Research On The Heat Transfer Model And Gasification Capacity Of LNG Air Ambient Vaporizer

With the advantages of high calorific value and easy storage and transportation,liquefied natural gas is usually regarded as the best choice for the main gas source in remote towns.Liquefied natural gas needs to be gasified in LNG station and reach a certain temperature before being transmitted to users through urban gas pipeline network.Air ambient vaporizers are favored by LNG stations,on account of gasifying liquid natural gas without additional energy consumption.Due to the lack of in-depth study on the gasification mechanism of air ambient vaporizers,it is difficult to accurately describe or quantitatively optimize the gasification capacity of LNG station.Designers lack reference basis in the selection and configuration of gasification system of LNG station,which brings many problems to the LNG station,such as the reliability and economy of gas supplying.In this paper,the air ambient vaporizer is taken as the research object,and the overall heat transfer model of LNG air ambient vaporizer close to the actual operation is established and solved.The method of combining numerical modeling with investigation and test is used to modify the model and analyze the heat transfer performance of air ambient vaporizer.On this basis,combining the economic model of air ambient vaporizer and reheater,the double-objective configuration optimization strategy is proposed,and the configuration optimization model of air ambient vaporizer is constructed,which has a certain reference value for the design and selection of air ambient vaporizer.Based on the analysis of the frosting process and heat transfer characteristics of the air side of the air ambient vaporizer,the total heat transfer coefficient equation of the air side of the finned tube under frosting and non-frosting conditions is derived by using the principles of energy conservation and mass conservation.And the heat transfer model of the air side of the finned tube is obtained.On this basis,the mechanism of flow boiling heat transfer in the tube is discussed,and the correlations of thermophysical parameters are selected.The calculation methods of single-phase heat transfer and two-phase heat transfer in the tube are proposed.Finally,the dynamic overall heat transfer model of LNG air ambient vaporizer is established and solved.Through the actual investigation and test,the actual operation data of the air ambient vaporizer are collected,and the actual operation data and the calculation results of the theoretical model are compared to clarify the accuracy of the original theoretical model calculation.From the two aspects of heat transfer mechanism and operation parameters,the reasons for the calculation error of the theoretical model are analyzed.On this basis,the relevant parameters of the original theoretical model are modified,so as to obtain the overall heat transfer theoretical model with high accuracy.Through the investigation and selection of reasonable equipment model,using the modified overall heat transfer model,the relationship between the outlet temperature,the length of each phase in the tube and the heat transfer coefficient with time is discussed,and then the influence of structural parameters(geometry and number of rows of finned tubes,number of fins)and operating parameters(ambient temperature and actual gasification volume)on the heat transfer performance of air ambient vaporizer is analyzed.On this basis,based on the operating conditions of the equipment,the suggestions for the design of the structural parameters of the air ambient vaporizer are put forward.By analyzing the limitation of conventional configuration of air ambient vaporizer and reheater,the configuration principle of air ambient vaporizer is enriched.The investment cost and investment benefit are taken as the optimization objectives of the configuration optimization model,and the double objective optimization model is established.The square sum weighted method is selected as the optimization method of the model,it is concluded that when the surplus coefficient is 1.5 ～ 2.0,the economic efficiency of the configuration scheme is better than that of the surplus coefficient 1.2 ～1.5.