1、INTERNATIONAL STANDARD IS0 10849 First edition 1996-04-I 5 Stationary source emissions - Determination of the mass concentration of nitrogen oxides - Performance characteristics of automated measuring systems gmissions de sources fixes - D - non-dispersive ultraviolet spectroscopy; - differential op
2、tical absorption spectrometry. NOTE 1 Commercial devices using the described tech- niques, that meet the requirements of this International Standard, are available. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this
3、International Standard. At the time of publi- cation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicat
4、ed below. Members of IEC and IS0 maintain registers of cur- rently valid International Standards. IS0 6879:1995, Air quality - Performance character- istics and related concepts for air quality measuring methods. IS0 7996: 1985, Ambient air - Determination of the mass concentration of nitrogen oxide
5、s - Chemiluminescence method. IS0 9096: 1992, Stationary source emissions - De- termination of concentration and mass flow rate of particulate material in gas-carrying ducts - Manual gravimetric method. IS0 9169:1994, Air quality - Determination of per- formance characteristics of measurement method
6、s. IS0 10396:1993, Stationary source emissions - Sampling for the automated determination of gas concentrations. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 automated measuring system (AMS): System that may be attached to a chimney to continuou
7、sly measure and record the mass concentration of nitro- gen oxides passing through the chimney. 3.2 analyser: Analytical part in an extractive AMS. 1 IS0 10849:1996(E) 0 IS0 3.3 verified (AMS): AMS previously verified against - the mass concentration of nitrogen oxides in waste gas this Internationa
8、l Standard. usually varies with time; 3.4 calibration gas: Gas of known, reliable and sta- ble composition that may be used to check the re- sponse of the AMS and should be used for the calibration of the AMS. 3.5 comparative measurements: Measurements that are taken on the same chimney in the same
9、sampling plane for the same period of time, with the AMS under test and with the comparative method providing pairs of measured values. 3.6 comparative method: Defined test method for the comparative measurements of stationary source emissions containing nitrogen oxides. This can be a manual method
10、or an AMS verified according to this International Standard, with a different measuring principle. NOTE 2 The naphthylethylenediamine (NEDA) method according to IS0 11564, has been proven to be a suitable manual method. Also, validated national standards with known performance characteristics (stand
11、ard deviation, lower detection limit, effect of interfering substances) may be applied. 3.7 standard deviation, sa: Measure of the working precision of the AMS. The standard deviation, SA, is derived from the differ- ence in the pairs of measured values of nitrogen ox- ides by the AMS under test and
12、 the comparative method, on the basis of a sufficient number of com- parative measurements spread over the period of un- attended operation (see annex A). % is the standard deviation of the compara- tive method. SD is the standard deviation of the paired val- ues. SX is the standard deviation of the
13、 blank readings. NOTES 3 It is not possible to determine directly the standard de- viation, s, of an AMS under repeatable working conditions or in a laboratory, because: - commercially available calibration gas mixtures contain- ing nitrogen monoxide do not have all the properties of actual waste ga
14、s and do not cover all possible influ- ences; - it is not possible to maintain the properties of a waste gas present in the waste gas flue in a waste gas sample transferred into a vessel. Therefore, the evaluation of the standard deviation, s, is performed by comparison with an independent manual me
15、thod or an analyser with a different principle of detection. Applying the comparative method in combination with the test for systematic errors ensures a satisfying accuracy of the automated measuring system. 4 The standard deviation, s, is a measure of the working precision under site conditions. T
16、herefore, it contains, in addition to random errors, the effects of interfering sub- stances, the effects of temperature changes and of any zero and span drifts, because they cannot be eliminated in prac- tice. The standard deviation, s, is an upper limiting value for the AMS. Known systematic error
17、s of the measured values of the independent comparative method are to be taken into account. 5 This procedure is suitable for finding the precision of the measuring result of the automated measuring method, as long as the standard deviation, s, of the measured values of the comparative method is sig
