ISO 13909-5:2016

INTERNATIONAL ISO
STANDARD 13909-5
Second edition
2016-07-01
Hard coal and coke — Mechanical
sampling —
Part 5:
Coke — Sampling from moving streams
Houille et coke — Échantillonnage mécanique —
Partie 5: Coke — Échantillonnage en continu
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

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 Parameters to be determined on samples . 2
4.2.3 Division of lots . 2
4.2.4 Basis of sampling . 2
4.2.5 Precision of sampling . 3
4.2.6 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 . 5
4.3.4 Number of sub-lots and number of increments in each sub-lot . 5
4.4 Minimum mass of sample . 8
4.5 Mass of primary increment . 9
4.6 Size analysis .10
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 Stratified random sampling .11
5.3.1 General.11
5.3.2 Time-basis stratified random sampling .12
5.4 Reference sampling .12
6 Design of mechanical samplers .12
6.1 Safety .12
6.2 Sampling System.12
6.2.1 General.12
6.2.2 Checking for precision and bias .13
6.2.3 Operation of sampler .13
6.3 Location of sampling equipment .13
6.4 General requirements for designing mechanical samplers .13
6.5 Design of falling-stream-type samplers .14
6.5.1 General.14
6.5.2 Cutter velocity .16
6.6 Cross-belt-type primary samplers .16
6.6.1 Operation .16
6.6.2 Design of cross-belt samplers .17
6.6.3 Maintenance of sampling equipment .18
7 Handling and storage of samples .19
8 Sample preparation .20
9 Minimization of bias .20
9.1 General .20
9.2 Spacing of increments .20
9.3 Incorrectly extracted increments .20
9.4 Preservation of integrity of sample .20
9.4.1 General.20
9.4.2 Precautions to reduce bias .21
10 Verification .21
Bibliography .22
iv © ISO 2016 – All rights reserved

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 13909-5:2001), 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
INTERNATIONAL STANDARD ISO 13909-5:2016(E)
Hard coal and coke — Mechanical sampling —
Part 5:
Coke — Sampling from moving streams
1 Scope
This part of ISO 13909 specifies procedures and requirements for the design and establishment
of sampling schemes for the mechanical sampling of coke from moving streams and the methods of
sampling used.
The diversity of types of equipment for sampling and the conditions under which mechanical sampling
is performed make it inappropriate to specify standard designs for samplers which will be applicable to
all situations.
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 13909-6, Hard coal and coke — Mechanical sampling — Part 6: Coke — 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 part of ISO 13909, 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 the precision required;
d) determine the method of combining the increments into a sample, or number of sub-lot samples,
and the method of sample preparation (see ISO 13909-6);
e) determine or assume the variability of the coke (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;
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) define the sampling interval (see Clause 5);
h) ascertain the nominal top size of the coke 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 cokes 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 coke-handling
process the sample is required and, as far as practicable, design the scheme accordingly.
4.2.2 Parameters to be determined on samples
The samples for moisture and physical tests may be collected separately or as one sample, which is then
divided. In this part of ISO 13909, a sample which is collected for the determination of moisture (and
possibly also for general analysis) is referred to as the moisture sample; a sample which is collected
for physical tests only is referred to as the physical sample. If a sample is used for the determination of
moisture and for physical tests, it is referred to as a common sample.
In mechanical sampling of coke, the only sample which can, in certain circumstances (see 4.2.6), be
processed automatically beyond the divided-increment stage is the moisture sample.
In order to achieve the desired precision, it may be necessary to take different numbers of increments
for the moisture and physical samples. Where a common sample is taken, the greater number of
increments shall be used.
4.2.3 Division of lots
A lot may be sampled as a whole or as a series of sub-lots, e.g. coke despatched or delivered over a
period of time, a ship load, a train load, a wagon load, or coke 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.
4.2.4 Basis of sampling
Sampling may be carried out on either a time-basis or a mass-basis.
In time-basis sampling, increments are taken at fixed time intervals with an increment mass, collected
with a fixed speed cutter, which is proportional to the flow rate at the time of extraction.
2 © ISO 2016 – All rights reserved

In mass-basis sampling, increments are taken at fixed mass intervals, using a belt weigher/mass
integrator, and fixed mass increments are extracted using a variable speed cutter or sample preparation
system which produces a fixed mass divided increment.
