Solid recovered fuels - Determination of the biomass content based on the 14C method

This Technical Report gives an overview of the suitability of 14C-based methods for the determination of the fraction of biomass carbon in solid recovered fuels, using detection by scintillation, gas ionization and mass spectrometry.

Feste Sekundärbrennstoffe - Bestimmung des Gehaltes an Biomasse nach de 14C-Methode

Combustibles solides de récupération - Détermination de la teneur en biomasse, basée sur la méthode du C14

Trdno alternativno gorivo - Določevanje vsebnosti biomase z metodo 14C

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SIST-TP CEN/TR 15591:2007
Solid recovered fuels - Determination of the biomass content based on the 14C method
Feste Sekundärbrennstoffe - Bestimmung des Gehaltes an Biomasse nach de 14C-
Combustibles solides de récupération - Détermination de la teneur en biomasse, basée
sur la méthode du C14
Ta slovenski standard je istoveten z: CEN/TR 15591:2007
75.160.10 Trda goriva Solid fuels
SIST-TP CEN/TR 15591:2007 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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CEN/TR 15591


February 2007
ICS 75.160.10
English Version
Solid recovered fuels - Determination of the biomass content
based on the C method
Combustibles solides de récupération - Détermination de la Feste Sekundärbrennstoffe - Bestimmung des Gehaltes an
14 14
teneur en biomasse, basée sur la méthode du C Biomasse nach de C-Methode

This Technical Report was approved by CEN on 1 January 2007. It has been drawn up by the Technical Committee CEN/TC 343.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.



Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15591:2007: E
worldwide for CEN national Members.

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CEN/TR 15591:2007 (E)
Contents Page
0 Introduction.4
1 Scope .7
2 Terms and definitions .7
3 Symbols and abbreviations .7
4 Methods of measurement .8
4.1 Principle.8
4.2 Sampling.8
4.3 Transport and storage.8
4.4 Preparation of the test portion from the laboratory sample .9
4.5 Analysis by Proportional Scintillation-counter Method (PSM) .9
4.6 Analysis by Β-ionisation (proportional gas counting) (BI).10
4.7 Analysis by Accelerator Mass Spectrometry (AMS) .10
5 Equipment and reagents.10
5.1 For the preparation of the test portion .10
5.2 For the analysis by PSM .11
5.3 For the analysis by Β-ionisation (BI) .11
5.4 For analysis by AMS (example from Utrecht University).11
6 Procedure .11
6.1 For sampling .11
6.2 For the preparation of the test portion .12
6.3 Procedure for analysis .13
7 Calculations.13
7.1 General.13
7.2 Calibration .14
7.3 Example for the calculation of a RDF sample analysed with PSM .15
8 Uncertainty of measurement (PMS and BI measurements) based in Poisson statistics.15
9 Strengths and weaknesses.16
9.1 Comparison of C based methods with SDM .16
9.2 Comparison of PSM, Gas Counting (BI) and AMS .17
10 Legislative aspects.17
10.1 General.17
10.2 Austria.17
10.3 The Netherlands.17
10.4 Finland .18
11 Conclusions .18
Annex A (informative) Origin of expertise present in the technical report.19
Annex B (informative) List of European lab's with radio carbon expertise.22
Bibliography .33


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CEN/TR 15591:2007 (E)

This document (CEN/TR 15591:2007) has been prepared by Technical Committee CEN/TC 343 “Solid
recovered fuels”, the secretariat of which is held by SFS.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.


