ISO 7936:1992
(Main)Hard coal — Determination and presentation of float and sink characteristics — General directions for apparatus and procedures
Hard coal — Determination and presentation of float and sink characteristics — General directions for apparatus and procedures
Describes sampling, preliminary treatment, test procedure using relative density separation methods, presentation of results. A general procedure for a centrifugal float and sink test is given in Annex A. A typical procedure for treating and testing a sample of raw coal is described in Annex B. Some practical hints on float and sink testing are given in annex C.
Houille — Détermination et présentation des caractéristiques de flottation et d'enfoncement — Principes directeurs relatifs à l'appareillage et aux modes opératoires
Črni premog - Ugotavljanje in predstavitev plovnih in potopnih lastnosti - Splošne smernice za napravo in postopke
General Information
Relations
Buy Standard
Standards Content (Sample)
SLOVENSKI STANDARD
SIST ISO 7936:1998
01-november-1998
ýUQLSUHPRJ8JRWDYOMDQMHLQSUHGVWDYLWHYSORYQLKLQSRWRSQLKODVWQRVWL6SORãQH
VPHUQLFH]DQDSUDYRLQSRVWRSNH
Hard coal -- Determination and presentation of float and sink characteristics -- General
directions for apparatus and procedures
Houille -- Détermination et présentation des caractéristiques de flottation et
d'enfoncement -- Principes directeurs relatifs à l'appareillage et aux modes opératoires
Ta slovenski standard je istoveten z: ISO 7936:1992
ICS:
73.040 Premogi Coals
SIST ISO 7936:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 7936:1998
---------------------- Page: 2 ----------------------
SIST ISO 7936:1998
INTERNATIONAL
STANDARD 7936
First edition
1992-04-15
Hard coal - Determination and presentation of
float and sink characteristics - General
directions for apparatus and procedures
Houille - Determination et prhsen ta tion des caractbristiques de
- Principes directeurs relatifs a
flottation et d’enfoncement
l’appareillage et aux modes op&atoires
Reference number
ISO 7936: 1992(E)
---------------------- Page: 3 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(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. Esch 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, govern-
mental and non-governmental, in liaison with ISO, also take patt in the
work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Inter-
national Standard requires approval by at least 75 O/o of the member
bodies casting a vote.
International Standard ISO 7936 was prepared by Technical Committee
ISO/TC 27, Solid mineral fuels, Sub-Committee SC 1, Coal preparation.
Terminology and Performance.
Annexes A and B form an integral part of this International Standard.
Annex C is for information only.
0 ISO 1992
All rights reserved. No part of this publication may be reproduced or utillzed in any form
or by any means, electronie or mechanical, including photocopying and microfilm, without
Permission in wrlting from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 * Switzerland
Printed in Switzerland
ii
---------------------- Page: 4 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
Introduction
The results of float and sink testing, presented in tabular and graphical
form, are the basis for the Provision of washability data. These results
are useful when designing and redesigning a plant, and in predicting,
controlling and assessing the Performance of a plant.
Where tests other than those for routine control purposes are carried
out, it is essential that there is precise instruction regarding size ranges
and relative density fractions to establish the scope of information and
accuracy required.
. . .
Ill
---------------------- Page: 5 ----------------------
SIST ISO 7936:1998
This page intentionally lefi blank
---------------------- Page: 6 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
INTERNATIONAL STANDARD
- Determination and presentation of float and sink
Hard coal
characteristics - General directions for apparatus and
procedures
ISO 941 l-l:-11, Solid mineral fuels - Mechanical
1 scope
sampling from moving streams - Part 1: Coal.
This International Standard describes general di-
ISO 1953:1972, Hard coais - Size anaiysis.
rections for the apparatus and procedures, using
relative density Separation methods, for determining
the float and sink characteristics of raw coal and of
3 Definitions
products from coal preparation plants.
For the purposes of this International Standard, the
A general procedure for a centrifugal float and sink
definitions given in ISO 1213-1 and ISO 1213-2 apply.
test is given in annex A. A typical procedure for
treating and testing a Sample of raw coal is de-
4 Sampling
scribed in annex B. Some practical hints on float
and sink testing are given in annex C.
4.1 General
Sampling shall be carried out in accordance with
ISO 1988.
2 Normative references
NOTE 1 A method for the mechanical sampling of coal
from moving streams will be covered in ISO 941 l-l.