The conditions under which mass-basis sampling may seem to offer the advantage of consistent
increment mass, for example highly variable flow rates, are those in which it is most difficult to
implement in practice.
Time-basis sampling is by far the simplest to implement and is the basis of this part of ISO 13909.
4.2.5 Precision of sampling
The required precision for a lot for each parameter to be measured shall be decided. The number of sub-
lots and minimum number of increments per sub-lot collected shall then be determined as described in
4.3.4, and the average mass of 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 cokes, the worst-case quality variation shall be assumed.
When sampling is in operation, a check shall be carried out to confirm that the desired precision has
been achieved using the procedure of duplicate sampling as described in ISO 13909-7.
If any subsequent change in precision is required, the number of sub-lots and 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 coke 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. moisture content. However, in some tests,
e.g. Micum Index, the testing errors are themselves large. In this case, it may be necessary to prepare
two or more test portions from the same sample (see 4.3.4.3) and use the mean of the determinations to
give a better precision.
4.2.6 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. For example, care shall be taken to avoid breakage of coke intended for physical testing and
loss of moisture from the moisture sample during storage. This may require, in some circumstances, a
limit on the minimum mass of primary increment (see 4.5 and Clause 8).
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).
The use of on-line crushing and division of the moisture sample for moisture determination should be
treated with caution because of the risk of bias caused by loss of moisture in the processing (see 6.2.2).
In particular, the crushing of hot coke is not recommended. If the bias is unacceptable, the sample shall
be left in the uncrushed state and the sample preparation carried out by manual methods. It should be
accepted, however, that some bias is inevitable, whether due to breakage or loss of moisture from hot
coke. The object, therefore, shall be to restrict such degradation or moisture loss to a minimum.
When a coke-sampling scheme is implemented, it shall be checked 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 coke 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.
NOTE The required overall precision for a lot is normally agreed between the parties concerned.
The theory of the estimation of precision is given in ISO 13909-7. Formula (1) is derived:
V
I
+V
PT
n
P = 2 (1)
L
m
where
P is the estimated overall precision of sampling, sample preparation and testing for the lot at
L
a 95 % confidence level, expressed as a percentage absolute;
V is the primary increment variance;
I
V is the preparation and testing variance;
PT
n is the number of increments to be taken from a sub-lot;
m is the number of sub-lots in the lot.
If the quality of a coke of a type not previously sampled is required, then, in order to devise a sampling
scheme, assumptions should 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.
If the same type of coke is sampled regularly, sampling schemes can be laid down using data derived
from previous sampling. The procedures given in ISO 13909-7 can be used to devise the optimum
scheme, thus keeping the sampling costs to a minimum.
4.3.2 Primary increment variance
The primary increment variance, V , depends upon the type and nominal top size of coke, the degree
I
of pre-treatment and mixing, the absolute value of the parameter to be determined and the mass of
increment taken.
The variability for moisture is usually higher than that for ash and hence, for the same precision, the
number of increments for moisture will be adequate for ash. If, however, a higher precision is required
for ash, the relevant primary increment variance shall be applied for each 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 coke to be sampled using one of the methods described in ISO 13909-7, or
b) assuming a value determined for a similar coke from a similar coke handling and sampling system.
If neither of these values is available, a value of 5 can be assumed initially and checked, after the
sampling has been carried out, using one of the methods described in ISO 13909-7.
4 © ISO 2016 – All rights reserved

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 coke to be sampled using one of the methods described in ISO 13909-7, or
b) assuming a value determined for a similar coke from a similar sample-preparation scheme.
If neither of these values is available, a value of 0,2 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 in each 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 coke 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.
There may be other practical reasons for dividing the lot, such as:
a) for convenience when sampling over a long period;
b) to keep sample masses manageable;
c) 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 coke. It is
recommended that, if moisture loss is suspected, a bias test is 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.
The quality of the lot shall be calculated as the weighted average of the values found for the sub-lots.
