1、BRITISH STANDARD BS3680-2C: 1993 ISO9555-3: 1992 Measurement of liquid flow in open channels Part 2: Dilution methods Part 2C: Methods of measurement using chemical tracers UDC 532.574.8:532.543BS3680-2C:1993 This British Standard, having been prepared under the directionof the Industrial-process Me
2、asurement and Control Standards Policy Committee, waspublished underthe authorityof the Standards Boardand comesinto effect on 15 May1993 BSI 04-1999 The following BSI references relate to the work on this standard: Committee reference PCL/3 Draft for comment 89/20311 DC ISBN 0 580 22155 5 Committee
3、s responsible for this British Standard The preparation of this British Standard was entrusted by the Industrial-process Measurement and Control Standards Policy Committee (PCL/-) to Technical Committee PCL/3, upon which the following bodies were represented: Clyde River Purification Board Departmen
4、t of the Environment Institute of Measurement and Control Institution of Water and Environmental Management National Rivers Authority Water Services Association of England and Wales Welsh Office The following bodies were also represented in the drafting of the standard, through subcommittees and pan
5、els: Institute of Hydrology Water Research Centre Amendments issued since publication Amd. No. Date CommentsBS3680-2C:1993 BSI 04-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Definitions and symbols 1 4 Tracers used 2 5 Trace
6、r measurement 3 6 Environmental factors affecting tracers 7 7 Techniques for tracer injection 9 8 Sampling techniques 9 9 Analysis and sources of error 9 10 Special requirements 10 Annex A (normative) General characteristics of commonly used tracers 11 List of references Inside back coverBS3680-2C:1
7、993 ii BSI 04-1999 National foreword This Part of BS3680 has been prepared under the direction of the Industrial-process Measurement and Control Standards Policy Committee. It is identical with ISO9555-3:1992 Measurement of liquid flow in open channels Tracer dilution methods for the measurement of
8、steady flow Part3 Chemical tracers, published by the International Organization for Standardization (ISO). This is one of a series of Parts of BS3680 on dilution methods, as follows: Part 2A, General. 1)2) Part 2B:1993, Methods of measurement using radioactive tracers. Part 2C:1993, Methods of measu
9、rement using chemical tracers. Part 2D:1993, Methods of measurement using fluorescent tracers. These four Parts of BS3680 supersede BS3680-2A:1964, BS3680-2B:1986, and BS3680-2C:1983, which are withdrawn. This British Standard calls for the use of substances that may be injurious to health if adequa
10、te precautions are not taken. It refers only to technical suitability and does not absolve the user from legal obligations relating to health and safety at any stage. Particular attention is therefore drawn to the possible use of sodium dichromate as a tracer. This practice is deprecated in the Unit
11、ed Kingdom because of the toxicity of sodium dichromate. Cross-references The Technical Committee has reviewed the provisions of ISO772:1988 and ISO9555-1, 1)2)to which normative reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A Brit
12、ish 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 Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a fron
13、t cover, an inside front cover, pagesi andii, pages1 to12, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover. 1) In preparation. 2) It is envisage
14、d that, when ISO9555-1 is published, it will be implemented in the UK as BS3680-2A.ISO9555-3:1992(E) BSI 04-1999 1 1 Scope This part of ISO9555 deals with the use of chemical tracers in discharge measurements by the dilution method. Apparatus and methods of general application are set out in ISO9555
15、-1 and are not repeated here, with the exception of those relating specifically to chemical tracers. Chemical tracers have several advantages as follows. a) As with fluorescent tracers, the handling of the tracer follows normal chemical laboratory practice, and no special equipment (e.g.radiation sh
16、ielding) is required. Care is still required, however, when handling concentrated tracer, to avoid contamination of samples and, with some tracers, for reasons of chemical toxicity. b) In general, chemical tracers are widely available commercially, and may be stored indefinitely. c) Analysis may be
17、possible using laboratory facilities currently used for water quality determination. d) In general, chemical tracers are photochemically stable. The disadvantages of chemical tracers are as follows: a) Their detection limits are relatively high and therefore a larger quantity of tracer is required f
