141. Spontaneous combustion is a phenomenon in which
A.All the fuel bums instantaneously producing high energy release
B.Fuel bums with less air
C.Coal bursts into flame without any external ignition source but by itself due to gradual increase in temperature as a result of heat released by combination of oxygen with coal
D.Explosion in furnace
142. The economiser is used in boilers to
A.Increase thermal efficiency of boiler
B.Economise on fuel
C.Extract heat from the exhaust flue gases
D.Increase flue gas temperature
143. An economiser in a boiler
A.Increases steam pressure
B.Increases steam flow
C.Decreases fuel consumption
D.Decreases steam pressure
144. 02 confent in atmospheric air on volume basis is
A.0.21
B.0.23
C.(d) 30%
D.0.4
145. 02 content in atmospheric air on weight basis is
A.0.21
B.0.23
C.0.3
D.0.4
146. Primary air is the air used to
A.Provide air around burners for obtaining optimum combustion
B.Transport and dry the coal
C.Convert CO (formed in lower zone of furnace) into CO2 at higher zone
D.Air-delivered by forced draft fan
147. Sulphur content of fuels is very important to the plant operators because it
A.Has high heating value
B.Retards electric precipitation
C.Promotes complete combustion
D.Has highly corrosive effect
Page 21 of 81