Optimization of liquefaction cycles applied to CO2 coming from onshore pipeline to offshore ship transportation

Abstract

In the field of the CO₂ transportation for the Carbon Capture, Utilization and Storage (CCUS) process chain, several analyses show that, for a large-scale CO₂ transportation, pipeline transportation is the preferred method on land due to its lower cost. Barges also present a feasible alternative if the capture site is near a waterway. Maritime transport becomes more advantageous than pipelines, particularly over long distances and across ocean. Despite the need to liquefy CO₂ and to add temporary storage facilities for loading and unloading onto ships, beyond a certain distance at fixed CO₂ transported and plant life, ship transport optimal at pressures of 7 or 15 bar depending on the type of vessel. Impurities in CO₂, arising from various industrial processes and variable performances of capture technologies, increase energy consumption during compression and could cause corrosion risks. Specifications for CO₂ ship transport limit the concentration of certain impurities with strict thresholds. Methods for purifying CO₂, such as the two-flash system and stripping column, have been proposed to meet these specifications. The studied CO₂ liquefaction methods show that hybrid cycles, combining open cycle with Joule-Thompson expansion and closed cycle with cooling machine offer reduced energy consumption and improved CO₂ recovery compared to open or closed cycles. In the presence of the maximum threshold of impurities in the pipeline, energy consumption can nearly double from 21.8 kWh/t_CO2 to 40.9 kWh/t_CO2, with the highest recovery rising 98.1 %. This research underscores the importance of optimizing CO₂ transport strategies to facilitate the deployment of CCUS technologies.