Indirect air CO₂ capture and refinement based on OTEC seawater outgassing

In this paper, we propose a low-cost method to capture and purify CO₂ from ocean water indirectly from the atmosphere. Atmospheric CO₂ dissolves in seawater following Henry's law. In open-cycle ocean thermal energy conversion (OC-OTEC), being a heat engine, large quantities of water are used to generate electricity from temperature differences in the ocean. CO₂ and other gases dissolved in seawater are extracted from seawater by a vacuum compressor, being essential for heat transfer in OC-OTEC. Non-condensable gases containing CO₂ from OC-OTEC are currently considered a waste gas stream. Based on literature, we calculate cold water non-condensables containing up to 14% CO₂. These non-condensables can be refined further to 80-90% purity with a water absorption process, inspired by those as used in the biogas industry. Levelized CO₂ capture and purification costs were estimated to be 15-35 euro per ton, as only refinement costs are allocated of a waste gas stream of OC-OTEC.