18、or each gauging than in the case of radioactive or fluorescent tracers. For practical reasons this may restrict their application to small discharges. However, for certain tracers, reconcentration techniques can permit the measurement of large discharges (of the order of1 000m 3 /s) where conditions
19、 of mixing and tracer loss are acceptable. b) With the exception of the conductivity method for sodium choride, the determination ranges of laboratory analysis methods are limited, so dilution of river samples may be necessary before analysis. This limitation means that the constant-rate injection m
20、ethod is preferable for chemical tracers (excepting tile conductivity method) since determination of the peak concentrations resulting from a sudden injection would be difficult. c) Natural background levels, particularly of conductivity (resulting from dissolved solids in natural waters), may be hi
21、gh and variable, and this necessitates the use of a larger amount of tracer than would be apparent from a consideration of detection limits only. d) It is not possible to use a carrier, as in the case of radioactive tracers, and losses by adsorption may be serious in some cases. 2 Normative referenc
22、e The following standard contains provisions which, through reference in this text, constitute provisions of this part of ISO9555. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this part of ISO9555 are encourage
23、d to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO772:1988, Liquid flow measurement in open channels Vocabulary and symbols. 3 Definitions and symbols 3.1 Defi
24、nitions Definitions relating to many aspects of flow measurement, including dilution methods, are given in ISO772. For the purposes of this part of ISO9555, the following definitions apply. 3.1.1 ion-selective electrode potentiometric probe, the output potential of which, when measured against a sui
25、table reference electrode, is proportional to the activity of the selected ion in the solution under test 3.1.2 interference error in the determination of a chemical ion, caused by the sensitivity of the analytical method to the presence of other ions in solution 3.1.3 Beer-Lambert law a physical la
26、w stating that the absorption of light energy by an absorbing medium varies exponentially with the light path length through the medium and with the molar concentration of the medium 3.1.4 colorimetry chemical analysis method based on the measurement of the absorption of visible light in a given ran
27、ge of wavelengths by substances in solution according to the Beer-Lambert lawISO9555-3:1992(E) 2 BSI 04-1999 3.1.5 atomic absorption flame spectrometry chemical analysis method based on the measurement of the absorption of visible light in a given range of wavelengths by a sample atomized in a flame
28、 according to the Beer-Lambert law 3.1.6 atomic emission flame spectrometry chemical analysis method based on the measurement of light in a given range of wavelengths emitted by a a sample atomized in a flame according to the Beer-Lambert law 3.1.7 adsorption removal of ions from solution by a solid
29、 surface 3.1.8 conductivity method technique for determining the concentration of the tracer by means of electrical conductivity 3.2 Symbols The symbols used in this part of ISO9555 are defined where they occur in the text. 3.3 Units of measurement The units of measurement used in this part of ISO95
30、55 are Sl units. 4 Tracers used 4.1 General The chemical tracers in common use are as follows: a) iodide as sodium iodide, solubility1800kgperm 3 ; b) lithium as lithium chloride, solubility600kgper m 3 ; c) chloride as sodium chloride, solubility350kgper m 3 ; d) chromium as sodium dichromate, solu
31、bility800kg per m 3 . Bromide and fluoride are satisfactory tracers but are not in common use. Other substances such as manganese sulfate and sodium nitrate have also been used. The general characteristics of commonly used chemical tracers are given in Annex A. 4.2 Iodide Sodium iodide and potassium
32、 iodide are highly soluble, and solutions of both have been used as tracers; sodium iodide is cheaper per unit mass of iodide. The iodide ion may be determined by catalytic spectrophotometry, or by using an ion-selective electrode. In each case the detection limit is approximately14g/l and a practic
33、al working range is104g/l to 1004g/l. Concentrations in natural fresh waters may reach24g/l but are usually much lower. The catalytic spectrophotometric method is preferred for laboratory analysis (see5.1.1.1) while the ion-selective electrode method may be applied in situ (see5.1.1.2 and5.2.1). 4.3
34、 Lithium Lithium is available as a variety of salts and the chloride is generally used for tracer studies. Lithium chloride is the cheapest chemical form for a given weight of lithium; lithium brine, which may contain up to83g of lithium per litre, is more convenient to handle than anhydrous lithium
