The Research On Recycling Technology Of LNG Cold Energy

With the progressively improvement of the people’s living standard and the development of our country’s economy, a system for supplying fuel gas for living becomes a system necessary for residential building. However, the gas resource of fuel gas system can’t be found everywhere, which is the reality we have to face. Currently, the general method to solve this problem is to build large LNG receiving stations or small LNG storage tank-stations.LNG is liquefied natural gas, and consumes a large amount of compressio n work during the process of its liquefaction, so that the natural gas is liquefying below-162℃. From the perspective of safety, our country’s LNG storage adopts ordinary pressure and low temperature storage; storage containers uses a cold insulation structure and low temperature resistant materials. During the process of LNG transforming into natural gas of normal temperature so as to supply to users, it will generate a lot of cold energy. According to the second law of thermodynamics, the lower a temperature of the cold energy is, the better a quality of the old energy will be, so the LNG cold energy is high quality energy.Based on summarizing a result of recycling cold energy of domestic and overseas, the present article is having systematacially discussed utilizing methods of cold energy, and obtains a general principle which the utilizing methods of cold energy should follow. After a detail analysis and study about gradient utilization of cold energy, consider that a reasonable system utilizing gradient utilization of cold energy should develop characteristic having a higher grade of LNG cold energy firstly and utilize cold energy for low temperature cycle power generation. However, in order to improve generating efficiency, the system of LNG cold energy power generation should be multistage. During transforming LNG utilized for power generation into natural gas of low temperature, an index of storing cold energy of natural gas has been reduced greatly. The natural gas should further recycle cold energy for freezing process, or should be directly used to produce air-conditioning cooling water, if there is a need.Another factor to limit utilizing methods of cold energy is the quantity of LNG cold energy. If the quantity is smaller, it is not suitable for gradient utilization, because the system of gradient utilization of cold energy is complex, benefits of recycling cold energy is difficult to recycle initial investment of the system. Thus, in the case of LNG storage tank-stations in miniature, the recycling of cold energy should adopt a simple system appropriately, for example, which is directly used for freezing or is directly used to produce air-conditioning cooling water. Although such recycling method wastes the quality of LNG cold energy, economic benefits are reasonable.By means of a design of the cold energy recycling system of LNG storage tank-stations of Towngas-Ben Xi new city branch and a computational analysis of initial investment and economic benefits thereof, the cold energy recycling has significant energy saving benefits, and has directly obtained economic benefits. LNG cold energy recycling has better social benefits and economic benefits.