1、Designation: D1945 03 (Reapproved 2010)D1945 14Standard 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 yea
2、r 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. Scope*1.1 This test method covers the determination of the chemical composition of natural gases and similar gaseous mixtu
3、res withinthe range of composition shown in Table 1. This test method may be abbreviated for the analysis of lean natural gases containingnegligible amounts of hexanes and higher hydrocarbons, or for the determination of one or more components, as required.1.2 The values stated in inch-poundSI units
4、 are to be regarded as standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information only and are not considered No other units of measurement are includedin this standard.1.3 This standard does not purport to address all of the safety concerns,
5、if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2597 Test Method for Analysis of Demethanized H
6、ydrocarbon Liquid Mixtures Containing Nitrogen and Carbon Dioxide byGas ChromatographyD3588 Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous FuelsE260 Practice for Packed Column Gas Chromatography3. Summary of Test Method3.1 Components in a representative
7、sample are physically separated by gas chromatography (GC) and compared to calibrationdata obtained under identical operating conditions from a reference standard mixture of known composition. The numerousheavy-end components of a sample can be grouped into irregular peaks by reversing the direction
8、 of the carrier gas through thecolumn at such time as to group the heavy ends either as C5 and heavier, C6 and heavier, or C7 and heavier. The composition ofthe sample is calculated by comparing either the peak heights, or the peak areas, or both, with the corresponding values obtainedwith the refer
9、ence standard.4. Significance and Use4.1 This test method is of significance for providing data for calculating physical properties of the sample, such as heating valueand relative density, or for monitoring the concentrations of one or more of the components in a mixture.5. Apparatus5.1 DetectorThe
10、 detector shall be a thermal-conductivity type, or its equivalent in sensitivity and stability. The thermalconductivity detector must be sufficiently sensitive to produce a signal of at least 0.5 mV for 1 mol % n-butane in a 0.25-mLsample.5.2 Recording InstrumentsEither strip-chart recorders or elec
11、tronic integrators, or both, are used to display the separatedcomponents. Although a strip-chart recorder is not required when using electronic integration, it is highly desirable for evaluationof instrument performance.1 This test method is under the jurisdiction of ASTM Committee D03 on Gaseous Fu
12、els and is the direct responsibility of Subcommittee D03.07 on Analysis of ChemicalComposition of Gaseous Fuels.Current edition approved Jan. 1, 2010Nov. 1, 2014. Published March 2010November 2014. Originally approved in 1962. Last previous edition approved in 20032010 asD194596(2003).D1945-96(2010)
13、. DOI: 10.1520/D1945-03R10.10.1520/D1945-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is
14、not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropri
15、ate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1
16、5.2.1 The recorder shall be a strip-chart recorder with a full-range scale of 5 mV or less (1 mV preferred). The width of the chartshall be not less than 150 mm. A maximum pen response time of 2 s (1 s preferred) and a minimum chart speed of 10 mm/minshall be required. Faster speeds up to 100 mm/min
17、 are desirable if the chromatogram is to be interpreted using manual methodsto obtain areas.5.2.2 Electronic or Computing IntegratorsProof of separation and response equivalent to that for a recorder is required fordisplays other than by chart recorder. Baseline tracking with tangent skim peak detec
18、tion is recommended.5.3 AttenuatorIf the chromatogram is to be interpreted using manual methods, an attenuator must be used with the detectoroutput signal to maintain maximum peaks within the recorder chart range.The attenuator must be accurate to within 0.5 % betweenthe attenuator range steps.5.4 S
19、ample Inlet System:5.4.1 The sample inlet system shall be constructed of materials that are inert and nonadsorptive with respect to the componentsin the sample. The preferred material of construction is stainless steel. Copper, brass, and other copper-bearing alloys areunacceptable.The sample inlet
