ISO 13909-6:2001
(Main)Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples
Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples
Houille et coke — Échantillonnage mécanique — Partie 6: Coke — Préparation des échantillons pour essai
L'ISO 13909-6:2001 décrit la préparation des échantillons de coke, de la combinaison de prélèvements primaires à la préparation d'échantillons pour des essais spécifiques.
Črni premog in koks - Mehansko vzorčenje - 6. del: Koks - Priprava preskusnih vzorcev
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INTERNATIONAL ISO
STANDARD 13909-6
First edition
2001-12-15
Hard coal and coke — Mechanical
sampling —
Part 6:
Coke — Preparation of test samples
Houille et coke — Échantillonnage mécanique —
Partie 6: Coke — Préparation des échantillons pour essai
Reference number
ISO 13909-6:2001(E)
© ISO 2001
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ISO 13909-6:2001(E)
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ISO 13909-6:2001(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precision of sample preparation . 2
5 Constitution of a sample . 2
6 Division . 4
7 Preparation of samples for specific tests . 16
8 Design of equipment for preparation . 20
Bibliography. 24
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ISO 13909-6:2001(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 13909 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 13909-6 was prepared by Technical Committee ISO/TC 27, Solid mineral fuels,
Subcommittee SC 4, Sampling.
ISO 13909 cancels and replaces ISO 9411-1:1994, Solid mineral fuels — Mechanical sampling from moving streams
— Part 1: Coal and ISO 9411-2:1993, Solid mineral fuels — Mechanical sampling from moving streams — Part 2:
Coke, of which it constitutes a technical revision. It also supersedes the methods of mechanical sampling of coal and
coke given in ISO 1988:1975, Hard coal — Sampling and ISO 2309:1980, Coke — Sampling.
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
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ISO 13909-6:2001(E)
Introduction
The objective of sample preparation is to prepare one or more test samples from the primary increments for
subsequent analysis. The requisite mass and particle size of the test sample depend on the test to be carried out.
The process of sample preparation may involve constitution of samples, reduction, division, mixing and drying or all
or a combination of these.
Primary increments may be prepared individually as test samples or combined to constitute samples either as taken
or after having been prepared by reduction and/or division. Samples may either be prepared individually as test
samples or combined on a weighted basis to constitute a further sample.
On-line sampling and sample-preparation systems can be usefully implemented when dealing with a coke or cokes
which are known to be free from handling problems, but only when this will not result in loss of moisture,
contamination by the sampling equipment or size degradation of physical samples.
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INTERNATIONAL STANDARD ISO 13909-6:2001(E)
Hard coal and coke — Mechanical sampling —
Part 6:
Coke — Preparation of test samples
1 Scope
This part of ISO 13909 describes the preparation of samples of coke from the combination of primary increments to
the preparation of samples for specific tests.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 13909. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 13909 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 579:1999, Coke — Determination of total moisture.
ISO 687:1974, Coke — Determination of moisture in the analysis sample.
ISO 13909-1:2001, Hard coal and coke — Mechanical sampling — Part 1: General introduction.
ISO 13909-5:2001, Hard coal and coke — Mechanical sampling — Part 5: Coke — Sampling from moving streams.
ISO 13909-7:2001, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of
sampling, sample preparation and testing.
ISO 13909-8:2001, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias.
3 Terms and definitions
For the purposes of this part of ISO 13909, the terms and definitions given in ISO 13909-1 apply.
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ISO 13909-6:2001(E)
4 Precision of sample preparation
From the equations given in ISO 13909-7, the estimated absolute value of the precision of the result obtained for the
lot at the 95 % confidence level,P , for continuous sampling is given by:
L
s
V
I
+V
PT
n
P = 2
(1)
L
m
where
V is the primary increment variance;
I
n is the number of increments in the sample;
V is the variance of preparation and testing for both off-line and on-line systems;
PT
m is the number of sub-lots.
The procedures given in this part of ISO 13909 are designed to achieve levels ofV of 0,05 or less for moisture
PT
tests. Better levels may be expected for other chemical characteristics.
For some preparation schemes, however, practical restrictions may prevent the preparation and testing variance
being as low as this. Under these circumstances, the user will have to decide whether to achieve the desired overall
precision by improving the preparation scheme or by dividing the lot into a greater number of sub-lots.
The errors occurring in the various stages of preparation and analysis, expressed in terms of variance, may be
checked by the methods given in ISO 13909-7.
5 Constitution of a sample
5.1 Introduction
Examples of the constitution of samples are shown in Figure 1.
Primary increments shall be taken in accordance with the procedures specified in ISO 13909-5.
Individual increments are usually combined to form a sample. A single sample may be constituted by combination of
increments taken from a complete sub-lot or by combining increments taken from individual parts of a sub-lot. Under
some circumstances, e.g. size analysis or bias testing, the sample consists of a single increment which is prepared
and tested.
Samples may also be prepared by the combination of other samples.
The procedures for increment combination (5.2) may vary according to whether the primary increments were taken
using a time-basis (5.2.1) or a mass-basis (5.2.2) sampling scheme.
5.2 Combination of increments
5.2.1 Time-basis sampling
The mass of the primary increments shall be proportional to the flow rate at the time of sampling. The primary
increments may be combined into a sample, either directly as taken or after having been prepared individually to an
appropriate stage by fixed-ratio division (see clause 6).
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ISO 13909-6:2001(E)
a) Example 1
b) Example 2
Figure 1 — Examples of the constitution of samples
5.2.2 Mass-basis sampling
If the primary increments are of almost uniform mass (see note), they may be combined into a sample, either directly
as taken or after having been prepared individually to an appropriate stage by fixed-ratio division (see clause 6).
NOTE Almost uniform mass has been achieved if the coefficient of variation of the increment masses is less than 20 % and there
is no significant correlation between the flow rate at the time of taking the increment and the mass of the increment (see
ISO 13909-5).
If the primary increments are not of almost uniform mass, they may only be combined into samples after having been
divided individually by fixed-mass division (see clause 6).
5.3 Combination of samples
When combining samples, the mass of the individual samples shall be directly proportional to the mass of the coke
from which they were taken in order to obtain a weighted mean of the quality characteristic for the sub-lot. Prior to
combination, division shall be by fixed-ratio (see clause 6).
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ISO 13909-6:2001(E)
6 Division
6.1 General
Since the cutter aperture will normally be at least three times the nominal top size, this will result in a very large
increment mass in many cases. The handling and preparation of such large increments would be either manpower or
equipment intensive. Division prior to further treatment may be necessary to provide a manageable sample mass.
Sample division can be
— on-line mechanically, or
— off-line mechanically or manually.
Whenever possible, mechanical methods are preferred to manual methods to minimize human error. Examples of
dividers are shown in Figure 2.
Mechanical dividers are designed to extract a part of the coke in a number of cuts of relatively small mass. When the
smallest mass of the divided sample that can be obtained in one pass through the divider is greater than that
required, further passes through the same divider or subsequent passes through further dividers may be necessary.
Manual division is normally applied when mechanical methods would result in loss of integrity, e.g. loss of moisture
or size degradation. Manual division of coke is also applied when the nominal top size of the coke is such as to make
the use of a mechanical divider impracticable. Manual methods may themselves result in bias, particularly if the mass
of coke to be divided is large.
6.2 Mechanical methods
6.2.1 General
Mechanical sample division may be carried out on an individual increment or a sample. Where samples are for
moisture or general analysis, it is permissible to install on-line crushing to a nominal top size of 16 mm followed by
sample division. Division shall be either by fixed-mass division or by fixed-ratio division subject to the conditions set
out in 6.2.2 and 6.2.3.
When crushing on-line, the risk of moisture loss should be considered, particularly if the coke is hot.
The uses to which the sample is to be put, the numbers, masses and size distribution of the test samples required
shall also be taken into account when deciding on the minimum mass of the sample.
When a coke is regularly sampled under the same conditions, the precision obtained for all the required quality
parameters shall be checked using the procedures of ISO 13909-7 and the minimum mass adjusted accordingly. The
masses shall not be reduced, however, below the minimum requirements laid down in the relevant analysis
standards.
