ASTM D1945-2003(2010) Standard Test Method for Analysis of Natural Gas by Gas Chromatography《气相色谱法分析天然气的标准试验方法》.pdf

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1、Designation: D1945 03 (Reapproved 2010)Standard Test Method forAnalysis of Natural Gas by Gas Chromatography1This standard is issued under the fixed designation D1945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las

2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the chemi-cal composition of natural gases and similar gaseous mixtureswith

3、in the range of composition shown in Table 1. This testmethod may be abbreviated for the analysis of lean naturalgases containing negligible amounts of hexanes and higherhydrocarbons, or for the determination of one or more compo-nents, as required.1.2 The values stated in inch-pound units are to be

4、 regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the

5、 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:2D2597 Test Method for Analysis of Demethanized Hydro-carbon Liquid Mixtures Containing Nitrogen and CarbonDi

6、oxide by Gas ChromatographyD3588 Practice for Calculating Heat Value, CompressibilityFactor, and Relative Density of Gaseous FuelsE260 Practice for Packed Column Gas Chromatography3. Summary of Test Method3.1 Components in a representative sample are physicallyseparated by gas chromatography (GC) an

7、d compared tocalibration data obtained under identical operating conditionsfrom a reference standard mixture of known composition. Thenumerous heavy-end components of a sample can be groupedinto irregular peaks by reversing the direction of the carrier gasthrough the column at such time as to group

8、the heavy endseither as C5and heavier, C6and heavier, or C7and heavier. Thecomposition of the sample is calculated by comparing eitherthe peak heights, or the peak areas, or both, with the corre-sponding values obtained with the reference standard.4. Significance and Use4.1 This test method is of si

9、gnificance for providing data forcalculating physical properties of the sample, such as heatingvalue and relative density, or for monitoring the concentrationsof one or more of the components in a mixture.5. Apparatus5.1 DetectorThe detector shall be a thermal-conductivitytype, or its equivalent in

10、sensitivity and stability. The thermalconductivity detector must be sufficiently sensitive to producea signal of at least 0.5 mV for 1 mol % n-butane in a 0.25-mLsample.5.2 Recording InstrumentsEither strip-chart recorders orelectronic integrators, or both, are used to display the separatedcomponent

11、s. Although a strip-chart recorder is not requiredwhen using electronic integration, it is highly desirable forevaluation of instrument performance.5.2.1 The recorder shall be a strip-chart recorder with afull-range scale of 5 mV or less (1 mV preferred). The width ofthe chart shall be not less than

12、 150 mm. A maximum penresponse time of2s(1spreferred) and a minimum chart speedof 10 mm/min shall be required. Faster speeds up to 1001This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysis ofChemical Compos

13、ition of Gaseous Fuels.Current edition approved Jan. 1, 2010. Published March 2010. Originallyapproved in 1962. Last previous edition approved in 2001 as D194596(2001).DOI: 10.1520/D1945-03R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at se

14、rviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.TABLE 1 Natural Gas Components and Range ofComposition CoveredComponent Mol %Helium 0.01 to 10Hydrogen 0.01 to 10Oxygen 0.01 to 20Nitrogen 0.01 to 100Carbon dioxide 0.0

15、1 to 20Methane 0.01 to 100Ethane 0.01 to 100Hydrogen sulfide 0.3 to 30Propane 0.01 to 100Isobutane 0.01 to 10n-Butane 0.01 to 10Neopentane 0.01 to 2Isopentane 0.01 to 2n-Pentane 0.01 to 2Hexane isomers 0.01 to 2Heptanes+ 0.01 to 11*A Summary of Changes section appears at the end of this standard.Cop

16、yright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.mm/min are desirable if the chromatogram is to be interpretedusing manual methods to obtain areas.5.2.2 Electronic or Computing IntegratorsProof of sepa-ration and response equivalent to th

17、at for a recorder is requiredfor displays other than by chart recorder. Baseline trackingwith tangent skim peak detection is recommended.5.3 AttenuatorIf the chromatogram is to be interpretedusing manual methods, an attenuator must be used with thedetector output signal to maintain maximum peaks wit

18、hin therecorder chart range. The attenuator must be accurate to within0.5 % between the attenuator range steps.5.4 Sample Inlet System:5.4.1 The sample inlet system shall be constructed ofmaterials that are inert and nonadsorptive with respect to thecomponents in the sample. The preferred material o

19、f construc-tion is stainless steel. Copper, brass, and other copper-bearingalloys are unacceptable. The sample inlet system from thecylinder valve to the GC column inlet must be maintained at atemperature constant to 61C.5.4.2 Provision must be made to introduce into the carriergas ahead of the anal

