【Daily Question 2019】Hydrogen production and hydrogenation section – Question No. 084

The characteristics include: ① Large fluctuations in the outlet pressure and inlet flow rate of the gas medium, and sometimes gas backflow may also occur. ② The pipeline network experiences periodic oscillations, with large amplitudes and low frequencies, accompanied by periodic \"roaring\" sounds. ③ The compressor vibrates intensely; both the casing and bearings experience strong vibrations, along with loud, periodic airflow noises.

Vibration intensifies, with obvious abnormal noises……

The characteristics include: ① Large fluctuations in the outlet pressure and inlet flow rate of the gas medium, and sometimes gas backflow may also occur. ② The pipeline network experiences periodic oscillations, with large amplitudes and low frequencies, accompanied by periodic \"roaring\" sounds. ③ The compressor vibrates intensely; both the casing and bearings experience strong vibrations, along with loud, periodic airflow noises.

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 inside 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 pressure at the compressor outlet, gas flowed back into the system piping. Repeating this process causes periodic axial, low-frequency, high-amplitude airflow oscillations in the unit and the piping 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.

1) When a centrifugal compressor operates at low flow rates, vortices are generated within the flow channels of the impeller and diffuser. The formation and disappearance of these vortices cause intermittent blockages and openings in the fluid flow channels, leading to periodic vibrations in the airflow and blades. This results in severe periodic vibrations and roaring noises inside the compressor; this phenomenon is known as \"surge\" in centrifugal compressors. (2) Surge phenomenon is very harmful to compressors. Intense pulsations and periodic oscillations of the airflow cause severe vibration of the blades, which increases the stress on the impeller and raises noise levels. This leads to intense vibrations throughout the entire unit, and it may damage the bearings and seals, resulting in shutdown or serious accidents.

The main reason for surge in centrifugal compressors is a decrease in load. When the compressor’s discharge volume falls below a certain limit, the operating point of the compressor experiences \"flutter\"; in this condition, gas enters and exits the compressor intermittently, subjecting the rotor to alternating loads, which causes vibration in the compressor body and propagates to the connected pipelines. If the piping network connected to the airframe has a small capacity and is tightly sealed, a periodic noise similar to the \"wheezing\" of an asthmatic patient can be heard ； If the pipeline network has a large capacity, periodic intermittent roaring noises occur during surge, and the check valve emits banging sounds. This leads to severe vibrations in the compressor and the connected pipeline system, and may even cause damage to the compressor. This phenomenon is known as the compressor’s \"surge\" phenomenon, and measures must be taken to prevent it.

①When the gas flow rate of a centrifugal compressor decreases to a certain level, insufficient volumetric flow leads to periodic and sudden severe separation of the gas from the rotating components, resulting in abrupt stall.

The characteristics include: ① Large fluctuations in the outlet pressure and inlet flow rate of the gas medium, and sometimes gas backflow may also occur. ② The pipeline network experiences periodic oscillations, with large amplitudes and low frequencies, accompanied by periodic \"roaring\" sounds. ③ The compressor vibrates intensely; both the casing and bearings experience strong vibrations, along with loud, periodic airflow noises.

The main reason for surge in centrifugal compressors is a decrease in load. When the compressor’s discharge volume falls below a certain limit, the operating point of the compressor experiences \"flutter\"; in this condition, gas enters and exits the compressor intermittently, subjecting the rotor to alternating loads, which causes vibration in the compressor body and propagates to the connected pipelines. If the piping network connected to the airframe has a small capacity and is tightly sealed, a periodic noise similar to the \"wheezing\" of an asthmatic patient can be heard ； If the pipeline network has a large capacity, periodic intermittent roaring noises occur during surge, and the check valve emits banging sounds. This leads to severe vibrations in the compressor and the connected pipeline system, and may even cause damage to the compressor. This phenomenon is known as the compressor’s “surge” phenomenon.