ISO TR 24094-2006 Analysis of natural gas - Validation methods for gaseous reference materials《天然气分析 气态标准物质的证实方法》.pdf

1、 Reference number ISO/TR 24094:2006(E) ISO 2006TECHNICAL REPORT ISO/TR 24094 First edition 2006-05-15 Analysis of natural gas Validation methods for gaseous reference materials Analyse du gaz naturel Mthodes de validation pour matriaux de rfrence gazeux ISO/TR 24094:2006(E) PDF disclaimer This PDF f

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6、O copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2006 All rights reservedISO/TR 24094:2006(E) ISO 2006 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 Normative re

7、ferences . 1 3 Development of the validation methods. 2 4 Results of the VAMGAS project 5 Annex A (informative) Report on the validation methods for gaseous reference materials 6 Bibliography . 47 ISO/TR 24094:2006(E) iv ISO 2006 All rights reservedForeword ISO (the International Organization for St

8、andardization) 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 rig

9、ht 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. International

10、 Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as a

11、n International Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it ma

12、y decide by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that s

13、ome 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. ISO/TR 24094 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. TECHNICAL REPORT ISO/TR 240

14、94:2006(E) ISO 2006 All rights reserved 1 Analysis of natural gas Validation methods for gaseous reference materials 1 Scope This Technical Report describes the validation of the calorific value and density calculated from current practice natural gas analysis by statistical comparison with values o

15、btained by measurement using a reference calorimeter and a density balance. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the refere

16、nced document (including any amendments) applies. ISO 6142, Gas analysis Preparation of calibration gas mixtures Gravimetric method ISO 6974-1, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 1: Guidelines for tailored analysis ISO 6974-2, Natural gas Det

17、ermination of composition with defined uncertainty by gas chromatography Part 2: Measuring-system characteristics and statistics for processing of data ISO 6974-3, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 3: Determination of hydrogen, helium, oxyge

18、n, nitrogen, carbon dioxide and hydrocarbons up to C8 using two packed columns ISO 6974-4, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 4: Determination of nitrogen, carbon dioxide and C1 to C5 and C6+ hydrocarbons for a laboratory and on-line measurin

19、g system using two columns ISO 6974-5, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 5: Determination of nitrogen, carbon dioxide and C1 to C5 and C6+ hydrocarbons for a laboratory and on-line process application using three columns ISO 6974-6, Natural

20、gas Determination of composition with defined uncertainty by gas chromatography Part 6: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and C1 to C8 hydrocarbons using three capillary columns ISO 6976, Natural gas Calculation of calorific values, density, relative density and Wob

21、be index from composition Guide to the expression of uncertainty in measurement (GUM), BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML, 1995 ISO/TR 24094:2006(E) 2 ISO 2006 All rights reserved3 Development of the validation methods The validation methods for gaseous reference materials (VAMGAS) project was estab

22、lished by a group of European gas companies as an approach to confirming the practices used in natural gas analysis and physical property calculations. The VAMGAS project proposed comparing the calorific value and density calculated from the current practices for natural gas analyses with values obt

23、ained by measurement using a reference calorimeter (located at the Ofgas, UK laboratory) and density balance (located at the Ruhrgas, Germany laboratory). Robust statistical comparisons allowed an assessment of the validity of the practices. The natural gas analysis practice covered by the VAMGAS pr

24、oject can be divided into the following steps: The gravimetric preparation of gas mixtures used as calibrants in the analysis of natural gas in accordance with ISO 6142. At the highest level, these mixtures are categorized as primary reference gas mixtures (PRMs) and are available from national inst

25、itutes such as Bundesanstalt fur Materialforschung und -prfung (BAM) of Germany and Nederlands Meetinstituut (NMi) of the Netherlands. The analysis of natural gas by gas chromatographic methods, such as those given is ISO 6974 (all parts). This is a multiple part International Standard that provides

26、 a number of different approaches to the gas chromatographic analysis of natural gas. ISO 6974-2 describes the processing of calibration and analytical data to determine the uncertainties on sample component concentrations that are required for the calculation of uncertainties on calculated physical

27、 property values of the sample gas. The calculation of the values of physical properties from the results of the gas chromatographic analyses as described in ISO 6976. The VAMGAS project was divided in two parts: a) Part 1: comparison of the calorific values and densities of two PRMs calculated from

28、 the gravimetric preparation data against the values obtained from the reference calorimeter and density balance (see Figure 1); b) Part 2: gas chromatography intercomparison exercise, in which calorific values and densities calculated from the analyses of two natural gases (with bracketing calibrat

29、ion using PRMs) were compared to the values obtained from the reference calorimeter and density balance (see Figure 2). The two separate exercises would enable problems arising from either the gravimetric preparation or the gas chromatographic analyses to be identified. The participants in the VAMGA

30、S project were Ruhrgas AG (Germany and project co-ordinator), Gasunie (the Netherlands), Gaz de France (France), BAM (Germany), NMi (the Netherlands) and Ofgem (previously Ofgas, the UK). In addition, a total of 18 laboratories participated in the gas chromatography intercomparison. The technical re