35、 chloride which is deliquescent and dissolves exothermically (see10.2.1). Lithium is normally determined either by atomic emission flame spectrometry or atomic absorption flame spectrometry, and the detection limits are typically0,14g/l and10mg/l respectively. Concentrations in open-channel flows ra
36、nge from less than0,14g/l in mountain streams to greater than10mg/l in mineral processing plant effluents. Sewage effluents, and some rivers receiving these, carl contain typically104g/l to504g/l. Destructive analysis uses a few millilitres of sample, but techniques such as flameless atomic absorpti
37、on spectrometry may be used if only very small sample volumes are available. 4.4 Chloride The conductivity method owes its popularity to the relative simplicity and low cost of conductivity meters that can be used in the field, and to the properties of the tracer (sodium chloride) which is character
38、ized by a high degree of electrolytic dissociation when dissolved in water, easy availability and low price, and a moderate solubility, with little dependence of solubility on temperature. Furthermore, sodium chloride is relatively harmless to animal and plant life in the concentrations used, and sh
39、ows little adsorption by vegetation and the materials of the streambed.ISO9555-3:1992(E) BSI 04-1999 3 A disadvantage of the conductivity method is the high background level, typically25mS/cm to500mS/cm, resulting from naturally occurring dissolved solids. Although the detection limit of sodium chlo
40、ride approaches0,5mg/l with generally available conductivity meters, the conductivity of natural waters is such that large quantities of sodium chloride may be required to give an accurately measurable change in the conductivity of the stream water. The tracer must be diluted with large quantities o
41、f water to obtain an injection solution with a specific gravity that is sufficiently low to avoid density segregation. 4.5 Chromium Chromium is used as a tracer in the form of sodium dichromate; the process of solution is endothermic. Hexavalent chromium at0,1mg/l can be analysed directly by colorim
42、etry using suitable reagents, but it is also possible to perform a preliminary reconcentration by extraction, and thus to improve the sensitivity of the method by a factor of10, or even100, to detect14g/l. Total chromium in similar concentration ranges is analysed by atomic absorption flame spectrom
43、etry. 5 Tracer measurement 5.1 Principles 5.1.1 Iodide 5.1.1.1 Catalytic spectrometric method The iodide ion in weak solution may be determined by its catalytic effect on the rate of the reaction between the ceric ion and arsenious acid. The yellow colour of a ceric solution is measured spectrometri
44、cally at a fixed time after the start of the reaction and the reduction in absorbance, caused by a faster reaction in the presence of iodide, is recorded. Close control of the temperature of the reacting solutions is essential. Concentrations of iodide are determined by reference to a calibration cu
45、rve. Standards for the preparation of the calibration curve are made up using a large “background” sample, taken from the flow upstream of or before the injection, as a diluent. Background coloration, turbidity or the presence in the water of substances capable of reducing ammonium cerium(IV) sulfat
46、e interfere in the procedure. Reaction mixtures derived from coloured or turbid waters have a lower transmission than those derived from distilled water, and this shift in transmission is more pronounced in those reaction mixtures containing higher concentrations of iodide, leading to a lowered grad
47、ient of the calibration curve for coloured waters. This behaviour and the curvilinear nature of the calibration curve mean that it is necessary to construct a calibration graph for each gauging exercise, using background water as a diluent. This procedure also has the advantage that any other unknow
48、n interfering substances are present at the same concentration in both the samples and the standards. 5.1.1.2 Ion-selective electrode method The ion-selective electrode (or more precisely the cell consisting of the ion-selective electrode, the sample and a reference electrode) produces a difference
49、in electrical potential which is related, within a certain range, to the activity of the iodide ion in solution. For solutions of concentration less than about0,000 1mol/l (12,7mg/l, or a molar solution of sodium iodide having a concentration of127g/l) the following equation holds: E = E 0 59,12 lg I (at25C) where In normal use, both the samples and the standards used to establish the calibration curve are brought to a constant total ionic strength by the addition of an equal volume of2mol/l analytical reagent grade potassium nitrate solution. The potential acro
