ÖNORM EN ISO 6976

This International Standard specifies methods for the calculation of the superior calorific value, inferior calorific value, density, relative density and Wobbe index of dry natural gases, natural gas substitutes and other combustible gaseous fuels, when the composition of the gas by mole fraction is known. The methods provide a means of calculating the properties of the gas mixture at commonly used metric reference conditions. The methods of calculation require values for various physical properties of the pure components; these values are provided in tables and their sources are identified. Methods are given for estimating the precision of calculated properties. The methods of calculation of the values of properties on either a molar or mass basis are applicable to any dry natural gas, natural gas substitute or other combustible fuel which is normally gaseous. For the calculation of the values of properties on a volumetric basis, the methods are restricted to gases consisting preponderantly of methane (not less than 0,5 mole fraction). Examples of calculations are given in annex D for the recommended methods of calculation. NOTES 1 The symbols used in this International Standard, together with their meanings, are given in annex A. 2 The qualifiers higher, upper, total and gross are, for the purposes of this International Standard, synonymous with superior; likewise, lower and net are synonymous with inferior. The term heating value is synonymous with calorific value; specific gravity is synonymous with relative density; Wobbe number is synonymous with Wobbe index; compressibility factor is synonymous with compression factor. 3 If the composition of the gas is known by volume fractions these must be converted to mole fractions (see annex C). Note, however, that the derived mole fractions will have uncertainties greater than those of the original volume fractions. 4 For the pu (...abbreviated)