ISO 20904:2020

INTERNATIONAL ISO
STANDARD 20904
Second edition
2020-02
Hard coal — Sampling of slurries
Houille — Échantillonnage des schlamms
Reference number
ISO 20904:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 20904:2020(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
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 20904:2020(E)

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles of sampling slurries . 2
4.1 General . 2
4.2 Sampling errors . 3
4.2.1 General. 3
4.2.2 Preparation error . 4
4.2.3 Delimitation and extraction errors . 4
4.2.4 Weighting error, E . 5
W
4.2.5 Periodic quality fluctuation error, E . 6
Q3
4.3 Sampling and overall variance . 6
4.3.1 Sampling variance. 6
4.3.2 Overall variance . 6
5 Sampling schemes . 7
6 Minimization of bias and unbiased increment mass .13
6.1 Minimizing bias .13
6.2 Volume of increment for falling stream samplers to avoid bias .14
6.3 Volume of increment for manual sampling to avoid bias .14
7 Precision of sampling and determination of increment variance .15
7.1 Overall precision .15
7.2 Primary increment variance .15
7.3 Preparation and testing variance .16
8 Number of sub-lots and number of increments per sub-lot .16
9 Minimum mass of solids in lot and sub-lot samples .17
9.1 General .17
9.2 Minimum mass of solids in lot samples .17
9.3 Minimum mass of solids in sub-lot samples .17
9.4 Minimum mass of solids in lot and sub-lot samples after size reduction .17
10 Time-basis sampling .18
10.1 General .18
10.2 Sampling interval .18
10.3 Cutters .18
10.4 Taking of increments .18
10.5 Constitution of lot or sub-lot samples .19
10.6 Division of increments and sub-lot samples .19
10.7 Division of lot samples .19
10.8 Number of cuts for division .19
11 Stratified random sampling within fixed time intervals.19
12 Mechanical sampling from moving streams .20
12.1 General .20
12.2 Design of the sampling system .20
12.2.1 Safety of operators .20
12.2.2 Location of sample cutters .20
12.2.3 Provision for duplicate sampling .20
12.2.4 System for checking the precision and bias.20
12.2.5 Minimizing bias .21
12.3 Slurry sample cutters .22
12.3.1 General.22
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 20904:2020(E)

12.3.2 Falling-stream cutters .22
12.3.3 Cutter velocities .22
12.4 Mass of solids in increments .22
12.5 Number of primary increments .23
12.6 Routine checking .23
13 Manual sampling from moving streams .23
13.1 General .23
13.2 Choosing the sampling location .23
13.3 Sampling implements .24
13.4 Mass of solids in increments .24
13.5 Number of primary increments .24
13.6 Sampling procedures .24
14 Sampling of stationary slurries .25
15 Sample preparation procedures .25
15.1 General .25
15.2 Reduction mills .25
15.3 Sample division.25
15.4 Chemical analysis samples . .25
15.5 Physical test samples .25
16 Packing and marking of samples .26
Annex A (informative) Examples of correct slurry devices .27
Annex B (informative) Examples of incorrect slurry sampling devices .30
Annex C (normative) Manual sampling implements .34
Bibliography .35
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 20904:2020(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 (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, Solid mineral fuels, Subcommittee
SC 4, Sampling.
This second edition cancels and replaces the first edition (ISO 20904:2006), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— an amendment to Figure 6 b) to read ― incorrect;
— correction to Figure 7 b).
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

