Development of Numerical Framework to Understand the Impact of Flow Hydrodynamics on CO2 Absorption in Gas-Liquid Contactor

The increase in global warming over past decades necessitates the development of efficient carbon capture storage systems (CCS) to combat climate change. Advancements in carbon capture technologies are necessary to understand technical challenges, enhance productivity and minimize energy penalties. One of the promising methods to remove carbon dioxide at atmospheric conditions is the application of biocatalytic textiles in CO2 reactive absorption process. These textiles are coated with immobilized enzymes such as carbonic anhydrase that facilitate the absorption of CO2 in low energy solvents. The textile scaffold with immobilized enzymes functions as a gas-liquid contactor where counter-current flow takes place between a liquid alkaline solution and the flue gas. Flow hydrodynamics has a significant impact on the performance of enzyme-based CO2 absorption in gas-liquid contactors. The absorption of CO2 in the liquid film is governed by convection, diffusion and reaction. It is a liquid phase-controlled mass transport phenomenon due to the diffusional limitations of CO2 within the liquid film. The complicated film hydrodynamics has an impact on the behavior of the gas-liquid interface and flow regime. Computational fluid dynamics (CFD) is a numerical simulation-based tool to model and analyze fluid flow behavior in complex systems. The application of CFD with the interface tracking method resolves the interface to develop a numerical framework for modeling CO2 mass transfer within the liquid film. In this work, PHASTA code, a finite element based CFD solver, coupled with the level set method is used to track the location of the evolving gas-liquid interface. The simulation framework with the capability of modeling the transport of CO2 provides a foundation to understand and optimize absorption systems leading to scale-up from lab to industrial applications. The utilization of immobilized enzymes depends on the flow distribution and the liquid film thickness, as it impacts the accessibility of CO2 to the immobilized enzyme active site in the gas-liquid contactor. Absorption rates from simulations are quantified by estimating the concentration gradient at the gas-liquid interface. Physical mass transfer coefficients are estimated by normalizing the absorption rates with the difference in concentration of CO2 at the interface and the average bulk concentration within the liquid film. The developed numerical framework is used for parametric study to understand the impact of film thickness, film velocity and the flow direction on the absorption rates of the gas-liquid contactor. Experimental data, combined with the numerical simulations will be used to understand the system limitations and prescribe reliable metrics for efficient biocatalytic reactor design.