ISO 10849:1996
(Main)Stationary source emissions — Determination of the mass concentration of nitrogen oxides — Performance characteristics of automated measuring systems
Stationary source emissions — Determination of the mass concentration of nitrogen oxides — Performance characteristics of automated measuring systems
Specifies the fundamental structure and the most important performance characteristics of automated measuring systems for oxides of nitrogen to be used on stationary source emissions, for example combustion plants. The procedures to determine the performance characteristics are also specified.
Émissions de sources fixes — Détermination de la concentration en masse des oxydes d'azote — Caractéristiques de performance des systèmes de mesurage automatiques
Emisije nepremičnih virov - Ugotavljanje masne koncentracije dušikovih oksidov - Delovne karakteristike avtomatskih merilnih sistemov
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SLOVENSKI STANDARD
SIST ISO 10849:1996
01-oktober-1996
(PLVLMHQHSUHPLþQLKYLURY8JRWDYOMDQMHPDVQHNRQFHQWUDFLMHGXãLNRYLKRNVLGRY
'HORYQHNDUDNWHULVWLNHDYWRPDWVNLKPHULOQLKVLVWHPRY
Stationary source emissions -- Determination of the mass concentration of nitrogen
oxides -- Performance characteristics of automated measuring systems
Émissions de sources fixes -- Détermination de la concentration en masse des oxydes
d'azote -- Caractéristiques de performance des systèmes de mesurage automatiques
Ta slovenski standard je istoveten z: ISO 10849:1996
ICS:
13.040.40 (PLVLMHQHSUHPLþQLKYLURY Stationary source emissions
SIST ISO 10849:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 10849:1996
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SIST ISO 10849:1996
INTERNATIONAL
IS0
STANDARD
10849
First edition
1996-04-I 5
Stationary source emissions -
Determination of the mass concentration
of nitrogen oxides - Performance
characteristics of automated measuring
systems
Emissions de sources fixes - Dhermina tion de la concentration en
masse des oxydes d ‘azote - Caracthristiques de performance des
syst&mes de mesurage automatiques
Reference number
IS0 10849: 1996(E)
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SIST ISO 10849:1996
IS0 10849:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 10849 was prepared by Technical Committee
lSO/TC 146, Air quality, Subcommittee SC 1, Stationary source
emissions.
Ann ex A forms an integral part of this International Standard. Annexes B
and C are for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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SIST ISO 10849:1996
0 IS0 IS0 10849:1996(E)
Introduction
Nitrogen oxides are produced during most combustion processes. In fossil
fuel combustion, nitrogen oxides are produced from nitrogen combined in
the fuel and from the oxidation of nitrogen in the air used for combustion.
The quantity of nitrogen oxides produced depends upon the nitrogen
content of the fuel, the boiler design, the burner design and the boiler
operating conditions.
In flue gases from conventional combustion systems, the nitrogen oxides
consist of approximately 95 % nitrogen monoxide (NO). The remaining
oxide is predominantly nitrogen dioxide (NO,) formed from the oxidation
of NO when the flue gas temperature decreases. These two oxides (NO
+ NO,) are generally designated as NO,. It should be noted that in other
processes the ratio of NO to NO, may be different and other nitrogen
oxides may be present.
There are numerous ways of determining nitrogen oxides in the gases of
combustion plants, both wet chemical/analytical methods and instru-
mental techniques.
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SIST ISO 10849:1996
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SIST ISO 10849:1996
IS0 10849:1996(E)
INTERNATIONAL STANDARD 0 IS0
Stationary source emissions - Determination of the
mass concentration of nitrogen oxides
- Performance
characteristics of automated measuring systems
cation, the editions indicated were valid. All standards
1 Scope
are subject to revision, and parties to agreements
based on this International Standard are encouraged
This International Standard specifies the fundamental
to investigate the possibility of applying the most re-
structure and the most important performance char-
cent editions of the standards indicated below.
acteristics of automated measuring systems for ox-
Members of IEC and IS0 maintain registers of cur-
ides of nitrogen to be used on stationary source
rently valid International Standards.
emissions, for example combustion plants. The pro-
cedures to determine the performance characteristics
IS0 6879: 1995, Air quality - Performance character-
are also specified. Furthermore, it describes methods
istics and related concepts for air quality measuring
and equipment to determine NO or NO, (NO + NO,)
methods.
in flue gases including the sampling system and
sample gas conditioning system. Dinitrogen monoxide
IS0 7996: 1985, Ambient air - Determination of the
(N,O) is not determined by the methods described in
mass concentration of nitrogen oxides -
this International Standard. The given performance
Chemiluminescence method.
characteristics refer to the complete measuring sys-
tem, from sampling to analyser.
IS0 9096:1992, Stationary source emissions - De-
termination of concentration and mass flow rate of
This International Standard describes extractive and
particulate material in gas-carrying ducts - Manual
non-extractive systems in connection with a range of
gravime tric method.
analysers that operate using, for example, the follow-
ing principles:
IS0 9169:1994, Air quality - Determination of per-
formance characteristics of measurement methods.
- chemiluminescence;
IS0 10396: 1993, Stationary source emissions -
- non-dispersive infrared spectroscopy;
Sampling for the automated determination of gas
concentrations.
- non-dispersive ultraviolet spectroscopy;
- differential optical absorption spectrometry.
3 Definitions
NOTE 1
Commercial devices using the described tech-
niques, that meet the requirements of this International
For the purposes of this International Standard, the
Standard, are available.
following definitions apply.
3.1 automated measuring system (AMS): System
2 Normative references that may be attached to a chimney to continuously
measure and record the mass concentration of nitro-
The following standards contain provisions which, gen oxides passing through the chimney.
through reference in this text, constitute provisions
of this International Standard. At the time of publi- 3.2 analyser: Analytical part in an extractive AMS.
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SIST ISO 10849:1996
IS0 10849:1996(E)
- the mass concentration of nitrogen oxides in waste gas
3.3 verified (AMS): AMS previously verified against
usually varies with time;
this International Standard.
- it is not possible to maintain the properties of a waste
gas present in the waste gas flue in a waste gas sample
3.4 calibration gas: Gas of known, reliable and sta-
transferred into a vessel.
ble composition that may be used to check the re-
sponse of the AMS and should be used for the
Therefore, the evaluation of the standard deviation, $A, is
calibration of the AMS.
performed by comparison with an independent manual
method or an analyser with a different principle of detection.
