Power Plant And Fuel System Practice Exam

Why are reheaters used in some steam turbines?

To increase exhaust steam temperature and pressure. To reheat exhaust steam between stages, reducing moisture in later stages and improving efficiency and turbine life. To reduce boiler feedwater temperature. To condense steam before the turbine.

Correct Answer:

To reheat exhaust steam between stages, reducing moisture in later stages and improving efficiency and turbine life.

Explanation:

Reheating between turbine stages keeps the steam hot after partial expansion, so it remains drier in the later stages. That reduction in moisture helps prevent blade erosion and reduces efficiency losses caused by wet steam, which translates into longer turbine life and smoother operation. At the same time, reheating increases the average temperature at which the steam expands, so more work can be extracted from each kilogram of steam, boosting overall cycle efficiency. It's not about increasing the exhaust steam pressure at the turbine exit—reheating adds heat, not pressure. It's also not about changing boiler feedwater temperature or condensing steam before it reaches the turbine; those functions belong to feedwater heating and the condenser, respectively.

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