20、system from the cylinder valve to the GC column inlet must be maintained at a temperature constantto 61C.61 C.5.4.2 Provision must be made to introduce into the carrier gas ahead of the analyzing column a gas-phase sample that has beenentrapped in a fixed volume loop or tubular section. The fixed lo
21、op or section shall be so constructed that the total volume,including dead space, shall not normally exceed 0.5 mL at 1 atm.0.5mL at 100 kPa. If increased accuracy of the hexanes andheavier portions of the analysis is required, a larger sample size may be used (see Test Method D2597). The sample vol
22、ume mustbe reproducible such that successive runs agree within 1 % on each component. A flowing sample inlet system is acceptable aslong as viscosity effects are accounted for.NOTE 1The sample size limitation of 0.5 mL or smaller is selected relative to linearity of detector response, and efficiency
23、 of column separation.Larger samples may be used to determine low-quantity components to increase measurement accuracy.5.4.3 An optional manifold arrangement for entering vacuum samples is shown in Fig. 1.TABLE 1 Natural Gas Components and Range ofComposition CoveredComponent Mol %Helium 0.01 to 10H
24、ydrogen 0.01 to 10Oxygen 0.01 to 20Nitrogen 0.01 to 100Carbon dioxide 0.01 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 t
25、o 1FIG. 1 Suggested Manifold Arrangement for Entering Vacuum SamplesD1945 1425.5 Column Temperature Control:5.5.1 IsothermalWhen isothermal operation is used, maintain the analyzer columns at a temperature constant to 0.3C0.3 Cduring the course of the sample run and corresponding reference run.5.5.2
26、 Temperature ProgrammingTemperature programming may be used, as feasible. The oven temperature shall not exceedthe recommended temperature limit for the materials in the column.5.6 Detector Temperature ControlMaintain the detector temperature at a temperature constant to 0.3C0.3 C during thecourse o
27、f the sample run and the corresponding reference run. The detector temperature shall be equal to or greater than themaximum column temperature.5.7 Carrier Gas ControlsThe instrument shall be equipped with suitable facilities to provide a flow of carrier gas through theanalyzer and detector at a flow
28、 rate that is constant to 1 % throughout the analysis of the sample and the reference standard. Thepurity of the carrier gas may be improved by flowing the carrier gas through selective filters prior to its entry into thechromatograph.5.8 Columns:5.8.1 The columns shall be constructed of materials t
29、hat are inert and nonadsorptive with respect to the components in thesample. The preferred material of construction is stainless steel. Copper and copper-bearing alloys are unacceptable.5.8.2 An adsorption-type column and a partition-type column may be used to make the analysis.NOTE 2See Practice E2
30、60.5.8.2.1 Adsorption ColumnThis column must completely separate oxygen, nitrogen, and methane. A 13X molecular sieve80/100 mesh is recommended for direct injection. A 5A column can be used if a pre-cut column is present to remove interferinghydrocarbons. If a recorder is used, the recorder pen must
31、 return to the baseline between each successive peak. The resolution (R)must be 1.5 or greater as calculated in the following equation:R1,2!5x22x1y21y132, (1)where x1, x2 are the retention times and y1, y2 are the peak widths. Fig. 2 illustrates the calculation for resolution. Fig. 3 is achromatogra
32、m obtained with an adsorption column.5.8.2.2 Partition ColumnThis column must separate ethane through pentanes,pentanes and carbon dioxide. If a recorder isused, the recorder pen must return to the base line between each peak for propane and succeeding peaks, and to base line within2 % of full-scale
33、 deflection for components eluted ahead of propane, with measurements being at the attenuation of the peak.Separation of carbon dioxide must be sufficient so that a 0.25-mL sample containing 0.1-mol % carbon dioxide will produce aclearly measurable response. The resolution (R) must be 1.5 or greater
34、 as calculated in the above equation. The separation shouldbe completed within 40 min, including reversal of flow after n-pentane to yield a group response for hexanes and heaviercomponents. Figs. 4-6 are examples of chromatograms obtained on some of the suitable partition columns.5.8.3 GeneralOther
35、 column packing materials that provide satisfactory separation of components of interest may be used (seeFig. 7). In multicolumn applications, it is preferred to use front-end backflush of the heavy ends.NOTE 3The chromatograms in Figs. 3-8 are only illustrations of typical separations. The operatin
