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1、INTERNATIONAL STANDARD IS0 10715 First edition 1997-06-01 Natural gas - Sampling guidelines Gaz na furel - Lignes directrices pour khantillonnage Reference number IS0 10715:1997(E) IS0 10715:1997(E) Contents 1 Scope 1 2 Definitions 1 3 Principles of sampling 3 4 Safety precautions . 5 5 Technical co
2、nsiderations 7 6 Materials used in sampling . 10 7 General preparation of equipment . 11 8 Sampling equipment . 12 9 Spot sampling 18 10 Direct sampling 19 11 Incremental sampling 21 Annexes A Use of a block valve in direct sampling 23 B Cleaning of steel sampling cylinders . 25 C Procedure for low-
3、pressure sampling into glass cylinders 26 D Procedure for sampling by the fill-and-empty method . 28 E Procedure for sampling by the controlled-rate method 30 F Procedure for sampling by the evacuated-cylinder method . 32 G Guidelines for the calculation of the residence time 34 H Students f-table 3
4、8 J Bibliography . 39 0 IS0 1997 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 the publisher. International Org
5、anization for Standardization Case postale 56 l CH-1211 Gen a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii -,-,- 0 IS0 IS0 10715:1997(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The wo
6、rk of preparing International Standards is normally carried out through IS0 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-governm
7、ental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voti
8、ng. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 IQ715 was prepared by Technical Committee lSO/TC 193, Natural gas, Subcomittee SC 1, Analysis of natural gas. Annexes A to J of this International Standard
9、are for information only. IS0 10715:1997(E) 0 IS0 Introduction This International Standard provides guidance on all aspects of the sampling of processed natural gas. Unless otherwise stated, all pressures up to 15 MPa in this International Standard are given as gauge pressures. The determination of
10、the composition and the properties of the gas is highly dependent on the sampling technique. Also of great importance are the design, construction, installation and maintenance of the sampling system as well as the conditions of sample transfer and transport. These guidelines cover sampling strategy
11、, details of sampling methods, the choice of sampling method and sampling equipment. This document procedure. is intended for use in those cases where sampling is not described as part of the analytical This document concentrates on sampling systems and procedures. Analyses from the samples collecte
12、d using these systems and procedures may be utilized in many different ways, including calculations to determine the calorific value of the gas stream, identification of contaminants contained in the gas stream, and compositional information to determine whether or not the stream meets contractual s
13、pecifications. iv INTERNATIONAL STANDARD o IS0 IS0 10715:1997(E) Natural gas - Sampling guidelines WARNING - The use of this International Standard may involve hazardous materials, operations and equipment. This standard does not purport to address all of the safety problems associated with its use.
14、 It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability or regulatory limitations prior to use. All sampling activities shall comply with local safety regulations. 1 Scope The purpose of this document is to provide c
15、oncise guidelines for the collection, conditioning and handling of representative samples of processed natural gas streams. It also contains guidelines for sampling strategy, probe location and the handling and design of sampling equipment. It considers spot, composite (incremental) and continuous s
16、ampling systems. This document gives consideration to constituents such as oxygen, hydrogen sulfide, air, nitrogen and carbon dioxide in the gas stream. This document does not include sampling of liquid streams or streams with multiphase flow. Traces of liquid, such as glycol and compressor oil, if
17、present, are assumed to be intrusive and not a part of the gas to be sampled. Their removal is desirable to protect the sampling and analytical equipment from contamination. This document can be used for custody transfer measurement systems and allocation measurement systems. 2 Definitions For the p
18、urposes of this International Standard, the following definitions apply: 21 direct sampling: Sampling in situations where there is a direct connection between the natura unit. 2.2 floating-piston cylinder: A container which has a moving piston separating the sample from a buffer gas. The pressures a
