Heat transfer modelling in adsorption-based direct air capture - Validation of a 1D model and simulation of an embedded heat exchanger using geometric heat transfer distribution

Despite the importance of accurate heat transfer modelling in the simulation of adsorption-based direct air capture (DAC), it has gained very little focus in the literature. This study addresses this gap by focusing on the role of heat transfer in dynamic 1D DAC modelling, and by introducing a method to simulate DAC heat transfer in 1D in the case of an embedded fin-tube heat exchanger. The 1D column model produced a satisfactory match with experimental temperature profiles in inert experiments and in DAC-relevant conditions. The 1D geometric distribution model introduced in this study clearly improved the match of 1D axial temperatures versus 3D steady-state and transient simulations, when compared to a conventional 1D modelling approach. The main difference between 1D and 3D models was an early CO2 breakthrough due to axially non-uniform velocity caused by the tube, which the 1D models could not replicate. Based on the results of this work, different heat transfer mechanisms play an important role especially in humid DAC and should be separately considered in 1D in most cases. The 1D geometric distribution model is expected to be useful in cases where axial temperature distribution is important, such as contactor optimization. However, while the results suggested predictiveness with condition variance, the need for heat transfer coefficient re-calibration should be assessed for example in staggered tube configurations. Additionally, the method does not yet cover variable velocity due to structural axial non-uniformity, which affects adsorption breakthrough profiles.