ISO 923:2022
(Main)Coal — Density separation equipment for coal — Performance evaluation
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
Relations
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 923:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO 923:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© 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
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 923:2022(E)
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
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 923:2022(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 (see 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 (see 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 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 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
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
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;
1
© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 923:2022(E)
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’).
2
© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 923:2022(E)
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.
3
© ISO 2022 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 923:2022(E)
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.
4
© ISO 2022 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 923:2022(E)
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
50
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.
5
© ISO 2022 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 923:2022(E)
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
50
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.
6
© ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 923:2022(E)
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.
7
© ISO 2022 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 923:2022(E)
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 diagram 3
represents a normal three-product separation as achieved in a jig. The middlings, M, may be collected
as a separate product, or recirculated, or otherwise dealt with, but provided that any recirculated
middlings are included in the reconstituted feed F, the argument is unaffected.
The efficiency of a three-product separation may be calculated in two different ways:
a) Method A, by regarding it as two distinct and individual separations, each with its own feed.
b) Method B, by regarding it as a single comprehensive separation, the feed for which is the
reconstituted raw coal.
To calculate the partition coefficients expressed as a percentage, the appropriate formulae for these
two methods, for the combinations of plant illustrated in the diagrams, are as follows:
For diagram 1
a) Method A: low-density cut 100CM()+R
CM++R
()
high-density cut 100M
()MR+
b) Method B: low-density cut 100C
CM++R
()
high-density cut 100M
()CM++R
The numerical factor 100 is used to convert the dimensionless partition coefficient to a percentage, %.
8
© ISO 2022 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 923:2022(E)
For diagram 2
a) Method A: high-density cut 100 CM+
()
()CM++R
low-density cut 100M
()CM+
b) Method B: high-density cut 100 CM+
()
()CM++R
low-density cut 100M
()CM++R
For diagram 3
a) Method A: high-density cut
100()CM+
()CM++R
low-density cut 100M
()CM+
b) Method B: high-density cut
100()MC+
()CM++R
low-density cut 100C
()CM++R
Although for Method A the formulae are identical for diagrams 2 and 3, in the latter case there is no
sharp dividing line between the first and second cuts. The first (high-density) cut separates the reject R
from the combination of the cleaned coal C and middlings M, and it is this combination that becomes the
feed to the second stage of the separation.
Method A enables the efficiency of each of the two separations to be studied individually, because only
the material that is admitted to the separator is included in the calculation. This is of advantage when
considering the performance of each machine or stage in the separation process.
Method B does not show up so emphatically the actual performance of the second machine or stage,
but by referring each separation back to the reconstituted raw feed, it facilitates comparisons of the
efficiency of the whole separation process in terms of the results on the original raw coal. (The sequence
of operations included in this complete process may include steps not shown in diagrams 1 to 3, for
example crushing of the middlings and its recirculation to the feed, which is common in jig washing
and may also occur in dense-medium separation and in some cases for spiral separator or water-only
cyclone separations.)
It is essential, whenever the efficiency of a three-product separation is expressed (for example, in
descriptions of plant and efficiency statements and guarantees), that it be clearly stated which of these
two bases has been used for the calculation. To facilitate this, it is proposed that Method A be described
as the equipment performance basis and Method B as the coal performance basis.
Tables B.1 to B.10 for the three-product separations are drawn up on the coal performance basis. When
calculations are made on the equipment performance basis, it is recommended that two-product tables
be used (one for each stage). It is possible, however, to deduce the results from the three-product table;
thus, partition coefficients for the second cut would be calculated on the equipment performance basis
as follows:
a) for diagram 1 (see Figure B.1 in Clause B.2), column (12) would be calculated from (7)/(9) instead
of (7)/(10) in Table B.7;
9
© ISO 2022 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 923:2022(E)
b) for diagrams 2 and 3 (see Figure B.1 in Clause B.2), column (13) would be calculated from (6)/(8)
instead of (9)/(10) in Table B.7.
B.3 Descriptions of the graphs (see Annex C)
B.3.1 Introduction
To calculate the efficiency, the data required in Clause B.4 (Tables B.1 to B.5) and Clause B.6 (Tables B.11
to B.15) should be represented in graphs. Graphs relating to the test results in Clause B.5 (Tables B.6 to
B.10) are shown in Figures C.1 to C.3. The graphs have been prepared from the data for a two-product
separation example. When calculating performance data for three-product separations, two of the
products may be calculated as one; for example, cleaned coal + middlings, or middlings + reject, to allow
the calculations to be undertaken.
Figure C.1 has been drawn to such a scale that the section of the partition curve relevant to the
calculation is shown. The scale will vary with every separation.
The construction and use of the graphs in Figures C.1 to C.3 are explained in B.3.2 to B.3.5.
Determination of many of the performanc
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.