EN 14791:2005

SLOVENSKI STANDARD
01-december-2005
(PLVLMHQHSUHPLþQLKYLURY±'RORþHYDQMHPDVQHNRQFHQWUDFLMHåYHSORYHJD
GLRNVLGD±5HIHUHQþQDPHWRGD
Stationary source emissions - Determination of mass concentration of sulphur dioxide -
Reference method
Emissionen aus stationären Quellen - Bestimmung der Massenkonzentration von
Schwefeldioxid - Referenzverfahren
Emissions de sources fixes - Détermination de la concentration massique du dioxide de
soufre - Méthode de référence
Ta slovenski standard je istoveten z: EN 14791:2005
ICS:
13.040.40 (PLVLMHQHSUHPLþQLKYLURY Stationary source emissions
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 14791
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2005
ICS 13.040.40
English Version
Stationary source emissions - Determination of mass
concentration of sulphur dioxide - Reference method
Emissions de sources fixes - Détermination de la Emissionen aus stationären Quellen - Bestimmung der
concentration massique du dioxide de soufre - Méthode de Massenkonzentration von Schwefeldioxid -
référence Referenzverfahren
This European Standard was approved by CEN on 30 September 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14791:2005: E
worldwide for CEN national Members.

Contents Page
Foreword .5
1 Scope .6
2 Normative references .6
3 Terms, definitions, symbols and abbreviations .6
3.1 Terms and definitions.6
3.2 Symbols.11
3.3 Abbreviations .12
4 Principle.13
4.1 General .13
4.2 Measuring principle .13
5 Reagents.13
5.1 General .13
5.2 Hydrogen peroxide .13
5.3 Water.13
5.4 Absorption solution, H O .13
2 2
5.5 Reagents for chromatographic analysis .14
5.5.1 Eluent solution .14
2−
-3
5.5.2 Standard sulphate stock solution, 10,4x10 mol/l SO .14
5.5.3 Regeneration solution for suppressor .14
5.6 Reagent for Thorin analysis.14
5.6.1 2-propanol [CH CH(OH)CH ].14
3 3
5.6.2 Barium perchlorate, standard volumetric solution, [Ba(CIO ) ] = 0,005 mol/l.14
4 2
5.6.3 Potassium hydroxide, standard volumetric solution, [KOH] = 0,1 mol/l.15
5.6.4 Perchloric acid, standard volumetric solution, [HClO ] = 0,1 mol/l.15
5.6.5 Thorin, {4-[2-arsonophenyl)-azo]-3-hydroxy-2,7 naphthalene-disulfonic acid disodium salt} 2
g/l solution.15
6 Sampling equipment.15
6.1 General .15
6.2 Sampling probe.15

6.3 Filter housing .16
6.4 Particle filter .16
6.5 Temperature controller.16
6.6 Absorbers.16
6.6.1 General .16
6.6.2 Test of absorption efficiency .17
6.7 Sampling pump .17
6.8 Gas volume meter.17
7 Sampling procedure .18
7.1 General requirements.18
7.2 Preparation and installation of equipment.18
7.2.1 Sampling location .18
7.2.2 Sampling point(s).18
7.2.3 Assembling the equipment .19
7.2.4 Heating of the sampling line .19
7.2.5 Leak test .19
7.3 Performing sampling .19
7.3.1 Introduction of the probe in the duct.19
7.3.2 Sampling.19
7.3.3 Rinsing of the sampling system and preparation of the samples.20
7.4 Measuring series.20
7.5 Field blank .20
7.6 Absorption efficiency .21
8 Analysis equipment .21
8.1 Ion chromatograph .21
8.2 Thorin method.22
8.2.1 General .22
8.2.2 Spectrophotometer (optional).22
8.2.3 Glass optical cuvette .22
9 Analytical procedure.22
9.1 General .22
9.2 Ion Chromatography method.22
9.2.1 General procedure .22
9.2.2 Interferences .23
9.2.3 Calibration .23
9.3 Thorin Method.24
9.3.1 Pre-treatment of sample solution before analysis for Thorin method.24
9.3.2 General procedure .24
9.3.3 Preparation of a chemical blank solution .25
9.3.4 Interferents .25
10 Determination of the characteristics of the method: sampling and analyse.26
10.1 General .26
10.2 Relevant performance characteristics of the method and performance criteria .26

10.2.1 General .26
10.2.2 Sampling procedure .26
10.2.3 Analyse procedure.27
10.3 Establishment of the uncertainty budget.28
11 Expression of results.29
12 Evaluation of the method in the field.31
13 Equivalence of Thorin and ion chromatography methods .31
13.1 General .31
13.2 Range.31
13.3 Matrix effect.31
13.4 Comparison of repeatability and trueness.31
14 Equivalence with an alternative method .31
15 Test report .32
Annex A (informative) Type of sampling equipment.33
Annex B (informative) Examples of absorbers.34
