An approach to estimating the boil-off rate of LNG in type C independent tank for floating storage and regasification unit under different filling ratio

The alternative terminal Floating Storage and Regasification Unit (FSRU) for gas storage and vaporization is rapidly expanding all over the world. FSRU with great storage capacity and long storage time is faced with the continually evaporation of liquefied natural gas (LNG), which result in the decrease of filling ratio. In order to improving the efficiency of electricity generation and utilization of the Boil-off Gas (BOG), accurate and efficient method to estimate the BOR under different filling ratio is in demand. An equivalent conductive model with the combination of adjacent fluid layer and flowing BOG is proposed in this paper to handle the complex convection from the multiphase simulation. Testified by experimental measurement, the highest relative error for BOR estimation is less than 4%, and also the heat transferred by evaporation can be estimated accurately under different filling ratio. With the valid temperature distribution got from this model, the initial condition of transient simulation under specific filling ratio can be given rapidly for further study. Furthermore, the comparison between numerical results and experimental measurement also reveals that the majority of heat is transferred from bulkhead during evaporation under lower filling ratio. Finally, the proposed approach is successfully applied for a case of 30,000 m3 FSRU, and proved to be a valid option to calculate BOR in the engineering field.