Natural gas - Calculation of thermodynamic properties - Part 2: Single-phase properties (gas, liquid, and dense fluid) for extended ranges of application (ISO 20765-2:2015)

ISO 20765-2:2015 specifies a method to calculate volumetric and caloric properties of natural gases, manufactured fuel gases, and similar mixtures, at conditions where the mixture may be in either the homogeneous (single-phase) gas state, the homogeneous liquid state, or the homogeneous supercritical (dense-fluid) state.

Erdgas - Berechnung thermodynamischer Eigenschaften - Teil 2: Einphaseneigenschaften (gasförmig, flüssig und dickflüssig) für den erweiterten Anwendungsbereich (ISO 20765-2:2015)

Gaz naturel - Calcul des propriétés thermodynamiques -- Partie 2: Propriétés des phases uniques (gaz, liquide, fluide dense) pour une gamme étendue d'applications (ISO 20765-2:2015)

L'ISO 20765-2:2015 spécifie une méthode de calcul des propriétés volumétriques et calorifiques des gaz naturels, des gaz naturels manufacturés, et des mélanges similaires, dans des conditions telles que le mélange peut exister à l'état gazeux homogène (phase unique), à l'état liquide homogène, ou à l'état supercritique homogène (fluide dense).

Zemeljski plin - Izračun termodinamičnih lastnosti - 2. del: Lastnosti enofaznih sistemov (plin, tekočina in gosta tekočina) za razširjen obseg uporabe (ISO 20765-2:2015)

Standard ISO 20765-2:2015 določa metodo za izračun volumetričnih in kaloričnih lastnosti zemeljskih plinov, gorivnih plinov in podobnih mešanic pri pogojih, v katerih je mešanica lahko v homogenem (enofaznem) plinastem stanju, homogenem tekočem stanju ali homogenem superkritičnem (gosto tekočem) stanju.

General Information

Status
Published
Public Enquiry End Date
02-Feb-2017
Publication Date
06-Nov-2018
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
29-Oct-2018
Due Date
03-Jan-2019
Completion Date
07-Nov-2018

Buy Standard

Standard
SIST EN ISO 20765-2:2018 - BARVE na PDF-str 29
English language
68 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

SLOVENSKI STANDARD
SIST EN ISO 20765-2:2018
01-december-2018
=HPHOMVNLSOLQ,]UDþXQWHUPRGLQDPLþQLKODVWQRVWLGHO/DVWQRVWLHQRID]QLK

VLVWHPRY SOLQWHNRþLQDLQJRVWDWHNRþLQD ]DUD]ãLUMHQREVHJXSRUDEH ,62



Natural gas - Calculation of thermodynamic properties - Part 2: Single-phase properties

(gas, liquid, and dense fluid) for extended ranges of application (ISO 20765-2:2015)

Erdgas - Berechnung thermodynamischer Eigenschaften - Teil 2:
Einphaseneigenschaften (gasförmig, flüssig und dickflüssig) für den erweiterten
Anwendungsbereich (ISO 20765-2:2015)

Gaz naturel - Calcul des propriétés thermodynamiques -- Partie 2: Propriétés des phases

uniques (gaz, liquide, fluide dense) pour une gamme étendue d'applications (ISO 20765-

2:2015)
Ta slovenski standard je istoveten z: EN ISO 20765-2:2018
ICS:
71.040.40 Kemijska analiza Chemical analysis
75.060 Zemeljski plin Natural gas
SIST EN ISO 20765-2:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 20765-2:2018
---------------------- Page: 2 ----------------------
SIST EN ISO 20765-2:2018
EN ISO 20765-2
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2018
EUROPÄISCHE NORM
ICS 75.060
English Version
Natural gas - Calculation of thermodynamic properties -
Part 2: Single-phase properties (gas, liquid, and dense
fluid) for extended ranges of application (ISO 20765-
2:2015)

