Fuel and Combustion MCQs

A coal with high ash content is undesirable, as

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It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber
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
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
All of the above
✅ The correct answer is option D.

Pick out the wrong statement.:

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Carburetted water gas is also called blue gas
Coals are divided in four species according to their carbon content in Seylor’s classification
Carbonisation time in a by-product coke oven is about 16 hours
Gross and net calorific value of a fuel is the same, if it does not contain hydrogen or hydrocarbons
✅ The correct answer is option A.

Presence of free moisture in coal during its high temperature carbonisation

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Reduces the coking time
Protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls
Increases the loss of fine coal dust from the ovens when charging
None of these
✅ The correct answer is option B.

Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because

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The hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot
It reduces its calorific value tremendously
It reduces its flame temperature tremendously
There are chances of explosion during preheating
✅ The correct answer is option A.