NOTE The procedures described for fixed-ratio division are the simplest to implement. Other procedures may be used, however,
provided that the mass of the divided sample is proportional to the mass of the feed, e.g. the number of cuts could be kept
constant by making the feed rate of each division proportional to the mass of coke to be divided.
6.2.2 Mass of cut
The cuts shall be of uniform mass throughout the division of an increment. In order to achieve this, the flow of coke
to the divider shall be uniform and the cutting aperture and speed of the cutter shall be constant. The method of
feeding the divider shall be designed to minimize any segregation caused by the divider.
The cutting aperture shall be at least three times the nominal top size of the coke to be divided.
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ISO 13909-6:2001(E)
Key
1Feed
2 Rotating cone
3 Adjustable slot
4 Divided sample
5 Reject
A stream of coke is allowed to fall onto a rotating cone; the adjustable slot with lips in the cone allows the stream to fall directly
onto the sample receiver for part of each revolution.
a) Rotating cone type
Figure 2 — Examples of dividers
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ISO 13909-6:2001(E)
Key
1Feed
2 Divided sample in rotating receivers
The coke stream flows to the hopper and this flow is intercepted by the top edge of a number of sector-shaped containers
dividing the flow into equal parts. Either the hopper or the containers may rotate. The machine can be controlled for the following
operations:
a) for dividing;
b) for collecting duplicates;
c) for collecting replicates.
b) Container type
Figure 2 — Examples of dividers (continued)
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ISO 13909-6:2001(E)
Key
1Feed
2 Reject
3 Divided sample
A chain mechanism as shown is equipped with buckets spread at equal pitch. The buckets travel in a single direction or change
direction at pre-set time periods. The bucket intercepts the free-falling coke stream to extract cuts which discharge to sample as
the bucket inverts.
c) Chain-bucket type
Figure 2 — Examples of dividers (continued)
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ISO 13909-6:2001(E)
Key
1 Slotted belt
2Feed
3 Inclined chute
4 Divided sample
5Reject
An endless belt having slots spaced at equal pitch with lips that act as cutting edges passes below a feed chute. The coke
stream is fed to the chute and, as each slot passes through the stream, a cut is taken. The stream which falls onto the plain part
of the belt is carried to rejects.
d) Slotted-belt type
Figure 2 — Examples of dividers (continued)
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ISO 13909-6:2001(E)
Key
Key 1Feed
1Feed 2 Rotating hopper
2 Reject 3Reject
3 Divided sample 4 Divided sample
A hollow shaft which is attached to one or more cutters rotates A rotating hopper receives a coke flow and discharges through
withinahousingas shown. Each cutter isdesignedtotake a spout. Stationary cutters are positioned in the path of the
cuts from the coke stream and to discharge via the hollow spout outlet, cuts are taken as each cutter is passed. One or
shaft. more cutters may be fitted.
e) Rotating chute type f) Rotating hopper and spout
Figure 2 — Examples of dividers (continued)
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ISO 13909-6:2001(E)
Key
1Feed
2 Divided sample
3Reject
The cutter-chute traverses the full coke stream and diverts a portion from the stream. When the coke stream is not being cut by
the chute, it is deflected by the angle plate to reject.
g) Cutter-chute type
Figure 2 — Examples of dividers (continued)
6.2.3 Interval between cuts
In order to minimize bias, the first cut for each mass to be divided shall be made at random within the first interval.
For secondary and tertiary dividers, the cycle time shall not be evenly divisible into the cycle time of the cutter which
precedes it.
For fixed-mass division, the interval between taking cuts shall be varied proportionally to the mass of coke to be
divided so that divided samples having almost uniform mass are obtained. The mass shall be fixed for the whole sub-
lot.
For fixed-ratio division, the interval between taking cuts shall be constant, irrespective of the variations of masses of
coke to be divided so that divided-sample masses are proportional to the mass of the feed. The ratio shall be fixed
for the whole sub-lot.
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ISO 13909-6:2001(E)
6.2.4 Division of individual increments
6.2.4.1 Number of cuts
The number of cuts for dividing an increment shall be determined as follows.
a) For fixed-mass division, the minimum number of cuts at any stage shall be six. An equal number of cuts shall be
taken from each increment in the sub-lot.
b) For fixed-ratio division, the minimum number of cuts from an increment of mean mass at any stage shall be six.
For subsequent division of divided increments, a minimum of one cut shall be taken from each cut from the preceding
division.
6.2.4.2 Minimum mass of divided increment
The minimum mass of the divided increment shall be such that the combined masses of all the divided increments in
the sub-lot shall, at each stage, be greater than the mass given in Table 1, corresponding to the nominal top size. If
the increment masses are too low to satisfy this requirement, the divided increment shall be crushed prior to further
division.
For moisture samples, there is a restriction of 70 kg on the maximum mass of sample to be crushed at one time
during off-line preparation.
NOTE The masses given in Table 1 are for guidance on the minimum mass for unknown or heterogeneous cokes. Whilst they
can usually be reduced for the moisture sample, they may be inadequate for the determination of, for example, oversize to 1%
division precision, particularly on very large cokes.
Table 1 — Minimum mass of sample after division
Nominal top size Minimum mass
mm kg
> 125 2000
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
41
6.2.5 Division of samples
6.2.5.1 Number of cuts
The sample shall be divided by taking a minimum of 60 cuts.
NOTE If, during preparation, the sample is thoroughly mixed and it can be established that the required precision can be
achieved, the number may be reduced to 20.
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ISO 13909-6:2001(E)
6.2.5.2 Minimum mass of divided sample
The mass of the divided sample shall not be less than the minimum mass in Table 1.
6.3 Manual methods
6.3.1 General
For the manual division methods given in 6.3.2 to 6.3.4, the mass of the divided sample shall not be less than the
minimum mass in Table 1, subject to there being sufficient mass for all test portions required.
6.3.2 Riffle method
A riffle (see Figure 3) is a sample divider that will, in a single pass of a sample, divide it into halves, one of which is
retained and the other normally rejected. The device is normally portable and, for sample division, is usually fed
manually, the coke being evenly distributed along its length. Adjacent slots feed opposite receivers.
The slot width shall be at least 2,5 times and, preferably, not more than 3 times the nominal top size of the coke. Each
half of the riffle shall have the same number of slots, which shall be at least eight and preferably more. All the
�
surfaces on which the coke might rest shall have a slope of at least 60 to the horizontal.
The coke shall be allowed to fall steadily into the riffle, ensuring that it is evenly distributed over all the slots. The coke
shall be allowed to fall freely, i.e. not towards one side of the riffle, and the rate of feed shall be controlled such that
the slots are never choked. Closed riffles are preferred.
Care shall be taken to minimize loss of dust and moisture. To this end, the receiver shall fit closely against the body
of the riffle and, for dry cokes and moisture samples, closed-type riffles shall be used.
When a stage of sample division requires two or more steps or passes, the sample retained at each step shall be
taken alternately from each side of the riffle.
6.3.3 Flattened-heap method
The procedure, which is illustrated in Figure 4, is as follows.
The sample is mixed thoroughly and spread to form a rectangle of uniform thickness of 40 mm to 50 mm on a mixing
plate, which is a smooth, non-absorbent and non-contaminating surface.
Avoid moisture loss from wet cokes which can result from over-mixing.
A matrix is marked on the spread sample to give a minimum of 4� 5 equal parts. An increment is taken, at random,
from each of the parts by inserting a scoop with a bump plate (see the last paragraph of this subclause) to the bottom
of the matrix layer. The increments shall be combined into a divided sample. It is essential that these operations be
performed quickly if loss of moisture is to be prevented.
The increments shall be of uniform mass. The minimum mass required for each nominal top size of coke is the mass
of the divided sample (see Table 1) divided by the number of parts of the flattened heap.
The scoop shall be flat bottomed and the width of the entry shall be at least three times the nominal top size of the
coke; the side walls shall be higher than the height of the heap and the depth shall be sufficient to allow the required
mass of increment to be taken.
