Fuels and Combustion Questions and Answers

Multiple Choice Questions and Answers on Fuels and Combustion

Question 1 : When incomplete combustion loss is high, the flue gas analysis shows large amount of

  1. CO2
  2. CO
  3. O2
  4. C

Answer : 2

Question 2 : The gas which contributes maximum to the heating value of natural gas is

  1. CO
  2. CO2
  3. H2
  4. CH4

Answer : 4

Question 3 : The temperature at which plastic layer formation takes place during carbonisation of coal varies from __________ °C.

  1. 100 to 150
  2. 350 to 450
  3. 550 to 650
  4. 700 to 850

Answer : 2

Question 4 : Yield of coke oven gas in low temperature carbonisation of coal is about __________ Nm3 /ton of dry coal.

  1. 60
  2. 160
  3. 500
  4. 750

Answer : 2

Question 5 : 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

  1. requirement of large volume combustion chamber.
  2. risk of explosion.
  3. chances of clinker formation.
  4. incomplete combustion of coal.

Answer : 2

Question 6 : Adiabatic flame temperature of a fuel is dependent on the initial temperature of

  1. fuel
  2. air
  3. both (1) & (2)
  4. neither (1) nor (2)

Answer : 3

Question 7 : Which of the following gaseous fuels has the lowest calorific value ?

  1. Gobar gas
  2. Refinery gas
  3. Converter gas
  4. Blast furnace gas

Answer : 4

Question 8 : Which of the following is not a by-product recovered in a high temperature coal carbonisation plant ?

  1. Benzol
  2. Pitch-cresosote mixture (PCM)
  3. Napthalene
  4. Ethylene

Answer : 4

Question 9 : Pensky-Marten apparatus is used for those oils, whose flash points are __________ °F.

  1. <120
  2. >120
  3. <90
  4. 90-110

Answer : 2

Question 10 : In high temperature carbonisation of coal compared to low temperature carbonisation

  1. yield of ammonia is less
  2. aromatic content of tar is low.
  3. H2 content in the coke oven gas is more.
  4. calorific value of the coke oven gas is lower.

Answer : 3

Question 11 : Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because

  1. the hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot.
  2. it reduces its calorific value tremendously.
  3. it reduces its flame temperature tremendously.
  4. there are chances of explosion during preheating.

Answer : 1

Question 12 : Which of the following is the most reactive (as regards the formation of CO + H2 from C + H2O) ?

  1. Blast furnace coke
  2. Low temperature coke
  3. Anthracite coal
  4. Sub-bituminous coal

Answer : 2

Question 13 : Calorific value of coal middling generated in coal washeries during washing of coal may be around __________ Kcal/kg.

  1. 1000
  2. 4000
  3. 6000
  4. 8000

Answer : 2

Question 14 : Flue gas discharge velocity through chimney of a big thermal power plant may be around __________ m/sec.

  1. 0.5
  2. 10
  3. 50
  4. 500

Answer : 2

Question 15 : Which of the following is used for making the explosive ‘TNT’ ?

  1. Benzol
  2. Toluene
  3. Pyridine
  4. Cerosote

Answer : 2

Question 16 : Gray King Assay and Swelling Index of a coal is a measure of its

  1. swelling characteristics.
  2. abradability.
  3. agglutinating properties.
  4. resistance to impact breakage.

Answer : 1

Question 17 : 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.

  1. < 37%
  2. >71%
  3. in between 37 & 71%
  4. none of these

Answer : 3

Question 18 : Prime coking coal is always blended with medium or non- coking coal before ear-bonisation

  1. to check against its excessive swelling during heating, which may exert high pressure and damage coke oven walls.
  2. because, it alone produces unreactive coke.
  3. both (1) and (2).
  4. neither (1) nor (2).

Answer : 3

Question 19 : Actual flame temperature is always lower than the adiabatic flame temperature, because there is

  1. no possibility of obtaining complete combustion at high temperature.
  2. always loss of heat from the flame.
  3. both (1) and (2).
  4. neither (1) nor (2).

Answer : 3

Question 20 : Coke oven gas consists mainly of

  1. H2, & CH4
  2. CO, & CO2
  3. H2, & CO
  4. CH4, & CO

Answer : 1

Question 21 : Higher percentage of ash in coal meant for the production of metallurgical grade coke

  1. decreases the hardness of coke.
  2. decreases the abrasion resistance of coke.
  3. causes brittleness in steel.
  4. none of these.

Answer : 4

Question 22 : Combustion of pulverised coal as compared to that of lump coal

  1. develops a non-luminous flame.
  2. develops a low temperature flame.
  3. can be done with less excess air.
  4. provides a lower rate of heat release.

Answer : 3

Question 23 : “Wobbe index’ is a characteristic of

  1. solid fuels
  2. gaseous fuels
  3. liquid fuels
  4. fat coals

Answer : 2

Question 24 : A coal with high ash content is undesirable, as

  1. it is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber.
  2. 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.
  3. 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.
  4. all (1), (2) and (3).

Answer : 4

Question 25 : Presence of free moisture in coal during its high temperature carbonisation

  1. reduces the coking time.
  2. protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls.
  3. increases the loss of fine coal dust from the ovens when charging.
  4. none of these.

