LNG储备库蒸发气回收工艺研究

Study of boil off gas recovery process in LNG repository

关键词:  LNG  储备库  BOG  回收  液化工艺  有效能  系统功耗

Key words:  LNG  repository  BOG  recovery  liquefaction process  effective energy  power consumption of system

摘要:

蒸发气(BOG—Boil Off Gas)的处理是LNG储备库必须考虑的关键问题之一,它关系着LNG储备库的能耗、安全及平稳运行。为减少因BOG放空而造成的巨大损失,有必要采用BOG回收技术。在分析适用于LNG储备库的BOG回收方法的基础上,又提出甲烷制冷剂液化循环、混合制冷剂液化循环及氮气膨胀制冷液化循环3种BOG再液化方案,进一步减少由LNG储备库运行所产生的热量损失。用HYSYS软件模拟工艺流程对比分析了3种方案所需制冷剂流量及系统功耗,结合有效能相关理论确定适用于LNG储备库的BOG再液化方案——混合制冷剂液化循环方案。该方案的压缩机轴功率比甲烷制冷剂再液化方案小15.30 kW,比氮气膨胀再液化方案小146.42 kW,且系统功耗相对较小；混合制冷剂液化循环方案系统有效能损失较氮气膨胀液化方案小22.06%,较甲烷制冷剂再液化方案小35.78%；此外,该方案所需制冷剂流量较少,适用于储备规模较大的LNG储备库。

Abstract:

The boil off gas (BOG) processing system is one of the key issues directly relating to the energy consumption, safe and steady operation of LNG repository. In order to reduce huge losses caused by the venting of BOG, it is necessary to adopt the BOG recovery technology in LNG repository. To reduce the energy loss caused by the heat leakage, three BOG reliquefaction processes (methane refrigerant liquefaction cycle, the mixed refrigerant liquefaction cycle and nitrogen expansion refrigeration liquefaction cycle) were proposed based on analyzing the BOG recovery methods of LNG repository. Using Aspen HYSYS software to simulate the BOG reliquefaction process, the refrigerant flow and the power consumption of the system needed in three processes were compared and analyzed, and the most suitable BOG reliquefaction process (the mixed refrigerant liquefaction cycle) in LNG repository was determined with the effective energy related theory. The shaft power of compressor is 15.30 kW less than that of the methane refrigerant liquefaction cycle process and 146.42 kW less than that of the nitrogen expansion refrigeration cycle process. Moreover, the effective energy loss of mixed refrigerant cycle system reduced 22.06% compared with that of the nitrogen expansion refrigeration cycle process, and lowered 35.78% than methane refrigerant liquefaction cycle process; the required refrigerant flow was small. It is applicable to LNG repository with large storage scale.