Gas infrastructure - Quality of gas - Group H

This European standard specifies gas quality characteristics, parameters and their limits, for gases classified as group H that are to be transmitted, injected into and from storages, distributed and utilized.
NOTE   For information on gas families and gas groups see EN 437.
This European standard does not cover gases conveyed on isolated networks.
For biomethane, additional requirements indicated in prEN 16723 1 apply.

Gasinfrastruktur - Beschaffenheit von Gas - Gruppe H

Diese Europäische Norm legt die Kenngrößen und Parameter sowie die zugehörigen Grenzwerte für die Beschaffenheit von als Gruppe H eingeteilten Gasen fest, die zu transportieren, in Speicher ein  und aus Speichern auszuspeisen, zu verteilen und zu verbrauchen sind.
ANMERKUNG   Für Informationen zu Gasfamilien und Gasgruppen siehe EN 437.
Diese Europäische Norm umfasst keine Gase, die in isolierten Netzen befördert werden.
Für Biomethan gelten die zusätzlichen Anforderungen nach EN 16723 1.

Infrastructures gazières - Qualité du gaz - Groupe H

Infrastruktura za plin - Kakovost plina - Skupina H (vključno z dopolnilom A1)

Ta evropski standard določa kakovostne karakteristike, parametre in njihove omejitve za pline iz skupine H, namenjene za prenos, vnos v vsebnike in odstranitev iz njih, distribucijo ter uporabo.
OPOMBA: Za več informacij o družinah in skupinah plinov glej standard EN 437.
Ta evropski standard ne zajema plinov, ki se prenašajo v izoliranih omrežjih.
Za biometan veljajo dodatne zahteve iz standarda prEN 16723 1.

General Information

Status
Published In Revision
Publication Date
06-Nov-2018
Technical Committee
Current Stage
9000 - Revision (Adopted Project)
Start Date
26-Nov-2020
Due Date
19-Feb-2021

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Gasinfrastruktur - Beschaffenheit von Gas - Gruppe HInfrastructures gazières - Qualité du gaz - Groupe HGas infrastructure - Quality of gas - Group H75.060Zemeljski plinNatural gasICS:Ta slovenski standard je istoveten z:EN 16726:2015+A1:2018SIST EN 16726:2016+A1:2018en,fr,de01-december-2018SIST EN 16726:2016+A1:2018SLOVENSKI

STANDARDSIST EN 16726:20161DGRPHãþD
SIST EN 16726:2016+A1:2018
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 16726:2015+A1
July
t r s z ICS
y wä r x r Supersedes EN
s x y t xã t r s wEnglish Version

Gas infrastructure æ Quality of gas æ Group H Infrastructures gazières æ Qualité du gaz æ Groupe H

Gasinfrastruktur æ Beschaffenheit von Gas æ Gruppe HThis European Standard was approved by CEN on

t v October
t r s w and includes Amendment
s approved by CEN on
t z March
t r s zä

egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä

translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä

CEN members are the national standards bodies of Austriaá Belgiumá Bulgariaá Croatiaá Cyprusá Czech Republicá Denmarká Estoniaá Finlandá Former Yugoslav Republic of Macedoniaá Franceá Germanyá Greeceá Hungaryá Icelandá Irelandá Italyá Latviaá Lithuaniaá Luxembourgá Maltaá Netherlandsá Norwayá Polandá Portugalá Romaniaá Serbiaá Slovakiaá Sloveniaá Spainá Swedená Switzerlandá Turkey and United Kingdomä

EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre:
Rue de la Science 23,
B-1040 Brussels

t r s z CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN

s x y t xã t r s w ªA sã t r s z ESIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 2 Contents Page European foreword ....................................................................................................................................................... 3 Introduction .................................................................................................................................................................... 4 1 Scope .................................................................................................................................................................... 5 2 Normative references .................................................................................................................................... 5 3 Terms and definitions ................................................................................................................................... 5 4 Reference conditions and pressure units ............................................................................................... 6 5 Requirements ................................................................................................................................................... 6 Annex A (normative)

