Combustion Mechanism, Equipment & Firing Methods ( Power Plant Engineering ) MCQs – Mechanical Engineering MCQs
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Mechanical Engineering MCQs – Combustion Mechanism, Equipment & Firing Methods ( Power Plant Engineering ) MCQs
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Pulverisation and Gasifiers
1. Temperature of preheated air used for the transportation of pulverised coal through pipes to the burner of a boiler furnace is restricted to a maximum limit of about 300° C to avoid the __________
a) requirement of large volume of combustion chamber
b) incomplete combustion of coal
c) risk of explosion
d) chances of clinker formation
Answer: c
Explanation: Temperature of preheated air used for the transportation of pulverised coal through pipes to the burner of a boiler furnace is restricted to a maximum limit of about 300° C to avoid the risk of explosion owing to the reacting mixture.
2. The temperature at which plastic layer formation takes place during carbonisation of coal varies from __________ °C.
a) 100-150
b) 350-450
c) 700-850
d) 550-650
Answer: b
Explanation: The temperature at which plastic layer formation takes place during carbonisation of coal varies from 350 to 450 °C.
3. Which of the following is not a by-product recovered in a high temperature coal carbonisation plant?
a) Benzol
b) Ethylene
c) Pitch-cresosote mixture (PCM)
d) Naphthalene
Answer: b
Explanation: Apart from Ethylene all the others are by-products obtained in high temperature coal carbonisation plant.
4. Pick out the wrong statement.
a) Regulation of furnace temperature and atmosphere (oxidising or reducing) is easily possible with pulverised fuel firing
b) Low grade coal can be used, but generally high volatile matter coals are more suitable for making pulverised fuel
c) Pulverised fuel can be completely burnt with less percentage of excess air compared to lump coal
d) None of the mentioned
Answer: d
Explanation: All the mentioned statements are correct.
5. Flue gas discharge velocity through chimney of a big thermal power plant may be around __________ m/sec.
a) 0.5
b) 500
c) 10
d) 50
Answer: c
Explanation: Flue gas discharge velocity through chimney of a big thermal power plant may be around 10 m/sec.
6. Calorific value of coal middling generated in coal washeries during washing of coal may be around __________ Kcal/kg.
a) 1000
b) 4000
c) 6000
d) 8000
Answer: b
Explanation: Calorific value of coal middling generated in coal washeries during washing of coal may be around 4000 Kcal/kg.
7. Combustion of pulverised coal as compared to that of lump coal __________
a) develops a non-luminous flame
b) can be done with less excess air
c) develops a low temperature flame
d) provides a lower rate of heat release
Answer: b
Explanation: Combustion of pulverised coal as compared to that of lump coal can be done with less excess air.
8. The decrease in the atomic number is not observed in case of __________
a) alpha emission
b) beta emission
c) gamma emission
d) none of the mentioned
Answer: b
Explanation: There is no change in the atomic number as the number of electrons remains the same.
Kinetic and Diffusion Control – I
1. Which of these is the outer most coating in the burning of a coke particle?
a) Oxygen
b) Carbon monoxide
c) Carbon dioxide
d) Ash Layer
Answer: a
Explanation: Oxygen, being a supporter of combustion helps in combustion of coke particle and so forms a layer on the periphery of the coke particle.
2. Which law deals with the rate of diffusion of Oxygen per unit surface area of the particle?
a) Kirchhoff’s Law
b) Plank’s Law
c) Fourier’s Law
d) Fick’s Law
Answer: d
Explanation: Fick’s Law deals with the rate of diffusion of Oxygen per unit surface area of the particle.
3. If d is the diffusion coefficient and t is the boundary layer thickness. Then the mass transfer coefficient k is given by?
a) k = d x t
b) k = d / t
c) k = d + t
d) k = d – t
Answer: b
Explanation: If d is the diffusion coefficient and t is the boundary layer thickness. Then the mass transfer coefficient k is given by,
k = d / t.
4. Gobar gas is produced by the __________ of ‘gobar’ (cow dung).
a) Fermentation
b) Condensation
c) Combustion
d) Distillation
Answer: a
Explanation: Fermentation is the process which converts cow’s dung into ‘Gobar Gas’.
5. Coking time in beehive coke oven is about __________
a) one week
b) 12 hours
c) 2-3 days
d) 2 weeks
Answer: c
Explanation: The total time of coking in a beehive oven is about 2-3 days.
6. __________ present in coal is not determined in its ultimate analysis.
a) Fixed Carbon
b) Total Carbon
c) Nitrogen
d) Hydrogen
Answer: a
Explanation: Fixed Carbon present in coal is not determined in its ultimate analysis. It is determined by Proximate analysis of Coal.
7. The maximum adiabatic flame temperature is attained when the fuel is burnt with __________
a) theoretically required amount of air
b) less than theoretically required amount of air
c) more than theoretically required amount of air
d) theoretically required amount of oxygen
Answer: d
Explanation: The maximum adiabatic flame temperature is attained when the fuel is burnt with theoretically required amount of Oxygen.
