Anti-Surge Measures for Backward-Curved Double-Inlet Centrifugal Fans

Anti-Surge Measures for Backward-Curved Double-Inlet Centrifugal Fans

Backward-curved double-inlet centrifugal fans should be selected within their high-efficiency range. Avoid arbitrarily increasing the selection coefficient, which causes the actual flow rate during operation to significantly exceed the design flow rate. When employing significant throttling, the fan is easily adjusted to operate within the surge zone. Therefore, during design and selection, the operating range must be kept well away from the surge zone. Should surge occur during system operation, the operating range can be adjusted by altering fan speed or changing the installation angle of the moving blades. These methods shift the fan's performance curve toward the low-flow region, thereby relocating the surge critical line to the low-flow zone. This also expands the fan's stable operating range. For some operational sites lacking the above adjustment capabilities where shutdown is impractical, a simple and rapid surge mitigation method involves installing a vent valve. Surge can be immediately eliminated. It must be noted that the gas vented to the atmosphere should be non-hazardous. If hazardous gases are present, they must be routed through a small pipe into the fan's intake duct. The disadvantage of this method is the waste of kinetic energy gained by the impeller, reducing the overall efficiency of the fan. However, due to its simplicity and significant effectiveness, it is widely applied in the regulation of backward-curved double-inlet centrifugal fans. Anti-surge ring. Installing anti-surge rings on the main ducts of backward-curved double-inlet centrifugal fans in subway or tunnel systems has become a common practice. These rings function as guide vanes, redirecting unstable airflow away from the blade passages and back toward the blades. Its drawback is that a portion of the airflow becomes unused under these conditions. Nevertheless, it broadens the fan's stable operating range and reduces the surge zone. Currently, this method serves as an effective solution for preventing nozzle vibration in axial flow backward-curved double-inlet centrifugal fans. It is widely adopted by manufacturers of backward-curved double-inlet centrifugal fans both domestically and internationally, and has become an indispensable protective measure in large-scale engineering bids in China. Additionally, installing surge grids at the top of the main duct blades can shift the surge and limited-flow zones of backward-curved double-inlet centrifugal fans, thereby expanding their stable operating range.