ISO 1928:2025

Coal and coke — Determination of gross calorific value

This document specifies a method for the determination of the gross calorific value of coal and coke at constant volume and at the reference temperature of 25 °C in a combustion vessel calorimeter calibrated by combustion of certified benzoic acid. The result obtained is the gross calorific value of the analysis sample at constant volume with all the water of the combustion products as liquid water. In practice, fuel is burned at constant (atmospheric) pressure and the water is not condensed but is removed as vapour with the flue gases. Under these conditions, the operative heat of combustion is the net calorific value of the fuel at constant pressure. The net calorific value at constant volume can also be used; formulae are given for calculating both values. General principles and procedures for the calibrations and the fuel tests are specified in the main text, whereas those pertaining to the use of a particular type of calorimetric instrument are described in Annexes A to C. Annex D contains checklists for performing calibration and fuel tests using specified types of calorimeters. Annex E gives examples illustrating some of the calculations. Annex F provides guidance around safe use, maintenance and testing of the calorimeter combustion vessel. NOTE Descriptors: solid fuels, coal, coke, tests, determination, calorific value, rules of calculation, calorimetry.

Charbon et coke — Détermination du pouvoir calorifique supérieur

General Information

• Status: Published
• Publication Date: 12-Aug-2025
• ICS: 73.040 - Coals
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 5 - Methods of analysis
• Drafting Committee: ISO/TC 27/SC 5 - Methods of analysis
• Current Stage: 6060 - International Standard published
• Start Date: 13-Aug-2025
• Due Date: 20-May-2026
• Completion Date: 13-Aug-2025

Relations

• Revises: ISO 1928:2020 - Coal and coke — Determination of gross calorific value
• Effective Date: 27-May-2023

Standards Content (Sample)

International
Standard
ISO 1928
Fifth edition
Coal and coke — Determination of
2025-08
gross calorific value
Charbon et coke — Détermination du pouvoir calorifique
supérieur
Reference number
© ISO 2025
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
3.1 Terms and definitions .2
3.2 Symbols .3
4 Principle . 6
4.1 Gross calorific value .6
4.2 Net calorific value .7
5 Reagents . 7
6 Apparatus . 8
7 Preparation of test sample .12
8 Calorimetric procedure .13
8.1 General . 13
8.2 Preparing the combustion vessel for measurement . 15
8.2.1 General procedure . 15
8.2.2 Using a combustion aid . 15
8.3 Assembling the calorimeter .16
8.4 Combustion reaction and temperature measurements .16
8.5 Analysis of products of combustion .17
8.6 Corrected temperature rise .17
8.6.1 Observed temperature rise, t − t .17
f i
8.6.2 Isoperibol and static-jacket calorimeters.17
8.6.3 Adiabatic calorimeters .18
8.6.4 Thermometer corrections . .19
8.7 Reference temperature .19
9 Calibration . 19
9.1 Principle .19
9.2 Calibrant .19
9.2.1 Certification conditions .19
9.2.2 Calibration conditions .19
9.3 Valid working range of the effective heat capacity . 20
9.4 Ancillary contributions . 20
9.5 Calibration procedure .21
9.6 Calculation of effective heat capacity for the individual test .21
9.6.1 Constant mass-of-calorimeter-water basis .21
9.6.2 Constant total-calorimeter-mass basis .21
9.7 Precision of the mean value of the effective heat capacity . 22
9.7.1 Constant value of ε . 22
9.7.2 ε as a function of the observed temperature rise . 22
9.8 Redetermination of the effective heat capacity . 23
10 Gross calorific value .23
10.1 General . 23
10.2 Coal combustions . 23
10.3 Coke combustions .24
10.4 Calculation of gross calorific value.24
10.4.1 General .24
10.4.2 Constant mass-of-calorimeter-water basis . 25
10.4.3 Constant total-calorimeter-mass basis . 26
10.4.4 ε as a function of the observed temperature rise . 26
10.5 Expression of results . 26