3.5 comparative measurements: Measurements
Applying the comparative method in combination with the
that are taken on the same chimney in the same
test for systematic errors ensures a satisfying accuracy of
sampling plane for the same period of time, with the the automated measuring system.
AMS under test and with the comparative method
4 The standard deviation, SA, is a measure of the working
providing pairs of measured values.
precision under site conditions. Therefore, it contains, in
addition to random errors, the effects of interfering sub-
stances, the effects of temperature changes and of any zero
3.6 comparative method: Defined test method for
and span drifts, because they cannot be eliminated in prac-
the comparative measurements of stationary source
tice.
emissions containing nitrogen oxides. This can be a
manual method or an AMS verified according to this
The standard deviation, SA, is an upper limiting value for the
International Standard, with a different measuring
AMS. Known systematic errors of the measured values of
principle.
the independent comparative method are to be taken into
account.
NOTE 2 The naphthylethylenediamine (NEDA) method
according to IS0 II 564, has been proven to be a suitable 5 This procedure is suitable for finding the precision of the
measuring result of the automated measuring method, as
manual method. Also, validated national standards with
long as the standard deviation, sc, of the measured values
known performance characteristics (standard deviation,
of the comparative method is significantly smaller than the
lower detection limit, effect of interfering substances) may
be applied. standard deviation, SD, of the difference in pairs of measured
values.
If the AMS under investigation has a substantially smaller
3.7 standard deviation, s*: Measure of the working
standard deviation, SA, than the comparative method, sc, the
precision of the AMS.
method above can still be used, although the value of SA
will have a large uncertainty. If the uncertainty in S, is un-
The standard deviation, q, is derived from the differ-
known and hence the limits of SA cannot be established, the
ence in the pairs of measured values of nitrogen ox-
value of SA can be used as a qualitative rather than a quan-
ides by the AMS under test and the comparative
titative assessment of the AMS performance.
method, on the basis of a sufficient number of com-
parative measurements spread over the period of un-
3.8 chimney: Stack or final exit duct on a stationary
attended operation (see annex A).
process used for the dispersion of residual process
gases.
compara-
is the standard deviation of the
SC
tive method.
3.9 mass concentration: Concentration of a sub-
stance in an emitted waste gas, expressed in milli-
is the standard deviation of the paired val-
grams per cubic metre.
NOTE 6 The concentration of nitrogen oxides can be ex-
is the standard deviation of the blank
SX
pressed as ppm, as milligrams of NO per cubic metre or as
readings.
milligrams of NO2 per cubic metre.
NOTES
NO: 1 ppm (V/V) = I,34 mg/m3
3 It is not possible to determine directly the standard de-
NO,: I ppm (V/V) = 2,05 mg/m3
viation, SA, of an AMS under repeatable working conditions
or in a laboratory, because:
Concentrations should be related to standard atmospheric
conditions (273 K, 101,3 kPa) and dry gas.
- commercially available calibration gas mixtures contain-
II the properties of Depending on national regula tions, the concen trations
ing nitrogen monoxide do not have a
all possible inf ‘Iu- should be referred to defined oxygen or carbon dioxide
actual waste gas and do not cover
concentrations.
ences;
2
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SIST ISO 10849:1996
IS0 10849:1996(E)
0 IS0
In most of the cases, it is considered that only nitro-
In this International Standard, all concentrations of nitrogen
oxides are expressed as milligrams of NO2 per cubic metre.
gen monoxide has to be measured, because the NO,
content is negligible. However, in some cases nitro-
3.10 stationary source emissions: Those gases
gen dioxide may occur in large quantities and has to
that have been emitted by a stationry plant or process
be taken into account, either by direct measurement
and are transported to a chimney for dispersion into
or by using a converter. The sampling will, however,
the atmosphere.
be difficult, due to the high reactivity of nitrogen di-
oxide.
3.11 calibration curve: Curve describing the de-
pendence of the measured signal on a given cali-
bration gas.
5 Description of the measuring
equipment
3.12 period of unattended operation: Maximum
admissible interval of time for which the performance
characteristics will remain within a predefined range
ng and sample gas
5.1 Sampli conditioning
without external servicing, e.g. refill, calibration, ad-
systems for extractive systems
justment. [ISO 68791
5.1 .I General
For long-term monitoring installations a mini-
NOTE 7
mum of 7 d of unattended operation is required.
A more detailed description of sampling and sample
gas conditioninq systems for extractive methods is
3.13 calibration: Setting and checking of the AMS
given in IS0 10396.
before determining the performance characteristics
or before beginning any measurement of NO,. Further
Figure 1 a) shows a typical arrangement of a complete
steps of the calibration of an AMS, like comparative
measuring system for NO. This system is suitable for
measurements, may be part of national regulations.
use with all the analysers that are described in 5.2.
4 Principle
In addition to this arrangement, there are also auto-
mated measuring systems for the NO, measurement
With extractive systems, a representative sample of
that heat the sample gas to above water and acid
gas is taken from the stack with a sampling probe and
dew-points (or the dew-point of other condensable
conveyed to the analyser through the sample line and
substances) to avoid losses of NO,. In this case, the
sample gas conditioning system.
system can be simplified. It is important that all the
components carrying the sample gas to the analyser
Non-extractive systems do not require any sampling
are also heated above water and acid dew-points.
transfers out of the stack. For the installation of these
systems, a representative place in the stack is to be
In the case that higher amounts of NO, are in the
chosen. /n-situ systems may sample a larger part of
sample gas, the use of a gas cooler can produce er-
the flue gas.
rors on the NO, measurement due to the solubility
of NO, in the condensed water and depending on the
The values from the analyser are recorded and/or
content of water vapour in the flue gas. A possible
stored by means of el ectronic data processing.
arrangement to avoid losses of NO, is shown in
figure 1 b).
