PA Fans

Primary air fans are one type of fan that can be used in certain boilers. They are often used as an alternative to pulveriser blowers on coal-fired boilers for power generation.

Primary air fans provide high-pressure air to the boiler system, which enters it through the APH. This air is used to dry coal and convey it to the furnace from the mill. It also feeds oxygen for primary combustion into the boiler. Both cold and hot primary air may be provided by the PA fan. In a common arrangement, cold ambient air discharged by the PA fan is separated, and part of the air goes through a heater, then tempered with some of the cold air or by some other form of regulating system to control the temperature. There are also arrangements where there are as many PA fans as there are mills, in which the fans are required to handle hot air.

These fans are often backward-curved fans, but may also be double-stage, variable-pitch axial fans. The fan needs to be sized to overcome pressure drop in the primary air system and avoid settling of coal in the ducts. A large margin is often left for the emergence of additional pressure drops involving wear on seals and other leaks that appear with aging equipment.

The heavy loads under which PA fans operate render them prone to balance and lubrication problems and tend to make for generally high maintenance costs. For this reason, it is important to find a reliable manufacturer experienced in fan design.