The following Standards contain provisions which,
through reference in this text, constitute provisions
The quantity of Sample, and consequently the de-
of this International Standard. At the time of publi-
gree of accuracy obtained in a float and sink test,
cation, the editions indicated were valid. All stan-
may be varied according to the purpose for which
dards are subject to revision, and Parties to
the test is being carried out. The three main cat-
agreements based on this International Standard
egories are
are encouraged to investigate the possibility of ap-
plying the most recent editions of the Standards in-
a) investigation of the characteristics of raw coal;
dicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
b) comprehensive plant efficiency tests;
ISO 923:1975, Coal cleaning tesfs - Expression and
c) plant control tests.
presentation of results.
ISO 1213.1:1982, Solid mineral fuels - Vocabulary
4.2 Raw coal
Part 1: Terms relating to coal preparation.
The mass of the bulk Sample should be sufficient to
ISO 1213,2:1971, Vocabulary of ferms relating to contain the minimum quantities in each fraction as
solid mineral fuels - Part 2: Terms relating to coal listed in table 1, which is for guidance only for use
sampling and analysis. with an unknown Sample. These masses may not be
practicable in the case of some plant products or
ISO 1988:1975, Hard coai - Sampling. bore core samples.
-~
1) To be published.
1
---------------------- Page: 7 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
The number of discrete particles to be aimed for in The total Sample mass 4 required for a float and
any size fraction should not be less than 2 000. The sink test is given by the following equation:
masses given in table 1 will generally ensure that
wir
the number of particles is adequate for raw coal.
-
-mx 100 . . .
(1)
mt
S
Because some coals give low yields in the inter-
where
mediate relative density fractions, there may be in-
sufficient material for analytical requirements. In
is the recommended mass of coarsest
wir
addition, the recommended mass ofthe Sample may
size fraction (from table 1);
have to be substantially increased to meet the fol-
lowing requirements: not less than 20 g and not less is the mass percent of the coarsest size
mS
than 10 particles in each relative density fraction.
fraction in the Sample.
Where taking a bulk Sample, it is better to over-
4.3 Plant products
Sample than to have insufficient material. In Order to
carry out testing on the larger sizes in table 1, the
For clean coal, the minimum mass of Sample re-
Sample may have to be of the Order of 10 t, or even
quired is normally 50 % greater than that required
greater.
for raw coal, to ensure that adequate amounts of
misplaced material are available.
In a newly opened mine, a trial shaft or other ap-
propriate location, the mass of bulk Sample taken Since the relative densities of some components,
should not be less than IO t. such as discard and middlings, are greater than that
of clean coal, the minimum masses of samples
For bore cores, the masses recommended in containing these components should be increased
table 1 are not often obtained. For this reason, core
proportionately. This ensures that these samples
plies or sections should be selected as large as
contain approximately the Same number of particles
possible, and subdivision of the crushed ply or sec-
as the corresponding clean coal Sample, and con-
tion Prior to float and sink testing should be avoided.
sequently a similar degree of accuracy will be ob-
tained in the test.
Samples should be taken as soon as practicable af-
Table 1 - Minimum mass for a given size fraction ter the material leaves the cleaning unit, in Order to
minimize breakage. Testing should then commence
Typical recommended
Size fractionl) (Square hole) as soon as possible.
masses for raw coal
mm
In sampling pulp, the mass of the (dried) solids
kg
should comply with the requirements of table 1. In-
crements shall be taken at regular time intervals
-250+ 125 1 000
over the total cross-section of the pulp stream, ei-
- 125+63 350
ther manually or by mechanical means, using a
- 63 + 31,5 180
sampling device having a capacity equal to at least
- 31,5 + 16,O
90
twice that of the recommended minimum mass of
- 16,O + 8,0 33 increment. Care should be taken to ensure that none
of the Sample is lost by splashing.
- 8,0 + 4,0 7
- 4,0 + 2,0 3
4.4 Plant control testing
- 2,0 + 1 ,o
195
- 1 ,o + 0,5
190
Routine samples are taken regularly for the purpose
- 0,5 + 0,063
095 of determining the average efficiency of a cleaning
plant. They may represent daily, weekly or longer
1) The sizes shown in this table may be sup- periods of running. The mass taken may be less
plemented or replaced by other sizes. Quantities
than that given in table 1, depending on the reason
within specified size ranges will be determined by the
for the test. However, if any dispute arises over the
number of Separations to be made and the quantitat-
accuracy of the results, Sample masses in accord-
ive distribution of the components in terms of relative
ante with 4.2 and 4.3 should be used.
densi ty.
4.5 Comprehenslve plant efflclency tests
Both the size distribution and the ash percentage of
A comprehensive cleaning plant efficiency test in-
the raw coal coming from a working face or mine
volves a systematic mass balance of all materials
will vary during a shift, as well as from day to day.
lt is essential that the duration of sampling be long entering and leaving the plant. In this case, the mass
and moisture content of the raw feed, the mass and
enough to cover such variations.
