Chlorine compressor surge

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Surge occurs for two main reasons: either the flow rate is low, or the outlet pressure is high, which causes the gas to flow back in time or to vibrate. To address this issue, one can open an air valve or a surge preventer valve, activate a return line, and at the same time reduce the opening of the outlet valve

High outlet pressure doesn’t necessarily lead to surge; a comprehensive analysis is needed, as individual data alone are meaningless.

Low flow rate or high outlet pressure.

As long as it ultimately results in the pipeline pressure being higher than the compressor outlet pressure, that will happen, right? Is that accurate?

Surge is an inherent characteristic of centrifugal compressors. When the pressure or flow rate at the compressor’s suction inlet suddenly drops below the minimum allowable operating level, severe rotational separation of the gas within the compressor occurs, leading to sudden stall (meaning a significant deviation in the flow direction of the gas at the inlet of the blades and in the blade inlet angles). In such situations, the impeller is unable to increase the gas pressure effectively, resulting in a decrease in the pressure at the compressor outlet. However, the pressure in the system piping did not drop immediately, which caused gas to flow back from the system piping toward the compressor; when the pressure in the system piping dropped below the compressor’s outlet pressure, gas flowed back into the system piping. Repeating this process causes periodic axial, low-frequency, high-amplitude airflow oscillations in the unit and the pipeline network. When operating at low load, the centrifugal chiller reduces the opening of the compressor vanes, resulting in a decrease in the flow rate of refrigerant involved in the cycle. As the compressor displacement decreases, the impeller’s ability to generate pressure head also diminishes, and at this point surge occurs. The operator should have the compressor performance curve with the surge line marked, so as to always know the position of the compressor’s operating point on the performance curve. To prioritize operational safety, an anti-surge line can be added at a flow rate that is 5% to 10% higher than the surge line, serving as a reminder to the operator. Reducing the operating speed can decrease the flow rate without causing surge, but the outlet pressure decreases as a result. Guide vane rotation mechanisms are installed at the primary stage or at various stages to adjust the angle of the guide vanes, so that the inlet shock angle does not become too large when the flow rate decreases, thereby preventing surge. A bypass pipe is installed at the compressor outlet; when it is necessary to reduce the flow rate delivered by the compressor during operation, the excess gas can either be vented or sent back into the intake pipe after pressure reduction. It is better to consume more flow rate and power rather than allow the compressor to operate with an insufficient flow rate, in order to prevent it from entering a surge condition. Temperature and flow rate monitoring instruments are placed at the compressor inlet, while pressure monitoring instruments are installed at the outlet. Alerts are generated promptly in case of any abnormalities or surges, and it is ideal for these systems to be connected to surge prevention control mechanisms as well as emergency shutdown systems. The operating personnel should understand the working principle of the compressor, keep an eye on the operating conditions of the machine at all times, be familiar with the operation of various monitoring and control systems, and strive to prevent the machine from entering a surge damage state. Once surge occurs, the flow rate must be increased immediately to exit surge or the machine must be shut down right away. After shutting down, the machine should be inspected to ensure there are no hidden hazards before it can be restarted.

One of the chlorine compressors in our plant has been triggering surge alarms frequently recently, but according to the DCS, there are no issues with the flow rate or outlet pressure. The pressure difference across the inlet filter once reached 14 kPa; the PLC controls it to rise from 35 to 65 each time. Is there a problem with the PLC’s control, or is there some other reason causing surging?

One of the chlorine compressors in our plant has been triggering surge alarms frequently recently, but according to the DCS, there are no issues with the flow rate or outlet pressure. The pressure difference across the inlet filter once reached 14 kPa; the PLC controls it to rise from 35 to 65 each time. Is there a problem with the PLC’s control, or is there some other reason causing surging?

There should be a surge screen in the DCS; check whether the operating condition has exceeded the anti-surge line It should be quite clear.