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ASTM D7940-14

(Practice)

Standard Practice for Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled Raman Spectroscopy

Standard Practice for Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled Raman Spectroscopy

SIGNIFICANCE AND USE
5.1 The composition of liquefied gas fuels (LNG, LPG) is important for custody transfer and production. Compositional determination is used to calculate the heating value, and it is important to ensure regulatory compliance. Compositional determination is also used to optimize the efficiency of liquefied hydrocarbon gas production and ensure the quality of the processed fluids.  
5.2 Alternatives to compositional measurement using Raman spectroscopy are described in Test Method D1945, Practice D1946, and Test Method D7833.  
5.3 The advantage of this standard over existing standards mentioned in 5.2 above, is that Raman spectroscopy can determine composition by directly measuring the liquefied natural gas. Unlike chromatography, no vaporization step is necessary. Since incorrect operation of on-line vaporizers can lead to poor precision and accuracy, elimination of the vaporization step offers a significant improvement in the analysis of LNG.
SCOPE
1.1 This standard practice is for both on-line and laboratory instrument-based determination of composition for liquefied natural gas (LNG) using Raman spectroscopy. The basic methodology can also be applied to other light hydrocarbon mixtures in either liquid or gaseous states, if the needs of the application are met, although the rest of this practice refers specifically to liquids. From the composition, gas properties such as heating value and the Wobbe index may be calculated. The components commonly determined according to this test method are CH4, C2H6, C3H8, i-C4H10, n-C4H10, iC5H12, n-C5H12, neo-C5H12, N2, O2. The applicable range of this standard is 200 ppmv to 100 mol %. Components heavier than C5 are not measured as part of this practice.
Note 1: Raman spectroscopy does not directly quantify the component percentages of noble gases, however, inerts can be calculated indirectly by subtracting the sum of the other species from 100 %.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
31-May-2014
ICS
75.060 - Natural gas
Technical Committee
D03 - Gaseous Fuels
Drafting Committee
D03.12 - On-Line/At-Line Analysis of Gaseous Fuels
Current Stage
Ref Project

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ASTM D7940-14 - Standard Practice for Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled Raman SpectroscopyASTM D7940-14 - Standard Practice for Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled Raman Spectroscopy
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ASTM D7940-14 - Standard Practice for Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled Raman Spectroscopy
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D7940 −14
Standard Practice for
Analysis of Liquefied Natural Gas (LNG) by Fiber-Coupled
1
Raman Spectroscopy
This standard is issued under the fixed designation D7940; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D1945 Test Method for Analysis of Natural Gas by Gas
Chromatography
1.1 This standard practice is for both on-line and laboratory
D1946 Practice for Analysis of Reformed Gas by Gas
instrument-based determination of composition for liquefied
Chromatography
natural gas (LNG) using Raman spectroscopy. The basic
D7833 Test Method for Determination of Hydrocarbons and
methodology can also be applied to other light hydrocarbon
Non-Hydrocarbon Gases in Gaseous Mixtures by Gas
mixtures in either liquid or gaseous states, if the needs of the
Chromatography
application are met, although the rest of this practice refers
3
2.2 BS EN Standards:
specifically to liquids. From the composition, gas properties
BS EN 60079-28 Explosive Atmospheres. Protection of
such as heating value and the Wobbe index may be calculated.
Equipment and Transmission Systems using Optical Ra-
The components commonly determined according to this test
diation
method are CH,C H,C H , i-C H , n-C H ,iC H ,
4 2 6 3 8 4 10 4 10 5 12
BS EN 60825-1 Safety of Laser Products Part 1: Equipment
n-C H , neo-C H ,N,O . The applicable range of this
5 12 5 12 2 2
Classification, Requirements and User’s Guide
standard is 200 ppmv to 100 mol %. Components heavier than
4
2.3 ISO Standards:
C5 are not measured as part of this practice.
ISO 6974-5 Natural Gas—Determination of Composition
NOTE1—Ramanspectroscopydoesnotdirectlyquantifythecomponent
with Defined Uncertainty by Gas Chromatography, Part 5:
percentagesofnoblegases,however,inertscanbecalculatedindirectlyby
Determination of nitrogen, carbon dioxide and C1 to C5
subtracting the sum of the other species from 100 %.
and C6+ hydrocarbons for a laboratory and on-line pro-
1.2 The values stated in SI units are to be regarded as
cess application using three columns
standard. No other units of measurement are included in this
standard.
3. Terminology
1.3 This standard does not purport to address all of the
3.1 Definitions: Refer to D4150 for definitions related to
safety concerns, if any, associated with its use. It is the
gaseous fuels.
responsibility of the user of this standard to establish appro-
3.2 Definitions of Terms Specific to This Standard:
priate safety and health practices and determine the applica-
3.2.1 Accumulations, n—while the exposure time is opti-
bility of regulatory limitations prior to use.
mized to control the amount of light entering the camera for a
single exposure, multiple exposures can be co-added to im-
2. Referenced Documents
prove signal-to-noise. The number of exposures co-added are
2
2.1 ASTM Standards:
referred to as accumulations.
D3588 Practice for Calculating Heat Value, Compressibility
3.2.2 charge-coupled device, n—silicon based two dimen-
Factor, and Relative Density of Gaseous Fuels
sional light sensor characterized by possessing a grid of
D4150 Terminology Relating to Gaseous Fuels
potential energy wells where light-generated free electrons
E691 Practice for Conducting an Interlaboratory Study to
collect and then are read out sequentially.
Determine the Precision of a Test Method
3.2.3 charge-coupled device (CCD) binning, v—process of
combining “bins” or pixel wells on the CCD.
1
ThistestmethodisunderthejurisdictionofASTMCommitteeD03onGaseous
3.2.4 Exposure Time, n—the CCD converts photons to
Fuels and is the direct responsibility of Subcommittee D03.12 on On-Line/At-Line
electrons over time for a measurement. The exposure time
Analysis of Gaseous Fuels.
CurrenteditionapprovedJune1,2014.PublishedJuly2014.Originallyapproved
in 2014. DOI: 10.1520/D7940-14.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from British Standards Institution (BSI), 389 Chiswick High Rd.,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM London W4 4AL, U.K., http://www.bsigroup.com.
4
Standards volume information, refer to the standard’s Document Summary page on Available from International Organization for Standardization (ISO), 1, ch. de
the ASTM website. la 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 States
1

