film on catalyst particle surface,was established.The effects of liquid film as well as the particle radius on products distribution characteristics were analyzed.The results showed that the C-atom selectivity of Fischer-Tropsch products obtained from the established numerical model agreed well with the classical ASF distribution.The highest reactant concentration appeared at the out surface of catalyst particle and decreased along the particle radius,while there was an opposite trend for product concentration.The CO concentration in main flow was higher than the average value in catalyst particle,while the product C5＋has the opposite distribution character.Moreover,the concentration difference between main flow and catalyst particle was largest at the inlet region,and decreased along the flow direction.Furthermore,the larger the catalyst particle,the more obvious the concentration difference along the particle radius of the components inside the particle.Thus smaller catalyst particle is good for decreasing the diffusion limitation,to avoid the＂dead region＂phenomenon,and the catalyst usage efficiency can also be enhanced.