ISO 6976:2016 天然气 热值、密度和相对密度及化合物沃泊指数的计算

标准编号：ISO 6976:2016

中文名称：天然气 热值、密度和相对密度及化合物沃泊指数的计算

英文名称：Natural gas — Calculation of calorific values, density, relative density and Wobbe indices from composition

发布日期：2016-08

标准范围

ISO 6976:2016规定了天然气、天然气替代品和其他可燃气体燃料的总热值、净热值、密度、相对密度、总沃泊指数和净沃泊指数的计算方法，前提是已知气体的摩尔分数组成。规定的方法提供了在常用参考条件下计算气体混合物特性的方法。摩尔分数按定义和为一。ISO 6974-1和ISO 6974-2中提供了通过色谱分析实现该要求的指南。计算方法要求纯组分的各种物理性质的值；表中提供了这些值以及相关的不确定性，并确定了它们的来源。给出了估算计算性质标准不确定度的方法。基于摩尔、质量或体积的特性值计算方法适用于任何天然气、天然气替代品或其他通常为气体的可燃燃料，但对于基于体积的特性，该方法仅限于参考条件下压缩系数大于0.9的混合物。附录D中给出了推荐计算方法的计算示例。注1:就本文件而言，限定词“高级”、“高级”、“高级”和“总计”是“总”的同义词；同样，“低级”和“低级”是“净”的同义词。术语“热值”是“热值”的同义词；“质量密度”和“比密度”是“密度”的同义词；“比重”是“相对密度”的同义词；“沃泊数”是“沃泊指数”的同义词；“压缩系数”是“压缩系数”的同义词。无量纲量分子量在数值上等于摩尔质量，单位为kg？kmol？1。注2:本文件中描述的方法不适用于明确的成分限制。然而，体积基础计算对参考条件下压缩系数大于0.9的混合物的限制设定了成分的隐含限制。注3:由于存在的任何水的摩尔分数通常无法从色谱分析中获得，因此通常的做法是以干气为基础计算物理性质，并在单独的程序中考虑水蒸气的影响。然而，如果已知水蒸气的摩尔分数，则可完全按照本文所述程序进行性能计算。ISO/TR 29922讨论了水蒸气对热值的影响，无论热值是直接测量还是计算的。注4:对于碳数为7或以上的脂肪族碳氢化合物，存在的任何异构体都包括在相同碳数的正常异构体中。注5:如果用户要求包括用单个伪组分替换（例如）分析未解析组分的C6+或C7+分组，则用户自己的任务是设置该伪组分的摩尔分数组成，从而设置其特性，以便适合特定应用中的用途。通过将适当的燃烧焓值设置为零，将任何所谓的“观众水”和“不可燃硫化氢”视为伪组分。

ISO 6976:2016 specifies methods for the calculation of gross calorific value, net calorific value, density, relative density, gross Wobbe index and net Wobbe index of natural gases, natural gas substitutes and other combustible gaseous fuels, when the composition of the gas by mole fraction is known. The methods specified provide the means of calculating the properties of the gas mixture at commonly used reference conditions.Mole fractions by definition sum to unity. Guidance on the achievement of this requirement by chromatographic analysis is available in ISO 6974？1 and ISO 6974？2.The methods of calculation require values for various physical properties of the pure components; these values, together with associated uncertainties, are provided in tables and their sources are identified.Methods are given for estimating the standard uncertainties of calculated properties.The methods of calculation of the values of properties on either a molar, mass or volume basis are applicable to any natural gas, natural gas substitute or other combustible fuel that is normally gaseous, except that for properties on the volume basis the method is restricted to mixtures for which the compression factor at reference conditions is greater than 0,9.Example calculations are given in Annex D for the recommended methods of calculation.NOTE 1 The qualifiers "superior", "higher", "upper" and "total" are, for the purposes of this document, synonymous with "gross"; likewise, "inferior" and "lower" are synonymous with "net". The term "heating value" is synonymous with "calorific value"; "mass density" and "specific density" are synonymous with "density"; "specific gravity" is synonymous with "relative density"; "Wobbe number" is synonymous with "Wobbe index"; "compressibility factor" is synonymous with "compression factor". The dimensionless quantity molecular weight is numerically equal to the molar mass in kg？kmol？1.NOTE 2 There are no explicit limits of composition to which the methods described in this document are applicable. However, the restriction of volume-basis calculations to mixtures with a compression factor greater than 0,9 at reference conditions sets implicit limits on composition.NOTE 3 Because the mole fraction of any water present is not normally available from chromatographic analysis, it is common practice to calculate the physical properties on a dry gas basis and to allow for the effects of water vapour in a separate procedure. However, if the mole fraction of water vapour is known then the property calculations can be carried out completely in accordance with the procedures described herein. The effects of water vapour on calorific value, whether the latter is directly measured or calculated, are discussed in ISO/TR 29922.NOTE 4 For aliphatic hydrocarbons of carbon number 7 or above, any isomer present is included with the normal isomer of the same carbon number.NOTE 5 If the user's requirement includes the replacement of, for example, a C6+ or C7+ grouping of analytically unresolved components by a single pseudo-component, then it is the user's own task to set the mole fraction composition, and hence properties, of this pseudo-component so as to be fit for purpose in the particular application. Any so-called "spectator water" and "non-combustible hydrogen sulfide" are treated as pseudo-components by setting the appropriate enthalpy of combustion values to zero.

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