气体膨胀式天然气带压液化流程的设计与优化

Simulation and optimal design of a natural gas pressurized liquefaction process with gas expansion refrigeration

天然气带压液化(PLNG)技术可在较高的压力和温度下储存液化天然气,为海上天然气的液化提供了可能,但对于PLNG流程的相关运行参数、性能优化方面的研究几乎还未见报道。为此,借鉴气体膨胀式天然气液化系统的优点,针对CO2含量较低的海上天然气设计了一种气体膨胀天然气带压液化流程,并利用HYSYS软件进行了模拟和优化。结果表明:①分别采用N2、50%N2+50%CH4、CH4作为制冷剂,以产品LNG的单位能耗为衡量指标,对流程的4个关键参数(进口天然气压力、LNG储存压力、气体制冷剂膨胀前压力及气体制冷剂膨胀前预冷温度)进行了优化分析,并得到了它们的最优值;②比较了N2、50%N2+50%CH4、CH4分别作为制冷剂时,流程的能耗情况,发现CH4是能耗最低的制冷剂;③将优化后的氮膨胀天然气带压液化流程与常规氮膨胀天然气液化流程进行比较,结果表明前者不仅占地面积小、流程简单、设备初始投资低,而且运行工况更优良、能耗更低(仅为0.218 9kWh/m3,比常规流程的能耗降低了46%)。

LNG can be stored under a rather high temperature and pressure with the aid of pressurized natural gas liquefaction （PLNG） technology, which also makes it possible for offshore natural gas to be liquefied. However, few literatures on this subject have ever been found up till now. In view of this, a natural gas pressurized liquefaction process with gas expansion refrigeration was designed, especially for the offshore natural gas with a low content of carbon dioxide. Then, the HYSYS software was adopted to simulate and optimize this process. First, N2, 50~ N2 --50% CH~, and CH4 were adopted respectively as refrigerants, the unit en- ergy consumption of LNG was regarded as the measurement index, and an optimal analysis was then performed of the 4 key parame- ters in this flow process： inlet natural gas pressure, LNG storage pressure, pressure and pre-cooling temperature of a gas refrigerant before expansion, the optimal values of which were also obtained. Second, through a comparative analysis, CH4 is found to be the refrigerant with the lowest energy consumption needed in the flow process. Third, by comparison, this optimized flow process has more advantages than ever before： less space occupied, simple flow process, and low initial equipment cost, and its energy consumption is reduced by 46% with only 0. 2189 kWh/m^3 as a result.