Study On The Pre-cooling Process Of Membrane Liquid Cargo Tank Of LNG Carriers

Natural Gas, as a clean and abundant hydrocarbon fuel, has the characteristics of high-efficiency, high-quality and cleanliness. The transportation of Natural Gas is carried out by LNG Carriers in forms of Liquefied Natural Gas. During the liquefied cargo operation of LNGC, pre-cooling process plays a vital role in its relation with ships’ economy as well as structural integrity of Liquefied Cargo Tank. With the development of China LNGC fleet, a lot of attention has been paid for the research of structural integrity and sloshing load of Liquefied Cargo Tank. Yet the study of liquefied cargo operation, particularly pre-cooling process has been rarely reported. Therefore, studying on variation principle of pre-cooling process of membrane liquefied cargo tank of LNGC is of great importance to the establishment of scientific rational pre-cooling program.This paper mainly focuses on the pre-cooling process of membrane liquefied cargo tank of LNGC, the main tasks and conclusions are as follows:First of all, the heat transfer mechanism of membrane liquefied cargo tank of LNGC was analyzed, enabling the calculation of its thermal load. Then the mathematical model of pre-cooling process such as pre-cooling timing model, minimum cargo flow rate and the model of temperature and pressure of Liquefied cargo tank over time were established so as to discuss variation principle of timing and minimum cargo flow rate.In addition, based on parent ship Dapeng Sun, the thermal load at the termination point of pre-cooling process and critical cargo flow rate were calculated. Then plane simulation of pre-cooling process was carried out with the help of MATLAB/Simulink Software, aiming at researching on the variation principle of temperature and pressure of liquefied cargo tank over time. According to the plane simulation results, scientific pre-cooling process, which contains three stages(rapid cooling stage, slow cooling stage and stable cooling stage) should be carried out differently according to different stages. And the optimum flow rate of Dapeng Sun was in the range of1200kg/h-1800kg/h.Last but not least,3D numerical simulation of pre-cooling process of membrane liquefied cargo tank was conducted based on CFD software Fluent. The temperature distribution field, velocity vector field, streamline field and natural gas volume distribution field were simulated so as to analyze the flow process, temperature field as well as heat transfer process during pre-cooling operation. What’s more, further research about the spatial distribution of cooling medium was carried out in this paper.