On axial flow compressor control
Thread Content
As shown in the figure, the pressure difference at the throat of the axial flow compressor is used in the anti-surge control of the compressor; why is BIC used to represent it in the figure? Instead of FIC? Is there any indication of backflow protection in the diagram?
Centrifugal anti-surge control includes flow control and outlet pressure control. In axial flow systems, surge is generally caused by high outlet pressure; controlling the vent valve can prevent this phenomenon. The input value for BIC is the pressure difference at the throat, along with an adjustment for the inlet temperature. These values are used in calculations to determine the maximum allowable discharge pressure, which is then compared with the current discharge pressure to calculate the MV value, thereby controlling the opening degree of the vent valve. Then why use throat pressure difference as the control variable? Since this variable has a functional relationship with the exhaust pressure, it actually also has a functional relationship with the flow rate. In fact, all of them use throat pressure differences, probably to facilitate calculation or to enable anti-stall control
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The conditions for surge are nothing other than low flow rate and high pressure ratio； The stationary vanes of axial flow compressors generally have a minimum opening angle that cannot be reduced to 0. The throat differential pressure makes it easier to calculate the operating point, providing an intuitive indication compared to the anti-surge line; in other words, as mentioned on the second floor, this facilitates surge control
:Hug: I studied Shaanxi Blower’s control system a little yesterday, and found that its throat pressure difference feature includes detection functions for surge protection and backflow prevention. Backflow occurs when there is a sudden increase in pressure in the downstream system, as a result of further surge conditions or failures in the process system.
Now, Shaanxi Blower also adds an alarm for the blockage curve
The flow rate is indicated by the pressure difference in the throat, rather than the actual flow rate measured by the flow rate sensor