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1、BRITISH STANDARD BS 4559-5.3: 1987 ISO 6145-3: 1986 Methods for Preparation of calibration gas mixtures Part 5: Dynamic volumetric methods Section 5.3 Periodic injections into a flowing gas stream ISO title: Gas analysis Preparation of calibration gas mixtures Dynamic volumetric methods Part 3: Peri
2、odic injections into a flowing gas stream UDC 543.27:54 13 185:53.089.62 Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 This British Standard, having been prepared under the direction of the Environment and Pollution Standa
3、rds Committee, was published under the authority of the Board of BSI and comes into effect on 31 December 1987 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference EPC/46 Draft for comment 85/51114 DC ISBN 0 580 16254 0 Committees responsible for this Bri
4、tish Standard The preparation of this British Standard was entrusted by the Environment and Pollution Standards Committee (EPC/-) to Technical Committee EPC/46, upon which the following bodies were represented: British Ceramic Research Association British Coal British Gas plc Cement Makers Federatio
5、n Chemical Industries Association Department of Energy (Gas Standards) Department of Trade and Industry (Electronics Application Division) Department of Trade and Industry (Laboratory of the Government Chemist) Department of Trade and Industry (Warren Spring Laboratory) Electricity Supply Industry i
6、n England and Wales GAMBICA (BEAMA Ltd.) Institute of Petroleum Institution of Chemical Engineers Institution of Gas Engineers Society of Chemical Industry Society of Glass Technology Society of Motor Manufacturers and Traders Limited Water-tube Boilermakers Association The following bodies were als
7、o represented in the drafting of the standard, through subcommittees and panels: British Compressed Gases Association British Laboratory Ware Association Amendments issued since publication Amd. No.Date of issueComments . Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006
8、, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 BSI 10-1999i Contents Page Committees responsibleInside front cover National forewordii 1Scope and field of application1 2Reference1 3Principle of the method1 4Practical example1 5Operating conditions of the example1 6Estimation of volume ratio2 7Calibra
9、tion of the system and sources of error2 8Numerical example: Binary mixture of methane in nitrogen2 Figure 1 Schematic representation of the method4 Figure 2 Schematic illustration of the apparatus for injection by plug cock5 Figure 3 Schematic representation of the functioning of the plug cock5 Fig
10、ure 4 Schematic representation of different positions of the plug6 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 ii BSI 10-1999 National foreword This Section of BS 4559 has been p
11、repared under the direction of the Environment and Pollution Standards Committee. It is identical with ISO 6145-3:1986 “Gas analysis Preparation of calibration gas mixtures Dynamic volumetric methods Part 3: Periodic injections into a flowing gas stream”, published by the International Organization
12、for Standardization (ISO). This Part of ISO 6145 was prepared as a result of discussions in Technical Committee 158, Gas analysis, in which the UK has participated. BS 4559 was first published in 1970 as a single standard under the title “Methods for the preparation of gaseous mixtures”. The present
13、 revision is being issued in Parts to implement methods prepared by ISO/TC 158 and to provide for revision, where necessary, of the methods included in the 1970 edition which was withdrawn in 1981. Part 5 of this standard covers the preparation of mixtures using dynamic volumetric methods. This Sect
14、ion covers periodic injections into a flowing gas stream. Other Sections in this Part of BS 4559 are as follows. Section 5.1: Methods of calibration; Section 5.2: Volumetric pumps method;1) Section 5.4: Continuous injection method; Section 5.5: Capillary method;1) Section 5.6: Sonic orifices; Sectio
15、n 5.7: Mass flow controllers method;1) Section 5.8: Diffusion method1). Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those use
16、d in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” and “part 3 of ISO 6145” appear, ref
17、erring to this standard, they should be read as “British Standard” and “Section 5.3 of BS 4559” respectively. Additional information. In clause 5, final paragraph and in 7.1, paragraph 3, in lines 5, 6 and 7, information has been included for guidance. In a British Standard such text is usually give