8. Height of coke oven is limited (say maximum up to 7 metres) mainly by the __________
a) problem of uniform heating along its height.
b) structural strength of silica bricks
c) problem in door cleaning
d) buckling of ram of pusher car at the time of coke pushing
Answer: a
Explanation: Height of coke oven is limited (say maximum up to 7 metres) mainly by the problem of Uniform heating as the heat is distributed along the height.
9. Which of the following has the highest calorific value?
a) Sub-bituminous
b) Anthracite
c) Lignite
d) Peat
Answer: b
Explanation: Among the given varieties of coal, the highest calorific value is possessed by the one which has the maximum carbon content. Here, Anthracite has the maximum Calorific Value.
Kinetic and Diffusion Control – II
1. Higher fuel combustion efficiency cannot be achieved by __________
a) preheating of fuel gases & combustion air
b) supplying correct amount of combustion air
c) reducing sulphur content in the fuel
d) adopting proper fuel firing technique & fuel preparation
Answer: c
Explanation: Higher fuel combustion efficiency cannot be achieved by reducing the sulphur content in the fuel as sulphur content has nothing much to do with the combustion efficiency.
2. Particular coal is said to be free burning when it __________
a) gives smokeless burning
b) shows little or no fusing action
c) burns completely
d) none of the mentioned
Answer: b
Explanation: When a coal shows little or no fusing action, it is said to be free burning.
3. Bunsen burner is an example of a/an __________ burner.
a) inside mixing/premix type
b) submerged combustion
c) rotary cup
d) outside mixing/diffusion flame/nozzle mix type
Answer: a
Explanation: Bunsen burner is an example of a/an inside mixing/premix type burner.
4. The cooling medium used in dry quenching of coke is __________
a) nitrogen
b) air
c) phenolic water
d) carbon dioxide
Answer: a
Explanation: The cooling medium used in dry quenching of coke is nitrogen.
5. High amount of sulphur and phosphorous in coke causes __________
a) increase in its strength
b) decrease in its calorific value
c) brittleness of steel made by using it
d) none of the mentioned
Answer: c
Explanation: Steel is made brittle by the presence of high amount of sulphur and phosphorus in coke.
6. Cannel coal and boghead coal are the examples of __________
a) liptobiolites
b) humic coals
c) sapropelic coals
d) none of the mentioned
Answer: c
Explanation: Cannel coal and boghead coal are the examples of Sapropelic Coals. Sapropelic Coals are rich in microscopic organic matter derived from waxy or resinous plant parts and have high yields of volatile matter.
7. The difference between total carbon and fixed carbon of coal will be minimum in case of __________
a) anthracite
b) lignite
c) bituminous
d) high temperature coke (V.M < 0.5%)
Answer: d
Explanation: The difference between total carbon and fixed carbon of coal will be minimum in case of high temperature coke. The high temperature coke has low volatile matter that is the erason for the same.
Diesel Engine And Gas Turbines Power Plant MCQs
8. Out of the following fuels, the difference between the net and gross calorific value is maximum in case of __________
a) fuel oil
b) blast furnace gas
c) bituminous coal
d) pitch
Answer: a
Explanation: The difference between the net and gross calorific value is maximum in case of
Fuel Oil.
9. Which of the following is the maximum coal producing state in India?
a) Orissa
b) West Bengal
c) Jharkhand
d) Assam
Answer: c
Explanation: Jamshedpur has the highest production of coal in India.
10. A good quality coal should have __________
a) low fusion point of ash
b) high sulphur
c) high ash content
d) none of the mentioned
Answer: d
Explanation: A good quality coal should have high concentration of carbon, low moisture content, etc.
11. __________ prohibits the use of alcohols directly in petrol engines.
a) High cost & difficult availability
b) Low octane number
c) Low flash point
d) Low calorific value
Answer: a
Explanation: High cost & difficult availability prohibits the use of alcohols directly in petrol engines.
12. The hottest part of the flame lies in its ___________ zone.
a) non-luminous
b) luminous
c) yellow
d) unburnt gases
Answer: a
Explanation: The hottest part of the flame lies in its non-luminous zone.
13. Percentage of methane in coke oven gas may be around __________
a) 5
b) 15
c) 25
d) 35
Answer: c
Explanation: Percentage of methane in coke oven gas may be around 25%.
Coal Firing Systems – I
1. __________ of the coal is the basis for Seylor’s coal classification.
a) Proximate analysis
b) Calorific value
c) Ultimate analysis
d) Caking index
Answer: c
Explanation: Ultimate Analysis of the coal is the basis for Seylor’s coal classification.
2. Yield of pitch from distillation of high temperature tar is around __________ percent.
a) 10
b) 25
c) 65
d) 100
Answer: c
Explanation: Yield of pitch from distillation of high temperature tar is around 65 percent.
3. Caking index of the coal blend used for the manufacture of metallurgical coke should be around __________
a) 5
b) 40
c) 21
d) 48
Answer: c
Explanation: Caking index is the ability of coal to be formed into cakes. Caking index of the coal blend used for the manufacture of metallurgical coke should be around 21.
