This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Pulverised Fuel Handling”.
1. Why do large power plants use pulverized fuel firing system?
a) Higher thermal efficiency
b) Uses high grade coal
c) Less smoke formation
d) Troubles created in this system are less
Explanation: Most of the large power plants use pulverized fuel firing system since it is higher in its thermal efficiency. And selection of it mainly depends upon the size of boiler unit, type of the coal available, nature of load on the plant, load factor, cost of the fuel and availability of skilled labors.
2. How is the fuel selected in the pulverized fuel system?
a) Depending on its size
b) Depending on its grade
c) Depending on volatile matter content
d) Depending the chemical composition
Explanation: In pulverized fuel firing system, coal with 20% volatile matter is considered as the best fuel for the plant, as high volatile coals are harder to grind when compared to low volatile coals. In stoker firing, the characteristics of the coal plays very important role in selection of coal.
3. What is the advantage of using pulverized fuel firing system?
a) Decreases maintenance of plant
b) Less wastage of the products
c) Less ash formation
d) No formation of clinkers
Explanation: The use of pulverized system increases the capital of and operating costs, but decreases maintenance of the plant and increases thermal efficiency. The pulverizer used to grind the coal should consume less power and should deliver the rated tonnage of coal.
4. What is unit pulverizer system also called?
a) Burner and pulverizer firing system
b) Central system firing system
c) Bin system firing system
d) Direct firing system
Explanation: The unit system is also called as the direct firing system. Most of the power plants with pulverized coal as the fuel are being installed with unit pulverizer. In this system each burner or a group of burner and pulverizer constitute a unit. The over head bunker supplies raw coal by gravity into a feeder where it is dried with the help of hot air.
5. On which factor is the coal fed to the pulverizing mill in pulverized fuel firing system?
a) Steam generating rate
b) Capacity of intake of coal
c) On the rate of speed of the feeder
d) Depending on the temperature that is governed inside the combustion chamber
Explanation: The feeder supplies coal too the pulverizing mill after drying coal in hot air. It is supplied at a variable rate governed by the combustion requirements of furnace and steam generating rate. In the pulverizing mill the coal is crushed to the required size (fine powder).
6. Which type of draught system is used in the pulverized fuel firing system?
a) Forced draught
b) Balanced draught
c) Induced draught
d) Natural draught
Explanation: Induced draught system is used in pulverized fuel firing system. The primary air from the Induced draught fan carries pulverized coal from the mill to the burner through short delivery pipe. In the separator, the big coal particles are separated from the fine dust these again fall down into the mill.
7. Which system was used before direct firing system in pulverized fuel firing?
a) Unit system
b) Burner and pulverizer system
c) Bin system
Explanation: Bin system was widely used before pulverizing equipment became reliable enough for continuous steady operation. This system employs a limited number of large capacity pulverizes at a central point to prepare coal for all the burners.
8. Why is direct firing system considered better than bin system in pulverizer fuel firing?
a) It has long operating procedure
b) The auxiliaries used in system consume large amount of power
c) The initial cost of system is very high
d) The transportation of coal is much more complex
Explanation: The bin system involves many stages of drying, storing and transportation and hence the process takes extra amount of time & chances of fire hazards are more. Never the less, it is still in use at many older plants.
9. Which separator is used to separate the pulverized coal in pulverized fuel firing?
a) Central inlet separator
b) Magnetic separator
c) Cyclone separator
d) Inertial separator
Explanation: Cyclones are mostly used for removing industrial dust from air or process gases. They are the principal type of gas-solid separator. The particulate is made to spin rapidly, heavier particle settle down and all the dust is removed out from the ducts. To also remove dust from the pulverized coal cyclone separator are used.
10. What is used to remove moisture air after cyclone separation in the pulverized fuel system?
a) Sponge pad
b) Dry filters
c) Fabric bag
d) Hot air
Explanation: A fabric bag filter is used to separate and exhaust the moisture air to the atmosphere and discharge the pulverized coal to storage bins, through the conveyor. This system uses all the equipment as used in unit system with higher capacity of each part. In addition to that the system also uses storage bins.
11. In what manner is the coal is fed to all the burners in pulverized fuel system?
a) Through a common feeder
b) Parallel feeding
c) From separate feeder
d) Series mesh feeding
Explanation: The pulverized coal is fed to the various burners through separate feeders. The bin may contain coal required for 12 to 24 hours of supply. The quantities of fuel and air can be regulated accurately and separately. This leads greater degree of flexibility.
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