The systems described here basically only measure
nitrogen monoxide. If, with the systems, the nitrogen
The sampling of gas shall be representative, that is,
dioxide content or the total quantity of the nitrogen
the sampling location shall be typical of the entire
oxides (NO + NO,) is to be determined, a converter
duct. The representativeness of the sampling location
to reduce nitrogen dioxide to nitrogen monoxide is to
requires confirmation by means of a network
be used. The converter may be a separate piece of
measurement in accordance with the guidelines given
equipment or incorporated into the NO analyser.
in IS0 10396. The sampling points for the network
measurement shall be located in accordance with
Systems also exist, mainly using ultraviolet tech-
IS0 9096. Checking of representativeness shall be
niques, that can monitor nitrogen dioxide directly.
done before the first installation of a measuring sys-
These systems are mostly combined with NO ana-
tem and shall be repeated in the case of uncertainty.
lysers.
3
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SIST ISO 10849:1996
IS0 10849:1996(E)
a) NO-measuring device
II
b) NO/NO,-measuring device
Key:
Flowmeter
9
1 Gas sampling probe
IO NO-analyser
2 Particulate filter
1 I Recorder
3 Heating
front of
12 Inlet for zero and calibration gas (preferably in
4 Sampling line
the filter) to check the complete system
(heated if necessary)
13 Bypass for excess gas
5 Sample cooler with condensate separator
14 Inlet for zero and span gas to check the analyser
Sample pump
6
15 Converter
7 Filter
16 NO/NO,-analyser
8 Needle valve
Examples of the installation of measuring devices
Figure 1 -
4
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SIST ISO 10849:1996
0 IS0 IS0 10849:1996(E)
The components described in 5.1.2.1 to 5.1.2.8 have, 30 I/h and 500 l/h, dependent upon the analyser and
the expected response time.
for example, proven to be successful for measure-
oil- and coal-fired plants (precautions
ments at gas-,
need be observed because of the high corrosiveness
of condensable acid gases, e.g. HCI, SO3 or NO,). 5.1.2.6 Secondary filter, to separate fine dust, with
a pore size of I pm to 2 pm, made for example from
glass fibre, sintered ceramics, stainless steel or PTFE
e. I
tjbre.
5.1.2 Components
probe, made of suitable,
5.1.2-l Sampling
corrosion-resistant material. For gas temperatures up 5.1.2.7 Flow controller and flowmeter, to set the
to 220 “C, polytetrafluoroethylene (PTFE) is an ac- required flow and constructed of corrosion-resistant
ceptable material. At temperatures > 250 “C, stain- material.
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 5.1.2.8 NOz/NO converter, necessary if NO, has to
ratio. Cooling may be considered necessary in order be measured with a NO analyser (only possible in
to maintain the gas concentrations in the flue gas. combination with extractive systems).
Different types of converters exist, for example:
5.1.2.2 Filter, made of ceramic or sinter metal with
- carbon converters;
10 pm pore size. The filter shall be heated above the
water or acid dew-point.
- carbon-molybdenum converters;
- stainless steel converters;
5.1.2.3 Sample line, made of PTFE or stainless
steel. The lines shall be operated 15 K above the
- thermal converters.
dew-point of condensable substances (generally the
water or acid dew-point). The inner diameter of the
In some situations (e.g. when ammonia is present in
line depends on the quantity of sample gas required,
the sample gas) interferences can occur depending
with 4 mm as a minimum (and preferably 4 mm to
on the operating temperature of the converter. In
8 mm).
these cases, it is necessary to take into account such
possibilities when selecting the converter type.
The converter can be bypassed with a three-way
5.1.2.4 Sample cooler or permeation drier, to
separate water vapour from the flue gas. The dew- valve. If the sample gas flows through the converter,
point shall be sufficiently below the ambient tem- the total quantity (NO + NO,) is obtained; when the
perature. A cooling temperature of 2 “C to 5 “C is converter is bypassed, the NO content is obtained.
The amount of NO, can be calculated as the differ-
convenient. Sufficient cooling is required for the vol-
ence between NO, and NO.
ume of gas being sampled and the amount of water
vapour that it contains.
The converter shall have an efficiency > 95 %, which
can be tested using calibration gases containing NO,
The design of the sample gas cooler shall be such that
in synthetic air, or with a converter efficiency tester.
absorption of NO, in the condensate is restricted to
This method is described in detail in IS0 7996 and it
a minimum. This ensures that loss of NO, dissolved
is not suitable if the NO analyser is prone to interfer-
in the condensate, which is drained from the sample
cooler, is at a minimum. ence by ozone.
The principle of an efficiency tester is shown in
The use of a permeation drier also ensures that NO,
figure2. A constant flow of a NO-calibration gas is
losses are negligible.
mixed with a constant flow of air or oxygen, that
contains different amounts of ozone, produced by an
5.1.2.5 Sampling pump (corrosion-resistant), of adjustable ozone generator. Ozone reacts with NO to
which the performance shall be such that it can sup- produce NO,. Thus the total amount of nitrogen ox-
ides (NO + NO,) remains constant, while the ratio
ply the connected analyser with its required gas flow.
(NO:NO,) changes .
The quantity of sample gas required can vary between
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SIST ISO 10849:1996
IS0 10849:1996(E)
6
Key:
1 NO-calibration gas
2 Needle valve
3 Flowmeter
4 Oxygen
5 Ozone generator (adjustable)
6 Bypass for excess test gas
7 Test gas for converter + analyser
Figure 2 - Principle of an efficiency tester for NOz/NO converters
If the converter efficiency is > 95 %, the signal of the
5.2 Measuring principles of analysers
analyser, combined with the tested converter, re-
The following examples describe typical principles
mains nearly constant. The signal of every different
found in existing analysers. The performance charac-
concentration is compared with the signal of the gas
teristics described in clause 6 are applicable both to
mixture containing NO only (with the ozone generator
existing equipment and to future developments.
switched off). At each different ozone concentration,
the concentration of NO and (NO + NO,) of the gas
5.2.1 Chemiluminescence method
mixture shall be determined. N,O is not converted to
NO. Dinitrogen pentoxide (N20s) is converted to NO.
The principle of the chemiluminescence method for
the determination of the mass concentration of nitro-
5.1.3 Dilution
gen oxides in ambient air is described in IS0 7996.
