Onboard the Norwegian Coast Guard vessel KV Bergen, as well as other LNG fuelled vessels, there has been reports of a sudden fall in the fuel tank system pressure, resulting in de-loading of the NG engines. This study examines the factors which caused the LNG tank pressure on KV Bergen to fall, leading to the de-loading of the Natural Gas (NG) engines. One reason for the drop in tank pressure is that external disturbances from rough seas destroy the liquid surface layer, causing an increase in the rate of condensation occurring inside the tank. The rate of heat and mass transferred to the vapor section by the Pressure Build Up (PBU) unit is less than the heat and mass absorbed during the mixing inside the LNG tank. A process is developed to calculate the possible fall in LNG tank pressure caused by complete mixing of the liquid and vapor.
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