20、yzing column a gas-phase sample that hasbeen entrapped in a fixed volume loop or tubular section. Thefixed loop or section shall be so constructed that the totalvolume, including dead space, shall not normally exceed 0.5mL at 1 atm. If increased accuracy of the hexanes and heavierportions of the ana

21、lysis is required, a larger sample size may beused (see Test Method D2597). The sample volume must bereproducible such that successive runs agree within 1 % oneach component. A flowing sample inlet system is acceptableas long as viscosity effects are accounted for.NOTE 1The sample size limitation of

22、 0.5 mL or smaller is selectedrelative to linearity of detector response, and efficiency of columnseparation. Larger samples may be used to determine low-quantitycomponents to increase measurement accuracy.5.4.3 An optional manifold arrangement for enteringvacuum samples is shown in Fig. 1.5.5 Colum

23、n Temperature Control:5.5.1 IsothermalWhen isothermal operation is used,maintain the analyzer columns at a temperature constant to0.3C during the course of the sample run and correspondingreference run.5.5.2 Temperature ProgrammingTemperature program-ming may be used, as feasible. The oven temperatu

24、re shall notexceed the recommended temperature limit for the materials inthe column.5.6 Detector Temperature ControlMaintain the detectortemperature at a temperature constant to 0.3C during thecourse of the sample run and the corresponding reference run.The detector temperature shall be equal to or

25、greater than themaximum column temperature.5.7 Carrier Gas ControlsThe instrument shall beequipped with suitable facilities to provide a flow of carrier gasthrough the analyzer and detector at a flow rate that is constantto 1 % throughout the analysis of the sample and the referencestandard. The pur

26、ity of the carrier gas may be improved byflowing the carrier gas through selective filters prior to its entryinto the chromatograph.5.8 Columns:5.8.1 The columns shall be constructed of materials that areinert and nonadsorptive with respect to the components in thesample. The preferred material of c

27、onstruction is stainlesssteel. Copper and copper-bearing alloys are unacceptable.5.8.2 An adsorption-type column and a partition-type col-umn may be used to make the analysis.NOTE 2See Practice E260.5.8.2.1 Adsorption ColumnThis column must completelyseparate oxygen, nitrogen, and methane. A 13X mol

28、ecularsieve 80/100 mesh is recommended for direct injection. A 5Acolumn can be used if a pre-cut column is present to removeinterfering hydrocarbons. If a recorder is used, the recorder penmust return to the baseline between each successive peak. Theresolution (R) must be 1.5 or greater as calculate

29、d in thefollowing equation:R1,2! 5x22 x1y21 y13 2, (1)where x1,x2are the retention times and y1,y2are the peakwidths. Fig. 2 illustrates the calculation for resolution. Fig. 3 isa chromatogram obtained with an adsorption column.5.8.2.2 Partition ColumnThis column must separateethane through pentanes

30、, and carbon dioxide. If a recorder isused, the recorder pen must return to the base line betweenFIG. 1 Suggested Manifold Arrangement for Entering Vacuum SamplesD1945 03 (2010)2each peak for propane and succeeding peaks, and to base linewithin 2 % of full-scale deflection for components eluted ahea

31、dof propane, with measurements being at the attenuation of thepeak. Separation of carbon dioxide must be sufficient so that a0.25-mL sample containing 0.1-mol % carbon dioxide willproduce a clearly measurable response. The resolution (R)must be 1.5 or greater as calculated in the above equation. The

32、separation should be completed within 40 min, includingreversal of flow after n-pentane to yield a group response forhexanes and heavier components. Figs. 4-6 are examples ofchromatograms obtained on some of the suitable partitioncolumns.5.8.3 GeneralOther column packing materials that pro-vide sati

33、sfactory separation of components of interest may beused (see Fig. 7). In multicolumn applications, it is preferred touse front-end backflush of the heavy ends.NOTE 3The chromatograms in Figs. 3-8 are only illustrations oftypical separations. The operating conditions, including columns, are alsotypi

34、cal and are subject to optimization by competent personnel.5.9 DrierUnless water is known not to interfere in theanalysis, a drier must be provided in the sample enteringsystem, ahead of the sample valve. The drier must removemoisture without removing selective components to be deter-mined in the an

35、alysis.FIG. 2 Calculation for ResolutionFIG. 3 Separation Column for Oxygen, Nitrogen, and Methane (See Annex A2)D1945 03 (2010)3NOTE 4See A2.2 for preparation of a suitable drier.5.10 ValvesValves or sample splitters, or both, are re-quired to permit switching, backflushing, or for simultaneousanal

36、ysis.5.11 ManometerMay be either U-tube type or well typeequipped with an accurately graduated and easily read scalecovering the range 0 to 900 mm (36 in.) of mercury or larger.The U-tube type is useful, since it permits filling the sampleloop with up to two atmospheres of sample pressure, thusexten

37、ding the range of all components. The well type inher-ently offers better precision and is preferred when calibratingwith pure components. Samples with up to one atmosphere ofpressure can be entered. With either type manometer the mmscale can be read more accurately than the inch scale. CautionFIG.

