利用LNG冷能的海水淡化流程比较

冷冻法海水淡化方法的制冷系统耗电量大,因而应用得并不广泛。另一方面,液化天然气(LNG)在其汽化过程中会释放出大量冷能。因此,将LNG蒸发和海水冻结两个过程结合起来可以在汽化LNG的过程中同时制取淡水。本文比较了两种冷冻法海水淡化的方案,即二次冷媒/海水直接接触法和二次冷媒/海水间接接触法。鉴于其简单和便于应用,选择间接接触法开展进一步研究。按照冷媒的不同工作状态提出了两种流程。在无相变流程中,二次冷媒在整个循环中保持在过冷液体状态。而在相变流程中,二次冷媒在冷冻海水时蒸发,并在汽化LNG时冷凝。在不同制冷温度下对两个流程的性能进行了分析。研究表明,相变流程制冷剂流量和功耗均较小。同时,研究结果说明利用LNG冷能进行海水淡化是可行的。

Process comparison of seawater desalination with LNG cold energy utilization

The freezing desalination method is not being used widely,since it needs refrigeration system that consumes much electricity power.On the other hand,liquefied natural gas(LNG)will release a lot of cold energy during its vaporization process.Thus,combining the two processes of LNG vaporization and seawater freezing will produce freshwater while gasifying LNG.In this paper,two kinds of seawater freezing desalination methods are compared,which are the secondary refrigerant/seawater direct-contact method and the secondary refrigerant/seawater indirect-contact method.The indirect-contacting method is then chosen for further study because it is simple and easy to be applied.Two processes are presented with different refrigerant conditions.In the non-phase-change process,the secondary refrigerant remains as subcooled liquid in the whole cycle.In the phase-change process,the secondary refrigerant is vaporized when freezing the seawater,and is condensed when gasifying the LNG.Performances of the two systems at different refrigerating temperatures are analyzed.The study shows that the phase-change process has smaller refrigerant mass flow rate and power consumption.The results show that it is practical to achieve seawater desalination by recovery of LNG cold energy.