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CEN/TR 15591:2007 (E)
0 Introduction
0.1 General
This document has been prepared as a result of the CEN/TC 343/WG 3 meeting in Amsterdam in April 2005.
It summarizes the state of the art in C-based methods applied to determining the biomass content of SRF;
as of yet no technical CEN standards for the application of C-based methods to determine biomass content
are available. The purpose of this Technical Report is to present the information available on this subject at
this moment to assess if an extension of the available methods for determining the biomass content of SRF is
required, wanted and technically possible.
Analytically proven standards exist for determining the biomass content of SRF by manual sorting and by
selective dissolution (CEN/TS 15440 [1]). In the Netherlands these methods are available as NTA (National
Technical Agreement) and have been in use for some years. Important advantages of these standards are
their applicability using basic laboratory equipment and available personnel. However, they are not applicable
to all kinds of solid recovered fuels. The manual sorting method fails if the constituents of the sample are
shredded too finely, if they are strongly intertwined or compressed or if they cannot be recognized visually.
The selective dissolution method fails if biomass constituents are present that do not dissolve, or fossil
components that do. Both methods fall short if fossil and biomass carbon are mixed at the molecular level. C
based methods do not use chemical or morphological properties of the sample but physical properties of the
carbon atoms themselves. Because C based methods are based on these physical properties they avoid the
problems of manual sorting and selective dissolution methods. On the other hand they need more
instrumentation and skilled personnel. They are proposed here as an addition to the manual sorting and
selective dissolution methods because they resolve analytical problems that are otherwise irresolvable.
The application of C based methods for similar purposes are not new [2] [3]. In this document the
information available in Europe and the USA concerning biomass carbon content determination in solid
recovered fuels with C based methods is presented to give the reader background information about
possibilities and drawbacks of these methods.
0.2 Basis of the C method
The C method is a well-known method in global use, for determining the age of carbon containing matter.
C is a radioactive isotope; its presence in the air is a result of the interaction of cosmic radiation and the
14 14
nitrogen in the atmosphere (see Figure 1). Fossil carbon contains no C, however a trace amount of C is
14 14
present in living matter. The C isotope is quickly converted to CO after formation and enters living matter
when atmospheric CO is converted in the biosphere by photosynthesis to sugars and further converted to
e.g. cellulose. The concentration of C in air is considered constant all over the world. In living material the
concentration of C is stable and in equilibrium with the air concentration. In dead material the concentration
14 14 14
of C slowly diminishes to zero as the radioactive C isotope decays. Measuring the amount of C in solid
recovered fuels is the basis for determining biomass content based on the C method.


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CEN/TR 15591:2007 (E)

Figure 1 – Illustration of the basis of the C method
Organic material is used for many purposes. One of the objectives is direct use as a fuel which is outside the
scope of this report. However, after completing their primary use, many of these organic materials may
ultimately be used in the form of solid recovered fuels.
Examples of organic materials in solid recovered fuels are:
 Packaging materials;
 Paper;
 Wood used in buildings;
 Kitchen waste;
 Waste (dung and offal) from the bio industry;
 Plastics;
 Car tires.
Carbon present in material produced by living organisms, immobilized as fuel in present times is called
biomass. Carbon present in material produced by living organisms immobilized as fuel in a past geological era
is called fossil fuel. The difference between the two is that CO from biomass or biomass origin does not

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CEN/TR 15591:2007 (E)
contribute to a higher concentration of CO in the atmosphere as its carbon has been recently extracted from
the atmosphere.
In solid recovered fuels, the combustible carbon originates from fossil (mainly in the form of plastics), mixed
sources like rubber tyres and packaging materials, and from biomass origin (e.g. wood, paper). Authorities
require that emissions of CO from fossil origin by companies is made known, thus, in order to determine
these companies, knowledge about the biomass content by total carbon content of mixed fuels should be
acquired. For this reason, methods such as the solid dissolution method and C method were developed.
International acceptance of a C based method can be expected, as can be illustrated by the recent
publication of ASTM, ASTM D 6866-05, Standard Test Method for determining the Bio based Content of

Natural Range Materials Using Radiocarbon and Isotope Ratio Mass Spectrometry Analysis [2].

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CEN/TR 15591:2007 (E)

1 Scope
This Technical Report gives an overview of the suitability of C-based methods for the determination of the
fraction of biomass carbon in solid recovered fuels, using detection by scintillation, gas ionization and mass
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
biodegradable carbon
mass fraction of the total carbon that is capable of undergoing biological anaerobic or aerobic decomposition
under conditions naturally occurring in the biosphere
biogenic carbon
mass fraction of total carbon that was produced in natural processes by living organisms but not fossilized or
derived from fossil resources
biomass carbon
equivalent to biogenic carbon
isotope abundance
fraction of atoms of a particular isotope of an element
extent of the agreement between the results of subsequent measurements of the same quantity, performed
under the same measuring conditions
extent of the agreement between the results of measurements of the same quantity, performed under variable
measuring conditions.
3 Symbols and abbreviations
This Technical Report uses the following symbols and abbreviations:
C Carbon isotope with an atomic mass of 14
AMS Accelerator Mass Spectrometry
β Beta particle, electron emitted during radioactive decay
BI Βeta Ionisation

