What is compressor surge?

Due to insufficient inlet flow and excessive outlet pressure, the compressor experiences periodic severe vibrations accompanied by a roaring sound

It generally occurs in centrifugal compressors, where low inlet flow or pressure leads to surge. The anti-surge line can be opened, or the flow rate at the outlet can be directed back to the inlet to supply additional flow and increase pressure

When operating under normal conditions, centrifugal compressors generally do not experience surge. Surge can occur due to changes in operating conditions resulting from process changes or equipment failures (i.e., changes in flow rate). The fundamental reasons lie in two aspects: First, when designing a compressor, the geometric shape of the impeller should be determined based on the operating conditions, that is, the required flow rate. This ensures that, within a certain range of air intake volumes, the gas enters the impeller at the optimal angle, resulting in minimal energy loss and maximum velocity energy; this allows the impeller to convert as much energy as possible into the gas, thereby increasing its speed and pressure. It is only when the aerodynamic parameters of the gas and the geometric parameters of the impeller are in harmony that a normal operating condition is achieved. When the operating conditions deviate beyond the allowable range, the pneumatic parameters and geometric parameters become inconsistent, which in turn leads to chaotic gas processing by the impeller. As a result, the efficiency of energy conversion decreases, and severe rotational separation of the gas occurs within the impeller, leading to sudden stall. The gas flow pattern becomes very poor and irregular. At this point, although the impeller is rotating and doing work on the gas, it is unable to effectively increase the gas pressure, resulting in a decrease in the compressor outlet pressure. II. However, surge does not occur just because the pressure at the compressor outlet decreases. Another reason is that the compressor outlet is usually connected to a piping system; if the capacity of this piping system is large, its response is not very sensitive. In such cases, the pressure in the piping system may not decrease immediately, and instead the pressure there might be higher than that at the compressor outlet. As a result, gas starts to flow back, and the compressor can resume supplying air only when the pressure in the piping system drops below that at the compressor outlet. After some time, the pressure in the piping system again becomes higher than that at the compressor outlet, leading to the same phenomenon once more, and this cycle repeats itself. The system experiences periodic axial low-frequency, high-amplitude airflow oscillations, which gives rise to surge. Summary: There are two aspects to the reasons. The internal reason is that under certain conditions, the gas flow inside the compressor experiences a severe sudden stall ； External factors: Related to the capacity and characteristic curve of the pipeline system. Internal factors can only cause surge to occur when external conditions are met.

During operation, when the inlet flow is reduced to the minimum required level, the outlet pressure drops. But the pressure in the export pipeline system remains high; fluctuations in pressure cause shocks. The vibration increases. Just like a person’s coughing, difficulty breathing – when they cough, the whole body trembles; once breathing becomes regular, it gets better. The same principle.

Very comprehensive; I’ve learned from it. Thank you for sharing.

Surge can sometimes be not a problem with the machine itself, but is also related to the system, such as the resistance characteristics of the pipelines.

Surge is a type of vibration that occurs under abnormal operating conditions in turbine compressors when the flow rate decreases to a certain level. A centrifugal compressor is a type of turbine compressor, and surge poses a serious threat to centrifugal compressors.

The anti-surge line opens at low compressor load.