assembler steam and gas turbine Interview Questions and Answers

1. What is a steam turbine?

   • Answer: A steam turbine is a rotary engine that extracts energy from pressurized steam and converts it into useful work. The steam expands as it passes through the turbine, causing the rotor to turn.

2. What is a gas turbine?

   • Answer: A gas turbine is a type of internal combustion engine that uses hot gas under pressure to turn a turbine. Unlike steam turbines, it uses a continuous combustion process to generate the hot gas.

3. Explain the Rankine cycle.

   • Answer: The Rankine cycle is a thermodynamic cycle used for steam turbine power plants. It consists of four processes: 1) Isentropic expansion in the turbine; 2) Constant pressure heat rejection in the condenser; 3) Isentropic compression in the pump; 4) Constant pressure heat addition in the boiler.

4. Explain the Brayton cycle.

   • Answer: The Brayton cycle is a thermodynamic cycle used for gas turbine engines. It consists of four processes: 1) Isentropic compression; 2) Constant pressure heat addition in the combustion chamber; 3) Isentropic expansion in the turbine; 4) Constant pressure heat rejection.

5. What are the advantages of steam turbines?

   • Answer: Advantages include high efficiency, relatively low operating costs (once built), and the ability to handle large power outputs.

6. What are the disadvantages of steam turbines?

   • Answer: Disadvantages include high initial capital cost, lower power-to-weight ratio compared to gas turbines, and slower response times to load changes.

7. What are the advantages of gas turbines?

   • Answer: Advantages include high power-to-weight ratio, faster response to load changes, simpler design compared to steam turbines, and lower maintenance requirements.

8. What are the disadvantages of gas turbines?

   • Answer: Disadvantages include lower efficiency compared to steam turbines at baseload, higher operating costs (due to fuel consumption), and higher emissions.

9. What is the difference between impulse and reaction turbines?

   • Answer: Impulse turbines utilize pressure drop to increase the velocity of the steam/gas before it hits the blades. Reaction turbines use the pressure drop across the blades themselves to generate thrust.

10. Explain the working principle of a steam turbine.

    • Answer: High-pressure steam enters the turbine, expanding and pushing against the blades of the rotor, causing rotation. The rotating shaft is connected to a generator or other equipment to produce power.

11. Explain the working principle of a gas turbine.

    • Answer: Air is compressed, mixed with fuel, ignited, and the hot gas expands, driving the turbine blades to rotate. Part of the turbine power is used to drive the compressor.

12. What is a combined cycle power plant?

    • Answer: A combined cycle power plant combines gas and steam turbines to improve overall efficiency. The hot exhaust gas from the gas turbine is used to generate steam for a steam turbine.

13. What is blade erosion in turbines?

    • Answer: Blade erosion is the gradual wearing away of turbine blades due to the impact of solid particles or moisture droplets in the working fluid.

14. What is blade fouling in turbines?

    • Answer: Blade fouling is the accumulation of deposits on turbine blades, reducing efficiency and increasing maintenance needs.

15. What are the different types of steam turbine configurations?

    • Answer: Common configurations include impulse, reaction, single-stage, multi-stage, and various combinations thereof (e.g., impulse-reaction).

16. What are the different types of gas turbine configurations?

    • Answer: Configurations include single-shaft, two-shaft, and three-shaft designs, each with varying compressor and turbine arrangements.

17. What is the role of a governor in a turbine?

    • Answer: The governor regulates the speed of the turbine by controlling the flow of the working fluid. It maintains a consistent output speed under varying loads.

18. What is the role of a nozzle in a steam turbine?

    • Answer: The nozzle accelerates the steam to high velocity before it enters the turbine blades, maximizing energy conversion.

19. What is the role of a diffuser in a gas turbine?

    • Answer: The diffuser slows down the hot gas after it leaves the turbine, recovering some of its pressure energy.

20. What are some common materials used for turbine blades?

    • Answer: Materials include nickel-based superalloys, titanium alloys, and advanced ceramics, chosen for their high-temperature strength and resistance to corrosion.

21. What is cavitation in steam turbines?

    • Answer: Cavitation is the formation of vapor bubbles in the steam flow due to low pressure, which can damage the turbine blades.

22. What is surging in gas turbines?

    • Answer: Surging is a phenomenon where the airflow in the compressor reverses direction, causing instability and potential damage.

23. How is the efficiency of a steam turbine affected by pressure and temperature?

    • Answer: Higher pressure and temperature at the inlet generally lead to higher efficiency, but there are practical limits imposed by material strength and cost.

24. How is the efficiency of a gas turbine affected by pressure and temperature?

    • Answer: Similar to steam turbines, higher pressure ratios and higher turbine inlet temperatures lead to higher efficiency. However, material limitations are even more critical for gas turbines.

25. What is reheat in steam turbines?

    • Answer: Reheat involves reheating the steam after it has passed through a portion of the turbine, improving overall cycle efficiency.

26. What is regeneration in gas turbines?

    • Answer: Regeneration involves using the hot exhaust gas from the turbine to preheat the compressed air before it enters the combustion chamber, improving efficiency.