18、nificantly smaller than the standard deviation, s, of the difference in pairs of measured values. If the AMS under investigation has a substantially smaller standard deviation, s, than the comparative method, s, the method above can still be used, although the value of s, will have a large uncertain
19、ty. If the uncertainty in s, is un- known and hence the limits of S, cannot be established, the value of s, can be used as a qualitative rather than a quan- titative assessment of the AMS performance. 3.8 chimney: Stack or final exit duct on a stationary process used for the dispersion of residual p
20、rocess gases. 3.9 mass concentration: Concentration of a sub- stance in an emitted waste gas, expressed in milli- grams per cubic metre. NOTE 6 The concentration of nitrogen oxides can be ex- pressed as ppm, as milligrams of NO per cubic metre or as milligrams of NO, per cubic metre. NO: 1 ppm (V/V)
21、 = 1.34 mg/m3 NO,: 1 ppm (V/V) = 2.05 mg/m3 Concentrations should be related to standard atmospheric conditions (273 K, 101.3 kPa) and dry gas. Depending on national regulations, the concentrations should be referred to defined oxygen or carbon dioxide concentrations. 2 SO 10849:1996(E) In this Inte
22、rnational Standard, all concentrations of nitrogen oxides are expressed as milligrams of NO, per cubic metre. 3.10 stationary source emissions: Those gases that have been emitted by a stationry plant or process and are transported to a chimney for dispersion into the atmosphere. 3.11 calibration cur
23、ve: Curve describing the de- pendence of the measured signal on a given cali- bration gas. 3.12 period of unattended operation: Maximum admissible interval of time for which the performance characteristics will remain within a predefined range without external servicing, e.g. refill, calibration, ad
24、- justment. ISO 68791 NOTE 7 For long-term monitoring installations a mini- mum of 7 d of unattended operation is required. 3.13 calibration: Setting and checking of the AMS before determining the performance characteristics or before beginning any measurement of NO,. Further steps of the calibratio
25、n of an AMS, like comparative measurements, may be part of national regulations. 4 Principle With extractive systems, a representative sample of gas is taken from the stack with a sampling probe and conveyed to the analyser through the sample line and sample gas conditioning system. Non-extractive s
26、ystems do not require any sampling transfers out of the stack. For the installation of these systems, a representative place in the stack is to be chosen. In-situ systems may sample a larger part of the flue gas. The values from the analyser are recorded and/or stored by means of electronic data pro
27、cessing. The systems described here basically only measure nitrogen monoxide. If, with the systems, the nitrogen dioxide content or the total quantity of the nitrogen oxides (NO + NO,) is to be determined, a converter to reduce nitrogen dioxide to nitrogen monoxide is to be used. The converter may b
28、e a separate piece of equipment or incorporated into the NO analyser. Systems also exist, mainly using ultraviolet tech- niques, that can monitor nitrogen dioxide directly. These systems are mostly combined with NO ana- lysers. In most of the cases, it is considered that only nitro- gen monoxide has
29、 to be measured, because the NO, content is negligible. However, in some cases nitro- gen dioxide may occur in large quantities and has to be taken into account, either by direct measurement or by using a converter. The sampling will, however, be difficult, due to the high reactivity of nitrogen di-
30、 oxide. 5 Description of the measuring equipment 5.1 Sampling and sample gas conditioning systems for extradive systems 5.1 .I General A more detailed description of sampling and sample gas conditioning systems for extractive methods is given in IS0 10396. Figure 1 a) shows a typical arrangement of
31、a complete measuring system for NO. This system is suitable for use with all the analysers that are described in 5.2. In addition to this arrangement, there are also auto- mated measuring systems for the NO, measurement that heat the sample gas to above water and acid dew-points (or the dew-point of
32、 other condensable substances) to avoid losses of NO*. In this case, the system can be simplified. It is important that all the components carrying the sample gas to the analyser are also heated above water and acid dew-points. In the case that higher amounts of NO, are in the sample gas, the use of
33、 a gas cooler can produce er- rors on the NO, measurement due to the solubility of NO, in the condensed water and depending on the content of water vapour in the flue gas. A possible arrangement to avoid losses of NO, is shown in figure 1 b). The sampling of gas shall be representative, that is, the
