Combined Cycle and Cogeneration Systems — MCQs – EE

1. What is the main advantage of a combined cycle power plant?
(A) Lower capital cost
(B) Higher efficiency
(C) Smaller footprint
(D) Simpler operation

2. In a combined cycle plant, which cycles are typically combined?
(A) Diesel and Gas
(B) Gas and Steam
(C) Steam and Hydel
(D) Diesel and Nuclear

3. What is the typical efficiency range of a modern combined cycle power plant?
(A) 25–35%
(B) 45–55%
(C) 55–62%
(D) 70–80%

4. Cogeneration is also known as:
(A) Combined Heat and Power (CHP)
(B) Hydroelectric Power
(C) Nuclear Power
(D) Solar Power

5. Which of the following is a primary fuel used in combined cycle plants?
(A) Coal
(B) Natural Gas
(C) Biomass
(D) Uranium

6. In a cogeneration system, the waste heat is mainly used for:
(A) Cooling purposes
(B) Electricity generation
(C) Heating or industrial processes
(D) Pumping water

7. What component in a combined cycle plant recovers heat from the gas turbine exhaust?
(A) Boiler
(B) Heat Recovery Steam Generator (HRSG)
(C) Condenser
(D) Economizer

8. What is the main limitation of a simple cycle gas turbine compared to combined cycle?
(A) Higher efficiency
(B) Lower efficiency
(C) Higher reliability
(D) Lower operating temperature

9. Which type of steam cycle is typically used in combined cycle plants?
(A) Rankine cycle
(B) Carnot cycle
(C) Brayton cycle
(D) Otto cycle

10. In a cogeneration plant, if electricity is produced first, it is called:
(A) Heat-driven system
(B) Back-pressure system
(C) Electricity-driven system
(D) Steam turbine system

11. What is the purpose of a condenser in a combined cycle plant?
(A) To produce steam
(B) To cool and condense exhaust steam
(C) To compress air
(D) To ignite fuel

12. Which is more efficient: combined cycle or simple cycle power plant?
(A) Combined cycle
(B) Simple cycle
(C) Both are equal
(D) Efficiency depends on fuel type

13. In cogeneration, the overall efficiency can reach up to:
(A) 35–45%
(B) 50–60%
(C) 70–90%
(D) 95–100%

14. What is a back-pressure turbine in cogeneration used for?
(A) To produce only electricity
(B) To generate steam at desired pressure for process
(C) To cool condensers
(D) To compress air

15. The typical exhaust temperature from a gas turbine in a combined cycle plant is around:
(A) 100–200°C
(B) 300–600°C
(C) 800–1000°C
(D) 1200–1500°C

16. What is the main disadvantage of cogeneration plants?
(A) Low efficiency
(B) High fuel consumption
(C) Higher initial cost and complex design
(D) Cannot use waste heat

17. Which of the following industries benefits most from cogeneration?
(A) Cement industry
(B) Textile industry
(C) Chemical and pulp & paper industry
(D) Software industry

18. The gas turbine in a combined cycle operates on which thermodynamic cycle?
(A) Rankine
(B) Brayton
(C) Otto
(D) Diesel

19. The steam turbine in a combined cycle operates on which cycle?
(A) Rankine
(B) Brayton
(C) Otto
(D) Diesel

20. In cogeneration, if heat is produced first, it is called:
(A) Heat-driven system
(B) Power-driven system
(C) Combined system
(D) Back-pressure system

21. What is the main environmental benefit of combined cycle plants?
(A) Less land use
(B) Reduced CO₂ emissions per unit of electricity
(C) Noise reduction
(D) Increased water consumption

22. Which component increases the efficiency of a combined cycle plant by using waste heat?
(A) HRSG
(B) Combustion chamber
(C) Cooling tower
(D) Fuel injector

23. Which fuel is least suitable for combined cycle plants?
(A) Natural gas
(B) Diesel
(C) Coal
(D) Light oil

24. What is the typical operating pressure of the steam in a combined cycle HRSG?
(A) 5–10 bar
(B) 20–40 bar
(C) 50–120 bar
(D) 200–300 bar

25. Combined cycle plants can be single-shaft or multi-shaft. In single-shaft plants, the gas and steam turbines:
(A) Operate independently
(B) Are mechanically coupled on one shaft
(C) Have separate generators
(D) Use diesel backup

26. The typical startup time for a combined cycle plant is:
(A) 15–30 minutes
(B) 1–2 hours
(C) 5–10 hours
(D) 24 hours

27. Which efficiency-improving method is commonly used in cogeneration?
(A) Reheating the gas turbine
(B) Using back-pressure turbines
(C) Increasing fuel flow only
(D) Using only diesel

28. What is the main difference between cogeneration and conventional power plants?
(A) Fuel type
(B) Use of waste heat for useful purposes
(C) Electricity voltage
(D) Plant size

29. What is a topping cycle in cogeneration?
(A) Steam cycle produces electricity first
(B) Heat is used for industrial process first
(C) Fuel is used for cooling
(D) Diesel generator cycle

30. Which component in a combined cycle plant improves overall plant flexibility?
(A) Condenser
(B) Gas turbine
(C) HRSG with supplementary firing
(D) Cooling tower