Design considerations for the marinisation of offshore direct air capture

Direct air capture is a method for removing carbon dioxide (CO2) directly from atmospheric air. To date, only land based installations have been considered, but with growing competition for land and resources, offshore locations are beginning to be contemplated. Offshore locations offer close proximity to vast renewable energy potential, and robust CO2 storage locations, but come with a large degree of uncertainty on performance and cost. The current study explores considerations for offshore operation, and reviews parallel technologies that have undergone similar transitions to use in offshore environments. A baseline energy calculation is completed under the assumption that air would need to be pre-treated prior to entering conventional DAC units. A design is proposed using wire mesh demister pads to collect and remove liquid particles containing salt from the air prior to entering the air contactor and coming into contact with capture materials. The pressure loss, and additional fan power required to overcome this is computed. Demister pads increase overall pressure drop by 20%–28% for solid sorbents, and by 79% for aqueous based DAC solvents, resulting in an additional fan energy requirement of 38.1 kWh/t-CO2 and 194.44 kWh/t-CO2 respectively. Until further experimental studies are completed to better understand the impacts, this design serves as a worst-case scenario for comparison. Once further experimental data becomes available, it can be determined whether the additional components for pre-treatment of air are necessary.