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ISO DIS 6974-1

2010 Edition, March 25, 2010

Complete Document

NATURAL GAS - DETERMINATION OF COMPOSITION AND ASSOCIATED UNCERTAINTY BY GAS CHROMATOGRAPHY - PART 1: GENERAL GUIDELINES AND CALCULATION OF COMPOSITION



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Superseded By: ISO 6974-1

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NOW A PUBLISHED STD * SEE ISO 6974-1
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Description / Abstract:

This Part of this Standard gives guidelines for the quantitative analysis of natural gas and describes the data processing requirements to determine component mole fractions. Part 2 of the Standard described the steps required to calculate the uncertainty in each component mole fraction. A number of analytical configurations, which fulfil the requirements stated in this Part, are presented in Part 3 and subsequent Parts of the Standard. Indicative application ranges for all Parts of this Standard are given in Annex A. This approach is suitable for a range of end applications, for example calibration of gas mixtures or to provide natural gas composition and uncertainty data to be used in the calculation of calorific value and other additive physical properties of the gas. Details of these end applications are provided in Part 3 and subsequent Parts of ISO 6974.

The analytical guidelines in this Part of the Standards provide for both single and multiple operation methods and either multi-point calibration or a performance evaluation of the analyser followed by single point calibration. Procedures are given for the calculation of the raw (unprocessed) and processed (e.g. normalised) mole fractions, and their associated uncertainties, for all components. The procedures can be used to handle data obtained from replicate or single analyses of a natural gas sample.

Compliance with this Standard requires:

• If only component mole fractions are required: This Part with a method of analysis that meets the requirements of, and is operated in accordance with this Part. This could be either one of Part 3 or subsequent Parts of this Standard or another chromatographic method of choice. Any chromatographic method not forming Part of this Standard shall be documented in the same manner and to the same detail as used to specify the methods in Part 3 and subsequent Parts of this Standard.

• If component mole fractions and associated uncertainties are required: This Part with Part 2 and a method of analysis that meets the requirements of, and is operated in accordance with this Part (as described in the above bullet point).

This Part of the Standard allows the use of three types of method: single operation, multiple operation with bridging and multiple operation without bridging. The last of these methods is a special case of a single operation method.

The main body of this Part of this Standard describes the ‘conventional normalisation' approach for calculating processed mole fractions from raw (unprocessed) mole fractions (see Section 5.5). When conventional normalisation is used for multiple operation without bridging methods, the uncertainties in the calculated mole fractions will be conservative. If a more accurate assessment of uncertainty is required, an alternative approach for normalisation using generalised least squares may be used – this is described in Annex B, which must be used with Part 2 of this Standard.

NOTE: Alternative analytical approaches are available including methane-by-difference (Annex C) and data Harmonization [1]
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