Coke is a hard gray fuel, it bears the same relation to coal as charcoal to wood. Coke is made in
brick furnaces with bituminous coal as the source. Coke is the most vital raw material fed in a blast
furnace operation and hot metal quality. A high quality coke should be able to support a smooth
origin of the blast furnace burden with as little degradation as possible while providing the lowest
amount of impurities, highest thermal energy, highest metal reduction, and optimum absorptivity
for the flow of gaseous and molten products.
Coke is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur
bituminous coal. The volatile constituents of the coal including water, coal-gas and coal-tar are
driven off by baking in an airless oven at temperatures as high 1000° C. Metallurgical coke is
produced by carbonization of coal at high temperatures to produce a macro-porous carbon material
of high strength and relatively large lump size. Metallurgical cokes must have a high strength to
support heavy loads in the blast furnace without disintegration.
Metallurgical coal is a special type of coal used to make metallurgical coke. There are two types
of metallurgical coal used to make coke;
Hard Coking Coal
Semisoft Coking Coal
These types of coal are ideal for coke because they melt, swell and re-solidify when placed into a
superheated furnace. These types of coal also have low levels of impurities. A third type of
metallurgical coal, PCI (Pulverized Coal Injection) is sometimes used in steel or iron making to
replace more-expensive coke.
The coking coal must have the following;
Low ash content
Low Sulphur content
Abrasive strength and hardness
Coke is created by heating metallurgical coal to around 2,000 degrees Fahrenheit. The coking
process takes about 12 to 36 hours in the oven to complete. After being taken out of the oven, the
coke is cooled with water or air to before it is either placed into storage or is put directly to the
blast furnace. The finished product is about two-thirds the weight of the original raw material.
Metallurgical Coke Manufacturing
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. The final product is a nearly pure carbon source with
sizes ranging from basketballs (foundry coke) to a fine powder (coke breeze).
Factors Affecting Quality
High quality coke is normally made from high quality coking coals. An excellence coal should not
generate high pressure on the coke oven wall and should shrink enough to allow easy removal
from the coking oven. The properties of coke and its performance in the process are influenced by
moisture content, density, weathering of coal, and several other factors.
Application of Metallurgical Coke
Coke is mainly used to make iron, which in turn used as the main ingredient in steel. In
iron making procedure iron ore, coke and small quantities of minerals used to collect
impurities are placed into a blast furnace. Superheated air is then blown into the furnace,
making the coke burn. The burning produces carbon monoxide which reacts with the iron
ore and heat to melt the iron. A tap at the bottom of the furnace allows molten iron, as well
as impurities, to flow out of the furnace.
Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. The
carbon monoxide produced by its combustion reduces iron oxide (hematite) in the
production of the iron product.
Blast Furnace Construction and Working
Blast furnace consists of a vertical steel shell, 100 ft. high & 21 ft. diameter and lined with
refractory material. It has a charging arrangement (Bell & Cone) at the top. Raw material is charged
by a skip car through this charging mechanism into the blast furnace. It has a means of running off
Pig iron & Slag at the bottom. Air is blown in near the bottom of the furnace. This forced draught
increases the speed of combustion & maintains the necessary high temperature. Cooling water is
circulated around the Bosh area in order to protect the furnace from high temp.
Figure 2 Sketch of Blast Furnace
Chemical Reactions Occurring In Blast Furnace Using Coke
In the blast furnace there are several chemical reactions taking place that eventually result in the
desired product (iron) being extracted;
The coke (carbon) burns with oxygen to produce carbon dioxide. This reaction is exothermic.
The CO2 then reacts with more coke to give carbon monoxide.
C + O2 CO2
CO2 + C 2CO
Carbon Monoxide (CO) acts as a reducing agent and reacts with the iron ore to give molten iron,
which trickles to the bottom of the furnace where it is collected.
Fe2O3 + 3CO 2Fe + 3CO2
The limestone in the furnace decomposes, forming calcium oxide. This is a fluxing agent and
combines with impurities to make slag, which floats on top of the molten iron and can be
CaO + SiO2 CaSiO3
Figure 1 Blast Furnace
Low Ash Metallurgical (LAM), hard coke is used in blast furnace for production of pig iron & in
the production of cast iron.
Low ash coke and low ash coal are widely used as a primary fuel where a uniform and high
temperature is required. Widely used in the manufacture of Silico Manganese, Pig Iron.
Fixed Carbon 83%
Volatile Matter 2%
Ash Content 13-15%
Size Greater than 60mm