36、g conditions, including columns, are also typicaland are subject to optimization by competent personnel.FIG. 2 Calculation for ResolutionD1945 1435.9 DrierUnless water is known not to interfere in the analysis, a drier must be provided in the sample entering system, aheadof the sample valve. The dri
37、er must remove moisture without removing selective components to be determined in the analysis.NOTE 4See A2.2 for preparation of a suitable drier.5.10 ValvesValves or sample splitters, or both, are required to permit switching, backflushing, or for simultaneous analysis.5.11 ManometerVacuum GaugeMay
38、 be either U-tube type or well type equipped with an accurately graduated and easilyread scale covering 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, thus extending the range of al
39、l components. The well type inherently offersbetter precision and is preferred when calibrating with pure components. Samples with up to one atmosphere of pressure can beFIG. 3 Separation Column for Oxygen, Nitrogen, and Methane (See Annex A2)FIG. 4 Chromatogram of Natural Gas (BMEE Column) (See Ann
40、ex A2)D1945 144entered. With either type manometer the mm scale can be read more accurately than the inch scale. Caution should be usedhandling mercury because of its toxic nature. Avoid contact with the skin as much as possible. Wash thoroughly after contact.Anytype of vacuum gauge may be used whic
41、h has a resolution of 0.14 kPa or better and covers the range of 0 to 120 kPa or larger.5.12 Vacuum PumpMust have the capability of producing a vacuum of 1 mm of mercury 0.14 kPa absolute or less.6. Preparation of Apparatus6.1 Linearity CheckTo establish linearity of response for the thermal conduct
42、ivity detector, it is necessary to complete thefollowing procedure:FIG. 5 Chromatogram of Natural Gas (Silicone 200/500 Column) (See Annex A2)FIG. 6 Chromatogram of Natural Gas (See Annex A2)D1945 1456.1.1 The major component of interest (methane for natural gas) is charged to the chromatograph by w
43、ay of the fixed-sizesample loop at partial pressure increments of 13 kPa (100 mm Hg) from 13 to 100 kPa (100 to 760 mm Hg) or the prevailingatmospheric pressure.6.1.2 The integrated peak responses for the area generated at each of the pressure increments are plotted versus their partialpressure (see
44、 Fig. 9).FIG. 7 Chromatogram of Natural Gas (Multi-Column Application) (See Annex A2)FIG. 8 Separation of Helium and HydrogenD1945 1466.1.3 The plotted results should yield a straight line.Aperfectly linear response would display a straight line at a 45 angle usingthe logarithmic values.6.1.4 Any cu
45、rved line indicates the fixed volume sample loop is too large. A smaller loop size should replace the fixed volumeloop and 6.1.1 through 6.1.4 should be repeated (see Fig. 9).6.1.5 The linearity over the range of interest must be known for each component. It is useful to construct a table noting the
46、response factor deviation in changing concentration. (See Table 2 and Table 3).6.1.6 It should be noted that nitrogen, methane, and ethane exhibit less than 1 % compressibility at atmospheric pressure. Othernatural gas components do exhibit a significant compressibility at pressures less than atmosp
47、heric.6.1.7 Most components that have vapor pressures of less than 100 kPa (15 psia) cannot be used as a pure gas for a linearity studybecause they will not exhibit sufficient vapor pressure for a manometer vacuum gauge reading to 100 kPa (760 mm Hg). kPa. Forthese components, a mixture with nitroge
48、n or methane can be used to establish a partial pressure that can extend the total pressureFIG. 9 Linearity of Detector ResponseTABLE 2 Linearity Evaluation of MethaneS/B diff = (low mole % high mole %) low mole % 100B area S mole % S/B mole % area S/B diff., % on lowvalue223 119 392 51 2.2858e-0724
49、2 610 272 56 2.3082e-07 0.98261 785 320 61 2.3302e-07 0.95280 494 912 66 2.3530e-07 0.98299 145 504 71 2.3734e-07 0.87317 987 328 76 2.3900e-07 0.70336 489 056 81 2.4072e-07 0.72351 120 721 85 2.4208e-07 0.57D1945 147to 100 kPa (760 mm Hg). kPa. Using Table 4 for vapor pressures at 38C (100F), 38 C, calculate the maximum pressure to whicha given component can be blended with nitrogen as follows:B 51003V!/i (2)P 5i 3M!/100 (3)where:B = blend pressure, max, kPa (mm Hg);B = blend pressure, max, kPa;V = vapor pressure, kPa (mm Hg
