Modeling CO ₂ and H ₂ O Co-desorption in an Internal Joule Heating-Assisted Vacuum-Structured Packed Bed DAC Contactor

Direct air capture (DAC) technologies offer a promising avenue for mitigating climate change by removing CO2 from the atmosphere. Innovations in energy-efficient DAC technologies are essential to increase their deployment and reduce costs, making them a more viable and accessible solution for carbon removal. Currently, DAC is an energy-intensive process, and reducing its energy consumption is vital for cost-effectiveness. This research focuses on enhancing the DAC process, specifically the regeneration phase, by utilizing structured packed beds coated with zeolite 13X. The goal is to achieve faster and more energy-efficient desorption of CO2 and H2O. We investigated the dynamic behavior of the co-desorption of CO2 and H2O during the solid-based DAC process that uses structured packed beds coated with zeolite 13X and heated by internal Joule heating via a two-dimensional unsteady-state, nonisothermal, two-scale heterogeneous model. The study examines how the magnitude and time evolution of the volumetric energy source heating the packed bed, along with CO2 and H2O uptake, coated zeolite layer thickness, and packed bed height affect the desorption process and energy consumption in DAC units, specifically comparing structured and random packing configurations. The results indicate that under similar starting regeneration conditions (same total mass of CO2 and H2O adsorbed in the unit, quantified in kilograms), the specific energy requirements associated with the CO2 desorption process are lower in a DAC unit with structured packing than in a unit with random-packing spherical zeolite particles. On the other side, at the same starting CO2 and H2O uptakes (quantified in mol/kg) and high CO2 uptake levels (>2.0 mol/kg), structured packing and packed beds with spherical particles exhibit similar specific energy requirements for CO2 and combined CO2 and H2O desorption processes. In DAC systems, using structured packing instead of randomly packed units for CO2 and H2O desorption can significantly reduce the duration of the desorption process and improve the H2O desorption efficiency.