34、 sampling location shall be typical of the entire duct. The representativeness of the sampling location requires confirmation by means of a network measurement in accordance with the guidelines given in IS0 10396. The sampling points for the network measurement shall be located in accordance with IS
35、0 9096. Checking of representativeness shall be done before the first installation of a measuring sys- tem and shall be repeated in the case of uncertainty. 3 IS0 10649:1996(E) a) NO-measuring crevice I 13 Key: 1 Gas sampling probe 2 Particulate filter 3 Heating 4 Sampling line (heated if necessary)
36、 t b) NO/NO,-measuring device 9 Flowmeter 10 NO-analyser 11 Recorder 12 Inlet for zero and calibration gas (preferably in front of the filter) to check the complete system 5 Sample cooler with condensate separator 13 Bypass for excess gas 6 Sample pump 14 Inlet for zero and span gas to check the ana
37、lyser 7 Filter 15 Converter 8 Needle valve 16 NO/NO,-analyser Figure 1 - Examples of the installation of measuring devices Q IS0 IS0 10849:1996(E) The components described in 5.1.2.1 to 5.1.2.8 have, for example, proven to be successful for measure- ments at gas-, oil- and coal-fired plants (precaut
38、ions need be observed because of the high corrosiveness of condensable acid gases, e.g. HCI, SO, or NO*). 5.1.2 Components 5.1.2.1 Sampling probe, made of suitable, corrosion-resistant material. For gas temperatures up to 220 “C, polytetrafluoroethylene (PTFE) is an ac- ceptable material. At tempera
39、tures 250 “C, stain- less steel and certain other materials can alter the ratio of NO:NO,. In this case, ceramic or glass ma- terial is required, if it is necessary to determine the ratio. Cooling may be considered necessary in order to maintain the gas concentrations in the flue gas. 5.1.2.2 Filter
40、, made of ceramic or sinter metal with 10 Frn pore size. The filter shall be heated above the water or acid dew-point. 5.1.2.3 Sample line, made of PTFE or stainless steel. The lines shall be operated 15 K above the dew-point of condensable substances (generally the water or acid dew-point). The inn
41、er diameter of the line depends on the quantity of sample gas required, with 4 mm as a minimum (and preferably 4 mm to 8 mm). 5.1.2.4 Sample cooler or permeation drier, to separate water vapour from the flue gas. The dew- point shall be sufficiently below the ambient tem- perature. A cooling tempera
42、ture of 2 “C to 5 “C is convenient. Sufficient cooling is required for the vol- ume of gas being sampled and the amount of water vapour that it contains. The design of the sample gas cooler shall be such that absorption of NO, in the condensate is restricted to a minimum. This ensures that loss of N
43、O2 dissolved in the condensate, which is drained from the sample cooler, is at a minimum. The use of a permeation drier also ensures that NO, losses are negligible. 5.1.2.5 Sampling pump (corrosion-resistant), of which the performance shall be such that it can sup- ply the connected analyser with it
44、s required gas flow. The quantity of sample gas required can vary between 30 I/h and 500 I/h, dependent upon the analyser and the expected response time. 5.1.2.6 Secondary filter, to separate fine dust, with a pore size of 1 pm to 2 pm, made for example from glass fibre, sintered ceramics, stainless
45、 steel or PTFE fibre. 5.1.2.7 Flow controller and flowmeter, to set the required flow and constructed of corrosion-resistant material. 5.1.2.8 NOz/NO converter, necessary if NO, has to be measured with a NO analyser (only possible in combination with extractive systems). Different types of converter
46、s exist, for example: - carbon converters; - carbon-molybdenum converters; - stainless steel converters; - thermal converters. In some situations (e.g. when ammonia is present in the sample gas) interferences can occur depending on the operating temperature of the converter. In these cases, it is ne
47、cessary to take into account such possibilities when selecting the converter type. The converter can be bypassed with a three-way valve. If the sample gas flows through the converter, the total quantity (NO + NO,) is obtained; when the converter is bypassed, the NO content is obtained. The amount of
48、 NO, can be calculated as the differ- ence between NO, and NO. The converter shall have an efficiency 95 %, which can be tested using calibration gases containing NO, in synthetic air, or with a converter efficiency tester. This method is described in detail in IS0 7996 and it is not suitable if the
49、 NO analyser is prone to interfer- ence by ozone. The principle of an efficiency tester is shown in figure2. A constant flow of a NO-calibration gas is mixed with a constant flow of air or oxygen, that contains different amounts of ozone, produced by an adjustable ozone generator. Ozone reacts with NO to produce NO,. Thus the total amount of nitrogen ox- ides (NO + NO*) remains constant, while the ratio (NO;NO,) changes.
