What are the Requirements of Metallurgical Coke?

Coke

Coke is formed by the destructive distillation of coal in coke oven. When bituminous coal is heated strongly in the absence of air, coke is formed. It is a white lustrous, dense, strong, porous and coherent mass.

The process of preparing coke from coal is known as ‘Carbonisation of coal’.

Coke is mostly used in metallurgical industry (in blast furnaces), so it is called as metallurgical coke.

Difference between Coal and Coke.

Coal	Coke
Coal is formed in nature as a result of the slow decomposition of vegetable matter.	Coke is formed by the destructive distillation of coal in a coke oven.
Coal burns with a long flame and can be used in reverberatory furnaces.	Coke burns with shorter flame and can be used in blast furnaces.
The physical nature of coal depends on its various forms like peat, lignite, bituminous coal and anthracite coal etc.	It is a white, lustrous, dense, strong, porous and coherent mass.

Carbonisation

Carbonisation is heating of coal in the absence of air at high temperature; it produces a residue coke, coal gas and tar.
Depending on the temperature of carbonisation, the following types of carbonization are employed.

Table 1.1: Difference between LTC and HTC

S. No	Low-temperature carbonisation	High-temperature carbonisation
1	Heating of coal is carried out at 500 700°C	It is carried out at 900-1200°C
2	Yield of coke is 75% 80%	Yield of coke is 65-75°C
3	It contains about of volatile matter 5% -15%	It contains about 1-3% of volatile matter
4	Mechanically it is not strong.	It is hard and has good mechanical strength.
5	Coke is good for domestic purpose.	It is suitable for metallurgical purpose.
6	The coke obtained is known as soft coke	It is hard and known as metallurgical coke.
7	Calorific value of gas is about 6500 – 9500u kcal/m³	It has about 5400-6000 kcal/m³

Coke is mostly used in metallurgical industry (in blast furnaces), so it called metallurgical coke.

Characteristics of metallurgical coke

The metallurgical coke should possess the following characteristics:

Purity : Moisture, sulphur, phosphorous and ash contents should be as low as possible.
Porosity : Coke should be porous in nature, so that oxygen can easily be in contact with the carbon of the coke.
Calorific value : The calorific value of coke should be high.
Cost : Coke should be cheap and easily available near the site of the metallurgical plant, so that the transportation cost is low.
Size : Coke should be of optimum size. It should not be too big or too small.
Strength : Coke should be hard and strong so that it can withstand the pressure developed in the furnaces.
Combustibility : Coke should burn easily. The rate of combustion depends only on the rate of oxygen / air supply.
Reactivity : Coke should not be too reactive. Intense heat is not obtained from the reactive coke. If the reactivity of coke is low, its calorific intensity becomes high and hence better will be the fuel value.