The generation and prevention of surge

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Generation and Prevention of Surge Surge is a vibration under abnormal working conditions that occurs in a turbine compressor (also called a vane compressor) when the flow rate is reduced to a certain extent. Centrifugal compressor is a form of turbine compressor, and surge is very harmful to centrifugal compressors. 8 * _ When surge occurs in LK centrifugal compressor, typical phenomena include:: @gT0rT 1) The outlet pressure of the compression mechanism initially increases, then drops sharply, and fluctuates greatly cyclically. ； vej 2) The flow rate of the compressor drops sharply and fluctuates significantly. In severe cases, air may even flow back into the suction pipe. ； SN#S~6 3) The current and power meter indications of the motor driving the compressor are unstable and fluctuate greatly. ； C&j:O 4) The machine produces strong vibration and abnormal air flow noise. S+HV mechanism research results show that the internal cause of surge is closely related to the detachment of gas in the leaf duct. 6x75E When the gas flow rate is reduced to a certain extent, the flow direction of the air flow inside the compressor seriously deviates from the installation direction of the blades, causing a large positive angle of attack between the inlet airflow angle and the blade inlet installation angle, resulting in a serious separation of the airflow on the convex surface of the blades in the blade passage. In addition, for the impeller of the centrifugal compressor, due to the existence and influence of axial vortex, etc., it is more likely to cause uneven speed in the blade passage, and the above-mentioned air flow detachment phenomenon is further aggravated. When the airflow detachment is serious, the gas in the leaf passages stagnates and the pressure suddenly drops, causing the high-pressure airflow behind the leaf passages to backflow to make up for the lack of flow and alleviate the airflow detachment phenomenon, and temporarily return it to normal. However, when the incoming gas is pressed out, the above phenomenon is repeated again due to the lack of replenishment of flow in the stage. In this way, the phenomenon of air flow separation and air flow backflow occurs over and over again, causing the compressor to generate a low-frequency and high-amplitude pressure pulsation. The machine also vibrates strongly and emits strong noise. This is the internal cause of surge. o'C, from the perspective of the compressor performance curve, when the compressor surges, its working point must enter the surge zone. Therefore, severe compressor surge is also closely related to the pipeline network. In other words, all external causes that can cause the joint working point of the compressor and the pipe network to enter the surge zone will cause surge. R@XMT In the actual operation of the compressor, the following factors will cause surge to occur: Ni9 1) Switching failure of the air separation system. The valve entering the main heat exchanger or molecular sieve adsorber cannot be opened in time, causing the discharge pressure of the air compressor to be extremely high, causing the pipe network characteristic curve to steepen sharply, and the joint working point of the compressor and the pipe network to move rapidly, entering the surge zone and causing surge. ； {jhd/{ 2} The compressor flow path is blocked. Due to cooler leakage or dust scaling, the flow path is rough and the local cross-section becomes smaller. ； | lA 3} Compressor air inlet resistance is large, such as filter blockage or impeller inlet blockage ； @ * 4} The quality of the power grid is not good, the power grid cycle drops or the voltage is too low, causing the motor to stall and causing the compressor flow to drop to the surge zone. ； W 5} During the compressor startup operation and pressure boosting process, the operation is not municipal, the pressure boosting speed is fast, and the opening of the inlet guide vane is small. ； ,Uc 6} The vent valve or anti-surge valve is not opened in time during electrical failure or chain shutdown. In order to prevent surge, centrifugal compressors are equipped with anti-surge automatic relief valves. Once the outlet pressure is too high and the compressor approaches the surge zone or surge occurs, the valve should automatically open. If it is not opened, it should be opened manually in time. The automatic relief valve should be checked and maintained regularly to make it flexible and easy to use. J Currently there are two widely used anti-surge measures:: &g!;] 1] Pressure control. It belongs to single parameter control. Usually equipped with a pressure regulator, the compressor operates at a set pressure. When the pressure is higher than the set pressure, the anti-surge valve opens and releases part of the pressure to keep the discharge pressure at the set pressure. At the same time, the anti-surge valve is interlocked with the motor, and the anti-surge valve automatically opens when the motor trips and shuts down. !\-8Ee 2] Dual parameter control. Dual parameters refer to pressure and flow control. It is more advanced in terms of control method. Because of the intelligent means, it is also more reliable. +'@G