Investigation On Vapor Liquid Equilibrium Of Methane And Non-hydrocarbons In Natural Gas

Natural gas is gaseous fossil fuel consisting primarily of methane.There may also be many other hydrocarbons(ethane,propane,butane,etc.)and non-hydrocarbons(nitrogen,helium,carbon dioxide,traces of hydrogen sulfide and water,etc)in natural gas.Separating non-hydrocarbons from methane in natural gas would not only improve the utilization efficiency of natural gas,but also generate additional economic value,which is important to the development and utilization of natural gas.It calls for relevant knowledge of phase equilibrium for the design and optimization of separation process.Thus,studying vapor liquid equilibrium(VLE)of methane and non-hydrocarbons in natural gas is of great significance.Since nitrogen and carbon dioxide are common compositions of natural gas and argon is precious gas resource in natural gas,the VLE investigations of methane with nitrogen,carbon dioxide and argon were studied in this paper.The main work of this paper was shown as follows.(1)Investigations about the vapor liquid equilibrium of the mixtures of methane and non-hydrocarbons(N2?CO2?Ar)from early period to recent years were developed.The research scopes,experimental methods and theoretical calculation methods were summarized to provide strong guidance for further researches.(2)A computer procedure was developed on the base of phase equilibrium theory.Four equations of state(SRK,PR,PRSV,NM)and five mixing rules(vdW,HV,MHV1,MHV2,LCVM)were adopted to correlate the VLE data collected from literatures,and different models were analyzed with the correlation results.It was found that MHV1 mixing rule and PR equation of state had the best accuracy for different mixtures of natural gas at different temperatures compared with the other mixing rules(vdW,HV,MHV2,LCVM)and equations of state(SRK,PRSV,NM).With the model parameters obtained from correlation,the thermodynamic properties of methane and non-III hydrocarbons were discussed deeply.In addition,the critical points of mixtures were studied,and accurate empirical method was given with optimized model parameters for different mixtures.(3)The previous experimental apparatus was improved by using a home-made gas pump to replace the original one,ameliorating heat insulation methods and reducing the dead volume of drain pipe section.The VLE data of Ar+CH4 from 95K to 135K were measured with the improved apparatus,which were important for the design and optimize of separation operation of methane and argon.The thermodynamic properties of the mixture were discussed with physical models of phase equilibrium to provide reliable basis for follow-up studies.