Study On Prediction And Optimization Of Pre-cooling Processof LNG Membrane Liquid Cargo Tank

As the adjustment of energy consumption and the limitation of gas pollution emission, the surge demand of natural gas is coming due to its qualities of clean and efficient. In order to offset the short of natural gas, the project of LNG will import the resource. It means the quantity of cargo operation will increase, leading the problem of usage of port and offshore. The pre-cooling operation of LNG tank will be conducted before bulk cargo loading to avoid CCS material failure due to huge cold energy released by LNG. So, the implementation of cargo handle and time consuming are determined by the pre-cooling operation. However, due to the lack of effective technical support, no reasonable pre-cooling scheme guides the pre-cooling operation of liquid tank, consuming too much time of the operation, reducing the economic benefits of LNG terminals.The investigation field of cargo tank for LNG carrier is mainly focused on the prediction method of pre-cooling operation, including lumped parameter method(LPM) and computational fluid dynamics(CFD) numerical method. Deficiencies are as following,(1) evolutions of space distribution of physical variables reflected the tank situation cannot be predicted by LPM,(2) ignoring the CCS model and the latent heat of phase change of LNG, treating the pre-cooling operation as steady process by CFD numerical prediction method. In this paper, the CCS as the essential part of the object was modeled and the latent heat of the phase change of LNG was considered. The numerical prediction of multi-physical fields of cargo tank in pre-cooling process was conducted through FLUENT based on CFD numerical method, and the optimization scheme of the pre-cooling operation based on the pre-cooling time was further studied.In this paper, full-scale model of a LNG transport carrier tank is implemented in numerical experiments. It mainly carried out two aspects: firstly, a prediction method for the temperature evolution of the CCS with the LNG phase change during the pre-cooling of the liquid tank is presented, secondly, rapid implementation of the pre-cooling operation in the premise of the safety as a principle, the optimization of the pre-cooling operation of the liquid tank was researched based on the prediction method. Through the investigation, the evolution law of the fluid flow and temperature field inside tank is obtained. The characteristics of temperature field variation of each layer of the cargo maintenance system of the liquid cabin are summarized. And by using the temperature distribution law of the fluid chamber(such as slice surface, line and point) in typical position of the system, the internal temperature variation mechanism of the cargo maintenance system is obtained. On the other hand, to guide the actual pre-cooling operation, by the study of effect factors of the pre-cooling process, the optimization of pre-cooling scheme of the liquid tank is put forward.The investigation results not only can provide direct technical support for the pre-cooling operation of LNG carrier tank, but also can provide reference for the development of the rules of LNG cargo operation for ship classification society. In addition, the research results of this project are also indirectly improve the use efficiency of the LNG terminals, to ease the shortage of available resources in the relevant areas of sea, and to improve the throughput of LNG terminals, and to achieve good economic and social benefits.