Gaz naturel - Calcul des propriétés thermodynamiques Erdgas - Berechnung thermodynamischer

-- Partie 2: Propriétés des phases uniques (gaz, liquide, Eigenschaften - Teil 2: Einphaseneigenschaften

fluide dense) pour une gamme étendue d'applications (gasförmig, flüssig und dicht-flüssig) für den

(ISO 20765-2:2015) erweiterten Anwendungsbereich (ISO 20765-2:2015)
This European Standard was approved by CEN on 31 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20765-2:2018 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 20765-2:2018
EN ISO 20765-2:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 20765-2:2018
EN ISO 20765-2:2018 (E)
European foreword

The text of ISO 20765-2:2015 has been prepared by Technical Committee ISO/TC 193 "Natural gas” of

the International Organization for Standardization (ISO) and has been taken over as EN ISO 20765-

2:2018 by Technical Committee CEN/TC 238 “Test gases, test pressures, appliance categories and gas

appliance types” the secretariat of which is held by AFNOR.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by March 2019, and conflicting national standards shall

be withdrawn at the latest by March 2019.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 20765-2:2015 has been approved by CEN as EN ISO 20765-2:2018 without any

modification.
---------------------- Page: 5 ----------------------
SIST EN ISO 20765-2:2018
---------------------- Page: 6 ----------------------
SIST EN ISO 20765-2:2018
INTERNATIONAL ISO
STANDARD 20765-2
First edition
2015-01-15
Natural gas — Calculation of
thermodynamic properties —
Part 2:
Single-phase properties (gas, liquid,
and dense fluid) for extended ranges
of application
Gaz naturel — Calcul des propriétés thermodynamiques —
Partie 2: Propriétés des phases uniques (gaz, liquide, fluide dense)
pour une gamme étendue d’applications
Reference number
ISO 20765-2:2015(E)
ISO 2015
---------------------- Page: 7 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2015 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 2

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Thermodynamic basis of the method ............................................................................................................................................. 4

4.1 Principle ........................................................................................................................................................................................................ 4

4.2 The fundamental equation based on the Helmholtz free energy ................................................................ 4

4.2.1 Background........................................................................................................................................................................... 4

4.2.2 The Helmholtz free energy ...................................................................................................................................... 5

4.2.3 The reduced Helmholtz free energy ................................................................................................................ 5

4.2.4 The reduced Helmholtz free energy of the ideal gas ........................................................................ 6

4.2.5 The pure substance contribution to the residual part of the reduced

Helmholtz free energy ................................................................................................................................................. 6

4.2.6 The departure function contribution to the residual part of the reduced

Helmholtz free energy ................................................................................................................................................. 7

4.2.7 Reducing functions ........................................................................................................................................................ 8

4.3 Thermodynamic properties derived from the Helmholtz free energy ................................................... 8

4.3.1 Background........................................................................................................................................................................... 8

4.3.2 Relations for the calculation of thermodynamic properties in the

homogeneous region .................................................................................................................................................... 9

5 Method of calculation ...................................................................................................................................................................................11

5.1 Input variables .....................................................................................................................................................................................11

5.2 Conversion from pressure to reduced density .........................................................................................................11

5.3 Implementation ...................................................................................................................................................................................12

6 Ranges of application ...................................................................................................................................................................................13

6.1 Pure gases .................................................................................................................................................................................................13

6.2 Binary mixtures ...................................................................................................................................................................................14

6.3 Natural gases .........................................................................................................................................................................................17

7 Uncertainty of the equation of state ..............................................................................................................................................18

7.1 Background .............................................................................................................................................................................................18

7.2 Uncertainty for pure gases ......... ................................................................................................................................................18

7.2.1 Natural gas main components...........................................................................................................................18

7.2.2 Secondary alkanes .......................................................................................................................................................19

7.2.3 Other secondary components ...........................................................................................................................21

7.3 Uncertainty for binary mixtures ...........................................................................................................................................21

