As a form of fan, a centrifugal fan can play the role of a blower or an induced draft fan in different fan systems. Anyone who has contact with the fan system may come into contact with a word, that is, stall. For people, the stall of the fan is relatively easy to understand, but will the centrifugal fan stall?
1)Definition of fan stall
Fan stall means that when the angle of attack of the airflow at the inlet of the moving blade is greater than 90 degrees, the airflow appears eddy currents at the entrance and exit of the moving blade of the fan, the fan cannot work normally, and the air volume and wind pressure drop or fluctuate significantly. From the fan characteristic curve, fan stall refers to the phenomenon in which the corresponding wind pressure or flow rate falls outside the theoretical stall line when the rotor blade is running at a certain opening.
Generally speaking, when the fan is running at a certain blade opening, the corresponding air pressure range after the flow rate must also match it. If it exceeds the range, it will enter a stall, that is, the operating point of the fan must be on the corresponding characteristic curve. Moving, if the operating point is outside the characteristic curve, it enters a stall.
2)the reasons for the centrifugal fan stall
According to the definition of fan stall, it can be known that the centrifugal fan will not stall under normal circumstances, but it will also occur with probability. When it is used as a blower or an induced draft fan, the reasons for stall are different:
1. Reasons for blower stall
(1) The inlet of the centrifugal fan is blocked, and the air volume is less than the flow rate of the corresponding rotor blade opening;
(2) The moving blade is opened large, but the secondary air door is opened too small;
(3) The air heater is seriously blocked, and the wind pressure is greater than the wind pressure of the corresponding moving blade opening.
2. The cause of the stall of the induced draft fan
(1) The air preheater is seriously blocked;
(2) The resistance of the flue is too large, and the wind pressure is greater than the wind pressure of the corresponding moving blade opening.
In addition, no matter whether the centrifugal fan is a blower or an induced draft fan, if the rotor blade adjustment mechanism fails, the external opening does not appear to be large, but the inside is actually in the fully open position. At this time, the centrifugal fan has too much output, which often leads to stall or load tripping. , but this reason is relatively rare.
3) the treatment method of centrifugal fan stall
1. Treatment of blower stall
If the centrifugal fan is blocked, close the rotor blade appropriately; if the wind pressure is too high, you can open the secondary air door; if the heater is blocked, only close the rotor blade to reduce the load; in addition, if there are two fans To deal with the stall caused by the large deviation, you can first open the secondary damper and adjust it carefully.
2. Treatment of induced draft fan stall
First, appropriately reduce the load of the centrifugal fan, properly close the opening of the moving blades, and reduce the full pressure of the fan. Alternatively, when the current of the centrifugal fan does not exceed the limit, the flue gas bypass baffle can be properly opened to slightly increase the flue gas resistance, but the flue gas flow can be greatly increased. Match with the blade opening.