2
---------------------- Page: 8 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
moisture content “as weighed” of all cleaned pro-
Table 2 - Size analysis
ducts, discard etc., and the volume and solids con-
---~
tent of the effluent will be required. The mass of all
Material Material
Size traction
Mass
materials is calculated to a uniform moisture basis,
retained passing
(Square hole)
and the feed entering and products leaving the plant
Oh Oh
mm
are balanced against each other. The efficiency of
the cleaning plant is assessed from the actual and
+ 125,0 Nil Nil 100,o
theoretical yields and ash percentages. The analysis
88,l
of the raw feed by computation from the masses and - 125,0 + 63,0 11,9 11,9
analyses of all the products is more reliable than
12,l 24,0 76,0
- 63,0 + 31,5
that obtained by direct examination, and it is there-
36,8 63,2
- 31,5 + 16,O 12,8
fore used for the calculation of the theoretical yields.
52,5 47,5
- 16,0 + 40 15,7
When a Screen analysis of a plant product is made 12,5 65,0 35,0
- 8,0 + 4,o
in connection with a cleaning plant efficiency test, it
- 4,0 IO,2 75,2 24,8
+ 2,o
will be found that there is some material below the
82,7 17,3
- 2,0 + 1,o
73
nominal bottom size being treated in the cleaning
88,3 11,7
- l,o + 0,5 596
unit. The mass and particle size range of this
undersize material should be recorded.
- 0,5 11,7 100,o Nil
Total 100,O
5.2 Pilot testing
Pilot testing is frequently carried out on a represen-
tative Sample, in Order to determine how the bulk
5 Preliminary treatment
material will behave. This knowledge enables the
Operator to plan the actual test in such a way that
unnecessary operations are avoided, so that the test
is carried out more expeditiously and with less ef-
fort. The Pilot test, or previous experience, may in-
dicate that it is advantageous to commence the
5.1 Size analysis Separation at either the highest or the lowest rela-
tive density.
The Sample should be spread out on an impervious
A Sample which will give a high yield at either of
base, preferably under Shelter, and allowed to dry
these densities should be separated at that density,
sufficiently for screening purposes. lt should then be
so that the bulk of the Sample tan be removed in
screened using a suitable range of apertures (typi-
one Operation.
cal sizes are given in table 2). Oversize material
may be broken by hand or machine-crushed ac-
In cases where there is only a small yield at one or
cording to the nominal top size required. If appli-
two consecutive relative density fractions, it is better
cable, the relevant part of the crusher circuit may
to combine these fractions before going through a
be simulated.
full treatment process. Within these limits it is poss-
ible to vary the procedure without affecting the out-
The quantity of material passing the 63 mm Screen
come of the test; in many cases its accuracy will be
is usually more than the amount required and it tan
improved and the time and labour involved will be
be divided before proceeding to the next size of
reduced.
Screen. Further division may be necessary at lower
sizes.
6 Float and sink testing
NOTE 2 The screening process described in this sub-
clause may be preceded by a Sample treatment Operation
6.1 Float and sink medium
designed to simulate the particle breakdown which may
occur in a coal preparation plant.
6.1.1 Basis of seleckion
Wet screening should be used, to ensure that fine
The medium which is to be used for the Separation
particles adhering to larger particles are included in
may be a mixture of organic liquids, aqueous sol-
the proper size fraction.
utions of inorganic salts, or solids in aqueous sus-
pensions. The choice of medium is also governed to
NOTE 3 Pulp and discard samples should be screened
some extent by the bulk and particle size of the coal
promptly to avoid excessive shale breakdown.
3
---------------------- Page: 9 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
being tested, by its rank and relative density, and raw coal will react with water will affect its behav-
by the purpose for which the Separation is being iour in the cleaning process, and any information
carried out. The most suitable range of relative which will provide guidance should be obtained for
densities will have to be determined by trial and er- reference purposes.
rar, but would normally include 1,3; 1,4; 1,5; 1,6; 1,7;
NOTE 4 Where water quality Problems at-e suspected,
1,8; 1,9 and 2,0., Relative densities less than 1,3 and
water of at least “potable” grade should be used to pre-
above 2,0 may also be required.
pare aqueous suspensions and inorganic solutions.
Additional Separation at intermediate relative den-
sities will be found useful where cumulative ash is
6.1.2 Organic iiiquids
increasing rapidly in relation to the cumulative yield.
