The questionnaire is based on the typical questions on Boiler Draft In a Thermal Power Station boiler. There are around 48 questions based on the subject. All questions are objective type questions.

1. BOILER DRAFT, AIR PREHEATERS & FLUE GAS
CLEANING SYSTEM
BOILER DRAFT & DRAFT CONTROL
Q. 1. What is Boiler Draught?
Ans. Draft is defined as the difference between atmospheric pressure and the static pressure
of combustion gases in a furnace, gas passage, flue or stack.
Q.2. How Natural Draft is produced?
Ans. A stack of sufficient height to cause the necessary pressure differential, creates natural
draft with the resulting air and flue gas flows.
Q.3. What are the types of Mechanical Draft created by fans?
Ans. Mechanical draft created by fans is of three types; a) Forced Draft, b) Induced Draft and c)
Balanced Draft.
Q.4. Natural draft depends on the temperature of Hot Gasses in the stack True / False.
Q.5. If the Stack height is increased, it will produce more draft. True/ False.
Q.6. In the forced draft system, the entire furnace casing is under a positive pressure. True/
False
Q.7. In the Induced Draft system the entire boiler is under negative pressure. True/ False
Q.8. The capacity of the ID Fan in case of Induced draft system will be more than the FD Fan
used for Forced Draft System. True/ False.
Q.9. In the Balanced Draft system maximum negative pressure is at the suction of ID Fan. True/
False.
Q.10. The Draft measurements at various points in the Boiler casing can reflect the cleanliness
of the boiler. True/ False
Q.11. Forced Draft Fan controls the Furnace pressure in the Balanced Draft System. True /
False. (Induced Draft fan controls the Furnace Pressure).
Q.12. Forced Draft Fan controls the combustion air supplied to the Boiler. True/ False.

2. Q.13. The air supplied for the purpose of conveying the coal/fuel to the boiler furnace is known
as Secondary air. True / False (It is the primary air which is used for conveying the coal to the
furnace)
Q.14. The primary and secondary air is heated in the Airheater before it is supplied for the
purpose. True/ False
Q.15. The purpose of supplying Primary air to the mill is to remove the surface moisture in the
raw coal and then to convey the pulverized coal to the boiler furnace. True/ False.
Q.16. Forced Draft Fans suction is from, a) atmosphere, b) Furnace, c) Airheater.
Q.17. Induced Draft Fan suction is from, a) Furnace, b) Airheater, c) ESP, d) Chimney.
Q.18. The secondary air heated in the Air Preheater is admitted, a) in the furnace windbox, b)
In ESP, c) in the chimney.
Q.18. The hot primary Air from the air Preheater is supplied to, a) the Furnace, b) The ESP, c)
Pulveriser.
Q.19. The tuning of secondary air is done by controlling the a) Suction Dampers, b) Blade pitch
control, c) guide vanes of the Forced Draft Fan.
Q.20. The air preheater bypass to avoid the corrosion of the cold end of the APH, is provided in
a) Flue gas path, b) Primary air path, c) the secondary air path.
Q.21. The air for cooling the scanners is provided by Scanner Fans from, a) FD Fan discharge, b)
PA Fan discharge, c) ID Fan Discharge.
Q.22. The Secondary air from the windbox enters into the furnace from the a) Secondary air
Dampers, b) Through the mill, c) Through the coal pipes.
Q.23. The Primary Air Fans in the 270 MW BHEL Boilers handle, a) Cold Air, b) Hot Air, c) Flue
gas.
Q.24. The PA supplied to the mill is a) a mixture of Hot and Cold air, b) only Hot air, c) Cold air.
Q.25. The Function of the Primary air is a) for drying of fuel, b) for transport of pulverized coal
from mill to furnace, c) both the above a and b.
Q.26. The Primary air demand is related to a) Boiler Load demand, b) ensure and maintain
Sufficient velocity of pulverized fuel, c) Both the above.
Q.27. The Furnace pressure is controlled by a) ID Fan b) FD Fan c) PA Fans.

3. Q.28. The air preheaters improve the Boiler Efficiency because; a) Flue gas temperature is
increased, b) The combustion air temperature is increased, c) ESP performance improves.
Q.29. The Air preheaters heat the combustion air with heat recovered from a) Waste steam, b)
Hot Flue gases, c) Turbine steam.
Q.30. The Air preheaters are a) Heat Excahagers, 2) Fans, c) Turbines.
Q.31. In the trisector Air Heater there is always some leakage from a) Air to Flue gas, b) Flue
gas to air, c) There is no leakage.
Q.32. The amount of Air leakage in the Rotating Air heaters is a) more, b) less than the Tubular
type air preheaters.
Q.33. The thrust bearing of the rotating trisector air preheater is located at the a) Top of the Air
heater, b) in the centre of the Airheater, c) at the lower end of the shaft.
Q.34. To avoid uneven thermal expansion and contraction resulting in damage to the rotating
wheel, a) The rotation must be started before starting the steam generator b) the rotation
may be started after boiler lightup, c) should be kept in rotation for some time after the steam
generator is shut down.
Q.35 With the addition of SO3 in the flue gas the Acid Dew Point a) Increases, b) Decreases, c)
has no effect.
Q.36. Erosion problems in Air Heater arise because of a) Fly ash in Flue gas, b) Temperature of
flue gas, c) Sulphur oxides in flue gas.
Q.37. Corrosion at the cold end of the airheater is due to a) Nitrogen in flue gas, b) Sulphur
oxides in Flue gas, c) Oxygen in Flue gas.
Q.38. The Fly Ash in pulverized fuel boilers is a) 80% of total ash, b) 20% of total ash, c) 50% of
total ash.
Q.39. The ash particles will settle down if the flue gas velocity is a) suddenly reduced, b)
Suddenly increased, c) no effect on change in velocity.
Q.40. What are the stages involved in Flue gas Cleaning?
Ans:- Three stages are involved in the process of Flue gas cleaning. A) Ash particle separation,
b) Collection of Ash Particles in the hopper and c) Handling of Ash so collected.
Q.41. State the three stages involved in the Electrostatic Precipitation Process?

4. Ans.:- Following are the stages involved in the precipitation process. A) Particle Charging, b)
Particle migration to collecting plates and c) Particle removal from the collecting
plates/electrodes
Q.42. Particle resistivity is an influencing factor for ESP Efficiency. True / False.
Q.43. The collecting Electrodes in the ESP are a) Rods, b) Plates, c) Screens.
Q.43. The emitting / Discharge electrodes are a) Plates, b) Spiral wires, c) Insulators.
Q.44. Rapping of the collecting and emitting electrodes is done to a) dislodge the ash from the
electrodes, b) to separate the ash from the flue gas, c) to take the ash to the ash handling
system.
Q.45. Resistivity of the fly ash can be reduced by conditioning by SO3, True / False.
Q.46. Excessive fouling of Discharge Electrodes will result in Low Precipitator Current. True /
False.
Q.47. Excessive fouling of Collecting Electrodes will result in Low Precipitator Voltage. True /
False.
Q.48. The gas to cloth ratio in the design of Febric Filter is expressed as face velocity in a)
m/sec, b) m2
, c) m3
.
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