The dilution technique is an alternative to hot gas If NO reacts with ozone (O,), NO, is formed. Part of
monitoring or sample gas drying. The flue gas is di- this NO, is in a photochemically excited state. When
luted with a dilution gas which shall be free from ni-
returning to the basic state, these NO, molecules can
trogen oxides. radiate light in the wavelength range of 590 nm to
3 000 nm. The intensity of this light depends on the
The dilution ratio shall be chosen according to the
NO content and is influenced by the pressure and
objectives of the measurement and shall be compat-
presence of other gases.
ible with the range of the analytical unit. It shall re-
main constant throughout the period of the test. The Figure 3 shows the basic arrangement of a
chemiluminescence analyser.
water dew-point shall be reduced so as to reduce the
risks of condensation in the gas loops. The measured
There are atmospheric pressure and low pressure
values always refer to the wet gas.
analysers, depending on the pressure in the reaction
chamber. Some analysers have built-in NO,/NO con-
Analysers which are used in combination with dilution
verters and, because of their structure, give signals
probes have measuring ranges which are typical for
for NO, NO, and NO, either simultaneously or in se-
ambient air analysers to 1 mg/m3,
(0 mm3
quence.
5 mg/m3, 10 mg/m3 or 25 mg/m3).
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SIST ISO 10849:1996
IS0 10849:1996(E)
15
6
2 3 4 3
r-------w--*
A -
- n
A IL
17
8 9
-s v
1
I
l-jr
I
m
Key:
9 Electronics
1 Sample inlet
pump 10 Oxygen inlet
2 Sample
3 Magnetic valve 1 I Pressure regulator
12 Ozone regulator
4 NOz/NO converter
13 Ozone filter
5 Flow regulator
14 Signal
6 Pressure regulator
7 Reaction chamber 15 Bypass
8 Photomultiplier
Basic arrangement of a chemiluminescence analyser
Figure 3 -
Gases which consist of molecules of different atoms
The measuring range of chemiluminescence ana-
absorb light of the characteristic wavelength in the
lysers used for emission measurements extends from
infrared spectral region.
10 mg/m3 to 20 000 mg/m3. The minimum measuring With the NDIR method,
range that is known to meet the performance char- spectral analysis of the IR radiation is omitted and the
total absorption of the NO molecule at I+-,-.,~~ =
acteristics of this International Standard is 0 mg/m3 to
1 876 cm-’ ( = 5,3 pm) is used for the measurement.
200 mg/m3.
Interference due to carbon dioxide (CO,) in the sam-
Figure4 shows an example of a typical NDIR analyser.
ple gas is possible, particularly in the presence of
due to quenching of the The radiation emitted from the IR source is divided
water vapour,
into two beams and then modulated, one beam
chemiluminescence. The extent of the quenching de-
passing through the measuring cell and the other
pends on the CO, and H,O concentrations and the
through the reference cell containing an IR inactive
type of analyser used. Any necessary corrections shall
gas, usually nitrogen. If the sample gas contains NO,
be made to the analyser output either by reference to
some of the IR energy is absorbed and the difference
correction curves supplied by the manufacturers or
in IR energy reaching the detector is proportional to
by calibrating with gases containing approximately the
the amount of NO present. The detector is designed
same concentration of CO, as the sample gas.
so that it is only sensitive to the NO-specific wave-
5.2.2 Non-dispersive infrared (NDIR) method lengths.
A special arrangement of the NDIR method is the gas
The most common application of the IR method are
filter correlation method.
analysers working according to the NDIR method.
7
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SIST ISO 10849:1996
IS0 10849:1996(E)
Key:
cell
1 Light source 5 Reference
2 Chopper motor 6 Detector
7 Electronics
3 Chopper wheel
4 Measuring cell 8 Signal
Figure 4 - Example of a NDIR analyser
nanometres. The two beams meet alternately via a
A minimum measuring range of 0 mg/m3 to
semipermeable mirror on the reference detector and
200 mg/m3 is possible. Each analyser can be used
the measuring detector. NO in the sample gas ab-
only for the scheduled concentration range.
sorbs resonant lines from the measuring beam and
Interference is possible, particularly with water va-
this absorption depends on the concentration of NO.
pour.
Thus, there are four signals at the two detectors and
they are processed in a microcomputer. The resultant
5.2.3 Non-dispersive ultraviolet (NDUV) method
signal represents a measure for the concentration of
NO. The microcomputer also converts the signals to
The described system is a typical example of the ap-
give a linear output.
plication of the NDUV method. However, other sys-
tems exist.
A minimum measuring range of 0 mg/m3 to
200 mg/m’ is possible with this method.
This method is based on the resonance absorption of
a line multiplet emerging from a hollow-cathode dis-
These UV instruments can suffer from interference
charge lamp through the NO monoxide in the sample
due to SO, in the flue gas sample. This interference
gas.
can be minimized by internal adjustments in the ana-
lysers. In addition, the presence of NO, or aromatic
Figure 5 shows the basic arrangement of the analyser.
compounds in the sample may cause slight interfer-
ence.
A hollow-cathode discharge lamp filled with nitrogen
and oxygen emits a line multiplet which is character-
istic of NO in the range of 226 nm. This beam con-
5.2.4 Non-extractive method (in situ)
sists of resonant lines which are absorbed by NO and
also of non-resonant lines. A rotary chopper wheel
There are two different kinds of in situ methods:
with two cells is connected to the hollow-cathode
discharge lamp. One of the cells is filled with con-
- traversal method (path monitor);
centrated NO, the other is empty. The resonant lines
of the beam are filtered through the cell filled with
- point method.
NO. Thus, two beams are obtained alternately: a
The signals from the in situ instruments always refer
measuring beam of resonant and non-resonant lines
to the wet gas. If the result of the measurement has
and a reference beam of non-resonant lines. Only the
to be referred to dry gas, a correction factor is
range around 226 nm is transmitted through a sub-
needed.
sequent interference filter with a bandwidth of several
---------------------- Page: 14 ----------------------
SIST ISO 10849:1996
IS0 10849:1996(E)
Key:
lamp 7 Semipermeable mirror
1 Hollow-cathode discharge
8 Measuring cell
2 Motor
9 Reference detector
3 NO cell
4 Empty cell 10 Measuring detector
5 Collimator 11 Electronics
Signal
12
6 Interference filter
Figure 5 - Example of a NDUV analyser
The system consists of the following major units: an
5.2.4.1 Traversal method
optical head unit, a reflector unit, a control box and
The traversal method takes into consideration a larger
two purging units.
volume of the waste gas than the point method. It
A deuterium lamp is used as a light source and radi-
uses an optical mode directly in the duct of gaseous
ates in the bandwidth from the ultraviolet to the vis-
effluents. It includes two modules, the first is a radi-
ible range. By using a special grid, radiation in the
ation emission module, the second ensures reception
wavelength range 218 nm to 233 nm is selected. The
of these radiations after passing through the gas
detector is an array of photodiodes. In addition, the
containing nitrogen oxides.
intensity of the light emitted from the light beam
The examples given in 5.2.4.1 .I and 5.2.4.1.2 briefly
which crosses the stack is measured with a reference
describe two instruments which meet the per-
detector.
formance characteristics of this International Stan-
The NO concentration is calculated from the intensity
dard.
of the different
...
