Coal Mill Coal Mill Objective Questions and Answers

Coal Mill Objective Questions and Answers

Coal Mill or Pulverised mill MCQ

1. What is the pulverization capacity of the ball mill?

a) 10 tons of coal per hour

b) 20 tons of coal per hour

c) 50 tons of coal per hour

d) 80 tons of coal per hour

Answer: 10 tons of coal per hour

2. What is done when there is requirement for more coal in the ball and race mill?

a) The primary air flow is increased

b) The combustion intensity is reduced

c) The secondary air flow sucks out the light coal particles

d) The hopper is fully opened

Answer: The primary air flow is increased

3. On what basis is selection of bowl mill is not done?

a) Total moisture content of coal

b) Volatile matter

c) Ash producing capacity

d) Grindability

Answer: Ash producing capacity

4. What is the purpose of rotary scoop shaped rejecter arms in impact mill?

a) To send back the coal back into grinder for second run

b) To throw the large particles back into the grinder

c) To eliminate ash from the pulverizer

d) To eliminate rocks and solid particles that has mixed up with the coal

Answer: To throw the large particles back into the grinder

5. Why pre-heater air and the tempered air are introduced in the pulverizer of ball mill?

a) To carry the ash out

b) To increase the combustion rate

c) To carry pulverized coal

d) To dry the coal by removing the moisture

Answer: To carry pulverized coal

6. The output of the mill can be controlled by the _________ located in the exhaust fan inlet duct.

a) Dampers

b) Blowers

c) Air duct

d) Ventilator’s

Answer: Dampers

7. Why ball and race mill is also called as contact mill?

a) Because of rolling action between the balls and races

b) Because of ramming action between balls and races

c) Because of swirling action of balls and races

d) Because of mixture of balls and races

Answer: Because of rolling action between the balls and races

8. What is the main disadvantage of race and ball mill pulverizer?

a) Mill requires extra floor area

b) It is directly connected to the motor

c) High power consumption

d) Greater wear

Answer: Greater wear

9. What type of feeder is used to supply the coal in ball and race mill?

a) Ring main feeder

b) Parallel feeder

c) Radial feeder

d) Rotating table feeder

Answer: Rotating table feeder

10. What is the purpose of fixed vanes in the ball and race mill?

a) Forms a cyclonic flow

b) For easy movement of the coal

c) For directing the airflow

d) For barring the exhaust air to enter back into mill

Answer: Forms a cyclonic flow

11. What is not the cause of mill fire?

a) Hot startup with normal load

b) Pyrite building from pyrite plows failure

c) Accumulation of coal dust in mill devices

d) Localized hot spots from poor primary air flow

Answer: Hot startup with normal load

12. How is pulverization done in bowl mill?

a) By bowl and steel balls

b) By bowl and roller

c) By bowl and impact hammer

d) By bowl and batan

Answer: By bowl and roller

13. Why are heavy impurities provided in the process of ball and race mill?

a) To resist upward thrust caused by secondary air stream

b) To resist downward thrust caused by primary air stream

c) To resist upward thrust caused by primary air stream

d) To resist downward thrust caused by secondary air stream

Answer: To resist upward thrust caused by primary air stream

14. What happens due to the pressure in the pulverizer?

a) Pulverized fuel is blown into boiler room

b) Increases the rate of combustion

c) Makes the process is vigorous

d) The large particles in the pulverized fuels are removed out

Answer: Pulverized fuel is blown into boiler room

15. In which mill is the pulverization of coal is made by the impact?

a) Hammer mill

b) Bowl mill

c) Ball mill

d) Ball and race mill

Answer: Hammer mill

16. How is coal pulverized in the ball mill?

a) By rotating the cylinder

b) By rolling the cylinder

c) By hammering the cylinder

d) By jolting the cylinder

Answer: By rotating the cylinder

17. What does the primary air that is induced by draught does in a bowl mill?

a) Blows away ash

b) Control the flow of coal

c) Provides air for the combustion

d) Draws heated air

Answer: Draws heated air

18. What is done in the primary stage of the grinding in impact mill?

a) Coal is reduced to fine granular state

b) Coal is broken down in medium pieces

c) Coal is dried up to remove the moisture content

d) Coal is mixed up with the other state of fuel to improve the combustion efficiency

Answer: Coal is reduced to fine granular state

19. Which force is used to throw away the heavy particles in the bowl mill?

a) Gravity force

b) Centrifugal force

c) Centripetal force

d) Spring force

Answer: Centrifugal force

20. Feeder output in cylinder of a ball mill is regulated on the basis of?

a) Cylinder capacity

b) No of balls

c) Level of coal

d) Rotation speed of cylinder

Answer: Level of coal

21. The pulverization is completed by a combination of crushing impact and _______ between grinding surfaces.

a) Accretion

b) Erosion

c) Attrition

d) Dissolution

Answer: Attrition

22. Which type of fan is used in the ball and race mill?

a) Forced draught fan

b) Balanced draught fan

c) Artificial draught fan

d) Natural draught fan

Answer: Forced draught fan

23. The output of the mill can be controlled by the Dampers located in the exhaust fan inlet duct

a) true

b) False

Answer: true

24. Ball and race mill is also called as contact mill Because of swirling action of balls and races

a) true

b) False

Answer: False

25. Pyrite building from pyrite plows failure is not the cause of mill fire

a) true

b) False

Answer: False