18、n as notes. 1) In preparation Cross-reference International StandardCorresponding British Standard BS 4559 Methods for preparation of calibration gas mixtures Part 5 Dynamic volumetric methods ISO 6145-1:1986Section 5.1:1987 Review of methods of calibration (Identical) Licensed Copy: sheffieldun she
19、ffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 BSI 10-1999iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British
20、Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incor
21、porated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c)
22、 BSI BS 4559-5.3:1987 BSI 10-19991 1 Scope and field of application This International Standard constitutes part 3 of ISO 6145, which deals with the various dynamic volumetric techniques used for the preparation of calibration gas mixtures. It describes the periodic injection techniques which enable
23、 a concentration range of each component of between 106 and 102 with 1 % variability to be obtained. The concentration is expressed as a volume ratio (V/V). 2 Reference ISO 6145-1, Gas analysis Preparation of calibration gas mixtures Dynamic volumetric methods Part 1: Methods of calibration. 3 Princ
24、iple of the method 3.1 Operating principle Complementary gas B flows continuously through the system. At regular time intervals, a volume V of gas B is replaced by an equivalent volume of gas A. A gas B (complementary gas) flows at a flow rate q in a tube T. A means is provided at a point P for peri
25、odically withdrawing a small sample of volume V of gas B and injecting an identical volume of gas A (the component for calibration) in place of gas B (Figure 1), such that the flow rate is unchanged. The volume VA of gas A together with gas B goes to a mixing chamber of volume V0 where the mixture i
26、s made homogeneous. 3.2 Area of validity Volume V0 shall be large compared with the volume delivered by the component B during the time t between two successive injections. In practice, the following relationship shall be fulfilled: 3qBt u V0 Gases A and B shall be at the same pressure and temperatu
27、re. 3.3 Principle of calculation At a rate of n injections per minute of volume V, the mean flow volume ratio of gas A is qA = nV, and the rate can be expressed as 4 Practical example Figure 2 shows a practical example of a plug cock arrangement. Figure 3 and Figure 4 show the schematic representati
28、on of the operation of a plug cock. The cock is arranged so that the four plug holes are always communicating two by two (a and c, or b and d) forming a single passage of volume V. A synchronous motor drives the plug within its housing, and the motor is fed by a pulse generator. Each pulse causes th
29、e plug to perform a half turn in x seconds, at a constant rotational speed, and it rests between pulses. In position 1, the plug is at rest while gas B is bypassed into the mixing chamber through check valves and the component for calibration (gas A) is drawn through the bubbler. After a given perio
30、d of time (adjustable), the cock is turned by one-half of a revolution. The time is a function of the desired volume ratio and sets the value of n (number of pulses per unit time). During movement of the cock to position 2, gas B passes through s, while gas A fills volume V expelling gas B, the pres
31、sure being limited by the action of the bubbler. As the plug moves to position 3, volume V (now filled with gas A) is entrained by gas B into the mixing chamber. At the same time, gas A is drawn over the bubbler. When the pulse terminates, the plug rests at position 4, equivalent to position 1. 5 Op
32、erating conditions of the example The injection system (see Figure 2) is supplied with gas A and is supplied with gas B by circuit 1 of pump P. Delivery flow rates of gases A and B shall be high enough to permit complete sweeping during passage between positions 2 and 3. Delivery volume V is about 0
33、,04 cm3, and the plug goes through a half turn in 5 s. Feed circuit 2 for gas B supplies gas at a variable flow rate (100 to 1 000 cm3/min) and serves to dilute the gas from M1 at point M2 (160 cm3). The sum of gas delivery flow rates from 1 and 2 shall be very stable, supplied by a piston metering
34、pump P driven by a synchronous motor. The gas mixture is ready for utilization after M2. It may also be feasible to employ the mixture from M2 and dilute it in gas B in a second stage, using a second arrangement identical to the first. In this case, volume ratios of less than 50 ppm (V/V) can be obt