INTERNATIONAL
IS0
STANDARD
10849
First edition
1996-04-I 5
Stationary source emissions -
Determination of the mass concentration
of nitrogen oxides - Performance
characteristics of automated measuring
systems
Emissions de sources fixes - Dhermina tion de la concentration en
masse des oxydes d ‘azote - Caracthristiques de performance des
syst&mes de mesurage automatiques
Reference number
IS0 10849: 1996(E)
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IS0 10849:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 10849 was prepared by Technical Committee
lSO/TC 146, Air quality, Subcommittee SC 1, Stationary source
emissions.
Ann ex A forms an integral part of this International Standard. Annexes B
and C are for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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0 IS0 IS0 10849:1996(E)
Introduction
Nitrogen oxides are produced during most combustion processes. In fossil
fuel combustion, nitrogen oxides are produced from nitrogen combined in
the fuel and from the oxidation of nitrogen in the air used for combustion.
The quantity of nitrogen oxides produced depends upon the nitrogen
content of the fuel, the boiler design, the burner design and the boiler
operating conditions.
In flue gases from conventional combustion systems, the nitrogen oxides
consist of approximately 95 % nitrogen monoxide (NO). The remaining
oxide is predominantly nitrogen dioxide (NO,) formed from the oxidation
of NO when the flue gas temperature decreases. These two oxides (NO
+ NO,) are generally designated as NO,. It should be noted that in other
processes the ratio of NO to NO, may be different and other nitrogen
oxides may be present.
There are numerous ways of determining nitrogen oxides in the gases of
combustion plants, both wet chemical/analytical methods and instru-
mental techniques.
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IS0 10849:1996(E)
INTERNATIONAL STANDARD 0 IS0
Stationary source emissions - Determination of the
mass concentration of nitrogen oxides
- Performance
characteristics of automated measuring systems
cation, the editions indicated were valid. All standards
1 Scope
are subject to revision, and parties to agreements
based on this International Standard are encouraged
This International Standard specifies the fundamental
to investigate the possibility of applying the most re-
structure and the most important performance char-
cent editions of the standards indicated below.
acteristics of automated measuring systems for ox-
Members of IEC and IS0 maintain registers of cur-
ides of nitrogen to be used on stationary source
rently valid International Standards.
emissions, for example combustion plants. The pro-
cedures to determine the performance characteristics
IS0 6879: 1995, Air quality - Performance character-
are also specified. Furthermore, it describes methods
istics and related concepts for air quality measuring
and equipment to determine NO or NO, (NO + NO,)
methods.
in flue gases including the sampling system and
sample gas conditioning system. Dinitrogen monoxide
IS0 7996: 1985, Ambient air - Determination of the
(N,O) is not determined by the methods described in
mass concentration of nitrogen oxides -
this International Standard. The given performance
Chemiluminescence method.
characteristics refer to the complete measuring sys-
tem, from sampling to analyser.
IS0 9096:1992, Stationary source emissions - De-
termination of concentration and mass flow rate of
This International Standard describes extractive and
particulate material in gas-carrying ducts - Manual
non-extractive systems in connection with a range of
gravime tric method.
analysers that operate using, for example, the follow-
ing principles:
IS0 9169:1994, Air quality - Determination of per-
formance characteristics of measurement methods.
- chemiluminescence;
IS0 10396: 1993, Stationary source emissions -
- non-dispersive infrared spectroscopy;
Sampling for the automated determination of gas
concentrations.
- non-dispersive ultraviolet spectroscopy;
- differential optical absorption spectrometry.
3 Definitions
NOTE 1
Commercial devices using the described tech-
niques, that meet the requirements of this International
For the purposes of this International Standard, the
Standard, are available.
following definitions apply.
3.1 automated measuring system (AMS): System
2 Normative references that may be attached to a chimney to continuously
measure and record the mass concentration of nitro-
The following standards contain provisions which, gen oxides passing through the chimney.
through reference in this text, constitute provisions
of this International Standard. At the time of publi- 3.2 analyser: Analytical part in an extractive AMS.
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IS0 10849:1996(E)
- the mass concentration of nitrogen oxides in waste gas
3.3 verified (AMS): AMS previously verified against
usually varies with time;
this International Standard.
- it is not possible to maintain the properties of a waste
gas present in the waste gas flue in a waste gas sample
3.4 calibration gas: Gas of known, reliable and sta-
transferred into a vessel.
ble composition that may be used to check the re-
sponse of the AMS and should be used for the
Therefore, the evaluation of the standard deviation, $A, is
calibration of the AMS.
performed by comparison with an independent manual
method or an analyser with a different principle of detection.
3.5 comparative measurements: Measurements
Applying the comparative method in combination with the
that are taken on the same chimney in the same
test for systematic errors ensures a satisfying accuracy of
sampling plane for the same period of time, with the the automated measuring system.
AMS under test and with the comparative method
4 The standard deviation, SA, is a measure of the working
providing pairs of measured values.
precision under site conditions. Therefore, it contains, in
addition to random errors, the effects of interfering sub-
stances, the effects of temperature changes and of any zero
3.6 comparative method: Defined test method for
and span drifts, because they cannot be eliminated in prac-
the comparative measurements of stationary source
tice.
emissions containing nitrogen oxides. This can be a
manual method or an AMS verified according to this
The standard deviation, SA, is an upper limiting value for the
International Standard, with a different measuring
AMS. Known systematic errors of the measured values of
principle.
the independent comparative method are to be taken into
account.
NOTE 2 The naphthylethylenediamine (NEDA) method
according to IS0 II 564, has been proven to be a suitable 5 This procedure is suitable for finding the precision of the
measuring result of the automated measuring method, as
manual method. Also, validated national standards with
long as the standard deviation, sc, of the measured values
known performance characteristics (standard deviation,
of the comparative method is significantly smaller than the
lower detection limit, effect of interfering substances) may
be applied. standard deviation, SD, of the difference in pairs of measured
values.
