The air preheater in a boiler is an important component that helps in improving the efficiency of the boiler system. It is responsible for heating the combustion air before it enters the furnace, which results in better fuel combustion and heat transfer.

The correct location of the air preheater in a boiler is between the forced draft fan and the furnace. This placement allows the preheated air to be supplied directly to the furnace for combustion. Let's understand why this is the ideal location:

1. Forced Draft Fan (FDF):
The forced draft fan is responsible for supplying the air required for combustion into the furnace. It creates a positive pressure inside the furnace and ensures the proper airflow. The air preheater is placed before the FDF to preheat the air before it enters the fan.

2. Air Preheater (APH):
The air preheater is a heat exchanger that transfers heat from the flue gases to the incoming combustion air. It consists of a series of tubes or plates through which the flue gases flow. As the hot flue gases pass over these tubes, they transfer their heat to the air flowing through them, thereby preheating it.

3. Furnace:
The furnace is the central combustion chamber where the fuel is burned. The preheated air from the air preheater is supplied to the furnace through the forced draft fan. This preheated air helps in achieving better fuel combustion by providing the required oxygen and temperature for efficient combustion.

Benefits of placing the air preheater between the forced draft fan and furnace:

- Improved Fuel Combustion: Preheating the combustion air results in better fuel combustion as it provides the necessary temperature and oxygen for efficient combustion. This leads to reduced fuel consumption and increased boiler efficiency.

- Enhanced Heat Transfer: The air preheater increases the overall heat transfer in the boiler system by recovering heat from the flue gases. This recovered heat is then utilized to preheat the incoming combustion air, thereby reducing the energy required to heat the air.

- Reduced Flue Gas Temperature: By extracting heat from the flue gases, the air preheater helps in lowering the temperature of the flue gases exiting the boiler. This reduces the heat loss through the chimney and increases the overall efficiency of the boiler system.

- Environmental Benefits: The preheating of combustion air reduces the emission of pollutants such as nitrogen oxides (NOx) and carbon monoxide (CO) by improving the combustion efficiency. This contributes to a cleaner and more environmentally friendly operation.

In conclusion, placing the air preheater between the forced draft fan and furnace in a boiler system is essential for achieving better fuel combustion, improved heat transfer, and increased overall efficiency.

Increase air temperature