1、BRITISH STANDARD BS EN ISO 6327:2008Gas analysis Deter- mination of the water dew point of natural gas Cooled surface condensation hygro- meters (ISO 6327:1981)ICS 75.060This British Standard, having been prepared under the directionof the Environment andPollution Standards Committee, was published
2、underthe authority of the Boardof This corrigendum renumbers BS 3156-10.3.1:198730 April 2009 as BS EN ISO 6327:2008 BSI and comes into effect on 31 July 1987 BSI 2009 The following BSI references relate to the work on this standard: Committee reference EPC/46 Draft for comment 79/54886 DC ISBN 978
3、0 580 59360 4 National Foreword The British Standard is the UK implementation of EN ISO 6327:2008. It is identical with ISO 6327:1981. It supersedes BS 3156-10.3.1:1987 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee PTI/15, Natural gas and gas analys
4、is. A list of organizations represented on this committee can be obtained on request to its secretary. Additional information. In paragraph 2 of 3.2 reference is made to the availability of published documents giving the relationship between saturated vapour pressure and temperature. A suitable refe
5、rence is “Steam Tables“ 1964, published by DSIR, National Engineering Laboratory, and obtainable from HMSO, 49 High Holbom, London, WC1. In the Table, reference is made to the “British Gas analytical methods“ publication 2.5.1, October 1971. This publication is obtainable from British Gas pic, Hinck
6、ley Operational Centre, Coventry Road, Hinckley, Leicestershire, LEI0 ONA. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Ame
7、ndments issued since publication Date of issue Comments BS EN ISO 6327:2008EUROPEANSTANDARD NORMEEUROPENNE EUROPISCHENORM ENISO6327 January2008 ICS75.060 EnglishVersion GasanalysisDeterminationofthewaterdewpointofnatural gasCooledsurfacecondensationhygrometers(ISO 6327:1981) AnalysedesgazDterminatio
8、ndupointderosedesgaz naturelsHygromtrescondensationsurfacerefroidie (ISO6327:1981) GasanalyseBestimmungdesWassertaupunktesvon ErdgasKondensationsHygrometermitgekhlter Oberflche(ISO6327:1981) ThisEuropeanStandardwasapprovedbyCENon15December2007. CENmembersareboundtocomplywiththeCEN/CENELECInternalReg
9、ulationswhichstipulatetheconditionsforgivingthisEuropean Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferencesconcerningsuchnational standardsmaybeobtainedonapplicationtotheCENManagementCentreortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialvers
10、ions(English,French,German).Aversioninanyotherlanguagemadebytranslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCENManagementCentrehasthesamestatusasthe officialversions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Bulgaria,Cyprus,CzechRepublic,Denmark,Estoni
11、a,Finland, France,Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Romania,Slovakia,Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG Managem
12、entCentre:ruedeStassart,36B1050Brussels 2008CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.ENISO6327:2008:E 2 Foreword The text of ISO 6327:1981 has been prepared by Technical Committee ISO/TC 193 “Natural gas” of the International Organization for S
13、tandardization (ISO) and has been taken over as EN ISO 6327:2008 by Technical Committee CEN/SS N21 “Gaseous fuels and combustible gas“, the secretariat of which is held by CMC. This European Standard shall be given the status of a national standard, either by publication of an identical text or by e
14、ndorsement, at the latest by July 2008, and conflicting national standards shall be withdrawn at the latest by July 2008. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identif
15、ying any or all such patent rights. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece
16、, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 6327:1981 has been approved by CEN as EN ISO 6327:2008 without any modif
17、ications. BS EN ISO 6327:2008 BSI 09-1999 i Contents Page 1 Scope 1 2 Field of application 1 3 Principle 1 4 Characteristics of the apparatus 1 5 Sources of error General precautions for operation 3 6 Elimination of hydrocarbon condensates 4 7 Accuracy 4 Annex Correction of water dew point 5 Table C
18、orrections to be deducted from water dew points in thepresenceofmethanol 5 Publications referred to Inside back cover BS EN ISO 6327:2008 blank BS EN ISO 6327:20081 1 Scope This International Standard describes hygrometers used for the determination of the water dew point of natural gases by detecti
19、ng water vapour condensation occurring on a cooled surface or by checking the stability of the condensation on this surface. 2 Field of application The water dew point of processed natural gases in transmission lines normally lies between 25C and +5C, which corresponds to water concentrations of50 t
