ANSWER KEY Power Plant Engineering Reviewer for Mechanical Engineer

Thermodynamics
 
1. In a Rankine cycle, what is the primary function of the condenser?
A. Convert heat energy into work
B. Increase the pressure of the steam
C. Reject waste heat and condense steam into liquid
D. Superheat the steam before entering the turbine
Answer: C
Explanation: The condenser removes waste heat and condenses exhaust steam into water, allowing it to be recirculated in the cycle.
 
2. What is the primary advantage of using a superheater in a steam power plant?
A. Reduces fuel consumption
B. Increases turbine efficiency by eliminating moisture
C. Increases condenser pressure
D. Reduces boiler maintenance
Answer: B
Explanation: A superheater increases steam temperature, reducing moisture content and improving turbine efficiency.
 
3. Which law of thermodynamics governs the efficiency limit of a heat engine?
A. Zeroth Law
B. First Law
C. Second Law
D. Third Law
Answer: C
Explanation: The Second Law of Thermodynamics states that heat engines cannot achieve 100% efficiency due to entropy increase.
 
4. Which thermodynamic cycle is most commonly used in gas turbine power plants?
A. Rankine Cycle
B. Otto Cycle
C. Brayton Cycle
D. Diesel Cycle
Answer: C
Explanation: The Brayton Cycle describes the operation of gas turbines, involving compression, heat addition, expansion, and exhaust.
 
5. What is the primary function of a feedwater heater in a power plant?
A. Increase boiler pressure
B. Preheat the feedwater using extracted steam
C. Reduce turbine exhaust pressure
D. Cool the exhaust gases
Answer: B
Explanation: Feedwater heaters improve efficiency by using extracted steam to preheat water before entering the boiler.
 
6. What is the purpose of reheating steam in a Rankine cycle?
A. Reduce fuel consumption
B. Enhance thermal efficiency 
C. Increase condenser pressure
D. Reduce cycle complexity
Answer: B
Explanation: Reheating increases the cycle’s efficiency by raising the average heat addition temperature, preventing moisture formation in turbines.
 
7. The thermal efficiency of an ideal Rankine cycle is improved by:
A. Increasing the condenser pressure
B. Lowering the boiler pressure
C. Increasing the boiler pressure
D. Increasing the moisture content of steam
Answer: C
Explanation: Higher boiler pressure increases the mean temperature of heat addition, improving thermal efficiency.
 
Power Generation Systems
 
8. In a coal-fired power plant, what component pulverizes coal before combustion?
A. Economizer
B. Superheater
C. Pulverizer
D. Condenser
Answer: C
Explanation: The pulverizer grinds coal into fine particles for efficient combustion in the boiler.
 
9. What is the main function of an economizer in a boiler system?
A. Superheat steam
B. Reduce fuel consumption by preheating feedwater
C. Remove flue gas pollutants
D. Increase the mass flow rate of steam
Answer: B
Explanation: An economizer captures waste heat from flue gases to preheat feedwater, improving efficiency.
 
10. In a steam turbine, what device is used to regulate steam flow to the blades?
A. Nozzles
B. Bearings
C. Condenser tubes
D. Governors
Answer: D
Explanation: Governors control steam flow to maintain turbine speed and stability.
 
11. What is the purpose of a cooling tower in a thermal power plant?
A. Heat the working fluid
B. Reduce temperature of exhaust gases
C. Dissipate waste heat from the condenser
D. Increase power output
Answer: C
Explanation: Cooling towers remove waste heat from the condenser and release it into the atmosphere.
 
12. In a hydroelectric power plant, what type of turbine is best suited for high-head, low-flow applications?
A. Pelton
B. Francis
C. Kaplan
D. Crossflow
Answer: A
Explanation: Pelton turbines are ideal for high-head, low-flow conditions as they use impulse force from water jets.
 
13. In a diesel power plant, which component is used to supply air to the engine?
A. Compressor
B. Turbocharger
C. Governor
D. Intercooler
Answer: B
Explanation: A turbocharger increases the air intake pressure, improving engine power and efficiency.
 
14. What type of fuel is primarily used in a gas turbine power plant?
A. Coal
B. Heavy fuel oil
C. Natural gas
D. Biomass
Answer: C
Explanation: Natural gas is the preferred fuel for gas turbines due to its high combustion efficiency and low emissions.
 
Environmental Impact
 
15. What is the primary pollutant produced by coal-fired power plants?
A. Carbon dioxide (CO₂)
B. Nitrogen gas (N₂)
C. Oxygen (O₂)
D. Methane (CH₄)
Answer: A
Explanation: Coal combustion releases large amounts of CO₂, contributing to climate change.
 