iii
10.6 Calculation to other bases .27
11 Precision .27
11.1 Repeatability limit .27
11.2 Reproducibility limit .27
12 Calculation of net calorific value .27
12.1 General .27
12.2 Calculations . 28
12.2.1 Calculation of net calorific value at constant pressure . 28
12.2.2 Calculation of net calorific value at constant volume . 29
13 Test report .30
Annex A (informative) Adiabatic calorimeters .32
Annex B (informative) Isoperibol and static-jacket calorimeters .36
Annex C (informative) Automated calorimeters . 41
Annex D (informative) Checklists for the design of combustion tests and their procedures .44
Annex E (informative) Examples to illustrate some of the calculations used in this document .49
Annex F (informative) Safe use, maintenance and testing of calorimeter combustion vessels .55
Bibliography . 61

iv
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
...

FINAL DRAFT
International
Standard
ISO/FDIS 1928
ISO/TC 27/SC 5
Coal and coke — Determination of
Secretariat: SA
gross calorific value
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Charbon et coke — Détermination du pouvoir calorifique 2025-05-14
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Voting terminates on:
2025-07-09
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Reference number
ISO/FDIS 1928:2025(en) © ISO 2025

FINAL DRAFT
ISO/FDIS 1928:2025(en)
International
Standard
ISO/FDIS 1928
ISO/TC 27/SC 5
Coal and coke — Determination of
Secretariat: SA
gross calorific value
Voting begins on:
Charbon et coke — Détermination du pouvoir calorifique
supérieur
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 1928:2025(en) © ISO 2025

ii
ISO/FDIS 1928:2025(en)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
3.1 Terms and definitions .2
3.2 Symbols .3
4 Principle . 6
4.1 Gross calorific value .6
4.2 Net calorific value .7
5 Reagents . 7
6 Apparatus . 8
7 Preparation of test sample .13
8 Calorimetric procedure .13
8.1 General . 13
8.2 Preparing the combustion vessel for measurement . 15
8.2.1 General procedure . 15
8.2.2 Using a combustion aid . 15
8.3 Assembling the calorimeter .16
8.4 Combustion reaction and temperature measurements .16
8.5 Analysis of products of combustion .17
8.6 Corrected temperature rise .17
8.6.1 Observed temperature rise, t − t .17
f i
8.6.2 Isoperibol and static-jacket calorimeters.17
8.6.3 Adiabatic calorimeters .19
8.6.4 Thermometer corrections . .19
8.7 Reference temperature .19
9 Calibration . 19
9.1 Principle .19
9.2 Calibrant .19
9.2.1 Certification conditions .19
9.2.2 Calibration conditions . 20
9.3 Valid working range of the effective heat capacity . 20
9.4 Ancillary contributions .21
9.5 Calibration procedure .21
9.6 Calculation of effective heat capacity for the individual test .21
9.6.1 Constant mass-of-calorimeter-water basis .21
9.6.2 Constant total-calorimeter-mass basis . 22
9.7 Precision of the mean value of the effective heat capacity . 23
9.7.1 Constant value of ε . 23
9.7.2 ε as a function of the observed temperature rise . 23
9.8 Redetermination of the effective heat capacity . 23
10 Gross calorific value .24
10.1 General .24
10.2 Coal combustions .24
10.3 Coke combustions .24
10.4 Calculation of gross calorific value. 25
10.4.1 General . 25
10.4.2 Constant mass-of-calorimeter-water basis . 25
10.4.3 Constant total-calorimeter-mass basis . 26
10.4.4 ε as a function of the observed temperature rise . 26
10.5 Expression of results . 26

iii
ISO/FDIS 1928:2025(en)
10.6 Calculation to other bases . 28
11 Precision .28
11.1 Repeatability limit . 28
11.2 Reproducibility limit . 28
12 Calculation of net calorific value .29
12.1 General . 29
12.2 Calculations . 29
12.2.1 Calculation of net calorific value at constant pressure . 29
12.2.2 Calculation of net calorific value at constant volume .31
13 Test report .32
Annex A (informative) Adiabatic calorimeters .33
Annex B (informative) Isoperibol and static-jacket calorimeters .
...

