Analysis Of Gasification Capacity And Influencing Factors Of LNG Air Temperature Gasifier

Liquefied Natural Gas(LNG)plays an important role in emergency peak regulation systems in towns and cities because of its high energy density,small footprint and convenient transportation.When LNG is used as an emergency peak-shaving gas source for town gas transmission and distribution systems,it should be stored,vaporized,pressure-regulated,metered and odorized through the process system of the LNG vaporization station,and then entered into the town gas pipeline network after meeting the requirements.The LNG ambient air vaporizer installed in the vaporization station changes the LNG from liquid to gas.The ambient air vaporizer(AAV)is a heat exchanger that uses the temperature difference between the cryogenic liquid and the ambient air,and is widely used for its energy saving,environmental protection and safety advantages.In engineering practice,the heat transfer performance of LNG ambient air vaporizer is influenced by factors such as air temperature,wind speed and direction,arrangement spacing and layout,etc.At present,relevant scholars at home and abroad lack in-depth research on the heat transfer performance of multi-tube integrated ambient air vaporizer.It is difficult to quantitatively analyze the gasification capacity based on the influence of multiple factors.The selection of gasification equipment and the formulation of operation plans lack theoretical basis,which seriously affects optimal design and efficient operation of LNG emergency peak-shaving gasification project.Based on the basic structure of LNG ambient air vaporizer,using the theory of heat transfer,fluid mechanics and thermodynamics,the gasification phase transition,turbulent convection heat transfer in the tube,and flow in the tube involved in the gasification process of LNG in the ambient air vaporizer are analyzed.The boiling heat transfer and the natural convection heat transfer process on the air side outside the tube are theoretically analyzed,and the applicable LNG gasification process simulation control equation and flow calculation model are determined in the CFD software.In the process of LNG gasification,the thermal property parameters of the LNG and supercritical natural gas in the vaporizer and the dry air outside the vaporizer are constantly changing.Based on the gas components and single gas thermal property parameters,the supercritical natural gas bubble point temperature is calculated using Aspen HYSYSYS software.According to the bubble point temperature,gas composition and single gas thermal property parameters,the Aspen HYSYS software was used to fit the supercritical natural gas thermal property parameters.The thermal property parameters of dry air are fitted according to the thermal property parameters of dry air at different temperature conditions.Finally,the fitted equations for density?,constant pressure specific heat capacity c_p,kinetic viscosity?and thermal conductivity?of supercritical gaseous natural and dry air as a function of temperature are derived for the accurate dynamic simulation of the vaporizer heat transfer process.According to the size of the LNG gasification equipment actually used in the project,the physical model of the ambient air vaporizer is established,and common control equations and turbulent flow calculation models in CFD software are selected.Custom input LNG,supercritical natural gas,dry air thermal properties parameters fitting calculation formula,consider the changes of environmental temperature,wind speed and direction factors,and simulate the ambient temperature field around a single vaporizer and the temperature change of the fluid in the tube.At the same time,considering the changes of influencing factors such as ambient temperature,wind speed and direction,arrangement and equipment spacing,the ambient temperature field around the ambient air vaporizers and the temperature changes of the fluid in the tubes were simulated.Based on the simulation results of the ambient temperature field around an ambient air vaporizer and the temperature variation of the fluid inside the tube,the gasification heat transfer performance of the ambient air vaporizer,concluding that the higher the environmental temperature,the better the heat transfer effect of the equipment;The higher the wind speed,the better the heat transfer effect of the ambient air vaporizer,but when the wind speed exceeds 4 m/s,the change in wind speed has less effect on the heat transfer performance of the vaporizer;when the wind direction is the same as the LNG main inlet flow,the heat transfer effect of the ambient air vaporizer is significantly better than when the other wind directions are used.From the analysis of the simulation results of the ambient temperature field around the three ambient air vaporizers and the fluid temperature variation inside the tubes,it is concluded that three ambient air vaporizers with a gasification capacity of 1500 Nm~3?h operating at the same time,when arranged in a single line,the distance between adjacent equipment is not less than 2 m to ensure normal operation of the equipment;and heat transfer is more effective when the wind direction is horizontally perpendicular to the LNG main inlet flow of the vaporizer.On the basis of the above simulation results and analysis conclusions,the design of LNG gasification stations should take into account the local ambient temperature,wind direction,wind speed and wind frequency,as well as the arrangement of gasification equipment and equipment spacing,to carry out a reasonable layout of ambient air vaporizer in order to improve the operation of equipment and save land for project construction.When using a square triangular arrangement,the greater the interval between the arrangements,the better the heat transfer effect of the equipment,and when the wind direction is against the direction of the LNG main inlet,the heat exchange effect of multiple ambient air vaporizers does not affect each other and the equipment gasification effect is better.