ASTM_D_7940_-_14.pdf

Designation:D794014Standard Practice forAnalysis of Liquefied Natural Gas(LNG)by Fiber-CoupledRaman Spectroscopy1This standard is issued under the fixed designation D7940;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.1.Scope1.1 This standard practice is for both on-line and laboratoryinstrument-based determination of composition for liquefiednatural gas(LNG)using Raman spectroscopy.The basicmethodology can also be applied to other light hydrocarbonmixtures in either liquid or gaseous states,if the needs of theapplication are met,although the rest of this practice refersspecifically to liquids.From the composition,gas propertiessuch as heating value and the Wobbe index may be calculated.The components commonly determined according to this testmethod are CH4,C2H6,C3H8,i-C4H10,n-C4H10,iC5H12,n-C5H12,neo-C5H12,N2,O2.The applicable range of thisstandard is 200 ppmv to 100 mol%.Components heavier thanC5 are not measured as part of this practice.NOTE1Raman spectroscopy does not directly quantify the componentpercentages of noble gases,however,inerts can be calculated indirectly bysubtracting the sum of the other species from 100%.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.Referenced Documents2.1 ASTM Standards:2D3588 Practice for Calculating Heat Value,CompressibilityFactor,and Relative Density of Gaseous FuelsD4150 Terminology Relating to Gaseous FuelsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodD1945 Test Method for Analysis of Natural Gas by GasChromatographyD1946 Practice for Analysis of Reformed Gas by GasChromatographyD7833 Test Method for Determination of Hydrocarbons andNon-Hydrocarbon Gases in Gaseous Mixtures by GasChromatography2.2 BS EN Standards:3BS EN 60079-28 Explosive Atmospheres.Protection ofEquipment and Transmission Systems using Optical Ra-diationBS EN 60825-1 Safety of Laser Products Part 1:EquipmentClassification,Requirements and Users Guide2.3 ISO Standards:4ISO 6974-5 Natural GasDetermination of Compositionwith Defined Uncertainty by Gas Chromatography,Part 5:Determination of nitrogen,carbon dioxide and C1 to C5and C6+hydrocarbons for a laboratory and on-line pro-cess application using three columns3.Terminology3.1 Definitions:Refer to D4150 for definitions related togaseous fuels.3.2 Definitions of Terms Specific to This Standard:3.2.1 Accumulations,nwhile the exposure time is opti-mized to control the amount of light entering the camera for asingle exposure,multiple exposures can be co-added to im-prove signal-to-noise.The number of exposures co-added arereferred to as accumulations.3.2.2 charge-coupled device,nsilicon based two dimen-sional light sensor characterized by possessing a grid ofpotential energy wells where light-generated free electronscollect and then are read out sequentially.3.2.3 charge-coupled device(CCD)binning,vprocess ofcombining“bins”or pixel wells on the CCD.3.2.4 Exposure Time,nthe CCD converts photons toelectrons over time for a measurement.The exposure time1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.12 on On-Line/At-LineAnalysis of Gaseous Fuels.Current edition approved June 1,2014.Published July 2014.Originally approvedin 2014.DOI:10.1520/D7940-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from British Standards Institution(BSI),389 Chiswick High Rd.,London W4 4AL,U.K.,http:/.4Available from International Organization for Standardization(ISO),1,ch.dela Voie-Creuse,CP 56,CH-1211 Geneva 20,Switzerland,http:/www.iso.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 indicates the amount of time allocated for capturing photons.The number of electrons is counted at the end of the allottedexposure time via a binning process.3.2.5 incident light,i,nmonochromatic light illuminatedinto sample.3.2.6 Raman Scattering Effect,nan energy transfer pro-cess between photons and molecules.In this photon-moleculeinteraction,scattered light has a different wavelength comparedto the incident wavelength.The Raman wavelength shiftspectrum is unique for each molecule because the shift isd