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ISO 13909-6:2001(E)
Key
1 Even number of slots
a) Open type b) Closed type
Figure 3 — Examples of riffles
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ISO 13909-6:2001(E)
Take the scoop sample with the aid of a bump plate which is inserted vertically through the flattened heap until it is in
contact with the bottom of the sample layer. The scoop is then inserted to the bottom of the spread coke and moved
horizontally until its open end comes into contact with the vertical bump plate. The scoop and bump plate are lifted
together to ensure that all particles are collected off the top of the mixing plate and that none fall off during lifting.
a) Spread the crushed sample into a rectangle with a
maximum thickness of 40 mm to 50 mm.
b) Arrange into 20 equal parts, e.g. into five equal parts
lengthwise and four equal parts breadthwise.
c) Take a scoopful of samples at random from each of the
20 parts by inserting the scoop to the bottom of the sample
layer. Combine the 20 scoopfuls into a divided sample.
d) Detail of taking an increment by using the bump plate
shown in c).
Figure 4 — Flattened-heap method
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ISO 13909-6:2001(E)
6.3.4 Strip-mixing and splitting method
Theprocedure,whichisillustratedinFigure5,is as follows.
Key
1Increment
2 Sampling frame
3 End plates (“book-ends”)
Figure 5 — Strip-mixing and splitting method
The coke sample is formed on a mixing plate, which is a smooth, non-absorbent, non-contaminating surface, into a
strip at least 10 times as long as it is wide by distributing the coke along the length of the strip as evenly as possible,
working randomly from end to end and from both sides of the strip. End plates shall be used to ensure that size
segregation only occurs laterally.
Increments shall be taken as a complete section across the strip. The width of each cross-section shall be not less
than 2,5 times the nominal top size of the coke.
NOTE 1 Special apparatus for the cutting out of increments may be constructed if desired.
Normally 20 increments are required. Fewer increments may be taken, subject to a minimum of 10, where the same
quality coke is regularly prepared under the same conditions and it has first been established that the required
precision can be obtained (see ISO 13909-7).
NOTE 2 Because of the efficient longitudinal mixing achieved in the formation of a strip, the same precision as that obtainable
with the flattened-heap method can be achieved with fewer increments.
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ISO 13909-6:2001(E)
7 Preparation of samples for specific tests
7.1 Types of test sample
The methods of preparation depend on the purpose for which the original sample was collected. Three types of
sample are usually required:
a) sample for determination of total moisture;
b) sample for general analysis;
c) sample for physical tests.
Additional samples may be required for testing for special properties. Where samples are to be used for the
determination of other special properties, it will be necessary to set aside part of the sample, either prior to
preparation or after an appropriate stage in the preparation.
A schematic diagram showing the alternative ways of constituting and preparing the various types of test sample is
showninFigure 6.
7.2 Preparation of samples for determining total moisture
7.2.1 General
A major problem with the preparation of test samples for the determination of moisture content is the risk of bias due
to inadvertent loss of moisture. The amount of this loss is dependent on such factors as the effectiveness of the
sealing of the sample containers, the level of moisture content of the sample, the ambient conditions, the type of
coke, and the reduction and division procedures used.
Precautions shall be taken to minimize loss of moisture due to the use of unsuitable containers and to evaporation
during handling.
All samples for moisture determination shall be kept in sealed containers in a cool place, under cover, before and
during preparation as well as during any interval between steps of sample preparation.
If excessive standing time causes bias, increase the number of sub-lots units to overcome these problems (see
ISO 13909-5).
Care shall also be taken to minimize loss of moisture during division by carrying out the operation as quickly as
possible and using mechanically operated dividers with limited ingress of air.
7.2.2 Procedure
The procedure for preparing the 1kg sample for the determination of total moisture is shown schematically in
Figure 6.
In the case of small coke, having a top size of 20 mm or less, only the process of sample division described in 7.2.5
is required.
It is essential that precautions be taken to prevent loss of moisture during these operations which shall be carried out
in an enclosed space, roofed over and made free from draughts. The total time taken to crush and divide the coke
shall not exceed 15 min and it is therefore essential to crush the coke quickly and mechanically. In addition, the mass
of sample crushed shall not exceed 70 kg.
Samples which are visibly wet and those for which the moisture is expected to exceed 15 % are partially dried before
reduction and division (see 7.2.3).
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ISO 13909-6:2001(E)
Figure 6 — Constitution and preparation of samples
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...
SLOVENSKI STANDARD
SIST ISO 13909-6:2002
01-junij-2002
1DGRPHãþD
SIST ISO 9411-1:1998
SIST ISO 9411-2:1998
ýUQLSUHPRJLQNRNV0HKDQVNRY]RUþHQMHGHO .RNV3ULSUDYDSUHVNXVQLK
Y]RUFHY
Hard coal and coke -- Mechanical sampling -- Part 6: Coke -- Preparation of test samples
Houille et coke -- Échantillonnage mécanique -- Partie 6: Coke -- Préparation des
échantillons pour essai
Ta slovenski standard je istoveten z: ISO 13909-6:2001
ICS:
73.040 Premogi Coals
SIST ISO 13909-6:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 13909-6:2002
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SIST ISO 13909-6:2002
INTERNATIONAL ISO
STANDARD 13909-6
First edition
2001-12-15
Hard coal and coke — Mechanical
sampling —
Part 6:
Coke — Preparation of test samples
Houille et coke — Échantillonnage mécanique —
Partie 6: Coke — Préparation des échantillons pour essai
Reference number
ISO 13909-6:2001(E)
© ISO 2001
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SIST ISO 13909-6:2002
ISO 13909-6:2001(E)
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SIST ISO 13909-6:2002
ISO 13909-6:2001(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precision of sample preparation . 2
5 Constitution of a sample . 2
6 Division . 4
7 Preparation of samples for specific tests . 16
8 Design of equipment for preparation . 20
Bibliography. 24
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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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 13909 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 13909-6 was prepared by Technical Committee ISO/TC 27, Solid mineral fuels,
Subcommittee SC 4, Sampling.
ISO 13909 cancels and replaces ISO 9411-1:1994, Solid mineral fuels — Mechanical sampling from moving streams
— Part 1: Coal and ISO 9411-2:1993, Solid mineral fuels — Mechanical sampling from moving streams — Part 2:
Coke, of which it constitutes a technical revision. It also supersedes the methods of mechanical sampling of coal and
coke given in ISO 1988:1975, Hard coal — Sampling and ISO 2309:1980, Coke — Sampling.
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
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Introduction
The objective of sample preparation is to prepare one or more test samples from the primary increments for
subsequent analysis. The requisite mass and particle size of the test sample depend on the test to be carried out.
The process of sample preparation may involve constitution of samples, reduction, division, mixing and drying or all
or a combination of these.
Primary increments may be prepared individually as test samples or combined to constitute samples either as taken
or after having been prepared by reduction and/or division. Samples may either be prepared individually as test
samples or combined on a weighted basis to constitute a further sample.
On-line sampling and sample-preparation systems can be usefully implemented when dealing with a coke or cokes
which are known to be free from handling problems, but only when this will not result in loss of moisture,
contamination by the sampling equipment or size degradation of physical samples.
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INTERNATIONAL STANDARD ISO 13909-6:2001(E)
Hard coal and coke — Mechanical sampling —
Part 6:
Coke — Preparation of test samples
1 Scope
This part of ISO 13909 describes the preparation of samples of coke from the combination of primary increments to
the preparation of samples for specific tests.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 13909. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 13909 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 579:1999, Coke — Determination of total moisture.
ISO 687:1974, Coke — Determination of moisture in the analysis sample.
ISO 13909-1:2001, Hard coal and coke — Mechanical sampling — Part 1: General introduction.
ISO 13909-5:2001, Hard coal and coke — Mechanical sampling — Part 5: Coke — Sampling from moving streams.
ISO 13909-7:2001, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of
sampling, sample preparation and testing.
ISO 13909-8:2001, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias.
3 Terms and definitions
For the purposes of this part of ISO 13909, the terms and definitions given in ISO 13909-1 apply.
