1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58hydrocarbon dewpoint calculationICS 75.060Natural gas Gas chromatographic requirements for BRITISH
2、STANDARDBS ISO 23874:2006BS ISO 23874:2006This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 March 2007 BSI 2007ISBN 978 0 580 50367 2Amendments issued since publicationAmd. No. Date Commentscontract. Users are responsible for its correct app
3、lication.Compliance with a British Standard cannot confer immunity from legal obligations. National forewordThis British Standard was published by BSI. It is the UK implementation of ISO 23874:2006.The UK participation in its preparation was entrusted to Technical Committee PTI/15, Natural gas and g
4、as analysis.A list of organizations represented on PTI/15 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a Reference numberISO 23874:2006(E)INTERNATIONAL STANDARD ISO23874First edition2006-11-15Natural gas Gas chromatographic
5、requirements for hydrocarbon dewpoint calculation Gaz naturel Exigences relatives la chromatographie en phase gazeuse pour le calcul du point de rose hydrocarbures BS ISO 23874:2006ii iiiContents Page Foreword iv 1 Scope 1 2 Normative references 1 3 Principle2 4 Materials .2 5 Apparatus .2 6 Perform
6、ance requirements .3 7 Sampling.3 8 Analytical procedure .4 9 Methods of test 7 10 Uncertainty in composition 9 11 Calculation of dewpoint temperature 9 12 Analytical uncertainty contribution to dewpoint temperature 9 Annex A (informative) Typical analytical conditions for C5to C12analysis 10 Annex
7、B (informative) Validation of fraction data12 Annex C (informative) Precision of area ratio 16 Annex D (informative) Recommendations on sample calibration gas introduction 20 Annex E (informative) Calculation of fraction quantities, boiling points and component uncertainties.22 Bibliography 26 BS IS
8、O 23874:2006iv 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 subjec
9、t 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)
10、 on all matters of electrotechnical standardization. International 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 committee
11、s are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. 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 he
12、ld responsible for identifying any or all such patent rights. ISO 23874 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. BS ISO 23874:20061Natural gas Gas chromatographic requirements for hydrocarbon dewpoint calculation 1 Scope This Internatio
13、nal Standard describes the performance requirements for analysis of treated natural gas of transmission or pipeline quality in sufficient detail so that the hydrocarbon dewpoint temperature can be calculated using an appropriate equation of state. It can be applied to gases that have maximum dewpoin
14、t temperatures (cricondentherms) between 0 C and 50 C. The pressures at which these maximum dewpoint temperatures are calculated are in the range 2 MPa (20 bar) to 5 MPa (50 bar). Major components are measured using ISO 6974 (all parts) and the ranges of components that can be measured are as define
15、d in ISO 6974-1. The procedure given in this International Standard covers the measurement of hydrocarbons in the range C5to C12. n-Pentane, which is quantitatively measured using ISO 6974 (all parts), is used as a bridge component and all C6and higher hydrocarbons are measured relative to n-pentane
16、. 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 referenced document (including any amendments) applies. ISO 6974-1, Natural gas
17、Determination of composition with defined uncertainty by gas chromatography Part 1: Guidelines for tailored analysis ISO 6974-2, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 2: Measuring-system characteristics and statistics for processing of data ISO
18、6974-3, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 3: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and hydrocarbons up to C8using two packed columns ISO 6974-4, Natural gas Determination of composition with defined uncertainty
19、by gas chromatography Part 4: Determination of nitrogen, carbon dioxide and C1to C5and C6+hydrocarbons for a laboratory and on-line measuring system using two columns ISO 6974-5, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 5: Determination of nitrogen
20、, carbon dioxide and C1to C5and C6+hydrocarbons for a laboratory and on-line process application using three columns ISO 6974-6, Natural gas Determination of composition with defined uncertainty by gas chromatography Part 6: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and C1t
21、o C8hydrocarbons using three capillary columns ISO 6975, Natural gas Extended analysis Gas-chromatographic method ISO 10715, Natural gas Sampling guidelines BS ISO 23874:20062 3 Principle For hydrocarbon gas mixtures such as natural gas, the phase boundary or dewpoint line distinguishing single-phas
22、e gas from gas-liquid mixtures is a complex function of pressure, temperature and composition. For a given composition, the pressure at which the dewpoint temperature is at a maximum is intermediate between those found in transmission and distribution operations. The analysis shall be comprehensive
23、for inert components and for hydrocarbons up to C12. It is not necessary to measure helium, hydrogen, water and sulfur compounds unless any of these is present at greater than 0,01 mole fraction. The analysis shall be performed in two parts. Major components (nitrogen, carbon dioxide and hydrocarbon
24、s from C1to C5) shall be analysed according to ISO 6974 (all parts). Higher hydrocarbons (C5to C12) shall be analysed to satisfy the requirements given in this International Standard. This allows the traceability of measurements according to ISO 6974 (all parts) to be extended to the higher hydrocar
25、bons. It is not possible to identify all the measured higher hydrocarbons, nor is it possible to obtain a reference gas mixture that contains more than a few representatives of the higher hydrocarbons. The analytical data are, therefore, handled with a number of simplifying assumptions. Unidentified
26、 components are allocated a carbon number or molar mass according to their positions in the chromatogram with respect to identified n-alkanes. Alkanes of carbon number 7 and above are summed by carbon number and treated as fractions for input to the dewpoint calculation. Average boiling points and d
27、ensities of fractions are calculated from the individual boiling points and quantities of the components that comprise them; individual-component boiling points are calculated by interpolation between the bracketing n-alkanes1. Sample components are quantified by comparison with n-pentane, which has
