Optimization Design Of Heat Exchanger System In The Process Of LNG Cold Energy Utilization

LNG cold energy utilization technology is an important energy conservation technology of downstream of LNG industry chain, whose engineering application has been developed maturely abroad, but made slow progress at home. One of the key reasons is that the available technology of heat exchangers requires large occupied area, high investment and complex control systems. Moreover, it is not suitable for widely application in small or medium sized LNG satellite stations and LNG vehicles. Pace of LNG cold energy utilization projects and development of related industry can be both boosted, by optimizing and innovating scheme and heat exchange system of LNG cold energy utilization.New types of LNG vertical heat exchange equipment and integrated equipment are proposed in the paper, to solve problems of large occupied area, high investment and so on. Project of ice-thermal-storage air-conditioner utilizing LNG was designed for an example. The result shows that the heat exchange area of LNG vertical heat exchanger and integrated heat exchanger has reduced by 71.8% and 14.5% respectively than the original process, when the cold amount is 160 k W and refrigerant pressure is at 0.2MPa. It illustrates that new schemes can effectively solve the problems mentioned above. In further comparison, vertical heat exchangers consume higher power because pump is needed for injecting refrigerant, while integrated heat exchangers need no external power. Therefore, the later one is better.An optimized scheme that mixing nitrogen into refrigerant is proposed based on the integrated equipment. Combined with the system leakage, continuous cooling(heating suspension) and other special conditions, the influence of nitrogen on the heat transfer system is studied. The result shows that, the heat transfer process is changed with the addition of nitrogen, phase transition temperature of the refrigerant is increased in restart condition, thus avoiding cold user blocking, making sure system safety. Meanwhile the detecting sensitivity of refrigerant leakage increased by 30.4%, enhanced operating flexibility greatly.New type of heat exchange scheme was applied in the engineering research of a 3kw air condition system in LNG truck. The optimal operation parameters were determined through the analysis of refrigerant flow and nitrogen flow. Economic analysis indicates that the investment of new-type air-conditioner of each LNG truck is 14 thousand Yuan, and 7128 Yuan of electricity cost can be saved annually. In a word, the project proposal is well performed in economy and security and has broad application prospects.