1、BSI Standards PublicationBS ISO 20765-2:2015Natural gas Calculation ofthermodynamic propertiesPart 2: Single-phase properties (gas, liquid,and dense fluid) for extended ranges ofapplicationBS ISO 20765-2:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 2076
2、5-2:2015.The UK participation in its preparation was entrusted to TechnicalCommittee PTI/15, Natural Gas and Gas Analysis.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a con
3、tract. Users are responsible for its correctapplication. The British Standards Institution 2015. Published by BSI StandardsLimited 2015ISBN 978 0 580 80807 4ICS 75.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authori
4、ty of theStandards Policy and Strategy Committee on 31 January 2015.Amendments issued since publicationDate Text affectedBS ISO 20765-2:2015 ISO 2015Natural gas Calculation of thermodynamic properties Part 2: Single-phase properties (gas, liquid, and dense fluid) for extended ranges of applicationGa
5、z naturel Calcul des proprits thermodynamiques Partie 2: Proprits des phases uniques (gaz, liquide, fluide dense) pour une gamme tendue dapplicationsINTERNATIONAL STANDARDISO20765-2First edition2015-01-15Reference numberISO 20765-2:2015(E)BS ISO 20765-2:2015ISO 20765-2:2015(E)ii ISO 2015 All rights
6、reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015All 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 wr
7、itten permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO
8、20765-2:2015ISO 20765-2:2015(E)Contents PageForeword v1 Scope . 12 Normative references 23 Terms and definitions . 24 Thermodynamic basis of the method . 44.1 Principle 44.2 The fundamental equation based on the Helmholtz free energy 44.2.1 Background. 44.2.2 The Helmholtz free energy 54.2.3 The red
9、uced Helmholtz free energy 54.2.4 The reduced Helmholtz free energy of the ideal gas 64.2.5 The pure substance contribution to the residual part of the reduced Helmholtz free energy . 64.2.6 The departure function contribution to the residual part of the reduced Helmholtz free energy . 74.2.7 Reduci
10、ng functions 84.3 Thermodynamic properties derived from the Helmholtz free energy . 84.3.1 Background. 84.3.2 Relations for the calculation of thermodynamic properties in the homogeneous region 95 Method of calculation .115.1 Input variables . 115.2 Conversion from pressure to reduced density .115.3
11、 Implementation . 126 Ranges of application .136.1 Pure gases . 136.2 Binary mixtures . 146.3 Natural gases . 177 Uncertainty of the equation of state 187.1 Background . 187.2 Uncertainty for pure gases . 187.2.1 Natural gas main components. 187.2.2 Secondary alkanes .197.2.3 Other secondary compone
12、nts . 217.3 Uncertainty for binary mixtures . 217.4 Uncertainty for natural gases 237.4.1 Uncertainty in the normal and intermediate ranges of applicability of natural gas 247.4.2 Uncertainty in the full range of applicability, and calculation of properties beyond this range .257.5 Uncertainties in
13、other properties 257.6 Impact of uncertainties of input variables . 258 Reporting of results 25Annex A (normative) Symbols and units .27Annex B (normative) The reduced Helmholtz free energy of the ideal gas 29Annex C (normative) Values of critical parameters and molar masses of the pure components 3
14、5Annex D (normative) The residual part of the reduced Helmholtz free energy 36Annex E (normative) The reducing functions for density and temperature .48Annex F (informative) Assignment of trace components .55 ISO 2015 All rights reserved iiiBS ISO 20765-2:2015ISO 20765-2:2015(E)Annex G (informative)
15、 Examples .57Bibliography .60iv ISO 2015 All rights reservedBS ISO 20765-2:2015ISO 20765-2:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally car
16、ried 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.
17、 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 differe
18、nt 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 b
19、e 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)
20、.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 ISOs adherence to the WTO principles i
21、n the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe 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 Calcula
22、tion 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 vBS ISO
23、 20765-2:2015BS ISO 20765-2:2015Natural gas Calculation of thermodynamic properties Part 2: Single-phase properties (gas, liquid, and dense fluid) for extended ranges of application1 ScopeThis part of ISO 20765 specifies a method to calculate volumetric and caloric properties of natural gases, manuf
24、actured 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, manufa
25、ctured 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
26、 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
27、 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
28、, 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
29、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 ap
30、plicable 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 pra
31、ctical usage is the calculation of properties of highly concentrated CO2mixtures 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 i
32、n 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 experi
33、mental 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 o
34、f 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.INTERNATIONAL STANDARD ISO 20765-2:2015(E) ISO 2015 All rights reser
35、ved 1BS ISO 20765-2:2015ISO 20765-2:2015(E)2 Normative referencesThe 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 th
36、e referenced document (including any amendments) applies.ISO 7504, Gas Analysis VocabularyISO 14532, Natural gas VocabularyISO 20765-1, Natural gas Calculation of thermodynamic properties Part 1: Gas phase properties for transmission and distribution applicationsISO 80000-5:2007, Quantities and unit
37、s Part 5: Thermodynamics3 Terms and definitionsFor 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 sc
38、hematic 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.01234567891011121314100 150 200 250 300 350
39、 400LIQUID PHASEbubblelinecritical pointTWO-PHASEVAPOUR-LIQUIDGASPHASEdewlinecricondenthermcricondenbarSUPERCRITICAL DENSE FLUIDSTATEPressure/MPaFigure 1 Phase diagram for a typical natural gas3.1bubble pressurepressure at which an infinitesimal amount of vapour is in equilibrium with a bulk liquid
40、for a specified temperature2 ISO 2015 All rights reservedBS ISO 20765-2:2015ISO 20765-2:2015(E)3.2bubble temperaturetemperature at which an infinitesimal amount of vapour is in equilibrium with a bulk liquid for a specified pressureNote 1 to entry: The locus of bubble points is known as the bubble l
41、ine.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 3.6.3.3cricondenbarmaximum pressure at which two-phase separation can occur3.4cricondenthermmaxim
42、um temperature at which two-phase separation can occur3.5critical pointunique saturation point along the two-phase vapour-liquid equilibrium boundary where both the vapour and liquid phases have the same composition and densityNote 1 to entry: The critical point is the point at which the dew line an
43、d 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 qui
44、te different from that shown in Fig. 1 for mixtures (including natural gases) containing, e.g., hydrogen or helium.3.6dew pressurepressure at which an infinitesimal amount of liquid is in equilibrium with a bulk vapour for a specified temperatureNote 1 to entry: More than one dew pressure may exist
45、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
46、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
47、vapour and liquid will have different compositions.3.7dew temperaturetemperature at which an infinitesimal amount of liquid is in equilibrium with a bulk vapour for a specified pressureNote 1 to entry: More than one dew temperature may exist at a specified pressure, similar to the example given in 3
48、.6.Note 2 to entry: The locus of dew points is known as the dew line.3.8supercritical statedense 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 3BS ISO 2076
49、5-2:2015ISO 20765-2:2015(E)4 Thermodynamic basis of the method4.1 PrincipleThe 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 t
