Assessment of CO2 capture and storage onboard LNG vessels driven by energy recovery from engine exhaust

The pressing need to significantly reduce global CO₂ emissions requires the decarbonization of the shipping industry. Currently, shipping relies on fossil fuels with a shift from heavy oil to liquefied natural gas. The main engine is the primary energy user onboard vessels, and its exhaust is the main CO₂ emission source. A potential path to reduce emissions onboard vessels is the capture, compression, and storage of CO₂ from the exhaust gases. This requires effective integration across the engine, the capture technology, the CO₂ compression, cooling, and storage. The integration of four alternative capture technology options is conceptually explored and assessed: chemical absorption, membranes, temperature swing adsorption, and cryogenic distillation. Integration schemes are developed for each of the four technologies that achieve carbon capture, compression, and storage driven by the exhaust gas waste heat as the only energy source. Heat and power requirements are met through heat integration and heat-to-power conversions using organic Rankine cycles (ORCs). The study was performed on an LNG vessel using LNG fuel in its main engine. Thermal capture technologies (absorption and adsorption) are observed to significantly outperform their alternatives (membranes and cryogenic distillation) and capture, compress, and store more than twice the amount of CO₂ emissions from the engine exhaust stream. Finally, the proposed integration schemes resulted in self-sustainable onboard capture systems without combusting additional fuel.