Coal and coke -- Determination of gross calorific value

This document specifies a method for the determination of the gross calorific value of a solid mineral fuel 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

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Publication Date
04-Oct-2020
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5060 - Close of voting Proof returned by Secretariat
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05-Sep-2020
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INTERNATIONAL ISO
STANDARD 1928
Fourth edition
2020-10
Coal and coke — Determination of
gross calorific value
Charbon et coke — Détermination du pouvoir calorifique supérieur
Reference number
ISO 1928:2020(E)
ISO 2020
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ISO 1928:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2020 – All rights reserved
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ISO 1928:2020(E)
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 ..................................................................................................................................................................................................................... 9

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 ......................................................................................................................................................15

8.4 Combustion reaction and temperature measurements ....................................................................................16

8.5 Analysis of products of combustion ...................................................................................................................................16

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 ......................................................................................................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 .......................................................................................................................................................................27

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ISO 1928:2020(E)

10.6 Calculation to other bases ..........................................................................................................................................................27

11 Precision ....................................................................................................................................................................................................................28

11.1 Repeatability limit .............................................................................................................................................................................28

11.2 Reproducibility limit .......................................................................................................................................................................28

12 Calculation of net calorific value.......................................................................................................................................................28

12.1 General ........................................................................................................................................................................................................28

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 ...................................................................30

13 Test report ................................................................................................................................................................................................................31

Annex A (informative) Adiabatic calorimeters .......................................................................................................................................32

Annex B (informative) Isoperibol and static-jacket calorimeters ......................................................................................36

Annex C (informative) Automated calorimeters ...................................................................................................................................42

Annex D (informative) Checklists for the design of combustion tests and their procedures .................45

Annex E (informative) Examples to illustrate some of the calculations used in this document ..........50

Annex F (informative) Safe use, maintenance and testing of calorimeter combustion vessels ...........56

Bibliography .............................................................................................................................................................................................................................62

iv © ISO 2020 – All rights reserved
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ISO 1928:2020(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. 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. 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 on the meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO's adherence to the WTO principles in the Technical

Barriers to Trade (TBT) see the following URL: Foreword — Supplementary information

This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5,

Methods of analysis.

This fourth edition cancels and replaces the third edition (ISO 1928:2009), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— change the document title within the scope of TC 27,
— editorially update symbols within formulae,
— update references,
— expand on some derivations,
— remove ambiguity around crucible masses, and
— specify the analysis sample.

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 2020 – All rights reserved v
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INTERNATIONAL STANDARD ISO 1928:2020(E)
Coal and coke — Determination of gross calorific value

WARNING — Strict adherence to all of the provisions specified in this document should 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 a solid mineral

fuel 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.
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 651, Solid-stem calorimeter thermometers
ISO 652, Enclosed-scale calorimeter thermometers

ISO 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample

ISO 1770, Solid-stem general purpose thermometers
ISO 1771, 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

ISO 17247, Coal and coke — Ultimate analysis
ISO 18283, Hard coal and coke — Manual sampling
© ISO 2020 – All rights reserved 1
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ISO 1928:2020(E)
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 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/
3.1.1
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
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
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)
3.1.4
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)
3.1.5
adiabatic calorimeter
calorimeter that has a rapidly changing jacket temperature

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
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.

2 © ISO 2020 – All rights reserved
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ISO 1928:2020(E)
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
reference temperature
international reference temperature for thermochemistry, 25 °C
Note 1 to entry: See 8.7.

Note 2 to entry: The temperature dependence of the calorific value of coal or coke is small, about 1 J/(g·K).

3.1.9
effective heat capacity of the calorimeter
amount of energy required to cause unit change in temperature of the calorimeter
3.1.10
corrected temperature rise

change in calorimeter temperature caused solely by the processes taking place within the

combustion vessel

Note 1 to entry: The change in temperature can be expressed in terms of other units: resistance of a platinum or

thermistor thermometer, frequency of a quartz crystal resonator, etc., provided that a functional relationship is

established between this quantity and a change in temperature. The effective heat capacity of the calorimeter

can be expressed in units of energy per such an arbitrary unit. Criteria for the required linearity and closeness in

conditions between calibrations and fuel tests are given in 9.3.
3.2 Symbols
c specific heat capacity of water at constant pressure
p,aq
c specific heat capacity of the sample
p,s
c dt heat capacity times the temperature change
c specific heat capacity of the crucible
p,cr

ΔC is the difference in heat capacity (m × c ) of the crucible used in the calibrations and

cr p,cr
that used in combustion of the fuel
dq heat flow into the calorimeter
(dt/dτ) the initial drift rate

