ISO 923:2022

Coal - Density separation equipment for coal - Performance evaluation

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.

Charbon — Equipement de séparation par masse volumique pour le charbon — Evaluation des performances

General Information

• Status: Published
• Publication Date: 03-Nov-2022
• ICS: 73.120 - Equipment for processing of minerals
• Technical Committee: ISO/TC 27/SC 1 - Coal preparation: Terminology and performance
• Drafting Committee: ISO/TC 27/SC 1 - Coal preparation: Terminology and performance
• Current Stage: 6060 - International Standard published
• Start Date: 04-Nov-2022
• Due Date: 07-Oct-2022
• Completion Date: 04-Nov-2022

Relations

• Revises: ISO 923:2000 - Coal cleaning equipment - Performance evaluation
• Effective Date: 23-Apr-2020

Overview

ISO 923:2022 - "Coal - Density separation equipment for coal - Performance evaluation" defines principles, test methods and presentation formats for evaluating density-based coal cleaning equipment. The third edition (2022) updates performance measures and example calculations, and is intended to enable consistent evaluation, comparison and prediction of separation performance for equipment that uses relative density (RD) as the primary separation characteristic (e.g., dense‑medium separators, jigs, spiral separators, hindered‑settling cleaners, shaking tables and water‑only cyclones).

Key topics and technical requirements

• Scope and applicability: Performance evaluation for RD‑based coal cleaning equipment; applicable equipment types are explicitly listed.
• Performance measures: Feed rate, reference density of separation (partition density / equal‑errors cut‑point), sharpness of separation (probable error, imperfection), correctly placed vs misplaced material, ash error, yield error, degree of difficulty (near‑density material), and bypass fractions (low‑density tail at RD 1.20 and high‑density tail at RD 2.70).
• Sampling & testing procedures: Representative sampling from feed and each product stream, size fractionation and float/sink analysis in line with established standards; maintain and report uniform feed-rate and test conditions.
• Analytical procedures: Use ISO 1953 (size analysis) and ISO 7936 (float and sink) approaches; determine RD ranges for floats and sinks for each size fraction.
• Expression and reporting of results: Multiple methods provided (partition curves, M‑curves/washability curves, ash/yield error, partition coefficients, imperfection). Annexes include recommended tabulations and graphical presentations for consistent reporting.
• Performance prediction & guarantees: Formulations permit comparison, prediction and contractual performance checks; test conditions and possible impacts of differing operational conditions must be reported.

Practical applications

• Standardizes how laboratories, plant engineers and equipment manufacturers:
  • Evaluate and benchmark separator accuracy and efficiency
  • Diagnose separation problems (sharpness, bypass, misplaced material)
  • Prepare performance guarantees and acceptance tests
  • Predict product quality (ash, yield) from test data
• Useful for commissioning, process optimization, tendering and regulatory/commercial reporting in coal preparation plants.

Who should use ISO 923:2022

• Coal preparation and beneficiation engineers
• Equipment manufacturers and suppliers (dense‑medium systems, jigs, cyclones, tables)
• Test laboratories and quality assurance teams
• Mine/process consultants and contract/claims specialists

Related standards (referenced)

• ISO 1170, ISO 1213‑1, ISO 1953, ISO 5048, ISO 7936, ISO 18283; see ISO 4077 (under preparation) for guidance on sample size reduction.

Keywords: ISO 923:2022, density separation equipment, coal cleaning, relative density, partition density, partition curves, ash error, yield error, bypass fractions, float and sink, performance evaluation.

Standards Content (Sample)

