Which of the following enters the super heater of a boiler ?

Question

Examoogle · Accepted Answer

Wet steam

Explanation: The superheater in a thermal power plant is designed to increase the temperature of steam above its saturation point to increase the overall cycle efficiency and prevent moisture damage in the turbine. It receives wet steam directly from the boiler drum, where evaporation is incomplete, and heats it to a superheated state.

Working Principle: The wet steam (mixture of liquid water and steam) leaves the boiler drum and passes through the tubes of the superheater, which are exposed to hot flue gases. During this process, the sensible heat is added to the saturated steam, evaporating any remaining moisture and increasing its temperature well above the saturation temperature ($T_{sat}$).

Key Formulas: $Q_{in} = m \cdot c_p \cdot (T_{super} - T_{sat})$ — Heat added in the superheater; $\eta_{thermal} = 1 - \frac{T_{cold}}{T_{hot}}$ — Carnot efficiency principle improvement via superheating

Key Points: Superheaters convert 'wet' steam into 'dry' or 'superheated' steam.; Prevents erosion of turbine blades caused by water droplets at high velocities.; Enhances the thermal efficiency of the Rankine cycle by increasing average heat addition temperature.; The process occurs at constant pressure in a primary superheater.

Advantages: Improved thermal efficiency of the power plant; Reduced risk of erosion in turbine blades; Increased work output per unit mass of steam

Disadvantages: Requires high-grade, heat-resistant materials (alloys); Increases the complexity and cost of the boiler unit

Applications: Thermal power plants; Industrial process steam systems

Additional Info: Wet steam contains liquid droplets; passing it through a turbine would cause pitting and mechanical failure of blades.. Options A and B are incorrect because water must be converted to phase-changed steam in the drum before reaching the superheater.. Option D is incorrect because steam that is already superheated does not 'enter' to become superheated; it has already passed that stage.

Answer: C is correct — Wet steam, which contains moisture, enters the superheater to be converted into dry superheated steam.

Exam Tip: Always remember that superheating strictly increases the quality of steam; it is the final stage of steam preparation before entering the high-pressure turbine.

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