预冷作业是大型液化天然气(Liquified Natural Gas,LNG)储罐投用前最关键的环节。预冷介质用量、预冷时间以及储罐各部分构件降温速率的控制是大型LNG储罐预冷作业得以顺利进行的重要保证。依托某大型LNG接收站项目,旨在较精确地计算预冷介质用量。选取最复杂的大型LNG储罐为研究主体,综合考虑保冷材料比热容变化、储罐日常蒸发、预冷介质输送管道漏热等因素,搭建有限元模型进行数值模拟计算,并利用上述结果计算预冷模型中的参数。预冷模型计算结果表明:大型LNG储罐预冷工作实施过程中,提高预冷降温速率可减少预冷介质用量和预冷时间,同时降低大型LNG储罐漏热所消耗的预冷介质占比,但需要注意储罐内元件的温差;考虑输送管线和机械结构漏热,预冷介质用量增多,与现场实际数据更吻合,相对误差不超过5%。研究结果对指导大型LNG储罐预冷操作具有参考价值。

Precooling operation is the most critical step before the commissioning of large Liquefied Natural Gas (LNG) storage tanks. The control of the amount of precooling agent, overall precooling duration, and cooling rate of various components of large storage tank is an important guarantee for the smooth precooling operation of large LNG storage tanks. Leveraging on a major LNG receiving terminal project, this study aims to accurately calculate the consumption of the precooling medium. The research focuses on the most complex large LNG storage tank of the project taking into account various factors, including the variation in specific heat capacity of cold insulation materials, daily evaporation from the tank, and heat loss in the precooling medium transportation piping. By developing a finite element model for numerical simulation, we are able to compute the necessary parameters within the precooling model. The calculation results of the precooling model show that by increasing the cooling rate during the precooling phase of the large LNG storage tank, there can be a significant reduction in both the amount of precooling medium required and the overall precooling duration. Additionally, this adjustment lessens the proportion of precooling medium lost due to heat loss. However, it is crucial to monitor the temperature differentials within the tank's components. Factoring in the heat loss from both the transportation piping and mechanical structure leads to an increased consumption of precooling medium, aligning more closely with on-site data, with a relative error of no more than 5%. The findings of this study offer guidance for actual precooling operations of large LNG storage tanks.