某LNG接收站再冷凝工艺优化及控制方案设计

发布时间：2018-12-28 12:05

【摘要】：液化天然气(Liquefied Natural Gas,即LNG)是当今世界发展最快的一种优质、清洁能源。作为液化天然气产业链中较为重要的环节——LNG接收站,是LNG气源与用户管网的连接单元。近些年来,我国在大规模推动LNG接收站的建设,截至2014年底,我国在建LNG接收站24座,已投产10座。LNG接收站工艺系统卸料、压缩机、泵等动设备运转、外界热量的导入、环境变化等因素将引起储罐、设备及管线内产生大量蒸发气(Boil Off Gas,即BOG)。BOG气体若处理不当,会影响装置的运行,造成资源浪费和环境污染等问题。因此,接收站BOG处理单元的稳定、安全、经济运行十分重要。目前,LNG接收站BOG处理工艺普遍采用再冷凝工艺。本论文利用Aspen HYSYS对某LNG接收站再冷凝工艺进行模拟分析及用能分析。结果表明：有效能损失最严重的单元为再气化系统,有效能损失占全流程的80%,其次是高压泵和压缩机,分别为17%,2.8%。在对某LNG接收站再冷凝工艺进行模拟分析及用能分析的基础上,对再冷凝工艺进行了参数优化与流程改进。通过灵敏度分析选取LNG流量、LNG中CH4含量、LNG外输压力及BOG排出压力为关键参数,采用响应面法分析关键参数的交互程度并拟合得到这四个参数关于总能耗关系的方程,将此方程代入Matlab,以总能耗为目标函数,求得最优操作参数,最终,总能耗降低15.06%。针对再冷凝工艺中外输气负荷低时运行困难及压缩机能耗高等问题,对再冷凝工艺进行改进,在两级压缩机中间增加一台再冷凝器,将部分BOG气体冷凝液化为LNG,用LNG泵增压,以达到缓解外输负荷低时一个再冷凝器难以运行及降低压缩机能耗的目的。经计算,改进工艺的压缩机能耗减少135.76kW,降低百分比约为45.56%,工艺总能耗降低13.98%,节能效果显著。同时对改进工艺进行主要设备计算及装置设备平面布置。本论文对改进工艺进行了控制方案初步设计,并着重对整个LNG接收站自控系统的核心设备——BOG压缩机及再冷凝器等的控制方案进行论述,以改善工艺的操作弹性,使装置能更好适应接收站输气负荷的波动。
[Abstract]:Liquefied natural gas (Liquefied Natural Gas,) is the world's fastest growing quality, clean energy. As an important link in LNG industry chain, LNG receiving station is the connection unit between LNG gas source and user network. In recent years, China has been promoting the construction of LNG receiving stations on a large scale. By the end of 2014, 24 LNG receiving stations were under construction in our country, and 10 of them had been put into production. The process systems of LNG receiving stations, such as unloading materials, compressors, pumps, and so on, operated and imported heat from the outside. Factors such as environmental change will cause a large amount of evaporative gas (Boil Off Gas,) in storage tanks, equipments and pipelines. If the gas is not treated properly, it will affect the operation of the device and lead to the waste of resources and environmental pollution. Therefore, the receiving station BOG processing unit stability, security, economic operation is very important. At present, the BOG treatment process of LNG receiving station generally adopts recondensation process. In this paper, Aspen HYSYS is used to simulate and analyze the recondensation process of a LNG receiving station. The results show that the unit with the most serious effective loss is the regasification system, and the efficiency loss accounts for 80% of the whole process, followed by the high pressure pump and compressor, which are 172.8% respectively. Based on the simulation analysis and energy use analysis of the recondensation process at a LNG receiving station, the parameter optimization and process improvement of the recondensation process are carried out. LNG flow rate, CH4 content in LNG, LNG transport pressure and BOG discharge pressure are selected as key parameters by sensitivity analysis. The interaction degree of key parameters is analyzed by response surface method and the equation of total energy consumption is obtained by fitting the four parameters. Taking the total energy consumption as the objective function, the optimal operating parameters are obtained by using this equation in Matlab,. Finally, the total energy consumption is reduced by 15.06. Aiming at the problems of difficult operation and high energy consumption of recondensing process when the gas transmission load is low at home and abroad, the recondensing process is improved, a recondenser is added in the middle of the two-stage compressor, and part of BOG gas condensing and liquefaction is added to the LNG pump for LNG,. In order to reduce the energy consumption of compressor, it is difficult for a recondenser to operate when the load is low. The calculated results show that the energy consumption of the improved process is reduced by 135.76kW, and the reduction percentage is about 45.56kW, the total energy consumption of the process is reduced by 13.98kW, and the energy saving effect is remarkable. At the same time, the main equipment calculation and the layout of the equipment are carried out. In this paper, the control scheme of the improved technology is designed, and the control scheme of BOG compressor and recondenser, which is the core equipment of the automatic control system of the whole LNG receiving station, is discussed in order to improve the operation flexibility of the process. The device can better adapt to the fluctuation of the gas load at the receiving station.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE83;TE974

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