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1、 Reference number ISO 6978-2:2003(E) ISO 2003 INTERNATIONAL STANDARD ISO 6978-2 First edition 2003-10-15 Natural gas Determination of mercury Part 2: Sampling of mercury by amalgamation on gold/platinum alloy Gaz naturel Dtermination de la teneur en mercure Partie 2: chantillonnage du mercure par am
2、algamation sur alliage or/platine Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 697
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6、elow. ISO 2003 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member bod
7、y 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 copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2003 All rights reserved Copyright International Organization for Standardization Provided by
8、 IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6978-2:2003(E) ISO 2003 All rights reserved iii Contents Page Forewordiv Introduction v 1 Scope1 2 Normat
9、ive references .1 3 Terms and definitions.1 4 Principle.1 5 Apparatus.2 6 Reagents and materials8 7 Preparation of sampling and analytical tubes .9 7.1 Filling9 7.2 Cleaning.9 7.3 Efficiency testing 9 8 Sampling9 8.1 General.9 8.2 Conditions for representative sampling.10 8.3 Sampling procedure at a
10、tmospheric pressure (see Figure 1).10 8.4 Sampling procedure at high pressure (see Figure 4).11 8.5 Removal of condensate from discarded sampling tubes.12 9 Mercury determination .12 9.1 Transfer of mercury to the analytical tube (double amalgamation) 12 9.2 Transfer of mercury to AAS or AFS instrum
11、ent.13 9.3 Calibration13 9.4 Blank test.13 10 Calculation.13 11 Precision16 12 Test report16 Bibliography .17 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo
12、 reproduction or networking permitted without license from IHS -,-,- ISO 6978-2:2003(E) iv ISO 2003 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International St
13、andards 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
14、 take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) 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 committee
15、s is to prepare International Standards. Draft International Standards adopted by the technical committees 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 possib
16、ility 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. ISO 6978-2 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. This first editio
17、n of ISO 6978-2, together with ISO 6978-1, cancels and replaces ISO 6978:1992, which has been technically revised. ISO 6978 consists of the following parts, under the general title Natural gas Determination of mercury: Part 1: Sampling of mercury by chemisorption on iodine Part 2: Sampling of mercur
18、y by amalgamation on gold/platinum alloy Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,-
19、ISO 6978-2:2003(E) ISO 2003 All rights reserved v Introduction Natural gases may contain considerable amounts of mercury, which are generally present in the elemental form. Gases with high mercury content have to be purified to avoid the condensation of mercury during processing and transport as wel
20、l as to be compliant with the demands of gas sales contracts. Low mercury concentrations are specified when natural gas is to be liquefied. This is to avoid severe corrosion problems, for instance in aluminium heat exchangers of liquefaction plants. Since the presence of hydrocarbons, in particular
21、aromatic hydrocarbons present in low concentrations in almost every natural gas, interferes in the determination of mercury by atomic absorption spectrometry (AAS) or atomic fluorescence spectrometry (AFS), mercury cannot be determined directly in natural gas. Therefore, prior to the analytical dete
22、rmination, mercury has to be collected and separated from aromatic hydrocarbons. The purpose of the determination of the mercury content can be to monitor gas quality, to monitor the operation of gas treatment plants for mercury removal. Several methods for the collection or enrichment of mercury fr
23、om natural gas have been developed. The collection of mercury from dry natural gas normally poses no particular problem. However, care should be taken when sampling mercury from natural gases under nearly condensing conditions (see ISO 6570). The two parts of ISO 6978 describe the principles of samp
24、ling and specify the general requirements for methods for sampling mercury and for determining total mercury in pipeline quality natural gas. This part of ISO 6978 specifies a method of sampling mercury by amalgamation on gold/platinum alloy thread whereas Part 1 specifies a method of sampling mercu
25、ry by chemisorption on iodine-impregnated silica gel. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license fr
26、om IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 6
27、978-2:2003(E) ISO 2003 All rights reserved 1 Natural gas Determination of mercury Part 2: Sampling of mercury by amalgamation on gold/platinum alloy WARNING The use of this part of ISO 6978 may involve hazardous materials, operations and equipment. This part of ISO 6978 does not purport to address a
28、ll of the safety problems, associated with its use. It is the responsibility of the user of this part of ISO 6978 to establish appropriate safety and health practices and to determine the applicability or regulatory limitations prior to use. 1 Scope This part of ISO 6978 specifies a method for the d
