Title : Carbon capture from flue gases and biogas at atmospheric pressure, existing technologies and development of an innovative technology based on physical absorption in membrane contactors
Abstract:
The majority of current CO? emissions occur at atmospheric pressure. Among the available capture technologies, chemical absorption combined with solvent regeneration in packed columns is the most advanced and the one most frequently considered for industrial deployment. Physical absorption is less energy intensive, but, due to hydrodynamic constraints, it cannot be carried out at atmospheric pressure in gravity-driven contactors. Hollow-fibre membrane contactors (HFMCs) offer a promising alternative to packed columns for gas-liquid mass transfer. In HFMCs, the hollow-fibre membrane forms a physical barrier between the gas and liquid phases, enabling efficient mass transfer without direct contact between the phases. Gas and liquid flow as separate single-phase streams, eliminating reliance on gravity and avoiding operational issues such as foaming and flooding. Thanks to their high surface-area-to-volume ratio, modular design, and operational flexibility, HFMCs enable significant process intensification.
We have developed a new carbon capture process that operates at atmospheric pressure and uses physical solvents. This process utilises cylindrical cross-flow HFMCs for both the absorption and solvent regeneration stages. The specific energy consumption of this process is significantly lower than that required by chemical absorption. For example, with an inlet CO? mole fraction of 0.09 and a carbon capture efficiency of 0.9, the specific energy required is about 1 GJ per tonne of carbon captured, which is more than three times lower than the specific energy requirements of optimised chemical absorption plants. For an inlet CO? mole fraction of 0.22, the specific energy requirement is even lower, at only around 0.50 GJ per tonne of carbon captured. However, due to the low solubility of CO? in physical solvents, the volumetric flow rate of the liquid circulating in the process is high. The large specific surface area of HFMCs results in significant friction and, consequently, a potentially considerable pressure drop. The geometric optimisation of the dimensions and shape of fibre bundles is essential to ensure the viability of this technology. In order to handle gas flow rates relevant to industrial applications, a numbering-up strategy of fibre bundles is required. To meet this challenge, multi-bundle contactors – comprising fibre bundles arranged in parallel, each with an optimal shape – have been designed. 1D calculations, validated by 3D CFD simulations, show that this strategy is effective, confirming the potential of the carbon capture process that has been developed.
