1. CHARACTERIZATION AND CHEMICAL
PROPERTIES OF COAL TO BE USED IN
METALLURGICAL PROCESSES
INTRODUCTION
Metallurgy is a domain of materials science and engineering that studies the physical and
chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures,
which are called alloys. Metallurgy is used to separate metals from their ore .Metallurgy is also
the technology of metals: the way in which science is applied to the production of metals, and
the engineering of metal components for usage in products for consumers and manufacturers.
Sub-categories
Metallurgy is subdivided into;
1. Ferrous metallurgy (also known as black metallurgy) . Ferrous metallurgy involves
processes and alloys based on iron.The production of ferrous metals accounts for 95
percent of world metal production.
2. Non-ferrous metallurgy (also known as colored metallurgy).Non-ferrous
metallurgy involves processes and alloys based on other metals.
Operations involved in metallurgy

2. Need to know about metallurgy?
Having no good understanding of ground or basis of a matter will make it a pandora's
box.So therefore,firstly it is needed to know what is metallurgical science and the
relation of coal with this.
Metallurgical coal
Definition: Metallurgical coal is a grade of low-ash, low-sulfur and low-phosphorus coal
that can be used to produce high grade coke.
• Coking coal is usually Bituminous coal. Some grades of Anthracite coal are also
used as metallurgical coal.
• Metallurgical coke is made from low ash, low sulfur bituminous coal, with special
coking properties, which is inserted into ovens and heated to 1000F to fuse fixed
carbon and inherent ash and drive off most of the volatile matter. Its production
is the main use of metallurgical coal.
• But different grades of these two ranks behaves differently under same conitions
giving different types.

3. Types: There are three main types of metallurgical coal:
• Hard coking coals (HCC)
• Semi-soft coking coal (SSCC)
• Pulverized coal injection (PCI) coal
Chemical characterization of Metallurgical Coal
• Metallurgical coal must contain moisture up to approximately 17 percent.
• About 0.5 to 2 percent of the weight of this coal is to be nitrogen.
• Its fixed carbon content should range up to approximately 85 percent.
• With ash content up to 12 percent by weight.
• Volatile matter may include sulfur and hydrocarbons.
• This coal provides approximately 10,500 to 15,000 BTU per pound as mined.
• Coke of this coal must have swelling index 2-6 and Type G1 to G9 of Gray king
assay to be used in iron making.
Determination of coal suitability:
Coal is not used directly in metallurgy rather coke produced from it.So,some tests have
to be made first to determine whether a rank or grade can be used in metallurgical
operations or not regarding their above mentioned chemical composition and
characterization that is explained below.
Coal assay:Coal analysis techniques are specific analytical methods designed to
measure the particular physical and chemical properties of coals. These methods are
used primarily to determine the suitability of coal for coking, power generation or for
iron ore smelting in the manufacture of steel.Special combustion tests are;
Ash fusion test
The behaviour of the coal's ash residue at high temperature is a critical factor in
selecting coals for steam power generation. Most furnaces are designed to remove ash
as a powdery residue. Coal which has ash that fuses into a hard glassy slag known as
clinker is usually unsatisfactory in furnaces as it requires cleaning. However, furnaces
can be designed to handle the clinker, generally by removing it as a molten liquid.Ash
fusion temperatures are determined by viewing a moulded specimen of the coal ash
through an observation window in a high-temperature furnace. The ash, in the form of a

4. cone, pyramid or cube, is heated steadily past 1000 °C to as high a temperature as
possible, preferably 1,600 °C (2,910 °F). The following temperatures are recorded;
3. Deformation temperature: This is reached when the corners of the mould first
become rounded
4. Softening (sphere) temperature: This is reached when the top of the mould
takes on a spherical shape.
5. Hemisphere temperature: This is reached when the entire mould takes on a
hemisphere shape
6. Flow (fluid) temperature: This is reached when the molten ash collapses to a
flattened button on the furnace floor.
Crucible swelling index (free swelling index)
The simplest test to evaluate whether a coal is suitable for production of coke is the free
swelling index test. This involves heating a small sample of coal in a standardised
crucible to around 800 degrees Celsius (1500 °F).After heating for a specified time, or
until all volatiles are driven off, a small coke button remains in the crucible. The cross
sectional profile of this coke button compared to a set of standardised profiles range
from 0-9 determines the Free Swelling Index.
Gray-King test
Method of assessing the coking property of coal; 20 g is heated in a silica tube to 600
degrees C and the residual product is compared with a standard series ranging from
non-coking (type A) to highly coking (G), all of which have the same volume as the
original. Cokes that expand (swell) on coking receive a subscript indicating the degree of
swelling.
Roga index
A coking test whereby finely crushed coal is mixed with anthracite and heated to
produce a coke button, which is then submitted to a standardised drum test. The Roga
index is then calculated by formula from the amount of minus 1 mm material obtained
from the drum test.
Drum tests
Used for examining the strength properties of coke. Sized coke is placed in a drum which
has lifters on the inside. As the drum is rotated for a set time or number of revolutions,
the pieces of coke are lifted and then dropped to the bottom of the drum. The coke is
then sized again, and the various drum indices are obtained from the amount of
oversize and undersize material.

