Analysis of the Causes of Backflow in Roof Axial Fans

Analysis of the Causes of Backflow in Roof Axial Fans

Backflow can be considered a dangerous operating condition for roof axial fans, but what causes backflow in these fans? First, due to a process system malfunction, system pressure rises sharply, causing airflow to flow backward into the roof axial fan. Second, the condition of the roof axial fan may further deteriorate. The fan enters a surge state. If this is not resolved in a timely manner, persistent backflow occurs due to the large capacity of the process system and ductwork network. Because of the high outlet pressure, the compressor cannot discharge gas smoothly; the rotational mechanical energy is converted into thermal energy, causing the blades to expand and leading to collisions between the moving and stationary blades, which damages the axial fan. Therefore, the fundamental countermeasures to prevent backflow are, first, to prevent the surge condition from worsening by strengthening anti-surge control, and second, to prevent the backflow of outlet gas. Backflow prevention is achieved through close integration between the logic control system and the anti-surge system. The logic system performs comprehensive judgment and processing based on the intensity and duration of the surge. This is broadly divided into three stages, during which various countermeasures can be implemented. 1. Adjust the anti-surge control system to eliminate the surge condition. 2. Eliminate the reverse flow condition in accordance with safe operating procedures. 3. Execute the automatic interlock shutdown procedure under mandatory conditions.