7.4 Uncertainty for natural gases ..................................................................................................................................................23

7.4.1 Uncertainty in the normal and intermediate ranges of applicability of

natural gas ..........................................................................................................................................................................24

7.4.2 Uncertainty in the full range of applicability, and calculation of properties

beyond this range .........................................................................................................................................................25

7.5 Uncertainties in other properties ........................................................................................................................................25

7.6 Impact of uncertainties of input variables ...................................................................................................................25

8 Reporting of results ........................................................................................................................................................................................25

Annex A (normative) Symbols and units .......................................................................................................................................................27

Annex B (normative) The reduced Helmholtz free energy of the ideal gas ..............................................................29

Annex C (normative) Values of critical parameters and molar masses of the pure components ......35

Annex D (normative) The residual part of the reduced Helmholtz free energy ..................................................36

Annex E (normative) The reducing functions for density and temperature ...........................................................48

Annex F (informative) Assignment of trace components .............................................................................................................55

© ISO 2015 – All rights reserved iii
---------------------- Page: 9 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)

Annex G (informative) Examples ...........................................................................................................................................................................57

Bibliography .............................................................................................................................................................................................................................60

iv © ISO 2015 – All rights reserved
---------------------- Page: 10 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(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 WTO principles in the Technical Barriers

to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 193, Natural Gas, Subcommittee SC 1, Analysis

of Natural Gas.

ISO 20765 consists of the following parts, under the general title Natural gas — Calculation of

thermodynamic properties:
— Part 1: Gas phase properties for transmission and distribution applications

— Part 2: Single-phase properties (gas, liquid, and dense fluid) for extended ranges of application

— Part 3: Two-phase properties (vapour-liquid equilibria)
© ISO 2015 – All rights reserved v
---------------------- Page: 11 ----------------------
SIST EN ISO 20765-2:2018
---------------------- Page: 12 ----------------------
SIST EN ISO 20765-2:2018
INTERNATIONAL STANDARD ISO 20765-2:2015(E)
Natural gas — Calculation of thermodynamic properties —
Part 2:
Single-phase properties (gas, liquid, and dense fluid) for
extended ranges of application
1 Scope

This part of ISO 20765 specifies a method to calculate volumetric and caloric properties of natural gases,

manufactured fuel gases, and similar mixtures, at conditions where the mixture may be in either the

homogeneous (single-phase) gas state, the homogeneous liquid state, or the homogeneous supercritical

(dense-fluid) state.

NOTE 1 Although the primary application of this document is to natural gases, manufactured fuel gases,

and similar mixtures, the method presented is also applicable with high accuracy (i.e., to within experimental

uncertainty) to each of the (pure) natural gas components and to numerous binary and multi-component mixtures

related to or not related to natural gas.

For mixtures in the gas phase and for both volumetric properties (compression factor and density)

and caloric properties (for example, enthalpy, heat capacity, Joule-Thomson coefficient, and speed of

sound), the method is at least equal in accuracy to the method described in Part 1 of this International

Standard, over the full ranges of pressure p, temperature T, and composition to which Part 1 applies. In

some regions, the performance is significantly better; for example, in the temperature range 250 K to

275 K (–10 °F to 35 °F). The method described here maintains an uncertainty of ≤ 0,1 % for volumetric

properties, and generally within 0,1 % for speed of sound. It accurately describes volumetric and

caloric properties of homogeneous gas, liquid, and supercritical fluids as well as those in vapour-liquid

equilibrium. Therefore its structure is more complex than that in Part 1.

NOTE 2 All uncertainties in this document are expanded uncertainties given for a 95 % confidence level

(coverage factor k = 2).