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4 Precision of sample preparation
From the equations given in ISO 13909-7, the estimated absolute value of the precision of the result obtained for the
lot at the 95 % confidence level,P , for continuous sampling is given by:
L
s
V
I
+V
PT
n
P = 2
(1)
L
m
where
V is the primary increment variance;
I
n is the number of increments in the sample;
V is the variance of preparation and testing for both off-line and on-line systems;
PT
m is the number of sub-lots.
The procedures given in this part of ISO 13909 are designed to achieve levels ofV of 0,05 or less for moisture
PT
tests. Better levels may be expected for other chemical characteristics.
For some preparation schemes, however, practical restrictions may prevent the preparation and testing variance
being as low as this. Under these circumstances, the user will have to decide whether to achieve the desired overall
precision by improving the preparation scheme or by dividing the lot into a greater number of sub-lots.
The errors occurring in the various stages of preparation and analysis, expressed in terms of variance, may be
checked by the methods given in ISO 13909-7.
5 Constitution of a sample
5.1 Introduction
Examples of the constitution of samples are shown in Figure 1.
Primary increments shall be taken in accordance with the procedures specified in ISO 13909-5.
Individual increments are usually combined to form a sample. A single sample may be constituted by combination of
increments taken from a complete sub-lot or by combining increments taken from individual parts of a sub-lot. Under
some circumstances, e.g. size analysis or bias testing, the sample consists of a single increment which is prepared
and tested.
Samples may also be prepared by the combination of other samples.
The procedures for increment combination (5.2) may vary according to whether the primary increments were taken
using a time-basis (5.2.1) or a mass-basis (5.2.2) sampling scheme.
5.2 Combination of increments
5.2.1 Time-basis sampling
The mass of the primary increments shall be proportional to the flow rate at the time of sampling. The primary
increments may be combined into a sample, either directly as taken or after having been prepared individually to an
appropriate stage by fixed-ratio division (see clause 6).
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a) Example 1
b) Example 2
Figure 1 — Examples of the constitution of samples
5.2.2 Mass-basis sampling
If the primary increments are of almost uniform mass (see note), they may be combined into a sample, either directly
as taken or after having been prepared individually to an appropriate stage by fixed-ratio division (see clause 6).
NOTE Almost uniform mass has been achieved if the coefficient of variation of the increment masses is less than 20 % and there
is no significant correlation between the flow rate at the time of taking the increment and the mass of the increment (see
ISO 13909-5).
If the primary increments are not of almost uniform mass, they may only be combined into samples after having been
divided individually by fixed-mass division (see clause 6).
5.3 Combination of samples
When combining samples, the mass of the individual samples shall be directly proportional to the mass of the coke
from which they were taken in order to obtain a weighted mean of the quality characteristic for the sub-lot. Prior to
combination, division shall be by fixed-ratio (see clause 6).
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6 Division
6.1 General
Since the cutter aperture will normally be at least three times the nominal top size, this will result in a very large
increment mass in many cases. The handling and preparation of such large increments would be either manpower or
equipment intensive. Division prior to further treatment may be necessary to provide a manageable sample mass.
Sample division can be
— on-line mechanically, or
— off-line mechanically or manually.
Whenever possible, mechanical methods are preferred to manual methods to minimize human error. Examples of
dividers are shown in Figure 2.
Mechanical dividers are designed to extract a part of the coke in a number of cuts of relatively small mass. When the
smallest mass of the divided sample that can be obtained in one pass through the divider is greater than that
required, further passes through the same divider or subsequent passes through further dividers may be necessary.
Manual division is normally applied when mechanical methods would result in loss of integrity, e.g. loss of moisture
or size degradation. Manual division of coke is also applied when the nominal top size of the coke is such as to make
the use of a mechanical divider impracticable. Manual methods may themselves result in bias, particularly if the mass
of coke to be divided is large.
6.2 Mechanical methods
6.2.1 General
Mechanical sample division may be carried out on an individual increment or a sample. Where samples are for
moisture or general analysis, it is permissible to install on-line crushing to a nominal top size of 16 mm followed by
sample division. Division shall be either by fixed-mass division or by fixed-ratio division subject to the conditions set
out in 6.2.2 and 6.2.3.
When crushing on-line, the risk of moisture loss should be considered, particularly if the coke is hot.
The uses to which the sample is to be put, the numbers, masses and size distribution of the test samples required
shall also be taken into account when deciding on the minimum mass of the sample.
When a coke is regularly sampled under the same conditions, the precision obtained for all the required quality
parameters shall be checked using the procedures of ISO 13909-7 and the minimum mass adjusted accordingly. The
masses shall not be reduced, however, below the minimum requirements laid down in the relevant analysis
standards.
NOTE The procedures described for fixed-ratio division are the simplest to implement. Other procedures may be used, however,
provided that the mass of the divided sample is proportional to the mass of the feed, e.g. the number of cuts could be kept
constant by making the feed rate of each division proportional to the mass of coke to be divided.
6.2.2 Mass of cut
The cuts shall be of uniform mass throughout the division of an increment. In order to achieve this, the flow of coke
to the divider shall be uniform and the cutting aperture and speed of the cutter shall be constant. The method of
feeding the divider shall be designed to minimize any segregation caused by the divider.
The cutting aperture shall be at least three times the nominal top size of the coke to be divided.
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Key
1Feed
2 Rotating cone
3 Adjustable slot
4 Divided sample
5 Reject
A stream of coke is allowed to fall onto a rotating cone; the adjustable slot with lips in the cone allows the stream to fall directly
onto the sample receiver for part of each revolution.
a) Rotating cone type
Figure 2 — Examples of dividers
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Key
1Feed
2 Divided sample in rotating receivers
The coke stream flows to the hopper and this flow is intercepted by the top edge of a number of sector-shaped containers
dividing the flow into equal parts. Either the hopper or the containers may rotate. The machine can be controlled for the following
operations:
a) for dividing;
b) for collecting duplicates;
c) for collecting replicates.
b) Container type
Figure 2 — Examples of dividers (continued)
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Key
1Feed
2 Reject
3 Divided sample
A chain mechanism as shown is equipped with buckets spread at equal pitch. The buckets travel in a single direction or change
direction at pre-set time periods. The bucket intercepts the free-falling coke stream to extract cuts which discharge to sample as
the bucket inverts.
c) Chain-bucket type
Figure 2 — Examples of dividers (continued)
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Key
1 Slotted belt
2Feed
3 Inclined chute
4 Divided sample
5Reject
An endless belt having slots spaced at equal pitch with lips that act as cutting edges passes below a feed chute. The coke
stream is fed to the chute and, as each slot passes through the stream, a cut is taken. The stream which falls onto the plain part
of the belt is carried to rejects.
d) Slotted-belt type
Figure 2 — Examples of dividers (continued)
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Key
Key 1Feed
1Feed 2 Rotating hopper
2 Reject 3Reject
3 Divided sample 4 Divided sample
A hollow shaft which is attached to one or more cutters rotates A rotating hopper receives a coke flow and discharges through
withinahousingas shown. Each cutter isdesignedtotake a spout. Stationary cutters are positioned in the path of the
cuts from the coke stream and to discharge via the hollow spout outlet, cuts are taken as each cutter is passed. One or
shaft. more cutters may be fitted.
e) Rotating chute type f) Rotating hopper and spout
Figure 2 — Examples of dividers (continued)
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Key
1Feed
2 Divided sample
3Reject
The cutter-chute traverses the full coke stream and diverts a portion from the stream. When the coke stream is not being cut by
the chute, it is deflected by the angle plate to reject.
g) Cutter-chute type
Figure 2 — Examples of dividers (continued)
6.2.3 Interval between cuts
In order to minimize bias, the first cut for each mass to be divided shall be made at random within the first interval.
For secondary and tertiary dividers, the cycle time shall not be evenly divisible into the cycle time of the cutter which
precedes it.
For fixed-mass division, the interval between taking cuts shall be varied proportionally to the mass of coke to be
divided so that divided samples having almost uniform mass are obtained. The mass shall be fixed for the whole sub-
lot.
