Numerical study of pressure build-up in vertical tanks for cryogenic flammables storage

Large-scale installations for cryogenic fluid storages, such as liquefied natural gas (LNG) and ethylene are critical units in the framework of the chemical and petrochemical industries. Modelling the thermal performance of such installations is therefore a critical task to enhance the safety and effectiveness of operations. In the present work, Computational Fluid Dynamics (CFD) is used to investigate the pressurisation behaviour of cryogenic storage tanks by applying the Volume-Of-Fluid method and taking into account vaporization-condensation phenomena. The boundary conditions are estimated from a 1-dimensional model to solve the heat transfer through the tank insulation layers, eventually taking into account accidental damages. The tank CFD model is preliminary validated against small-scale experimental data obtained for cryogenic nitrogen and then extended to the simulation of an industrial cylindrical tank, whose volume is 100m3. The effect of fluid, i.e. ethylene and LNG (modelled as pure methane), filling level and possible insulation damage, on natural convection driving liquid stratification and ultimately tank pressurisation is analysed. Specific performance indexes are proposed to efficiently compare the different scenarios.