EN ISO 21640:2021

SLOVENSKI STANDARD
01-september-2021
Nadomešča:
SIST EN 15359:2012
Trdna alternativna goriva - Specifikacije in razredi (ISO 21640:2021)
Solid recovered fuels - Specifications and classes (ISO 21640:2021)
Feste Sekundärbrennstoffe - Spezifikationen und Klassen (ISO 21640:2021)
Combustibles solides de récupération - Spécifications et classes (ISO 21640:2021)
Ta slovenski standard je istoveten z: EN ISO 21640:2021
ICS:
75.160.10 Trda goriva Solid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 21640
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2021
EUROPÄISCHE NORM
ICS 75.160.10 Supersedes EN 15359:2011
English Version
Solid recovered fuels - Specifications and classes (ISO
21640:2021)
Combustibles solides de récupération - Spécifications Feste Sekundärbrennstoffe - Spezifikationen und
et classes (ISO 21640:2021) Klassen (ISO 21640:2021)
This European Standard was approved by CEN on 1 May 2021.

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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21640:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 21640:2021) has been prepared by Technical Committee ISO/TC 300 "Solid
recovered materials, including solid recovered fuels" in collaboration with Technical Committee
CEN/TC 343 “Solid Recovered Fuels” the secretariat of which is held by SFS.
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 November 2021, and conflicting national standards
shall be withdrawn at the latest by November 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15359:2011.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 21640:2021 has been approved by CEN as EN ISO 21640:2021 without any modification.

INTERNATIONAL ISO
STANDARD 21640
First edition
2021-05
Solid recovered fuels — Specifications
and classes
Combustibles solides de récupération — Spécifications et classes
Reference number
ISO 21640:2021(E)
©
ISO 2021
ISO 21640:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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Phone: +41 22 749 01 11
Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 21640:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 2
5 Principles . 2
6 Classification . 2
7 Specifications . 3
7.1 General . 3
7.2 Origin . 4
7.3 Traded forms of solid recovered fuels . 6
7.4 Properties obligatory to specify . 7
7.5 Properties non-obligatory to specify . 8
8 Compliance rules . 9
8.1 Compliance rules for classification . 9
8.1.1 General compliance rules . 9
8.1.2 Start-up or considerable changes in the production .10
8.1.3 Exemptions .10
8.2 Compliance rules for specification .10
8.2.1 General compliance rules .10
8.2.2 Exemptions .11
9 Requirements and declaration of conformity .11
Annex A (normative) Template for the specification of solid recovered fuels .12
Annex B (informative) Fuel preparation .14
Annex C (informative) Template for declaration of conformity .16
th
Annex D (informative) Calculation of standard deviation, median and 80 percentile .18
Annex E (informative) Examples of establishing of compliance with SRF classification .20
Annex F (informative) Examples of establishing of compliance with SRF specification .24
Bibliography .26
ISO 21640:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO 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.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 300 Solid recovered fuels.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved

ISO 21640:2021(E)
Introduction
The objective of this document is to provide a common classification and specification system for solid
recovered fuels (SRF) to enable efficient trading of SRF, to promote their safe use in energy conversion
activities and to increase the public trust. The document facilitates a good understanding between
seller and buyer, supports purchase, trans border movements, use and supervision as well as an
effective communication with equipment manufacturers. The classification and specification system
support authority permission procedures and ease the reporting on environmental issues.
SRF are produced from non-hazardous waste. The input waste can be production specific waste,
municipal solid waste, industrial waste, commercial waste, construction and demolition waste, sewage
sludge etc. It is thus obvious that SRF are a heterogeneous group of fuels. A well-defined system for
classification and specification is therefore of significant importance to reach the above-mentioned
objectives and intentions.
This document covers all types of SRF and will thus have a wide field of application. The aim of producing
a solid recovered fuel is to use it for energy purposes at the highest possible energy efficiency.
This document describes the compliance rules for SRF according to this classification system.
Classification enables statistical information of SRF properties in the market, thus increasing
transparency in the use of non-hazardous waste in SRF and demonstrating development of this business
field.
