不同径高比柱状载氧体固定床CLC非均相反应及共轭传递过程的数值分析

Numerical Analyses of Heterogeneous Reaction and Conjugate Transport Processes in Fixed-bed CLC with Columnar Oxygen Carriers of Various Diameter-to-Height Ratios

为了解柱状载氧体的外形如何影响组分扩散与复杂间隙流动,并最终影响整体气固非均相反应性能,采用计算流体力学(CFD)方法对不同径高比的柱状载氧体的固定床化学链燃烧(CLC)过程进行了数值分析。结果表明:柱状载氧体颗粒的径高比越大,填充床反应器中气流平均速度和床层压降越大;相比于常规的圆柱载氧体颗粒,薄片状或棒状颗粒具有更大的比表面积和更短的组分扩散距离,能够缓解多孔颗粒载氧体中的内扩散限制,从而提高整体气固非均相反应速率和载氧体转化率;在相同径高比下,薄片状颗粒填充床具有更大的内扩散传质速率和对流传质速率,综合共轭传质能力更强。

In order to understand how the shape of the columnar oxygen carrier affect the component diffusion and complex interstitial flow,and ultimately affect the overall gas-solid heterogeneous reaction performance,a computational fluid dynamics(CFD)method was applied to numerically analyze the fixed-bed chemical looping combustion(CLC)process with columnar oxygen carriers of various diameter-to-height ratios.Results show that the larger the diameter-to-height ratio of columnar oxygen carrier particles is,the higher the airflow mean velocity and pressure drop in the packed bed reactor are.Compared with conventional cylindrical particles,thin lamellar or rod-shaped particles have larger specific surface area and shorter diffusion distance,which can alleviate the intra-particle diffusion limitation in porous oxygen carriers and thus accelerate the overall gas-solid heterogeneous reaction rate and oxygen carrier conversion.In addition,for the same diameter-to-height ratio,the thin lamellar particles exhibit greater diffusion and convective mass transfer rates,leading to a greater conjugate mass transfer capacity.