As stated in 4.2, each relative density fraction should Where the Separation is critical, particularly in finer
weigh at least 20 g and should contain at least 10 sizes, the use of organic liquids is preferred (see
discrete particles. note 5) because of their low viscosity, low volatility
and inertness towards shales. Some organic liquids
Where it is known or suspected that the Sample will
and their physical proper-Ces are listed in table 3.
disintegrate or otherwise react on contact with water
or aqueous solutions, Separations are to be carried
NOTE 5 Some organic liquids may influence subsequent
out using organic liquids. However, the fact that the analyses.
Table 3
- Typical physical properties of organic liquids used in float and sink analysis
Distillation range or
Relative Vapour pressure
Flammable
Organic liquid boiling Point at Viscosity at 20 OC
at 20 OC
density
100 kN/m (100 kPa )
kPa (kN/m*)
“C mPa-s (mN*s/m*)
- -
Yes
White spirit 0,77 30 to 200
Yes
Petroleum spiritl) 2) 0,73 37 to 185 0,548 25,33
2,93 Yes
Toluene 0,87 110,7 0,588
Kerosene 0,75 165 to 230 1,365 0,ll Yes
0,68 Yes
o-Xylene 0,88 144,4 0,810
m-Xylene 0,86 139,o 0,620 0,85 Yes
p-Xylene 0,86 138,4 0,648 0,92 Yes
No
Bromoform 2,79 150,o 2,152 (at 15 “C) 0,60
(tribromomethane)
2,96 0,Ol No
Sym tetrabromoethane 239 12,0
(acetylene tetrabromide)
1,61 1,83 No
Tetrachloroethylene 120,8 190
(perchloroethylene)
SAFETY PRECAUTIONS
Particular attention is drawn to the fact that many solvent vapours present a serlous health hazard and hence adequate
Ventilation, preferably down-draught, is essential.
As the use of some organic liquids is governed by safety regulations, the user is urged to ensure compliance with the
relevant statutory regulations.
1) Nlixtures of air and Petroleum spirit vapour are highly explosive.
2) If Petroleum spirit is used it should be lead’free.
4
---------------------- Page: 10 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
Where relative densities of 1,O and less are re- 6.1.3 Inorganic solutions
quired, mixtures of perchloroethylene and one of the
less dense liquids may be used. Where relative
densities of 1,6 to 2,9 are required, mixtures of
perchloroethylene and one or more of the more
dense liquids may be used.
Inorganic solutions may often be used in place of
organic liquids, but not where any portion of the
NOTE 6 Tetrabromoethane and bromoform have ex-
Sample is subject to disintegration in water to an
tremely low vapour pressures. After use, it is therefore
extent which will influence the accuracy of the test.
necessary to rinse them from the Sample by a more rap-
idly evaporating solvent.
For samples of less than 8 mm particle size, be-
Cause of the effect of viscosity on the Separation
Organic liquids are costly but are frequently pre-
process, longer times of Separation are required.
ferred to aqueous solutions, since the products of
The quantity of Sample immersed at any one time
the Separation are easier to deal with and prolonged
therefore has to be controlled to achieve complete
washing and drying times are unnecessary because
Separation.
of the volatility of the solvents. They should be used
sparingly and it is recommended that solvent re-
Zinc chloride is a commonly used inorganic salt, but
covery be practised, particularly by drainage, after
it has several disadvantages which should be con-
the coal is removed from the Separation tank.
sidered carefully. Zinc chloride solutions are cor-
rosive and hence care should be exercised in the
SAFETY PRECAUTIONS
choice of the Container used in the test. Further-
more, the pores of the Sample frequently become
Particular attention is drawn to the fact that many
permeated by the zinc chloride Solution which is
solvent vapours are toxic and present a serious
difficult to remove even with prolonged washing with
health hazard, and hence adequate Ventilation is es-
fresh water. The presence of residual zinc chloride
sential, preferably down-draught (see figure 3). Suitl
may introduce errors in mass and may also affect
able protection to avoid contact with the skin is also
the analysis of the ash.
required. Many countries have statutory require-
ments concerning the use of organic liqulds wlth
WARNING - Zinc chloride must not be allowed to
respect to toxicity and fire; these should be ob-
contact the skln.
served.
Where contamination by zinc chloride is Iikely to af-
Equation (2) may be used to calculate the volumes
fett any of the coal analysis results, a measure of
of liquids required in formulating a mixture at the
the level of zinc chloride in the wash water should
desired relative density. lt is important that the rel-
be established.
ative density of the resultant mixture be checked, for
example by means of a hydrometer with maximum
scale divisions of 0,002.
