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Natural Gas - Extended Analysis - Gas-Chromatographic Method
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This International Standard describes the specifications for the quantitative analysis of the following components of natural gas:
- saturated hydrocarbons from C1 to C5
- hydrocarbon fractions from C6 upwards
- aromatic compounds as benzene and toluene
|The gas-chromatographic methods determine the components in the following ranges:|
|oxygen:||0,001 % (n/n) to 0,5 % (n/n)|
|helium:||0,001 % (n/n) to 0,5 % (n/n)|
|hydrogen:||0,001 % (n/n) to 0,5 % (n/n)|
|argon:||0,001 % (n/n) to 0,5 % (n/n)|
|nitrogen:||0,001 % (n/n) to 40 % (n/n)|
|carbon dioxide:||0,001 % (n/n) to 40 % (n/n)|
|methane:||50 % (n/n) t0 100 % (n/n)|
|ethane:||0,02 % (n/n) t0 15 % (n/n)|
|propane:||0,001 % (n/n) t0 5 % (n/n)|
|higher hydrocarbons:||The method can measure hydrocarbon components from 10−6 (n/n) up to their maximum concentration, which is compatible with the requirement that the gas is free from hydrocarbon condensate at any pressure in the range 1 × 102 kPa to 7 × 103 kPa.|
This method is not intended for the determination of oxygen compounds (water vapour, methanol, glycols) or sulfur compounds.
It is not possible to make unambiguous identifications of hydrocarbons above C6. Even where “spiking” a gas mixture with known components shows where they elute, it cannot be stated with certainty that such a component is the only one with that retention time. Unidentified components are classified according to the carbon number which the analysis indicates to be appropriate. While this is a necessary simplification, it does allow a reasonable quantitative value to be obtained.
This method is intended for use in situations where the hexanes plus compositional breakdown and/or the complete analysis is desired.
The method is not intended for dense phase gases whose pressure exceeds the cricondebar (critical condensation pressure), or for gas samples containing any measurable hydrocarbon condensate, liquid water or process fluid such as methanol or glycols (see ISO 6570-1 and ISO 10715).
Gases which have been treated for transmission are unlikely to contain detectable levels of hydrocarbons above C12. Samples taken from nearer the well head, before the gas has reached gas treatment plants, may contain hydrocarbons to C16 or above.
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June 15, 1986
ISO TC 193/SC 1