Computational Fluid Dynamics and Mass Transfer Analysis of Direct AIr Capture Systems

Direct air capture (DAC) of carbon dioxide can play an important role in combatting global warming driven by CO2 emissions. DAC systems based on solid CO2 sorbents have shown promising performance in the laboratory; the current focus is to develop methods that will enable design of a large-scale DAC installation with low cost of capture. Wind-driven DAC systems have the potential to reduce both capital and operating costs by eliminating fans and other mechanical flow driving devices. Optimization of a wind-driven system requires consideration of flow resistance in the air contactor, interactions between the large installation and the wind, and sorbent sensitivity to local environmental conditions. We have developed a novel computational fluid dynamics (CFD) tool to predict contactor performance based on the flow design, sorbent characteristics, and local atmospheric and climatic conditions at the installation site. The tool uses a porous media approach to model the effects of the contactor's small flow passages within a much larger installation. The tool includes a model of the sorbent's CO2 uptake as a function of ambient temperature and relative humidity derived from empirical data. Finally, the tool combines sorption and flow performance predictions with annual wind speed and direction data for various locations in the United States to evaluate the site-specific performance of the contactor design. The analysis tool enables assessment of favorable installation sites for a given wind-driven DAC system, prediction of annual CO2 capture, and specification of design requirements for cost-effective implementation.