This document also describes how the supplier can establish specifications and a declaration of
conformity to the different ISO standards for SRF.
It is important to emphasise that despite the standardisation of SRF, the standard should not be
interpreted as end-of-waste criteria. Such criteria can be set at national or regional levels, but then in
legislation and not in this document. Also, it should be noted that the waste used for the SRF production
should be such waste streams that are not suitable for re-use, preparation for re-use or efficient
material recycling.
Figure 1 illustrates a simplified flow chain for SRF, from input of non-hazardous waste to end use of
SRF. This document has an interface to all the stages in the chain, from point of acceptance to point of
delivery. The fuel is not considered an SRF until it is specified and classified according to this document.
Requirements for how the input waste is collected and how to use the SRF are not part of this document.
Figure 1 — Solid recovered fuels chain – This document on specifications and classes is
applicable after production up to the point of delivery
ISO 21640:2021(E)
NOTE This document is applicable to trading and storage of SRF. However, if during storage or trade the
SRF is mixed with other SRF or other fuels, then the classification and specifications are no longer valid. If sold
further, then the mixing would constitute an SRF production.
vi © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 21640:2021(E)
Solid recovered fuels — Specifications and classes
1 Scope
This document specifies a classification system for solid recovered fuels (SRF), and a template
containing a list of characteristics for the specification of their properties, enabling trade and use of
SRF supporting the protection of the environment.
SRF are produced from non-hazardous waste.
NOTE 1 Untreated municipal solid waste as such cannot be considered SRF. Untreated municipal solid waste
can however be feedstock to plants producing SRF.
NOTE 2 Chemically treated solid biofuels that do not contain halogenated organic compounds or heavy metals
at levels higher than those in typical virgin material, can be defined as solid biofuels and thus be part of the
[1]
standard series ISO 17225 .
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21637, Solid recovered fuels — Vocabulary
ISO 21645, Solid recovered fuels — Methods for sampling
ISO 21654, Solid recovered fuels — Determination of calorific value
ISO 21656, Solid recovered fuels — Determination of ash content
ISO 21660-3Solid recovered fuels — Determination of moisture content using the oven dry method —
Part 3: Moisture in general analysis sample
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21637 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
classification of solid recovered fuels
categorizing of solid recovered fuels into classes focusing on the key properties – NCV, Cl and Hg that
are defined by boundary values
3.2
specification of solid recovered fuels
list of properties that characterizes solid recovered fuels
Note 1 to entry: Templates for such specifications are given in Annex A in this document.
ISO 21640:2021(E)
4 Symbols and abbreviations
The symbols and abbreviations used in this document comply with the SI system of units as far as
possible.
Table 1 — Symbols and abbreviations
Symbol Definition
(d) dry (dry basis)
d particle diameter where x denominates the share of particles passing through a sieve of that size
x
(ar) as received
A Designation for ash content on dry basis A [% in mass]
(d)
ρ Designation for bulk density as received [kg/m ]
M Designation for moisture content as received on wet basis, M [% in mass]
ar
P Designation for the particle size of the main fraction (> 95 % in mass) related to size intervals.
NCV Designation for net calorific value as received, q [MJ/kg or kWh/kg or MWh/t] at constant
p, net, ar
pressure
VM Designation for volatile matter on dry basis [% in mass]
NOTE 1 MJ/kg equals 0,277 8 kWh/kg (1 kWh/kg equals 1 MWh/t and 1 MWh/t are 3,6 MJ/kg). 1 g/cm
equals 1 kg/dm . 1 mg/kg equals 0,000 1 % in mass.
5 Principles
The classification system is based on three important characteristics, referred to as the main SRF
characteristics: an economic characteristic (net calorific value), a technical characteristic (chlorine
content) and an environmental characteristic (mercury content). The characteristics are chosen to give
a stakeholder an immediate but simplified picture of the fuel in question.
The classes also impose limitations on what can be called SRF restricting it with a minimum net calorific
value as well as maximum values of chlorine and mercury. Fuel outside the ranges of the classes shall
not be defined as SRF.
