Solid biofuels - Determination of grindability - Hardgrove type method for thermally treated biomass fuels (ISO/TS 21596:2021)

This document describes a method for determination of grindability of graded thermally treated and densified biomass fuels such as classified in ISO/TS 17225-8, for the purposes of preparing fuels with a defined particle size distribution for effective combustion in pulverized fuel boilers.
The grindability characteristics determined by the test method provide guidance as to the pulverizing mill performance when utilizing such fuels.
Apart from pelletized materials as described in ISO/TS 17225-8, the method can also be applied to non-compressed or non-densified thermally treated biomass as specified in ISO 17225-1 Table 14 and Table 15.
The results created with this method are not relevant for large wood chips, since limitations apply for large pulverizing coal mills, which are typically not used for grinding materials such as chips.

Biogene Festbrennstoffe - Bestimmung der Mahlbarkeit - Hardgrove-Verfahren für thermisch behandelte Brennstoffe aus Biomasse (ISO/PRF TS 21596:2021)

Dieses Dokument beschreibt ein Verfahren zur Bestimmung der Mahlbarkeit von klassifizierten thermisch behandelten und gepressten Brennstoffen aus Biomasse, wie sie in ISO/TS 17225-8 klassifiziert werden, zur Herstellung von Brennstoffen mit einer festgelegten Partikelgrößenverteilung für eine wirksame Verbrennung in Heizkesseln für pulverisierte Brennstoffe. Die mit dem Prüfverfahren bestimmten Mahlbarkeitseigenschaften geben Hinweise auf das Leistungsverhalten der Pulverisiermühle bei der Verwendung derartiger Brennstoffe.
Neben pelletierten Materialien, wie in ISO/TS 17225-8 beschrieben, kann das Verfahren auch auf nicht gepresste thermisch behandelte Biomasse, wie in ISO 17225-1:2021, Tabelle 14 und Tabelle 15 festgelegt, angewendet werden.
Die mit diesem Verfahren erzielten Ergebnisse sind für große Holzhackschnitzel nicht relevant, da für große Kohlenstaubmühlen, die typischerweise nicht zur Zerkleinerung von Materialien wie z. B. Hackschnitzeln verwendet werden, Einschränkungen gelten.

Biocombustibles solides - Détermination de la broyabilité - Méthode de type Hardgrove pour les combustibles de biomasses traitées thermiquement (ISO/TS 21596:2021)

Trdna biogoriva - Določanje stopnje mletja - Metoda trdega grozda za toplotno obdelana goriva iz biomase (ISO/TS 21596:2021)

General Information

Status
Published
Public Enquiry End Date
30-Sep-2021
Publication Date
23-Nov-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
11-Nov-2021
Due Date
16-Jan-2022
Completion Date
24-Nov-2021

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SLOVENSKI STANDARD
SIST-TS CEN ISO/TS 21596:2022
01-januar-2022
Trdna biogoriva - Določanje stopnje mletja - Metoda trdega grozda za toplotno
obdelana goriva iz biomase (ISO/TS 21596:2021)

Solid biofuels - Determination of grindability - Hardgrove type method for thermally

treated biomass fuels (ISO/TS 21596:2021)
Biogene Festbrennstoffe - Bestimmung der Mahlbarkeit - Hardgrove-Verfahren für
thermisch behandelte Brennstoffe aus Biomasse (ISO/PRF TS 21596:2021)

Biocombustibles solides - Détermination de la broyabilité - Méthode de type Hardgrove

pour les combustibles de biomasses traitées thermiquement (ISO/TS 21596:2021)
Ta slovenski standard je istoveten z: CEN ISO/TS 21596:2021
ICS:
75.160.40 Biogoriva Biofuels
SIST-TS CEN ISO/TS 21596:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST-TS CEN ISO/TS 21596:2022
---------------------- Page: 2 ----------------------
SIST-TS CEN ISO/TS 21596:2022
CEN ISO/TS 21596
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
November 2021
TECHNISCHE SPEZIFIKATION
ICS 75.160.40
English Version
Solid biofuels - Determination of grindability - Hardgrove
type method for thermally treated biomass fuels (ISO/TS
21596:2021)