29、etermination of total mercury content of pipeline quality natural gas using a sampling method by amalgamation on gold/platinum (Au/Pt) alloy thread. This method is applicable to the sampling of raw natural gas when no condensation is present. At atmospheric pressure, this method is suitable for the
30、determination of mercury content within the range of 0,01 g/m3 to 100 g/m3 in natural gas samples. At higher pressures (up to 8 MPa), this sampling method is suitable for the determination of mercury contents within the range of 0,001 g/m3 to 1 g/m3. The collected mercury is determined by measuring
31、the absorbance or fluorescence of mercury vapour at 253,7 nm. NOTE ISO 6978-1 gives a sampling method suitable for the determination of mercury contents in natural gas by chemisorption on iodine-impregnated silica gel for the working range of 0,1 g/m3 to 5 000 g/m3 for sampling at pressures up to 40
32、 MPa. 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 10715, Natural g
33、as Sampling guidelines ISO 14532, Natural gas Vocabulary Guide to the expression of uncertainty in measurement (GUM), BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 14532 apply. 4 Principle Sampling is perfor
34、med at a temperature at least 10 C higher than the dewpoint of the gas sampled. The gas is passed through two quartz glass sampling tubes in series containing fine gold/platinum alloy thread. The mercury is collected on the gold/platinum alloy thread by amalgamation. Subsequently, each sampling tube
35、 is separately heated to 700 C to desorb the mercury from the amalgam. The released mercury is transferred by Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo
36、 reproduction or networking permitted without license from IHS -,-,- ISO 6978-2:2003(E) 2 ISO 2003 All rights reserved a stream of air onto an analytical tube filled with gold/platinum alloy thread (double amalgamation). This second quartz glass tube is then heated to 800 C and the mercury is transf
37、erred to an AAS or AFS for measurement at 253,7 mm. This sampling method is suitable for the determination of mercury content in natural gas in the range of 0,01 g/m3 to 100 g/m3 for sampling at atmospheric pressure and 0,001 g/m3 to 1 g/m3 for sampling at high pressure. To avoid diffusion of mercur
38、y from the surface into the gold/platinum alloy thread, which would reduce the recovery of mercury under the specified transfer conditions, it is necessary to determine the amount of collected mercury within one week after sampling. Other sorption materials such as gold-impregnated silica with a hig
39、h specific surface may be used instead of fine gold/platinum alloy thread, provided they show equivalent method performance in the natural gas matrix. Unless otherwise specified, gas volumes are expressed in cubic metres (m3) at 273,15 K and 1 013,25 hPa. NOTE The comparability of the two sampling t
40、echniques has been demonstrated by interlaboratory tests at two different concentration levels. 5 Apparatus The parameters influencing the measurement shall be traceable to national or International Standards. The uncertainty of the volume measurement (volume, temperature and pressure of the gas as
41、well as ambient air pressure) directly contributes to the uncertainty of the determined mercury content of the gas. Therefore suitable measuring equipment, calibrated against a commonly accepted reference, shall be used to minimize the uncertainty of the volume measurement to less than 1 %. 5.1 Samp
42、ling apparatus (see Figure 1). 5.1.1 Apparatus for sampling at atmospheric pressure, typically comprising the following: 5.1.1.1 Heated bypass valve. 5.1.1.2 Heated flow control valve (needle type). 5.1.1.3 Three-way valve, for the second bypass. 5.1.1.4 Aluminium block, capable of being heated to u
43、 100 C (see Figure 2) and dividable into two halves with a central bore coated with a layer (about 2 mm) of silicon rubber for keeping the quartz glass sampling tubes filled with gold/platinum alloy thread (see Figure 3) during sampling at elevated temperature (if necessary) and equipped with a temp
44、erature gauge (not shown in Figure 1). 5.1.1.5 Flow meters (three): one for flowrates u 50 l/min; two for flowrates u 5 l/min. 5.1.1.6 Gas meter, suitable for measuring flowrates of u 5 l/min, capable of allowing adjustment of the bypass flow and the volume measurement and equipped with the followin
45、g: a) pressure gauge; b) temperature gauge, for measuring temperatures between 0 C to 40 C. 5.1.1.7 Barometer, required for measuring the ambient air pressure. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing
46、, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6978-2:2003(E) ISO 2003 All rights reserved 3 Key 1 pipeline 7 three-way valve 2 sampling valve 8 aluminium block for heating 3 first bypass 9 flow indicator 4 bypass valve 10 g
47、as meter 5 flow control valve 11 temperature gauge 6 second bypass 12 pressure gauge Figure 1 Sampling apparatus Dimensions in millimetres Key 1 heating plug 2 silicon rubber (glued) 3 division line Figure 2 Heating box (heatable aluminium box) Copyright International Organization for Standardizatio
48、n Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/08/2007 09:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6978-2:2003(E) 4 ISO 2003 All rights reserved Dimensions in millimetres Key 1 gold/platinum wire (350 Au/150 Pt alloy) 2 indentation 3 O-ring Figure 3 Quartz glass sampling and analytical tubes 5.1.2 Apparatus for