Only fuels derived from non-hazardous waste that meet the SRF ISO Standards can be classified as SRF.
The classification itself is not enough for an intending user or other stakeholders. The level of detailed
information needed depends on several different factors. Such factors can be; the end use of the SRF,
legislative demands, character of the input material, and the technology used either in production or
end use of the SRF. Relevant fuel properties are thus to be given in the specification of the SRF. Some of
the fuel properties are deemed so important that they are obligatory to specify whereas others can be
recorded voluntarily, e.g. upon request of the user.
It is important that SRF meet specified quality requirements which are to be determined based on a
defined lot size by a minimum number of measurements.
6 Classification
The classification system (Table 2) for SRF is based on limit values for three important fuel
characteristics. These are the net calorific value (NCV); chlorine content (Cl); mercury content (Hg).
Due to the statistical distribution pattern of the characteristics the values shall be presented as:
2 © ISO 2021 – All rights reserved

ISO 21640:2021(E)
— NCV (ar) mean (arithmetic);
— Cl (d) mean (arithmetic);
th
— Hg (ar) median and 80 percentile
The average, median, and percentiles are determined on the quantity of SRF as specified in Clause 8.
th
NOTE 1 80 percentile is the value on or below which 80 % of the observations fall.
[2]
Not all kinds of SRF are suited for all types of energy recovery installations, see CEN/TR 15508 .
Each of the classification characteristic is divided into 5 classes. The SRF should be assigned a class
number from 1 to 5 for each characteristic. A combination of the class numbers makes up a class code
(see example below). The characteristics should be considered as equal important and thus no single
class number determines the code. The class code shall be included in the specification as described in
Clause 9.
th
For mercury, the higher of the two statistical values (median and 80 percentile) in a Hg data set
determines the class.
th
EXAMPLE An SRF with a median value of 0,03 and 80 percentile value of 0,07 belongs to Hg class 3
(according to Table 2).
NOTE 2 The performances of the plant where SRF is used are depending on the properties of the SRF and
more significantly on the design and operating conditions of such a plant.
NOTE 3 The limit values used for different classes must not be mixed up with limit values set by the competent
authority in an environmental permit or other equally binding documents.
NOTE 4 The specific transfer factor for mercury of a given process and the proportion of SRF will determine
[2]
which classes can be used. Examples of transfer factors for existing processes are given in CEN/TR 15508 .
Table 2 — Classification for solid recovered fuels
Classes
Classification charac- Statistical meas-
Unit
teristic ure
1 2 3 4 5
Net calorific value
Mean MJ/kg (ar) ≥ 25 ≥ 20 ≥ 15 ≥ 10 ≥ 3
(NCV)
Chlorine (Cl) Mean % in mass (d) ≤ 0,2 ≤ 0,6 ≤ 1,0 ≤ 1,5 ≤ 3
Median mg/MJ (ar) ≤ 0,02 ≤ 0,03 ≤ 0,05 ≤ 0,10 ≤ 0,15
Mercury (Hg)
th
80 percentile mg/MJ (ar) ≤ 0,04 ≤ 0,06 ≤ 0,10 ≤ 0,20 ≤ 0,30
7 Specifications
7.1 General
The SRF shall be specified according to the template in Annex A. Annex A consists of properties that
are obligatory to specify. If the producer and the end user have agreed upon additional properties to be
specified, those should be documented in a similar way.
For specification of the properties in Annex A, determination shall be made according to ISO test
methods for SRF. Technical specifications or regional/national standards can be used if no ISO test
method is available. For additional properties, ISO test methods are recommended but other relevant
methods can be used. If other methods are used, it shall be stated in the SRF specification.
ISO 21640:2021(E)
7.2 Origin
The specification of origin is based on the origin and source of waste input material as described in
Table 3. The material accepted for SRF production are those that are not suitable for material recycling.
