ISO 13909-2:2016

INTERNATIONAL ISO
STANDARD 13909-2
Second edition
2016-07-01
Hard coal and coke — Mechanical
sampling —
Part 2:
Coal — Sampling from moving streams
Houille et coke — Échantillonnage mécanique —
Partie 2: Charbon — Échantillonnage en continu
Reference number
ISO 13909-2:2016(E)
©
ISO 2016

---------------------- Page: 1 ----------------------
ISO 13909-2:2016(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 13909-2:2016(E)

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Establishing a sampling scheme . 1
4.1 General . 1
4.2 Design of the sampling scheme . 2
4.2.1 Material to be sampled . 2
4.2.2 Division of lots . 2
4.2.3 Basis of sampling . 2
4.2.4 Precision of sampling . 2
4.2.5 Bias of sampling. 3
4.3 Precision of results . 3
4.3.1 Precision and total variance . 3
4.3.2 Primary increment variance . 4
4.3.3 Preparation and testing variance . 4
4.3.4 Number of sub-lots and number of increments per sub-lot . 4
4.4 Minimum mass of sample . 7
4.5 Mass of primary increment . 9
4.6 Size analysis . 9
5 Methods of sampling .10
5.1 General .10
5.2 Time-basis sampling .11
5.2.1 Method of taking primary increments .11
5.2.2 Sampling interval .11
5.2.3 Mass of increment .11
5.3 Mass-basis sampling .11
5.3.1 Method of taking primary increments .11
5.3.2 Sampling interval .12
5.3.3 Mass of increment .12
5.4 Stratified random sampling .12
5.4.1 General.12
5.4.2 Time-basis stratified random sampling .13
5.4.3 Mass-basis stratified random sampling .13
5.5 Reference sampling .13
6 Design of mechanical samplers .13
6.1 Safety .13
6.2 Information .13
6.3 Basic requirements .13
6.4 Location of sampling equipment .14
6.5 Provision for checking precision .14
6.6 Provision for testing for bias .14
6.7 General requirements for designing mechanical samplers .14
6.8 Design of falling-stream-type samplers .14
6.8.1 General.14
6.8.2 Cutter velocity .15
6.9 Cross-belt-type primary samplers .17
6.9.1 Operation .17
6.9.2 Design of cross-belt samplers .20
6.10 Maintenance and checking of sampling equipment .21
7 Handling and storage of samples .22
8 Sample preparation .23
© ISO 2016 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 13909-2:2016(E)

9 Bias .23
9.1 Minimization of bias .23
9.2 Checking for precision and bias .24
10 Verification .24
Annex A (normative) Evaluation of sampling equipment for mass-basis sampling .25
Bibliography .30
iv © ISO 2016 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 13909-2:2016(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 4,
Sampling.
This second edition cancels and replaces the first edition (ISO 13909-2:2001), which has been
technically revised.
ISO 13909 consists of the following parts, under the general title Hard coal and coke — Mechanical
sampling:
— Part 1: General introduction
— Part 2: Coal — Sampling from moving streams
— Part 3: Coal — Sampling from stationary lots
— Part 4: Coal — Preparation of test samples
— Part 5: Coke — Sampling from moving streams
— Part 6: Coke — Preparation of test samples
— Part 7: Methods for determining the precision of sampling, sample preparation and testing
— Part 8: Methods of testing for bias
Annex B forms a normative part of this part of ISO 13909. Annex A of this part of ISO 13909 is for
information only.
© ISO 2016 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 13909-2:2016(E)
Hard coal and coke — Mechanical sampling —
Part 2:
Coal — Sampling from moving streams
1 Scope
This part of ISO 13909 specifies procedures and requirements for the design and establishment
of mechanical samplers for the sampling of coal from moving streams and describes the methods of
sampling used.
[1]
It does not cover mechanical sampling from stationary lots which is dealt with in ISO 13909-3 .
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 13909-1:2016, 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 13909-7, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision
of sampling, sample preparation and testing
ISO 13909-8, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
ISO 21398, Hard coal and coke — Guidance to the inspection of mechanical sampling systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 apply.
4 Establishing a sampling scheme
4.1 General
The general procedure for establishing a sampling scheme is as follows.
a) Define the quality parameters to be determined and the types of samples required.
b) Define the lot.
c) Define or assume the precision required (see 4.3.1).
d) Determine the method of combining the increments into samples and the method of sample
preparation (see ISO 13909-4).
e) Determine or assume the variability of the coal (see 4.3.2) and the variance of preparation and
testing (see 4.3.3). Methods for determining variability and the variance of preparation and testing
are given in ISO 13909-7.
© ISO 2016 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 13909-2:2016(E)

