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Fuels And Combustion
Quiz 6
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Q.1
Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because
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
Q.2
Pick out the wrong statement.
LPG is also used as fuel for automobiles & small furnaces and for cutting & welding of metals
The minimum temperature, at which a petroleum oil vapor catches fire and continues to burn, is called its flash point
Each ton of petroleum oil on distillation produces about 30-50 Nm³ of gas
Maximum yield of naphthalene is obtained on distillation of crude oil
Q.3
Fuel combustion is never cent per cent efficient due to
Incomplete combustion
Dry gas/stack gas loss
Moisture loss
All of the above
Q.4
Coal is pulverised before burning in large capacity boiler furnaces mainly to
Ensure its complete combustion
Facilitate easy ash removal
Enhance its calorific value
Provide trouble free operation
Q.5
Gasification of the solid fuel converts its organic part into combustible by interaction with air/oxygen and steam so as to obtain a secondary gaseous fuel of high calorific value having no ash. Gasification reactions are normally carried out at about __________ °C.
400-500
900-1000
1400-1500
1700-1800
Q.6
High excess air in combustion of fuels results in
Increased fuel consumption
Incomplete combustion
Smoky flame
None of these
Q.7
Combustion of pulverised fuel
Requires larger combustion chamber than rich gaseous fuel
In a metallurgical furnace does not contaminate the product in the furnace by ash from fuel
Suppresses the discharge of fine dust and grit into atmosphere
All of the above
Q.8
For every 10% increase in the excess air; the fuel consumption increases by __________ percent.
0.1
2
5
10
Q.9
Correct viscosity of furnace oil at the burner tip for proper atomisation is about 25 centistokes. To reduce the viscosity of high viscosity furnace oil (250 centistokes) to the correct atomisation viscosity (i.e. 25 cst), it should be preheated to about____°C.
70
85
105
145
Q.10
Benzene is used
As a motor fuel
As an explosive
For making insecticides (e.g., DDT, BHC etc.), detergent & rubber (SBR)
As a perfume
Q.11
Wood charcoal is obtained by the destructive distillation of wood. It is used in the production of activated carbon, which is not used for the
Decolourisation of sugar
Solvent recovery from air and gases
Absorption of gases and vapor
Electrode manufacture
Q.12
Spontaneous combustion of coal on storage results due to
Inadequate ventilation
Low temperature oxidation
Storage in large heaps with small surface to volume ratio
All of the above
Q.13
Coalification means the
Process of conversion of lignite into anthracite
Underground gasification of coal
Complete combustion of coal
Direct hydrogenation of coal
Q.14
As time passes, the calorific value of stored coal
Decreases
Increases
Remains unaltered
May increase or decrease (depends on the method of storage)
Q.15
'Fuel' can be defined as a substance which produces heat by
Combustion
Nuclear fission
Nuclear fusion
All of the above
Q.16
Tolerable concentration of toxic carbon monoxide in atmospheric air is about __________ PPm.
50
1000
5000
10000
Q.17
The internal energy of the combustion products is __________ compared to that of reactants.
More
Less
Equal
More or less ; (depends on the state of fuel.)
Q.18
Fixed carbon in coal is defined as
That present in volatile matters
The total quantity of carbon present in the coal
Hundred minus the percentage of volatile matter, ash and moisture
The one which is present in the residue after combustion
Q.19
The most matured coal out of the following is
Lignite
Semi-anthracite
Sub-bituminous
Bituminous
Q.20
Bright coal
Contains more than 90% durain
Contains more than 90% fussain
Contains mainly vitrain & clarain and is generally coking
Is non-coking
Q.21
Bituminous coal
Ignites less easily than anthracite
Is generally coking
Burns with smoky yellow flame
Both B and C
Q.22
Water gas constitutes mainly of
CO & H₂
CO & N₂
CO₂ & H₂
CH₄ & H₂
Q.23
If the specific heat of gaseous products of combustion of a fuel is high, the abiabatic flame temperature will be
Low
High
Very high, if the fuel is of low calorific value
None of these
Q.24
Cannel coal
Is non-coking
Has a high volatile matter content and burns with a luminous smoky flame
Is a non-banded coal which can be ignited easily with a match stick or candle flame, hence is so named
All of the above
Q.25
In flue gas analysis by Orsat's apparatus, carbon monoxide is absorbed by
Cuprous chloride
Potassium hydroxide
Alkaline pyrogallol solution
None of these
Q.26
Low temperature carbonisation of coal produces
Metallurgical coke
Soft coke
Very low calorific value coke oven gas
No by-products
Q.27
Caking coal is desirable for
Burning on travelling grate
Coke making
Burning on firebars
All of the above
Q.28
When steam is passed over coal resulting in the endothermic reaction represent by, C + H₂O = CO + H₂, it is called the __________ of coal.