For fixed-ratio division, the interval between taking cuts shall be constant, irrespective of the variations of masses of
coke to be divided so that divided-sample masses are proportional to the mass of the feed. The ratio shall be fixed
for the whole sub-lot.
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6.2.4 Division of individual increments
6.2.4.1 Number of cuts
The number of cuts for dividing an increment shall be determined as follows.
a) For fixed-mass division, the minimum number of cuts at any stage shall be six. An equal number of cuts shall be
taken from each increment in the sub-lot.
b) For fixed-ratio division, the minimum number of cuts from an increment of mean mass at any stage shall be six.
For subsequent division of divided increments, a minimum of one cut shall be taken from each cut from the preceding
division.
6.2.4.2 Minimum mass of divided increment
The minimum mass of the divided increment shall be such that the combined masses of all the divided increments in
the sub-lot shall, at each stage, be greater than the mass given in Table 1, corresponding to the nominal top size. If
the increment masses are too low to satisfy this requirement, the divided increment shall be crushed prior to further
division.
For moisture samples, there is a restriction of 70 kg on the maximum mass of sample to be crushed at one time
during off-line preparation.
NOTE The masses given in Table 1 are for guidance on the minimum mass for unknown or heterogeneous cokes. Whilst they
can usually be reduced for the moisture sample, they may be inadequate for the determination of, for example, oversize to 1%
division precision, particularly on very large cokes.
Table 1 — Minimum mass of sample after division
Nominal top size Minimum mass
mm kg
> 125 2000
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
41
6.2.5 Division of samples
6.2.5.1 Number of cuts
The sample shall be divided by taking a minimum of 60 cuts.
NOTE If, during preparation, the sample is thoroughly mixed and it can be established that the required precision can be
achieved, the number may be reduced to 20.
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6.2.5.2 Minimum mass of divided sample
The mass of the divided sample shall not be less than the minimum mass in Table 1.
6.3 Manual methods
6.3.1 General
For the manual division methods given in 6.3.2 to 6.3.4, the mass of the divided sample shall not be less than the
minimum mass in Table 1, subject to there being sufficient mass for all test portions required.
6.3.2 Riffle method
A riffle (see Figure 3) is a sample divider that will, in a single pass of a sample, divide it into halves, one of which is
retained and the other normally rejected. The device is normally portable and, for sample division, is usually fed
manually, the coke being evenly distributed along its length. Adjacent slots feed opposite receivers.
The slot width shall be at least 2,5 times and, preferably, not more than 3 times the nominal top size of the coke. Each
half of the riffle shall have the same number of slots, which shall be at least eight and preferably more. All the
�
surfaces on which the coke might rest shall have a slope of at least 60 to the horizontal.
The coke shall be allowed to fall steadily into the riffle, ensuring that it is evenly distributed over all the slots. The coke
shall be allowed to fall freely, i.e. not towards one side of the riffle, and the rate of feed shall be controlled such that
the slots are never choked. Closed riffles are preferred.
Care shall be taken to minimize loss of dust and moisture. To this end, the receiver shall fit closely against the body
of the riffle and, for dry cokes and moisture samples, closed-type riffles shall be used.
When a stage of sample division requires two or more steps or passes, the sample retained at each step shall be
taken alternately from each side of the riffle.
6.3.3 Flattened-heap method
The procedure, which is illustrated in Figure 4, is as follows.
The sample is mixed thoroughly and spread to form a rectangle of uniform thickness of 40 mm to 50 mm on a mixing
plate, which is a smooth, non-absorbent and non-contaminating surface.
Avoid moisture loss from wet cokes which can result from over-mixing.
A matrix is marked on the spread sample to give a minimum of 4� 5 equal parts. An increment is taken, at random,
from each of the parts by inserting a scoop with a bump plate (see the last paragraph of this subclause) to the bottom
of the matrix layer. The increments shall be combined into a divided sample. It is essential that these operations be
performed quickly if loss of moisture is to be prevented.
The increments shall be of uniform mass. The minimum mass required for each nominal top size of coke is the mass
of the divided sample (see Table 1) divided by the number of parts of the flattened heap.
The scoop shall be flat bottomed and the width of the entry shall be at least three times the nominal top size of the
coke; the side walls shall be higher than the height of the heap and the depth shall be sufficient to allow the required
mass of increment to be taken.
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Key
1 Even number of slots
a) Open type b) Closed type
Figure 3 — Examples of riffles
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Take the scoop sample with the aid of a bump plate which is inserted vertically through the flattened heap until it is in
contact with the bottom of the sample layer. The scoop is then inserted to the bottom of the spread coke and moved
horizontally until its open end comes into contact with the vertical bump plate. The scoop and bump plate are lifted
together to ensure that all particles are collected off the top of the mixing plate and that none fall off during lifting.
a) Spread the crushed sample into a rectangle with a
maximum thickness of 40 mm to 50 mm.
b) Arrange into 20 equal parts, e.g. into five equal parts
lengthwise and four equal parts breadthwise.
c) Take a scoopful of samples at random from each of the
20 parts by inserting the scoop to the bottom of the sample
layer. Combine the 20 scoopfuls into a divided sample.
d) Detail of taking an increment by using the bump plate
shown in c).
Figure 4 — Flattened-heap method
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6.3.4 Strip-mixing and splitting method
Theprocedure,whichisillustratedinFigure5,is as follows.
Key
1Increment
2 Sampling frame
3 End plates (“book-ends”)
Figure 5 — Strip-mixing and splitting method
The coke sample is formed on a mixing plate, which is a smooth, non-absorbent, non-contaminating surface, into a
strip at least 10 times as long as it is wide by distributing the coke along the length of the strip as evenly as possible,
working randomly from end to end and from both sides of the strip. End plates shall be used to ensure that size
segregation only occurs laterally.
Increments shall be taken as a complete section across the strip. The width of each cross-section shall be not less
than 2,5 times the nominal top size of the coke.
NOTE 1 Special apparatus for the cutting out of increments may be constructed if desired.
Normally 20 increments are required. Fewer increments may be taken, subject to a minimum of 10, where the same
quality coke is regularly prepared under the same conditions and it has first been established that the required
precision can be obtained (see ISO 13909-7).
NOTE 2 Because of the efficient longitudinal mixing achieved in the formation of a strip, the same precision as that obtainable
with the flattened-heap method can be achieved with fewer increments.
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7 Preparation of samples for specific tests
7.1 Types of test sample
The methods of preparation depend on the purpose for which the original sample was collected. Three types of
sample are usually required:
a) sample for determination of total moisture;
b) sample for general analysis;
c) sample for physical tests.
Additional samples may be required for testing for special properties. Where samples are to be used for the
determination of other special properties, it will be necessary to set aside part of the sample, either prior to
preparation or after an appropriate stage in the preparation.
A schematic diagram showing the alternative ways of constituting and preparing the various types of test sample is
showninFigure 6.
7.2 Preparation of samples for determining total moisture
7.2.1 General
A major problem with the preparation of test samples for the determination of moisture content is the risk of bias due
to inadvertent loss of moisture. The amount of this loss is dependent on such factors as the effectiveness of the
sealing of the sample containers, the level of moisture content of the sample, the ambient conditions, the type of
coke, and the reduction and division procedures used.
Precautions shall be taken to minimize loss of moisture due to the use of unsuitable containers and to evaporation
during handling.
All samples for moisture determination shall be kept in sealed containers in a cool place, under cover, before and
during preparation as well as during any interval between steps of sample preparation.
If excessive standing time causes
...
NORME ISO
INTERNATIONALE 13909-6
Première édition
2001-12-15
Houille et coke — Échantillonnage
mécanique —
Partie 6:
Coke — Préparation des échantillons
pour essai
Hard coal and coke — Mechanical sampling —
Part 6: Coke — Preparation of test samples
Numéro de référence
ISO 13909-6:2001(F)
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ISO 13909-6:2001(F)
Sommaire Page
Avant-propos. iv
Introduction . v
1 Domaine d'application. 1
2 Références normatives . 1
3 Termes et définitions. 1
4 Fidélité de la préparation de l'échantillon . 2
5 Constitution d'un échantillon . 2
6 Division . 4
7 Préparation des échantillons pour des essais spécifiques . 16
8 Conception de l'équipement pour la préparation. 20
Bibliographie . 25
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Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 3.