4. High excess air in combustion of fuels results in __________
a) smoky flame
b) increased fuel consumption
c) incomplete combustion
d) none of the mentioned
Answer: b
Explanation: High excess air in combustion of fuels results in increased fuel consumption. More the quantity of air in the fuel, more lean a mixture becomes.
5. The heat of combustion of a fuel __________
a) is equal to the heat of formation
b) is always negative
c) can’t be known without calculating it
d) is always positive
Answer: b
Explanation: The heat of combustion of a fuel is always negative as always some heat has to be given (supplied) to the fuel for burning it.
6. _________ has the widest inflammability limit (explosion limit) of all the gases.
a) Carbon monoxide
b) Methane
c) Hydrogen
d) Acetylene
Answer: d
Explanation: Acetylene has the widest inflammability limit (explosion limit) of all the gases. That is another factor due to which the gas is used in Gas welding.
7. What are the main constituents of benzol?
a) benzene, toluene & xylene
b) tar & creosote
c) ammonia & phenol
d) anthracene & phenol
Answer: a
Explanation: Benzol comprises of benzene, toluene and xylene.
8. With increase in moisture content of coal, its __________
a) calorific value increases sometimes
b) bulk density always decreases
c) clinkering tendency during combustion increases
d) none of the mentioned
Answer: d
Explanation: None of the mentioned factors behave in the manner when the moisture content increases.
9. Oxygen percentage (by weight) in atmospheric air is?
a) 22
b) 20
c) 19
d) 21
Answer: d
Explanation: 21 % of the atmospheric air is Oxygen.
10. In flue gas analysis by Orsat’s apparatus, carbon dioxide is absorbed by __________
a) cuporus chloride
b) dilute potassium carbonate
c) potassium hydroxide
d) alkaline pyragllol solution
Answer: c
Explanation: In flue gas analysis by Orsat’s apparatus, carbon dioxide is absorbed by potassium hydroxide.
Coal Firing Systems – II
1. Presence of free moisture in coal is most disadvantageous during __________
a) combustion of fire slacks on the grates
b) its pulverisation
c) handling (e.g. when emptying wagons)
d) none of the mentioned
Answer: b
Explanation: As pulverisation of coal is a power consuming process, the presence of free moisture in coal is most disadvantageous.
2. Abrasion index of blast furnace coke should be around __________ percent.
a) 20
b) 35
c) 80
d) 55
Answer: c
Explanation: Abrasion index of blast furnace coke should be around 80 percent. More this abrasion index, which is an indicator of Abrasion; more is the combustibility.
3. Which of the following petrographic constituents of coal is non-coking?
a) Durain
b) Vitrain
c) Clarain
d) Fussain
Answer: d
Explanation: Among the mentioned petrographic constituents, Fussain is non-coking.
4. ‘Fat’ coal means a coal having __________
a) low ash content
b) non-smoking tendency
c) high volatile matter
d) low calorific value
Answer: c
Explanation: ‘Fat’ coal means a coal having high volatile matter.
5. Initial pressure of oxygen introduced into the ‘bomb’ of the bomb calorimeter for determination of calorific value of coal/fuel oil may be around __________ atm.
a) 20-30
b) 60-65
c) 95-100
d) 3-5
Answer: a
Explanation: Initial pressure of oxygen introduced into the ‘bomb’ of the bomb calorimeter for determination of calorific value of coal/fuel oil may be around 20-30 atm.
6. Proximate analysis of coal determines its __________ content.
a) moisture, ash, sulphur & volatile matter
b) moisture, volatile matter, ash & fixed carbon
c) moisture, sulphur, nitrogen & fixed carbon
d) none of the mentioned
Answer: b
Explanation: Proximate analysis of coal determines its moisture, volatile matter, ash & fixed carbon content.
7. If the specific heat of gaseous products of combustion of a fuel is high, the abiabatic flame temperature will be?
a) very high, if the fuel is of low calorific value
b) low
c) high
d) none of the mentioned
Answer: b
Explanation: If the specific heat of gaseous products of combustion of a fuel is high, the abiabatic flame temperature will below.
8. “Overfire burning” in a furnace is a phenomenon characterised by the __________
a) burning of carbon monoxide and other incombustibles in upper zone of furnace by supplying more air
b) supply of excess fuel
c) supply of excess air
d) none of the mentioned
Answer: a
Explanation: “Overfire burning” in a furnace is a phenomenon characterised by the burning of carbon monoxide and other incombustibles in upper zone of furnace by supplying more air.
9. Atomising steam to fuel oil ratio in a burner should be around __________
a) 0.5
b) 1.5
c) 2.5
d) 3.5
Answer: a
Explanation: A low atomising fuel oil ratio is favourable enough to ensure good combustion.
10. Presence of free moisture in coal during its high temperature carbonisation __________
a) increases the loss of fine coal dust from the ovens when charging
b) protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls
c) reduces the coking time
d) none of the mentioned
Answer: b
Explanation: The presence of free moisture in coal during its high temperature carbonisation protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls.