This set of Energy Engineering Questions and Answers for Experienced people focuses on “Type of Stokers – 2”.
1. Where is the place at which the volatile matter and fine particles burnt in the spreader stoker?
a) Over the grate
b) In steam gauge
c) In the suspension
d) In the coal bed
Explanation: The air supplied by the forced draught fan enters the furnace through the openings provided in the grate. A portion of this air is used to burn the fuel on the grate and remaining air is utilized to burn the volatile matter and fine particles in suspension.
2. From where is the over fire or secondary air is supplied through in the sprinkler stoker?
a) Air duct
c) Air damper
Explanation: Over fire or secondary air is supplied through nozzle. The secondary air creates high turbulence and completes the combustion of volatile matter and fine particles of the coal. The unburnt coal and ash are deposited on the grate which should be removed periodically.
3. In which manner is the coal supplied from feeder to spreader in spreader stoker?
a) Feeding in alternate bulks
b) Feeding at regular intervals
c) Feeding in continuous stream
d) Feeding whenever necessary
Explanation: The feeder is a slow speed rotating drum on which large numbers of small blades are mounted. It supplies coal to the spreaders in continuous stream. The speed of the feeder can be adjusted as per the load on plant. The feeders are operated with variable speed drive to control the combustion as per the requirement. The feeders may be reciprocating ram, endless belt or spiral worm.
4. Why are the blades of shaft in spreader stoker twisted?
a) For supporting combustion by supplying more amount of air
b) To draw in large amount of coal
c) For uniform distribution of coal
d) To restrict the supply of coal
Explanation: Spreader consists of rapidly rotating shaft carrying blades. These blades are twisted to provide uniform distribution of the coal over the grate. The fast rotating blades hit the coal particles coming from the feeder and throw into the furnace. The distribution of coal over the grate depends on the rotating speed of the spreader and on the size of the coal.
5. How much capacity of heat is possible to produce by the travelling grate stoker?
a) 80 * 106 kJ/m2.hr
b) 40 * 106 kJ/m2.hr
c) 25 * 106 kJ/m2.hr
d) 65 * 106 kJ/m2.hr
Explanation: The spreader stoker has wide applications with respect to the fuels used as well as to the boiler sizes. A wide variety and poor quality coal can be burnt efficiently with this type of stoker. This type of stoker can be used for boiler capacities of 80 tons to 150 tons of steam per hour. The heat release rate of 80 * 106 kJ/m2 hr is possible with travelling grate.
6. Which mechanism is used to supply coal in the single retort stoker?
b) Chain bucket
c) Screw conveyor
d) Air blowers
Explanation: The fuel is placed in the large hopper on the front of the furnace. Then it is further fed by reciprocating ram or screw conveyor into the bottom of the horizontal trough. The ash formed after burning of coal is collected at other end.
7. What are provided for the supply of air in single retort stoker?
b) Air ducts
d) Air blowers
Explanation: The air is supplied through the tuyeres provided along the upper edge of the grate. The ash and clinkers are collected on the ash plate provided with dumping arrangement. The coal feeding capacity of a single retort stoker varies from 100 to 2000 kg per hour.
8. Which mechanism is used for the uniform distribution of the coal in multi retort stoker?
a) Reciprocating ram
c) Screw conveyor
d) Steam jet blowers
Explanation: the multi retort stoker consists of a series of alternate retorts and tuyere boxes for supply of air. Each retort is fitted with a reciprocating ram for feeding and pusher plates for the uniform distribution of coal. The coal falling from the hopper is pushed forward during the inward stroke ram.
9. The low pressure air entering into the extension grate is supplied to ______________ in the multi retort stoker.
a) At incandescent zone
b) Thinner fuel bed
c) At inlet dampers
d) At extension grate
Explanation: The primary air is supplied from the main wind box to the fuel bed situated below the stoker. The partly burnt coal moves on to the extension grate. The low pressure air entering into the extension grate, wind from main wind box is supplied to the thinner fuel bed on the extension grate. The quantity supplied can be regulated by air damper.
10. What is the reason for using forced draft in multi retort stoker?
a) Maintaining combustion for longer periods
b) Helps in blowing away the ash and clinkers
c) Causes rapid combustion
d) Maintains the intensity of fire
Explanation: Forced draught causes rapid combustion. It is also necessary to introduce ‘over fire’ when high volatile coals are used to prevent the smoke formation. Combustion control is introduced into the stoker drive either by varying the ram stoke or by changing the rate of reciprocation.
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