| With the diversification of global energy resources, liquefied natural gas(LNG) as a clean, efficient energy has been rapid development in recent years. Storage and transportation of LNG terminals is very important part in LNG industry chain, you need to discharge pipelines and storage tanks and other equipment for pre-cooling when initial unloading LNG.Equipment within the station must first to be finished the commissioning work before put into use and the pre-cooling is its important aspects of the commissioning work. If the pre-cooling process control is not good, it can cause structural damage to the tank, you can’t continue to use, even worse it can make serious accidents caused by leakage of LNG. So the pre-cooling work is a very dangerous and very important work.Precooling study was to determine the pre-cooling time, pre-cooling process for the fluid rate and temperature drop regularity of the tank. Aiming at the domestic LNG terminals, this paper outlined LNG terminals processes, introduced the technology and systems within the station, elaborated the material selection of LNG unloading pipes and large storage tanks, production operations, pre-cooling control requirements. According to different pre-cooling medium, introduced two pre-cooling solutions and the advantages and disadvantages of each option are analyzed and compared.Either way to take pre-cooling, determine the fluid rate of pre-cooling process, control the rate of temperature drop is fundamental to complete the pre-cooling operation. Therefore, it’s need to study the law of pre-cooling tank in theory and get relevant control parameters in pre-cooling process. Through the analysis of large thermal storage tank and heat transfer calculation to verify the performance of the tank insulation, established a pre-cooling time model, pre-cooling fluid supply rate model and temperature, pressure mathematical model. By comparison with the actual data obtained pre-cooling model results are reliable. According to the theoretical model and takeing the 160,000 m3 large storage tanks for example, calculated the total amount of consumption and supercritical fluid supply rate of liquid storage tanks, analysised tank temperature variation with time, proposed specific rate of liquid and temperature drop control program for pre-cooling.As the study of theoretical model made a simplified hypothesis, in order to fully analyze the effect of pre-cooling tanks, taking into account that experimental study subject to greater restrictions, therefore, useing computational fluid dynamics software FLUENT to build tanks 10,000m3 simulation model. Simulated the temperature field, velocity field and flow field distribution of the pre-cooling process tanks, drew the conclusion that there is a large unevenness in the spatial. Through data on the physical and temperature monitoring points obtained by simulation analysis has gotten rapid temperature drop regions and the temperature difference between the larger point regions. It’s indeed to note the temperature drop of tank bottom and center area of the temperature monitoring. By simulating different inlet velocity analysis of the law of the tank temperature drop, comeing a conclusion that pre-cooling process to select a reasonable rate for the fluid tank can better control the temperature drop, giveing a liquid nitrogen tank for pre-cooling liquid 10000m3 rate plan.Finally, according to the literature survey, the results of model calculations and simulate analysis, summarized the overall pre-cooling scheme proposed receiving station. Research work in this paper can provide a theoretical basis for field operations precooling. There is certain guiding significance on the production run of LNG terminal. |
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