BS EN ISO 6974-5:2014

Natural gas. Determination of composition and associated uncertainty by gas chromatography. Isothermal method for nitrogen, carbon dioxide, C1 to C5 hydrocarbons and C6+ hydrocarbons | Status: Current, Under review

1 Scope This part of this International Standard describes a gas chromatographic method for the quantitative determination of the content of nitrogen, carbon dioxide and C1 to C5 hydrocarbons individually and a composite C6+ measurement, which represents all hydrocarbons of carbon number 6 and above in natural gas samples. It is applicable to the analysis of gases containing constituents within the working ranges given in Table 1. Table 1 — Component working ranges Component Mole fraction % Min. Max. Nitrogen N2 0,1 22 Carbon dioxide CO2 0,05 15 Methane CH4 34 100 Ethane C2H6 0,1 23 Propane C3H8 0,05 10 iso-Butane i-C4H10 0,01 2,0 n-Butane n-C4H10 0,01 2,0 neo-Pentane neo-C5H12 0,005 0,35 iso-Pentane i-C5H12 0,005 0,35 n-Pentane n-C5H12 0,005 0,35 Hexanes + C6+ 0,005 0,35 NOTE 1 The working ranges in Table 1 are those for which the method has been shown to be satisfactory, and are offered for guidance. However, there is no reason why wider ranges should not be used, provided that the successful measurement of such wider ranges has been demonstrated. NOTE 2 Hydrocarbons above n-pentane are expressed as the “pseudo-component” C6+ which is measured as one composite peak and calibrated as such. The properties of C6+ are calculated from an extended analysis of the individual C6 and higher hydrocarbons. NOTE 3 Oxygen is not a normal constituent of natural gas and would not be expected to be present in gas sampled to an online instrument. If any oxygen is present as a result of air contamination, it will be measured with the nitrogen. The resulting measured (nitrogen + oxygen) value will be in error to a small extent because of the slight difference between the detector responses of oxygen and nitrogen. NOTE 4 The helium and argon contents are assumed to be sufficiently small and unvarying that they need not be analysed for. NOTE 5 The gas sample shall not contain any hydrocarbon condensate and/or water.