A cryogenic tank thermodynamic process model for marine applications

The maritime industry’s accelerated transition to low- and zero-carbon energy is driving the adoption of marine fuels such as LNG, ammonia, hydrogen, and CO₂ seaborne transport from carbon capture. These substances require cryogenic storage and handling, with complex onboard systems of tanks, piping, and process equipment. At the core is the cryogenic tank, where complex vapour-liquid equilibrium due to external heat ingress determine boil-off and pressure dynamics during ship operations. This work introduces a generic thermodynamic model for cryogenic tanks that accommodates various fuel and CO₂ mixtures and integrates with marine cryogenic gas handling system models. The model accounts for multicomponent vapour-liquid equilibrium, vapour superheating, environmental and interphase heat transfer, flash evaporation during loading, and spray cooling via droplet evaporation. These capabilities enable the simulation of pressure accumulation, loading/unloading, boil-off management, internal transfers, and spray cooling processes. Developed through a process modelling framework, the tank model is able to interface with models of valves, pipes, pumps, and be used in multi-tank configurations. A comprehensive set of validation and verification studies is presented and discussed using both published experimental data and measurements from an actual LNG-fuelled vessel, confirming its predictive accuracy. Finally, simulations across different tank geometries, ship operations and cryogenic substances demonstrate the model’s ability in providing insight and supporting complex ship operations and design challenges.