Question 49 QMED04 - Boiler Technician-Watertender

The Correct Answer is A ### Explanation for Option A (superheated steam) **Superheated steam** is steam that has been heated to a temperature above its saturation point at a given pressure. This process dramatically increases the steam's energy content and, crucially, ensures that the steam is completely dry (contains no liquid water droplets). Main propulsion turbines, especially in modern marine engineering, utilize superheated steam because: 1. **Increased Efficiency:** Higher temperature means higher thermal energy, leading to a greater temperature differential between the inlet and exhaust, maximizing the conversion of heat energy into mechanical work (power). 2. **Erosion Prevention:** Dry steam prevents the rapid erosion and pitting of turbine blades. Liquid water droplets traveling at high velocity would strike the blading, causing damage and reducing the lifespan of the turbine. --- ### Why Other Options Are Incorrect **B) desuperheated steam:** Desuperheated steam is steam whose temperature has been reduced from its superheated state, typically by injecting water. While desuperheated steam is used for auxiliary systems (like heating or gland sealing) that cannot tolerate very high temperatures, it is not the preferred or primary steam supply for the highly efficient, high-speed main propulsion turbines. **C) wet steam:** Wet steam is steam that contains suspended liquid water droplets. Using wet steam in main turbines causes severe erosion damage to the turbine blades and significantly reduces thermal efficiency due to the lower energy content compared to dry or superheated steam. **D) saturated steam:** Saturated steam is steam at the temperature corresponding to its saturation pressure. While it is $100\%$ dry when it leaves the boiler drum, it is only marginally stable. Any slight temperature drop or heat loss will cause immediate condensation, turning it into wet steam before it reaches the turbine. This rapid condensation and the lower energy content make it unsuitable for high-power, high-efficiency main propulsion applications.