20、o200ppm (V/V), according to the pressure of the gas. The hygrometers considered in this International Standard may be used for determining water vapour pressure, without requiring calibration, in a system operating under total pressures greater than or equal to atmospheric pressure. The relationship
21、 between water vapour partial pressure and the observed dew point confers on the method the quality of absolute measurement. If the test atmosphere contains gases which condense at a temperature in the region of, or above, that of the water dew point, it is very difficult to detect the condensed wat
22、er vapour. 3 Principle 3.1 Principle of the apparatus With this type of apparatus, which determines the water content of a gas by measuring the corresponding dew point, a surface (generally a metallic mirror), the temperature of which may be artificially lowered and accurately measured, is exposed t
23、o a sample of the gas being tested. The surface is then cooled to a temperature at which condensation occurs and is observed as dew. Below this temperature, condensation increases with time, whilst above it, condensation decreases or does not occur. This surface temperature is then (for practical ap
24、plications) taken as the dew point of the gas flowing through the apparatus. 3.2 Determination of water vapour pressure The partial water vapour pressure in the gas samples is the saturated vapour pressure corresponding to the observed dew point, provided that the gas in the hygrometer is at the sam
25、e pressure as the gas at the time of sampling. Published documents are available giving the relationship between saturated vapour pressure and temperature. It should be noted that if methanol is present, this method determines methanol in addition to water. However, if the methanol content is known,
26、 the Annex gives, for information, correction factors allowing determination of the actual water dew point. 3.3 Precautions to be taken It is essential that all sample lines be as short as possible and be sized to produce a negligible pressure drop during measurement. The sample lines and the hygrom
27、eter, apart from the mirror, shall be above the water dew point temperature. 4 Characteristics of the apparatus 4.1 General Condensation apparatus may be designed in various ways. The differences lie mainly in the nature of the condensation surface, the methods used for cooling the surface and for c
28、ontrolling its temperature, the methods used for measuring the surface temperature and the method of detecting the condensation. The mirror and its associated components are normally placed in a small cell through which a sample of the gas flows; at high pressures, the mechanical strength and leak t
29、ightness of the cell have to be suitable. It is recommended that the mirror should be easily removable for cleaning. Adequate precautions shall be taken if measurements are to be made in the presence of condensable hydrocarbons. Measurements can be carried out manually or automatically. CAUTION: Man
30、ufacturers instructions should be carried out before gas at high pressure is admitted to the cell. BS EN ISO 6327:20082 4.2 Automatic and manual types Devices for measuring dew point can be designed to make isolated measurements at different times or to make more or less continuous measurements. For
31、 isolated measurements, methods of mirror cooling may be chosen which require continuous attention by the operator responding to changes in the condensed deposit which is observed by the naked eye. If there is less moisture in the gas sample, i.e. if the gas has a lower dew point, the rate at which
32、water vapour flows through the apparatus per unit time decreases so that condensation forms more slowly, and it becomes more difficult to judge whether condensation is increasing or diminishing. Observation of the deposit can be made easier by using a photoelectric cell or any other device which is
33、sensitive to light, if a simple indicator is needed, while maintaining manual control of the cooling device. With certain types of manually operated instruments, it is very difficult to observe the water dew point in the presence of condensed hydrocarbons. In such cases, a liquid paraffin bubbler ma
34、y be used to assist such observations. It is very important, however, that the principles involved and the limitations in the use of such a bubbler are understood. An equilibrium is established between the gas passing through the bubbler and the liquid paraffin oil contained in it, at the temperatur