Annex C (informative) Example of assessment of compliance or reference method for SO with
requirements on emission measurements.35
Annex D (informative) Evaluation of the method .43
Annex E (informative) Test of equivalency of Thorin method and ion chromatography .50
Annex ZA (informative) Relationship with EU Directives .60
Bibliography.61
Foreword
This European Standard (EN 14791:2005) has been prepared by Technical Committee CEN/TC 264 “Air quality”,
the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by May 2006, and conflicting national standards shall be withdrawn at the latest by
May 2006.
This European Standard has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive(s).
For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this European Standard.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
1 Scope
This European Standard describes a manual method for sampling and determining SO content in ducts and
stacks emitting to the atmosphere by two analytical methods: Ion chromatography and Thorin method.
This European Standard is the Standard Reference Method (SRM) for periodic monitoring and for calibration or
control of Automatic Measuring Systems (AMS) permanently installed on a stack, for regulatory purposes or other
purposes. To be used as the SRM, the user shall demonstrate that the performance characteristics of the method
are better than the performance criteria defined in this European Standard and that the overall uncertainty of the
method is less than ± 20,0 % relative at the daily Emission Limit Value (ELV).
An Alternative Method to this SRM may be used provided that the user can demonstrate equivalence according to
the Technical Specification CEN TS 14793, to the satisfaction of his national accreditation body or law.
This Standard Reference Method has been evaluated during field tests on waste incineration, co-incineration and
large combustion installations. It has been validated for sampling periods of 30 min in the range of
3 3 3
(0,5 to 2 000) mg/m SO for Ion Chromatography variant and 5 mg/m to 2 000 mg/m SO for Thorin method
2 2
according to emission limit values laid down in the following Council Directives:
 Council Directive 2001/80/EC on the limitation of emissions of certain pollutants into the air from large
combustion plants;
 Council Directive 2000/76/EC on waste incineration plants.
The limit values of EU Directives are expressed in mg SO /m , on dry basis and at the reference conditions of

273 K and 101,3 kPa.
2 Normative references
The following referenced documents are indispensable for the application of this European Standard. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ENV 13005, Guide to the expression of uncertainly in measurement.
EN 13284-1, Stationary source emissions — Determination of low range mass concentration of dust — Part 1:
Manual gravimetric method.
CEN/TS 14793, Stationary source emission — Intralaboratory validation procedure for an alternative method
compared to a reference method.
3 Terms, definitions, symbols and abbreviations
3.1 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1.1
absorber
device in which sulphur oxide is absorbed into an absorption liquid
3.1.2
absorption efficiency (εε)
εε
ratio ε of quantity of the analyte q collected in the first absorber divided by the quantity of the analyte collected in
the first and the second absorber (q + q )
1 2
ε = q / (q + q )
1 1 2
3.1.3
analytical detection limit (L )
D
concentration value of the measurand below which there is at least 95 % level of confidence that the measured
value corresponds to a sample free of that measurand
3.1.4
automatic measuring system (AMS)
measuring system permanently installed on site for continuous monitoring of emissions
NOTE 1 An AM is a method which is traceable to a reference method.
NOTE 2 Apart from the analyser, an AMS includes facilities for taking samples (e.g. probe, sample gas lines, flow meters,
regulators, delivery pumps) and for sample conditioning (e.g.dust filter, moisture removal devices, converters, diluters). This
definition also includes testing and adjusting devices, that are required for regular functional checks.