The method described here is also applicable with no increase in uncertainty to wider ranges of

temperature, pressure, and composition for which the method of Part 1 is not applicable. For example, it

is applicable to natural gases with lower content of methane (down to 0,30 mole fraction), higher content

of nitrogen (up to 0,55 mole fraction), carbon dioxide (up to 0,30 mole fraction), ethane (up to 0,25 mole

fraction), and propane (up to 0,14 mole fraction), and to hydrogen-rich natural gases. A practical usage is

the calculation of properties of highly concentrated CO mixtures found in carbon dioxide sequestration

applications.

The mixture model presented here is valid by design over the entire fluid region. In the liquid and

dense-fluid regions the paucity of high quality test data does not in general allow definitive statements

of uncertainty for all sorts of multi-component natural gas mixtures. For saturated liquid densities of

LNG-type fluids in the temperature range from 100 K to 140 K (–280 °F to –208 °F), the uncertainty is

≤(0,1 – 0,3) %, which is in agreement with the estimated experimental uncertainty of available test data.

The model represents experimental data for compressed liquid densities of various binary mixtures

to within ±(0,1 – 0,2) % at pressures up to 40 MPa (5800 psia), which is also in agreement with the

estimated experimental uncertainty. Due to the high accuracy of the equations developed for the binary

subsystems, the mixture model can predict the thermodynamic properties for the liquid and dense-fluid

regions with the best accuracy presently possible for multi-component natural gas fluids.

© ISO 2015 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 7504, Gas Analysis — Vocabulary
ISO 14532, Natural gas — Vocabulary

ISO 20765-1, Natural gas — Calculation of thermodynamic properties — Part 1: Gas phase properties for

transmission and distribution applications
ISO 80000-5:2007, Quantities and units — Part 5: Thermodynamics
3 Terms and definitions

For the purposes of this document, the terms and definitions in ISO 80000-5:2007 and/or ISO 20765-1,

ISO 7504, ISO 14532, and the following apply.

NOTE 1 See Annex A for the list of symbols and units used in this part of ISO 20765.

NOTE 2 Figure 1 is a schematic representation of the phase behaviour of a typical natural gas as a function of

pressure and temperature. The positions of the bubble and dew lines depend upon the composition. This phase

diagram may be useful in understanding the definitions below.
SUPERCRITICAL
cricondenbar
DENSE FLUID
STATE
critical point dew
line
LIQUID PHASE
TWO-PHASE
cricondentherm
bubble
VAPOUR-
LIQUID
line
GAS
PHASE
100 150 200 250 300 350 400
Figure 1 — Phase diagram for a typical natural gas
3.1
bubble pressure

pressure at which an infinitesimal amount of vapour is in equilibrium with a bulk liquid for a

specified temperature
2 © ISO 2015 – All rights reserved
Pressure/MPa
---------------------- Page: 14 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)
3.2
bubble temperature

temperature at which an infinitesimal amount of vapour is in equilibrium with a bulk liquid for a

specified pressure
Note 1 to entry: The locus of bubble points is known as the bubble line.

Note 2 to entry: More than one bubble temperature may exist at a specific pressure. Moreover, more than one

bubble pressure may exist at a specified temperature, as explained in the example given in 3.6.

3.3
cricondenbar
maximum pressure at which two-phase separation can occur
3.4
cricondentherm
maximum temperature at which two-phase separation can occur
3.5
critical point

unique saturation point along the two-phase vapour-liquid equilibrium boundary where both the vapour

and liquid phases have the same composition and density

Note 1 to entry: The critical point is the point at which the dew line and the bubble line meet.

Note 2 to entry: The pressure at the critical point is known as the critical pressure and the temperature as the

critical temperature.