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 20904:2020(E)
Hard coal — Sampling of slurries
1 Scope
This document sets out the basic methods for sampling fine coal, coal rejects or tailings of nominal top
size <4 mm that is mixed with water to form a slurry. At very high ratios of fine solids to water when the
material assumes a soft plastic form, the mixture is correctly termed a paste. Sampling of pastes is not
covered in this document.
The procedures described in this document primarily apply to sampling of coal that is transported
in moving streams as a slurry. These streams can fall freely or be confined in pipes, launders, chutes,
spirals or similar channels. Sampling of slurries in stationary situations, such as a settled or even a well-
stirred slurry in a tank, holding vessel or dam, is not recommended and is not covered in this Document.
This document describes procedures that are designed to provide samples representative of the slurry
solids and particle size distribution of the slurry under examination. After draining the slurry sample of
fluid and measuring the fluid volume, damp samples of the contained solids in the slurry are available
for drying (if required) and measurement of one or more characteristics in an unbiased manner and
with a known degree of precision. The characteristics are measured by chemical analysis or physical
testing or both.
The sampling methods described are applicable to slurries that require inspection to verify compliance
with product specifications, determination of the value of a characteristic as a basis for settlement
between trading partners or estimation of a set of average characteristics and variances that describes
a system or procedure.
Provided flow rates are not too high, the reference method against which other sampling procedures
are compared is one where the entire stream is diverted into a vessel for a specified time or volume
interval. This method corresponds to the stopped-belt method described in ISO 13909-2.
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 1213-1, Solid mineral fuels — Vocabulary — Part 1: Terms relating to coal preparation
ISO 1213-2, Solid mineral fuels — Vocabulary — Part 2: Terms relating to sampling, testing and analysis
ISO 13909-1, Hard coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 13909-8, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 1213-1, ISO 1213-2 and
ISO 13909-1 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/
© ISO 2020 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 20904:2020(E)

4 Principles of sampling slurries
4.1 General
For the purposes of this document, a slurry is defined as fine coal, coal rejects or tailings of nominal top
size <4 mm that is mixed with water, which is frequently used as a convenient form to transport coal,
rejects or tailings though plant circuits by means of pumps and pipelines and under gravity in launders
or chutes or through long distances in slurry pipelines. Tailings from wet plants are also discharged as
a slurry through pipelines to the tailings dam. In many of these operations, collection of increments at
selected sample points is required for evaluation of the coal or rejects in the slurry.
A lot or sub-lot sample is constituted from a set of unbiased primary increments from a lot or sub-
lot. The sample container is weighed immediately after collection and combination of increments to
avoid water loss by evaporation or spillage. Weighing is necessary to determine the mass percentage
of solids in the lot or sub-lot sample. The lot or sub-lot sample can then be filtered, dried and weighed.
Alternatively, the lot or sub-lot sample may be sealed in plastic bags after filtering for transport and
drying at a later stage.
Except for samples for which their characteristics are determined directly on the slurry, test samples
are prepared from lot or sub-lot samples after filtering and drying. Test portions may then be taken
from the test sample and analysed using an appropriate and properly calibrated analytical method or
test procedure under specified conditions.
The objective of the measurement chain is to determine the characteristic of interest in an unbiased
manner with an acceptable and affordable degree of precision. The general sampling theory, which is
based on the additive property of variances, can be used to determine how the variances of sampling,
sample preparation and chemical analysis or physical testing propagate and hence determine the total
variance for the measurement chain. This sampling theory can also be used to optimize mechanical
sampling systems and manual sampling methods.
If a sampling scheme is to provide representative samples, it is necessary that all parts of the slurry
in the lot have an equal opportunity of being selected and appearing in the lot sample for testing. Any
deviation from this basic requirement can result in an unacceptable loss of accuracy. A sampling scheme
having incorrect selection techniques, i.e. with non-uniform selection probabilities, cannot be relied
upon to provide representative samples.
Sampling of slurries should preferably be carried out by systematic sampling on a time basis (see
Clause 10). If the slurry flow rate and the coal-solids concentration vary with time, the slurry volume
and the dry solids mass for each increment will vary accordingly. It is necessary to show that no
systematic error (bias) is introduced by periodic variation in quality or quantity where the proposed
sampling interval is approximately equal to a multiple of the period of variation in quantity or quality.
Otherwise, stratified random sampling should be used (see Clause 11).
Best practice for sampling slurries is to mechanically cut freely falling streams (see Clause 12), with a
complete cross-section of the stream being taken during the traverse of the cutter. Access to freely falling
streams can sometimes be engineered at the end of pipes or by incorporating steps or weirs in launders
and chutes. If samples are not collected in this manner, non-uniform concentration of coal solids in the
slurry due to segregation and stratification of the solids can lead to bias in the sample that is collected.
Slurry flow in pipes can be homogenous with very fine particles dispersed uniformly in turbulent
suspension along the length and across the diameter of the pipe. However, more commonly, the slurry in
a pipe has significant particle-concentration gradients across the pipe and there can be concentration
fluctuations along the length of the pipe. These common conditions are called heterogeneous flow.
Examples of such flow are full-pipe flow of a heterogeneous suspension or partial-pipe flow of a fine
suspension above a slower moving or even stationary bed of coarser particles in the slurry.
For heterogeneous flow, bias is likely to occur where a tapping is made into the slurry pipe to locate
either a flush-fitting sample take-off pipe or a sample tube projecting into the slurry stream for
extraction of samples. The bias is caused by non-uniform concentration profiles in the pipe and the
2 © ISO 2020 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 20904:2020(E)