f) Establish the number of sub-lots and the number of increments per sub-lot required to attain the
desired precision (see 4.3.4).
g) Decide whether to use time-basis or mass-basis sampling (see Clause 5) and define the sampling
intervals in minutes for time-basis sampling or in tonnes for mass-basis sampling.
h) Ascertain the nominal top size of coal for the purpose of determining the minimum mass of sample
(see 4.4 and Table 1).
NOTE The nominal top size may initially be ascertained by consulting the consignment details, or by visual
estimation, and may be verified, if necessary, by preliminary test work.
i) Determine the minimum average increment mass (see 4.5).
4.2 Design of the sampling scheme
4.2.1 Material to be sampled
The first stage in the design of the scheme is to identify the coal to be sampled. Samples may be
required for technical evaluation, process control, quality control and for commercial reasons by both
the producer and the customer. It is essential to ascertain exactly at what stage in the coal-handling
process the sample is required and, as far as practicable, to design the scheme accordingly. In some
instances, however, it may prove impracticable to obtain samples at the preferred points and, in such
cases, a more practicable alternative is required.
4.2.2 Division of lots
A lot may be sampled as a whole or as a series of sub-lots, e.g. coal dispatched or delivered over a period
of time, a ship load, a train load, a wagon load or coal produced in a certain period, e.g. a shift.
It may be necessary to divide a lot into a number of sub-lots in order to improve the precision of the
results. For lots sampled over long periods, it may be expedient to divide the lot into a series of sub-lots,
obtaining a sample for each.
4.2.3 Basis of sampling
Sampling may be carried out on either a time-basis or a mass-basis. In time-basis sampling, the sampling
interval is defined in minutes and seconds and the increment mass is proportional to the flow rate at
the time of taking the increment. In mass-basis sampling, the sampling interval is defined in tonnes
and the mass of increments constituting the sample is uniform. Of these two alternatives, time-basis
sampling is easier to implement and verify, because only a fixed speed cutter and a timing device are
required. On the other hand, for mass-basis sampling, a conveyor belt weightometer is required as well
as a device that is controlled sufficiently to adjust the primary cutter speed increment by increment to
achieve uniform increment mass.
4.2.4 Precision of sampling
After the desired sampling precision has been selected, the number of sub-lots and the minimum
number of increments per sub-lot collected shall be determined as described in 4.3.4, and the average
mass of the primary increments shall be determined as described in 4.5.
For single lots, the quality variation shall be assumed as the worst case (see 4.3.2). The precision of
sampling achieved may be measured using the procedure of replicate sampling (see ISO 13909-7).
At the start of regular sampling of unknown coals, the worst-case quality variation shall be assumed,
in accordance with 4.3.2. When sampling is in operation, a check may be carried out to confirm that the
desired precision has been achieved, using the procedures described in ISO 13909-7.
2 © ISO 2016 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 13909-2:2016(E)

If any subsequent change in precision is required, the number of sub-lots and of increments shall be
changed as determined in 4.3.4 and the precision attained shall be rechecked. The precision shall also
be checked if there is any reason to suppose that the variability of the coal being sampled has increased.
The number of increments determined in 4.3.4 applies to the precision of the result when the sampling
errors are large relative to the testing errors, e.g. for moisture content.
4.2.5 Bias of sampling
It is of particular importance in sampling to ensure, as far as possible, that the parameter to be measured
is not altered by the sampling and sample preparation process or by subsequent storage prior to testing.
This may require, in some circumstances, a limit on the minimum mass of primary increment (see 4.5).
When collecting samples for moisture determination from lots over an extended period, it may be
necessary to limit the standing time of samples by dividing the lot into a number of sub-lots (see 4.3.4).
Sampling systems shall be tested for bias in accordance with the methods given in ISO 13909-8.
4.3 Precision of results
4.3.1 Precision and total variance
In all methods of sampling, sample preparation and analysis, errors are incurred and the experimental
results obtained from such methods for any given parameter will deviate from the true value of that
parameter. While the absolute deviation of a single result from the “true” value cannot be determined,
it is possible to make an estimate of the precision of the experimental results. This is the closeness with
which the results of a series of measurements made on the same coal agree among themselves, and the
deviation of the mean of the results from an accepted reference value, i.e. the bias of the results (see
ISO 13909-8).
It is possible to design a sampling scheme by which, in principle, an arbitrary level of precision can be
achieved.
The desired overall precision for a lot is normally agreed between the parties concerned. In the absence
of such agreement, a value of one tenth of the ash content may be assumed up to 10 % ash, subject to a
maximum of 1 % absolute for ash contents above 10 %.
The theory of the estimation of precision is discussed in ISO 13909-7. The following formula is derived:
V
I
+V
PT
n
P =2 (1)
L
m
where
P is the estimated index of overall precision of sampling, sample preparation and testing for
L
the lot, expressed as a percentage absolute;
V is the primary increment variance;
I
n is the number of increments per sub-lot;
m is the number of sub-lots in the lot;
V is the preparation and testing variance.
PT
If the quality of a coal of a type not previously sampled is required, then in order to devise a sampling
scheme, assumptions have to be made about the variability (see 4.3.2). The precision actually achieved
for a particular lot by the scheme devised can be measured by the procedures given in ISO 13909-7.
© ISO 2016 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 13909-2:2016(E)

