Boiler equipped with primary air fan

The primary air fan is one of the three main types of fans in a coal-fired power plant boiler, forming the core power equipment of the boiler flue gas system together with the forced draft fan (secondary air fan) and induced draft fan. Its main task is to provide sufficient high-pressure primary air to the boiler combustion system, undertaking key functions such as fuel delivery, drying, sealing, and combustion support.

The primary air fan outlet air is divided into hot and cold paths: hot primary air is heated by an air preheater and then sent to the pulverizing system for drying and carrying pulverized coal; cold primary air is used to regulate the temperature of the air-coal mixture. After mixing, both types of air together transport the pulverized coal to the furnace and provide oxygen for the initial combustion stage. In circulating fluidized bed boilers, the primary air also needs to be divided into multiple paths to achieve functions such as bed fluidization, coal feeding, and sealing.

As of 2026, primary air fans mostly adopt a centrifugal design, featuring high pressure head, large flow rate, and high stability, and are widely used in thermal power generation, industrial boilers, and incineration systems.

Centrifugal primary air fans mainly consist of an impeller, a volute casing, a main shaft, bearing housings, and a coupling. When the motor drives the impeller to rotate at high speed through the coupling, the air between the blades is thrown towards the outer edge of the impeller under centrifugal force, increasing its kinetic and pressure energy. After the gas enters the volute casing, the flow velocity decreases as the flow cross-section gradually expands, and some of the kinetic energy is further converted into static pressure energy. The air at the center of the impeller is discharged, creating a certain degree of vacuum. Air outside the intake port is continuously drawn in under atmospheric pressure—as the impeller continues to rotate, air is continuously drawn in and expelled, achieving continuous gas delivery.

The following data represents partial performance specifications. If you require specific parameters not listed, please contact us for customized design service.

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