Chemical Engineering - Fuels and Combustion

26. 

Higher percentage of ash in coal meant for the production of metallurgical grade coke

A. decreases the hardness of coke.
B. decreases the abrasion resistance of coke.
C. causes brittleness in steel.
D. none of these.

Answer: Option D

Explanation:

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27. 

Combustion of pulverised coal as compared to that of lump coal

A. develops a non-luminous flame.
B. develops a low temperature flame.
C. can be done with less excess air.
D. provides a lower rate of heat release.

Answer: Option C

Explanation:

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28. 

'Wobbe index' is a characteristic of

A. solid fuels
B. gaseous fuels
C. liquid fuels
D. fat coals

Answer: Option B

Explanation:

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29. 

A coal with high ash content is undesirable, as

A. it is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber.
B. the ash in molten condition gets absorbed in the pores of the refractory lining of the furnace and causes its spalling due to different co-efficient of expansion/contraction of the refractory and the ash.
C. the ash retains the sulphur & phosphorus and thus affects the quality of products in metallurgical furnace apart from increasing the slag volume. Besides, it may fuse and stick to the boiler tubes thereby reducing the heat transfer.
D. all (a), (b) and (c).

Answer: Option D

Explanation:

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30. 

Presence of free moisture in coal during its high temperature carbonisation

A. reduces the coking time.
B. protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls.
C. increases the loss of fine coal dust from the ovens when charging.
D. none of these.

Answer: Option B

Explanation:

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