Les projets de Normes internationales adoptés par les comités techniques sont soumis aux comités membres
pour vote. Leur publication comme Normes internationales requiert l'approbation de 75 % au moins des
comités membres votants.
L'attention est appelée sur le fait que certains des éléments de la présente partie de l'ISO 13909 peuvent faire
l'objet de droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour
responsable de ne pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO 13909-6 a été élaborée par le comité technique ISO/TC 27, Combustibles minéraux solides,
sous-comité SC 4, Échantillonnage.
L'ISO 13909 annule et remplace l'ISO 9411-1:1994, Combustibles minéraux solides — Échantillonnage
mécanique sur minéraux en mouvement — Partie 1: Charbon et l'ISO 9411-2:1993, Combustibles minéraux
solides — Échantillonnage mécanique sur minéraux en mouvement — Partie 2: Coke, dont elle constitue une
révision technique. Elle remplace également les méthodes d'échantillonnage mécanique du charbon et du
coke données dans l'ISO 1988:1975, Charbons et lignites durs — Échantillonnage et l'ISO 2309:1980,
Coke — Échantillonnage.
L'ISO 13909 comprend les parties suivantes, présentées sous le titre général Houille et coke —
Échantillonnage mécanique:
Partie 1: Introduction générale
Partie 2: Charbon — Échantillonnage en continu
Partie 3: Charbon — Échantillonnage sur lots statiques
Partie 4: Charbon — Préparation des échantillons pour essai
Partie 5: Coke — Échantillonnage en continu
Partie 6: Coke — Préparation des échantillons pour essai
Partie 7: Méthodes pour la détermination de la fidélité de l'échantillonnage, de la préparation de
l'échantillon et de l'essai
Partie 8: Méthodes de détection du biais
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ISO 13909-6:2001(F)
Introduction
L'objectif de la préparation des échantillons est de préparer un ou plusieurs échantillons pour essai à partir
des prélèvements primaires pour une analyse ultérieure. La masse requise et la granulométrie de l'échantillon
pour essai dépendent de l'essai à effectuer.
Le processus de préparation des échantillons peut comprendre l'ensemble des opérations suivantes ou
certaines d'entre-elles combinées: constitution, réduction, division, mélange et séchage des échantillons.
Les prélèvements primaires peuvent être préparés individuellement en tant qu'échantillons pour essai ou en
combinaison pour constituer des échantillons soit tels quels, soit après une préparation par réduction et/ou
division. Les échantillons peuvent être préparés soit individuellement en tant qu'échantillons pour essai, soit
en combinaison sur une base pondérée afin de constituer un autre échantillon.
Il peut s'avérer utile de mettre en oeuvre des systèmes d'échantillonnage et de préparation des échantillons
en ligne lorsqu'il s'agit d'un coke, ou de cokes, connu(s) pour ne poser aucun problème de manutention, pour
autant que cela n'entraîne pas de perte d'humidité, de contamination par le matériel d'échantillonnage ou de
dégradation dimensionnelle des échantillons physiques.
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NORME INTERNATIONALE ISO 13909-6:2001(F)
Houille et coke — Échantillonnage mécanique —
Partie 6:
Coke — Préparation des échantillons pour essai
1 Domaine d'application
La présente partie de l'ISO 13909 décrit la préparation des échantillons de coke, de la combinaison de
prélèvements primaires à la préparation d'échantillons pour des essais spécifiques.
2 Références normatives
Les documents normatifs suivants contiennent des dispositions qui, par suite de la référence qui y est faite,
constituent des dispositions valables pour la présente partie de l'ISO 13909. Pour les références datées, les
amendements ultérieurs ou les révisions de ces publications ne s'appliquent pas. Toutefois, les parties
prenantes aux accords fondés sur la présente partie de l'ISO 13909 sont invitées à rechercher la possibilité
d'appliquer les éditions les plus récentes des documents normatifs indiqués ci-après. Pour les références non
datées, la dernière édition du document normatif en référence s'applique. Les membres de l'ISO et de la CEI
possèdent le registre des Normes internationales en vigueur.
ISO 579:1999, Coke — Détermination de l'humidité totale
ISO 687:1974, Coke — Détermination de l'humidité de l'échantillon pour analyse
ISO 13909-1:2001, Houille et coke — Échantillonnage mécanique — Partie 1: Introduction générale
ISO 13909-5:2001, Houille et coke — Échantillonnage mécanique — Partie 5: Coke — Échantillonnage en
continu
ISO 13909-7:2001, Houille et coke — Échantillonnage mécanique — Partie 7: Méthodes pour la détermination
de la fidélité de l'échantillonnage, de la préparation de l'échantillon et de l'essai
ISO 13909-8:2001, Houille et coke — Échantillonnage mécanique — Partie 8: Méthodes de détection du biais
3 Termes et définitions
Pour les besoins de la présente partie de l'ISO 13909, les termes et définitions donnés dans l'ISO 13909-1
sont applicables.
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ISO 13909-6:2001(F)
4 Fidélité de la préparation de l'échantillon
À partir des équations données dans l'ISO 13909-7, la valeur absolue estimée de la fidélité du résultat obtenu
pour le lot à un niveau de confiance de 95 %, P , pour l'échantillonnage continu est donné par l'équation
L
suivante:
V
I
+V
PT
n
P = 2 (1)
L
m
où
V est la variance primaire du prélèvement;
I
n est le nombre de prélèvements par sous-lot;
V est la variance de la préparation et des essais à la fois pour les systèmes en ligne et hors ligne;
PT
m est le nombre de sous-lots.
Les modes opératoires expliqués dans la présente partie de l'ISO 13909 ont pour objectif d'arriver à des
niveaux de V équivalant à 0,05 ou moins pour les essais d'humidité. Si des diviseurs mécaniques sont
PT
utilisés, de meilleurs niveaux peuvent être atteints.
Toutefois, dans certains programmes de préparation, la variance de la préparation et des essais peut ne pas
être aussi faible en raison de restrictions d'ordre pratique. Dans ce cas, l'utilisateur devra décider s'il veut
obtenir la fidélité globale souhaitée en améliorant le programme de préparation ou en divisant le lot en un
nombre supérieur de sous-lots.
Les erreurs se produisant aux diverses étapes de la préparation et de l'analyse, exprimées en termes de
variance, peuvent être vérifiées à l'aide de la méthode décrite dans l'ISO 13909-7.
5 Constitution d'un échantillon
5.1 Introduction
Des exemples de constitution des échantillons sont représentés à la Figure 1.
Les prélèvements primaires doivent être recueillis conformément aux modes opératoires spécifiés dans
l'ISO 13909-5.
Les prélèvements individuels sont généralement combinés pour former un échantillon. Un simple échantillon
peut être constitué de la combinaison de prélèvements pris sur l'intégralité d'un sous-lot ou en combinant des
prélèvements pris sur des parties individuelles d'un sous-lot. Dans certains cas comme l'analyse
granulométrique ou la détection du biais, l'échantillon est constitué d'un seul prélèvement qui est préparé et
soumis à l'essai. Des échantillons peuvent également être préparés grâce à la combinaison d'autres
échantillons.
Des échantillons peuvent également être préparés en combinant d'autres échantillons.
Les modes opératoires relatifs à la combinaison de prélèvements (5.2) peuvent varier selon que les
prélèvements primaires ont été effectués à l'aide d'un programme d'échantillonnage basé sur le temps (5.2.1)
ou basé sur la masse (5.2.2).