This can, as an example, include reject streams from packaging recycling/sorting. The main origin-
based solid recovered groups are:
1. Non- hazardous industrial waste
There are several waste streams generated within industry and commerce that could be used to
produce SRF. Different industrial sectors typically generate different kinds of wastes, like manure
from agriculture or fibre reject streams from pulp and paper industry. For this reason, there are
several subcategories (Table 3). However packaging waste are generated many different industries
and commerce operations. In this case they are often quite similar and are thus not specified for
individual industries. In this post is also included the packaging materials from construction
projects.
2. Non-hazardous construction and demolition waste
Construction waste and demolition waste differ from each other because constructing means
building something new while waste from demolition normally comes from old structures. In
renovation projects, both construction and demolition typically take place simultaneously, and thus
generates both types of waste. The waste from the construction and demolition industry used for
SRF production are mainly different wood and plastic fractions although also bituminous mixtures
considered as non-hazardous waste can be used. The possibility to source separate materials at
construction and demolition sites can be limited thus often resulting in a mixed waste fraction.
3. Non-hazardous waste from waste management facilities
Waste received at waste management facilities are treated in diverse ways. It can be water
treatment, composting, anaerobic treatment, sorting, crushing and densifying. When doing these
treatments, the plants will end up with different waste streams aimed for recycling, recovery or
disposal. Some of these can be used for the production of SRF.
4. Non-hazardous waste from material recycling facilities
During the recycling process, there will be material that does not fulfil the quality criteria. These
reject streams can be potentially used for the production of SRF.
5. Non-hazardous municipal solid waste and similar non-hazardous commercial waste
Although an untreated mixed municipal waste stream could not be called SRF, it still can be sorted
and used for the production of SRF. Municipal solid waste includes bulky waste and waste from
gardens and parks as well as waste from markets. Source separated material streams (e.g. paper,
plastics etc.) are not intended as direct input material for SRF production but are rather intended
for material recycling. Reject from these kinds of materials can be found above under bullet 4 Non-
hazardous waste from material recycling facilities.
6. Non- hazardous waste not otherwise specified in the list
If the waste origin is not covered in the above categories, it shall be declared here. The origin of the
waste should be described as clearly as possible.
It is not unusual that waste fractions that are intended for production of SRF (or for combustion) are
mixed during the logistic chain, thus there could be waste from different origins in the same transport.
However, the principle is to give as much detail about the origin as possible. Thus, if waste has been
collected from different industries (and not being packaging waste) then the separate codes of origins
shall be stated according to Table 3.
4 © ISO 2021 – All rights reserved

ISO 21640:2021(E)
Table 3 — Sources of input material for the production of SRF
1.1.1 plastic waste (except packaging)
1.1 wastes from agricul-
ture, horticulture, aqua- 1.1.2 absorbed urine and manure (including spoiled straw),
culture, forestry, hunting collected separately and treated off-site
and fishing
1.1.3 other non- hazardous waste
1.2.1 mechanically separated rejects from pulping of waste-
paper and cardboard
1.2 wastes from pulp,
paper and cardboard pro- 1.2.2 fibre rejects, fibre-, filler- and coating-sludges from
duction and processing mechanical separation
1.2.3 other non- hazardous waste
1.3.1 non-hazardous wood waste from chemically treated
1.3 waste from wood
wood
processing, production of
panels and furniture
1.3.2 other non-hazardous waste
1. Non- hazardous
1.4.1 waste from composite materials (impregnated textile,
industrial waste
elastomer, plastomer)
1.4 wastes from the tex-
1.4.2 waste from unprocessed textile fibres
tile industry
1.4.3 waste from processed textile fibres