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
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
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or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
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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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
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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.
iv
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 tabulation of test results, and Annex C
gives graphical presentations.
Annex A
(informative)
Methods of expressing performance
Formula Derived from Remarks
Separation
density
a) Partition Partition curves
density
Describes one characteristic of the separation but does not indicate
M-curves
A.1
its accuracy.
b) Equal-
Washability
errors
curves
cut-point
(density)
M-curves
Misplaced Measure of quantity of misplaced material (without reference to its
A.2
Washability
material quality) at the separation density.
curves
M-curves
Total of cor-
Measure of quantity of correctly placed material at the separation
A.3 rectly placed
Washability
density (without reference to its quality).
material
curves
M-curves
Reflects both the quantity and quality of misplaced material in terms
A.4 Ash error of the specific property of coal (percentage of ash) that the separation
Washability
is designed to control; i.e. measures qualitative efficiency.
curves
M-curves
Reflects both the quantity and quality of misplaced material and
A.5 Yield error
Washability
measures quantitative efficiency.
curves
M-curves
Organic
A.6 Related to yield error but expressed as a percentage.
Washability
efficiency
curves
A.7 Error area Partition curves Measure of quantity of misplaced material in terms of density.
NOTE 1 Meyer (M)-curves and washability curves describe graphically the character of the raw coal and of the products, in
terms of mass and ash. Partition curves describe only the products in terms of mass and density; they can be constructed
without the necessity to determine ash.
NOTE 2 M-curves have wider direct applications than washability curves, especially, for example, in three-product
separations. The construction of such curves is described in ISO 7936.
NOTE 3 Partition density (dp, d ); known as the Tromp cut-point, the density corresponding to 50 % recovery as read from
a partition curve and écart probable (moyen); epm (means probable error) which is one half of the difference between the
densities corresponding to the 75 % and 25 % ordinates as shown in the partition curve.
NOTE 4 The écart probable (moyen) and imperfection reflect the influence of changes in the separation process rather than
in the raw coal, in contrast to the formulae derived from M-curves or washability curves, which reflect changes in the raw
coal as well as in the separation process.
NOTE 5 The separation density, although not a measure of efficiency, is an important characteristic of the separation and is
essential to any comprehensive statement of the results of a given test.
NOTE 6 The misplaced material and the total of correctly placed material at the separation density, the ash error, the yield
error, the organic efficiency and the error area can all be used for performance guarantee tests and occasional control tests
to give an indication of the accuracy of a given separation on a given coal, and hence of economic efficiency; but they are of
little value in the prediction of probable results of cleaning a range of coals by one specific process.
NOTE 7 Partition coefficients, écart probable (moyen) and imperfection are valuable for the purpose of prediction but do not
give an adequate indication of the accuracy of a given separating operation on a particular coal.
Formula Derived from Remarks
Partition
A.8 Partition curves Special applications only.
coefficients
Écart probable Gives an indication of the quantitative errors inherent in the separating
A.9 Partition curves
(moyen) process at a given separation density.
Modification of écart probable (moyen) to include the effect of varying
A.10 Imperfection Partition curves
separation density.
Product
A.11 Yield loss States results without reference to accuracy of separation.
samples
Bypass –
A.12 Partition curve Sample degradation following sampling can give a false result for bypass.
low-density tail
Bypass –
A.13 high-density Partition Curve Sample degradation following sampling can give a false result for bypass.
tail
NOTE 1 Meyer (M)-curves and washability curves describe graphically the character of the raw coal and of the products, in
terms of mass and ash. Partition curves describe only the products in terms of mass and density; they can be constructed
without the necessity to determine ash.
NOTE 2 M-curves have wider direct applications than washability curves, especially, for example, in three-product
separations. The construction of such curves is described in ISO 7936.
NOTE 3 Partition density (dp, d ); known as the Tromp cut-point, the density corresponding to 50 % recovery as read from
a partition curve and écart probable (moyen); epm (means probable error) which is one half of the difference between the
densities corresponding to the 75 % and 25 % ordinates as shown in the partition curve.
NOTE 4 The écart probable (moyen) and imperfection reflect the influence of changes in the separation process rather than
in the raw coal, in contrast to the formulae derived from M-curves or washability curves, which reflect changes in the raw
coal as well as in the separation process.
NOTE 5 The separation density, although not a measure of efficiency, is an important characteristic of the separation and is
essential to any comprehensive statement of the results of a given test.
NOTE 6 The misplaced material and the total of correctly placed material at the separation density, the ash error, the yield
error, the organic efficiency and the error area can all be used for performance guarantee tests and occasional control tests
to give an indication of the accuracy of a given separation on a given coal, and hence of economic efficiency; but they are of
little value in the prediction of probable results of cleaning a range of coals by one specific process.
NOTE 7 Partition coefficients, écart probable (moyen) and imperfection are valuable for the purpose of prediction but do not
give an adequate indication of the accuracy of a given separating operation on a particular coal.
Annex B
(informative)
Recommendations for standard methods of presenting coal
cleaning test data
B.1 Description of the tables
Two sets of tables are required (see Clauses B.4 to B.6):
a) for two-product separation (cleaned coal and reject);
b) for three-product separation (cleaned coal, middlings and reject).
For convenience, an identical layout has been adopted for both sets of tables but, in those intended for
use with two-product separations, the columns that relate only to three-product separation have been
left blank to avoid confusion.
Each set of tables is presented in two ways.
a) Blank tables, to show the method of printing (see Form 1 and Form 3 in Clauses B.4 and B.6,
respectively).
b) Tables completed by filling in the figures relating to test results. For example, Form 2 and Form 4
shown in Clauses B.5 and B.6 give the results of a test using a Baum jig washer.
NOTE The example described in this annex was carried out prior to the publication of ISO 7936. The particle
sizes used therefore are not in accordance with those specified in this document.
For the test described in this example, the dense medium cyclone was supplied with coal sized at
-50 mm and +2,0 mm. The tables and figures used refer to the fraction sized between 31,5 mm and
4 mm. The fine material below 4 mm was removed from the samples before carrying out float-and-sink
analysis.
For a full analysis of the test, tables similar to those given for the 31,5 mm to 4,0 mm size would be
required for the other sizes of the raw coal, in this instance 50 mm to 31,5 mm, and 4 mm to 2 mm.
Such tables would enable the performance on the different sizes to be compared. By adding together the
results on the four individual sizes, a further set of tables can be constructed giving cumulative data for
the whole of the 50 mm to 2 mm coal fed to the process unit.
In this test, two products were made: cleaned coal and reject. The reject is the material discharged at
the cyclone underflow (spigot) and the cleaned coal is discharged at the cyclone overflow. The tables
headed "two- product separation" are built up from float-and-sink analysis at various relative densities
from 1,30 to 2,20 on samples of each of the feed and products. The density intervals used are strongly
dependent on the type of separator and the expected density of separation. For dense medium cyclones,
0,025 density intervals are recommended within ±0,1 of the expected reference density of separation,
d . For other separators, intervals of 0,05 within ±0,2 of the expected d .
50 50
The figures in the tables headed "three-product separation" have been calculated from these same
figures for a spiral separator example.
B.2 Expression of efficiency in the three-product separation
Three-product separation can be regarded as a combination of two distinct two-product separations
(i.e. a low-density cut and a high-density cut), whether these two stages are in fact carried out in
different separating vessels or in different parts of the same vessel.
The diagrams in Figure B.1 illustrate different combinations of the two stages.
Key
F feed (reconstituted raw coal), mass units
C cleaned coal, mass units
R reject, mass units
M intermediate product (middlings), mass units
Figure B.1 — Different combinations of the two stages
Diagrams 1 and 2 represent typical arrangements for a two-stage separation, the only difference
being that the low-density cut comes first in diagram 1 and second in diagram 2, whereas diagr
...