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Abstract Significant carbon sequestration capacity (up to 10 Gigatons/yr) will be needed by 2050 to limit the Earth’s temperature rise to < 1.5 °C. The current worldwide capacity is ∼40MT/yr, which highlights the need for the development of new and scalable sequestration approaches. One novel technology for long-term sequestration of CO2 is the deposition of CO2 hydrates (ice-like solids made with water and CO2) on the seabed (under marine sediments or with artificial sealing). This involves rapid formation of CO2 hydrate slurries in a bubble column reactor (BCR) by bubbling CO2 gas at high flow rates in a BCR with the unreacted CO2 being recirculated; this approach is being pioneered by the present research group. This study utilizes recent experimental results on ultra-fast hydrate formation to conduct a techno-economic analysis of the hydrate slurry-making process. All analysis is conducted for a 1 Megaton/yr sequestration project, which is expected to run for 30 years. Our analysis shows that the total cost of hydrate slurry production is $16.2/ton. Such projects would require an initial investment of $74M, and the energy requirement will be 641 MWh/day. Contributions of each part of the process to the total cost are identified. Our results show that gas recirculation in a BCR contributes minimally (0.04%) to the overall energy requirement. Furthermore, the cost of BCR is only 0.3% of the total investment cost. This suggests that a low conversion of gas into hydrates in each pass of the BCR is not detrimental from a techno-economic standpoint. The findings of this study set the stage for more detailed analysis of hydrates-based sequestration, which is essential to add this technology to the existing bank of established carbon sequestration solutions. 

Abstract Novel energy efficient and scalable carbon capture and sequestration technologies are critical to meeting the goals of the Paris Agreement. In this study, we present a first-order system-level assessment of an integrated carbon capture and carbon sequestration plant that couples electrochemical CO2 capture from oceanwater with co-located long-term carbon sequestration as CO2 hydrates (ice-like solids) on the seabed. Separate recent experimental results associated with electrochemical capture and hydrate formation form the basis for this energetics-focused analysis, which evaluates power consumption of all the key components associated with capture and sequestration. Hydrates can be formed from both pure water as well as seawater, and the implications of including a desalination plant to provide pure water for hydrate formation are studied. All analysis is conducted for a 1 plant which captures and sequesters 1 megaton CO2 annually. Our results indicate the carbon capture will consume significantly more energy than carbon sequestration despite the use of a low-energy consuming electrochemical technique. From a sequestration standpoint, there are clear benefits to forming hydrates at high pressures, since the elevated formation rates reduce the number of hydrate formation reactors significantly. It is also seen that the addition of a desalination plant to provide pure water for hydrate formation (which speeds up hydrate formation) will not affect the energetics of the overall process significantly; however the CAPEX and operational aspects of including a desalination plant need to be analyzed in greater detail. Overall, this study seeds a novel CCS concept which can be deployed via decommissioned oil-gas platforms to capture CO2 from surface oceanwater and store CO2 right below on the seabed after appropriate sealing (artificial or natural).