Carbonisation
Oxidation
Coalification
Gasification
Q.29
Yield of charcoal in high temperature carbonisation of wood is about __________ percent.
10
25
50
75
Q.30
The main product of high temperature carbonisation of coal is
Coke
Ammonia
Tar
Coke oven gas
Q.31
With increase in the temperature of carbonisation of coal
Hydrogen content of coke oven gas increases due to cracking of hydrocarbons
Methane content in the coke oven gas decreases and carbon monoxide content increases
Calorific value of the coke oven gas decreases due to cracking of hydrocarbons which is not compensated by increase in CO & H? content
All of the above
Q.32
Flue gas discharge velocity through chimney of a big thermal power plant may be around __________ m/sec.
0.5
10
50
500
Q.33
C/H ratio is the maximum in case of
Coal
Furnace oil
Natural gas
Naphtha
Q.34
Optimum preheating temperature for pitch creosote mixture (PCM) which is also termed as C.T.F-200, before atomisation through burners is
200 °F
200 °C
200 °K
200 °R
Q.35
The sequence of absorption in flue gas analysis by Orsat's apparatus is respectively
CO₂, O₂, CO
CO, O₂, CO₂
CO₂, CO, O₂
O₂, CO₂, CO
Q.36
High temperature carbonisation of coal produces
Inferior coke compared to low temperature carbonisation
Less of gases compared to liquid products
Large quantity of tar compared to low temperature carbonisation
None of these
Q.37
Coke made in narrower by-product coke ovens (as compared to wider ovens) is
Less reactive
Stronger
Smaller in size
All of the above
Q.38
Ammonia content in raw coke oven gas is about __________ gm/Nm³.
1
15
50
100
Q.39
Anthracite can be used for
Recarbonising steel
Making carbon electrodes
Blending with highly coking coal to check its swelling which helps in saving coke even walls from damage and to produce high strength coke
All of the above
Q.40
Anthracite coal
Contains more volatile matter than bituminous coal
Ignites more easily than bituminous coal
Is essentially a coking coal
Burns with short, bluish, yellow-tipped flame producing very little smoke
Q.41
Which adsorbant is used for removing sulphur compounds (S Q, H₂S, RSH etc.) removal from coke oven gas in by-products recovery plant ?
Silica gel
Diatomaceous earth
Basalt
Bog iron (i.e., moist ferric hydroxide)
Q.42
Number of macrocomponents present in coal according to Stopes are
Four
Five
Six
Two
Q.43
Calorific value of
Light paraffinic fuel oils is equal to that of equivalent olefins
N-paraffin is lower than that of iso-paraffins of the same compounds
Light paraffinic fuel oils is higher than that of equivalent olefins
Light paraffinic fuel oils is lower than that of equivalent olefins
Q.44
Beehive coke oven
Facilitates by-products recovery
Takes 2-3 days for coking of coal but requires no external fuel for heating
Gives larger yield of coke (around 85%) as compared to by-product ovens
Produces coke with very poor strength
Q.45
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.
< 37%
>71%
In between 37 & 71%
None of these
Q.46
A sooty flame can be made non-luminous by
Admitting more gas
Shutting gas supply
Admitting more air
Shutting air supply
Q.47
The maximum adiabatic flame temperature in air is __________ the maximum flame temperature in pure oxygen.
Lower than
Higher than
Same as
Not related to
Q.48
Caking index of the coal blend used for the manufacture of metallurgical coke should be around
5
21
40
48
Q.49
Height of coke oven is limited (say maximum upto 7 metres) mainly by the
Problem of uniform heating along its height
Structural strength of silica bricks
Problem in door cleaning
Buckling of ram of pusher car at the time of coke pushing
Q.50
Fusion point of coal ash increases with increase in its __________ content.
Iron sulphate
Iron silicate
Lime and magnesia
All of the above
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