If the AMS under investigation has a substantially smaller
3.7 standard deviation, s*: Measure of the working
standard deviation, SA, than the comparative method, sc, the
precision of the AMS.
method above can still be used, although the value of SA
will have a large uncertainty. If the uncertainty in S, is un-
The standard deviation, q, is derived from the differ-
known and hence the limits of SA cannot be established, the
ence in the pairs of measured values of nitrogen ox-
value of SA can be used as a qualitative rather than a quan-
ides by the AMS under test and the comparative
titative assessment of the AMS performance.
method, on the basis of a sufficient number of com-
parative measurements spread over the period of un-
3.8 chimney: Stack or final exit duct on a stationary
attended operation (see annex A).
process used for the dispersion of residual process
gases.
compara-
is the standard deviation of the
SC
tive method.
3.9 mass concentration: Concentration of a sub-
stance in an emitted waste gas, expressed in milli-
is the standard deviation of the paired val-
grams per cubic metre.
NOTE 6 The concentration of nitrogen oxides can be ex-
is the standard deviation of the blank
SX
pressed as ppm, as milligrams of NO per cubic metre or as
readings.
milligrams of NO2 per cubic metre.
NOTES
NO: 1 ppm (V/V) = I,34 mg/m3
3 It is not possible to determine directly the standard de-
NO,: I ppm (V/V) = 2,05 mg/m3
viation, SA, of an AMS under repeatable working conditions
or in a laboratory, because:
Concentrations should be related to standard atmospheric
conditions (273 K, 101,3 kPa) and dry gas.
- commercially available calibration gas mixtures contain-
II the properties of Depending on national regula tions, the concen trations
ing nitrogen monoxide do not have a
all possible inf ‘Iu- should be referred to defined oxygen or carbon dioxide
actual waste gas and do not cover
concentrations.
ences;
2
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IS0 10849:1996(E)
0 IS0
In most of the cases, it is considered that only nitro-
In this International Standard, all concentrations of nitrogen
oxides are expressed as milligrams of NO2 per cubic metre.
gen monoxide has to be measured, because the NO,
content is negligible. However, in some cases nitro-
3.10 stationary source emissions: Those gases
gen dioxide may occur in large quantities and has to
that have been emitted by a stationry plant or process
be taken into account, either by direct measurement
and are transported to a chimney for dispersion into
or by using a converter. The sampling will, however,
the atmosphere.
be difficult, due to the high reactivity of nitrogen di-
oxide.
3.11 calibration curve: Curve describing the de-
pendence of the measured signal on a given cali-
bration gas.
5 Description of the measuring
equipment
3.12 period of unattended operation: Maximum
admissible interval of time for which the performance
characteristics will remain within a predefined range
ng and sample gas
5.1 Sampli conditioning
without external servicing, e.g. refill, calibration, ad-
systems for extractive systems
justment. [ISO 68791
5.1 .I General
For long-term monitoring installations a mini-
NOTE 7
mum of 7 d of unattended operation is required.
A more detailed description of sampling and sample
gas conditioninq systems for extractive methods is
3.13 calibration: Setting and checking of the AMS
given in IS0 10396.
before determining the performance characteristics
or before beginning any measurement of NO,. Further
Figure 1 a) shows a typical arrangement of a complete
steps of the calibration of an AMS, like comparative
measuring system for NO. This system is suitable for
measurements, may be part of national regulations.
use with all the analysers that are described in 5.2.
4 Principle
In addition to this arrangement, there are also auto-
mated measuring systems for the NO, measurement
With extractive systems, a representative sample of
that heat the sample gas to above water and acid
gas is taken from the stack with a sampling probe and
dew-points (or the dew-point of other condensable
conveyed to the analyser through the sample line and
substances) to avoid losses of NO,. In this case, the
sample gas conditioning system.
system can be simplified. It is important that all the
components carrying the sample gas to the analyser
Non-extractive systems do not require any sampling
are also heated above water and acid dew-points.
transfers out of the stack. For the installation of these
systems, a representative place in the stack is to be
In the case that higher amounts of NO, are in the
chosen. /n-situ systems may sample a larger part of
sample gas, the use of a gas cooler can produce er-
the flue gas.
rors on the NO, measurement due to the solubility
of NO, in the condensed water and depending on the
The values from the analyser are recorded and/or
content of water vapour in the flue gas. A possible
stored by means of el ectronic data processing.
arrangement to avoid losses of NO, is shown in
figure 1 b).
The systems described here basically only measure
nitrogen monoxide. If, with the systems, the nitrogen
The sampling of gas shall be representative, that is,
dioxide content or the total quantity of the nitrogen
the sampling location shall be typical of the entire
oxides (NO + NO,) is to be determined, a converter
duct. The representativeness of the sampling location
to reduce nitrogen dioxide to nitrogen monoxide is to
requires confirmation by means of a network
be used. The converter may be a separate piece of
measurement in accordance with the guidelines given
equipment or incorporated into the NO analyser.
in IS0 10396. The sampling points for the network
measurement shall be located in accordance with
Systems also exist, mainly using ultraviolet tech-
IS0 9096. Checking of representativeness shall be
niques, that can monitor nitrogen dioxide directly.
done before the first installation of a measuring sys-
These systems are mostly combined with NO ana-
tem and shall be repeated in the case of uncertainty.
lysers.
3
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IS0 10849:1996(E)
a) NO-measuring device
II
b) NO/NO,-measuring device
Key:
Flowmeter
9
1 Gas sampling probe
IO NO-analyser
2 Particulate filter
1 I Recorder
3 Heating
front of
12 Inlet for zero and calibration gas (preferably in
4 Sampling line
the filter) to check the complete system
(heated if necessary)
13 Bypass for excess gas
5 Sample cooler with condensate separator
14 Inlet for zero and span gas to check the analyser
Sample pump
6
15 Converter
7 Filter
16 NO/NO,-analyser
8 Needle valve
Examples of the installation of measuring devices
Figure 1 -
4
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0 IS0 IS0 10849:1996(E)
The components described in 5.1.2.1 to 5.1.2.8 have, 30 I/h and 500 l/h, dependent upon the analyser and
the expected response time.
for example, proven to be successful for measure-
oil- and coal-fired plants (precautions
ments at gas-,
need be observed because of the high corrosiveness
of condensable acid gases, e.g. HCI, SO3 or NO,). 5.1.2.6 Secondary filter, to separate fine dust, with
a pore size of I pm to 2 pm, made for example from
glass fibre, sintered ceramics, stainless steel or PTFE
e. I
tjbre.