Biocombustibles solides - Détermination de la Biogene Festbrennstoffe - Bestimmung der

broyabilité - Méthode de type Hardgrove pour les Mahlbarkeit - Hardgrove-Verfahren für thermisch

combustibles de biomasses traitées thermiquement behandelte Brennstoffe aus Biomasse (ISO/TS

(ISO/TS 21596:2021) 21596:2021)

This Technical Specification (CEN/TS) was approved by CEN on 28 September 2021 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to

submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS

available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in

parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

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. CEN ISO/TS 21596:2021 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST-TS CEN ISO/TS 21596:2022
CEN ISO/TS 21596:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST-TS CEN ISO/TS 21596:2022
CEN ISO/TS 21596:2021 (E)
European foreword

This document (CEN ISO/TS 21596:2021) has been prepared by Technical Committee ISO/TC 238

"Solid biofuels" in collaboration with Technical Committee CEN/TC 335 “Solid biofuels” the secretariat

of which is held by SIS.

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.

Any feedback and questions on this document should be directed to the users’ national standards

body/national committee. A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to announce this Technical Specification: 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/TS 21596:2021 has been approved by CEN as CEN ISO/TS 21596:2021 without any

modification.
---------------------- Page: 5 ----------------------
SIST-TS CEN ISO/TS 21596:2022
---------------------- Page: 6 ----------------------
SIST-TS CEN ISO/TS 21596:2022
TECHNICAL ISO/TS
SPECIFICATION 21596
First edition
2021-10
Solid biofuels — Determination of
grindability — Hardgrove type method
for thermally treated biomass fuels
Biocombustibles solides — Détermination de la broyabilité —
Méthode de type Hardgrove pour les combustibles de biomasses
traitées thermiquement
Reference number
ISO/TS 21596:2021(E)
© ISO 2021
---------------------- Page: 7 ----------------------
SIST-TS CEN ISO/TS 21596:2022
ISO/TS 21596:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© 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 on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2021 – All rights reserved
---------------------- Page: 8 ----------------------
SIST-TS CEN ISO/TS 21596:2022
ISO/TS 21596:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus .................................................................................................................................................................................................................... 2

5.1 Standard HGI mill ................................................................................................................................................................................. 2

5.2 Sieves ............................................................................................................................................................................................................... 2

5.3 Glass measuring cylinder .............................................................................................................................................................. 2

5.4 Sieving machine ..................................................................................................................................................................................... 3

5.5 Balance .......................................................................................................................................................................................................... 3

5.6 Cutting mill ................................................................................................................................................................................................ 3

6 Sampling and sample preparation .................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Moisture conditions ........................................................................................................................................................................... 3

6.3 Pre-grinding and sieving ............................................................................................................................................................... 3

6.4 Sample size ................................................................................................................................................................................................. 3

7 Procedure ....................................................................................................................................................................................................................3

8 Calculation .................................................................................................................................................................................................................. 4

9 Reproducibility ...................................................................................................................................................................................................... 5

10 Test report .................................................................................................................................................................................................................. 5

Annex A (normative) Calibration curve and thermally treated biomass grindability index

(TTBGI) values for the reference materials............................................................................................................................ 6

Bibliography ................................................................................................................................................................................................................................ 9

iii
© ISO 2021 – All rights reserved
---------------------- Page: 9 ----------------------
SIST-TS CEN ISO/TS 21596:2022
ISO/TS 21596:2021(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 238, Solid biofuels, in collaboration with

the European Committee for Standardization (CEN) Technical Committee CEN/TC 335, Solid biofuels, in

accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

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.
© ISO 2021 – All rights reserved
---------------------- Page: 10 ----------------------
SIST-TS CEN ISO/TS 21596:2022
ISO/TS 21596:2021(E)
Introduction

Grindability characteristics are of fundamental importance during solid biofuel preparation for energy

conversion processes, requiring a predictable particle size distribution. Particles that are too large or

too wide in their distribution may result in feeding problems as well as un-burnt fuel passing through

the conversion process. Also, in case of processing of biomass for pre-treatment, consistency in particle

size determines the yield of such pre-treatment as well as the quality of the final solid biofuel.