3.1.5
calibration of an AMS
statistical relationship between values of the measurand indicated by the measuring system (AMS) and the
corresponding values given by the standard reference method (SRM) used during the same period of time and
giving a representative measurement on the same sampling plane
NOTE The result of calibration permits to establish the relationship between the values of the SRM and the AMS
(calibration function).
3.1.6
calibration of the SRM
set of operations that establish, under specified conditions, the relationship between values of quantities indicated
by a measuring instrument or measuring system, and the corresponding values realized by standard reference
methods implemented in the state of the art in order to provide representative results
[VIM]
3.1.7
chemical blank value
sulphate ion content of an unexposed sample of the absorption solution, plus reagents that are added to the
solution before analysis if necessary
3.1.8
emission limit value (ELV)
emission limit value according to EU Directives on the basis of 30 min, 1 h or 1 day
3.1.9
field blank
value determined by a specific procedure used to ensure that no significant contamination has occurred during all
steps of the measurement and to check that the operator can achieve a quantification level adapted to the task
3.1.10
influence quantity
quantity that is not the measurand but that affects the result of the measurement
[adapted VIM 2.7]
Examples
 ambient temperature;
 atmospheric pressure;
 presence of interfering gases in the flue gas matrix.
3.1.11
measurand
particular quantity subject to measurement
[VIM 2.6]
3.1.12
measurement series
several successive measurements carried out on the same sampling plane and at the same process operating
conditions
[EN 13284-1]
3.1.13
measuring system
complete set of measuring instruments and other equipment assembled to carry out specified measurements
[VIM 4.5]
3.1.14
performance characteristic
one of the quantities (described by values, tolerances, range, …) assigned to equipment in order to define its
performance
3.1.15
repeatability in the laboratory
closeness of the agreement between the results of successive measurements of the same measurand carried out
under the same conditions of measurement
NOTE 1 Repeatability conditions include:
 same measurement procedure;
 same laboratory;
 same sampling equipment, used under the same conditions;
 same location;
 repetition over a short period of time.
NOTE 2 Repeatability may be expressed quantitatively in terms of the dispersion characteristics of the results.
In this European Standard the repeatability is expressed as a value with a level of confidence of 95 %.
[VIM 3.6]
3.1.16
repeatability in the field
closeness of the agreement between the results of simultaneous measurements of the same measurand carried
out with two equipments under the same conditions of measurement
NOTE 1 These conditions include:
 same measurement procedure;
 two equipments, the performances of which are fulfilling the requirements of the reference method, used under the same
conditions;
 same location;
 implemented by the same laboratory;
 typically calculated on short periods of time in order to avoid the effect of changes of influence parameters (e.g. 30 min).
NOTE 2 Repeatability may be expressed quantitatively in terms of the dispersion characteristics of the results.
In this European Standard the repeatability under field conditions is expressed as a value with a level of confidence
of 95 %.
3.1.17
reproducibility in the field
closeness of the agreement between the results of simultaneous measurements of the same measurand carried
out with several sets of equipment under the same conditions of measurement
NOTE 1 These conditions are called field reproducibility conditions and include:
 same measurement procedure;
 several sets of equipment, the performance of which fulfils the requirements of the reference method, used under the same
conditions;
 same location;
 implemented by several laboratories.
NOTE 2 Reproducibility may be expressed quantitatively in terms of the dispersion characteristics of the results.
In this European Standard the reproducibility under field conditions is expressed as a value with a level of
confidence of 95 %.
