ISO 923:2022

INTERNATIONAL ISO
STANDARD 923
Third edition
2022-11
Coal — Density separation equipment
for coal — Performance evaluation
Charbon — Equipement de séparation par masse volumique pour le
charbon — Evaluation des performances
Reference number
© ISO 2022
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Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Performance measures . 1
5 Performance criteria . 2
6 Performance determination parameters . 3
7 Analytical procedures . .3
8 Expression of performance .4
Annex A (informative) Methods of expressing performance . 5
Annex B (informative) Recommendations for standard methods of presenting coal cleaning
test data . 7
Annex C (informative) Graphs .26
Bibliography .29
iii
Foreword
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and Coke, Subcommittee SC 1,
Coal preparation: Terminology and performance.
This third edition cancels and replaces the second edition (ISO 923:2000), which has been technically
revised.
The main changes are as follows:
— example calculations have been updated to reflect a dense medium separation, which is most
commonly employed in industry;
— performance measures have been updated to include the bypass fractions;
— new versions of the tables for two and three product separations included to align with currently
common applications.
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.
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INTERNATIONAL STANDARD ISO 923:2022(E)
Coal — Density separation equipment for coal —
Performance evaluation
1 Scope
This document describes the principles and methods for evaluating the performance of density
separation equipment used for coal cleaning operations. Testing and sampling procedures are specified,
and methods of presenting test results are detailed. Performance parameters are recommended and
defined, and their determination is formulated, thereby permitting their use in evaluating, comparing
and predicting performance levels of coal cleaning operations.
This document is applicable to the following types of coal cleaning equipment using relative density
(RD) as the main characteristic for separation:
a) dense-medium separators;
b) jigs;
c) other density-based separators, including spiral separator, hindered settling cleaners, shaking
table, water-only cyclone, etc.
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 1170, Coal and coke — Calculation of analyses to different bases
ISO 1213-1, Coal and coke — Vocabulary — Part 1: Terms relating to coal preparation
ISO 1953, Hard coal — Size analysis by sieving
ISO 5048, Continuous mechanical handling equipment — Belt conveyors with carrying idlers — Calculation
of operating power and tensile forces
ISO 7936, Coal — Determination and presentation of float and sink characteristics — General directions
for apparatus and procedures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1213-1 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/
4 Performance measures
The following criteria are used:
a) the feed rate, expressed as mass per unit time and/or volume per unit time basis;
b) reference density of separation;
c) sharpness of separation;
d) correctly placed and misplaced material;
e) ash error and yield error;
f) the degree of difficulty of separation;
g) the bypass fractions;
h) material characteristics.
The above criteria will be influenced by test conditions, which should therefore be fully reported.
Conditions, including feed rate, should be kept uniform, monitored and maintained within prescribed
tolerance limits during a test.
Where performance test results are used for prediction, the impacts of different process conditions to
those tested should be taken into account.
5 Performance criteria
For the standard expression of performance of a cleaning operation, the following criteria apply:
a) the feed rate, expressed as mass per unit time and/or volume per unit time basis;
— It is essential to maintain the feed rate as uniform as possible throughout the performance test
and determine it over the duration of the test by the most accurate method available.
— Where the feed to the equipment is by belt conveyor, the feed rate shall be determined in
accordance with ISO 5048.
b) the reference density of separation, preferably expressed as both partition density and equal-
errors cut-point (density);
c) the sharpness of separation expressed in terms of probable error and imperfection;
d) the distribution of correctly placed and incorrectly placed material in each product, presented
graphically with respect to relative density (RD), and the particular value of misplaced material in
each product, determined at the reference density of separation;
e) the ash error expressed as the difference between the actual ash in the cleaned coal and the
theoretical ash at the actual yield value;
f) the yield error expressed as the difference between the actual yield and the theoretical yield at the
actual clean-coal ash value;
g) the degree of difficulty of separation expressed in terms of near-density material (and by other
relevant characteristics);
h) the bypass of low-density material to reject at an RD of 1,20 (the ‘low-density tail’);
i) the bypass of high-density material to clean coal at an RD of 2,70 (the ‘high-density tail’).
6 Performance determination parameters
The equipment to be tested, the feed composition and the means of handling the feed and products,
vary widely. A single international standard to cover all cases is not applicable. The following general
procedures shall be followed.
a) Samples shall be taken from the feed and from each of the products. The sampling techniques,
number of increments and increment mass shall ensure that all samples taken are representative
and shall conform to existing international standards where available. Sampling of coal is covered
by ISO 18283 and size analysis of coal is covered by ISO 1953.
To enable checking of results and assessment of the effects of degradation, representative samples
shall be taken from all relevant streams to and from the equipment to be tested.
b) It is essential to determine the feed rate and the percentage yield to each of the products on an air-
dry or dry basis in accordance with ISO 1170. This shall be achieved in accordance with one of the
procedures given below.
Determine the mass of each product by one or more of the following methods, which are listed in order
of reliability.
a) By direct weighing of the whole of each product collected over the duration of the test or through
continuous weighing and integration over the duration of the test.
b) By taking regular timed increments over the duration of the test.
c) By determining the mass of each product collected simultaneously over a selected period of the
test.
d) By calculation of mass balance using all available analytical parameters, which typically include
ash, size distribution and density distribution.
NOTE 1 If it is feasible to measure both the mass of the feed (e.g. by belt weigher, weigh hopper, flowmeter)
and the mass of the products, this provides a check.
NOTE 2 If the mass of one of the products cannot be obtained, it can be derived from a mass balance between
the feed and other product(s).
NOTE 3 Where the solids are conveyed by a fluid, it can be more convenient to make volumetric measurements.
Representative samples should be taken from streams to determine free moisture or total moisture
mass fraction or mass fraction of solids as appropriate, so that results can be reported on a dry or air-
dry basis.
7 Analytical procedures
The methods and procedures of size analysis and float-sink analysis shall be in accordance with
ISO 1953 and ISO 7936, respectively.
The feed sample and each of the product samples should be separated into various particle size fractions
depending on the degree of detail required. Because the performance of coal cleaning equipment is
usually different for different size particles, the size ranges should be as specified in ISO 7936.
1)
ISO 4077 should also be considered as it discusses options to reduce sample mass by limiting analysis
top-size if the float-and-sink analysis standard (see ISO 7936) cannot otherwise be conformed to.
The relative density of the lowest density floats fraction and highest density sinks fraction each need to
be determined.
1) Under preparation. Stage at the time of publication: ISO/DIS 4077:2022.
8 Expression of performance
Methods for the expression of the results of coal cleaning tests and the performance of the separation
processes are given in Annex A.
For the purpose of meeting the requirements stated in the Scope, no single method suffices by itself.
Annex B describes recommended methods for the calculation and tabulatio
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