The effectiveness of combustion in a pulverized fuel furnace depends strongly on the reactivity and

particle size distribution of the pulverized fuel among other factors. For coal, the Hardgrove Grindability

Index (HGI) test was developed to characterize the relative grindability of a particular quality of coal

relative to a pre-determined standard quality of coal (ASTM D409). The HGI test is an empirical batch

method that simulates the continuous grinding and crushing operation of a ball, table or tube type of

industrial coal pulverizer, herein also called coal mill. The HGI value is an indication of the degree of

grinding required to reach a particular particle size necessary for effective combustion.

Manufacturers of coal pulverizers for preparation of pulverized coal for combustion in coal burning

plants provide curves that show the relationships between the HGI for coal, coal mill capacity in terms

of tonne/h and coal mill power in kW. This is done as part of the boiler contract and guarantees. It

also serves as a first indication as to how to operate a mill when pulverizing different coals with

predetermined standard properties. A HGI of 50, which is standard industry convention, implies that

100 % capacity in tonnes per hour (as indicated) can be reached for the coal at a fineness of 70 % less

than 75 microns and 99,5 % less than 300 microns. If a coal has a HGI of less than 50 it implies some

level of pulverizer capacity loss while on the other hand, a HGI higher than 50 indicates some level

of pulverizer capacity gain. The HGI method is internationally accepted and quoted as part of the

specification of coal for international trade.

Grindability may also be applied to thermally pre-treated compressed biomass materials, such as

pellets, for pulverization in coal mills. Pre-treatment methods for biomass fuels such as torrefaction,

steam treatment or hydro-thermal carbonization (HTC) upgrade the properties of biomass making it

more effective as a fuel. With increasing interest in the use of such pre-treated biomass fuels for direct

co-firing applications in conventional pulverized coal boilers, this method herein describes a laboratory

procedure for determination of the grindability of pre-treated biofuels for powder fuel preparation.

The HGI determination is subject to many limitations, including the fact that measurements can be

insensitive to the heterogeneous properties of coal that arise from different mineral contents, maceral

constituents and levels of maturity. Three relevant adaptations are applied to the standard HGI method

in order to extend its applicability to thermally pre-treated biomass fuels. The adaptations and their

justification are as follows:
— Amount of sample used for the test determination.
— Particle size used as basis for defining grindability.
— Reference materials for establishing the calibration curve.
0.1 Amount of the sample used for test determination

Coal pulverizers are volumetric devices but with the densities of coals being fairly similar, the capacity

of these devices is expressed in mass units per hour. In contrast different biomass materials have

different densities. Therefore, the sample amount was changed to the volume (75 ± 0,5) cm of input

material, which approximates the bulk volume of the standard reference coal samples with a particle

size between 1,18 mm and 600 μm.
0.2 Particle size used as basis for defining grindability

The standard HGI test for coal uses the mass of particles passing a sieve with an aperture size of 75 μm

as criteria for determining the grindability and the resulting HGI value. The furnace volume is designed

from the knowledge of coals to be utilized so as to provide an adequate residence time for c

...