3.1.18
sampling location
specific area close to the sampling plane where the measurement devices are set up
3.1.19
sampling plane
plane normal to the centreline of the duct at the sampling position
[EN 13284-1]
3.1.20
sampling point
specific position on a sampling plane at which a sample is extracted
[EN 13284-1]
3.1.21
standard reference method (SRM)
measurement method recognised by experts and taken as a reference by convention, which gives, or is presumed
to give, the accepted reference value of the concentration of the measurand (3.1.11) to be measured
3.1.22
uncertainty
parameter associated with the result of a measurement, that characterises the dispersion of the values that could
reasonably be attributed to the measurand
3.1.22.1
standard uncertainty u
uncertainty of the result of a measurement expressed as a standard deviation u
3.1.22.2
combined uncertainty u
c
standard uncertainty u attached to the measurement result calculated by combination of several standard
c
uncertainties according to GUM
3.1.22.3
expanded uncertainty U
quantity defining a level of confidence about the result of a measurement that may be expected to encompass a
specific fraction of the distribution of values that could reasonably be attributed to a measurand
U = k x u
NOTE In this European Standard, the expanded uncertainty is calculated with a coverage factor of k = 2, and with a level of
confidence of 95 %.
3.1.22.4
overall uncertainty U
c
expanded combined standard uncertainty attached to the measurement result calculated according to GUM
U = k x u
c c
3.1.23
uncertainty budget
calculation table combining all the sources of uncertainty according to EN ISO 14956 or ENV 13005 in order to
calculate the overall uncertainty of the method at a specified value
3.2 Symbols
C mass concentration of sulphur dioxide in the sample gas, in milligrams per cubic metre (of gas)
m
repeatability confidence interval, in milligrams per cubic metre
Cl
r
Cl reproducibility confidence interval, in milligrams per cubic metre
R
f equivalent mass of sulphur dioxide of 1 mm of titration solution (barium perchlorate standard
a
volumetric solution) used for titration in Thorin method, in milligrams per millilitre
f ratio of the volume of the pre-treated sample solution (sample absorption solution pre-treated
v
before analyse) to the volume of the aliquot taken for the titration in Thorin method
L limit of detection, in milligrams per litre of SO
D
L limit of quantification, in milligrams per litre of SO
Q
m weight of the sample solution (absorption solution used for sampling + rinsing solution), in grams
s
P absolute pressure at the gas volume meter, in kilopascals
m
P standard pressure: 101,3 kPa
std
P saturation vapour pressure of water at volume gas meter temperature, in kilopascals
sat (Tm)
q mass concentration of sulphate in sample absorption solution, in milligrams per litre (of solution)
s
q mass concentration of sulphate in chemical blank solution, in milligrams per litre (of solution)
cb
r repeatability, in milligrams per cubic metre or percentage
R reproducibility, in milligrams per cubic metre or percentage
R peak resolution S : volume of titration solution used for titration of sample absorption solution, in
s s
millilitre
S volume of titration solution used for titration of chemical blank solution, in millilitre
cb
S repeatability standard deviation, in milligrams per cubic metre or percentage
r
S reproducibility standard deviation, in milligrams per cubic metre or percentage
R
S maximum allowable repeatability standard deviation, in milligrams per cubic metre
r limit
S volume of titration solution used for the titration of the aliquot of the pre-treated sample solution, in
s
millilitres
t retention time of the first peak, in seconds
t retention time of the second peak, in seconds
T temperature at the gas meter, in Kelvin
j
T mean temperature at the gas volume meter in Kelvin
m
T standard temperature, 273 K
std
V reading at the gas volume meter at the beginning of the sampling period in cubic metres
V reading at the gas volume meter at the end of the sampling period in cubic metres
V dry gas volume measured, corrected to standard conditions, in cubic metres
m (std)
V volume of the sample solution (absorption solution used for sampling + rinsing solution), in litres
s
w peak width, on the time axis, of the first peak, in seconds
w peak width on the time axis, of the second peak, in seconds
ε absorption efficiency in percentage
σ conductivity in micro-siemens per metre
ρ density of a liquid at 20 °C compared to water's at 4 °C in kilogrammes per litre
χ volume content in percentage
3.3 Abbreviations
PE Polyethene
PTFE Polytetrafluoroethene
4 Principle
4.1 General
This European Standard describes the Standard Reference Method (SRM) with two alternative analytical
techniques for determining sulphur dioxide (SO ) content emitting to atmosphere from ducts and stacks. The
specific components and the requirements for the measuring system are described. A number of performance
characteristics with associated minimum performance criteria are specified for the measuring system (see Tables 2
and 3 in 10.2). These performance characteristics and the overall uncertainty of the method shall meet the
specifications given in this European Standard.
