ISO 502:2015

INTERNATIONAL ISO
STANDARD 502
Third edition
2015-06-15
Coal — Determination of caking power
— Gray-King coke test
Charbon — Détermination du pouvoir agglutinant — Essai Gray-King
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagent . 1
4.1 Standard electrode carbon (see 10.1) . 1
5 Apparatus . 2
6 Preparation of sample . 2
7 Procedure. 3
7.1 Coals with a Gray-King coke type within the range A to G (see 10.3) . 3
7.2 Coals with a Gray-King coke type greater than G (see 10.3) . 3
8 Expression of results . 3
9 Precision of the method . 3
9.1 General . 3
9.2 Repeatability . 4
9.3 Reproducibility . 4
10 Notes on procedure . 4
11 Test report . 5
Annex A (normative) Determination of the bulk density of electrode carbon .11
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 05,
Methods of analysis.
This third edition cancels and replaces the second edition (ISO 502:1982), which has been technically
revised.
iv © ISO 2015 – All rights reserved

Introduction
The purpose of the Gray-King coke test, which is one of the parameters adopted for the International
Classification of Hard Coal by Type by the United Nations Economic Commission for Europe, is to assess
the caking properties of a type of coal or a blend of coals by carbonizing under standard conditions.
Although the Gray-King test and the Roga test both assess the caking properties of a coal, they do
not measure precisely the same parameters and are not recommended to be regarded as alternative
methods.
INTERNATIONAL STANDARD ISO 502:2015(E)
Coal — Determination of caking power — Gray-King coke
test
1 Scope
This International Standard specifies a method of assessing the caking power of coal under standard
conditions.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 1014, Coke — Determination of true relative density, apparent relative density and porosity
3 Principle
The sample is heated under standard conditions to a final temperature of 600 °C. The coke residue
obtained is classified by reference to a series of standard residues. If the coke residue produced is so
swollen that it fills the cross-section of the retort tube, the determination is repeated with the coal
admixed with a suitable quantity of electrode carbon or equivalent material. For these highly swelling
coals, the Gray-King coke type is defined by the minimum amount of electrode carbon required to
produce a strong hard coke residue of the same volume as the original coal and electrode carbon mixture.
4 Reagent
4.1 Standard electrode carbon (see 10.1)
High temperature electrode carbon:
Moisture less than 1 %
Volatile matter less than 1,5 %
Ash less than 5 %
3 3
Bulk density at 25 °C (see Annex A) 1,00 g/cm to 1,05 g/cm
Relative density at 25 °C (see 10.2) 2,05 to 2,09
Size analysis:
Retained on 212 μm test sieve nil
Through 212 μm test sieve, retained on 125 μm test sieve less than 26 %
Through 125 μm test sieve, retained on 63 μm test sieve 10 % to 40 %
Through 63 μm test sieve 50 % to 85 %
It is recommended that a dust mask is used while using the inert carbonaceous material which can
contain undesirable trace elements from the original processing of this material.
5 Apparatus
5.1 Furnace, horizontal electric, 50 mm internal diameter and 300 mm long, with one end closed and
the other carrying a plug of insulating material which is bored centrally with a hole 25 mm in diameter.
The winding of the furnace shall be such that the middle 200 mm is at a uniform temperature within ±5 °C
at both 300 °C and 600 °C. Alternatively, the furnace may be constructed from an electrically-heated
aluminium-bronze block, with one or several, bores of 25 mm diameter. The furnace shall be insulated and
located in a cover of metal or other suitable material, and shall be equipped with a suitable thermocouple,
lying above the retort tube when the latter is in position and with the junction at the centre of the furnace.
An indicator shall be provided for showing the furnace temperature with an accuracy of ±5 °C. A suitable
means of controlling the energy input shall also be provided to permit an increase in temperature at a rate
of 5 °C/min. A multiple tube furnace to allow simultaneous determinations is convenient. The furnace
may be of the fixed type or mounted on rails. Suitable furnaces are shown in Figure 2 and Figure 3.
5.2 Retort tube (see Figure 4), a heat-resistant glass or transparent silica tube, 20 mm internal diameter
and 300 mm long, closed at one end, with a side arm, 8 mm internal diameter and 50 mm long, sealed in
at a distance of about 20 mm from the open end. The tube shall be smooth and either of uniform bore or
with a slight taper (19 mm to 21 mm) such that the open end is the larger.
5.3 Distance rod, with a flat disk at one end to assist in the packing of the coal and to indicate the free
end of the coal sample in the retort tube.
5.4 Receiver and outlet tube
A glass vessel of adequate size, suitably supported and attached to the side arm of the retort tube, fitted
with an outlet tube leading to atmosphere or to a piece of small bore silica tubing at the end of which the
gas leaving the receiver can be burned through Bunsen burner (in a fume cabinet) to ensure toxic fumes
are burnt before venting to the atmosphere through the fume cabinet.
The receiver may conveniently be a U-tube which can be immersed in water.
The outlet shall be open to the atmosphere to prevent pressure build-up.
Fumes are toxic and it is recommended that the process is carried out in a fume cupboard.
The tar receiver should be cleared on a regular basis, by placing tar in a heat resistant crucible and
burning off in a furnace.
WARNING — THE FUMES ARE TOXIC AND DUE CARE SHOULD BE EXERCISED IN THEIR DISPOSAL.
6 Preparation of sample
The coal used for the determination of the Gray-King coke type is the analysis sample ground to pass a
sieve of 212 μm aperture. If necessary, expose the sample in a thin layer for the minimum time required
for the moisture content to reach approximate equilibrium with the laboratory atmosphere.
Before commencing the determination, mix the air-dried sample thoroughly for at least 1 min, preferably
by mechanical means. The sample shall be prepared on the same day as the determination is carried out.
2 © ISO 2015 – All rights reserved

7 Procedure
7.1 Coals with a Gray-King coke type within the range A to G (see 10.3)
Raise the temperature of the furnace until it is steady at 325 °C.
Weigh on a scoop 20,0 g ± 0,1g of the sample and transfer it to the retort tube (5.2), held in such a manner
that the coal cannot enter the side arm. Complete the transfer with a soft brush and allow the coal to fall
to the far end of the retort tube. Hold the tube horizontally, insert the distance rod (5.3) so that the face
of the disk is 150 mm from the closed end of the retort tube and spread the coal into a layer of uniform
depth by shaking and turning. Withdraw the distance rod and insert a flattened pad of asbestos wool or
a notched asbestos disk to retain the coal in position. Without disturbing the position of the coal, close
the open end of the retort tube with a heat-resisting stopper. Connect the receiver (5.4) to the side arm
and insert the retort tube in position in the furnace (5.1) so that the centre of the coal layer coincides
with the centre of the furnace. If the furnace is mounted on rails, clamp the retort tube in a horizontal
position and run the furnace into position.
Raise the energy input to the furnace in such a manner that the temperature of 325 °C is regained in 3
min to 7 min and maintain a uniform rate of rise of 5 °C/min thereafter until a temperature of 590 °C
is reached. At this point, regulate the energy input to the furnace so that a temperature of 600 °C is
reached, and maintain this temperature for 15 min.
Withdraw the retort tube (or retract the furnace) and allow it to cool. Detach the receiver, remove the
stopper and s
...