Pt - Pp
V V
. . .
mE tpm- (2)
PP
6.1.4 Solids In aqueous Suspension
V is the volume of the liquid with higher
m
relative density;
Insoluble material with a medium to high relative
is the volume of mixture desired;
vt
density and the correct particle size distribution may
be used to give a relatively stable Suspension of low
is the relative density of the denser liq-
Pm
viscosity. Examples of suitable materials are given
uid;
in table 4.
is the desired relative density of the mix-
Pt
ture;
is the relative density of the less dense
PP
liquid.
---------------------- Page: 11 ----------------------
SIST ISO 7936:1998
ISO 7936:1992(E)
The apparatus for separating the float fraction from
Table 4
- Suitable
...
INTERNATIONAL
STANDARD 7936
First edition
1992-04-15
Hard coal - Determination and presentation of
float and sink characteristics - General
directions for apparatus and procedures
Houille - Determination et prhsen ta tion des caractbristiques de
- Principes directeurs relatifs a
flottation et d’enfoncement
l’appareillage et aux modes op&atoires
Reference number
ISO 7936: 1992(E)
---------------------- Page: 1 ----------------------
ISO 7936:1992(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. Esch 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, govern-
mental and non-governmental, in liaison with ISO, also take patt in the
work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Inter-
national Standard requires approval by at least 75 O/o of the member
bodies casting a vote.
International Standard ISO 7936 was prepared by Technical Committee
ISO/TC 27, Solid mineral fuels, Sub-Committee SC 1, Coal preparation.
Terminology and Performance.
Annexes A and B form an integral part of this International Standard.
Annex C is for information only.
0 ISO 1992
All rights reserved. No part of this publication may be reproduced or utillzed in any form
or by any means, electronie or mechanical, including photocopying and microfilm, without
Permission in wrlting from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 * Switzerland
Printed in Switzerland
ii
---------------------- Page: 2 ----------------------
ISO 7936:1992(E)
Introduction
The results of float and sink testing, presented in tabular and graphical
form, are the basis for the Provision of washability data. These results
are useful when designing and redesigning a plant, and in predicting,
controlling and assessing the Performance of a plant.
Where tests other than those for routine control purposes are carried
out, it is essential that there is precise instruction regarding size ranges
and relative density fractions to establish the scope of information and
accuracy required.
. . .
Ill
---------------------- Page: 3 ----------------------
This page intentionally lefi blank
---------------------- Page: 4 ----------------------
ISO 7936:1992(E)
INTERNATIONAL STANDARD
- Determination and presentation of float and sink
Hard coal
characteristics - General directions for apparatus and
procedures
ISO 941 l-l:-11, Solid mineral fuels - Mechanical
1 scope
sampling from moving streams - Part 1: Coal.
This International Standard describes general di-
ISO 1953:1972, Hard coais - Size anaiysis.
rections for the apparatus and procedures, using
relative density Separation methods, for determining
the float and sink characteristics of raw coal and of
3 Definitions
products from coal preparation plants.
For the purposes of this International Standard, the
A general procedure for a centrifugal float and sink
definitions given in ISO 1213-1 and ISO 1213-2 apply.
test is given in annex A. A typical procedure for
treating and testing a Sample of raw coal is de-
4 Sampling
scribed in annex B. Some practical hints on float
and sink testing are given in annex C.
4.1 General
Sampling shall be carried out in accordance with
ISO 1988.
2 Normative references
NOTE 1 A method for the mechanical sampling of coal
from moving streams will be covered in ISO 941 l-l.
The following Standards contain provisions which,
through reference in this text, constitute provisions
The quantity of Sample, and consequently the de-
of this International Standard. At the time of publi-
gree of accuracy obtained in a float and sink test,
cation, the editions indicated were valid. All stan-
may be varied according to the purpose for which
dards are subject to revision, and Parties to
the test is being carried out. The three main cat-
agreements based on this International Standard
egories are
are encouraged to investigate the possibility of ap-
plying the most recent editions of the Standards in-
a) investigation of the characteristics of raw coal;
dicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
b) comprehensive plant efficiency tests;
ISO 923:1975, Coal cleaning tesfs - Expression and
c) plant control tests.
presentation of results.
ISO 1213.1:1982, Solid mineral fuels - Vocabulary
4.2 Raw coal
Part 1: Terms relating to coal preparation.
The mass of the bulk Sample should be sufficient to
ISO 1213,2:1971, Vocabulary of ferms relating to contain the minimum quantities in each fraction as
solid mineral fuels - Part 2: Terms relating to coal listed in table 1, which is for guidance only for use
sampling and analysis. with an unknown Sample. These masses may not be
practicable in the case of some plant products or
ISO 1988:1975, Hard coai - Sampling. bore core samples.
-~
1) To be published.
