Abstract:

The structured packing is extensively utilized in gas-liquid separation processes due to its ability to provide a high specific surface area and a low pressure drop. The performance of the structured packing depends on the local gas-liquid distribution, and the perforation has a significant impact on the gas-liquid flow inside the packings. However, the influence of perforation on liquid flow of corrugated plate is often ignored in previous studies. In this study, a gas-liquid two-phase flow CFD model was established under the framework of VOF. The microscale flow of the CO₂ absorbent on the surface of corrugated plate of structured packing in the absorption tower of Huaneng Zhengning 1.5×10⁶t/a carbon capture project was simulated, and the hydrodynamics of typical absorbents on the corrugated plate in the presence of perforations were discussed. The simulations revealed that when the spray density was 20m³/(m²·h), the existence of perforation led to rivulet flow separation and droplet formation, but had little effect on liquid holdup and interfacial area. The liquid maintained a steady rivulet flow along the channels in the absence of perforations, while the liquid flowed in the form of droplets in the presence of perforations. Remarkably, the physical properties of absorbents exerted a significant impact on the liquid flow morphology. The decrease of Ka (i.e., the surface tension decreased or the viscosity increased) resulted in an increase in the time required for the flow to reach the steady state, liquid hold, interfacial area, and wetting area. The influence of contact angle (i.e., the surface texture of the corrugated plate) was effectively studied by modifying the wall boundary conditions. The flow morphology of the 30%MEA on the corrugated plate with perforations transitioned from droplet flow to rivulet flow and finally to film flow as the contact angle decreased. In addition, at a contact angle of 20°, the interfacial area predicted by simulation was consistent with that predicted by the Olujic model, whereas the predicted holdup was marginally lower than that suggested by Billet-Schultes model, yet the overall trend was relatively consistent.

Key words: carbon capture, structured packings, CO₂ absorbent, CFD simulation

摘要：

规整填料因能够提供较大比表面积的同时产生较低压降而被广泛应用在化工气液分离过程。填料性能取决于局部气液分布，射孔对填料内部气液流动有较大影响，以往研究往往忽略了填料波纹板表面射孔。本文在VOF框架下建立了填料内气液两相流动的CFD模型，针对华能正宁1.5×10⁶t/a碳捕集项目吸收塔内规整填料波纹板表面CO₂吸收剂流动开展了模拟，探讨了开孔波纹板上典型吸收剂的流体力学特性。模拟结果表明当喷淋密度为20m³/(m²·h)时，射孔的存在导致了溪流流动分离和大量液滴形成，但对持液率和界面面积率影响较小，未开孔波纹板上液体主要以稳定溪流形式沿着波谷流动，而开孔波纹板上则以液滴形式流动。吸收剂溶液物性显著影响填料表面液体流动形貌，随着溶液Ka（Kapitza数）减小（即表面张力降低或黏度增加），流动达到稳态所需时间、持液率、界面面积率和润湿率均增加。通过改变壁面边界条件，有效地研究了接触角（波纹板表面纹理）的影响。随着接触角减小，观察到30%MEA水溶液在开孔波纹板上的流动形式由液滴流转变为溪流继而转变为膜状流，这导致了持液率、界面面积率和润湿率也随着接触角的减小而增加。此外，当接触角为20°时，模拟预测的界面面积率与Olujic模型预测的结果高度一致，持液率的预测结果略低于Billet-Schultes模型预测的结果，整体趋势有较高的一致性。

关键词: 碳捕集, 规整填料, CO₂吸收剂, CFD模拟