ISO/TR 29922:2017
(Main)Natural gas — Supporting information on the calculation of physical properties according to ISO 6976
Natural gas — Supporting information on the calculation of physical properties according to ISO 6976
ISO/TR 29922:2017 acts as a repository for those manifold technical details which justify and explain the methods presented in the third edition of ISO 6976 but which are not directly needed in the everyday routine implementation of the standard. Each main clause addresses a specific aspect of the calculational method described in ISO 6976:2016, and is intended to be self-sufficient and essentially independent of each other clause. For this reason, the user should not expect the whole to be accessible to study as a sequentially coherent narrative.
Gaz naturel — Informations supplémentaires pour le calcul des propriétés physiques selon l'ISO 6976
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 29922
First edition
2017-03
Natural gas — Supporting information
on the calculation of physical
properties according to ISO 6976
Gaz naturel — Informations supplémentaires pour le calcul des
propriétés physiques selon l’ISO 6976
Reference number
ISO/TR 29922:2017(E)
©
ISO 2017
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ISO/TR 29922:2017(E)
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ISO/TR 29922:2017(E)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols, units and abbreviated terms . 1
4.1 Quantities . 1
4.2 Subscripts . 3
4.3 Superscripts . . 3
4.4 Abbreviated terms . 3
5 Enthalpy of combustion of the ideal gas and its variation with temperature .4
5.1 Preamble . 4
5.2 Standard enthalpy of combustion at 25 °C . 4
5.3 Standard enthalpy of combustion at other temperatures . 5
5.4 Formulation of the ideal-gas enthalpy . 6
5.5 Illustrative examples . 7
5.6 Uncertainty in enthalpy of combustion . 8
6 Non-ideality: Variation of real-gas enthalpy of combustion with pressure .9
6.1 Preamble . 9
6.2 Formulation of the enthalpic correction .10
6.3 Estimation of the enthalpic correction .12
6.4 Conclusion .13
7 Non-ideality: Compression factor effect on volume-basis calorific values .13
7.1 Compression factor .13
7.2 Virial equation of state .14
7.3 Estimation of mixture compression factor .15
7.4 Limitations of the modified IGT-32 method .17
7.5 Uncertainty in compression factor .18
8 Quantitation of volumetric non-ideality .18
8.1 Second virial coefficients of pure components .18
8.1.1 Preliminary procedures .18
8.1.2 Improved procedure .19
8.2 Summation factors of pure components . .21
8.2.1 Overview .21
8.2.2 Major components of natural gas .21
8.2.3 Hydrogen and helium .22
8.3 Compression factors of the permanent gases .23
8.4 Pure component uncertainties .25
8.4.1 Uncertainty of second virial coefficients .25
8.4.2 Truncation error .25
8.4.3 Linearization error . .27
8.4.4 Berlin versus Leiden .28
8.4.5 Hydrogen and helium .29
8.4.6 Water .30
8.4.7 Combination of uncertainties .31
8.5 Mixture uncertainty .31
9 Miscellaneous data .31
9.1 Atomic weights of the elements .31
9.1.1 Atomic weights 2007.31
9.1.2 Atomic weights 2009 and 2011 .32
9.1.3 Discussion .34
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ISO/TR 29922:2017(E)
9.2 Composition and molecular weight of dry air .35
10 Effects of water vapour on calorific value .36
10.1 Preamble .36
10.2 Excluded volume effect .37
10.3 Latent heat (enthalpic) effect .38
10.4 Compression factor effect .39
10.5 Combination of effects .39
10.6 Spectator water .40
10.7 Effect of humid air .41
10.7.1 Preamble .41
10.7.2 Stoichiometric combustion with oxygen.42
10.7.3 Combustion of dry gas with excess dry air.42
10.7.4 Combustion of wet gas with excess dry air .43
10.7.5 Combustion of wet gas with excess humid air .43
11 Summary, discussion and selection of the calorific value of methane .45
11.1 Standard enthalpy of combustion .45
11.1.1 Background.45
11.1.2 Selection of data .45
11.1.3 Recalculation of Rossini values .46
11.1.4 Evaluation of selected data .48
11.1.5 Selected value and uncertainty .52
11.2 Derived calorific values .52
11.3 Comparisons between calorimetric methodologies .54
12 Calorific values on a mass basis .56
12.1 Calorific values on a mass basis for components of natural gas .56
12.2 Alternative (non-normative) method of calculation for mass-basis calorific values .57
13 Calorific values on a volume basis .60
13.1 Calorific values on a volume basis for components of natural gas .60
13.2 Alternative (non-normative) method of calculation for volume-basis calorific values .60
14 Approximate conversion between reference conditions .63
14.1 Factors for conversion between metric reference conditions .63
14.2 Equations for conversion between metric reference conditions.65
14.3 Expression of non-SI reference (base) pressures in metric units .65
15 Mathematical and methodological issues relating to estimation of uncertainty.66
15.1 Principles .66
15.2 Input data .68
15.2.1 Preamble .68
15.2.2 Reference conditions .68
15.2.3 Composition data .68
15.2.4 Physical property data .69
15.3 Uncertainty of the calculational method .70
15.4 Evaluation of sensitivity coefficients .70
15.4.1 Preamble .70
15.4.2 Analytical method .71
15.4.3 Finite difference method .73
15.4.4 Monte Carlo method .73
16 Detailed derivation of uncertainty equations in ISO 6976:2016 .73
16.1 Principles and assumptions .73
16.2 General formulation .74
16.3 Effects of correlations .75
16.3.1 Correlation between mole fractions .75
16.3.2 Correlation between molar masses .76
16.3.3 Correlation between physical properties .78
16.4 Uncertainty equations for basic properties .78
16.4.1 Molar mass .78
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ISO/TR 29922:2017(E)
16.4.2 Molar-basis gross calorific value .79
16.4.3 Molar-basis net calorific value .79
16.4.4 Summation factor .80
16.4.5 Compression factor .80
16.5 Uncertainty equations for compound properties .81
16.5.1 Mass-basis gross calorific value .81
16.5.2 Mass-basis net calorific value .82
16.5.3 Volume-basis gross calorific value .83
16.5.4 Volume-basis net calorific value .84
16.5.5 Density .86
16.5.6 Relative density .87
16.5.7 Gross Wobbe index.88
16.5.8 Net Wobbe index .89
16.6 Repeatability and reproducibility.91
17 Computer implementation of recommended methods .92
17.1 Compiled BASIC shareware program .92
17.2 Spreadsheet implementation .94
Bibliography .97
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ISO/TR 29922:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www . i so .org/ iso/ foreword .html.