Calculation of methane number of gaseous fuels for engines ........................... 9 A.1 Introduction ...................................................................................................................................................... 9 A.2 Calculation of methane number ................................................................................................................ 9 A.3 Example 1: 2H-gas ........................................................................................................................................ 10 A.4 Example 2: enriched biomethane ........................................................................................................... 16 A.5 Example 3: 2H-gas with hydrogen addition ........................................................................................ 17 Annex B (informative)

Sulfur ................................................................................................................................ 31 B.1 General ............................................................................................................................................................. 31 B.2 Total sulfur from Odorants ....................................................................................................................... 31 Annex C (informative)

Water dew point and hydrocarbon dew point .................................................. 35 C.1 Water dew point ........................................................................................................................................... 35 C.2 Hydrocarbon dew point ............................................................................................................................. 35 Annex D (informative)

Background for not including a Wobbe Index range into this standard .......................................................................................................................................................... 36 D.1 General ............................................................................................................................................................. 36 D.2 A common European Wobbe index range ........................................................................................... 38 Annex E (informative)

Hydrogen - Admissible Concentrations in natural gas systems .................. 39 Annex F (informative)

Sampling .......................................................................................................................... 40 Annex G (informative)

A–deviations .................................................................................................................. 41 Bibliography ................................................................................................................................................................. 47

SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 3 European foreword This document (EN 16726:2015+A1:2018) has been prepared by Technical Committee CEN/TC 234 “Gas infrastructure”, the secretariat of which is held by DIN. 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 January 2019, and conflicting national standards shall be withdrawn at the latest by January 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. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association. This document includes Amendment 1 approved by CEN on 2018-03-28. This document supersedes EN 16726:2015. The start and finish of text introduced or altered by amendment is indicated in the text by tags !". The need for a European Standard concerning the specification of the quality of gases of group H is derived from the mandate M/400 issued to CEN by the European Commission. According to this mandate the goal is to define specifications that are as wide as possible within reasonable costs. This means that the specifications enhance the free flow of gas within the internal EU market, in order to promote competition and security of supply minimizing the negative effects on gas infrastructure and gas networks, efficiency and the environment and allow appliances to be used without compromising safety. Some requirements specified in this European Standard, Clause 5, cannot be applied in !Denmark", Germany, Hungary and the Netherlands due to existing conflicting national legislation. The related A-Deviations are listed in Annex G. 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. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 4 Introduction This European standard sets requirements for gas quality with the aim to allow the free flow of gas between the CEN member states and to enable the security of supply taking into account the impact on the whole value chain from gas production and supply to end uses. However, at the moment of publication of this European standard, a common Wobbe Index range cannot be defined because of different regulations in CEN Member States and limited knowledge of the influence of broadening Wobbe Index range on integrity, efficiency and safe use of appliances in some countries (see Annex D). In order to find a common Wobbe Index range, further studies, such as the Gas Quality Harmonization Implementation Pilot, are necessary. The Wobbe Index should be defined when the pending results of these studies are available. The common Wobbe Index range should be implemented in a revised standard in due time. For hydrogen, at present it is not possible to specify a limiting value which would generally be valid for all parts of the European gas infrastructure (see Annex E). Responsibility and liability issues in the context of this European standard are subject to European or national regulations. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 5 1 Scope This European standard specifies gas quality characteristics, parameters and their limits, for gases classified as group H that are to be transmitted, injected into and from storages, distributed and utilized. NOTE For information on gas families and gas groups see EN 437. This European standard does not cover gases conveyed on isolated networks. For biomethane, additional requirements indicated in prEN 16723-1 apply. 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. EN ISO 13443, Natural gas — Standard reference conditions (ISO 13443) EN ISO 14532, Natural gas — Vocabulary (ISO 14532) ISO 14912, Gas analysis — Conversion of gas mixture composition data 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN ISO 14532 and the following apply. 3.1 isolated network network where transmission, distribution and utilization of gas are combined and which is physically unconnected to other networks 3.2 entry point point at which gas enters a gas distribution or gas transmission system 3.3 interconnection point physical point connecting adjacent entry-exit systems or connecting an entry-exit system with an interconnector [SOURCE: Commission Regulation (EU) No 984/2013, modified] 3.4 maximum operating pressure maximum pressure at which a network can be operated continuously under normal conditions expressed as absolute pressure Note 1 to entry: Normal conditions are: no fault in any device or stream. [SOURCE: EN 1594:2013, 3.23, modified] SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 6 3.5 application equipment that utilizes the transported and distributed gas Note 1 to entry: Some examples of gas applications are: gas appliances (domestic or commercial), processes (chemical or industrial), power plants, vehicles, greenhouses etc. 4 Reference conditions and pressure units Unless stated otherwise all volumes are given for the real dry gas at ISO standard reference conditions of 15 °C (288,15 K) and 1013,25 mbar (101,325 kPa). Unless otherwise stated all pressures are absolute pressures. Whenever data on the volume, gross calorific value (GCV), energy and Wobbe Index are communicated, it shall be specified under which reference conditions these values were calculated. In assessing compliance with this European standard parameters should be determined directly at ISO standard reference conditions. If the properties are only available at other reference conditions and the actual gas composition is not known then conversion to ISO standard reference conditions shall be carried out using the procedure described in EN ISO 13443. NOTE Besides the ISO standard reference conditions, particular in gas transmission, normal reference conditions (25/0 °C) are used according to the Network Code Interoperability and Data exchange. These are indicated in Table 1 for information. 5 Requirements Gas shall comply with the requirements given in Table 1 and shall be accepted for conveyance. Table 1 — Requirements Parameter Unit Limits based on standard reference condition 15 °C/15°C Limits