35、ained with an accuracy of 4 % relative. C flow rate of gas A full flow rate - - qA q - n V q - -= Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 2 BSI 10-1999 6 Estimation of volume ratio If q is the delivery flow rate of g
36、as from mixing chamber M1, and q is the complementary gas delivery flow rate in circuit 2 at the entrance to mixing chamber M2, then the following relationships hold: At the exit of M1: At the exit of M2: These formulae are useful for obtaining an approximation from the data on V, n and q + q, but t
37、he accuracy of flow rate nV is difficult to reach by conventional methods. 7 Calibration of the system and sources of error 7.1 General The pressures and temperatures of gases A and B are the same at the level of the revolving cock, defining the delivered quantity of gas A for every cycle of the coc
38、k. The pressure and temperature in the metering pump define the delivery flow rate of gas B. If the difference in pressures in circuit 1 and circuit 2 is neglected, the difference in temperature between the cock and the metering pump (around 10 K, when the temperature equilibrium is reached) leads t
39、o a significant effect (about 3 %). These temperatures may be measured by thermocouples or mercury thermometers, one fixed on the rotating cock and one immersed in the pump oil. A satisfactory approach is to define a “geometrical dilution factor”, FDG: which is only valid for an operation with the s
40、ame temperature in the cock and in the pump. The actual operation leads, after equilibrium of the system, to: a) Tr, temperature of the cock, slightly higher than the ambient temperature; b) Tp, temperature of the oil of the metering piston pump, 35 to 40 C with ambient temperature around 20 C. NOTE
41、Tr and Tp are expressed in degrees Celsius for numerical examples but the units are converted into kelvins for calculations. When in use, the actual dilution factor FD is The calibration of the system is obtained by the measurement of FDG during an actual operation on a pure gas A, leading to Tr and
42、 Tp. The measurement of CAM is performed at the outlet of the system by an analytical comparison method 7.2 Calibration error The calibration error, Cal, is expressed as relative uncertainty: where CAM/CAM comes from the comparison method, using for example: a) a calibration gas mixture of known con
43、centration CAE CAE2) b) an analytical method of comparison leading to 7.3 Precision error When the system is calibrated for this set of conditions (n, V and q + q), the precision error, f, comes only from the error of measurement of the two temperatures Tr and Tp, at the time of mixture generation:
44、The effects of temperature dependent volume variations in the pump and in the plug are negligible. 8 Numerical example: Binary mixture of methane in nitrogen 8.1 Estimation of FDG, temperature conditions With C n.V q - -= C n.V qq+ -= FDG qq+ n.V - -= 2) If the complementary gas is the same for this
45、 calibration mixture as for gas B of the system, the purity of this gas does not act significantly as a correction factor on FD = 1/CA. n= 4 V= 0,051 4 cm3 of methane q + q= 1 061 cm3 of nitrogen per minute FDG 5 160 (taken from manufacturers instructions) Licensed Copy: sheffieldun sheffieldun, na,
46、 Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 BSI 10-19993 At equilibrium of the system, Tr = 25 0,1 C = 298,2 0,1 K Tp = 36,6 0,1 C = 309,8 0,1K 8.2 Preparation of a mixture, by a static volumetric method, around 200 ppm of methane in nitrogen 8.3 Gas chromatograp
47、hic (FID) comparison of CAE and CAM from which 8.4 Calibration results and error In this example of a set of conditions (n, V and q + q), a periodical check has to be made on the results, which may be affected by mechanical wear. Further calibrations checked over a period of one year give consistent
48、 results (5 293, 5 299, 5 323 26) with Tr variations from 22,7 to 25 C and Tp variations from 35,8 to 38 C. 8.5 Precision error When using this set of conditions, measuring Tp and Tr, at the time of mixture production, with an error of 0,1 K around 288,16 to 313,16 K (15 to 40 C), there is a precisi
49、on error of: f 0,7 103 8.6 Overall error on day-to-day use This result depends mainly on the calibration (calibration mixture and analytical method). Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 08:27:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4559-5.3:1987 4 BSI 10-1999 Figure 1 Schematic representation of the method Licensed Copy: sheffieldun sheffieldun, na, Fri Dec