4.2 Measuring principle
A representative sample of gas is extracted via a heated temperature-controlled probe. The sample is filtered and
drawn through hydrogen peroxide absorber solutions for a specified time and at a controlled flow rate. The sulphur
dioxide in the sampled gas is absorbed and oxidised to sulphate ion. The mass concentration of sulphate in the
absorption solutions is subsequently determined using ion chromatography or by titration with a barium perchlorate
solution using Thorin as indicator. SO is also absorbed and transformed in sulphate ion and is therefore an
interferent.
This European Standard has been validated with a 0,3 % H O absorption solution up to 1 000 mg/m and with a
2 2
3,0 % H O absorption solution up to 2 000 mg/m . Typical concentration of the absorption solution is 0,3 % H O .
2 2 2 2
However, for concentrations higher than 1 000 mg/m it is recommended, in case of a bad efficiency either to
decrease the flow or to increase the concentration.
5 Reagents
5.1 General
During the analysis, use only reagents of recognised analytical grade.
Normal, accepted laboratory safety practices and cleaning procedures for glassware should be followed during
reagent preparation.
WARNING — Use the reagents in accordance with the appropriate health and safety regulations.
5.2 Hydrogen peroxide
Commercially available solution of H O mass content 30 %, = 1,11 kg/l.
ρ
;
2 2
5.3 Water
–1
H O; ultra pure water with conductivity σ < 10 µS m .
5.4 Absorption solution, H O
2 2
The absorption solution is a hydrogen peroxide solution (5.2) diluted to a mass concentration of 0,3 % H O in
2 2
water (5.3). For concentrations higher than 1 000 mg/m it is suggested in case of a bad efficiency, either to
decrease the flow, or increase the concentration of the absorption solution.
For the preparation of the mass concentration of 0,3 % H O in water, thoroughly mix about 10 ml of 30 % of H O
2 2 2 2
(5.2) with 500 ml of water (5.3) and make up to 1 000 ml with water (5.3). Store the solution in a glass or PE bottle
in a dark place and for no longer than one week.
WARNING — Decomposition of the solution may occur and may lead to the explosion of the storage bottle.
It is recommended that the lid of this bottle is not closed too tightly or to use a security cap.
NOTE Cleanliness of the glassware is important to avoid a possible decomposition of hydrogen peroxide.
5.5 Reagents for chromatographic analysis
5.5.1 Eluent solution
The choice of eluent depends on the manufacturer's separator column and detector. For the exact composition of
the eluent, use a validated solvent for the method and/or refer to the instructions given by the manufacturer.
-3
NOTE For an ion chromatograph using the suppressor technique, a typical eluent is a solution of 1,7 x 10 mol/l NaHCO
-3
and 1,8 x 10 mol/l Na CO .
2 3
2−
-3
5.5.2 Standard sulphate stock solution, 10,4x10 mol/l SO
-3
Use a commercially available sulphate stock solution of 1 000 mg/l sulphate (10,4 x 10 mol/l) with a minimum
content of 99,0 %. As an alternative prepare the standard solution as follows:
Dissolve 1,814 g of analytical grade potassium sulphate (K SO ) in water (5.3) and dilute to a 1 000 ml volumetric
2 4
2 -
flask. 1 ml of stock solution corresponds to 1 mg of SO .
NOTE Calibration standards are prepared by diluting the standard stock solution with the absorption solution as specified
in 9.2.3.2.
5.5.3 Regeneration solution for suppressor
For the exact composition of the suppressor regeneration solution, refer to the instructions given by the
manufacturer of the suppressor.
-3
NOTE An example is a solution of 12,5 x 10 mol/l H SO .
2 4
5.6 Reagent for Thorin analysis
5.6.1 2-propanol [CH CH(OH)CH ]
3 3
Use commercially available 2-propanol [CH CH(OH)CH ] in analytical grade (minimum content 99,8 %).
