Boil-Off Rate In LNG Storage Tanks As A Function Of Initial Liquid Temperature

Abstract

This work presents simulations performed using the online tool BoilFAST, where the boil-off rate in a Liquefied Natural Gas (LNG) tank has been investigated for various starting temperatures, and for different storage tank dimensions. The simulations have been performed to investigate whether BoilFAST can be used for analyzing LNG boil-off and for assessing the fuel tank size and geometry for a maritime vessel. Sloshing in maritime LNG storage tanks is known to cause pressure drops which may compromise the supply pressure to the gas engine. A novel and cost saving means to combat this risk could be to heat the LNG during bunkering to a temperature equal to the equilibrium temperature at which the vapor pressure equals the minimum required pressure of the engine. However, if the LNG is overheated, this may compromise the requirement of 15 days of holding time of the LNG in the tank without exceeding the maximum allowable pressure. Simulations show that when the LNG is heated prior to filling into the storage tank, the fulfillment of the holding time requirement depends on the tank geometry, as well as the filling degree and temperature gradient through the tank walls.