28、 been measured according to ISO 6974 (all parts), using relative response factors based on their allocated carbon numbers. NOTE When using ISO 6974 (all parts), n-pentane can be measured as a direct component that is also present in the calibration-gas mixture, or as an indirect component using a re
29、sponse factor relative to a different component (for example, n-butane) in the calibration gas mixture. In either case, the uncertainty on the quantity of n-pentane can be calculated according to ISO 6974-2. 4 Materials 4.1 Certified-reference gas mixture for major components (CRM1), such as is requ
30、ired for ISO 6974 (all parts). Depending upon the working range and the accuracy required, more than one CRM can be needed. 4.2 Certified-reference gas mixture, for higher hydrocarbons (CRM2), containing as a minimum, n-pentane, n-hexane, benzene, cyclohexane, n-heptane, toluene, methylcyclohexane a
31、nd n-octane. Ideally, the CRM2 should also contain n-nonane, n-decane, n-undecane and n-dodecane in methane. The mole fractions of components in CRM2 shall be chosen to be appropriate for the application, provided that the mixture is stable and free from the possibility of condensation in transport,
32、 storage and in use. 5 Apparatus 5.1 Measurement system for major components, comprised of a sample introduction and transfer unit, a separation unit, a detection unit, an integrator and a data reduction system, capable of meeting the analytical requirements described in 6.1. BS ISO 23874:20063ISO 6
33、974 (all parts) describes equipment suitable for this part of the analysis. 5.2 Measurement system for higher hydrocarbons, comprised of a sample-introduction and transfer unit, a separation unit, a detection unit, an integrator and a data-reduction system, capable of meeting the analytical requirem
34、ents described in 6.2. Annex A describes a system that has been shown to be suitable. The user is responsible for demonstrating in each case that his/her chosen system is also suitable. 6 Performance requirements 6.1 Major components The system for measurement of major components shall have performa
35、nce as described in ISO 6974 (all parts). 6.2 Higher hydrocarbons The system for measurement of higher hydrocarbons shall satisfy the following requirements: be capable of measuring alkanes up to and including n-dodecane; be capable of measuring individual alkanes at a concentration of 0,000 000 1 m
36、ole fraction (0,1 ppm 1) or less; be able to distinguish and measure benzene, toluene, cyclohexane and methylcyclohexane as individual components; use a detection system that can, at least in principle, measure all hydrocarbons in the range C5to C12; use a detection system that has a predictable res
37、ponse to hydrocarbons based on mass or carbon content, such that unidentified components of known molar mass or carbon number can be measured relative to other known components in the sample or in the calibration gas; NOTE 1 It is most likely that the detection system is a flame ionization detector
38、(FID). use a separation procedure such that the boiling points of unidentified components can be calculated by interpolation between those of known n-alkanes. NOTE 2 Increasing the column temperature at a constant rate throughout the analysis (linear temperature programming) allows such interpolatio
39、n. NOTE 3 Annex A describes a configuration that has been found to be suitable for the requirements of 6.2. 7 Sampling Carry out representative sampling in such a way that the sample represents the gas, particularly the higher hydrocarbons, at the time of sampling. Sampling and sample transfer shall
40、 be performed in accordance with ISO 10715. 1) ppm is a deprecated unit. BS ISO 23874:20064 8 Analytical procedure 8.1 Major components Follow the procedure specified in ISO 6974 (all parts). 8.2 Higher hydrocarbons The analytical procedure consists of the following steps. All of these steps shall b
41、e carried out when the method is first introduced, and some of them when changes in equipment cause historical measurement data to be no longer valid. For normal use, steps may be left out provided that the procedures and equipment remain under statistical control. 8.2.1 Step 1 Precision Since quant
42、itative information is derived by comparing the response of unknown components with that of n-pentane, which has been measured according to ISO 6974 (all parts), the precision information of interest is that of the ratio of component responses to that of n-pentane. Perform a number of repeat analyse
43、s on a typical natural gas and, for each analysis, calculate the ratio of the area of each peak to the area of n-pentane. For each peak, calculate the mean and the standard deviation of the ratios from all analyses. Where component data are to be summed into fractions or groups (see 9.3), calculate
44、the ratio of the total peak area for that fraction or group to the area of n-pentane. For each fraction, calculate the mean and the standard deviation of the ratios. Convert both sets of mean and standard deviation data into natural logarithms, plot the natural logarithm of the standard deviation, l
45、n s, as a function of natural logarithm of the area ratio, ln RA, and perform a first-order regression analysis on the data. Annex C shows a worked example. Calculate the 95 % confidence limits for the regression line and plot these on the same graph. Select values of a and b in Equation (1) by tria
46、l and error such that ln s = a + b ln RA(1) results in a straight line that closely approximates to the upper 95 % confidence line (see Annex C). This line now defines the precision of measurement, as given in Equation (2): s = exp(a + b ln RA) (2) This standard deviation is used as the standard unc
47、ertainty for each peak or fraction. 8.2.2 Step 2 Relative response factors When using a flame ionization detector, relative response factors, FRR, are claimed to be proportional to carbon number. Under most circumstances this is true, but variations from ideal operating conditions can cause this ass
48、umption to be false, and so it is necessary that it be checked. This is all the more necessary for other types of detector. The procedure below uses the known composition of CRM2 to check the relative response factors. The most likely outcome is that the factors are directly related to carbon number
49、, but the uncertainty with which this is validated shall be taken into account in the overall uncertainty calculation. Since n-pentane is the reference component, the response factor is conveniently expressed as a relative carbon response factor, FRR,C, to that of n-pentane. Perform a number (not less than 5) of repeat analyses using CRM2. Measure the mean peak area response for each component and the equivalent standard deviations. BS ISO 23874:20065 Calculate the
