Simulation And Optimization Of Natural Gas Liquefactuin Process Based On Ejector

There are a large amount of remote gas fields and associated gases which are not developed because of the lack of mature and economic technologies.Small-scale LNG plant is considered to be the most suitable technology to utilize the remote gas fields.Among them,the high-pressure ejected natural gas liquefaction process is widely used in the exploitation of compressed gas wells due to its simple start-up and shutdown,convenient installation and high system reliability.As the core equipment of the liquefaction process,the performance of ejector will directly affect the capability of the liquefaction process,such as the unit energy consumption of the process and the liquefaction ratio.Therefore,this paper will focus on the study of the ejector.In recent years,the application of ejector has been greatly expanded,but the ejector model is not integrated in the commonly used process simulation software such as Aspen Plus,Aspen HYSYS and Pro II.In order to establish the natural gas liquefaction process with the ejector in Aspen HYSYS software,this paper constructs the ejector model in Aspen HYSYS by combining the existing model of Aspen HYSYS and combining the thermodynamic model of the ejector.However,for the constructed ejector model,the parameters that need to be determined include nozzle efficiency,mixing efficiency and diffusion efficiency.In order to determine the specific values of the input parameters,this paper presents a method to obtain the above efficiency parameters through the numerical simulation results.Since the ejector efficiency is greatly affected by the working fluid pressure and the ejector outlet pressure.Therefore,it is unreasonable to set mixing efficiency and diffusion efficiency as constants.In this paper,a hybrid model of the ejector is established to ensure the accuracy of the ejector module during the optimization.Firstly,a reasonable range of operating parameters is obtained through CFD simulation,and then a simulated sample is generated by uniform design,and the correlation between the ejector efficiency and operating parameters is obtained by fitting the ejector efficiency parameters of the sample.And input the established efficiency correlation into the ejector module from the spreadsheet in Aspen HYSYS.Finally,based on the above research,a simulation of the ejector-based natural gas liquefaction process was built in Aspen HYSYS software.Aiming at the disadvantage of high energy consumption in the natural gas liquefaction process,the natural gas liquefaction process was optimized with the unit energy consumption of the process as the objective function.The optimization results show that the unit energy consumption of the optimized process is 0.308 k W.h/Nm3,which is 8.18% lower than the process before optimization,and the total exergy loss of the optimized liquefaction process is203.86 k W,which is 16.26% lower than the process before optimization.