1.4.4 other non- hazardous waste
1.5.1 plastic waste (except packaging)
1.5 wastes from organic 1.5.2 solid wastes other than solid wastes containing haz-
chemical processes ardous substances
1.5.3 other non- hazardous waste
1.6 wastes from shaping
and physical and mechan-
ical surface treatment of
plastics
1.7.1 paper and cardboard packaging
1.7.2 plastic packaging
1.7.3 wooden packaging
1.7 packaging waste
1.7.4 composite packaging
1.7.5 mixed packaging
1.7.6 textile packaging
2.1.1 wood
2.1 wood and plastic
2.1.2 plastic (except packaging)
2. Non- hazardous 2.2 bituminous mixtures,
2.2.1 bituminous mixtures that are not considered as haz-
construction and coal tar and tarred prod-
ardous waste
demolition waste ucts
2.3.1 insulation materials (polyurethane and polystyrene)
2.3 other construction
and demolition wastes
2.3.2 mixed construction and demolition waste
3.1.1 non-composted fraction of municipal and similar
3.1 wastes from aerobic
wastes
treatment of solid wastes
3.1.2 non-composted fraction of animal and vegetable waste

3.2 wastes from anaer-
3.2.1 non-digestible fraction of municipal, industrial and
obic treatment of solid
other waste
waste
3.3.1 sludge from treatment of urban wastewater
3.3.2 other solid waste from treatment of urban wastewater
3.3 sludge from wastewa-
3.3.3 sludge from treatment of industrial wastewater
ter treatment plants
3.3.4 other non-hazardous solid waste from treatment of
industrial wastewater
ISO 21640:2021(E)
Table 3 (continued)
3.4.1 paper and cardboard waste
3. Non-hazardous
3.4 wastes from the
waste from waste 3.4.2 textile waste
mechanical treatment of
management facilities
3.4.3 wood waste
waste (for example sort-
3.4.4 plastic and rubber waste
ing, crushing, compact-
ing, pelletising)
3.4.5 other non-hazardous wastes (including mixtures of
materials) from mechanical treatment of wastes
3.5 end-of-life vehicles 3.5.1 end of life tyres
from different means
3.5.2 plastic waste (except packaging)
of transport (including
off-road machinery) and
wastes from dismantling
3.5.3 other non-hazardous waste from end-of-life vehicles
of end-of-life vehicles and
vehicle maintenance
4.1.1 paper and cardboard waste
4.1.2 textile waste
4.1 reject fractions
4 Non-hazardous
from material recycling 4.1.3 wood waste
waste from material
facilities, not otherwise
4.1.4 plastic waste
recycling facilities
mentioned
4.1.5 other non-hazardous waste from material recycling
facilities
5.1 residual municipal
solid waste
5. Non-hazardous
5.2.1 wood waste
municipal solid waste
5.2 bulky waste 5.2.2 plastic waste (except packaging)
or similar non-haz-
5.2.3 mixed combustible bulky waste
ardous commercial
waste
5.3 other municipal solid 5.3.1 waste from markets
waste or similar commer-
5.3.2 park and garden waste
cial waste
6 Non-hazardous
any non-hazardous waste that is not defined by the codes above, to be specified by the
waste not otherwise
supplier
specified in the list
NOTE 1 There can be national legislation demanding the use of national or regional waste catalogues/lists
codes in the specification. In these cases, that information can also be stated in the specification table.
NOTE 2 Some waste streams of biomass origin can fulfil requirement for a solid biofuel and can be specified
[1]
according to ISO 17225-1 .
NOTE 3 The list of origins has been developed from the base of the European waste catalogue but been heavily
modified and simplified to accommodate the streams most commonly used as input material for SRF production.
7.3 Traded forms of solid recovered fuels
Solid recovered fuels are traded in many varied sizes and shapes. The size and shape influence the
handling of the fuel as well as its combustion properties. Recovered fuels can be delivered in the forms
shown in Table 4. Other forms are also present on the market.
6 © ISO 2021 – All rights reserved

ISO 21640:2021(E)
Table 4 — Examples of major traded forms of solid recovered fuels
Form name Description
Chips Prepared by cutting with sharp tools, particle
sizes often between 5-100 mm
Crushed material Prepared by crushing or shredding
Example:
Fluff
Densified fuels Prepared by mechanical compression
Example:
Pellets
Briquettes
Bales Compressed or loose material bound to squares
or cylinders, indicative size 1-2 m
Example:
Big square bales Some bales are wrapped in plastic to decrease
Round bales (cylindrical) odour problems and to increase fire safety dur-
ing transport and storage.