5.1.2 Components
probe, made of suitable,
5.1.2-l Sampling
corrosion-resistant material. For gas temperatures up 5.1.2.7 Flow controller and flowmeter, to set the
to 220 “C, polytetrafluoroethylene (PTFE) is an ac- required flow and constructed of corrosion-resistant
ceptable material. At temperatures > 250 “C, stain- material.
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 5.1.2.8 NOz/NO converter, necessary if NO, has to
ratio. Cooling may be considered necessary in order be measured with a NO analyser (only possible in
to maintain the gas concentrations in the flue gas. combination with extractive systems).
Different types of converters exist, for example:
5.1.2.2 Filter, made of ceramic or sinter metal with
- carbon converters;
10 pm pore size. The filter shall be heated above the
water or acid dew-point.
- carbon-molybdenum converters;
- stainless steel converters;
5.1.2.3 Sample line, made of PTFE or stainless
steel. The lines shall be operated 15 K above the
- thermal converters.
dew-point of condensable substances (generally the
water or acid dew-point). The inner diameter of the
In some situations (e.g. when ammonia is present in
line depends on the quantity of sample gas required,
the sample gas) interferences can occur depending
with 4 mm as a minimum (and preferably 4 mm to
on the operating temperature of the converter. In
8 mm).
these cases, it is necessary to take into account such
possibilities when selecting the converter type.
The converter can be bypassed with a three-way
5.1.2.4 Sample cooler or permeation drier, to
separate water vapour from the flue gas. The dew- valve. If the sample gas flows through the converter,
point shall be sufficiently below the ambient tem- the total quantity (NO + NO,) is obtained; when the
perature. A cooling temperature of 2 “C to 5 “C is converter is bypassed, the NO content is obtained.
The amount of NO, can be calculated as the differ-
convenient. Sufficient cooling is required for the vol-
ence between NO, and NO.
ume of gas being sampled and the amount of water
vapour that it contains.
The converter shall have an efficiency > 95 %, which
can be tested using calibration gases containing NO,
The design of the sample gas cooler shall be such that
in synthetic air, or with a converter efficiency tester.
absorption of NO, in the condensate is restricted to
This method is described in detail in IS0 7996 and it
a minimum. This ensures that loss of NO, dissolved
is not suitable if the NO analyser is prone to interfer-
in the condensate, which is drained from the sample
cooler, is at a minimum. ence by ozone.
The principle of an efficiency tester is shown in
The use of a permeation drier also ensures that NO,
figure2. A constant flow of a NO-calibration gas is
losses are negligible.
mixed with a constant flow of air or oxygen, that
contains different amounts of ozone, produced by an
5.1.2.5 Sampling pump (corrosion-resistant), of adjustable ozone generator. Ozone reacts with NO to
which the performance shall be such that it can sup- produce NO,. Thus the total amount of nitrogen ox-
ides (NO + NO,) remains constant, while the ratio
ply the connected analyser with its required gas flow.
(NO:NO,) changes .
The quantity of sample gas required can vary between
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IS0 10849:1996(E)
6
Key:
1 NO-calibration gas
2 Needle valve
3 Flowmeter
4 Oxygen
5 Ozone generator (adjustable)
6 Bypass for excess test gas
7 Test gas for converter + analyser
Figure 2 - Principle of an efficiency tester for NOz/NO converters
If the converter efficiency is > 95 %, the signal of the
5.2 Measuring principles of analysers
analyser, combined with the tested converter, re-
The following examples describe typical principles
mains nearly constant. The signal of every different
found in existing analysers. The performance charac-
concentration is compared with the signal of the gas
teristics described in clause 6 are applicable both to
mixture containing NO only (with the ozone generator
existing equipment and to future developments.
switched off). At each different ozone concentration,
the concentration of NO and (NO + NO,) of the gas
5.2.1 Chemiluminescence method
mixture shall be determined. N,O is not converted to
NO. Dinitrogen pentoxide (N20s) is converted to NO.
The principle of the chemiluminescence method for
the determination of the mass concentration of nitro-
5.1.3 Dilution
gen oxides in ambient air is described in IS0 7996.
The dilution technique is an alternative to hot gas If NO reacts with ozone (O,), NO, is formed. Part of
monitoring or sample gas drying. The flue gas is di- this NO, is in a photochemically excited state. When
luted with a dilution gas which shall be free from ni-
returning to the basic state, these NO, molecules can
trogen oxides. radiate light in the wavelength range of 590 nm to
3 000 nm. The intensity of this light depends on the
The dilution ratio shall be chosen according to the
NO content and is influenced by the pressure and
objectives of the measurement and shall be compat-
presence of other gases.
ible with the range of the analytical unit. It shall re-
main constant throughout the period of the test. The Figure 3 shows the basic arrangement of a
chemiluminescence analyser.
water dew-point shall be reduced so as to reduce the
risks of condensation in the gas loops. The measured
There are atmospheric pressure and low pressure
values always refer to the wet gas.
analysers, depending on the pressure in the reaction
chamber. Some analysers have built-in NO,/NO con-
Analysers which are used in combination with dilution
verters and, because of their structure, give signals
probes have measuring ranges which are typical for
for NO, NO, and NO, either simultaneously or in se-
ambient air analysers to 1 mg/m3,
(0 mm3
quence.
5 mg/m3, 10 mg/m3 or 25 mg/m3).
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IS0 10849:1996(E)
15
6
2 3 4 3
r-------w--*
A -
- n
A IL
17
8 9
-s v
1
I
l-jr
I
m
Key:
9 Electronics
1 Sample inlet
pump 10 Oxygen inlet
2 Sample
3 Magnetic valve 1 I Pressure regulator
12 Ozone regulator
4 NOz/NO converter
13 Ozone filter
5 Flow regulator
14 Signal
6 Pressure regulator
7 Reaction chamber 15 Bypass
8 Photomultiplier
Basic arrangement of a chemiluminescence analyser
Figure 3 -
Gases which consist of molecules of different atoms
The measuring range of chemiluminescence ana-
absorb light of the characteristic wavelength in the
lysers used for emission measurements extends from
infrared spectral region.