35、e and pressure of the bubbler. This involves the following reactions: a) The first gas passing through fresh liquid paraffin loses water to the paraffin until equilibrium is achieved, at which time the water content of the exit gas is the same as that of the inlet gas. Therefore, the temperature of
36、the bubbler must be above that of the water dew point of the gas to be tested and sufficient gas must be passed into the bubbler for equilibrium to be established before observations can be made. b) Until equilibrium is established, heavy hydrocarbon components pass from the gas into the liquid para
37、ffin. It is this exchange that reduces the volume of potentially condensable hydrocarbons in the gas, thereby reducing the masking effect of the condensed hydrocarbon liquid. As there is a continuing exchange of components, the liquid paraffin becomes saturated with condensible hydrocarbons the cont
38、ent of which increases in the gas. The liquid paraffin must then be replaced and the bubbler conditioned before further observations can be made. The device can be fully automated by using the output signal of the photoelectric cell to stabilize the mirror at the required condensation temperature. A
39、utomatic operation is indispensable for continuous reading or recording. 4.3 Mirror illumination Manual devices can involve observation of condensation with the naked eye; if a photoelectric cell is used, the mirror is illuminated by a light source built into the test cell. The lamp and photoelectri
40、c cell can be arranged in various ways, provided that diffusion in the direction of the light source from the mirror is reduced by the polishing of the mirror. In any case, the mirror must be clean before use. In the absence of any condensation, the diffused light falling on the photocell must be re
41、duced. The effects of light diffused from internal surfaces of the cell can be reduced by blackening these surfaces and this precaution can be supplemented by an arrangement of the optical system so that only the mirror is illuminated and the photocell views only the mirror. 4.4 Methods for cooling
42、the mirror and controlling its temperature The following methods are used for reducing and adjusting the mirror temperature. The methods described in4.4.1 and4.4.2 require constant attention from the operator and are not suitable for automatic devices. For automatic devices, two cooling methods are
43、used: indirect contact with a coolant or cooling by the thermoelectric (Peltier) effect as described in4.4.3 and4.4.4. In any case, the rate of cooling of the mirror shall not exceed1C per minute. 4.4.1 Solvent evaporation A volatile liquid in contact with the rear face of the mirror can be evaporat
44、ed and cooled by an air flow. Hand bellows are generally used for this purpose, but an adjustable source of low pressure compressed air or any other suitable pressurized gas is preferable. The liquid used can be ethylene oxide, a very efficient liquid giving cooling of the mirror of approximately30C
45、, without effort, when hand bellows are used. However, if toxicity is a risk, acetone can be used to obtain cooling of approximately20C with hand bellows or even greater cooling with compressed air or other suitable pressurized gas. BS EN ISO 6327:20083 4.4.2 Gas cooling by adiabatic expansion The m
46、irror can be cooled by discharging onto its rear face a gas which has just expanded through a nozzle. Compressed carbon dioxide, available from small cylinders, is often used for this purpose, but other gases such as compressed air, compressed nitrogen, propane or halogenated hydrocarbons can also b
47、e used. Mirror temperatures of at least40C below the gas sample temperature can be obtained. 4.4.3 Indirect contact with a coolant The mirror is connected to a cooler through a thermal resistor. Normally, a solid copper rod is plunged into the cooler and connected to the mirror by a small piece of i
48、nsulating material forming the thermal resistor. The mirror is heated by an electric element. Current intensity should be controlled so that the mirror temperature can be adjusted easily and accurately. Using liquid nitrogen as coolant, temperatures of 70C to 80C may be obtained; for temperatures do
49、wn to approximately 50C (according to the apparatus design), a mixture of solid carbon dioxide plus acetone may be used, and for temperatures around 30C liquefied propane can be used. 4.4.4 Cooling by thermoelectric (Peltier) effect A single stage Peltier effect element normally allows maximum cooling of a
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