ISO 20905:2024

International
Standard
ISO 20905
Second edition
Coal preparation — Determination of
2024-10
dust/moisture relationship for coal
Préparation du charbon — Détermination de la relation
particules/humidité du charbon
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Safety . 1
5 Apparatus and equipment . 2
6 Reagent . 2
7 Sample — Initial . 2
8 Sample preparation — Initial. 3
8.1 Initial total moisture .3
8.2 Moisture adjustment .4
9 Sample preparation — Reagent . 4
10 Dust determination . 5
10.1 Environment and equipment checks .5
10.2 Dust testing .5
11 Calculation . 6
12 Report . 6
13 Precision . 6
Annex A (informative) Worked example . 7
Annex B (informative) Worksheet example . 10
Bibliography .12

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 27, Coal and Coke, Subcommittee SC 1, Coal
preparation: Terminology and performance.
This second edition cancels and replaces the first edition (ISO 20905:2004), of which it constitutes a minor
revision. The changes compared to the previous edition are as follows:
— the title of ISO/TC 27 was changed from "Solid mineral fuels" to "Coal";
— some terminology was changed to align with ISO rules, for example the terms "percentage", "weight" and
"weighing".
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
Introduction
The development of the dust/moisture curve provides an indication of the likely response of different
coal types to drying or water addition during mining and handling processes. The dust/moisture curve
provides a good basis for comparing the response of different coal types. Understanding the dust/moisture
characteristics of a coal allows minimized water addition to the product for dust suppression. This in turn
assists in water conservation at mines and other handling facilities, as well as minimizing the total moisture
of the product.
This document describes a reliable measurement of dustiness of coal and extends to cover the relationship
between dust and total moisture utilizing the Rio Tinto Dust Tumbler Test. This test provides a quantitative
measure of the dustiness of a coal that can be used to predict operational dust problems and is also suitable
for the assessment of dust suppression chemicals.
The Rio Tinto Dust Tumbler Test was developed using rotating equipment in a controlled temperature and
humidity environment and uses a stream of air to remove particles which become airborne during the
tumbling process. It is a batch test in which dust particles (−150 µm particles) are collected in a filter bag
of known mass and their mass is determined. From this mass, a dust number, calculated as the mass yield
of dust multiplied by 100 000, is determined for the test total moisture. Only 1 kg of sample is required for
each dust test, but eight sample lots are required to develop the dust/moisture curve for a particular coal,
i.e. approximately 10 kg is required for each coal type.
This dust test can be repeated with subsamples at different coal total moisture levels to develop a dust/
moisture curve. The slope of the curve provides information on how sensitive the dustiness is to changes in
total moisture and a dust number of 10 has been used to provide a comparison between coals.
The test has been successfully used for several years on many coals and other bulk materials. The results
have been correlated with the operating practice. The method has been applied to the evaluation of dust-
control products and the determination of dust-elimination total moisture requirements for coal-handling
systems.
v
International Standard ISO 20905:2024(en)
Coal preparation — Determination of dust/moisture
relationship for coal
1 Scope
This document sets out a laboratory procedure for the dust testing of higher rank coals. The procedure
defines a means of evaluating the dust/moisture relationship characteristic of a coal and a dust extinction
moisture (DEM).
NOTE In this document, an experimental dust number of 10 has been used in the example given in Annex A.
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 589, Hard coal — Determination of total moisture
ISO 7886-1, Sterile hypodermic syringes for single use — Part 1: Syringes for manual use
3 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
dust
particles of size 150 µm or less entrained in an air stream
3.2
dust extinction moisture
DEM
total moisture at which a dust number of 10 is attained on the dust/moisture curve
Note 1 to entry: DEM is a useful point for comparing different coals and the effectiveness of reagents.
4 Safety
The following safety precautions shall be observed:
— To prevent nitrogen build-up within the laboratory, the exhaust tube of the minimum-free-space oven
shall remain clear of obstruction.
— Safety glasses shall be worn at all times.
— The exhaust tube of the minimum-head-space oven shall remain free of obstruction to prevent nitrogen
build-up within the laboratory.

— A dust mask shall be worn when handling coal.
— Cloth or leather gloves shall be worn when using ovens.
— The hazards associated with a reagent shall be determined prior to use. Instructions on all relevant
material safety data sheets shall be followed.
5 Apparatus and equipment
The following apparatus and equipment is required.
5.1 Humidity- and temperature-controlled laboratory, with relative humidity of 63 % ± 2 % and
temperature of 20 °C ± 2 °C.
5.2 Dust-test apparatus, with a rotating drum of 30 cm diameter and 30 cm effective length, as shown in
Figure 1. The required drum speed is 29 r/min, and the desired airflow through the drum is 175 L/min.
5.3 Double filter bags, single use only.
5.4 Electronic thermohydrograph.
5.5 Tachometer.
5.6 Laminar flow differential-pressure manometer.
5.7 Stopwatch.
5.8 Capped bottles, of capacity 250 mL, wide mouth, polypropylene.
5.9 Top loading balance, which has a minimum capacity of 1 g and is readable to the nearest 0,01 g.
5.10 Laboratory trays.
5.11 Minimum-free-space drying oven.
6 Reagent
Tap water is used in solution and sample preparation.
7 Sample — Initial
Before testing, remove the particles greater than 6,3 mm. Do not crush and replace this removed fraction as
the sample's particle size distribution will be altered.
Prepare sufficient sample to provide 1,2 kg for each dust determination over the desired range of total
moisture or reagent concentrations as well as 1,2 k
...