ASTM_D_4784_-_93_2015.pdf

Designation:D478493(Reapproved 2015)Standard Specification forLNG Density Calculation Models1This standard is issued under the fixed designation D4784;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis specification is a description of four mathematical models of the equation of state for LNG-likemixtures that were adopted in 1988.The four models include an extended corresponding states model,a cell model,a hard sphere model,and a revised Klosek and McKinley model.Each of the models hasbeen optimized to the same experimental data set which included data for pure nitrogen,methane,ethane,propane,iso and normal butane,iso and normal pentane,and mixtures thereof.For LNG-likemixtures(mixtures of the orthobaric liquid state at temperatures of 120K or less and containing at least60%methane,less than 4%nitrogen,less than 4%each of iso and normal butane,and less than 2%total of iso and normal pentane),all of the models are estimated to predict densities to within 0.1%of the true value.These models were developed by the National Institute of Standards and Technology(formerly the Bureau of Standards)upon culmination of seven years of effort in acquiring physicalproperties data,performing extensive experimental measurements using specially developedequipment,and in using these data to develop predictive models for use in density calculations.1.Scope1.1 This specification covers LNG density calculation mod-els2for use in the calculation or prediction of the densities ofsaturated LNG mixtures from 90 to 120K to within 0.1%oftrue values given the pressure,temperature,and composition ofthe mixture.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Significance and Use2.1 The models in this specification can be used to calculatethe density of saturated liquid natural gas in the temperaturerange 90 to 120K.The estimated uncertainty for the densitycalculations is 60.1%.The restrictions on composition of theliquefied natural gas are:methane60%or greaternitrogenless than 4%n-butaneless than 4%i-butaneless than 4%pentanesless than 2%It is assumed that hydrocarbons with carbon numbers of sixor greater are not present in the LNG solution.3.Models3.1 Extended Corresponding StatesThe extended corre-sponding states method is defined by the following equations:ZiP,T#5 ZoP hii,o/fii,o,T/fii,o#(1)GiP,T#5 fii,oGoP hii,o/fii,o,T/fii,o#2 RT lnhii,o!(2)where:Z=compressibility factor,G=Gibbs free energy,P=pressure,1This standard is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.08 on ThermophysicalProperties.Current edition approved June 1,2015.Published July 2015.Originally approvedin 1988.Last previous edition approved in 2010 as D4784 93(2010).DOI:10.1520/D4784-93R15.2The formulation of the models and the supporting work was done by theNational Bureau of Standards under the sponsorship of British Gas Corp.,ChicagoBridge and Iron Co.,Columbia Gas Service Corp.,Distrigas Corp.,Easco Gas LNG,Inc.,El Paso Natural Gas,Gaz de France,Marathon Oil Co.,Mobil Oil Corp.,Natural Gas Pipeline Co.,Phillips Petroleum Co.,Shell International Gas,Ltd.,Sonatrach,Southern California Gas Co.,Tennessee Gas Pipeline,Texas EasternTransmission Co.,Tokyo Gas Co.,Ltd.,and Transcontinental Gas Pipe Line Corp.,through a grant administered by the American Gas Association,Inc.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 T=temperature,o=reference fluid,andi=fluid for which properties are to be obtained via theequation of state for the reference fluid and thetransformation functions fii,oand hii,oare introduced toallow extension of the method to mixtures.The two defining Eq 1 and Eq 2 are necessary since there aretwo transformation functions.In this case,an equation of statefor methane was chosen for the reference fluid.During thecourse of the study it was necessary to modify the equation ofstate to give a realistic vapor liquid phase boundary down to atemperature of 43K.This modification was necessary toaccommodate the very low reduced temperatures of the heavierhydrocarbons and was accomplished without changing theperformance of the equation of state above the triple point ofmethane.The fii,oand hii,oare defined asfii,o5Tcii/Tco!ii,oTri,Vri!(3)andhii,o5Vcii,o/Vco!ii,oTri,Vri!(4)where:ii,o5 11wi2 wo!n12 n2 n Tri1n32 n4/Tri!Vri2 n5!#(5)a