Handling of compressor surge

There are two forms of surge in gas compressors: one is caused by an excessively small opening degree of the suction valve ahead of the compressor, and the other is resulting from high outlet pressure. The usual approach to dealing with surge is by reducing the pressure behind the machine. Turbine-driven turbo compressors do not experience surge due to low suction pressure. Surge can also occur within a certain range due to the low output capacity of the turbine. But the treatment is also intended to reduce the pressure behind the compressor. Perhaps due to regional differences, textbooks on chemical engineering principles are generally used as a reference, and the term used for \"pump\" seems to vary. Pumps are divided into positive-displacement types and turbine types. Positive-displacement pumps come in various forms, such as piston-type and gear-type, etc. For the standardization of discussions, it is best to use a unified classification. It’s just a suggestion, for reference only.

When referring to rotational speed, it usually pertains to centrifugal compressors, that is, what the predecessors called turbines. Regarding the prevention of surge: In the case of constant-speed compressors, surge is generally prevented through surge valves, and the compressor unit itself should also have a surge protection system that can respond and make adjustments. In the case of variable-speed compressors, this goal can be achieved by changing the speed, but as a standard approach, a surge prevention system should still be used to prevent surging from occurring, with this method serving as an alternative. Furthermore, changes in speed pose certain risks to the unit equipment itself.

What you are referring to is probably a centrifugal compressor; I’m not sure whether it is driven by a motor or by a turbine； In short, during surge, the first step should be to open the anti-surge valve, and then the speed should be adjusted up or down depending on the specific circumstances. Controlling surge prevention by increasing or decreasing rotation speed is risky: if the inlet flow rate remains constant, increasing the rotation speed will cause the unit’s operating point to move further into the surge zone ； If there is an adequate amount of intake air, surge (backflow) caused by the discharge pressure being lower than the pipeline network pressure can be prevented by increasing the rotation speed. Therefore, anti-surge analysis and control cannot rely solely on addition, subtraction, and switching. Appropriate control measures should be taken based on the cause of the surge.

Is the most direct solution to surge caused by low inlet flow rate to open the anti-surge valve?