3 3
5.6.2 Barium perchlorate, standard volumetric solution, [Ba(CIO ) ] = 0,005 mol/l
4 2
Use a commercially available barium perchlorate solution (80 % 2-propanol/20 % water) with concentration of
0,005 mol/l Ba(CIO ) , or prepare the standard solution as follows:
4 2
Dissolve 1,7 g of anhydrous barium perchlorate [Ba(CIO ) ] in about 200 ml of water in a 1 000 ml one-mark
4 2
volumetric flask. Make up to the mark with 2-propanol (5.6.1) and mix well.
Titrate the solution accurately against a 0,005 mol/l standard volumetric sulphuric acid solution.
1 ml of exactly 0,005 mol/l barium perchlorate solution is equivalent to a mass of sulphur dioxide of 0,320 mg;
(f = 0,320 mg/ml).
a
5.6.3 Potassium hydroxide, standard volumetric solution, [KOH] = 0,1 mol/l
Use a commercially available solution of 0,1 mol/l KOH in water.
NOTE This reagent is only necessary if the sampling gas contains high concentration of acid components (e.g. SO >
3 3 3
100 mg/m or HCl > 200 mg/m or NO > 400 mg/m ).

5.6.4 Perchloric acid, standard volumetric solution, [HClO ] = 0,1 mol/l
Prepare an approximate 1 % solution of perchloric acid by mixing 16 ml of a commercially available solution of
60 % perchloric acid in water (5.3) and make up to 1 000 ml with water. Store this solution in a glass or PE bottle.
NOTE This reagent is only necessary if the sampling gas contents high concentrations of alkali components (e.g.
NH > 50 mg/m ).
5.6.5 Thorin, {4-[2-arsonophenyl)-azo]-3-hydroxy-2,7 naphthalene-disulfonic acid disodium salt} 2 g/l
solution
Thorin is also known as Thoron or Thoronol, the sodium salt of
4-1(2-arsonophenyl)-azol-3-hydroxy-2,7 -naphthalene -disulfonic acid.

Dissolve 0,2 g of Thorin in water (5.3) in a 100 ml one-mark volumetric flask. Make up to the mark with water and
mix well.
Store this solution in a bottle made of glass or polyethylene.
6 Sampling equipment
6.1 General
A known volume of flue gas is extracted representatively from a duct or a chimney during a certain period of time at
a controlled flow rate. A filter removes the dust in the sampled volume, thereafter the gas stream is passed through
a series of absorbers containing an absorption solution.
All parts of the sampling equipment upstream of the first absorber shall not react with or adsorb SO (i.e.

borosilicate glass, quartz glass, PTFE or titanium are suitable materials).
If an unheated gas connector line is used between the heated filter and the first absorber, it shall be thoroughly
rinsed with fresh absorption solution after sampling and the rinsing solutions shall be combined with the sample.
An example of a suitable sampling train is shown in Figure A.1 in Annex A.
6.2 Sampling probe
In order to access the representative measurement point(s) of the sampling plane, probes of different lengths and
inner diameters may be used, but the residence time of the sample gas in the probe shall be minimised.
The probe may be marked before sampling in order to demonstrate that the representative measurement point(s) in
the measurement plane has (have) been reached.
The procedure described in 7.2.2 shall be used when the operator suspects that the flue gas is inhomogeneous.
When droplets are present in the flue gases, they may contain SO dissolved in it. In that case, the probe is
equipped with a nozzle and an isokinetic sampling shall be performed according to EN 13284-1.
NOTE 1 It is possible to perform the sampling of SO and HCl simultaneously with the same probe without nozzle providing
no droplets are present.
NOTE 2 SO and H O can be measured simultaneously by using the same probe without nozzle and the same side stream
2 2
absorbers, providing no droplets are present in the flue gases.
The sampling probe shall be surrounded by a heating jacket capable of producing a controlled temperature of at
least 120 °C or 20 °C higher than the (acid) dew point of gases and shall be protected and positioned using an
outer tube.
6.3 Filter housing
The filter housing may be located either:
 directly in front of the probe behind the entry nozzle (in-stack filtration); or
 directly behind the probe (out-stack filtration).