5. Hydrogen content
Utilization of the reducing properties of gaseous hydrogen in metallurgy to gain metals
from ores by reducing processes represents a much wider sphere.Hydrogen significantly
influences the course of combustion and improves the kinetics of reducing reactions,
even when in small amounts. Reduction through hydrogen is considerably less
endothermic than direct reduction by carbon, which improves the heat balance of the
blast furnace. Thanks to his small density, the presence of hydrogen influences the
reduction of the total density of gas circulating through the blast furnace and the
reduction of its viscosity. It leads to a decrease in pressure loss in the furnace stack, as
well as a decrease in taken out dust, and results in the efficient increase of iron
production, is not negligible in any case.This hydrogen is from the hydrogen content of
coal plus provided from outside.Here an equation is given as for the reaction of
hydrogen in blast furnace;
Fe3O4+H2----->3FeO=H2O
Oxygen content
The more oxygen-containing groups in coal the more reactivity of coke and the less its
strength after reaction.
Material Specifications
Data for the coal that is to be used in metallurgy is required to provide:
Volatile matter content (air dried),sulphur content (air dried),total moisture content
and finally ash content– up to two (‘.00) decimal places, in % ,free swelling index (FSI) –
up to one (‘.0) decimal place and G index value – whole integer.
Uses of metallurgical coal
• Coke is a fuel with few impurities and a high carbon content, made from coal.The
form known as petroleum coke, or pet coke, is derived from oil refinery coker
units or other cracking processes.
• Coke is used in preparation of producer gas which is a mixture of carbon
monoxide (CO) and nitrogen (N2).
• Producer gas is produced by passing air over red-hot coke.
• Coke is also used to manufacture water gas.
• It is also used in iron making and for raising steams in engines.

6. References(Retrieved 3 April 2018)
1.https://en.wikipedia.org/wiki/Metallurgy (Definition taken only)
2.https://www.thebalance.com/bituminous-coal-characteristics-applications-1182545
3. https://en.wikipedia.org/wiki/Metallurgical_coal (Definition taken only)
4.https://en.wikipedia.org/wiki/Coal_assay (Definition taken only)
5.Dave Osborne (ed), The Coal Handbook: Towards Cleaner Production: Volume 1: Coal
Production Elsevier, 2013 ISBN 085709730X, table 2.5 page 47
6.Coal Analytical Methods Blackwell Scientific Press, 1984.
7.ASTM D3889-38 = American Society for Testing and Materials. Standard Specifications for
Classification of Coal by Rank. D388-38 in 1964 Book of ASTM Standards; Part 19, Gaseous Fuels;
Coal and Coke. Philadelphia, Pa., 1964, pp. 71-76.
8.THE STEEL INDEX: METHODOLOGY AND SPECIFICATIONS GUIDE Publication 2017
9.Valia, Hardarshan S. Coke Production for Blast Furnace Ironmaking. Steelworks.
URL: www.steel.org
10.World Coal Institute. Coal & Steel (2007).
URL: www.worldcoal.org
11.https://www.thebalance.com/what-is-metallurgical-coal-2340012
12.https://www.sciencedirect.com/science/article/pii/S1026309813000436
13.J. Tuma, Evaluation of iron-bearing materials reducibility by a mathematic model
Metallurgical Papers (4) (1988), pp. 26-32
14.https://www.oxbow.com/Products_Industrial_Materials_Metallurgical_Coke.html
15.https://www.researchgate.net/post/What_is_the_effect_of_oxygen_content_of_coal
16.http://eyrie.shef.ac.uk/eee/cpe630/comfun4.html
17.http://www.transcoalenergy.com/coal_terminology.php

7. References(Retrieved 3 April 2018)
1.https://en.wikipedia.org/wiki/Metallurgy (Definition taken only)
2.https://www.thebalance.com/bituminous-coal-characteristics-applications-1182545
3. https://en.wikipedia.org/wiki/Metallurgical_coal (Definition taken only)
4.https://en.wikipedia.org/wiki/Coal_assay (Definition taken only)
5.Dave Osborne (ed), The Coal Handbook: Towards Cleaner Production: Volume 1: Coal
Production Elsevier, 2013 ISBN 085709730X, table 2.5 page 47
6.Coal Analytical Methods Blackwell Scientific Press, 1984.
7.ASTM D3889-38 = American Society for Testing and Materials. Standard Specifications for
Classification of Coal by Rank. D388-38 in 1964 Book of ASTM Standards; Part 19, Gaseous Fuels;
Coal and Coke. Philadelphia, Pa., 1964, pp. 71-76.
8.THE STEEL INDEX: METHODOLOGY AND SPECIFICATIONS GUIDE Publication 2017
9.Valia, Hardarshan S. Coke Production for Blast Furnace Ironmaking. Steelworks.
URL: www.steel.org
10.World Coal Institute. Coal & Steel (2007).
URL: www.worldcoal.org
11.https://www.thebalance.com/what-is-metallurgical-coal-2340012
12.https://www.sciencedirect.com/science/article/pii/S1026309813000436
13.J. Tuma, Evaluation of iron-bearing materials reducibility by a mathematic model
Metallurgical Papers (4) (1988), pp. 26-32
14.https://www.oxbow.com/Products_Industrial_Materials_Metallurgical_Coke.html
15.https://www.researchgate.net/post/What_is_the_effect_of_oxygen_content_of_coal
16.http://eyrie.shef.ac.uk/eee/cpe630/comfun4.html
17.http://www.transcoalenergy.com/coal_terminology.php