Note 3 to entry: A mixture of given composition may have one, more than one, or no critical points. In addition,

the phase behaviour may be quite different from that shown in Fig. 1 for mixtures (including natural gases)

containing, e.g., hydrogen or helium.
3.6
dew pressure

pressure at which an infinitesimal amount of liquid is in equilibrium with a bulk vapour for a

specified temperature

Note 1 to entry: More than one dew pressure may exist at the specified temperature. For example, isothermal

compression at 300 K with a gas similar to that shown in Figure 1: At low pressure the mixture is a gas. At just

above 2 MPa (the dew pressure), a liquid phase initially forms. As pressure increases more liquid forms in the

two-phase region, but a further increase in pressure reduces the amount of liquid (retrograde condensation) until

at about 8 MPa where the liquid phase disappears at the upper dew pressure, and the mixture is in the dense gas

phase. In the two-phase region, the overall composition is as specified, however the coexisting vapour and liquid

will have different compositions.
3.7
dew temperature

temperature at which an infinitesimal amount of liquid is in equilibrium with a bulk vapour for a

specified pressure

Note 1 to entry: More than one dew temperature may exist at a specified pressure, similar to the example given in 3.6.

Note 2 to entry: The locus of dew points is known as the dew line.
3.8
supercritical state

dense phase region above the critical point (often considered to be a state above the critical temperature

and pressure) within which no two-phase separation can occur
© ISO 2015 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 20765-2:2018
ISO 20765-2:2015(E)
4 Thermodynamic basis of the method
4.1 Principle

The method is based on the concept that natural gas or any other type of mixture can be completely

characterized in the calculation of its thermodynamic properties by component analysis. Such an

analysis, together with the state variables of temperature and density, provides the necessary input

data for the calculation of properties. In practice, the state variables available as input data are generally

temperature and pressure, and it is thus necessary to first iteratively determine the density using the

equations provided here.

These equations express the Helmholtz free energy of the mixture as a function of density, temperature,

and composition, from which all other thermodynamic properties in the homogeneous (single-phase)

gas, liquid, and supercritical (dense-fluid) regions may be obtained in terms of the Helmholtz free energy

and its derivatives with respect to temperature and density. For example, pressure is proportional to

the first derivative of the Helmholtz energy with respect to density (at constant temperature).

NOTE These equations are also applicable in the calculation of two-phase properties (vapour-liquid

equilibria). Additional composition-dependent derivatives are required and are presented in Part 3 of this

International Standard.

The method uses a detailed molar composition analysis in which all components present in amounts

exceeding 0,000 05 mole fraction (50 ppm) are specified. For a typical natural gas, this might include

alkane hydrocarbons up to about C or C together with nitrogen, carbon dioxide, and helium. Typically,

7 8

isomers for alkanes C and higher may be lumped together by molar mass and treated collectively as the

normal isomer.

For some fluids, additional components such as C , C , water, and hydrogen sulfide may be present and

9 10

need to be taken into consideration. For manufactured gases, hydrogen, carbon monoxide, and oxygen

may also be present in the mixture.

More precisely, the method uses a 21-component analysis in which all of the major and most of the minor

components of natural gas are included (see Clause 6). Any trace component present but not identified as one

of the 21 specified components may be assigned appropriately to one of these 21 components (see Annex F).

4.2 The fundamental equation based on the Helmholtz free energy
4.2.1 Background
[1]

The GERG-2008 equation was published by the Lehrstuhl für Thermodynamik at the Ruhr-Universität

Bochum in Germany as a new wide-range equation of state for the volumetric and caloric properties of

[2] [1]

natural gases and other mixtures. It was originally published in 2007 and later updated in 2008.

[3]

The new equation improves upon the performance of the AGA-8 equation for gas phase properties and

in addition is applicable to the properties of the liquid phase, to the dense-fluid phase, to the vapour-

liquid phase boundary, and to properties for two-phase states. The ranges of temperature, pressure,

and composition to which the GERG-2008 equation of state applies are much wider than the AGA-8

equation and cover an extended range of application. The Groupe Européen de Recherches Gazières

(GERG) supported the development of this equation of state over several years.

The GERG-2008 equation is explicit in the Helmholtz free energy, a formulation that enables all

thermodynamic properties to be expressed analytically as functions of the free energy and of its

derivatives with respect to the state conditions of temperature a
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.