based on normal reference condition 25°C /0°C (for information) Reference standards for test methodsd (informative) Min. Max. Min. Max. Relative density no unit 0,555 0,700 0,555 0,700 EN ISO 6976,

EN ISO 15970 Total sulfur without odorant mg/m3 not applicable 20a not applicable 21a EN ISO 6326-5,

EN ISO 19739 For sulfur in high pressure networks and on interconnection points the maximum acceptable sulfur content for conveyance is 20 mg/m3, where in high pressure networks non-odorized gas is current practice. However, for existing practices with respect to transmission of odorized gas between high pressure networks higher sulfur content value up to 30 mg/m3 may be accepted. NOTE On distribution networks the odorization is considered as a national safety issue. Some information about sulfur odorant content is given in Annex B. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 7 Parameter Unit Limits based on standard reference condition 15 °C/15°C Limits

based on normal reference condition 25°C /0°C (for information) Reference standards for test methodsd (informative) Min. Max. Min. Max. Hydrogen sulphide + Carbonyl sulphide

(as sulfur) mg/m3 not applicable 5a not applicable 5a EN ISO 6326-1,
EN ISO 6326-3,

EN ISO 19739 Mercaptan sulfur without odorant (as sulfur) mg/m3 not applicable 6a not applicable 6a EN ISO 6326-3,

EN ISO 19739 Oxygen mol/mol not applicable 0,001 % or 1 %
(see below) not applicable 0,001 % or 1 %
(see below) EN ISO 6974-3,
EN ISO 6974-6,

EN ISO 6975 At network entry points and interconnection points the mole fraction of oxygen shall be no more than 0,001 %, expressed as a moving 24 hour average. However, where the gas can be demonstrated not to flow to installations sensitive to higher levels of oxygen, e.g. underground storage systems, a higher limit of up to 1 % may be applied. Carbon dioxide mol/mol not applicable 2,5 % or 4 %

see below not applicable 2,5 % or 4 %

see below EN ISO 6974 parts 1 to 6, EN ISO 6975 At network entry points and interconnection points the mole fraction of carbon dioxide shall be no more than 2,5 %. However, where the gas can be demonstrated not to flow to installations sensitive to higher levels of carbon dioxide, e.g. underground storage systems, a higher limit of up to 4 % may be applied. Hydro carbon dew pointb,c °C not applicable

