Novel fuel-efficient cryogenic carbon capture system for the combustion exhaust of LNG-powered ships

Abstract

The traditional carbon capture technologies such as alcohol-amine decarburization, membrane separation, etc., are difficult to be used to cope with carbon emissions for ships, due to the power-hungry combustion exhaust pressurization consumption, poor economic benefits of carbon capture, etc. This paper presents a novel cryogenic desublimation CO₂ capture system (CDCC) coupled with LNG cold energy for LNG-powered ships. The proposed system not only significantly reduces the energy consumption of exhaust gas boosting but also utilizes waste cold energy from the LNG fuel gas supply system (FGSS). This enables the CO₂ gas to condense and separate at low temperatures. Through simulation and parameter optimization, the CO₂ capture rate and purity of CO₂ product can reach 92.87 % and 96.49 % respectively, with an energy consumption of 5.72 MJ/kg. To evaluate the CDCC performance, the typical monoethanolamine chemical absorption process (MEA) under the same flue gas inlet conditions and the consistent CO₂ product outlet temperature and pressure is also simulated. Comparative simulation with the MEA process shows similar CO₂ capture rates (87.13 % for MEA and 87.18 % for CDCC), but MEA achieves higher product purity by 2.58 %. However, MEA exhibits significantly higher energy consumption (33.28 MJ/kg) compared to CDCC (5.90 MJ/kg). Investigation into process parameters, engine powers, and CO₂ product parameters demonstrates CDCC's robustness in energy consumption, capture rate, and purity. The proposed CDCC system is well-suited for LNG-powered ships, which can be attributed to atmospheric exhaust gas treatment and self-contained utilization of cold energy.