16. What technology is used to reduce sulfur dioxide emissions in power plants?
A. Electrostatic precipitators
B. Flue gas desulfurization (scrubbers)
C. Catalytic converters
D. Cyclone separators
Answer: B
Explanation: Flue gas desulfurization (scrubbers) remove sulfur dioxide to minimize acid rain formation.
 
17. What is the primary advantage of a combined-cycle power plant?
A. Lower capital cost
B. Higher efficiency due to waste heat recovery
C. Simpler operation
D. Requires less cooling water
Answer: B
Explanation: Combined-cycle plants use both gas and steam turbines, recovering waste heat for improved efficiency.
18. What is the main environmental concern of nuclear power plants?
A. Carbon emissions
B. Water pollution
C. Radioactive waste disposal
D. Noise pollution
Answer: C
Explanation: The primary issue is the disposal of radioactive waste, which requires long-term containment.
 
19. Which renewable energy source is commonly used in geothermal power plants?
A. Solar radiation
B. Wind energy
C. Earth's heat
D. Biomass combustion
Answer: C
Explanation: Geothermal plants harness heat from the Earth's interior to generate electricity.
 
20. What is the primary function of an electrostatic precipitator in a coal-fired power plant?
A. Reduce NOₓ emissions
B. Remove particulate matter from flue gases
C. Convert sulfur dioxide to sulfate
D. Increase combustion efficiency
Answer: B
Explanation: Electrostatic precipitators remove fine particles from flue gas by using electrostatic forces.
 
21. Which of the following gases contributes most to global warming from power plants?
A. Nitrogen (N₂)
B. Oxygen (O₂)
C. Sulfur dioxide (SO₂)
D. Carbon dioxide (CO₂)
Answer: D
Explanation: CO₂ is the primary greenhouse gas emitted by fossil fuel power plants, contributing to climate change.
 
Safety and Maintenance
 
22. What is the purpose of a boiler safety valve?
A. Reduce energy losses
B. Prevent excessive pressure buildup
C. Control feedwater flow
D. Regulate steam temperature
Answer: B
Explanation: Safety valves prevent pressure from exceeding safe limits, avoiding explosions.
 
23. Which maintenance strategy involves replacing components before they fail?
A. Reactive maintenance
B. Preventive maintenance
C. Corrective maintenance
D. Run-to-failure maintenance
Answer: B
Explanation: Preventive maintenance replaces parts on a schedule to avoid unexpected failures.
 
24. What is the most common cause of turbine blade failure?
A. Electrical faults
B. Water hammer
C. Fatigue and creep
D. Condensation in steam lines
Answer: C
Explanation: Prolonged exposure to high temperature and stress causes fatigue and creep in turbine blades.
 
25. What type of fire extinguisher is best suited for electrical fires in power plants?
A. Water
B. Foam
C. CO₂
D. Dry powder
Answer: C
Explanation: CO₂ extinguishers are ideal for electrical fires as they do not conduct electricity.
 
26. Which method is commonly used to detect leaks in a steam pipeline?
A. Thermographic imaging
B. Sound level measurement
C. Color testing
D. Ultrasonic testing
Answer: D
Explanation: Ultrasonic testing detects high-frequency sound waves from steam leaks.
 
27. What is the main purpose of a blowdown system in a boiler?
A. Prevent corrosion by removing impurities
B. Increase boiler pressure
C. Reduce steam moisture content
D. Preheat feedwater
Answer: A
Explanation: Blowdown removes dissolved solids and impurities, preventing scale buildup and corrosion.
 
28. What is the primary safety concern in a nuclear power plant?
A. Cooling tower failure
B. Overheating of steam turbines
C. Radioactive material leakage
D. Excessive carbon emissions
Answer: C
Explanation: Nuclear power plants must prevent radioactive leaks to ensure environmental and human safety.
 
29. What method is commonly used to test the integrity of a boiler tube?
A. Dye penetrant testing
B. Radiographic inspection
C. Magnetic particle inspection
D. Ultrasonic thickness measurement
Answer: D
Explanation: Ultrasonic thickness testing detects thinning of boiler tubes due to corrosion or erosion.
 
30. Which of the following is a common cause of boiler tube failure?
A. Low feedwater temperature
B. Thermal fatigue and creep
C. Low flue gas temperature
D. Excessive condenser vacuum
Answer: B
Explanation: Boiler tubes are subjected to high temperatures and stress, leading to thermal fatigue and creep over time.