1、Reference number ISO 6570:2001(E) ISO 2001 INTERNATIONAL STANDARD ISO 6570 First edition 2001-06-15 Natural gas Determination of potential hydrocarbon liquid content Gravimetric methods Gaz naturel Dtermination de la teneur en hydrocarbures liquides potentiels Mthodes gravimtriquesISO 6570:2001(E) P
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5、1 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 body in the coun
6、try 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.ch Web www.iso.ch Printed in Switzerland ii ISO 2001 All rights reservedISO 6570:2001(E) ISO 2001 All rights reserved iii Contents Page Foreword.iv Introducti
7、on.v 1 Scope 1 2 Normative references 1 3 Principle2 4 Apparatus requirements .2 4.1 Measurement installation2 4.2 Check for correct installation operation .5 5 Sampling.10 5.1 General10 5.2 Sampling conditions .10 5.3 Sample line.10 5.4 Direct sampling10 5.5 Indirect sampling .10 6 Procedure .11 6.
8、1 Determination of potential hydrocarbon liquid content11 6.2 Determination of water formation 12 7 Expression of results 12 7.1 Method A Manual weighing method12 7.2 Method B Indirect automatic method14 8 Uncertainty of measurement 15 8.1 Achievable uncertainty .15 8.2 Gas leakage15 8.3 Bath liquid
9、 16 8.4 Wet gas .16 8.5 Condensate leakage 16 8.6 Variations in bath temperature and pressure in the gas/liquid cyclone separator 16 8.7 Premature condensation.16 9 Test report 16 Annex A (informative) Selection of measurement temperature and pressure17 Annex B (informative) Examples of the line-up
10、of the apparatus 18 Annex C (informative) Example of calibration of the differential pressure gauge for the indirect automatic method Method B19 Annex D (informative) Example of an indirect automatic measurement Method B.21ISO 6570:2001(E) iv ISO 2001 All rights reserved Foreword ISO (the Internatio
11、nal 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 subject for which a technical committee has been
12、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) on all matters of electrotechnical standar
13、dization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. 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
14、 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. International Standard ISO 6570 was prepared
15、 by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. This first edition cancels and replaces ISO 6570-1:1983 and ISO 6570-2:1984, which have been technically revised. Annexes A to D of this International Standard are given for information only.ISO 6570:2001(E)
16、 ISO 2001 All rights reserved v Introduction Under certain conditions, higher hydrocarbons present in natural gas or similar gases may condense and the condensate formed can cause difficulties in the operation of gas transport and distribution systems. Dew-point measurements, by condensation on a mi
17、rror, may give an indication of the conditions under which condensation starts. However, these measurements give no further information about the amount of liquid to be expected under operating conditions. For proper operation of transport and distribution systems, a knowledge of the quantities of c
18、ondensate formed as a function of temperature and pressure is required. This knowledge is also required for the design of production and treatment systems as well as for subsequent handling and disposal of the liquid. The methods described in this International Standard are intended for the determin
19、ation of the quantity of hydrocarbon condensate formed from a natural gas or similar gas as a function of the temperature and pressure of the gas. Instruments based on different measurement principles can give a figure related to potential condensate content or dew point. The dew point can only be d
20、etermined by performing measurements at different temperatures followed by extrapolation of the measurements to a potential hydrocarbon liquid content ( PHLC ) value of zero. The methods described in this International Standard can be used to calibrate such instruments.INTERNATIONAL STANDARD ISO 657
21、0:2001(E) ISO 2001 All rights reserved 1 Natural gas Determination of potential hydrocarbon liquid content Gravimetric methods WARNING The use of this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all of the
22、safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and to determine the applicability or regulatory limitations prior to use. 1 Scope This International Standard describes the principles of
23、, and general requirements for, two gravimetric methods for the determination of the potential hydrocarbon liquid content of natural gas, or similar gas, at a given pressure and temperature. Two methods are specified in this International Standard to determine the amount of condensate in a sample ga
24、s: Method A: a manual weighing method; Method B: an indirect automatic weighing method based on the indication of the pressure difference caused by the accumulation of condensate in a vertical tube. The manual weighing method is a reference method for the indirect automatic method (Method B). The in
25、direct automatic method (Method B) is suitable for semi-continuous control. NOTE Unless otherwise specified, gas volumes are in cubic metres at 273,15 K and 101,325 kPa. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute prov
26、isions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of th
27、e normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6976:1995, Natural gas Calculation of calorific values, density, relative density
28、 and Wobbe index from composition ISO 10715:1997, Natural gas Sampling guidelines ISO 12213-1:1997, Natural gas Calculation of compression factor Part 1: Introduction and guidelines ISO 12213-2:1997, Natural gas Calculation of compression factor Part 2: Calculation using molar-composition analysis I
29、SO 12213-3:1997, Natural gas Calculation of compression factor Part 3: Calculation using physical propertiesISO 6570:2001(E) 2 ISO 2001 All rights reserved 3P r i n c i p l e Determination of the quantity of hydrocarbon condensate which can be formed at a pressure (p) and a temperature (T) by passin