19、re in balance on both sides of the piston. ,I gas to be sampled and the analytica I 2.3 flow-proportional incremental sampler: A sampler which collects gas over a period of time and at a rate that is proportional to the flow rate in the sampled pipeline. 2.4 - high-pressure natural gas: Natural gas
20、with a pressure exceeding 0,2 MPa. NOTE - The maximum for this International Standard is 15 MPa. -,-,- IS0 10715:1997(E) 0 IS0 2.5 hydrocarbon dew point: The temperature, at a given pressure, at which hydrocarbon vapour condensation begins. 2.6 incremental sampler: A sampler which accumulates a seri
21、es of spot samples into one composite sample. 2.7 indirect sampling: Sampling in situations where there is no direct connection between the natural gas to be sampled and the analytical unit. 2.8 liquid separator: A unit, in the sample line, used to collect liquid fall-out. 2.9 low-pressure natural g
22、as: Natural gas having a pressure between 0 and 0,2 MPa. 2.10 purging time: The period of time during which a sample purges a piece of equipment. 2.11 representative sample: A sample having the same composition as the natural gas sampled when the latter is considered as a homogeneous whole. 2.12 res
23、idence time: The time it takes for a sample to flow through a piece of equipment. 2.13 retrograde condensation: Retrograde behaviour describes the non-ideal phase properties of hydrocarbon gas mixtures, such as natural gas. Retrograde condensation is the production of a liquid phase of heavy hydroca
24、rbons at a particular pressure and temperature where, at that same temperature, the gas stays in a single phase at a higher pressure as well as at a lower pressure. NOTE - See also 5.2. 2.14 sample container: A container for collecting the gas sample when indirect sampling is necessary. 2.15 sample
25、line: A line provided to transfer a sample of the gas to the sampling point. It may include devices which are necessary to prepare the sample for transportation and analysis. 2.16 sample probe: A device inserted into the gas line to be sampled and to which a sample line is connected. 2.17 sampling p
26、oint: A point in the gas stream where a representative sample can be collected. 2.18 spot sample: A sample of specified volume taken at a specified place at a specified time from a stream of gas. 2.19 transfer line: A line provided to carry the sample to be analysed from the sample point to the anal
27、ytical unit. 2.20 water dew point: The temperature, at a given pressure, at which water vapour condensation begins /. 2 0 IS0 IS0 10715: 1997(E) 3 Principles of sampling 3.1 Sampling methods The main function of sampling is to take an adequate sample that is representative of the gas. The main disti
28、nction in sampling is between direct and indirect sampling methods. In the direct sampling method, the sample is drawn from a stream and directly transferred to the analytical unit. In the indirect sampling method, the sample is stored before it is transferred to the analytical unit. The main classi
29、fications of the indirect sampling method are spot sampling and incremental sampling. Figure 1 - Survey of direct and indirect sampling methods The information needed from the analysis of natural gas falls into two basic categories: averaged and limit values. i 3.1 .I Averaged values A typical examp
30、le is the calorific value. Custody transfer requires the time- or flow-averaged calorific value. Commercial agreements determine the period and method of averaging. 3.1.2 Limit values Most gas custody transfer contracts contain specification limits on composition or on gas properties. Direct samplin
31、g can be applied, but often the requirements are such that also indirect sampling has to be applied. 3.2 Sampling frequency This subclause gives guidelines for the establishment of the sampling frequency. Mostly the sampling frequency is a matter of common sense. Information on the properties of the
32、 gas stream in the past and about expected (systematic) future changes determines the sampling frequency. Generally, pipeline gas composition will have daily, weekly, monthly, semi-annual and seasonal variations. Compositional variations will also occur because of gas treatment equipment and reservo
33、ir changes. All of these environmental and operational considerations shall be taken into account when selecting a sampling interval. The statistical approach in this paragraph is only intended to support the common-sense approach. In this context, the required sampling frequency is the number of sa
34、mples to be taken in a certain period of time in order to obtain meaningful results. 3 -,-,- IS0 10715:1997(E) The formula for calculating the number of samples is: I - n* =,Xj where d n S is the error margin required; is the number of samples; is the standard deviation; 0 IS0 f is Students f-factor