31、port from the VAMGAS is given in Annex A. ISO/TR 24094:2006(E) ISO 2006 All rights reserved 3Figure 1 Schematic concept of part 1 of the VAMGAS project ISO/TR 24094:2006(E) 4 ISO 2006 All rights reservedFigure 2 Schematic concept of part 2 of the VAMGAS project ISO/TR 24094:2006(E) ISO 2006 All righ

32、ts reserved 5 4 Results of the VAMGAS project The project report provides results on two sets of comparisons. a) The results of the exercise using the PRMs showed statistical agreement between the calorific values and densities calculated from the gravimetric preparation data and the values of these

33、 physical properties obtained from direct measurement using reference instruments. b) The results of the gas chromatographic intercomparison showed statistical agreement between the calorific values and densities calculated from gas chromatographic analyses, carried out using PRMs as calibrants, and

34、 the values of these physical properties obtained from direct measurements using reference instruments. It can be concluded that the VAMGAS project has validated the current systems of natural gas analyses and calculation of physical property data involving the previously mentioned ISO International

35、 Standards. As a result, all parties in the supply and use of natural gas, whether supplier or consumer, can have confidence in these. The current ISO International Standards for calibration gas preparation and natural gas analysis, if carefully applied, give values of calorific value and density th

36、at are in agreement with values that were independently determined by reference measurements. This also includes the tabulated values in ISO 6976, which are used in calculations of thermal energy for billing/fiscal transfer purposes. The VAMGAS project was carried out as an integrated project to stu

37、dy the complete system of natural gas analysis involving the gravimetric preparation of calibration gas mixtures, the gas chromatographic analysis and calculation of physical properties. Reference measurements of the physical properties were applied during the VAMGAS project as a means of assessing

38、the system. It is stressed that readers take account of the whole project; and it is totally wrong to take isolated parts and results of the project and use these for other purposes in the belief that the project results justify such an approach. For example, in the first part of the project compari

39、son was made between the physical property values calculated from the gravimetric preparation data of the PRMs and the values obtained from the reference measurements. It is important not to use the results from this part of the project to justify using reference measurements of a physical property

40、to validate the composition of a prepared natural gas mixture. There are three reasons. The VAMGAS project was not designed to investigate the applicability, or otherwise, of such a procedure. The VAMGAS project was designed to investigate whether or not a cylinder of gas designated as a PRM can pro

41、vide gas of the composition given on the certificate attached to that cylinder. In the preparation of the PRMs, the national institutes have rigorous procedures including a system of validating the mixture composition by gas chromatographic analysis to give confidence in the composition of the gas m

42、ixture. Whereas it is true that a gas mixture of known composition has an unique calorific value or density, the same is not true of the reverse relationship: a specific calorific value or density does not have a corresponding unique gas composition; in fact a calorific value or density can result f

43、rom an almost infinite number of different gas compositions. Hence, it is not technically feasible to validate gas mixture compositions using measurements of a physical property. As a simple illustration, consider the manufacture of a multi-component mixture containing both isomers of butane. If, by

44、 mistake, the same isomer was added twice then the resulting mixture would have the same calorific value and density as the required mixture but the composition would be incorrect. Measurements of the calorific value or density would appear to validate the mixture composition when it was, in fact, i

45、n error. ISO/TR 24094:2006(E) 6 ISO 2006 All rights reservedAnnex A (informative) Report on the validation methods for gaseous reference materials A.1 General A.1.1 Summary In the first part of the project, 12 primary reference gas mixtures were produced by BAM and NMi. As regards composition, the g

46、as mixtures produced were similar to type L Groningen gas and type H North Sea gas. The superior calorific value, H s , molar mass, M, and density at normal conditions of the mixtures were calculated from the component concentrations specified by the producers. The calculated data were then compared

47、 with the results of direct measurements of physical properties. The methods used for direct measurement of physical properties were reference calorimetry 1and precision densitometry 2 . Statistically significant agreement was found between the calculated data and the measurements. Table A.1 Compari

48、son of experimental (M exp ) and calculated (M calc ) values of the molar mass for different PRMs aGas mixture Type of gas M expg/mol M calcg/mol Relative difference % BAM 9605 4933 L 18,564 3 18,564 6 0,002 NMi 0602E L 18,542 7 18,543 0 0,002 BAM 9605 4902 H 18,793 1 18,796 6 0,018 NMi 9497C H 18,9

49、46 5 18,946 9 0,002 aCalculations are made in accordance with ISO 6976. In the second stage, 20 natural gas samples was taken from the natural gas transmission system of Ruhrgas AG. These samples included both type L Groningen gas and type H North Sea gas. Gas samples were taken in batches, so that the compressed gas cylinders filled with each of the two types were of identical composition. The homogeneity of the batches, i.e. the agreement between the compositions of the samples in the