LNG船液货舱预冷过程

PRIOR COOLING PROCESS IN TANKS OF AN LNG CARRIER VESSEL

LNG船在装货前要向液舱内喷入少量LNG或液氮进行降温,喷入的LNG吸热降温并需使液舱温度达到一定值后才能开始正常的装货,预冷过程影响到LNG船液货舱的安全。对LNG船液货舱的预冷过程进行了分析,提出预冷过程的数学模型,由此得出预冷理论规律。同时,以12.5×104m3的MOSS型LNG船为母型船进行了理论推导、编写计算程序和实际计算,并与实船试验进行比较分析,得出LNG船预冷的实际规律,对船舶实际航行中的预冷计划和节约预冷时间具有指导意义。

Before LNG can be transferred from shore to ship, a tiny quantity of LNG and/or liquid nitrogen will have to be sprayed in the tanks to decrease the temperature inside; the normal loading will not start until the temperature in the tanks reaches a certain point because the cool-down process has great effect on the safety of the LNG carrier room. Through analysis on the whole cool-down process, this paper built up a mathematical model and then derived its rule in theory. Taking a MOSS-type LNG carrier vessel with a capacity of 125 thousand m3 as a case of study, this paper used this model to deduce, program and calculate the computation process and obtained the factual law of the cool-down process by comparison analysis on the actual practices of this type LNG carrier. Through this study, operators will be able to understand well both the theory and the discipline of the cool-down process so as to have a perfect plan of reducing cooling-down time and saving energy on the prior cooling process when transferring LNG to ship.