1.Fire tube boilers are safer than water tube boilers.
a) True
b) False
Explanation: In event of sudden and major tube failure steam explosion may occur in furnace of fire tube boiler due to rush of high pressure water into hot combustion chamber. Water tube boiler does not contain such tubular heating surfaces so no such problem arises there.
2. Which of the following material is not used in the boiler furnace walls?
a) Fire clay
b) Concrete
c) Silica
d) Kaolin
Explanation: Fire clay, Silica and Kaolin have property of resisting change in shape, weight or physical property at higher temperature. Concrete have no such properties at higher temperature so it is not suitable for that. The construction of boiler furnace varies from plain refractory walls to completely water cooled walls depending upon the characteristics of fuel used and firing methods.
3. Which of the following statement about economiser of steam power plant is wrong?
a) Economiser increases the Boiler Efficiency about 5 to 15%
b) It uses the heat of flue gases used by boiler going to the chimney.
c) Economiser increases the temperature of intake air
d) It require regular maintenance and cleaning
Explanation: Economiser is used to rise the temperature of feed water. Air preheater is used to raise the temperature of intake air. Flue gases after heating boiler water Still possesses sufficient heat energy which if not used will waste. Economiser and air preheater uses that heat energy to work and hence increase the thermal efficiency of power plant about 15%.
4. Which of the following are the most widely used condensers in modern thermal power plants?
a) Surface condensers
b) Low level counter flow type jet condenser
c) High level counter flow type jet condenser
d) Parallel flow type jet condenser
Explanation: Power plants mostly use surface condensers because from these condensers condensate can be used as feed water requiring less pumping power. In case of jet condensers exhaust steam mixes with the cooling water hence condenses and cooling water are mixed so condensing cannot be recovered for the use of feed water.
5. Read the following statements about feed water heaters
I. Open or contact heaters are also called Deaerator.
II. Open or contact heaters constructed to remove non-condensable gases from feed water.
a) Only statement I. is correct
b) Only statement II. is correct
c) I. and II. are correct
d) I. and II. are wrong
Explanation: Dissolved gases can cause corrosion inside the boiler so they must be removed from feed water. Feed water heaters are used to heat the feed water by means of bled steam before it is supplied to the boiler. The amount of non-condensable gases decreases with increase in temperature of water in open heaters hence called Deaerator.
6. Which of the following is a part of air and fuel gas circuit?
a) Condenser
b) Economiser
c) Air preheater
c) Cooling tower
Explanation: In air and fuel gas circuit air is drawn from the atmosphere by a forced draught fan or induced draught fan through the air preheater. In air preheater that air is heated by the heat of flue gases passing to the chimney and then admitted to the furnaces. Cooling tower and Condenser are parts of Cooling water circuit and Economiser is part of Feed water and steam circuit.
7. Which of the following is not a type of steam turbine?
a) Impulse turbine
b) Reaction turbine
c) Pelton wheel turbine
d) Axial flow type turbine
Explanation: Pelton wheel turbine is a water turbine. Impulse and reaction turbines are the steam turbines characterized by the action of steam on moving blades. Axial and radial flow turbine and steam turbines are characterized by type of flow of steam over blades
8. Which statement about impulse turbine is true?
a) Steam expands over blades
b) Steam expends completely in stationary nozzels
c) Steam expends partially over nozzle and turbine blades
d) Steam expends over blades incompletely
Explanation: In an impulse turbine the steam expands completely in the stationary nozzles. No pressure drop occurs over the moving Blade Runner. During expansion steam attains a high velocity and impinges against the blades fixed on the rotor Periphery resulting in the impulsive force on the moving blades which sets the rotor rotating
9. Which statement about reaction turbine is false?
a) Steam does not expand in nozzle
b) Blades acts like nozzles
c) Steam expands as flows over the rotor blades
d) Steam continuously losses its heat as flows over the rotor blades
Explanation: The expansion of steam in reaction turbine totally occurs when it flows over the turbine blades. The expansion of steam as it flows over the blades is adiabatic any friction losses between the steam and the blades are converted into heat which in turn will reheat the steam.
10. Reaction turbines are characterized by ___________
a) relatively low RPM and steam expension over nozzle
b) relatively high RPM and steam expension over nozzle
c) relatively low RPM and steam expension over rotor blades
d) relatively high RPM and steam expansion over rotor blades
Explanation: In reaction turbine steam does not expand in nozzle but expands as flows over the rotor blades. Reaction turbines are characterized by relatively low RPM. As steam expands over the turbine blades, causes the reaction force over the turbine which rotates the turbine.