As stated in 4.3.1, the precision is determined by the variability of the coke, the number of increments
and sub-lots and the preparation and testing variance. By transposing Formula (1), it can be shown that
the number of increments per sub-lot for a desired precision for a lot can be estimated from Formula (2):
4V
I
n = (2)
mP −4V
LPT
Determine the number of sub-lots required for practical reasons and then estimate the number of
increments in each for the desired precision using Formula (2). If n is a practicable number, the initial
scheme is established. However, if n is less than 10, take 10 increments per sub-lot.
If n is impracticably large, increase the number of sub-lots using one of the following methods:
a) increase m to a number corresponding to a convenient mass or time, recalculate n 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
Formula (3):
44Vn+ V
lP1 T
m= (3)
nP
1 L
Adjust m upwards, if necessary, to a convenient number and recalculate n.
NOTE This method of calculating the number of increments required per sub-lot for a certain precision from
the primary increment variance and the preparation and testing variance will generally give an overestimate of
the required number. This is because it is based on the assumption that the quality of coke varies in a random
manner. 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.
The designer of a sampling scheme should cater for the worst case anticipated and may then use
higher values for V than may actually occur when the scheme is in operation. When the sampler is
I
commissioned, the precision of the result can be estimated and adjusted (see ISO 13909-7), by
increasing or decreasing the number of increments in the sample, keeping the same increment mass so
that the required precision can be achieved at minimum cost.
Example 1
The lot is 35 000 t of 40 × 20 mm coke delivered in one day. The primary increment variance and
preparation and testing variance for moisture content have been determined as follows.
Primary increment variance for moisture content, V = 5.
I
Preparation and testing variance for moisture content, V = 0,10.
PT
The required precision, P = 1,0 % moisture content.
L
a) Initial number of sub-lots
For convenience and to avoid the sample standing for too long, take three shift samples, (i.e. m = 3).
b) Number of increments per sub-lot
45×
n = =77, using Formula (2)
31×−40× ,10
Therefore, split the lot into three sub-lots and take 10 increments from each.
Example 2
The lot is 100 000 t of 100 × 25 mm coke delivered as 5 000 t/day over two 8-hour shifts.
The primary increment variance, V , for moisture content is unknown, so initially assume a value of 5.
I
Required precision P = 0,25 % moisture content.
L
Preparation and testing variance for moisture content, V , from experience assume a value of 0,20.
PT
a) Initial number of sub-lots
For the preliminary calculation, assume a daily sample is constituted, i.e. m = 20, in order to avoid
the risk of moisture loss by overnight storage of sample increments.
b) Number of increments per sub-lot
45×
n = = 44,4 using Formula (2)
20×−02,,54×02
This number will result in too large a mass to crush as a single moisture sample for each sub-lot
[almost 2 tonnes for a typical increment mass of about 45 kg using Formula (4)]. Therefore, increase
the number of sub-lots to 40, i.e. one per shift.
6 © ISO 2016 – All rights reserved

45×
n = =≈11,712
40×−02,,54×02
Hence, take 12 increments per shift, i.e. one every 40 min, resulting in a moisture sample of about
540 kg for each sub-lot. However, if the equipment available for crushing the sample is not robust
enough for this sample mass, further increase the number of sub-lots.
Example 3
The lot is 9 000 t of 40 × 25 mm coke.
The primary increment variance for moisture content V = 5.
I
The preparation and testing variance for moisture content, V , from experience is assumed to
PT
be 0,20.
The desired precision P = 0,5 % moisture content.
L
a) Number of sub-lots
For convenience, split the lot into 2 sub-lots, i.e. m = 2.
b) Number of increments per lot
45× 20
n = = ≈−66.7
−03,
20×−(,54),×02
This 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.
It could be decided that 40 increments is the maximum practicable number in a sub-lot and from
Formula (3).
45×+44××00,2
m = =≈52, 6
40×05,
This gives a practical sampling method of dividing the lot into six sub-lots of 1 500 tonnes each,
taking 40 increments from each.
4.3.4.2 Moisture sample
The sampling variance for moisture content may vary in the range 0,2 to 5 depending on the absolute
value of the moisture content, the size range of the coke and the extent of cutting, screening and mixing
it has undergone prior to sampling. For example, a closely graded, highly cut small-sized industrial coke
sampled on delivery to the customer would have a much lower variance than an uncut coke sampled at
the wharf or a very large coke on despatch from the producer’s works. It may be known from experience
what level of variance is to be expected.
