Calculation of the anti-surge valve opening
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I would like to ask everyone: what is the most accurate method for calculating the opening degree of an anti-surge valve? What opening degree should the anti-surge valve have in order to prevent the compressor from entering surge mode without causing overshoot? Surge is generally caused by too low a flow rate at the compressor inlet; opening the anti-surge valve serves to increase the flow rate. It would be useful to establish a correspondence between the position of the operating point within the anti-surge zone and the flow rate in the anti-surge duct. For example, when the operating point lies on the SCL anti-surge control line, the corresponding flow rate in the anti-surge duct is 0%, while when it lies on the SLL anti-surge limit line, the flow rate is 100%. When the operating point is in the area between the SCL and SLL lines, the corresponding flow rate is 50%. The opening command for the anti-surge valve can then be determined using the flow characteristic curve of that valve. If the flow characteristic curve is linear, it will correspond to valve openings of 0%, 100%, and 50% respectively. This ensures that the anti-surge valve remains closed when the operating point is on the control lines, and that it is fully open when the operating point exceeds the SLL line. The area between SCL and SLL represents proportional control, with a one-to-one correspondence with the flow rate in the anti-surge duct; the valve opening command is then derived from this flow characteristic curve. Is this approach reasonable? Most anti-surge controllers today use PID control. What are the advantages of PID control over the proportional control mentioned earlier? How should the PID parameters be set to be optimal?
The surge phenomenon in turbine compressors is divided into two types. One type is the vibration that occurs when the suction negative pressure reaches a certain value ； One is the vibration caused by overpressure at the compressor outlet. I can’t understand foreign languages, but everything used on site is very useful. The first phenomenon is caused by an insufficient suction volume when the device starts up; this type of issue hardly ever occurs, and it is required to turn the device off before it starts. The second method can be directly controlled by the pressure signal. However, for some gases that cannot have a venting requirement, it is controlled through the circulation rate. Some of the guide vane self-adjustment devices installed in compressors in the early stages proved ineffective in actual use, and most of them were removed. I’m not sure how well this logic applies in actual production settings. Stay tuned for the next episode :)
When the operating point is in the area between the SCL and SLL lines, proportional control and PID regulation operate simultaneously; generally, the method with the greater effect is chosen to control the anti-surge valve. This approach prevents excessive movement of the surge point, as well as situations where the PID output cannot keep up in time, resulting in delayed opening of the anti-surge valve and ultimately causing surge. This is a classic anti-surge control strategy, and many manufacturers incorporate this approach in their control systems