DIN EN ISO 6327-2008 Gas analysis - Determination of the water dew point of natural gas - Cooled surface condensation hygrometers (ISO 6327 1981) English version of DIN EN ISO 6327.pdf

1、April 2008DEUTSCHE NORM English price group 8No part of this standard may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 75.060!$Mg*“1426807www.di

2、n.deDDIN EN ISO 6327Gas analysis Determination of the water dew point of natural gas Cooled surface condensation hygrometers (ISO 6327:1981)English version of DIN EN ISO 6327:2008-04Gasanalyse Bestimmung des Wassertaupunktes von Erdgas Kondensations-Hygrometer mit gekhlter Oberflche (ISO 6327:1981)E

3、nglische Fassung DIN EN ISO 6327:2008-04www.beuth.deDocument comprises 9 pagesDIN EN ISO 6327:2008-04 2 National foreword This standard has been prepared by Technical Committee ISO/TC 193 “Natural gas”. The responsible German body involved in its preparation was the Normenausschuss Materialprfung (M

4、aterials Testing Standards Committee), Technical Committee NA 062-05-73 AA Gasanalyse und Gas-beschaffenheit. EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 6327 January 2008 ICS 75.060 English Version Gas analysis - Determination of the water dew point of natural gas - Cooled surface cond

5、ensation hygrometers (ISO 6327:1981) Analyse des gaz - Dtermination du point de rose des gaz naturels - Hygromtres condensation surface refroidie (ISO 6327:1981) Gasanalyse - Bestimmung des Wassertaupunktes von Erdgas - Kondensations-Hygrometer mit gekhlter Oberflche (ISO 6327:1981) This European St

6、andard was approved by CEN on 15 December 2007. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concern

7、ing such national standards may be obtained on application to the CEN Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own

8、language and notified to the CEN Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania

9、, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN

10、 All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 6327:2008: EForeword The text of ISO 6327:1981 has been prepared by Technical Committee ISO/TC 193 “Natural gas” of the International Organization for Standardization (ISO) and has b

11、een 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 endorsement, at the latest by J

12、uly 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 identifying any or all such patent ri

13、ghts. 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, Hungary, Iceland, Ireland, I

14、taly, 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 modifications. DIN EN ISO 6327:2008

15、-04 EN ISO 6327:20082 : - 1 Scope This International Standard describes hygrometers used for the determination of the water dew Point of natura1 gases by detec- ting water vapour condensation occurring on a cooled surface or by checking the stability of the condensation on this surface. 3.2 Determin

16、ation 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 same pressure as the gas at the time of sampling. Published documents are available giving t

17、he relationship be- tween saturated vapour pressure and temperature. 2 Field of application The water dew Point of processed natura1 gases in transmission lines normally lies between - 25 OC and + 5 OC, which cor- responds to water concentrations of 50 to 200 ppm (V/ v), according to the pressure of

18、 the gas. The hygrometers considered in this International Standard may be used for determining water vapour pressure, without requir- ing calibration, in a System operating under total pressures greater than or equal to atmospheric pressure. The relationship between water vapour partial pressure an

19、d the observed dew Point confers on the method the quality of absolute measure- ment. 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 water vapour. 3 Principle 3.1 Principle of

20、 the apparatus With this type of apparatus, which determines the water con- tent of a gas by measuring the corresponding dew Point, a sur- face (generally a metallic mirror), the temperature of which may be artificially lowered and accurately measured, is exposed to a Sample of the gas being tested.

21、 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 applications) taken as the dew Point

22、of the gas flowing through the apparatus. lt should be noted that if methanol is present, this method determines methanol in addition to water. However, if the methanol content is known, the annex gives, for information, correction factors allowing determination of the actual water dew Point. 3.3 Pr

23、ecautions to be taken lt is essential that all Sample lines be as short as possible and be sized to produce a negligible pressure drop during measure- ment. The Sample lines and the hygrometer, apart from the mirror, shall be above the water dew Point temperature. 4 Characteristics of the apparatus

24、4.1 General Condensation apparatus may be designed in various ways. The differentes lie mainly in the nature of the condensation surface, the methods used for cooling the surface and for controlling its temperature, the methods used for measuring the surface temperature and the method of detecting t

25、he 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 tightness of the cell have to be suitable. lt is recommmended that the mirror should be easily removable for clea

26、ning. Adequate precautions shall be taken if measurements are to be made in the presence of condensable hydrocarbons. Measurements tan be carried out manually or automatically. Caution : Manufacturers instructions should be carried out before gas at high pressure is admitted to the cell. 3 EN ISO 63

27、27:2008:DIN EN ISO 6327:2008-04 Lkvices for measuring dew point tan be designed tcd make isoiated measurements at different times or to make more or iess continuous measurements. For isolated measurements, imethods of mir-kor cooling may be Chosen which require con- tinwous attention by the Operator

28、 responding to changes in the zcndensed deposit which is observed by the naked eye. Bf there !s jess moisture in the gas Sample, i.e. if the gas has a lower (3ebv Point, the rate at which water vapour flows through the apparatus per unit time decreases so that condensation forms more siowjy, and it

29、becomes more difficult to judge whether eowdensation is increasing or diminishing. Observation sf the deposi; tan be made easier by using a photoelectric cell or any ,-%er deiice which is sensitive to Iight, if a simple indicator SS -ice if a photoelectric cell is used, the mirror is 4uminated by a