The committee responsible for this document is ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis
of natural gas.
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ISO/TR 29922:2017(E)
Introduction
Both international and intranational custody transfer of natural gas usually require precise
determination of both the quantity and the quality of the gas to be traded. ISO 6976:2016, which cancels
and replaces ISO 6976:1995, specifies methods for the calculation of those properties, often known
as the combustion properties, which (in part) describe gas quality, namely gross (superior) and net
(inferior) calorific value, density, relative density, gross and net Wobbe index. The methods provide the
means of calculating the properties, including uncertainties, of any natural gas, natural gas substitute,
or similar combustible gaseous fuel of known composition at commonly used reference conditions.
Some 80-odd years ago, in the Introduction to Hyde and Mills’ classic text Gas Calorimetry, Sir Charles
[109]
Vernon (‘CV’) Boys wrote the words “ … I hesitate to give the number of actual tests of the calorific
value of gas which are made every year, but . it will be evident that any machinery set up to ascertain
its value must be extensive . The fact is that no single commodity generally purchased by the public is so
carefully watched and maintained of its guaranteed quality as gas … ”. Since that time, the technology of
gas calorimetry has changed beyond either recognition or imagination, but the truth of the sentiment
expressed remains unchanged and refers every bit as much to 2017 as it did to 1932.
This document acts as a repository for those manifold technical details which justify and explain the
methods presented in the new third (2016) edition of ISO 6976 but which are not directly needed in its
everyday routine implementation. In short, it is conceived and intended as a complete(ish) knowledge
base which provides full and proper technical authentication of ISO 6976.
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TECHNICAL REPORT ISO/TR 29922:2017(E)
Natural gas — Supporting information on the calculation of
physical properties according to ISO 6976
1 Scope
This document acts as a repository for those manifold technical details which justify and explain the
methods presented in the third edition of ISO 6976 but which are not directly needed in the everyday
routine implementation of the standard.
Each main clause addresses a specific aspect of the calculational method described in ISO 6976:2016,
and is intended to be self-sufficient and essentially independent of each other clause. For this reason,
the user should not expect the whole to be accessible to study as a sequentially coherent narrative.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6976 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Symbols, units and abbreviated terms
4.1 Quantities
Symbol Meaning Unit
a atomic index for carbon in the generalized molecular species C H N O S —
a b c d e
b atomic index for hydrogen in the generalized molecular species C H N O S —
a b c d e
c atomic index for nitrogen in the generalized molecular species C H N O S —
a b c d e
d atomic index for oxygen in the generalized molecular species C H N O S —
a b c d e
e atomic index for sulfur in the generalized molecular species C H N O S —
a b c d e
g coefficients in equation for B —
−1
h molar enthalpy kJ·mol
k coverage factor —
m number of sets of values —
n number of determinations in a set of values —
p pressure (absolute) kPa
q exact input quantity in calculation of Y (varies)
r correlation coefficient —
s summation factor —
t Celsius temperature °C
u(Y) standard uncertainty of Y (varies)
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ISO/TR 29922:2017(E)
Symbol Meaning Unit
u(Y,Y’) covariance of Y and Y’ (varies)
w repeatability or reproducibility (varies)
x mole fraction —
y inexact input quantity in calculation of Y (varies)
−1
A atomic mass (atomic weight) kg·kmol
3 -1
B second virial coefficient m ·mol
6 −2
C third virial coefficient m ·mol
−1 −1
Cp molar isobaric heat capacity kJ·mol ·K
−3
D (mass) density kg·m
−3
Đ molar density mol·m
−1
E non-random (systematic) bias from the true value of Hc kJ·mol
F function that generates property Y —
G relative density —
−1
Hc molar-basis calorific value (negative enthalpy of combustion) kJ·mol
−1
Hf enthalpy of formation kJ·mol
−1
Hm mass-basis calorific value MJ·kg
−3
Hv volume-basis calorific value MJ·m
3( j-1) -( j-1)
J j-th virial coefficient m ·mol
−1
L molar enthalpy of vaporization of wa
...
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