G specific rate constant, which is evaluated from the time-temperature measurements of the

rating periods, the fore- and the after-period
g drift rate (dt/dτ) in the rating periods
g final drift rate (drift rate in the after-period)
g initial drift rate (drift rate in the fore-period)
k is the Newton’s law cooling constant
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ISO 1928:2020(E)
l length of ignition wire (fuse)
wire

L is the latent heat of vaporization of water at 25 °C and constant pressure (43 988 J/mol)

L is the latent heat of vaporization at 25 °C and constant pressure of the water present in the

analysis sample and formed from the hydrogen in it
M moisture in the analysis sample
m mass of combustion vessel water
M total moisture mass fraction of the fuel for which the calculation is required
m mass of benzoic acid
m mass of crucible
m mass of sample
m mass of wire (fuse)
fuse
m mass of fuel sample burned
m mass of combustion aid
p initial pressure of oxygen
P power of stirring
Q contribution from combustion of the fuse
fuse
Q contribution from oxidation of the ignition wire
ign

Q contribution from formation of nitric acid (from liquid water and gaseous nitrogen and

oxygen)

Q correction for taking the sulfur from the aqueous sulfuric acid in the combustion vessel to

gaseous sulfur dioxide
q gross calorific value at constant pressure of the dry (moisture-free) fuel
p,gr,d

q net calorific value at constant pressure for air-dried fuel with moisture mass fraction

p,net,M
q net calorific value at constant pressure of the dry (moisture-free) fuel
p,net,d

q net calorific value at constant pressure of the fuel with moisture mass fraction M

p,net,M
q certified gross calorific value at constant volume for benzoic acid
V,ba
q gross calorific value at constant volume of the fuel as analysed
V,gr
q gross calorific value at constant volume of the dry (moisture-free) fuel
V,gr,d

q gross calorific value at constant volume of the fuel with moisture mass fraction M

V,gr,m T
q net calorific value at constant volume
V,net
q net calorific value at constant volume of the dry (moisture-free) fuel
V,net,d

q net calorific value at constant volume for air-dried fuel with moisture mass fraction

V,net,M
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ISO 1928:2020(E)

q net calorific value at constant volume of the fuel with moisture mass fraction M

V,net,M
q gross calorific value at constant volume of a combustion aid
V,2
R the universal gas constant, equal to 8,315 J/mol K
T the reference temperature for calorific value, i.e. 298,15 K (25 °C)

Δn contraction in volume of the gaseous phase for the combustion reaction, expressed in

terms of moles per gram of sample, on an air-dried basis
t calorimeter temperature
t the correction of 1 applied after the ignition of the sample
Δm heat capacity from the mass of the crucible
Δt heat-leak correction, which is the contribution from the heat exchange
t final temperature of the main period (equal to the reference temperature)
τ time, a minutes after the end of the main period
t temperature, a minutes after the end of the main period
f+τ
t − t observed temperature rise
f i
Δt observed temperature rise
t initial temperature of the main period (at the time of firing the charge)
t thermostat (jacket) temperature
t − t thermal head

t successive temperature readings, taken at 1 min intervals during the main period

t the integrated mean temperature
t is equal to t and is the temperature at the beginning of the main period
0 i

t is the temperature reading, taken during the main period, at the nth one-minute interval,

t (= t ) being the reading taken at the end
n f
t mean temperature in the after-period
t mean temperature in the fore-period
t temperature at the time τ ,
x x

t is the temperature that the calorimeter eventually attains if left running for an extended

period of time, which is the asymptotic temperature of an isoperibol calorimeter
(at “infinite” time)
t reference temperature
ref
V is the volume of the barium hydroxide solution used
V is the volume, of the hydrochloric acid solution used
V volume of combustion vessel water, may be substituted, as appropriate, for m
aq, aq
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ISO 1928:2020(E)
V Combustion vessel volume

W The work done against the atmosphere when the water is expanded at constant pressure to

vapour at 25 °C

W Δn multiplied by RT to interpret the volume change in terms of the associated work done

2 g
by the atmosphere to maintain constant pressure

w hydrogen mass fraction of the sample less the hydrogen contained in the moisture mass

fraction

w hydrogen, mass fraction of the moisture-free fuel (includes the hydrogen from the water of

H,d
hydration of the mineral matter as well as hydrogen in the coal substance)
w nitrogen, mass fraction of the moisture-free fuel
N,d
w oxygen, mass fraction of the moisture-free fuel
O,d
w the volatile-matter mass fraction of the sample with moisture mass fraction, M
V T
w the ash mass fraction of the sample with moisture mass fraction, M
A T
ε effective heat capacity of the calorimeter

ε best estimate (corresponds to “mean” value) of ε from linear regression of ε as a function of

the observed temperature rise (t − t )
f i
ε effective heat capacity of calorimeter on a “tot
...

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