different trajectories followed by particles of different masses due to their inertia, resulting in larger or
denser particles being preferentially rejected from or included in the sample.
In slurry channels such as launders, heterogeneous flow is almost always present, and this non-
uniformity in particle concentration is usually preserved in the discharge over a weir or step. However,
sampling at a weir or step allows complete access to the full width and breadth of the stream, thereby
enabling all parts of the slurry stream to be collected with equal probability.
Sampling of slurries in stationary situations, such as a settled or even a well-stirred slurry in a tank,
holding vessel or dam is not recommended, because it is virtually impossible to ensure that all parts
of the slurry in the lot have an equal opportunity of being selected and appearing in the lot sample for
testing. Instead, sampling should be carried out from moving streams as the tank, vessel or dam is
filled or emptied.
4.2 Sampling errors
4.2.1 General
The processes of sampling, sample preparation and measurement are experimental procedures, and
each procedure has its own uncertainty appearing as variations in the final results. When the average
of these variations is close to zero, they are called random errors. More serious variations contributing
to the uncertainty of results are systematic errors, which have averages biased away from zero. There
are also human errors that introduce variations due to departures from prescribed procedures for
which statistical analysis procedures are not applicable.
The characteristics of the solids component of a slurry can be determined by extracting samples from
the slurry stream, preparing test samples and measuring the required quality characteristics. The total
[5][6]
sampling error, E , can be expressed as the sum of a number of independent components . Such a
T
simple additive combination is not possible if the components are correlated. The total sampling error,
E , expressed as a sum of its components, is given by Formula (1):
T
EE=+EE++EE++EE+ (1)
TQ1Q2Q3W DE P
where
E is short-range quality fluctuation error associated with short-range variations in quality of
Q1
the solids component of the slurry;
E is long-range quality fluctuation error associated with long-range variations in quality of the
Q2
solids component of the slurry;
E is periodic quality fluctuation error associated with periodic variations in quality of the solids
Q3
component of the slurry;
E is weighting error associated with variations in slurry flow rate;
W
E is increment delimitation error introduced by incorrect increment delimitation;
D
E is increment extraction error introduced by incorrect increment extraction from the slurry;
E
E is the preparation error introduced by departures (usually unintentional) from correct prac-
P
tices, e.g. during constitution of the lot sample, draining and filtering away the water, and
transportation and drying of the sample.
The short-range quality fluctuation error consists of two components, as shown by Formula (2):
EE=+E (2)
Ql FG
where
© ISO 2020 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 20904:2020(E)

E is the fundamental error due to variation in quality between particles;
F
E is the segregation and grouping error.
G
The fundamental error results from the composition heterogeneity of the lot, i.e. the heterogeneity that
is inherent to the composition of each particle making up the solids component of the lot. The greater
the differences in the compositions of particles, the greater the composition heterogeneity and the
higher the fundamental error variance. The fundamental error can never be completely eliminated.
It is an inherent error resulting from the variation in composition of the particles in the slurry being
sampled.
The segregation and grouping error results from the distribution heterogeneity of the sampled
[6]
material . The distribution heterogeneity of a lot is the heterogeneity arising from the manner in
which particles are distributed in the slurry. It can be reduced by taking more increments, but it can
never be completely eliminated.
A number of the components of the total sampling error, namely E , E and E , can be minimized or
D E P
reduced to an acceptable level by correct design of the sampling procedure.
4.2.2 Preparation error
In this context, the preparation error, E , includes errors associated with non-selective
...