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___________________?

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. 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

3. The main function of primary air in pulverised coal fired burner is to_________________?

   A. Burn CO to CO2
   B. Dry and transport the coal
   C. Have proper combustion by supplying it around the burner
   D. Preheat the tertiary air used for complete combustion of CO to CO2

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

   A. Scale losses of the furnace stock
   B. Calorific value of the fuel
   C. Flame temperature
   D. None of these

5. Use of pulverised coal in boiler furnace provides___________________?

   A. High calorific value
   B. Better combustion
   C. Smokeless burning
   D. Less erosion on furnace walls

6. In case of pulverised coal fired steam boiler, the secondary air serves the main purpose of__________________?

   A. Transportation of coal
   B. Drying of coal
   C. Combustion of coal by supplying it around the burner
   D. Preheating the primary air

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. Bunsen burner is an example of a/an _____________ burner?

   A. Inside mixing/premix type
   B. Outside mixing/diffusion flame/nozzle mix type
   C. Rotary cup
   D. Submerged combustion

9. 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

10. Which of the following will be unsuitable for dust cleaning from flue gas at 400°C from a pulverised coal fired boiler ?

    A. Multicyclones
    B. Bag filter
    C. Wet scrubber
    D. Hydrocyclones