Fibre cake Prepared from fibrous waste by dewatering
Granulate Usually in the size of 1-10 mm, produced either
through agglomeration of powder or by grinding
material down to appropriate size
7.4 Properties obligatory to specify
The following properties shall be specified according to the specification template in Annex A:
Class code shall be filled in as described in Clause 6. Actual values on the fuel prop-
erties included in the classification system shall be filled in as well. These
are net calorific value, chlorine and mercury content
Origin of the input waste used for preparation of the SRF shall be specified. It can
be done either by text or by the three-digit codes according to 7.2.
Traded form of the SRF shall be specified. Examples of forms are pellets, bales, briquettes,
chips, flakes, fluff and powder. For reference see 7.3. Other forms can be
used and shall then be specified separately
Particle diameter (d ) in the fuel shall be specified by sieving or equivalent techniques, and be
x
expressed as d , where d is the particle size on the distribution curve where
x
x % in mass passes. The value could either be stated as a fixed value or as
a P-designated value (see Annex A and example in Annex F)
Ash content (A) shall be specified on dry bases according to ISO 21656
Moisture content (M) shall be specified as received according to ISO 21660-3
Net calorific value (NCV) shall be specified both as received and on dry bases according to ISO 21654.
The values shall be expressed as an arithmetic mean on both dry and as
received basis.
Chemical properties the chlorine content shall be specified based on dry basis and given as
an arithmetic mean, the content of each heavy metal separately shall be
specified as median on dry basis. The heavy metals are antimony, arsenic,
cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel,
thallium, tin and vanadium.
ISO 21640:2021(E)
7.5 Properties non-obligatory to specify
Other properties than the ones specified in Annex A can be of interest for the end user and can be used
as an effective communication tool with producers, power plant builders and equipment manufacturers.
The producers and the users should agree upon which properties (if any) that are relevant. Some of the
more common properties that can be of interest are:
Biomass content the fraction of biomass can be expressed by weight, by energy content or
by carbon content. The biomass content in percent by carbon content is
necessary to calculate the emission of biomass or fossil carbon dioxide per
unit of SRF. The determination is recommended to be done according to
[3]
ISO 21644 .
Composition is the percentage in mass of main fractions of wood, paper, plastics, rubber,
textiles etc. The number of fractions to be specified is agreed between the
producer and the user. The basis (dry or wet) should be specified.
Fuel preparation depends on the input waste and the field of application. Since the prepara-
tion effects the properties of the fuel it can be of interest to describe. The
description also gives valuable information to the end-user that could be
used when planning how to store, transport and handle the fuel. Common
fuel preparation techniques are given in Annex B. Annex B can also be used
as a template.
Physical properties example of other parameters that can be used for specification of the SRF are:
— particle size distribution (including defining fines and coarse material)
— bulk density (ρ) and the result to be expressed as an arithmetic mean
on as received basis,
[4]
— volatile matter (VM), where it is recommended to use ISO 22167 and
the result expressed as median in percent in mass on dry basis,
— bridging behaviour,
— self-heating properties,
— the ash melting behaviour.
Chemical properties such as major and trace elements in the fuel can be specified.
— carbon (C), hydrogen (H), nitrogen (N) and sulphur (S) is recommended
[5]
to be determined according to ISO 21663 and expressed as an
arithmetic mean on dry basis,
— halogens (F, Br, I) expressed as median on dry basis,
— trace elements expressed as median on dry basis.
There are several other properties that can be used for defining SRF. Such properties, like dusting,
odour, ignition temperature, can be added to the list of informative parameters in the template.
8 © ISO 2021 – All rights reserved

ISO 21640:2021(E)
8 Compliance rules
8.1 Compliance rules for classification
8.1.1 General compliance rules
The compliance rules for classification are illustrated by examples in Annex E.
For each characteristic specified in the classification system, the compliance of a particular SRF shall be
established by demonstration that the results of the measured properties conform to the limit values
defined for that class. The compliance is based on
— a defined maximum lot size of 1 500 tonnes
— a minimum number of increments as well as a minimum size of those increments to form a composite
sample
— a minimum number of measurements to be performed.