1
---------------------- Page: 5 ----------------------
ISO 7936:1992(E)
The number of discrete particles to be aimed for in The total Sample mass 4 required for a float and
any size fraction should not be less than 2 000. The sink test is given by the following equation:
masses given in table 1 will generally ensure that
wir
the number of particles is adequate for raw coal.
-
-mx 100 . . .
(1)
mt
S
Because some coals give low yields in the inter-
where
mediate relative density fractions, there may be in-
sufficient material for analytical requirements. In
is the recommended mass of coarsest
wir
addition, the recommended mass ofthe Sample may
size fraction (from table 1);
have to be substantially increased to meet the fol-
lowing requirements: not less than 20 g and not less is the mass percent of the coarsest size
mS
than 10 particles in each relative density fraction.
fraction in the Sample.
Where taking a bulk Sample, it is better to over-
4.3 Plant products
Sample than to have insufficient material. In Order to
carry out testing on the larger sizes in table 1, the
For clean coal, the minimum mass of Sample re-
Sample may have to be of the Order of 10 t, or even
quired is normally 50 % greater than that required
greater.
for raw coal, to ensure that adequate amounts of
misplaced material are available.
In a newly opened mine, a trial shaft or other ap-
propriate location, the mass of bulk Sample taken Since the relative densities of some components,
should not be less than IO t. such as discard and middlings, are greater than that
of clean coal, the minimum masses of samples
For bore cores, the masses recommended in containing these components should be increased
table 1 are not often obtained. For this reason, core
proportionately. This ensures that these samples
plies or sections should be selected as large as
contain approximately the Same number of particles
possible, and subdivision of the crushed ply or sec-
as the corresponding clean coal Sample, and con-
tion Prior to float and sink testing should be avoided.
sequently a similar degree of accuracy will be ob-
tained in the test.
Samples should be taken as soon as practicable af-
Table 1 - Minimum mass for a given size fraction ter the material leaves the cleaning unit, in Order to
minimize breakage. Testing should then commence
Typical recommended
Size fractionl) (Square hole) as soon as possible.
masses for raw coal
mm
In sampling pulp, the mass of the (dried) solids
kg
should comply with the requirements of table 1. In-
crements shall be taken at regular time intervals
-250+ 125 1 000
over the total cross-section of the pulp stream, ei-
- 125+63 350
ther manually or by mechanical means, using a
- 63 + 31,5 180
sampling device having a capacity equal to at least
- 31,5 + 16,O
90
twice that of the recommended minimum mass of
- 16,O + 8,0 33 increment. Care should be taken to ensure that none
of the Sample is lost by splashing.
- 8,0 + 4,0 7
- 4,0 + 2,0 3
4.4 Plant control testing
- 2,0 + 1 ,o
195
- 1 ,o + 0,5
190
Routine samples are taken regularly for the purpose
- 0,5 + 0,063
095 of determining the average efficiency of a cleaning
plant. They may represent daily, weekly or longer
1) The sizes shown in this table may be sup- periods of running. The mass taken may be less
plemented or replaced by other sizes. Quantities
than that given in table 1, depending on the reason
within specified size ranges will be determined by the
for the test. However, if any dispute arises over the
number of Separations to be made and the quantitat-
accuracy of the results, Sample masses in accord-
ive distribution of the components in terms of relative
ante with 4.2 and 4.3 should be used.
densi ty.
4.5 Comprehenslve plant efflclency tests
Both the size distribution and the ash percentage of
A comprehensive cleaning plant efficiency test in-
the raw coal coming from a working face or mine
volves a systematic mass balance of all materials
will vary during a shift, as well as from day to day.
lt is essential that the duration of sampling be long entering and leaving the plant. In this case, the mass
and moisture content of the raw feed, the mass and
enough to cover such variations.
2
---------------------- Page: 6 ----------------------
ISO 7936:1992(E)
moisture content “as weighed” of all cleaned pro-
Table 2 - Size analysis
ducts, discard etc., and the volume and solids con-
---~
tent of the effluent will be required. The mass of all
Material Material
Size traction
Mass
materials is calculated to a uniform moisture basis,
retained passing
(Square hole)
and the feed entering and products leaving the plant
Oh Oh
mm
are balanced against each other. The efficiency of
the cleaning plant is assessed from the actual and
+ 125,0 Nil Nil 100,o
theoretical yields and ash percentages. The analysis
88,l
of the raw feed by computation from the masses and - 125,0 + 63,0 11,9 11,9
analyses of all the products is more reliable than
12,l 24,0 76,0
- 63,0 + 31,5
that obtained by direct examination, and it is there-
36,8 63,2
- 31,5 + 16,O 12,8
fore used for the calculation of the theoretical yields.
