This set of Iron Making Multiple Choice Questions & Answers (MCQs) focuses on “Selection of Coal For Coke Making”.
1. What are the categories in which you can classify Indian coal as potential coke making coal?
a) Prime variety coal, semi coking coal, weak coking coal
b) Hard coking coal, soft coking coal
c) Anthracite coal, bituminous coal, peat
d) Charcoal, rock coal
View Answer
Explanation: Indian coal can be divided into prime variety coal, semi coking coal and weak coking coal according to their potential of being converted to coke. Hard coking coal and soft coking coal are classification of Australian coal which is being imported by Indian steel companies to meet huge demand of coking coal. Anthracite, bituminous and peat are classification of coal according to carbon content and cannot be used to relate coke making qualities.
2. In recent years coke as a fuel has been replaced by auxiliary fuels. The coke rate has been reduced from 700kg to 350kg per ton of hot metal. However, coke still has a very crucial function in BF where it cannot be dispensed with nor can it be substituted by anything else. What is the crucial function that coke performs?
a) Acts a fuel
b) Produces and regenerates reducing gases
c) Acts as a spacer in the bosh region where all other materials are either plastic or molten
d) Carburizes iron to decrease its melting point
View Answer
Explanation: Coke as fuel has been somewhat substituted by auxiliary fuel injection practice. Coke has an unalienable role of maintaining bed permeability in the bosh region and acts as a spacer for upward flow of hot blast.
3. What processing route can be adopted to reduce ash content in coal?
a) Calcination
b) Roasting
c) Grinding followed by washing
d) Jigging
View Answer
Explanation: Coal with high ash content can be detrimental for blast furnace operation. The extra ash is removed by grinding the coal and washing it. The ash being lighter floats and is washed away leaving behind the coal.
4. Why is the coal found in north eastern part of India not suitable for coke making even if it has high carbon content?
a) The coal has high ash content
b) The coal has high content of Sulphur (2%-7%)
c) The coal is rich in volatile matter
d) The coal is fragile in nature
View Answer
Explanation: The coal reserves found in north eastern part of India is anthracite and is rich in carbon content. However, the coal contains 2%-7% Sulphur which exceeds the usable limit. Since Sulphur of coke directly joins the hot metal and cannot be satisfactorily removed in blast furnace, it adversely affects steel making economically.
5. What is the optimum amount of volatile matter (dry ash free) that must be present in coal to carbonization and produce coke of suitable porosity?
a) 10%-20%
b) 20%-32%
c) 5%-10%
d) 30%-40%
View Answer
Explanation: The optimum volatile matter content in coal to be converted into BF coke is 20%-32%. The amount of volatile matter in coal determines its porosity and the extent of cellular structure. However, too much volatile matter degrades the strength of the coke.
6. Which of the following tests are used to assess the reactivity and physical properties of coal used for coke making?
a) Tumbling test
b) Micum test
c) Abrasion test
d) CRI followed by CSR
View Answer
Explanation: CRI stands for Coke Reactivity Index and CSR stands for coke strength after reaction, this combination of test can be used to test physical properties of coal suitable for coking. CRI and CSR both depend on the porosity of the coal. Tumbling test, micum test and abrasion test are used to assess strength of coke and often of little significance.
7. What ‘reflectance’ of constituents of coal indicate?
a) Tells about the thermal stability of each constituents
b) Tells about light reflecting property of each constituents
c) Tells about the strength of each constituents
d) Tells about the carbon content of each constituent
View Answer
Explanation: Coal is mainly composed of macerals of three types namely vitrinite, inertinite and liptinite. These macerals are of different origin and were formed under different conditions of temperature and pressure. Reflectance of a constituent of coal indicates the maximum temperature history of the macerals. This temperature is closely related to the thermal stability of these constituents.
8. What is the optimum fluidity for coking coals?
a) < 100ddpm
b) > 200ddpm and < 400ddpm
c) > 400ddpm
4) > 300ddpm and < 400ddpm
View Answer
Explanation: Fluidity of coal indicates the extent to which it can become plastic during the process of coking making. Fluidity indicates the rheological properties of coal. A high fluidity is desired in coking coal for proper bonding of carbon particles. The optimum fluidity of coking coal is > 400ddpm.
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