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UDC 662.6
IS0
D I Z AT IO N
ORGANIZATION FOR STAND AR
I NT ERN AT I ON AL
IS0 RECOMMENDATION
R 351
DETERMINATION OF TOTAL SULPHUR IN COAL
BY THE HIGH TEMPERATURE COMBUSTION METHOD
1st EDITION
December 1963
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IS0 Recommendations and IS0 Standards
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belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized bherefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 351, Determination oj Totul Sulphur in Coal by the
High Temperuture Combustion Method, was drawn up by Technical Committee ISO/TC 27,
Solid Mineral Fuels, the Secretariat of which is held by the British Standards Institution
(B. S.I.).
Work on this question by the Technical Committee began in 1951 and led, in 1957,
to the adoption of a Draft IS0 Recommend a t' ion.
In May 1958, this Draft 1SO Recommendation (No. 241) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial
nature, by the following Member Bodies:
Austria
India Portugal
Belgiutn
Israel Republic
Burma Italy of South Africa
Chile Japan Spain
Czechoslovakia
Mexico United Kingdom
Denmark
Netherlands U.S.S.R.
Germany New Zealand Yugoslavia
Greece Poland
One Member Body opposed the approval of the Draft: France.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in December 1963, to accept it as an IS0 RECOMMENDATION
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IS0 / R 351 - 1963 (E)
IS0 Recommendation R 351 Decem ber 1963
DETERMINATION OF TOTAL SULPHUR IN COAL
BY THE HIGH TEMPERATURE COMBUSTION METHOD
1. PRINCIPLE
Coal is burnt in a stream of xygen, in a tube fwnace at a temperature of 1250 or 1350 "C, and
the oxides of sulphur formed, together with any chlorine liberated, are absorbed in hydrogen
peroxide and determined volumetrically. A correction is made to take account of any chlorine
liberated. A suitable additive prevents the retention of sulphur in the ash.
2. APPARATUS
All graduated apparatus should be of the best analytical quality obtainable, and the balance used
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should be sensitive to 0.1 mg.
2.1 Furnace, capable of heating a tube of approximately 28 mm external diameter over a length
OF approximately 15 cm to a maximum temperature of 1250 or 1350 OC. The furnace may,
conveniently, be heated electrically, using either silicon carbide resistance rods (controlled
by a variable transformer) or a resistance wire (controlled by a variable resistance).
2.2 Aluminous porcelain tube, of approximately 28 niin external diameter, 3 rnm wall thickness
and 65 cm length, which is gas-tight at the working temperature. A straight tube is most
convenient and is used in conjunction with an adapter of fused silica having a bell-shaped
end, which gives a narrow clearance with the inner wall of the heated tube, and a heat-
resistant stopper (acrylonitrile or chloroprene is suitable). Alternatively, the tube may have,
at the exit, a beak end, with a tubulure to enable condensation products to be washed out
after a test; or a straight tube of aluminous porcelain may be used in conjunction with a
borosilicate glass adapter, having a cap-shaped end which fits on the outer wall of the tube.
2.3
Oxygen cylinder, fitted with a needle valve to control the rate of flow of oxygen, and a
flow meter to measure up to 700 ml/min if the determination is to be carried out at 1250 OC,
or 300 ml/min if the determination is to be carried out at 1350 OC. The oxygen should,
as a precautionary measure, be passed through a U-tube packed with soda-asbestos.
2.4 Combustion boats, of iron-free, unglazed porcelain, 62.5 mm long, 12.5 mm wide and
10 mm deep.
2.5 Heat-resistant wire, about 1.5 mm thick, and having a bent end to remove the boats from
the tube.
2.6 Silica pusher, with a disk end for pushing the boat into the hot zone. The pusher passes
through a T-piece fitted into the bung at the inlet end of the tube and is held in a rubber
sleeve (see note below) which fits over the free arm of the T-piece. The sleeve prevents the
escape of oxygen (which enters at the stem of the T) although permitting movement of
the pusher.
NOTE. - The rubber sleeve should be changed periodically to avoid leakage.
2.7 Two absorbers, of about 150 ml capacity, which may be large boiling tubes, wide-necked
bottles or Drechsel bottles, each containing a sintered glass disk of 15 to 40 pm maximum
pore size in the gas distribution tube. The diameter is such that the disk is covered to a
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IS0 / R 351 - 1963 (E)
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IS0 / R 351 - 1963 (E)
depth of at least 2.5 cm by the absorbing solution. The silica adapter, or the reaction tube
fitted with a tubulure, is connected to the first absorber. This is connected in series with the
second absorber.
Alternatively, one may use a single narrow absorber with a sintered glass disk of 15 to 40 pm
maximum pore size, about 35 mm diameter and 15 cm deep, so that the bubbler is covered
to a depth of at least 9 cm.
To avoid leakage at the rubber sleeve of the inlet end due to the resistance of the sintered
glass bubbler, the second absorber is connected to a water-pump through a pressure regulator
containing mercury with an open-ended tube dipping into it.
A convenient assembly ;f the above apparatus is illustrated in the figure.
3. REAGENTS
All reagents should be of analytical reagent quality and distilled water should be used throughout.
3.1 Kaolin or
3.2 Ferric phosphate, if the determination is to be carried out at 1250 OC; or
3.3 Aluminium oxide (alumina) finely divided, if the determination is to be carried out at 1350 OC.
3.4 Hydrogen peroxide solution, 1 per cent (by volume), neutralized with the sodium borate
solution (3.6).
3.5 Mercuric oxycyanide solution, saturated. Filter, neutralize with the sulphuric acid (3.7) and
store in a dark-glass bottle; do not keep longer than 4 days.
3.6 Sodium borate solution, 0.050 N.
3.7 Sulphuric acid, 0.025 N.
3.8 Mixed indic
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