SLOVENSKI STANDARD
kSIST FprEN ISO/TS 21596:2021
01-september-2021
Trdna biogoriva - Določanje stopnje mletja - Metoda trdega grozda za toplotno
obdelana goriva iz biomase (ISO/PRF TS 21596:2021)

Solid biofuels - Determination of grindability - Hardgrove type method for thermally

treated biomass fuels (ISO/PRF TS 21596:2021)
Biogene Festbrennstoffe - Bestimmung der Mahlbarkeit - Hardgrove-Verfahren für
thermisch behandelte Brennstoffe aus Biomasse (ISO/PRF TS 21596:2021)

Biocombustibles solides - Détermination de la broyabilité - Méthode de type Hardgrove

pour les combustibles de biomasses traitées thermiquement (ISO/PRF TS 21596:2021)

Ta slovenski standard je istoveten z: FprCEN ISO/TS 21596
ICS:
75.160.40 Biogoriva Biofuels
kSIST FprEN ISO/TS 21596:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
kSIST FprEN ISO/TS 21596:2021
---------------------- Page: 2 ----------------------
kSIST FprEN ISO/TS 21596:2021
TECHNICAL ISO/TS
SPECIFICATION 21596
First edition
Solid biofuels — Determination
of grindability — Hardgrove type
method for thermally treated biomass
fuels
PROOF/ÉPREUVE
Reference number
ISO/TS 21596:2021(E)
ISO 2021
---------------------- Page: 3 ----------------------
kSIST FprEN ISO/TS 21596:2021
ISO/TS 21596:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© 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

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
kSIST FprEN ISO/TS 21596:2021
ISO/TS 21596:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus ..................................................................................................................................................................................................................... 2

5.1 Standard HGI mill ................................................................................................................................................................................. 2

5.2 Sieves ............................................................................................................................................................................................................... 2

5.3 Glass measuring cylinder ............................................................................................................................................................... 2

5.4 Sieving machine ..................................................................................................................................................................................... 3

5.5 Balance ........................................................................................................................................................................................................... 3

5.6 Cutting mill ................................................................................................................................................................................................. 3

6 Sampling and sample preparation .................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Moisture conditions ............................................................................................................................................................................ 3

6.3 Pre-grinding and sieving ................................................................................................................................................................ 3

6.4 Sample size ................................................................................................................................................................................................. 3

7 Procedure..................................................................................................................................................................................................................... 3

8 Calculation .................................................................................................................................................................................................................. 4

9 Reproducibility ...................................................................................................................................................................................................... 5

10 Test report ................................................................................................................................................................................................................... 5

Annex A (normative) Calibration curve and Thermally Treated Biomass Grindability Index

(TTBGI) values for the reference materials ............................................................................................................................. 6

Bibliography ................................................................................................................................................................................................................................ 9

© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 5 ----------------------
kSIST FprEN ISO/TS 21596:2021
ISO/TS 21596:2021(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 238 Solid biofuels.

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 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
kSIST FprEN ISO/TS 21596:2021
ISO/TS 21596:2021(E)
Introduction

Grindability characteristics are of fundamental importance during solid biofuel preparation for energy

conversion processes, requiring a predictable particle size distribution. Particles that are too large or

too wide in their distribution may result in feeding problems as well as un-burnt fuel passing through

the conversion process. Also, in case of processing of biomass for pre-treatment, consistency in particle

size determines the yield of such pre-treatment as well as the quality of the final solid biofuel.

The effectiveness of combustion in a pulverized fuel furnace depends strongly on the reactivity and

particle size distribution of the pulverized fuel among other factors. For coal, the Hardgrove Grindability

Index (HGI) test was developed to characterize the relative grindability of a particular quality of coal

relative to a pre-determined standard quality of coal (ASTM D 409). The HGI test is an empirical batch

method that simulates the continuous grinding and crushing operation of a ball, table or tube type of

industrial coal pulverizer, herein also called coal mill. The HGI value is an indication of the degree of

grinding required to reach a particular particle size necessary for effective combustion.

