大型LNG储罐内压力及蒸发率的影响因素分析

LNG在储罐内的蒸发对LNG储罐的安全有着非常大的影响。为此,以3×104m3的LNG储罐为例,在分析研究的基础上,基于质量守恒及能量守恒原理,建立了预测LNG储罐内压力及蒸发率的模拟模型,经试验验证该模型的计算结果较为准确可靠。利用该模型分析了密闭LNG储罐内压力及蒸发率的影响因素。结果发现:密闭LNG储罐存在1个"最优直径"和"最优充满率";LNG储罐保温层导热系数越大,LNG储罐内压力上升得越快,LNG安全储存时间就越短;环境温度越高,密闭LNG储罐的压力上升得越快,LNG安全储存时间越短;LNG含氮量、外界大气压对LNG储罐内的压力影响不大;LNG含氮量越高其的蒸发率越低,向LNG储罐内充注氮气可以有效地降低LNG储罐内液体的蒸发率。该项成果将为LNG储罐的设计及运行提供技术支持。

Controlling factors of internal pressure and evaporation rate in a huge LNG storage tank

The LNG evaporation is crucially important for the safety of a LNG storage tank. Hereby, a 30000 m3 LNG storage tank was taken as a case study, a simulation model of forecasting the internal pressure and the evaporation rate based on the conservation of mass and energy. The calculation results of this model are reliable in accuracy after experimental verification. By use of this model, the controlling factors of the internal pressure and LNG evaporation rate in the closed LNG storage tank are analyzed. The results show that (1)"the optimal diameter" and "the filling rate limit" both exist in a closed LNG storage tank; (2)the higher the heat conductivity of the tank's insulating layer, or the higher the environment temperature is, the faster the internal pressure of the tank increases, thus, the shorter the safe storage time of the LNG in the tank; (3)the nitrogen content in the stored LNG and the outside atmosphere pressure have little effect on the internal pressure of the tank; and (4) the higher content of the nitrogen in the LNG, the lower the LNG evaporation rate in the tank, so filling nitrogen into the LNG tank can effectively decrease the evaporation rate in the tank. This study provides technical support for the design and operation of LNG storage tanks in China.