Question

During a regeneration process, some steam is extracted from the turbine and is used to heat the liquid water leaving the pump. This does not seem like a smart thing to do since the extracted steam could produce some more work in the turbine. How do you justify this action?

Short answer

Answer: Extracting steam from the turbine and using it to heat the liquid water leaving the pump in a regeneration process is considered a justified action because it increases the overall thermal efficiency of the power plant. Although it may seem counterintuitive, this action minimizes heat loss, saves fuel consumption, reduces thermal stress on the system components, and enhances the performance of the thermal power plant, which ultimately outweighs the potential decrease in output work.

Step-by-step solution

Understand Thermal Efficiency in Thermal Power Plants

Thermal efficiency is a measure of how well a thermal power plant converts heat into useful work. The higher the thermal efficiency, the more work is obtained from the same amount of heat input, and the less heat is wasted. The efficiency of a thermal power plant can be improved by minimizing the heat rejection, or in other words, by maximizing the heat transfer within the system.

Discussing Heat Transfer and Carnot Cycle Assumption

Heat transfer is the process by which thermal energy is exchanged between the working fluid and the surroundings. In an ideal thermal power plant, we assume a reversible Carnot cycle that involves two isothermal processes and two adiabatic processes. However, in practice, the Rankine cycle is commonly used to represent the working principle of a thermal power plant, which has some irreversible processes and is not as efficient.

Introduce Regeneration in Thermal Power Plants

Regeneration is a practical method to improve the thermal efficiency of a power plant operating on the Rankine cycle. By extracting some steam from the turbine and using it to heat the liquid water leaving the pump, we decrease the temperature difference between the working fluid and the heat source. This results in a reduction of heat losses and hence higher thermal efficiency.

Explain the Benefits of Regeneration

By extracting steam to heat the liquid water, less heat is required from the external source (boiler). This saves fuel consumption and reduces the operating cost. Additionally, regeneration can minimize the temperature difference between the working fluid and the surroundings, leading to a decreased risk of thermal stress on the system components and increasing the lifespan of the plant.

Justifying the Action of Extracting Steam

In conclusion, extracting steam from the turbine and using it to heat the liquid water leaving the pump in the regeneration process may seem counterintuitive as it could produce more work in the turbine. However, this action increases the overall thermal efficiency of the power plant by minimizing heat loss, saving fuel consumption, and reducing thermal stress on the system components. Therefore, despite somewhat decreasing the output work, this action significantly improves the performance of the thermal power plant and is thus justified.