Fuels and Combustion - Section 1 (3)

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Fuels and Combustion - Section 1

Fuels and Combustion is a field and there are problems available to
solve in this category. You will find the MCQs and can solve them easily.

17.

Actual flame temperature is always lower than the adiabatic flame temperature, because there is

A.	no possibility of obtaining complete combustion at high temperature.
B.	always loss of heat from the flame.
C.	both (a) and (b).
D.	neither (a) nor (b).

Answer: Option C

Explanation:

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18.

Prime coking coal is always blended with medium or non- coking coal before ear-bonisation

A.	to check against its excessive swelling during heating, which may exert high pressure and damage coke oven walls.
B.	because, it alone produces unreactive coke.
C.	both (a) and (b).
D.	neither (a) nor (b).

Answer: Option C

Explanation:

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19.

Explosion limit of blast furnace gas is 37 to 71% gas in gas-air mixture. It means that the blast furnace gas will explode when burnt in a confined space, if its concentration in the gas-air mixture is __________ percent.

A.	< 37%
B.	>71%
C.	in between 37 & 71%
D.	none of these

Answer: Option C

Explanation:

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20.

Gray King Assay and Swelling Index of a coal is a measure of its

A.	swelling characteristics.
B.	abradability.
C.	agglutinating properties.
D.	resistance to impact breakage.

Answer: Option A

Explanation:

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21.

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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22.

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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23.

'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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24.

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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