(41b) Computational Analysis of the Effect of Structured Packing Design on Absorption Column Hydrodynamics for Post-Combustion Carbon Capture Applications

Solvent-based, post-combustion carbon capture technologies have a potential for reducing carbon emissions from fossil fuel-fired power plants and industrial sources where CO₂ emissions are inherently harder to mitigate, such as steel or cement industries. A prominent technology to achieve this is by retrofitting absorption columns to the existing infrastructure. While these systems have been among the less costly alternatives for carbon capture, they still impose a considerable energy penalty to the operation of power plants or industrial facilities [1]. The optimization of CO₂ capture rate in the solvent-based absorption process is complex as it depends on several factors including CO₂ solubility, solvent reaction kinetics, and temperature effects on the solubility, reaction rates, surface tension, and thermophysical properties of the solvent and the flue gas. The overall heat and mass transfer also depends on the hydrodynamics, which in turn, is affected by the packing geometry. Identification of packing geometries for optimal CO₂ capture in such columns necessitates the understanding of key interactions between three-dimensional flow patterns and packing walls, reaction kinetics, and heat and mass transfer effects.

With the aim of obtaining a fundamental understanding of these interactions, we have developed a multiphase computational fluid dynamics (CFD) modeling strategy to model the reacting flow of monoethanolamine (MEA) solvent through absorption columns with structured packing. In this framework, we incorporate the reaction kinetics, composition, and temperature-dependent thermophysical properties of the MEA-H₂O-CO₂ system from the Institute for Design of Advanced Energy Systems (IDAES) process engineering computational framework. We model the two phases as multi-component inhomogeneous reacting mixtures of MEA-H2O-CO₂ solution and flue gas, and numerically solve species transport separately within each phase. A six species, two-chemical reactions mechanism [2] is used to model kinetics of the MEA-H2O-CO₂ system.

Previously, the CFD simulations have been used to predict the performance of reference packing geometries in terms of the CO₂ capture rates at different solvent or gas inflow temperatures and liquid loads. In the current work, we systematically quantify the effects the design of the structured packing has on the column hydrodynamics, by performing detailed CFD simulations for different geometrical configurations and operating conditions. We then obtain correlations between the structural features of the packing and the key hydrodynamic metrics, such as liquid holdup, interfacial area, wetted area, and pressure drop, and we explain the relationships between them in terms of fundamental metrics that describe the distribution of liquid film thickness and structure of the liquid-gas interface. Insights developed from these analyses are expected to guide the future development of packing designs for optimal CO₂ absorption performance.

Acknowledgement:

The authors graciously acknowledge funding from the U.S. Department of Energy, Office of Fossil Energy and Carbon Management, through the Carbon Capture Program.

Disclaimer:

This project was funded by the Department of Energy, National Energy Technology Laboratory an agency of the United States Government, through a support contract. Neither the United States Government nor any agency thereof, nor any of its employees, nor the support contractor, nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof, or any of their contractors.

References:

1. Wilcox, J., 2012. Carbon capture. Springer Science & Business Media.
2. Akula, P., Eslick, J., Bhattacharyya, D. and Miller, D.C., 2021. Model Development, Validation, and Optimization of an MEA-Based Post-Combustion CO2 Capture Process under Part-Load and Variable Capture Operations. Industrial & Engineering Chemistry Research, 60(14), pp. 5176-5193.