27. What is intercooling in gas turbines?

    • Answer: Intercooling involves cooling the air between compressor stages, reducing the work required for compression and improving efficiency.

28. Explain the concept of isentropic efficiency.

    • Answer: Isentropic efficiency compares the actual performance of a turbine or compressor to its ideal isentropic performance (constant entropy process).

29. What are some common faults in steam turbines?

    • Answer: Common faults include blade erosion, blade fouling, seal leaks, governor malfunctions, and bearing problems.

30. What are some common faults in gas turbines?

    • Answer: Common faults include compressor fouling, hot gas path corrosion, turbine blade erosion, combustion chamber problems, and seal leaks.

31. How is the performance of a steam turbine monitored?

    • Answer: Monitoring includes measuring steam pressure and temperature, rotational speed, vibration levels, and oil temperature and pressure.

32. How is the performance of a gas turbine monitored?

    • Answer: Monitoring includes measuring gas temperature and pressure, compressor pressure ratio, rotational speed, vibration levels, and fuel flow rate.

33. What are the environmental concerns associated with steam turbines?

    • Answer: Primary concerns include greenhouse gas emissions from the fuel used to generate steam.

34. What are the environmental concerns associated with gas turbines?

    • Answer: Concerns include greenhouse gas emissions, NOx emissions, and particulate matter emissions.

35. What is the role of lubrication in turbines?

    • Answer: Lubrication reduces friction and wear on bearings and other moving parts, extending the lifespan and ensuring efficient operation.

36. What is the role of sealing in turbines?

    • Answer: Sealing prevents leakage of steam or gas, maintaining pressure and preventing environmental hazards.

37. What are the different types of bearings used in turbines?

    • Answer: Common bearing types include journal bearings, thrust bearings, and tilting pad bearings.

38. What is the significance of thermal stresses in turbines?

    • Answer: Thermal stresses due to temperature gradients can cause warping, cracking, and ultimately, failure of turbine components.

39. How are thermal stresses mitigated in turbine design?

    • Answer: Mitigation strategies include careful material selection, optimized cooling systems, and design features that minimize temperature gradients.

40. What is the role of a condenser in a steam power plant?

    • Answer: The condenser converts the exhaust steam from the turbine back into water, creating a vacuum that improves turbine efficiency and allowing the water to be reused in the boiler.

41. What are different types of steam traps used in steam turbines?

    • Answer: Various types exist, including thermodynamic traps, thermostatic traps, and float and thermostatic traps. Each type operates using a different mechanism to prevent steam loss while allowing condensate to drain.

42. What are the maintenance considerations for steam turbines?

    • Answer: Regular inspections, lubrication checks, blade cleaning, and periodic overhauls are crucial for maintaining optimal performance and preventing failures.

43. What are the maintenance considerations for gas turbines?

    • Answer: Regular inspections, cleaning of the compressor and combustion chamber, blade inspections, and periodic overhauls are critical to maintain gas turbine performance and reliability.

44. Describe the process of turbine blade inspection.

    • Answer: Inspection involves visual examination for damage, measurement of blade dimensions, and potentially non-destructive testing (NDT) methods like ultrasonic testing or dye penetrant testing to detect internal flaws.

45. What are the different types of fuel used in gas turbines?

    • Answer: Gas turbines can burn a variety of fuels, including natural gas, liquid fuels (such as kerosene or diesel), and even some types of biomass fuels.

46. How is the fuel efficiency of a gas turbine measured?

    • Answer: Fuel efficiency is typically expressed as heat rate (BTU/kWh) or specific fuel consumption (lb/kWh) and depends on several factors including load, ambient temperature, and the type of fuel used.

47. What is the role of a combustion chamber in a gas turbine?

    • Answer: The combustion chamber is where the fuel and air are mixed and ignited, producing hot gas that drives the turbine.

48. What are the different types of combustion chambers used in gas turbines?

    • Answer: Various designs exist, including annular, can, and can-annular types, each with its own advantages and disadvantages.

49. Explain the concept of pressure ratio in a gas turbine.

    • Answer: The pressure ratio is the ratio of the outlet pressure to the inlet pressure of the compressor and is a key parameter affecting the overall efficiency.

50. What are the factors affecting the life of a turbine blade?

    • Answer: Factors include material properties, operating temperature, blade stresses, and the presence of corrosive or erosive substances in the working fluid.

51. How are turbine blades cooled?

    • Answer: Cooling methods include convective cooling using air or steam, impingement cooling, film cooling, and internal cooling passages.

52. What is the significance of vibration monitoring in turbines?

    • Answer: Vibration monitoring helps detect imbalances, misalignments, and other problems that can lead to damage or failure, allowing for proactive maintenance.

53. What are some advanced technologies used in modern steam turbines?

    • Answer: Advanced technologies include improved blade designs, advanced materials, enhanced cooling methods, and advanced control systems.

54. What are some advanced technologies used in modern gas turbines?

    • Answer: Advanced technologies include advanced materials, advanced cooling systems for blades, lean premixed combustion, and improved compressor designs.

55. How do steam and gas turbines contribute to renewable energy generation?

    • Answer: They can be integrated into hybrid systems using renewable sources like solar or geothermal energy to generate steam or heat the working fluid.

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