10 mg/m3 to 20 000 mg/m3. The minimum measuring With the NDIR method,
range that is known to meet the performance char- spectral analysis of the IR radiation is omitted and the
total absorption of the NO molecule at I+-,-.,~~ =
acteristics of this International Standard is 0 mg/m3 to
1 876 cm-’ ( = 5,3 pm) is used for the measurement.
200 mg/m3.
Interference due to carbon dioxide (CO,) in the sam-
Figure4 shows an example of a typical NDIR analyser.
ple gas is possible, particularly in the presence of
due to quenching of the The radiation emitted from the IR source is divided
water vapour,
into two beams and then modulated, one beam
chemiluminescence. The extent of the quenching de-
passing through the measuring cell and the other
pends on the CO, and H,O concentrations and the
through the reference cell containing an IR inactive
type of analyser used. Any necessary corrections shall
gas, usually nitrogen. If the sample gas contains NO,
be made to the analyser output either by reference to
some of the IR energy is absorbed and the difference
correction curves supplied by the manufacturers or
in IR energy reaching the detector is proportional to
by calibrating with gases containing approximately the
the amount of NO present. The detector is designed
same concentration of CO, as the sample gas.
so that it is only sensitive to the NO-specific wave-
5.2.2 Non-dispersive infrared (NDIR) method lengths.
A special arrangement of the NDIR method is the gas
The most common application of the IR method are
filter correlation method.
analysers working according to the NDIR method.
7
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IS0 10849:1996(E)
Key:
cell
1 Light source 5 Reference
2 Chopper motor 6 Detector
7 Electronics
3 Chopper wheel
4 Measuring cell 8 Signal
Figure 4 - Example of a NDIR analyser
nanometres. The two beams meet alternately via a
A minimum measuring range of 0 mg/m3 to
semipermeable mirror on the reference detector and
200 mg/m3 is possible. Each analyser can be used
the measuring detector. NO in the sample gas ab-
only for the scheduled concentration range.
sorbs resonant lines from the measuring beam and
Interference is possible, particularly with water va-
this absorption depends on the concentration of NO.
pour.
Thus, there are four signals at the two detectors and
they are processed in a microcomputer. The resultant
5.2.3 Non-dispersive ultraviolet (NDUV) method
signal represents a measure for the concentration of
NO. The microcomputer also converts the signals to
The described system is a typical example of the ap-
give a linear output.
plication of the NDUV method. However, other sys-
tems exist.
A minimum measuring range of 0 mg/m3 to
200 mg/m’ is possible with this method.
This method is based on the resonance absorption of
a line multiplet emerging from a hollow-cathode dis-
These UV instruments can suffer from interference
charge lamp through the NO monoxide in the sample
due to SO, in the flue gas sample. This interference
gas.
can be minimized by internal adjustments in the ana-
lysers. In addition, the presence of NO, or aromatic
Figure 5 shows the basic arrangement of the analyser.
compounds in the sample may cause slight interfer-
ence.
A hollow-cathode discharge lamp filled with nitrogen
and oxygen emits a line multiplet which is character-
istic of NO in the range of 226 nm. This beam con-
5.2.4 Non-extractive method (in situ)
sists of resonant lines which are absorbed by NO and
also of non-resonant lines. A rotary chopper wheel
There are two different kinds of in situ methods:
with two cells is connected to the hollow-cathode
discharge lamp. One of the cells is filled with con-
- traversal method (path monitor);
centrated NO, the other is empty. The resonant lines
of the beam are filtered through the cell filled with
- point method.
NO. Thus, two beams are obtained alternately: a
The signals from the in situ instruments always refer
measuring beam of resonant and non-resonant lines
to the wet gas. If the result of the measurement has
and a reference beam of non-resonant lines. Only the
to be referred to dry gas, a correction factor is
range around 226 nm is transmitted through a sub-
needed.
sequent interference filter with a bandwidth of several
---------------------- Page: 12 ----------------------
IS0 10849:1996(E)
Key:
lamp 7 Semipermeable mirror
1 Hollow-cathode discharge
8 Measuring cell
2 Motor
9 Reference detector
3 NO cell
4 Empty cell 10 Measuring detector
5 Collimator 11 Electronics
Signal
12
6 Interference filter
Figure 5 - Example of a NDUV analyser
The system consists of the following major units: an
5.2.4.1 Traversal method
optical head unit, a reflector unit, a control box and
The traversal method takes into consideration a larger
two purging units.
volume of the waste gas than the point method. It
A deuterium lamp is used as a light source and radi-
uses an optical mode directly in the duct of gaseous
ates in the bandwidth from the ultraviolet to the vis-
effluents. It includes two modules, the first is a radi-
ible range. By using a special grid, radiation in the
ation emission module, the second ensures reception
wavelength range 218 nm to 233 nm is selected. The
of these radiations after passing through the gas
detector is an array of photodiodes. In addition, the
containing nitrogen oxides.
intensity of the light emitted from the light beam
The examples given in 5.2.4.1 .I and 5.2.4.1.2 briefly
which crosses the stack is measured with a reference
describe two instruments which meet the per-
detector.
formance characteristics of this International Stan-
The NO concentration is calculated from the intensity
dard.
of the different signals, the stored NO spectrum and
5.2.4.1 .I Figure 6, which is typical for path moni- with reference to the stack gas temperature.
tors, shows the principle of the first instrument.
The range of application depends on the diameter of
This instrument uses the ultraviolet part of the spec- the stack; a minimum measuring range of 0 mg/m3 to
trum, namely the range 218 nm to 233 nm. Gases
150 mg/m3 is possible.
other than NO and SO, do not absorb at all in this
Sulfur dioxide (SO,) is a possible interferent and can
wavelength range, or only with very small or constant
also be measured with this method.
absorption coefficients.
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IS0 10849:1996(E)
24 23
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Key:
1 Deuterium lamp 13 Swivel window*)
2 Condenser 14 Diaphragm*)
3 Filter wheel and control filters 15 Front window
4 Beam splitter 16 Objective mirror
5 Position sensor 17 Concave grid mirror
6 Pre-amplifiers 18 Dete
...
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