«2 not applicable
«2 ISO 23874,

ISO/TR 12148 at any pressure from 0,1 to 7 MPa (70 bar) absolute pressure Water dew pointb,c at 7 MPa (70 bar) or, if less than 7 MPa (70 bar), at maximum operating pressure of the system in which the gas flows °C not applicable

«8 not applicable
«8 EN ISO 6327,
EN ISO 18453,

EN ISO 10101 parts 1 to 3 Methane number no unit 65 not applicable 65 not applicable see normative

Annex A SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 8 Parameter Unit Limits based on standard reference condition 15 °C/15°C Limits

based on normal reference condition 25°C /0°C (for information) Reference standards for test methodsd (informative) Min. Max. Min. Max. Contaminants The gas shall not contain constituents other than listed in Table 1 at levels that prevent its transportation, storage and/or utilization without quality adjustment or treatment. a Figures are indicated without post-comma digits due to analytical uncertainty. b Under given climatic conditions, a higher water dew point and hydrocarbon dew point may be accepted at national level. c For further information on water dew point and hydrocarbon dew point see Annex C. d Test methods other than those listed in the reference standards indicated in Table 1 may be applied, provided their fitness for purpose can be demonstrated. Gas quality shall not impede safety of gas appliances and operations of end users. Appropriate measures shall be taken. NOTE Applications are sensitive towards variations of the gas quality depending on the type of application and the degree of variation. For sampling, reference is made to Annex F. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 9 Annex A (normative)

Calculation of methane number of gaseous fuels for engines A.1 Introduction The methane number of a gaseous fuel can be calculated from its composition according to several different methods, all of which can give different results. For the purposes of compliance with this European standard the methodology described in this Annex shall be employed. The method is based on the original data of the research program performed by AVL Deutschland GmbH /1/ for FVV (the Research Association for Combustion Engines) but employs amendments implemented in 2005 and 2011 by MWM GmbH. These amendments have been unpublished until the publication of this European standard. The method requires input of composition in the form of volume fractions at reference conditions of 0 °C and 101,325 kPa and expressed as a percentage. Composition is more likely to be available either as mole fraction (e.g. in the natural gas transmission and distribution industry) or as mass fraction (e.g. in the automotive fuel industry) and conversion to volume fraction shall be performed using the methods in ISO 14912. Numerical examples are provided so as to enable software developers to validate implementations of the methodology described in this annex. As an aid to validation a relatively large number of decimal places has been retained. For expression of the final result rounding to zero decimal points is recommended. A.2 Calculation of methane number A.2.1 Applicability The method described in this European Standard is applicable to gaseous fuels comprising the following gases: carbon monoxide; butadiene; butylene; ethylene; propylene; hydrogen sulphide; hydrogen; propane; ethane; butane; methane; nitrogen and carbon dioxide. The method treats hydrocarbons other than those specified as butane and is therefore applicable to gaseous fuels containing such higher hydrocarbons. The numerical examples provided in this annex are appropriate to gases of the second family and hence consider mixtures comprising methane, ethane, propane, butane, nitrogen and carbon dioxide. Hydrogen is also included in one example because of the growing interest in injection of hydrogen into gas pipelines. During the preparation of this standard MWM GmbH has confirmed that the method is applicable to both 2H and 2L gases. Oxygen and water vapour shall be ignored and the fuel gas composition shall be calculated on a dry, oxygen-free basis. A.2.2 General approach The methane number of a gaseous fuel is calculated from its composition in five steps. The steps are outlined below and discussed more fully in turn in A.3. Additional examples are discussed in A.4 and A.5. Table A.10 provides results of calculations for further software validation purposes. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 10 a) The composition of the gaseous fuel is simplified by converting it into an inert-free mixture comprising the combustible compounds carbon monoxide, ethylene, propylene, hydrogen sulphide, hydrogen, propane, ethane, butane and methane. For gases of the second family conveyed in pipeline systems carbon monoxide, ethylene, propylene, hydrogen sulphide are unlikely to be present at concentrations that would impact on methane number and can be ignored. b) The simplified mixture is sub-divided further into a number of partial ternary mixtures. The number and particular partial ternary mixtures chosen is decided by inspection of available ternary systems in a given order, including those systems that contain the relevant combustible compounds. Selection is ceased when all combustible compounds are contained in at least two ternary systems. c) The composition and fraction of the selected partial mixtures is adjusted iteratively so as to minimize the difference between the methane numbers of each partial mixture. d) The methane number of the simplified mixture is determined from the weighted average of the methane number of the selected partial mixtures. e) Finally, the methane number of the gaseous fuel is calculated by correcting the methane number of the simplified mixture to allow for the presence of inerts in the original fuel gas. A.3 Example 1: 2H-gas A.3.1 Simplification of the composition of the gaseous fuel The description of the calculation is illustrated by reference to a 2H-gas of composition shown in Table A.1. The composition of the gas (column 1) is simplified by increasing the quantity of butanes to allow for the presence of butadiene, butylene, pentanes and hydrocarbons of carbon number greater than 5. The adjustment made is as follows: — Butadiene and butylene are replaced with an equivalent amount of butanes by multiplying their quantities by 1. — Pentanes are replaced with an equivalent amount of butanes by multiplying the quantity of pentanes by 2,3. — Hydrocarbons of carbon number greater than 5 (“hexanes+”) are replaced with an equivalent amount of butanes by multiplying the quantity of hexanes+ by 5,3. In the case of example 1 the quantity of butanes

