Use of preheated air for combustion of fuel in the furnace, increases the___________________?

Related Mcqs:

1. Furnace oil consumption in a furnace for a given duty employing preheated combination air (at 300°) may be reduced by about ______________ percent as compared to the use of atmospheric combustion air?

   A. 5
   B. 10
   C. 20
   D. 35

2. 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 combustion chamber
   B. Risk of explosion
   C. Chances of clinker formation
   D. Incomplete combustion of coal

3. Which of the following is not increased by using preheated combustion air in place of ordinary air at room temperature ?

   A. Calorific value of the fuel
   B. Flame temperature achieved
   C. Speed of combustion of fuel
   D. Heat transfer rate to the stock in the furnace

4. For the case of a fuel gas undergoing combustion with air, if the air/fuel ratio is increased, the adiabatic flame temperature will_____________________?

   A. Increase
   B. Decrease
   C. Increase or decrease depending on the fuel type
   D. Not change

5. 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?

   A. 70
   B. 85
   C. 105
   D. 145

6. As the C/H ratio of the fuel increases, the amount of CO2 formed on combustion _______________ for the same percentage of excess air?

   A. Decreases
   B. Increases
   C. Remain same
   D. May increase or decrease depending on the type of fuel

7. 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. 71%
   C. In between 37 & 71%
   D. None of these

8. Incomplete combustion of fuel in the furnace is judged by high _____________ of the flue gases?

   A. CO content
   B. Dew point
   C. CO2 content
   D. O2 content

9. Fuel gases containing hydrocarbons (e.g. coke oven gas) are not preheated before burning, mainly because __________________?

   A. The hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot
   B. It reduces its calorific value tremendously
   C. It reduces its flame temperature tremendously
   D. There are chances of explosion during preheating

10. Deficiency of combustion air during combustion of a gaseous fuel_____________________?

    A. Lengthens the flame
    B. Causes heat loss of fuel by its partial combustion
    C. Both A. & B.
    D. Shortens the flame