If condensation is liable to occur in the sampling probe or in the filter housing, then a heated out-stack filter housing
shall be used. For out-stack filtration, the filter housing shall be heated at a controlled temperature of at least
120 °C or 20 °C higher than the (acid) dew point of gases. It shall be connected to the probe without any cold path
between the two.
Filter housings of different designs may be used, but the residence time of the sample gas shall be minimised.
NOTE 1 The filter housing shall have the possibility to be jointed with the probe thereby avoiding leaks.
NOTE 2 A stop valve after the filter housing can be useful to prevent back flush of absorption solution into the probe or into
the filter when sampling in flue gases under unfavourable conditions (e.g. high depression in the duct).
NOTE 3 In special cases where the sample gas temperature is > 200 °C, the heating jacket around the sampling probe, filter
housing and connector line may be switched off. However the temperature in the sampled gas just after the filter housing,
should not fall below 20 °C above the (acid) dew point temperature.
6.4 Particle filter
The filter shall have an efficiency better than 99,5 % on a test aerosol with a mean particle diameter of 0,3 µm, at
the maximum flow rate anticipated, (or 99,9 % on a test aerosol of 0,6 µm mean diameter).
Glass filters cannot be used because glass reacts with SO , but ceramic, quartz or PTFE are suitable materials.
6.5 Temperature controller
A temperature controller is required for the filter housing. It shall be capable of controlling temperature with an
uncertainty of ± 2,5 K or better.
6.6 Absorbers
6.6.1 General
For efficient absorption two absorbers shall be placed in series.
NOTE Downstream of these absorbers, an extra empty absorber may be used as a liquid trap and as a protection for the
downstream equipment.
Some examples of absorbers are given in Annex B.
The absorption efficiency of the first absorber shall be better than 95 % or the concentration of sulphate ion in the
second absorber shall be less than the detection limit. This efficiency shall be checked periodically at the normal
flow rate according to the procedure described in 6.6.2. Except when the absorption efficiency shall be checked,
the solutions from the two absorbers can be combined and analysed together.
NOTE Cooling of the absorbers may be useful to avoid excessive evaporation from the first absorption bottle.
6.6.2 Test of absorption efficiency
Place a suitable volume of absorption solution into each of the two absorbers, where the first absorber is denoted 1
and the second absorber 2. Assemble the apparatus to obtain a sampling train as illustrated in Figure A.1.
Carry out sampling in normal conditions. At the end of the sampling period, switch off the sampling pump, record
the time and volume on the gas meter.
Remove the absorber from the sampling train and transfer the sample solutions from absorber 1 and 2 into
two separate sample bottles. If a trap is used behind the absorbers to collect any solution carry-over, its contents
shall be combined with the sample of bottle 2. Rinse each absorber with the absorption solution (5.4) thoroughly
and particularly the fritted glass dividers to recover the absorption solution trapped in it and add the rinsing
solutions to the appropriate absorber sample. Rinse all the unheated parts of the sampling system between the
filter and the absorber 1 and add the rinsing to the content of bottle 1.
Analyse samples 1 and 2 as described in clause 9 to determine the sulphate content, q and q . Calculate the
s1 s2
absorption efficiency ε of absorber 1 as follows:
Absorption efficiency of absorber 1 in % is ε = q x 100 / (q + q ).
s1 s1 s2
6.7 Sampling pump
Leak-free pump capable of sampling gas at a set flow-rate.
3 3
A sampling flow rate between 0,06 m /h to about 0,2 m /h allows to reach a good absorption with a low pressure
of -10 kPa to -30 kPa.
NOTE 1 A small surge tank may be used between the pump and the rotameter to eliminate the pulsation effect of the
diaphragm pump on the rotameter.
NOTE 2 A rotameter (optional) facilitates the adjustment of the nominal sampling flow-rate.
NOTE 3 A regulating valve (optional) is useful for adjusting the sample gas flow-rate.
6.8 Gas volume meter
Any dry or wet gas volume meter may be used providing the volume is measured with a relative uncertainty not
exceeding ± 2 % at actual conditions.
The gas volume-meter shall
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