52,5 47,5
- 16,0 + 40 15,7
When a Screen analysis of a plant product is made 12,5 65,0 35,0
- 8,0 + 4,o
in connection with a cleaning plant efficiency test, it
- 4,0 IO,2 75,2 24,8
+ 2,o
will be found that there is some material below the
82,7 17,3
- 2,0 + 1,o
73
nominal bottom size being treated in the cleaning
88,3 11,7
- l,o + 0,5 596
unit. The mass and particle size range of this
undersize material should be recorded.
- 0,5 11,7 100,o Nil
Total 100,O
5.2 Pilot testing
Pilot testing is frequently carried out on a represen-
tative Sample, in Order to determine how the bulk
5 Preliminary treatment
material will behave. This knowledge enables the
Operator to plan the actual test in such a way that
unnecessary operations are avoided, so that the test
is carried out more expeditiously and with less ef-
fort. The Pilot test, or previous experience, may in-
dicate that it is advantageous to commence the
5.1 Size analysis Separation at either the highest or the lowest rela-
tive density.
The Sample should be spread out on an impervious
A Sample which will give a high yield at either of
base, preferably under Shelter, and allowed to dry
these densities should be separated at that density,
sufficiently for screening purposes. lt should then be
so that the bulk of the Sample tan be removed in
screened using a suitable range of apertures (typi-
one Operation.
cal sizes are given in table 2). Oversize material
may be broken by hand or machine-crushed ac-
In cases where there is only a small yield at one or
cording to the nominal top size required. If appli-
two consecutive relative density fractions, it is better
cable, the relevant part of the crusher circuit may
to combine these fractions before going through a
be simulated.
full treatment process. Within these limits it is poss-
ible to vary the procedure without affecting the out-
The quantity of material passing the 63 mm Screen
come of the test; in many cases its accuracy will be
is usually more than the amount required and it tan
improved and the time and labour involved will be
be divided before proceeding to the next size of
reduced.
Screen. Further division may be necessary at lower
sizes.
6 Float and sink testing
NOTE 2 The screening process described in this sub-
clause may be preceded by a Sample treatment Operation
6.1 Float and sink medium
designed to simulate the particle breakdown which may
occur in a coal preparation plant.
6.1.1 Basis of seleckion
Wet screening should be used, to ensure that fine
The medium which is to be used for the Separation
particles adhering to larger particles are included in
may be a mixture of organic liquids, aqueous sol-
the proper size fraction.
utions of inorganic salts, or solids in aqueous sus-
pensions. The choice of medium is also governed to
NOTE 3 Pulp and discard samples should be screened
some extent by the bulk and particle size of the coal
promptly to avoid excessive shale breakdown.
3
---------------------- Page: 7 ----------------------
ISO 7936:1992(E)
being tested, by its rank and relative density, and raw coal will react with water will affect its behav-
by the purpose for which the Separation is being iour in the cleaning process, and any information
carried out. The most suitable range of relative which will provide guidance should be obtained for
densities will have to be determined by trial and er- reference purposes.
rar, but would normally include 1,3; 1,4; 1,5; 1,6; 1,7;
NOTE 4 Where water quality Problems at-e suspected,
1,8; 1,9 and 2,0., Relative densities less than 1,3 and
water of at least “potable” grade should be used to pre-
above 2,0 may also be required.
pare aqueous suspensions and inorganic solutions.
Additional Separation at intermediate relative den-
sities will be found useful where cumulative ash is
6.1.2 Organic iiiquids
increasing rapidly in relation to the cumulative yield.
As stated in 4.2, each relative density fraction should Where the Separation is critical, particularly in finer
weigh at least 20 g and should contain at least 10 sizes, the use of organic liquids is preferred (see
discrete particles. note 5) because of their low viscosity, low volatility
and inertness towards shales. Some organic liquids
Where it is known or suspected that the Sample will
and their physical proper-Ces are listed in table 3.
disintegrate or otherwise react on contact with water
or aqueous solutions, Separations are to be carried
NOTE 5 Some organic liquids may influence subsequent
out using organic liquids. However, the fact that the analyses.