ISO/FDIS 1928:2025(en)
ISO /TC 27/SC 05/WG 12 5
Secretariat: SA
Date: 2025-03-2104-30
Coal and coke — Determination of gross calorific value
Charbon et coke — Détermination du pouvoir calorifique supérieur
FDIS stage
ISO/FDIS 1928:2025(en)
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
and microfilm, or posting on the internet or an intranet, without prior written permission in writing. Permission can be
requested from either ISO at the address below or ISO'sISO’s member body in the country of the requester.
ISO copyright office
Case postale 56 • CP 401 • Ch. de Blandonnet 8
CH-12111214 Vernier, Geneva 20
Tel.Phone: + 41 22 749 01 11
Fax + 41 22 734 10 79
E-mail: [e-mail]
Website: [e-mail]
Field Code Changed
Web
PrintedPublished in Switzerland

ii
ISO/FDIS 1928:2025(en)
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
4 Principle . 6
5 Reagents . 7
6 Apparatus . 8
7 Preparation of test sample . 14
8 Calorimetric procedure . 14
9 Calibration . 21
10 Gross calorific value . 26
11 Precision . 30
12 Calculation of net calorific value . 30
13 Test report . 34
Annex A (informative) Adiabatic calorimeters . 35
Annex B (informative) Isoperibol and static-jacket calorimeters . 39
Annex C (informative) Automated calorimeters . 45
Annex D (informative) Checklists for the design of combustion tests and their procedures . 48
Annex E (informative) Examples to illustrate some of the calculations used in this document . 54
Annex F (informative) Safe use, maintenance and testing of calorimeter combustion vessels . 61
Bibliography . 68

iii
ISO/FDIS 1928:2025(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This fifth edition cancels and replaces the thirdfourth edition (ISO 1928:20092020), which has been
technically revised.
The main changes are as follows:
— — change the document title within the scope of TC 27;
— — title changechanged from solid mineral fuels to coal and coke;— editorially update;
— updated symbols within formulae;
— — editorial update of Forward; — update references, including the year of publication to withdrawn
standards listed in normative references;
— — allowance for alternative material for calorimeter can;— expand;
— expanded on some derivations and added units of measure to some equations;
— — removeremoved ambiguity around crucible masses;
— — specifyspecified the analysis sample;
— — more concise wording around the use of a combustion aid and determining a correction value;
iv
ISO/FDIS 1928:2025(en)
— — warnings now included in body of text;.;
— — the addition of alternate ignition methods.
Any feedback or questions on this document shall be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
Field Code Changed
v
ISO/FDIS 1928:2025(en)
Coal and coke — Determination of gross calorific value
WARNING — Strict adherence to all of the provisions specified in this document needis needed to
ensure against explosive rupture of the combustion vessel, or a blow-out, provided that the
combustion vessel is of proper design and construction and in good mechanical condition.
1 Scope
This document specifies a method for the determination of the gross calorific value of coal and coke at constant
volume and at the reference temperature of 25 °C in a combustion vessel calorimeter calibrated by
combustion of certified benzoic acid.
The result obtained is the gross calorific value of the analysis sample at constant volume with all the water of
the combustion products as liquid water. In practice, fuel is burned at constant (atmospheric) pressure and
the water is not condensed but is removed as vapour with the flue gases. Under these conditions, the operative
heat of combustion is the net calorific value of the fuel at constant pressure. The net calorific value at constant
volume can also be used; formulae are given for calculating both values.
General principles and procedures for the calibrations and the fuel tests are specified in the main text, whereas
those pertaining to the use of a particular type of calorimetric instrument are described in
Annexes AAnnexes A to CC. Annex D. Annex D contains checklists for performing calibration and fuel tests
using specified types of calorimeters. Annex EAnnex E gives examples illustrating some of the calculations.
Annex FAnnex F provides guidance around safe use, maintenance and testing of the calorimeter combustion
vessel.
NOTE Descriptors: solid fuels, coal, coke, tests, determination, calorific value, rules of calculation, calorimetry.
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.
1)
ISO 651 (:1975),, Solid-stem calorimeter thermometers
1)
ISO 652 (:1975),, Enclosed-scale calorimeter thermometers
ISO 687, Coke — Determination of moisture in the general analysis test sample
1)
ISO 1770 (:1981),, Solid-stem general purpose thermometers
1)
ISO 1771 (:1981),, Enclosed-scale general purpose thermometers
ISO 5068--2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test sample by
drying in nitrogen
ISO 13909--4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples of coal