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ISO 13909-6:2001(F)
5.2 Combinaison de prélèvements
5.2.1 Échantillonnage basé sur le temps
La masse des prélèvements primaires doit être proportionnelle au débit au moment de l'échantillonnage. Les
prélèvements primaires peuvent être combinés pour former un échantillon, soit pris directement tels quels,
soit après les avoir préparés individuellement à une étape appropriée par une division à rapport constant
(voir Article 6).
a) Exemple 1
b) Exemple 2
Figure 1 — Exemples de constitution des échantillons
5.2.2 Échantillonnage basé sur la masse
Si les prélèvements primaires ont une masse quasi uniforme (voir la Note), ils peuvent être combinés pour
former un échantillon, soit pris directement tels quels, soit après les avoir préparés individuellement à une
étape appropriée par une division à taux fixe (voir Article 6).
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ISO 13909-6:2001(F)
NOTE Une masse quasi uniforme est obtenue si le coefficient de variation de la masse des prélèvements est
inférieur à 20 % et s'il n'y a pas de corrélation importante entre le débit au moment du prélèvement et la masse du
prélèvement (voir l'ISO 13909-5).
Si les prélèvements primaires n'ont pas une masse quasi uniforme, ils ne peuvent être combinés pour former
des échantillons qu'après avoir été divisés individuellement par une division à masse constante (voir Article 6).
5.3 Combinaison des échantillons
Lors de la combinaison des échantillons, la masse des échantillons individuels doit être proportionnelle à la
masse du coke dans lequel ils ont été prélevés afin d'obtenir une moyenne pondérée de la caractéristique de
qualité pour le sous-lot. Avant la combinaison, une division à rapport constant doit être effectuée
(voir Article 6).
6 Division
6.1 Généralités
Étant donné que la largeur de l'ouverture du dispositif de prélèvement sera normalement égale à trois fois la
dimension maximale nominale, la masse de prélèvement sera souvent très importante. La manutention et la
préparation de prélèvements de ce type exigeraient un important déploiement de personnel et d'équipements.
Une division préalable à tout autre traitement peut s'avérer nécessaire pour obtenir une masse d'échantillon
praticable.
Une division peut être effectuée
mécaniquement en ligne, ou
mécaniquement hors ligne ou manuellement.
Chaque fois que c'est possible, il y a lieu de privilégier les méthodes mécaniques aux méthodes manuelles
afin de minimiser toute erreur humaine. Des exemples de diviseurs sont illustrés à la Figure 2.
Les diviseurs mécaniques sont conçus pour extraire une ou plusieurs parties du coke dans un certain nombre
de coupes de masse relativement petite. Lorsque la plus petite masse de l'échantillon divisé pouvant être
obtenue par un seul passage dans l'appareil est plus importante que celle requise, d'autres passages dans le
même appareil ou dans d'autres appareils peuvent s'avérer nécessaires.
Une division manuelle est généralement opérée lorsque les méthodes mécaniques risquent d'entraîner une
perte d'intégrité (par exemple: perte d'humidité ou dégradation dimensionnelle). Une division manuelle du
coke est également opérée lorsque la dimension maximale nominale du coke est telle que l'utilisation d'un
diviseur mécanique serait peu pratique. Les méthodes manuelles peuvent elles-mêmes induire un biais, en
particulier si la masse du coke à diviser est importante.
6.2 Méthodes mécaniques
6.2.1 Généralités
La division mécanique peut être effectuée sur un prélèvement individuel ou un échantillon. Sur des
échantillons destinés à un essai pour humidité ou analyse générale, il est permis de prévoir un broyage en
ligne pour obtenir une dimension maximale nominale de 16 mm, et de procéder ensuite à une division de
l'échantillon. La division doit être soit une division à masse constante soit une division à rapport constant,
sous réserve des conditions définies en 6.2.2 et 6.2.3.
En cas de broyage en ligne, il convient de tenir compte du risque de perte d'humidité, en particulier si le coke
est chaud.
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ISO 13909-6:2001(F)
Les utilisations prévues de l'échantillon, les nombres, les masses et la distribution granulométrique des
échantillons pour essai doivent également être pris en considération lorsqu'il s'agit de décider de la masse
minimale de l'échantillon.
Lorsqu'un coke est régulièrement échantillonné dans des conditions identiques, la fidélité obtenue pour tous
les échantillons pour essai requis doit également être contrôlée à l'aide des modes opératoires de
l'ISO 13909-7. La masse minimale doit être ajustée en conséquence. Toutefois, les masses ne doivent pas
être inférieures aux exigences minimales établies dans les normes d'analyse pertinentes.
NOTE Les modes opératoires décrits pour la division à rapport constant sont les plus simples à mettre en œuvre.
D'autres modes opératoires peuvent être utilisés pour autant que la masse de l'échantillon divisé soit proportionnelle à la
masse d'entrée. Par exemple le nombre de coupes peut être maintenu constant en utilisant, pour chaque division, un débit
d'entrée proportionnel à la masse du coke à diviser.
6.2.2 Masse de la coupe
Les coupes doivent présenter une masse uniforme tout au long de la division d'un prélèvement. Pour ce faire,
le débit de coke au niveau du diviseur doit être uniforme et l'ouverture de coupe doit être constante. La
méthode d'alimentation du diviseur doit être étudiée de manière à minimiser la ségrégation causée par le
diviseur.
L'ouverture de coupe doit au moins être égale à trois fois la dimension maximale nominale du coke à diviser.
Légende
1 alimentation
2 cône rotatif
3 fente réglable
4 échantillon divisé
5 rejets
Un écoulement de coke tombe sur un cône rotatif; une fente réglable avec rebords ménagée dans le cône permet à
l'écoulement de tomber directement sur le collecteur d'échantillons pendant une partie de chaque révolution.
a) Diviseur à cône rotatif
Figure 2 — Exemples de diviseurs
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ISO 13909-6:2001(F)
Légende
1 alimentation
2 échantillon divisé dans des collecteurs rotatifs
Le coke est déversé dans la trémie puis l'écoulement de coke est intercepté par l'arête supérieure d'un certain nombre de
récipients disposés en secteurs, permettant de diviser l'écoulement en portions égales. Soit la trémie ou soit les récipients
peuvent tourner. La machine peut être contrôlée pour les opérations suivantes:
1) division;
2) collecte des échantillons dédoublés;
3) collecte des subdivisés.
b) Diviseur à récipients
Figure 2 — Exemples de diviseurs (suite)
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ISO 13909-6:2001(F)
Légende
1 alimentation
2 rejet
3 échantillon divisé
Comme illustré, un mécanisme à chaîne est muni de godets répartis à égale distance. Les godets se déplacent dans un
seul sens ou le sens de déplacement change à intervalles de temps prédéterminés. Le godet intercepte l'écoulement du
coke tombant en chute libre afin d'en extraire des coupes qui sont recueillies comme échantillons lorsque le godet se
renverse.
c) Diviseur à chaîne à godets
Figure 2 — Exemples de diviseurs (suite)
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ISO 13909-6:2001(F)
Légende
1 bande fendue
2 alimentation
3 goulotte inclinée
4 échantillon divisé
5 rejet
Une bande sans fin comportant des fentes équidistantes dont les lèvres servent de dispositifs de prélèvement défile sous
une goulotte d'alimentation. L'écoulement du coke s'effectue dans la goulotte et, une coupe est prélevée chaque fois
qu'une fente passe sous l'écoulement. La portion de l'écoulement qui tombe sur la partie pleine de la bande est dirigée
vers le rejet.
d) Diviseur à bande avec fentes
Figure 2 — Exemples de diviseurs (suite)
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ISO 13909-6:2001(F)
Légende Légende
1 alimentation 1 alimentation
2 rejet 2 trémie rotative
3 échantillon divisé 3 rejets
4 échantillon divisé
Un arbre creux, relié à un ou plusieurs dispositifs de
prélèvement, tourne dans une enceinte, comme illustré.
