by Mohammed Vasi April 20, 2020
Boiler systems in Thermal Power plants use different types of Centrifugal Fans to supply air required for combustion, deliver fuel to the burners, circulate the gases for better heat transfer and remove exhaust gases. Based on the boiler size and airflow requirement, different types of fans are used with varied capabilities.
Two types of fans used in a boiler power plant are- A. Draft Fans and B. Other Process Fans
- DRAFT FANS
Draft fans play an important role in thermal power plants because they are responsible for maintaining the flow of gases through the boiler system. Two types of Draft fans are used in the power plants, which are -1. Forced Draft fans and 2. Induced Draft Fans.
Forced Draft Fans: Forced Draft fans used in a power plant are centrifugal fans, utilizing radial airflow blading or variable pitch axial fans. Forced Draft Fans (FD) supply the air necessary for fuel combustion by pushing air through the combustion air supply system and into furnace. These fans are located at the inlet of boiler to push high pressure fresh air into combustion chamber, where it mixes with the fuel to produce positive pressure.
The key difference between a forced draft and an induced draft fan is, FD fan forces outside air into the heating system whereas an ID fan draws flue gases from the system out into the atmosphere. Both FD fan and ID fan operate in such a manner that it balances the air system in the boiler to make the combustion process efficient.
In Power plants, where coal is used as fuel for combustion, FD fans are used as secondary air fans to regulate proper combustion and maximize the efficiency of the fuel. A typical FD fan arrangement uses inlet and outlet dampers to control and maintain the required air pressure inside the system. These fans have a wheel at the center that is hung on the shaft along with inlet boxes, silencer, filter, and rain hood.
As compared to ID fans, FD fans are more efficient, easier to maintain, and have cleaner operating conditions. The most common centrifugal fans used as FD fans are backward curved and airfoil centrifugal fans.
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