On surge and backflow control of fan axial flow compressors
Thread Content
The pressure difference in the throat is essentially the intake air flow rate, and the exhaust pressure can also be considered as the exhaust air flow rate. Surge is generally prevented and controlled by increasing the inlet air flow rate, the static blade angle, and the rotational speed through the opening degree of the surge valve. How can reducing the exhaust pressure increase the intake air flow? Under what circumstances does backflow generally occur, after surge has taken place? Does rotational speed cause the exhaust pressure to increase?
Firstly, the rotation speed is usually kept within the normal range, with variable-frequency motors used to adjust the frequency and supplement power; therefore, there is generally no need to worry about the speed suddenly dropping too low. Of course, if the rotational speed suddenly drops and the outlet pressure falls, the high reaction pressure will force air back into the main fan, damaging the unit; this is known as surge or reverse flow. Secondly, backflow occurs on the premise of surge, which is a phenomenon that can arise under various circumstances – for example, when there is a blockage at the inlet of the main fan, or when the reaction pressure is too high. This leads to a decrease in the volume of air exiting the fan, or even to the reverse flow of air back into the unit. If the flow rate at the unit’s inlet is not sufficient to counteract this reverse flow, surge will occur. Excessive vibration can cause the unit to shut down. Moreover, pressure changes can result in the main fan drawing in air in the opposite direction, causing the catalyst to flow back. High-temperature, high-pressure catalyst particles flowing back into the main fan can damage it, resulting in incalculable losses. That’s about all for now