38、4 Chromatogram of Natural Gas (BMEE Column) (See Annex A2)FIG. 5 Chromatogram of Natural Gas (Silicone 200/500 Column) (See Annex A2)D1945 03 (2010)4should be used handling mercury because of its toxic nature.Avoid contact with the skin as much as possible. Washthoroughly after contact.5.12 Vacuum P

39、umpMust have the capability of producinga vacuum of 1 mm of mercury absolute or less.6. Preparation of Apparatus6.1 Linearity CheckTo establish linearity of response forthe thermal conductivity detector, it is necessary to completethe following procedure:FIG. 6 Chromatogram of Natural Gas (See Annex

40、 A2)FIG. 7 Chromatogram of Natural Gas (Multi-Column Application) (See Annex A2)D1945 03 (2010)56.1.1 The major component of interest (methane for naturalgas) is charged to the chromatograph by way of the fixed-sizesample loop at partial pressure increments of 13 kPa (100 mmHg) from 13 to 100 kPa (1

41、00 to 760 mm Hg) or the prevailingatmospheric pressure.6.1.2 The integrated peak responses for the area generated ateach of the pressure increments are plotted versus their partialpressure (see Fig. 9).6.1.3 The plotted results should yield a straight line. Aperfectly linear response would display a

42、 straight line at a 45angle using the logarithmic values.6.1.4 Any curved line indicates the fixed volume sampleloop is too large. A smaller loop size should replace the fixedvolume loop and 6.1.1 through 6.1.4 should be repeated (seeFig. 9).6.1.5 The linearity over the range of interest must be kno

43、wnfor each component. It is useful to construct a table noting theresponse factor deviation in changing concentration. (See Table2 and Table 3).6.1.6 It should be noted that nitrogen, methane, and ethaneexhibit less than 1 % compressibility at atmospheric pressure.Other natural gas components do exh

44、ibit a significant com-pressibility at pressures less than atmospheric.6.1.7 Most components that have vapor pressures of lessthan 100 kPa (15 psia) cannot be used as a pure gas for alinearity study because they will not exhibit sufficient vaporpressure for a manometer reading to 100 kPa (760 mm Hg)

45、.For these components, a mixture with nitrogen or methane canbe used to establish a partial pressure that can extend the totalpressure to 100 kPa (760 mm Hg). Using Table 4 for vaporpressures at 38C (100F), calculate the maximum pressure towhich a given component can be blended with nitrogen asfollo

46、ws:B 5 100 3 V!/i (2)P 5 i 3 M!/100 (3)where:B = blend pressure, max, kPa (mm Hg);V = vapor pressure, kPa (mm Hg);i = mol %;P = partial pressure, kPa (mm Hg); andM = manometer pressure, kPa (mm Hg).6.2 . Procedure for Linearity Check:6.2.1 Connect the pure-component source to the sample-entry system

47、. Evacuate the sample-entry system and observethe manometer for leaks. (See Fig. 1 for a suggested manifoldarrangement.) The sample-entry system must be vacuum tight.6.2.2 Carefully open the needle valve to admit the purecomponent up to 13 kPa (100 mm Hg) of partial pressure.6.2.3 Record the exact p

48、artial pressure and actuate thesample valve to place the sample onto the column. Record thepeak area of the pure component.6.2.4 Repeat 6.2.3 for 26, 39, 52, 65, 78, and 91 kPa (200,300, 400, 500, 600, and 700 mm Hg) on the manometer,recording the peak area obtained for sample analysis at each ofthe

49、se pressures.6.2.5 Plot the area data (x axis) versus the partial pressures(y axis) on a linear graph as shown in Fig. 9.6.2.6 An alternative method is to obtain a blend of all thecomponents and charge the sample loop at partial pressure overthe range of interest. If a gas blender is available, the mixtureFIG. 8 Separation of Helium and HydrogenD1945 03 (2010)6can be diluted with methane thereby giving response curves forall the components. (WarningIf it is not possible to obtaininformation on the linearity of the available gas chromatographdetec