35、 (see table H.1 in annex H). This equation shall be solved by iteration: an initial value of f is estimated, and used to calculate a revised value of n, which is used, in turn, to give a new value of t. The error margin, the number of samples and the standard deviation shall be taken over the same p
36、eriod of time. 3.2.1 Error margin There are two different cases of error margins. One case is related to the determination of averaged values. In most custody transfer contracts, these values are given as an indication of the accuracy. The other is related to the determination of limit values. Custo
37、dy transfer contracts specify the limits but rarely give an indication of the accuracy. In these cases, the difference between the last measured value, or the last years average, and the limit value is the error margin. 3.2.2 Number of samples The number of samples is the number of samples to be tak
38、en in a defined period. It is equivalent to the number of partial samples in incremental sampling. 3.2.3 Students f-factor Students f-factor allows for the finite sample size, and is to be found in standard statistical tables. The value depends on the claimed certainty (typically 95 %) and the “degr
39、ees of freedom”, here to be taken as the number of measurements minus one (n-1). EXAMPLE 1 Determination of the monthly average caloric value d = 0,4 % (error margin required from custody transfer contract for monthly averaged value) s= 0,6 % (estimated variation over a one-month period) First estim
40、ate, taking n = 7: f= 2,45 for 6 degrees of freedom and a certainty of 0,975 single-sided (equals 0,95 double-sided) 1 - 06 n2 =2,45xL 04 J n=14 First iteration, taking n = 14: 4 0 IS0 IS0 10715:1997(E) recalculate for i! = 2,16 for 13 degrees of freedom, and a certainty of 0,975 single-sided (equal
41、s 0,95 double-sided) 1 - 06 n2 =2,16x-L 04 1 n=ll Second iteration, taking n = 11: recalculate for t= 2,23 for IO degrees of freedom, and a certainty of 0,975 single-sided (equals 0,95 double-sided) - ni =2,23x 06 04 9 n=ll EXAMPLE 2 Total sulfur determination Last measured concentration 20 mg/m3 an
42、d the contract limit value 50 mg/m3. d = 30 mg/m” (difference between limit value from custody transfer contract and last measured value) s = IO mg/m” standard deviation in spot sample results (in the past year) f = 4,30 n - 1 taken as 2, level of certainty 95% n = 2 Three samples are enough. Recalc
43、ulation indicates that two samples are not enough. 4 Safety precautions , 4.1 General Sampling and sample handling shall follow all relevant national and company-related safety regulations In the case of inadequate regulations, those responsible for sampling shall establish detailed procedures. Spec
44、ifications for equipment shall also be established. Personnel involved shall be properly trained and educated to a level such that they are able to take necessary responsibility. 4.2 Personnel The person responsible for the department/section which is to perform the sampling shall be satisfied that
45、the sampling can be performed within relevant safety regulations. 5 IS0 10715:1997(E) 0 IS0 Those performing sampling or installing sampling equipment shall have the necessary training and education to evaluate potential safety hazards in general. The above personnel shall have the authority to prev
46、ent sampling or installation of sampling equipment which is unsuitable or unsafe. 4.3 Equipment Equipment regularly. used in the sampling of high-pressure natural gas shall be inspected and recertificated if required Documentation shall be available and up to date. Equipme nt shall be designed to me
47、et relevant sampling conditions, e.g. pressure chemical compat ibility, vibration, thermal expansion and/o thermal contraction. 9 te mperature, corrosivity, flow, Glass cylinders shall not be exposed to pressure. If provided for, end caps shall be installed on cylinders during transportation and sto
48、rage. Cylinders shall have volume, working pressure and test pressure permanently stamped. Cylinders shall have a test pressure of at least I,5 times the working pressure. Cylinders shall be protected against damage during transportation and storage. Transportation boxes or cartons designed for the
49、individual type of cylinder shall be available. Cylinders shall be accompanied by labels or paperwork with relevant information protected against damage. Cylinders and associated accessories shall be inspected and leak-tested periodically. Permanent transfer and sampling lines shall be properly secured. Breakable connections shall have easy access for leak-testing. Outlets shall be equipped with double block and bleed valves. End caps shall be connected to
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