= 0,2100 + 0,1900 + (0,0400 + 0,0500) × 2,3 + 0,0600 × 5,3

= 0,9250 (Column 2) The simplified mixture is then re-normalized to 100 % (Column 3). SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 11 A.3.2 Selection of the ternary systems A.3.2.1 Ternary mixtures The ternary mixtures are chosen from the following list: — A1:

Methane – Hydrogen – Ethane — A2:

Propane – Ethane – Butane — A3: Hydrogen – Propane - Propylene — A4: Methane – Ethane – Propane — A5: Methane – Hydrogen – Propane — A6: Methane – Hydrogen – Butane — A7: Methane – Propane – Butane — A8: Methane – Ethane – Butane — A9: Methane – Ethylene – Butane — A10: Methane – Hydrogen Sulphide – Butane — A11: Methane – Ethane – Hydrogen Sulphide — A12: Methane – Propylene — A13: Ethane – Propylene — A14: Carbon Monoxide – Hydrogen — A15: Ethane – Ethylene — A16: Propane – Ethylene — A17: Butadiene — A18: Butylene NOTE Mixtures A12 – A16 are clearly not ternary systems; however, for ease of mathematical treatment the coefficients have been adjusted so as to allow the expression of the methane number using a single equation. A.3.2.2 Range of applicability of ternary mixture data The range of applicability of most ternary systems is wide (each component can vary from 0 to 100 %). However, for some ternary systems there is a reduced range of applicability. This is a major issue when selecting ternary mixtures. The range of applicability of each ternary system is specified in Table A.2, expressed as maximum and minimum content of each component. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 12 A.3.2.3 Factors affecting the ternary system selection process The ternary systems are selected in accordance with three main considerations: a) The number of gases in the ternary system that are present in the simplified mixture. Priority is always given to ternary systems that have all three of their components present in the simplified mixture. Systems with two of their components present in the simplified mixture are acceptable if insufficient systems with three components present in the simplified mixture are available. b) Where there is a choice of ternary systems, the system with the highest fitness, Wj, takes priority. c) Each component in the simplified mixture shall be represented in at least two ternary systems. Fitness of a system is calculated from the following formula: ()()==+=∑1100,15inii,jjiiV,minVmaxWVsum (A.1) where n is the number of components in the simplified mixture Vi is the volume fraction of component i in the simplified mixture Vmaxi,j is the maximum content of component i for the range of applicability of system j Vsumi is the sum of all maximum contents of component i for the range of applicability of all systems, i.e. ()()===+∑18,1100,15jiijiVsumminVmax (A.2) Values of Vsumi are independent of the composition of the simplified mixture. However, Wj is dependent upon the composition of the simplified mixture and so shall be calculated prior to selection. Note that this also means that the choice of ternary mixtures may be different for mixtures containing the same components, but in different proportions. In the case of example 1, the calculation of Vsumi and Wj is shown in Tables A.3 and A.4. A.3.2.4 Description of the ternary system selection process The aim is to identify the optimum number of ternary systems that meet the three criteria described in A.3.2.3 and this is achieved by consideration of each component present in the simplified mixture in the following sequence: 1) Carbon Monoxide 2) Butadiene 3) Butylene 4) Ethylene 5) Propylene 6) Hydrogen Sulphide SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 13 7) Hydrogen 8) Propane 9) Ethane 10) Butane 11) Methane Step 1: For the first component in the simplified mixture, one ternary system that contains that component