---------------------- Page: 1 ----------------------
D7940−14
indicates the amount of time allocated for capturing photons. 3.3.3 LNG—Liquefied natural g
...

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1.5 TDL absorption spectroscopy measures molar ratios such as ppmv or mole percentage. Volumetric ratios (ppmv and %) are not pressure d...

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5.1 The measurement of hydrogen sulfide in natural gas is important because of gas quality specifications, the corrosive nature of H2S on pipeline materials, and the effects of H2S on utilization equipment.  
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1.2 Typically, sulfur dioxide and mercaptans may cause positive interferences. In some cases, nitrogen dioxide can cause a negative interference. Most detector tubes will have a “precleanse” layer designed to remove certain interferences up to some maximum interferent level. Consult manufacturers' instructions for specific interference information.  
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5.1 The measurement of mercaptans in natural gas is important, because mercaptans are often added as odorants to natural gas to provide a warning property. The odor provided by the mercaptan serves to warn consumers (for example, residential use) of natural gas leaks at levels that are well below the flammable or suffocating concentration levels of natural gas in air. Field determinations of mercaptans in natural gas are important because of the tendency of the mercaptan concentration to decline over time.  
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SCOPE
1.1 This test method covers a rapid and simple field determination of mercaptans in natural gas pipelines. Available detector tubes provide a total measuring range of 0.5 to 160 ppm by volume of mercaptans, although the majority of applications will be on the lower end of this range (that is, under 20 ppm). Besides total mercaptans, detector tubes are also available for methyl mercaptan (0.5 to 100 ppm), ethyl mercaptan (0.5 to 120 ppm), and butyl mercaptan (0.5 to 30 mg/M3 or 0.1 to 8 ppm).  
Note 1: Certain detector tubes are calibrated in terms of milligrams per cubic metre (mg/M3) instead of parts per million by volume. The conversion is as follows for 25 °C (77 °F) and 760 mm Hg.
1.2 Detector tubes are usually subject to interferences from gases and vapors other than the target substance. Such interferences may vary among brands because of the use of different detection principles. Many detector tubes will have a precleanse layer designed to remove interferences up to some maximum level. Consult manufacturer's instructions for specific interference information. Hydrogen sulfide and other mercaptans are usually interferences on mercaptan detector tubes. See Section 6 for interferences of various methods of detection.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see 8.3.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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