The function of an economizer in a steam power plant is to increase the enthalpy of feed water.

An economizer is a heat exchanger that is typically installed in the flue gas path of a steam power plant between the boiler and the chimney. Its main function is to recover heat from the flue gases and transfer it to the feed water before it enters the boiler. This process helps to increase the overall efficiency of the power plant by reducing the amount of fuel required to generate steam.

Key points:
- Heat recovery: The main function of an economizer is to recover heat from the flue gases. Flue gases exiting the boiler usually have a high temperature, typically around 500 to 600 degrees Celsius. By passing these hot gases through the economizer, the heat energy is transferred to the feed water, which is then preheated before entering the boiler. This reduces the amount of fuel needed to raise the temperature of the feed water to the desired level.

- Enthalpy increase: The enthalpy of a substance is a measure of its total energy content. In the case of the feed water in a steam power plant, increasing its enthalpy means increasing its temperature. The economizer achieves this by transferring heat from the flue gases to the water. As the feed water passes through the economizer, it absorbs heat from the flue gases, causing its temperature to rise. This preheated water then enters the boiler, where it is further heated to produce steam.

- Efficiency improvement: By preheating the feed water, the economizer helps to improve the overall efficiency of the steam power plant. This is because a significant amount of heat energy is recovered from the flue gases, which would otherwise be wasted. By utilizing this heat energy to preheat the feed water, the amount of fuel required to raise the temperature of the water to the desired level is reduced. This leads to lower fuel consumption and higher overall efficiency of the power plant.

- Cost savings: The use of an economizer in a steam power plant can result in significant cost savings. By reducing the amount of fuel required, the plant can save on fuel expenses. Additionally, the higher efficiency achieved through the use of an economizer can also lead to reduced emissions, which can result in compliance with environmental regulations and potential cost savings associated with emission credits.

In conclusion, the function of an economizer in a steam power plant is to increase the enthalpy of feed water by recovering heat from the flue gases. This helps to improve the overall efficiency of the power plant and leads to cost savings in terms of fuel consumption and potential emissions-related expenses.