The demonstration shall be based on the measurements of 10 lots. This can either be in the form of lot
1-10, 11-20, etc or in the form of 1-10, 2-11, etc. The maximum weight of a lot for classification shall be no
more than 1 500 tonnes. The compliance shall be documented in a quality monitoring system.
For each lot, at least one measurement of each characteristic shall be performed. The sampling procedure
is illustrated in Figure 2. For sampling, ISO 21645 shall be applied. A sub-sample of the laboratory
sample (retained sample) shall be kept for a period of minimum 6 months in case of a cross check is
needed. In order to reduce the quantity for the storage of the retained sample a particle size reduction
and sample division can be performed. The retained sample should be taken into consideration when
determining the minimum laboratory sample size according to ISO 21645.
Figure 2 — Illustration of sampling and sample procedure. Number and size of increments
depend on the heterogeneity of the SRF and on required accuracy and precision
ISO 21640:2021(E)
The comparison for NCV and Cl with the limit values of the classes is made by taking the arithmetic
mean of 10 measurements into account.
th
The class code for Hg is established using median and 80 percentile based on data sets of 10
consecutive measurements. For process control reasons, it is recommended to calculate the median
th
and the 80 -percentile value after the measurement of every lot (e.g. for data sets No. 1 to No. 10 / No. 2
to No. 11 / etc.) and to consider the brief time variation of the analytical results.
EXAMPLE The class code of a SRF having a mean net calorific value of 19 MJ/kg (ar), a mean chlorine content
th
of 0,5 % in mass (d) and a median mercury content of 0,016 mg/MJ (ar) with 80 percentile value of 0,05 mg/MJ
(ar) is designated as:
Class code NCV 3; Cl 2; Hg 2.
For other examples, see Annex E-F.
If there are significant changes in the properties of input materials or in the production process that
result in a change of class code, see 8.1.2.
8.1.2 Start-up or considerable changes in the production
After the start of the production of SRF or after a notable change in the production, the minimum of 10
measurement results can be obtained on one or several lots as defined above. When several composite
samples are taken on the same lot they shall be taken independently.
Within the characterisation period it is recommended to use as a prediction method for virgin producers
the 50 % rule for Hg classification. This prediction method is working according to the principle of a
conservative classification (indirect safety margin).
NOTE The 50 % rule means that classification is determined by comparing the measurement results to 50 %
[2]
of the class limits (median and/or 80-percentile). More details are available in CEN/TR 15508 .
8.1.3 Exemptions
If the producer can show that due to the nature of the input material used for the production of SRF,
Hg is always in class 1 when the 50 % rule is applied according to Clause 6, then Hg will not have to
be analysed in every lot. (See 8.1.2 for description of the 50 % rule). This exemption is applicable
after the start-up of the production of SRF when at least 10 measurement results are available. All 10
measurement results must be within the class 1 limit. In this case the validity shall be checked at least
once every year.
This exemption will only be accepted as long as there are no significant changes in the properties of
input materials that would result in a change of class for Hg.
For large streams of solid recovered fuels not every lot has to be measured. The maximum lot size
remains with 1 500 tonnes and at minimum two lots per month have to be measured. In any case, for
each lot a laboratory sample must be taken and shall be kept for a period of minimum 12 months.
8.2 Compliance rules for specification
8.2.1 General compliance rules
For the chemical properties according to 7.4 and Annex A, the compliance rules specified for the
classification apply.
If the producer and user have agreed upon additional properties to be specified (see 7.5), they can also
agree upon lot size up to a maximum of 1 500 tonnes and the number of measurements to consider for
10 © ISO 2021 – All rights reserved

ISO 21640:2021(E)
compliance. These elements should be stated in the specification. In case these elements are not defined
in the SRF specification, then the lot size and compliance rules specified for the classification apply.
8.2.2 Exemptions
If the producer can show that due to the nature of the input material used for the production, one or
more normative properties according to Annex A are not relevant, then the user and the producer can
agree upon reducing the samples that should be analysed. In this case the validity shall be checked
at least once every year.
...