A PA fan, or primary air fan, is a specialised combustion air fan used mainly on coal fired boilers to supply and control primary air to the burners. In many power plants and large industrial boilers, solid fuel is pulverised and carried to the burners by a stream of air. The PA fan provides this air at the pressure and flow needed for both fuel transport and stable combustion.
In a typical pulverised coal system, coal is ground in mills and mixed with a controlled amount of air. This air coal mixture is then blown through pipes to the burner nozzles in the furnace. The primary air fan delivers the energy that moves the mixture and also supplies part of the oxygen needed for combustion. Without a correctly sized and controlled PA fan, the fuel would not reach the burners at the right speed and concentration, and flame stability and efficiency would suffer.
The PA fan works together with other draft fans, especially the FD (forced draft) fan and ID (induced draft) fan. While the FD fan provides secondary and tertiary air for complete combustion and overall furnace pressure control, the PA fan focuses on the primary air path. Operators adjust PA fan flow to maintain the designed air to fuel ratio in the coal pipes, which is essential to avoid slagging, high carbon in ash or excessive unburned fuel.
In addition to fuel transport, the PA fan has an important role in drying the coal. Pulverisers often rely on hot primary air drawn from the air heater to evaporate moisture in the coal as it is ground. The PA fan must deliver enough hot air at the correct temperature to remove this moisture without causing overheating or fire in the mill. Balancing drying needs with burner requirements is a key part of PA fan control.
From a design perspective, PA fans are usually centrifugal fans or high pressure axial fans capable of generating the higher pressures needed to overcome mill, piping and burner losses. They are built for continuous duty, and their performance has a direct impact on boiler output, efficiency and emission levels. Many modern installations use variable frequency drives to adjust PA fan speed in line with boiler load, which saves energy and improves control.
In summary, the function of a PA fan is to supply and control primary air for coal transport and initial combustion in boilers and similar systems. It is a critical part of the air and flue gas system, working closely with FD and ID fans to keep the furnace burning safely and efficiently.