30、g a representative sample of the gas through an apparatus where it is first brought to the pressure (p) and then cooled to the temperature (T). The temperature and pressure are selected according to the specific application (see annex A). Prior to reducing the pressure of the sample of gas to that r
31、equired for the determination, the gas is heated, so that, after pressure reduction, the temperature is well above the dew-point temperature of the gas. Downstream of the reducer, the sample is cooled isobarically in a cooling bath to the required measurement temperature. The quantity of liquid accu
32、mulated during the measurement period is determined by either direct manual weighing of the collected liquid or weighing of the condensate cyclone separator at the start and at the end of a measurement period (Method A). Alternatively, the quantity of liquid accumulated in a vertical measuring tube
33、may be determined automatically (indirect automatic weighing) by indication of the pressure difference caused by the liquid accumulated in a vertical measuring tube. 4 Apparatus requirements WARNING The instrumentation used for this method shall comply with local legal regulations for application in
34、 hazardous areas. 4.1 Measurement installation The general arrangement is shown in Figure 1. Examples of the line-up of the apparatus are given in annex B. 4.1.1 Gas-line connecting tubes, made of stainless steel with an internal diameter ranging between 2 mm and 4mm. If mist is present in the gas,
35、all tubing up to the point where the mist is evaporated or separated shall have an internal diameter compatible with that of the sample line (4.1.2). 4.1.2 Sample line, the length of which is kept to a minimum and temperature-controlled along its length to at least the point where it enters the part
36、 of the installation where the measurement is made. An example of a sample line is given in Figure 2. The sample line can be heated by fitting a plastic hose concentrically around the line through which water flows at the desired temperature. For this purpose, a temperature-controlled bath can be us
37、ed from which the water to be circulated is drawn and to which it returns after circulation. The minimum temperature of the sample line can be checked easily by measuring the return temperature. The sample valve and its vicinity shall be heated or at least thermally insulated. 4.1.3 Drying tube (opt
38、ional), for eliminating water vapour present in sufficiently large quantities in the gas. Care shall be taken to avoid interferences with the determination of potential hydrocarbon liquid content. Under certain conditions, the presence of water vapour can lead to the formation of hydrate which is de
39、trimental to the determination. It is, therefore, necessary that the water dew point of the sample be lowered by passing it through a drying tube packed with anhydrous calcium sulfate or a similar water absorption agent which does not absorb hydrocarbons. In such cases, it is necessary to monitor th
40、e water dew point downstream to the drying tube so as to check the degree of saturation of the absorption agent. Install the drying tube upstream of a dust filter in order to prevent particles of the drying agent from entering the measurement installation.ISO 6570:2001(E) ISO 2001 All rights reserve
41、d 3 If the presence of water vapour does not lead to hydrate formation, the drying tube may be omitted and the amount of water formed under the measurement conditions determined. If hydrocarbon mist is present in the sample, and a drying tube is used, ensure that the mist is evaporated by heating be
42、fore allowing the sample to pass through the drying tube. 4.1.4 Dust filter, preferably of a 5 m pore size, which does not adsorb hydrocarbons. 4.1.5 Heat exchangers, pressure regulators and controllers, installed on the gas line with the heat exchanger immediately upstream to each pressure regulato
43、r so as to ensure that the gas temperature after pressure reduction remains at least 5 K above the dew point. The pressure controller can be placed upstream or downstream from the cooling bath in the measurement installation (see annex B). 4.1.5.1 Heat exchanger (see example in Figure 3), through wh
44、ich water, maintained at the required temperature, is circulated from a thermostatically controlled bath so as to maintain the temperature constant in the gas line. 4.1.5.2 Pressure regulator and pressure controller, to ensure the maximum variation from its set-point with the pressure measurement in
45、 the gas/liquid cyclone separator is 10 kPa. 4.1.6 Measurement instruments for temperature and pressure, capable of recording or monitoring the following: a) gas temperature and pressure in the gas/liquid cyclone separator; b) ambient temperature and pressure; c) gas temperature in the gas transmiss
46、ion line, or in the cylinder from which the sample is taken (optional); d) gas temperature after pressure reduction (optional); e) temperature of the bath (optional); f) gas pressure before pressure reduction (optional); g) gas pressure after pressure reduction (optional). If proven experimentally t
47、hat the difference between the temperature of the gas in the cyclone separator and the temperature of the cooling bath is less than 0,1 K, the temperature of the cooling bath may be measured instead. The pressure can be measured in the sample line just before or just after the cyclone separator. 4.1
48、.7 Gas flow meter, capable of making either mass or volumetric measurements for either wet or dry gas. If a mass flow meter is used, it is necessary that the density of the gas be known. The flow rate of the gas passing through the installation is limited by the cooling capacity of the bath, the hea
49、t transmission between the cooling coil and bath and the temperature drop to which the sample is subjected. The flow rate shall, therefore, be limited to a value that will ensure that the gas is cooled to the bath temperature (see 4.1.9.3). Check the accuracy of the meter at regular intervals. The choice of gas meter shall be made taking into account the required accuracy, flow rate and the nature of the natural gas. The maximum permissible error in the flow meter shall be 1 % of the measured value. The me