30、light Source built into the test cell. The lamp c;nd photoeiectric cell tan be arranged in various ways, pro- vided that diffusion in the direction of the light Source from the mirror is reduced by the polishing of the mirror. In any case, the :-Gor must be clean before use. In the absence of any co

31、ndensation, -he aiffused light failing cr; the phototeil must be reduced. The effects of BEght diffused from internal surfaces of the cell tan be reduced Dy blackening these surfaces ahd this precaution EX be stipplernen-ted by an arrangement sf the optical system so that only the mirror Os illumina

32、ted and the photocell vievvs oniy the ,mirror. The following methods are used for reducing and adjusting the mirror temperature. The methods described in 4.4% and 4.42 require constant tter-hn frcmi the operatot- and are 7laC suitabhe for autcmatic devices. 521) automatic deviees, two cooling method

33、s are used : indirect cantact with a coslant EX- csoling by the thermoelectric (Peitier) effect as described In 4.4.3 and 4.44. In any case; the rate :isl eooirng 0-F the a-riu- shall not exceed 1 “C per n?inGie. A volatile liquid in contact v for temperatures down to approximately - 50 OC Iaccordin

34、g to the apparatus design), a mixture of solid carbon dioxide plus acetone may be used, and for temperatures around - 30 OC liquefied propane tan be used. 4.4.4 Cooiing by tkerrn6eBeetric (Peltier) effect A single Stage Peltier effect element normally allows maximum cooling of approximately 50 “C. W

35、ith two stages, coo!ing of approximately 70 OC tan be obtained. 4 DIN EN ISO 6327:2008-04 EN ISO 6327:2008l-he mirror temperature tan be adjusted by varying the current in the Peltier effect elements, but thermal inertia tends to be high, and more rapid adjustment is achievable by maintaining a cons

36、tant cooling current, connecting the mirror to a thermal resistance, and heating the mirror with an adjustable electric heating device. 4.5 Temperature measurement lt is essential that the temperature of the mirror on which the deposit is formed is measured as accurately as possible. To avoid temper

37、ature differentes on the surface, a mirror of high thermal conductivity is preferred. Manual devices generally in- corporate a mercury thermometer, and with automatic devices a thermoelectric probe is used (for example a resistance ther- mometer, a thermistor or a thermocouple). 51.3 Impurities in v

38、apour form Hydrocarbons tan condense on the mirror. In principle these do not interfere because hydrocarbon surface tension is very different from that of water. They spread on the mirror and form a continuous layer which does not diffuse light. Manual detection of condensates is, nevertheless, not

39、easy because although the dew Point is very much lower than the condensa- tion temperature of hydrocarbons, only a few water droplets tan be detected in a large hydrocarbon droplet (sec clause 6). 5 Sources of error - General precautions for Operation The presence of a hydrocarbon condensate does no

40、t modify the water dew Point since the condensates are not miscible. If the gas contains methanol, this will be deposited with the water, and a dew Point for the mixture water and methanol will be obtained. ff hydrocarbons are also present, then two con- densates are formed, one aqueous, the other o

41、ily. In this case, the condensation temperature of the aqueous condensate is not due solely to the water content. 5.1 Interfering substances 5.2 Cold wall error 5.1.1 General Substances other than the gas or water vapour tan enter the device and affect its operational characteristics. Such substance

42、s may be solid particles, dust, etc., which tan be deposited on the mirror. Vapour other than water vapour tan condense on the mirror. Gases soluble in water, voluntarily or accidentally introduced into the test cell, tan also induce an observed dew Point different from the dew Point which would cor

43、respond to the actual water vapour content. lt is essential that the Parts of the pipes and device other than the mirror are at a temperature greater than the condensation temperature; if not, water vapour will condense at the coldest Points and modify the moisture content of the gas Sample. 5.3 Equ

44、ilibrium temperature approach of the risk of greatly exceeding the actual condensation tem- If the quantity of water conveyed to the mirror per unit time is small, the mirror shall be cooled as slowly as possible because perature without observing the first deposit. 5.1.2 Solid impurities If solid i

45、mpurities are absolutely insoluble in water, they do not modify the observed condensation temperature, but tan hinder condensation Observation. In an automatic device, without a compensation device for such impurities, these tend to obstruct the Operation of the device if the amount of conden- sate

46、is low. Defects resulting from an excess of solid impurities on the mirror generally result in an unexpected increase of the mirror temperature for a few minutes and call for dismantling of the device and cleaning of the mirror. (lt is essential for this pur- pose that the hygrometric cell tan be ra

47、pidly dismounted.) lt may be desirable to remove solid impurities by using a non- hygroscopic filterl) to avoid such difficulties. The quantity of dew which tan normally be observed with the naked eye is about 10-5 g/cm? Automatic devices, if very sen- sitive, tan detect considerably lower quantitie

48、s of water. lf a manual device is necessary, and especially for lower Points, the following precautions shall always be taken : dew a) The mirror cooling rate shall be as small as possible in the condensation temperature range. (It is good practice to carry out a rapid test to determine the approxim

49、ate conden- sation temperature before an accurate measurement is made.) To prevent the influence of dust particles, some automatic b) The mean value of the temperature measured at the devices are fitted with a “calibration” sequence. This consists time of first dew appearance, while the mirror temperature of an optional superheating of the mirror, so as to remove all slowly decreases, and of the temperature at which dew condensate, water and hydrocarbons, followed by a rebalanc- disappears, while the mirror temperature slowly increases, ing of the measur