is selected. The priority of selection is as follows: a) Ternary systems with all three components present in the simplified mixture have priority over systems having one or two components present. b) The ternary mixture with the highest fitness has priority. Step 2: Consideration is then given to the second component in the simplified mixture. If this component is not present in the ternary system selected for the first component, then a ternary system is selected for this component using the same priority of selection as in step 1. If, however, the ternary system selected for the first component contains the second component, then the selection proceeds for the third component (step 3). Step 3: Consideration is then given to third, fourth, fifth, etc. components in the same manner as Steps 1-2. Step 4: When all components in the simplified mixture have been examined once, steps 1-3 are repeated in the same component order. If any component is represented in only one selected ternary mixture, then an additional ternary mixture is selected, again using the same priority of selection as in step 1. The selection process ends when all components in the simplified mixture are represented in at least two ternary systems. In the case of example 1: — The first component in the simplified mixture is propane and this is present in four ternary systems that have all their components present in the simplified mixture – A2, A4, A7 and A8. In this case, A4 is selected because it has the largest value of fitness (i.e. 10,3138). — The second component in the simplified mixture is ethane and this is already represented in system A4, so no ternary mixture is selected. — The third component of the simplified mixture, butane, is not represented in system A4, so system selection continues and system A8 is selected because it has the highest value of fitness (10,2859). — The fourth component in the simplified mixture is methane and this is already represented in systems A4 and A8, so no ternary mixture is selected. — Selection is repeated with the first component in the simplified mixture, propane, and ternary system A7 is selected because it has the next highest value of fitness (9,6263; system A4 has already been selected). All components in the simplified mixture are now represented in at least two of the ternary systems selected and the selection process ends. The systems selected are therefore: A4, A7 and A8. SIST EN 16726:2016+A1:2018

EN 16726:2015+A1:2018 (E) 14 A.3.3 Sub-division of the inert-free mixture into the selected partial mixtures The simplified mixture is divided into the selected partial ternary mixtures. A preliminary division of the simplified mixture is made by assigning each component equally between the ternary systems in which it is represented. In the case of example 1, three ternary systems – A4, A7 and A8 – are selected. The preliminary division is made by assigning: methane equally between A4, A7 and A8; ethane equally between A4 and A8; propane equally between A4 and A7; and butanes equally between A7 and A8 (Columns 4, 6 and 8). A.3.4 Calculation of the methane number of the partial mixtures The methane number of each partial mixture is calculated from the general formula ()=====∑∑67,00jiijtijijMNaxy (A.3) Where x and y are the volume fractions of the first and second components in each partial ternary mixture, expressed as a percentage. In order to calculate the methane number of each partial mixture, therefore, the composition of each is normalized to 100 %. In the case of example 1 the composition of each partial mixture is calculated by renormalizing to 100 % (Columns 5, 7 and 9). Table A.2 lists the values of coefficients ai,j for the partial ternary systems A1–A18. In the case of example 1 applic

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