LNG接收站管道预冷温度—应力模型

LNG接收站管道预冷是保证接收站能够顺利运行的关键之一,但是预冷有可能导致管道应力损伤,具有较大的风险隐患。为了有效地指导LNG接收站管道预冷工作,针对大型LNG接收站管道预冷作业,基于CFD建立预冷温度模型,从网格优化、动力松弛因子、相变模型选择等方面进行计算控制,实现了多组分、多相、大尺度、长时间预冷多相流的快速、稳定计算;结合温度差值算法建立LNG接收站管道预冷应力模型,实现了温度模型和应力模型的耦合,据此分析预冷温度变化造成的热应力作用,基于子模型技术实现对峰值应力区域的应力、疲劳寿命的精细评估,并对某油田公司LNG接收站的预冷作业进行分析。研究结果表明:①依据案例管道结构的不同,管道内气液状态具有较大差异;②管道位移较大点位于在拐角位置,应力较大值集中在三通、四通的连接位置;③案例预冷工作条件下,疲劳损伤弱点在某三通接头倒角处。结论认为,所建模型计算结果的精度高,可为LNG接收站管道预冷设计和作业提供技术支持,具有较好的推广应用价值。

A temperature–stress model for pipeline pre-cooling in an LNG receiving terminal

Pipeline pre-cooling in an LNG receiving terminal is one of the key factors in ensuring the smooth operation of the receiving terminal. However, pre-cooling may bring stress damage to pipelines, so there are great risks and hidden troubles. In order to provide effective guidance for pipeline pre-cooling in an LNG receiving terminal, this paper established a pre-cooling temperature model based on CFD for the pipeline pre-cooling operation of large LNG receiving terminals. In this model, the computation control is conducted from the aspects of grid optimization, dynamic relaxation factor and phase change model selection, and the fast and stable calculation of multicomponent, multiphase, large scale and long time pre-cooled multiphase flow is realized. Then, combined with the temperature difference algorithm, the stress model for pipeline pre-cooling was established, and the coupling of temperature model and stress model was accomplished. Based on this, the thermal stress effect caused by the pre-cooling temperature change was analyzed. Moreover, the stress and fatigue life in the range of peak stress were precisely evaluated by means of the sub-model technology. Finally, the pre-cooling operation in an LNG receiving terminal in one certain oilfield company was analyzed. And the following research results were obtained. First, the state of the gas and liquid in the pipeline varies greatly due to the different structures of the case pipeline. Second, the larger displacement of the pipeline is located at the corner, and the larger stress concentrates at the connections of tee and cross joints. Third, under the pre-cooling working condition of the case, the fatigue damage weakness is at the chamfer of a tee joint. In conclusion, the calculation results of this newly established model are of high accuracy, so this model can provide technical support for the design and operation of pipeline pre-cooling in LNG receiving terminals and its popularization and application value is high.