4.3.2 Primary increment variance
The primary increment variance, V , depends upon the type and nominal top size of coal, the degree
I
of pre-treatment and mixing, the absolute value of the parameter to be determined and the mass of
increment taken.
The number of increments required for the general-analysis sample and the moisture sample shall be
calculated separately using the relevant values of increment variance and the desired precision. If a
common sample is required, the number of increments required for that sample shall be the greater of
the numbers calculated for the general-analysis sample and the moisture sample respectively.
NOTE For many coals, the increment variance for ash is higher than that for moisture and hence, for the same
precision, the number of increments required for the general-analysis sample will be adequate for the moisture
sample and for the common sample.
The value of the primary increment variance, V , required for the calculation of the precision using
I
Formula (1) can be obtained by either
a) direct determination on the coal to be sampled using one of the methods described in ISO 13909-7, or
b) assuming a value determined for a similar coal from a similar coal handling and sampling system.
If neither of these values is available, a value of V = 5 for the ash content of unwashed and blended coals
I
and V = 3 for the ash content of washed coals can be assumed initially and checked, after the sampling
I
has been carried out, using one of the methods described in ISO 13909-7.
4.3.3 Preparation and testing variance
The value of the preparation and testing variance, V , required for the calculation of the precision
PT
using Formula (1) can be obtained by either
a) direct determination on the coal to be sampled using one of the methods described in ISO 13909-7, or
b) assuming a value determined for a similar coal from a similar sample preparation scheme.
If neither of these values is available, a value of 0,20 for ash content can be assumed initially and
checked, after the preparation and testing has been carried out, using one of the methods described in
ISO 13909-7.
4.3.4 Number of sub-lots and number of increments per sub-lot
4.3.4.1 General
The number of increments taken from a lot in order to achieve a particular precision is a function of the
variability of the quality of the coal in the lot, irrespective of the mass of the lot. The lot may be sampled
as a whole, resulting in one sample, or divided into a number of sub-lots resulting in a sample from each.
Such division may be necessary in order to achieve the required precision, and the necessary number of
sub-lots shall be calculated using the procedure given in 4.3.4.2.
Another important reason for dividing the lot is to maintain the integrity of the sample, i.e. to avoid
bias after taking the increment, particularly, in order to minimize loss of moisture due to standing. The
need to do this is dependent on factors such as the time taken to collect samples, ambient temperature
and humidity conditions, the ease of keeping the sample in sealed containers during collection and the
particle size of the coal. It is recommended that, if moisture loss is suspected, a bias test be carried
out to compare the quality of a reference sample immediately after extraction with the sample after
standing for the normal time. If bias is found, the sample standing time should be reduced by collecting
samples more frequently, i.e. increasing the number of sub-lots.
There may be other practical reasons for dividing the lot such as the following:
a) for convenience when sampling over a long period;
4 © ISO 2016 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 13909-2:2016(E)

b) to keep sample masses manageable.
The designer of a sampling scheme should cater for the worst case anticipated and will then tend to
use a higher value for V than may actually occur when the system is in operation. On implementing a
I
new sampling scheme, a check on the actual precision being achieved should be carried out using the
methods described in ISO 13909-7. This may indicate that some changes are required to achieve the
required precision, in which case, the number of sub-lots and increments shall be recalculated using
the procedures given in 4.3.4.2.
4.3.4.2 Calculation of number of sub-lots and increments
The number of sub-lots and number of increments required per sub-lot are established using the
following procedure.
Determine the minimum number of sub-lots required for practical reasons (see 4.3.4.1).
Estimate the number of increments, n, in each sub-lot for a desired precision from the following formula
[obtained by transposing Formula (1)]:
4V
I
n= (2)
2
mP −4V
LPT
A value of infinity or a negative number indicates that the errors of preparation and testing are such
that the required precision cannot be achieved with this number of sub-lots. In such cases, or if n is
impracticably large, increase the number of sub-lots by one of the following means.
a) Choose a number corresponding to a convenient mass, recalculate n from Formula (2) and repeat
this process until n is a practicable number.
b) Decide on the maximum practicable number of increments per sub-lot, n , and calculate m from
1
Formula (3).
44Vn+ V
IP1 T
m= (3)
2
nP
1 L
Adjust m upwards, if necessary, to a convenient number and recalculate n.
Take n as 10 if the final calculated value is less than 10.
NOTE The formulae given in 4.3.4.2 will generally estimate a higher number for the required number of
increments. This is because it is based on the assumption that the quality of coal has no serial correlation;
however, serial correlation is always present to some degree. In addition, because a certain amount of preparation
and testing is required when measuring the increment variance, the preparation and testing errors are included
more than once.
Example 1
The lot is 20 000 t delivered in 5 000 t train loads and the required precision, P , is 0,25 % ash. The
L
quality variation is known and the following values have been determined:
primary increment variance, V = 0,5;
I
preparation and testing variance, V = 0,05.
PT
a) Initial number of sub-lots
It has been decided that the minimum number of sub-lots shall be four. Therefore, take sub-lots of
5 000 t each (i.e. one sub-lot per
...