Answer : 2

Question 26 : A coal having high amount of volatile matter

  1. would require smaller combustion chamber.
  2. produces very little of tar and gas on carbonisation.
  3. ignites easily and burns with long smoky flame.
  4. all (a), (b) and (c).

Answer : 4

Question 27 : Carbon Content by weight in air dried wood may be about __________ percent.

  1. 10
  2. 25
  3. 50
  4. 80

Answer : 3

Question 28 : Which of the following accentuates clinker-ing trouble on furnace grate burning coal ?

  1. Low reactivity of carbonised residue containing high proportions of iron & sulphur.
  2. Low forced draught and fuel bed temperature.
  3. Thick fire bed and preheated primary air.
  4. All (1), (2) and (3).

Answer : 4

Question 29 : Natural draught produced by a chimney depends upon the

  1. density of the chimney gases.
  2. height of the chimney.
  3. both (1) and (2).
  4. neither (1) nor (2).

Answer : 3

Question 30 : Gross & net calorific value is the same for

  1. blast furnace gas
  2. coke oven gas
  3. L.D. converter gas
  4. none of these

Answer : 3

Question 31 : Pick out the wrong statement.

  1. LPG is also used as fuel for automobiles & small furnaces and for cutting & welding of metals.
  2. The minimum temperature, at which a petroleum oil vapor catches fire and continues to burn, is called its flash point.
  3. Each ton of petroleum oil on distillation produces about 30-50 Nm3 of gas.
  4. Maximum yield of naphthalene is obtained on distillation of crude oil.

Answer : 2

Question 32 : Stack heat losses can be minimised by

  1. controlling the excess air.
  2. oxygen enrichment of combustion air.
  3. using low c.v. fuels.
  4. maintaining proper draft in the furnace.

Answer : 1

Question 33 : Laboratory gas is obtained by the cracking of

  1. gasoline
  2. diesel
  3. fuel oil
  4. kerosene

Answer : 4

Question 34 : Bituminous coal

  1. ignites less easily than anthracite.
  2. is generally coking.
  3. burns with smoky yellow flame.
  4. both (2) and (3).

Answer : 4

Question 35 : Ratio of primary air to secondary air increases with increase in the rank of coal, because the

  1. high rank coals have higher amount of volatile matter.
  2. ratio of fixed carbon to volatile matter increases.
  3. oxygen content progressively decreases.
  4. calorific value of the coal increases.

Answer : 2

Question 36 : Junker’s calorimeter is used to determine the calorific value of

  1. pulverised coal
  2. gaseous fuels
  3. fuel oil
  4. none of these

Answer : 2

Question 37 : Combustion reaction of fuels is a/an __________ reaction.

  1. auto catalytic
  2. exothermic
  3. endothermic
  4. none of these

Answer : 2

Question 38 : Improper storage condition results in the weathering of coal and spontaneous combustion, which increases its

  1. caking index.
  2. yield of carbonised products.
  3. friability & oxygen content.
  4. calorific value.

Answer : 3

Question 39 : Which of the following constituents of coal is the most important in the production of coke?

  1. Moisture
  2. Ash
  3. Volatiles
  4. Carbon

Answer : 4

Question 40 : High temperature in gasification of coal favours

  1. high production of CO2.
  2. low production of CO2.
  3. high production of CO.
  4. both (2) and (3).

Answer : 4

Question 41 : Which of the following is not used as a binder in coal briquetting ?

  1. Tar
  2. Molasses
  3. Pitch
  4. Line

Answer : 4

Question 42 : Size of blast furnace grade coke is __________ mm.

  1. 25-80
  2. 0-15
  3. 15-25
  4. >100

Answer : 1

Question 43 : Presence of __________ in a dry gaseous fuel does not contribute to its calorific value.

  1. sulphur
  2. oxygen
  3. hydrogen
  4. carbon

Answer : 2

Question 44 : The internal energy of the combustion products is __________ compared to that of reactants.

  1. more
  2. less
  3. equal
  4. more or less ; (depends on the state of fuel.)

Answer : 2

Question 45 : Which of the following is not a product of tar distillation ?

  1. Phenol & naphthalene
  2. Benzol & pitch
  3. Anthracene & creosote
  4. None of these

Answer : 4

Question 46 : Higher efficiency in the combustion of solid fuel can not be achieved by

  1. proper fuel preparation.
  2. keeping the flue gas exhaust temperature very high.
  3. adopting efficient-fuel firing technique & equipment.
  4. supplying correct quantity of combustion air.

Answer : 2

Question 47 : A coal containing very high percentage of durain is called __________ coal.

  1. bright
  2. splint
  3. non-banded
  4. boghead

Answer : 2

Question 48 : During combustion of gaseous fuels, deficiency of air

  1. lengthens the flame.
  2. tends to shorten the flame.
  3. does not affect the flame length.
  4. increases the flame temperature.

Answer : 1

Question 49 : Gross and net calorific value of a fuel will be the same

  1. if its ash content is zero.
  2. ifits carbon content is very low.
  3. if its hydrogen/hydrogen compound content is zero.
  4. under no circumstances.

Answer : 3

Question 50 : Low temperature carbonisation

  1. is mainly for producing the smokeless domestic coke.
  2. is meant for the production of ‘metallurgical coke’.
  3. produces higher quantity of gas than high temperature carbonisation.
  4. produces less quantity of tar than high temperature carbonisation.

Answer : 1