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CEN/TR 15591:2007 (E)
BP Before Present (before 1950)
CPM Counts per minute
DPM Disintegrations per minute
ETS Emissions Trading Scheme
GM Geiger Müller
LSC Liquid Scintillation Counter or Liquid Scintillation Counting
PSM Proportional Scintillation-counter Method
PMT Photo Multiplicator Tube
RSD Relative Standard Deviation
SDM Selective Dissolution Method
SRF Solid Recovered Fuel
STP Standard Temperature and Pressure (273,15 K (or 0 °C) and 101,325 Pa (or 760 mmHg))
4 Methods of measurement
4.1 Principle
The principle of the C method is to determine the biomass content by total carbon by measuring the amount
14 14
of C present in the sample. This method utilizes the isotope abundance of C similar to the way the age of
objects is measured for archaeological purposes. In all organisms living ashore, C has a known isotope
abundance equal to its isotope abundance in atmospheric CO . As soon as an organism dies, the isotope
14 14
abundance of C in its organic material starts to decrease because C is an unstable isotope with a half-life
of 5 730 yr. The isotope abundance of C may be considered zero after ten half lives or 60 000 yr. The
biomass content by total carbon of a material is calculated as the proportion of the isotope abundance of C
in that material and the isotope abundance of C in the atmosphere at the time when the biomass was laid
The method is especially useful for determining biomass carbon content, however, the relationship between
biomass carbon content and biomass content should be determined for every type of waste; a limitation that is
also valid for other existing methods. When information is available about how carbon atoms are chemically
bound, the amount of bio energy can be calculated.
4.2 Sampling
For the C based methods sampling procedures that are similar to those for determining major elements [4]
are used. As carbon is one of the major components in solid recovered fuel, problems with homogeneity are
not to be expected with laboratory samples. Typical particle size of the sample material should be ≤ 0,2 mm.
4.3 Transport and storage
For transport and storage of the samples, the same requirements are fulfilled as for normal lab samples. As
part of the solid recovered fuel consists of organic material, dry and cool storage is applied to prevent
conversion of the biomass part by microbiological activities.

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4.4 Preparation of the test portion from the laboratory sample
For the PSM and BI methods sample sizes of 1 g or more are used. However at the 1 g level problems still
arise with homogeneity of the sample; the use of a lab scale combustion device (e.g. rotary kiln) is
recommended, allowing sample amounts of 5 g to 20 g.
The AMS method only needs a few milligrams of sample. In this case combustion of samples at a scale of
approximately 1g is necessary. After combustion the carbon is present in a gas phase as CO , and the next
step is preparing a mg size sample from the gaseous combustion products.
4.5 Analysis by Proportional Scintillation-counter Method (PSM)
PSM (also called Liquid Scintillation Counter method, LSC) determines the isotope abundance of C indirectly
through its emission of β (beta, electron) particles. The β particles are detected through interacting with a
solution of a scintillation molecule. This is possible only if the carbon is homogeneously distributed in the
solution, as the β particles must be able to interact with the solution instead of being quenched in the solid fuel.
Homogeneous distribution may be attained by four different methods:
 Conversion to CO , followed by absorption in an organic amine and mixing this absorbent with the
scintillation fluid. The amine is produced using fossil carbon, in order not to cause a blank signal.
 Conversion to CO , followed by absorption in a BaCl or CaCl solution, and
2 2 2
 after drying and grinding, transfer of BaCO or CaCO into the scintillation fluid forming a suspension;
3 3
 regeneration of CO from the precipitate, which is absorbed in an organic amine, and mixing this
absorbent with the scintillation fluid.
 Conversion to CO , followed by adsorption on a solid medium, regeneration of CO which is absorbed in
2 2
an organic amine, and mixing this absorbent with the scintillation fluid.
 Liquid fuels may be directly mixed with the scintillation fluid.
The scintillation fluid consists of a solvent and a dissolved fluorescent agent, the fluor. When a β is emitted, it
rapidly transfers its energy to solvent molecules (< 5 ns) in the form of heat, ionisation and excitation. A part of
the excited solvent molecules transfers energy to fluor molecules; the remaining energy is lost as heat by
various quenching processes. A part of the excited fluor molecules release their energy in the form of photons
in the blue part of the visible spectrum; again, the remaining energy is lost as heat by various quenching
processes. A part of the photons are detected in the form of a light flash; the intensity is proportional to the β’s
initial energy. The remaining photons are lost by quenching, by reabsorption by the fluor, or by not being
detected because of geometry. The standard addition technique can be used to determine quenching effects.
In practice, a pair of light detectors – classically, PMT’s – are used for two reasons:
 It is necessary to compensate for geometry effects: an event close to a detector will produce a stronger
signal because more photons will reach the detector. This is done by adding the signals of the detectors;
 Events caused by background radiation should be excluded, by admitting only those pulses that are seen
by both detectors simultaneously (window size approximately 20 ns). A predefined intensity ratio
threshold is set in order to exclude most events that occur outside the sample vial.
The remaining background counts occur mainly by decay of other naturally radioactive isotopes such as K,
212 212 214 214 137
Bi, Pb, Bi, and Pb and / or Cs.

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CEN/TR 15591:2007 (E)
The overall a priori efficiency of the detection is unknown. Therefore, the method has to be calibrated with
samples of known C isotope abundance.
4.6 Analysis by Β-ionisation (proportional gas counting) (BI)
The Β Ionisation method determines the isotope abundance of C indirectly. This method employs the
emission of β particles by C, like PSM. It detects β particles by means of discharge current pulses between
high-voltage electrodes in a proportional gas counter. Those pulses are initiated by the β particles. The
detection principle resembles the way a Geiger-Mueller (GM) counter works, the difference being details of the
electron avalanche in the counter.
To use this method, the sample has to be in the form of CO or converted to CO , as is also the case for most
2 2
applications of PSM.
The sensitivity of the gas counter is proportional to the contained gas quantity, and therefore to the specific
mass/pressure of the gas and to the volume of the detector. In practice, 1,4 g carbon may be loaded (up to 10
l CO at STP (Standard Temperature and Pressure)). Assuming a counting efficiency of 80 %, the
performance based on counting statistics may be in the same order of magnitude as the performance of the
liquid scintillation method. However, it is not necessary to absorb the CO in a liquid, the method may be more
manageable than PSM and use less consumables.
4.7 Analysis by Accelerator Mass Spectrometry (AMS)
The accelerator mass spectrometry method determines the presence of C directly. The atoms in the sample
are converted into a beam of ions. Accelerating them in an electric field, deflecting them in a magnetic field
and detecting them in an ion detector determine the relative isotope abundances of these ions.
AMS is a form of mass spectrometry that uses a high potential electrostatic field, which serves not only to
accelerate them but also to specifically form only C ions that are allowed into the spectrometer, excluding all
other ionic species. This greatly enhances sensitivity without compromising selectivity.
AMS uses only a few mg of sample, and the sample processing and counting time is considerably less time
consuming compared with β counting. Logistic turnaround times of two weeks or less are possible. Due to the
complex accelerator system cost is presently still higher but this issue may change in the near future due to
the rather mature state of small accelerators. AMS may be even more attractive if reliable gas-ion-sources
(now under development) may become routinely available, because the CO can be fed directly into the
5 Equipment and reagents
5.1 For the preparation of the test portion
5.1.1 Oxygen bomb
Commercially available oxygen bombs for determining the caloric values are used for the combusting the test
In some cases intermediate storage of the combustion gases in a tedlar gas bag is used. The combustion
gases from the oxygen bomb can then be released in a short time, and afterwards the combustion gases can
be processed at the desired flow rate using a small gas pump. For longer storage of combustion gases
gasbags with an aluminium layer are advised, as losses are observed in other types of materials.
If the carbon content in the sample is calculated from the amount of CO present in the combustion gases,
impingers filled with concentrated phosphoric acid and zinc pellets are used to remove water, and sulphur and
halogen oxidation products, prior to the absorption of the CO .

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5.1.2 Rotary kiln oven
For very inhomogeneous samples a lab scale rotary kiln oven is used to combust several grams of sample.
The sample is burned in the rotary kiln in an oxygen stream at ± 800 °C and the formed combustion gases are
cleaned with impingers and the formed CO is absorbed into the organic amine solution. The CO
2 2
concentration in the combustion gases is measured simultaneously with the CO and oxygen concentration to
ensure the complete combustion of the sample.
5.2 For the analysis by PSM
 1-methoxy-propane-3-amine absorption liquid;
 Sodium hydroxide solution (1 M);
 Scintillation cocktail, miscible with the used amine;
 Scintillation vials, glass, 20 ml;
 Scintillation counter.
The instruments [5] are able to use scintillation vials with a volume of at least 10 ml. Shielding from
background radiation is applied as much as possible. The background level required is 12 DPM or less. To
achieve this, the instruments are placed inside a heavy-walled room and shielded with a so-called lead castle,
made from lead with a minimum of radioactive isotopes. Therefore lead preferably produced before 1600 AD
is used. Well-known sources of low background lead are lead ballasts from sunken sail ships.
5.3 For the analysis by Β-ionisation (BI)
The instruments used for BI measurements are home made high tech devices developed at divers
radiocarbon institutes. No commercial systems are available. Gas (in this case purified CO derived from
combustion gases) is loaded and counted in a copper counting tube (ultra pure copper) and the desired low
background is obtained by applying heavy shielding with lead and anti-coincidence filtering of cosmic radiation.
Usually BI devices are located below ground level, e.g. in cellars to obtain extra protection against cosmic
radiation. Typical counting times are several days for low-level measurements.
5.4 For analysis by AMS (example from Utrecht University)
The AMS-facility in the Van de Graaff laboratory of Utrecht University is based on the 6 MV tandem Van de
Graaff accelerator, which has been used originally for precision research of nuclear spectroscopy. The
accelerator has been adapted for AMS with stable beam transmission and minimal beam loss. Precision
measurements are made with fast switching between isotope beams in an automated scheme. Ions are
selected on mass with a bending magnet and injected into a particle accelerator, where they become
accelerated. Ions emerging the accelerator are selected on energy and mass and finally detected. The stable
isotope is collected in a Faraday cup and its yield is determined from the accumulated charge. The rare
isotope is identified and counted in a detector.
6 Procedure
6.1 For sampling
The procedures for sampling are similar to the procedures that are used for proximate-ultimate analysis of
solid recovered fuels.

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6.2 For the preparation of the test portion
6.2.1 General
The procedures for the preparation of the test portion are similar to the procedures for the determination of the
caloric value in the case of oxygen bomb combustion. When the lab scale rotary kiln oven is used, samples
prepared for lab analysis are used. In some cases CO , directly collected in the flue gas of full-scale
installations, is used to determine the biomass carbon content in fuels.
6.2.2 For PSM
After combustion of the sample, the formed CO is absorbed in a sodium hydroxide solution, barium chloride
solution or an organic amine, such as 1-methoxy-propane-3-amine, where CO is absorbed by formation of a
carbamate. Because this reaction is exothermic, the absorption flask is cooled. When the total carbon content
is determined by the gravimetric determination of the precipitated barium carbonate or the determination of the
density of the organic amine, scrubbers for the removal of water (concentrated phosphoric acid) or halogens
(zinc pellets) are used. For the collection of carbon dioxide from the exhaust gas of the oxygen bomb in a
number of cases a gasbag is used for intermediate storage.
When an absorption flask is loaded with a known volume of CO absorbent, e.g. with 1-methoxy-propane-3-
amine, the absorbing capacity of 1-methoxy-propane-3-amine of about 4,8 mmol/ml is to be taken into
account; no more than 80 % of this capacity is used. The flask is cooled in ice during the absorption process.
After absorption, the absorption fluid is mixed with a scintillation cocktail. Those cocktails are commercially
available; their exact composition is not specified. In some cases the absorbent and scintillation cocktail is
mixed in a 1:1 ratio before absorption, so that problems with evaporation, and crystallization of carbamates
can be avoided.
Although not within the scope of this document,

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