Table 3
- Typical physical properties of organic liquids used in float and sink analysis
Distillation range or
Relative Vapour pressure
Flammable
Organic liquid boiling Point at Viscosity at 20 OC
at 20 OC
density
100 kN/m (100 kPa )
kPa (kN/m*)
“C mPa-s (mN*s/m*)
- -
Yes
White spirit 0,77 30 to 200
Yes
Petroleum spiritl) 2) 0,73 37 to 185 0,548 25,33
2,93 Yes
Toluene 0,87 110,7 0,588
Kerosene 0,75 165 to 230 1,365 0,ll Yes
0,68 Yes
o-Xylene 0,88 144,4 0,810
m-Xylene 0,86 139,o 0,620 0,85 Yes
p-Xylene 0,86 138,4 0,648 0,92 Yes
No
Bromoform 2,79 150,o 2,152 (at 15 “C) 0,60
(tribromomethane)
2,96 0,Ol No
Sym tetrabromoethane 239 12,0
(acetylene tetrabromide)
1,61 1,83 No
Tetrachloroethylene 120,8 190
(perchloroethylene)
SAFETY PRECAUTIONS
Particular attention is drawn to the fact that many solvent vapours present a serlous health hazard and hence adequate
Ventilation, preferably down-draught, is essential.
As the use of some organic liquids is governed by safety regulations, the user is urged to ensure compliance with the
relevant statutory regulations.
1) Nlixtures of air and Petroleum spirit vapour are highly explosive.
2) If Petroleum spirit is used it should be lead’free.
4
---------------------- Page: 8 ----------------------
ISO 7936:1992(E)
Where relative densities of 1,O and less are re- 6.1.3 Inorganic solutions
quired, mixtures of perchloroethylene and one of the
less dense liquids may be used. Where relative
densities of 1,6 to 2,9 are required, mixtures of
perchloroethylene and one or more of the more
dense liquids may be used.
Inorganic solutions may often be used in place of
organic liquids, but not where any portion of the
NOTE 6 Tetrabromoethane and bromoform have ex-
Sample is subject to disintegration in water to an
tremely low vapour pressures. After use, it is therefore
extent which will influence the accuracy of the test.
necessary to rinse them from the Sample by a more rap-
idly evaporating solvent.
For samples of less than 8 mm particle size, be-
Cause of the effect of viscosity on the Separation
Organic liquids are costly but are frequently pre-
process, longer times of Separation are required.
ferred to aqueous solutions, since the products of
The quantity of Sample immersed at any one time
the Separation are easier to deal with and prolonged
therefore has to be controlled to achieve complete
washing and drying times are unnecessary because
Separation.
of the volatility of the solvents. They should be used
sparingly and it is recommended that solvent re-
Zinc chloride is a commonly used inorganic salt, but
covery be practised, particularly by drainage, after
it has several disadvantages which should be con-
the coal is removed from the Separation tank.
sidered carefully. Zinc chloride solutions are cor-
rosive and hence care should be exercised in the
SAFETY PRECAUTIONS
choice of the Container used in the test. Further-
more, the pores of the Sample frequently become
Particular attention is drawn to the fact that many
permeated by the zinc chloride Solution which is
solvent vapours are toxic and present a serious
difficult to remove even with prolonged washing with
health hazard, and hence adequate Ventilation is es-
fresh water. The presence of residual zinc chloride
sential, preferably down-draught (see figure 3). Suitl
may introduce errors in mass and may also affect
able protection to avoid contact with the skin is also
the analysis of the ash.
required. Many countries have statutory require-
ments concerning the use of organic liqulds wlth
WARNING - Zinc chloride must not be allowed to
respect to toxicity and fire; these should be ob-
contact the skln.
served.
Where contamination by zinc chloride is Iikely to af-
Equation (2) may be used to calculate the volumes
fett any of the coal analysis results, a measure of
of liquids required in formulating a mixture at the
the level of zinc chloride in the wash water should
desired relative density. lt is important that the rel-
be established.
ative density of the resultant mixture be checked, for
example by means of a hydrometer with maximum
scale divisions of 0,002.
Pt - Pp
V V
. . .
mE tpm- (2)
PP
6.1.4 Solids In aqueous Suspension
V is the volume of the liquid with higher
m
relative density;
Insoluble material with a medium to high relative
is the volume of mixture desired;
vt
density and the correct particle size distribution may
be used to give a relatively stable Suspension of low
is the relative density of the denser liq-
Pm
viscosity. Examples of suitable materials are given
uid;
in table 4.
is the desired relative density of the mix-
Pt
ture;
is the relative density of the less dense
PP
liquid.
---------------------- Page: 9 ----------------------
ISO 7936:1992(E)
The apparatus for separating the float fraction from
Table 4
- Suitable solids for aqueous suspensions
the sink fraction may consist of a basket with a
movable partition which allows the float and sink
Relative
Nominal
Material
Comments
fractions to be dealt with simultaneously while
densi ty
top size
keeping them separate. Alternatively, a tank with a
Pm
fine mesh base made to fit inside another tank,
forms a useful means of recovering floats and sinks
Finely ground
2,4 to 2,6 250
Discard from a
separately. In this case, the floats are skim
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.