Manufacturers of coal pulverizers for preparation of pulverized coal for combustion in coal burning

plants provide curves that show the relationships between the HGI for coal, coal mill capacity in terms

of tonne/h and coal mill power in kW. This is done as part of the boiler contract and guarantees. It

also serves as a first indication as to how to operate a mill when pulverizing different coals with

predetermined standard properties. A HGI of 50, which is standard industry convention, implies that

100 % capacity in tonnes per hour (as indicated) can be reached for the coal at a fineness of 70 % less

than 75 microns and 99,5 % less than 300 microns. So, if a coal has a HGI of less than 50 it implies

some level of pulverizer capacity loss while on the other hand, a HGI higher than 50 indicates some

level of pulverizer capacity gain. The HGI method is internationally accepted and quoted as part of the

specification of coal for international trade.

Grindability may also be applied to thermally pre-treated compressed biomass materials, such as

pellets, for pulverization in coal mills. Pre-treatment methods for biomass fuels such as torrefaction,

steam treatment or hydro-thermal carbonization (HTC) upgrade the properties of biomass making it

more effective as a fuel. With increasing interest in the use of such pre-treated biomass fuels for direct

co-firing applications in conventional pulverized coal boilers, this method herein describes a laboratory

procedure for determination of the grindability of pre-treated biofuels for powder fuel preparation.

The HGI determination is subject to many limitations, including the fact that measurements can be

insensitive to the heterogeneous properties of coal that arise from different mineral contents, maceral

constituents and levels of maturity. Three relevant adaptations are applied to the standard HGI method

in order to extend its applicability to thermally pre-treated biomass fuels. The adaptations and their

justification are as follows:
— Amount of sample used for the test determination.
— Particle size used as basis for defining grindability.
— Reference materials for establishing the calibration curve.
0.1 Amount of the sample used for test determination

Coal pulverizers are volumetric devices but with the densities of coals being fairly similar, the capacity

of these devices is expressed in mass units per hour. In contrast different biomass materials have

different densities. Therefore, the sample amount was changed to the volume (75 ± 0,5) cm of input

material, which approximates the bulk volume of the standard reference coal samples with a particle

size between 1,18 mm and 600 μm.
0.2 Particle size used as basis for defining grindability

The standard HGI test for coal uses the mass of particles passing a sieve with an aperture size of 75 μm

as criteria for determining the grindability and the resulting HGI value. The furnace volume is designed

from the knowledge of coals to be utilized so as to provide an adequate residence time for complete

combustion. Combustion efficiency depends in part on fuel particle size especially for pulverized coal

© ISO 2021 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 7 ----------------------
kSIST FprEN ISO/TS 21596:2021
ISO/TS 21596:2021(E)

furnaces. As the combustion efficiency also depends on the reactivity, which is linked to volatile matter

content of fuels, the particle size for high-volatile fuels, such as thermally treated biomass, would not

necessarily need to meet the strict fineness requirements for coal powders. Therefore, a sieve with an

aperture size of 500 μm is used for determination of grindability of thermally treated biomass. This

adaptation also has positive implications on the repeatability of the determination.

0.3 Reference materials for establishing the calibration curve

In the standard HGI test for coal, four references coals are needed for calibrating a HGI mill. This enables

reproducibility of the results across different labs. For the thermally treated biomass grindability

index determination, this is the very first step. The thermally treated biomass grindability index is

an index for materials originating from biomass. The sieving behavior of biomass materials differs

fundamentally from that of coals due to the difference in the sphericity of the coal particles. Biomass

materials, including thermally treated biomass, are more fibrous and have lengthy dust particles

compared to coals. Thermal treatment processes, such as torrefaction, modifies the property of biomass

by making biomass more like charcoal. Woody charcoal is a product of slow pyrolysis, which degrades

the fibrous nature of the biomass. This consequently improves its grindability as well as the sphericity

of the pulverized fuel.

The adapted grindability method uses wood pellets (ISO 17225-2:2021 A1 class pellets) and wood

based charcoal (ISO 17225-1:2021 Table 14) as calibration reference materials. These biomass reference

materials will be given assigned Thermally Treated Biomass Grindability Index (TTBGI) values as a

result of the procedures described in the Annex A. The materials are available c
...

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