Une trémie rotative reçoit un écoulement de coke et le
Chaque dispositif de prélèvement est conçu pour
décharge dans une goulotte. Des dispositifs de
effectuer des prélèvements sur l'écoulement de coke et
prélèvement fixes sont placés sur le trajet de l'orifice de
pour les décharger par l'intermédiaire de l'axe creux.
sortie de la goulotte. Les coupes sont prélevées à
chaque passage au-dessus d'un dispositif de coupe. Le
diviseur peut être muni d'un ou de plusieurs dispositifs
de coupe.
e) Diviseur à goulotte rotative f) Diviseur à trémie et goulotte rotatives
Figure 2 — Exemples de diviseurs (suite)
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ISO 13909-6:2001(F)
Légende
1 alimentation
2 rejets
3 échantillon divisé
Une goulotte de prélèvement traverse entièrement l'écoulement de coke et en dévie une portion. L'écoulement de coke
qui n'est pas prélevé par la goulotte est dévié par la plaque inclinée vers le rejet.
g) Diviseur à goulotte de prélèvement
Figure 2 — Exemples de diviseurs (suite)
6.2.3 Intervalle entre les fractions granulométriques
Afin de minimiser le biais, la première coupe pour chaque masse à diviser doit être effectuée de manière
aléatoire dans le premier intervalle. En ce qui concerne les dispositifs de coupe secondaires et tertiaires, la
durée du cycle opératoire ne doit pas être divisible par la durée du cycle opératoire d'un dispositif de
prélèvement situé en amont.
Pour une division à masse constante, l'intervalle entre deux coupes doit être déterminé en fonction de la
masse de coke à diviser, de manière à ce que les échantillons divisés présentent une masse quasiment
uniforme. La masse doit être constante pour l'intégralité du sous-lot.
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ISO 13909-6:2001(F)
Pour une division à rapport constant, l'intervalle entre deux coupes doit être constant, quelles que soient les
variations des masses de coke à diviser, de manière que la masse des échantillons divisés soit
proportionnelle à la masse d'alimentation. Le rapport doit être constant pour l'intégralité du sous-lot.
6.2.4 Division de prélèvements individuels
6.2.4.1 Nombre de coupes
Le nombre de coupes pour la division d'un prélèvement doit être déterminé comme suit.
a) Pour une division à masse constante, le nombre minimal de coupes à n'importe quelle étape doit être de
six. Un nombre égal de coupes doit être pris sur chaque prélèvement dans le sous-lot.
b) Pour une division à rapport constant, le nombre minimal de coupes sur un prélèvement de masse
moyenne doit être de six.
Pour une division ultérieure de prélèvements divisés, une coupe au minimum doit être prélevée sur chaque
coupe résultant de la division précédente.
6.2.4.2 Masse minimale d'un prélèvement élémentaire divisé
La masse minimale d'un prélèvement élémentaire divisé doit être telle que les masses combinées de tous les
prélèvements divisés dans le sous-lot doivent, à chaque étape, être supérieures à la masse indiquée dans le
Tableau 1, en fonction de la dimension maximale nominale. Si la masse du prélèvement est trop faible pour
satisfaire cette exigence, le prélèvement divisé doit être concassé avant une nouvelle division.
Dans le cadre des échantillons pour humidité, une limite de 70 kg est imposée sur la masse maximale de
l'échantillon à concasser au cours de la préparation hors ligne.
NOTE Les masses spécifiées dans le Tableau 1 sont indicatives pour la masse minimale relative aux cokes inconnus
ou hétérogènes. Bien qu'elles puissent généralement être réduites pour constituer l'échantillon pour humidité, elles
peuvent s'avérer inadéquates pour la détermination, par exemple, du refus supérieur avec une fidélité de 1 % de la
division, en particulier sur des très gros cokes.
Tableau 1 — Masse minimale d'un échantillon après division
Dimension maximale nominale Masse minimale
mm 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 6
8,0 4
5,6 2
4,0 1
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ISO 13909-6:2001(F)
6.2.5 Division des échantillons
6.2.5.1 Nombre de coupes
L'échantillon doit être divisé en prenant au minimum 60 coupes.
NOTE Si, au cours de la préparation, l'échantillon est entièrement homogénéisé et s'il peut être établi que la fidélité
requise peut être atteinte, ce nombre peut être ramené à 20.
6.2.5.2 Masse minimale d'un échantillon divisé
La masse minimale de l'échantillon divisé ne doit pas être inférieure à la masse minimale indiquée dans le
Tableau 1.
6.3 Méthodes manuelles
6.3.1 Généralités
Pour les méthodes de division manuelle expliquées de 6.3.2 à 6.3.4, la masse de l'échantillon divisé ne doit
pas être inférieure à la masse minimale indiquée dans le Tableau 1, pour autant qu'il y ait une masse
suffisante pour toutes les prises d'essai requises.
6.3.2 Méthode à riffles
Un diviseur d'échantillons à riffles (voir Figure 3) est un diviseur d'échantillon qui, lors d'un seul passage d'un
échantillon, le divise en deux moitiés, la première étant conservée et la seconde généralement rejetée. Cet
appareil est habituellement portable et, dans le cas de la division d'un échantillon, est normalement alimenté
manuellement, le coke étant distribué de manière égale sur toute sa longueur. Les fentes adjacentes
alimentent les collecteurs opposés.
La largeur de la fente doit au moins être égale à 2,5 fois, et de préférence 3 fois au maximum, la dimension
maximale nominale du coke. Chaque section du riffle doit comporter le même nombre de fentes, soit huit
fentes au moins et, de préférence, davantage. Toutes les surfaces sur lesquelles le coke peut séjourner
doivent présenter une inclinaison de 60° au moins par rapport à l'horizontale.
Le coke doit tomber régulièrement dans le riffle et être distribué équitablement sur toutes les fentes. Le coke
doit tomber librement, c'est-à-dire qu'il ne doit pas tomber uniquement d'un côté du diviseur et le débit
d'alimentation doit être contrôlé de sorte que les fentes ne soient jamais obstruées. Les diviseurs à riffles de
type fermé sont privilégiés.
Il faut veiller à minimiser la perte de poussière et d'humidité. À cette fin, le collecteur doit être étroitement
ajusté au corps du riffle. En ce qui concerne les échantillons pour humidité et les cokes secs, des diviseurs
d'échantillons à riffles de type fermé doivent être utilisés.
Lorsqu'un étage de la division des échantillons nécessite deux étapes ou passages ou plus, l'échantillon
retenu à chaque étape doit être prélevé alternativement de chaque côté du diviseur.
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ISO 13909-6:2001(F)
Légende
1 nombre égal de fentes
a) Type ouvert b) Type fermé
Figure 3 — Exemples de diviseur à riffles
6.3.3 Méthode du tas aplati
Le mode opératoire, illustré à la Figure 4, est le suivant.
L'échantillon est soigneusement mélangé et étendu pour former un rectangle d'épaisseur uniforme (de 40
à 50 mm) sur une table de mélange lisse, non absorbante et non contaminante.
Éviter la déshydratation des cokes humides due à une excessive homogénéisation.
Tracer une matrice sur l'échantillon étalé de manière à obtenir au minimum 4 × 5 portions égales. Un
prélèvement élémentaire, jusqu'au fond de la couche, est effectué au hasard sur chacune des portions à l'aide
d'une pelle d'échantillonnage et d'une plaque de butée (voir dernier alinéa du présent paragraphe). Les
prélèvements doivent être combinés en un échantillon divisé. Il est essentiel que ces opérations soient
effectuées rapidement afin d'éviter toute perte d'humidité.
Les prélèvements doivent être de masse uniforme. La masse minimale requise pour chaque dimension
maximale nominale est la masse de l'échantillon divisé (voir Tableau 1) divisée par le nombre de portions du
tas aplati.
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ISO 13909-6:2001(F)
La pelle doit avoir un fond plat et la largeur de l'entrée doit être égale à au moins trois fois la dimension
maximale nominale du coke. Les parois latérales doivent être plus hautes que la hauteur du tas et la
profondeur doit être suffisante pour pouvoir prélever la masse de prélèvement requise.
Prélever l'échantillon à l'aide de la plaque de butée enfoncée verticalement dans le tas aplati jusqu'à ce
qu'elle touche le fond de la couche d'échantillon. Insérer alors la pelle jusqu'au fond de la couche de coke et
la déplacer à l'horizontale dans l'échantillon étalé jusqu'à ce que le bout de la pelle touch
...
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