晃荡条件下LNG系统中气液分离器分离特性模拟研究

发布时间：2019-05-10 13:26

【摘要】：随着我国天然气能源消费占比的逐渐增高,国内的天然气资源已经无法满足市场需求,大力发展海上天然气技术将是缓解能源压力的一种主要方式。在海上天然气液化流程中,分离器作为两相分离的关键设备,分离出的液相冷剂为换热器提供冷量,气相为后续流程提供制冷剂。重力式分离器以其结构简单、易大型化的特点,多应用于海洋平台及浮式油轮上,其分离效果对换热器的性能乃至液化系统影响很大,因此对分离器的分离特性进行研究十分必要。本文采用FLUENT软件对设计的重力式气液分离器进行数值模拟。首先介绍了FLUENT软件所用到的数值计算方法;其次,简化重力分离器的模型以便用于数值模拟,划分网格、进行了网格无关性验证并验证了模型的准确性;最后,选定数值模拟所需的计算模型、边界条件等,并将分离效率作为分离器分离特性的评价指标。本文主要针对海上晃荡工况,因此要研究晃荡条件对分离特性的影响。真实海况下,影响晃荡的主要因素包括横摇、纵摇和垂荡。根据分离器结构的对称性,将其简化为横摇和垂荡。针对这两种晃荡工况,分别研究不同振幅与周期条件下,重力分离器气体出口液相流量与分离效率的变化情况。经研究可知,分离器出口液相流量与分离效率随时间发生正弦变化,且晃荡工况使分离效率下降:振幅越大,流量波动越剧烈,分离器对两相流的分离效果越差;周期增大,流量波动越平缓,分离效果越好。在天然气液化流程中,不同阶段的混合冷剂组分不同,运行参数也有所差异;相关联设备尺寸与运行工况的差异导致分离器结构参数的变化。在同一晃荡条件下,分别研究不同制冷剂流量、干度、分离器直径、高度、进出口管径对分离效果的影响,对结果分析可知,不同的运行及结构参数对分离特性有不同的影响规律。最后,根据晃荡参数、运行参数、结构参数的研究结果,对分离器的结构加以改进。分别研究挡板、多孔隔板联箱及二者共同作用下分离器的分离特性,分析结果可知:分离效率随着挡板角度的增大而减小;多孔隔板联箱在稳定流场方面有明显作用,且分离效率随着联箱孔隙率的增大而减小;二者共同作用下,分离器性能有明显提升。
[Abstract]:With the increasing proportion of natural gas energy consumption in China, the domestic natural gas resources have been unable to meet the market demand. Vigorously developing offshore natural gas technology will be a main way to alleviate the energy pressure. In the offshore natural gas liquefaction process, the separator is the key equipment for two-phase separation, the separated liquid phase coolant provides cooling capacity for the heat exchanger, and the gas phase provides refrigerants for the subsequent process. Gravity separator is widely used in offshore platforms and floating tankers because of its simple structure and easy to be large-scale. Its separation effect has a great influence on the performance of heat exchanger and even on liquefaction system. Therefore, it is necessary to study the separation characteristics of the separator. In this paper, FLUENT software is used to simulate the designed gravity gas-liquid separator. Firstly, the numerical calculation method used in FLUENT software is introduced. Secondly, the model of gravity separator is simplified for numerical simulation, grid division, grid independence verification and verification of the accuracy of the model. Finally, the calculation model and boundary conditions needed for numerical simulation are selected, and the separation efficiency is taken as the evaluation index of separation characteristics of separator. In this paper, the influence of sloshing conditions on separation characteristics should be studied because of the sloshing condition at sea. In real sea conditions, the main factors affecting sloshing include rolling, pitching and swinging. According to the symmetry of separator structure, it is simplified as rolling and swinging. According to these two sloshing conditions, the variation of liquid flow rate and separation efficiency at the gas outlet of gravity separator under different amplitude and period conditions is studied respectively. The results show that the liquid flow rate and separation efficiency at the outlet of the separator change sine with time, and the sloshing condition makes the separation efficiency decrease: the larger the amplitude is, the more violent the flow rate fluctuates, and the worse the separation effect of the separator on the two-phase flow is. With the increase of cycle, the calmer the flow fluctuation is, the better the separation effect is. In the natural gas liquefaction process, the components of the mixed coolant in different stages are different, and the operation parameters are also different, and the difference between the size of the associated equipment and the operating conditions leads to the change of the structure parameters of the separator. Under the same sloshing condition, the effects of different refrigerants flow rate, dryness, separator diameter, height and inlet and outlet pipe diameter on the separation effect were studied, and the results were analyzed. Different operation and structural parameters have different effects on the separation characteristics. Finally, according to the research results of sloshing parameters, operation parameters and structural parameters, the structure of the separator is improved. The separation characteristics of the separator under the action of baffle, porous partition header and the two are studied respectively. the results show that the separation efficiency decreases with the increase of baffle angle. The porous partition header plays an obvious role in stabilizing the flow field, and the separation efficiency decreases with the increase of the porosity of the header, and the performance of the separator is obviously improved under the combined action of the two.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE967

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