1)
Withdrawn.
ISO/FDIS 1928:2025(en)
ISO 17247, Coal and coke — Ultimate analysis
ISO 18283, Coal and coke — Manual sampling
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1.1 3.1.1
gross calorific value at constant volume
absolute value of the specific energy of combustion for unit mass of a solid fuel burned in oxygen in a
calorimetric combustion vessel under the conditions specified
Note 1 to entry: The products of combustion are assumed to consist of gaseous oxygen, nitrogen, carbon dioxide and
sulfur dioxide, of liquid water (in equilibrium with its vapour) saturated with carbon dioxide under the conditions of the
combustion vessel reaction, and of solid ash, all at the reference temperature.
Note 2 to entry: Gross calorific value is expressed in units of joules/gram.
3.1.2 3.1.2
gross calorific value at constant pressure
absolute value of the specific energy of combustion, for unit mass of a solid fuel burned in oxygen at constant
pressure, instead of constant volume in a calorimetric combustion vessel
Note 1 to entry: The hydrogen in the fuel, reacting with gaseous oxygen to give liquid water, causes a decrease in the
volume of the system. When the fuel carbon reacts with gaseous oxygen, an equal volume of gaseous carbon dioxide is
formed and, hence, no change in volume occurs in combustion of the carbon. The oxygen and nitrogen in the fuel both
give rise to an increase in volume.
3.1.3 3.1.3
net calorific value at constant volume
absolute value of the specific energy of combustion, for unit mass of a solid fuel burned in oxygen under
conditions of constant volume and such that all the water of the reaction products remains as water vapour
(in a hypothetical state at 0,1 MPa), the other products being as for the gross calorific value, all at the reference
temperature (3.1.8(3.1.8))
3.1.4 3.1.4
net calorific value at constant pressure
absolute value of the specific heat (enthalpy) of combustion, for unit mass of the fuel burned in oxygen at
constant pressure under such conditions that all the water of the reaction products remains as water vapour
(at 0,1 MPa), the other products being as for the gross calorific value, all at the reference temperature
(3.1.8(3.1.8))
3.1.5 3.1.5
adiabatic calorimeter
calorimeter that has a rapidly changing jacket temperature
ISO/FDIS 1928:2025(en)
Note 1 to entry: The inner calorimeter chamber and the jacket exchange no energy because the water temperature in
both is identical during the test. The water in the external jacket is heated or cooled to match the temperature change in
the calorimeter proper.
3.1.6 3.1.6
isoperibol calorimeter
calorimeter that has a jacket of uniform and constant temperature
Note 1 to entry: These calorimeters have the inner chamber surrounded by a water jacket in which the temperature is
maintained at ambient temperature. The outer jacket acts like a thermostat and the thermal conductivity of the interspace
between the two chambers is kept as small as possible.
3.1.7 3.1.7
aneroid calorimeter
calorimeter system without fluid, where the calorimeter can, stirrer and water are replaced by a metal block
and the combustion vessel itself constitutes the calorimeter
Note 1 to entry: Characteristically, these calorimeters have a small heat capacity, leading to large changes in
temperature. Therefore, smaller masses of sample are used. A calorimeter of this kind requires more frequent
calibrations.
3.1.8 3.1.8
reference temperature
international reference
...