It is recommended that the number of increments initially required be sufficient to give a mass of
sample greater than the mass given in Table 1, subject to a minimum of 10 increments.
The variance for ash and other chemical properties is usually less than for moisture content. However,
it is often desired to obtain a higher precision for the ash result and hence the number of increments
should be calculated for each and the greater number taken for the moisture sample.
Table 1 — Minimum mass of sample
Nominal top size Minimum mass
m kg
> 125 2 000
125 1 000
90 500
63 250
45 125
31,5 60
22,4 30
16,0 15
11,2 8
10,0 6
8,0 4
5,6 2
4 1
4.3.4.3 Physical sample
The cokes to be sampled within the scope of this part of ISO 13909 will exhibit large differences in
physical strength, size, size range, and size distribution. In addition, many different parameters,
e.g. Micum test, porosity, percentage retained on a particular sieve, mean size, etc., can be determined
on the samples. Sample preparation errors may be zero when the test is done on the whole sample or
large when division of the sample takes place.
Furthermore, it is usually not possible to determine the individual increment variances for tests such as
the Micum test, because the increment mass is too small.
It will be found with many physical tests that the only way to achieve the required precision will be either
a) to divide the lot into sub-lots, or
b) to prepare two or more test portions from the sample, taking the mean of the test results for
the sample.
The precision for the particular parameter required shall then be checked and the number of increments
adjusted according to the procedure specified in ISO 13909-7.
4.4 Minimum mass of sample
For most parameters, particularly size grading and those that are particle-size related, the precision
of the result is limited by the ability of the sample to represent all the particle sizes in the mass of coke
being sampled.
The minimum mass of sample is dependent on the nominal top size of the coke, the precision required
for the parameter concerned, and the relationship of that parameter to particle size. Some such
relationship applies at all stages of preparation. The attainment of this mass will not, in itself, guarantee
the required precision. This is also dependent on the number of increments in the sample and their
variability (see 4.3.4).
The masses specified in Table 1 are for guidance on the minimum mass for unknown or heterogeneous
cokes. While they can usually be reduced for the moisture sample, they may be inadequate for the
determination of, for example, oversize to 1 % precision of sampling and division, particularly on very
large cokes.
8 © ISO 2016 – All rights reserved

When a coke is regularly sampled under the same circumstances, the precision obtained for all the
required quality parameters shall be checked in accordance with ISO 13909-7 and the masses adjusted
accordingly. However, the masses shall not be reduced below the minimum requirements laid down in
the relevant analysis standards.
Account shall also be taken of the uses to which the sample is to be put and the numbers, masses and
size distribution of the test samples required.
4.5 Mass of primary increment
The mass, m , in kilograms, of an increment taken by a mechanical cutter with cutting edges normal to
I
the stream at the discharge of a moving stream can be calculated from Formula (4):
Cb
−3
m =×10 (4)
I
36, v
c
where
C is the flow rate, in tonnes per hour;
b is the cutter aperture width, in millimetres;
v is the cutter speed, in metres per second.
C
For a cross-belt sampler, the mass, m , in kilograms, of increment can be calculated from Formula (5):
I
Cb
−3
m =×10 (5)
I
36, v
B
where
C is the flow rate, in tonnes per hour;
b is the cutter aperture width, in millimetres;
v is the belt speed, in metres per second.
B
'
The minimum average mass of primary increment to be collected, m , is calculated from Formula (6):
I
m
' S
m = (6)
I
n
where
m is the minimum mass of sample (see Table 1);
S
n is the minimum number of increments taken from the sub-lot (see 4.3.4).
In most mechanical systems, the mass of primary increment collected [see Formulae (4) and (5)] will
greatly exceed that necessary to make up a sample of the required mass. In some systems, the primary
increments are therefore divided, either as taken or after reduction, in order to avoid the mass of the
sample becoming excessive.
Providing the design of the cutter complies with the requirements of 6.5 or 6.6, the extraction of an
increment from the coke stream will be unbiased whatever the flow rate at the time. Even if flow rates
are variable, increments taken at low flow rates, and hence of mass less than the average, will not be
subject to extraction bias. Therefore, this part of ISO 13909 does not specify an absolute minimum
increment mass.
