【作者】 黄美斌；

【导师】 林文胜；

【作者基本信息】 上海交通大学 ， 制冷及低温工程， 2010， 硕士

【摘要】 LNG的温度很低,含有宝贵低温冷能,所以在其气化时,有很多冷量可以利用,目前,国内外对LNG冷能利用的研究越来越多,有低温发电,冷库,空调,空分,低温粉碎,相变储能等方面。淡水是人类的生存资源,淡水的缺乏已经越来越严重,海水淡化技术受到了广泛的重视,具体分为蒸馏法,膜法和冷冻法三种,其中冷冻法海水淡化技术是需要冷能来使得海水结晶的,由此考虑把LNG冷能和冷冻法海水淡化相结合起来,形成了本论文“利用液化天然气冷能的海水淡化技术与装置的研究开发”。通过理论分析和实验研究,设计的海水淡化装置,实现了节能减排的目标。本文着重进行以下几方面的理论和实验研究,取得了一定的进展和成果。(1)选择了三种海水淡化冷冻法进行比选,即直接接触法,真空法和间接法。经过计算分析,得出直接接触法传热效率高,设备尺寸小,不消耗额外的电能,但其结晶过程复杂,技术成熟度低,缺乏基础研究理论知识。真空法是热质交换过程,所需LNG流量较少,但真空泵耗能较大,真空条件难以控制,技术成熟度较低。间接冷冻法技术较为成熟,操作比较简单,有借鉴的成熟产品。所以本实验选用间接冷冻方式来设计样机。(2)对中间冷媒进行比选,使得冷媒要满足低温条件下运行,也要满足具体实验的要求,最后选择了环保冷媒R410A。同时根据冷媒在运行时是否发生相变而提出了两种方案,通过软件的模拟分析,有相变流程具有流量小,功耗低的特点,最后选择它作为本课题的流程方案。(3)对海水结晶器(制冰桶)进行比选,分析比较了板冰机和片冰机各自的优缺点,片冰机由于具有传热效率高,能连续使得海水结晶,脱冰过程不需要热源等优势而被选用。对整个实验流程中的关键参数进行模拟计算,给出的换热系数随冰层厚度,冰层厚度随时间的关系图,得出在结晶过程中换热系数一直在减小,冰层生长速度也在慢慢减小。(4)分别研究了不同冷媒蒸发温度,布水盘喷头数量,海水流量对脱盐效果的影响,实验证明冷媒的蒸发温度越高,喷头数量越多,海水流量越大时,海水形成的冰晶纯度较高,脱盐效果好。本实验装置每消耗1kg液化天然气能获得2kg的冰融水,淡水流量到达了150L/h,充分利用了冷能,达到了节能减排的目标。更多还原

【Abstract】 LNG has valuable cold energy because its low temperature. when it gasifies, there is a lot of cold energy which can be used. More and more countries pay attention to the research of LNG cold energy utilization, including low-temperature power generation, cold storage, air condition, air separation, cryogenic comminution, phase-change energy storage and so on. Fresh water is a kind of human survival resources. Lack of fresh water has become increasingly serious, so desalination technology has been widely appreciated, which is classified into three methods: distillation, membrane and freezing. In freezing desalination, cold energy is need for water crystallization, so LNG cold energy and freezing desalination method can be combined together. This paper just studies "freezing desalination with LNG cold energy utilization". In the paper, through theoretical analysis and experimental research,a energy-saving seawater desalination device with LNG cold energy utilization is designed. This article focuses on theoretical and experimental research and has some results.(1) Comparing three kinds of seawater freezing desalination methods: direct-contacting method, vacuum method and indirect-contacting method. Through calculation and analysis, direct-contacting method has many advantages such as high heat transfer efficiency, small equipment size, consuming no power, but its crystallization process is complex and lack theoretical knowledge in basic research. Vacuum method is a kind of heat and mass transfer process, requiring less flow rate of LNG. However, vacuum bump consumes much energy and vacuum condition is difficult to be controlled. It also lacks theoretical knowledge. Indirect freezing method is more mature, relatively simple, having product reference. Therefore, this experiment uses indirect-contacting method to the design seawater desalination experiment device.(2) The middle refrigerant is selected, which must meet the low temperature operating conditions and specific experiment requirements. R410A is finally selected as middle refrigerant which is a kind of environmentally friendly refrigerant. At the same time, two cycle schemes are presented in accordance with the phase of middle refrigerant, which are non-phase-change process and phase-change process. Through software simulation and analysis, the phase-change process has advantages: small flow rate and low power consumption. So the phase-change process is finally selected as experiment process.(3) Seawater crystallizers (ice-making buckets) are compared and selected, including plate ice machine and tube ice machine. Through analysis and comparison, the plate ice machine has advantages: high heat transfer efficiency, continuous crystallization, removing ice without heat source. So it is chose as seawater crystallizer. Otherwise, the key parameters of entire experimental process is simulated and calculated. The diagrams of heat transfer coefficient vs. ice and ice thickness vs. time are given. The diagrams show that heat transfer coefficient and ice growth rate always reduces.(4) The experiments study that different parameters affect rate of desalination, including refrigerant evaporation temperature, the number of seawater distribution nozzles and seawater flow rate. The experiments show that higher refrigerant evaporation temperature, more seawater distribution nozzles and bigger seawater flow rate will lead to higher purity of ice. In this study, 2kg ice melt water can be got by consuming 1kg LNG. Freshwater flow reaches 150L/h. Cold energy is been fully used and the requirements of energy-saving and emission-decreasing are achieved.更多还原