Under some conditions, e.g. high ambient temperature, increments which are smaller than those
corresponding to the design capacity of the system may suffer from disproportionate changes in
quality, e.g. loss in moisture, and precautions need to be taken to prevent this. If such losses cannot
be prevented and are found to cause bias, such means as buffer hoppers shall be used. Alternatively,
increments can themselves be retained temporarily in a buffer hopper until there is sufficient mass to
ensure passage, without introducing bias into the system, through an on-line preparation system. On
no account shall a primary sampler be switched off at low flow rates to avoid low mass increments.
When measuring primary increment variance (see ISO 13909-7:2016, Clause 6) at preliminary stages in
the design of the sampling scheme, use increment masses that are close to those expected to be taken by
the system, based on similar coke from similar sampling systems. After implementation of the sampling
scheme, the precision of the result can be estimated and adjusted (see ISO 13909-7), by increasing or
decreasing the number of increments in the sample, keeping the same increment mass.
4.6 Size analysis
Within the scope of this part of ISO 13909, the coke products to be sampled will exhibit differences
in size and amount of fines. In addition, the parameters to be determined (percentage retained on a
particular sieve, mean size, etc.) may differ from case to case. Furthermore, when sample division is
applied, division errors shall be taken into account, whereas they are non-existent if sizing is performed
without any preceding division.
Take these factors into account when applying the techniques for calculating numbers of increments for
a particular precision (see 4.3.1 to 4.3.4). In the absence of any information on increment variance etc.,
initially take 25 increments per sample.
The precision for the particular parameter required shall then be checked and the number of increments
adjusted according to the procedure described in ISO 13909-7.
Minimization of degradation of samples used for determination of size distribution is vital to reduce
bias in the measured size distribution. To prevent particle degradation, it is essential to keep free-fall
drops to a minimum. Trial tests should be made in accordance with the method given in ISO 13909-8 to
determine the degree of degradation.
5 Methods of sampling
5.1 General
Sampling shall be carried out by systematic sampling on a time-basis. The procedures of sample
preparation vary in accordance with the type of sampling employed (see ISO 13909-6).
It is essential that each increment taken from a stream represents the full width and depth of the stream.
The consistency of loading of the belt should be controlled, as far as possible, so that sampling is as
efficient as possible. The flow should be made reasonably uniform over the whole cross-section of the
stream at all times, by means of controlled loading or suitable devices such as feed hoppers, ploughs, etc.
It is essential that the increment does not completely fill or overflow the sampling device. With
mechanized sampling devices, the increment mass may be considerably larger than that necessary
to produce the calculated minimum sample mass. Hence, a system of primary increment division
(see ISO 13909-6) may be necessary to divide the increment to a manageable mass.
All processes and operations upstream of the sampling location shall be examined for characteristics
which could produce periodic variations in belt loading or quality and which may coincide with the
operation of primary samplers. Such periodicity may arise from the cycle of operations or feeder
systems in use. If necessary modify the sampling interval, or employ stratified random sampling, to
remove the possibility of bias.
10 © ISO 2016 – All rights reserved

5.2 Time-basis sampling
5.2.1 Method of taking primary increments
In order that the increment mass is proportional to the coke flow rate in mechanical sampling, the
speed of the cutter shall be constant throughout the sampling of the entire sub-lot (see 6.5.1).
Primary increments shall be taken at pre-set equal time intervals throughout the lot or sub-lot. If the
calculated number of increments has been taken before the handling has been completed, additional
increments shall be taken at the same interval until the handling operation is completed.
5.2.2 Sampling interval
The time interval, ∆t, in minutes, between taking primary increments by time-basis sampling is
determined by Formula (7):
60m
SL
Δt ≤ (7)
Gn
where
m is the mass of the sub-lot, in tonnes;
SL
G is the maximum flow rate on the conveyor belt, in tonnes per hour;
n is the number of primary increments in the sample (see Clause 4).
The designer of mechanical systems should ensure that, for all cokes using the system, the time taken
for the sampling or processing of an increment shall be less than the time between increments under
maximum flow rate.
In order to minimize the possibility of any bias being introduced, a random start within the first
sampling interval is recommended.
5.2.3 Mass of increment
The mass of the primary increment corresponding to the average flow rate (total mass/operating
time) of the coke stream shall be not less than the minimum average increment mass calculated from
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