Urgent! Urgent! Urgent! Question: Reasons for vibration

Our plant has an ammonia synthesis gas compressor, powered by a fully condensed steam turbine. The compressor consists of a low-pressure section, a high-pressure section, and a circulation section; the high-pressure section and the circulation section are located within the same cylinder. The main problem at present is that when the compressor operates at no load, it can reach its rated speed with low vibration levels. However, once the anti-surge valve in the high-pressure section is closed to increase the pressure, the shaft vibration in that section begins to fluctuate in a sawtooth pattern. If more load is applied and the compression ratio is increased further, the vibration levels rise suddenly, leading to an automatic shutdown of the compressor. Yet the cause of this phenomenon remains unknown Our vibration values show three high readings at the four measurement points, with only one being stable. I need the help of all the forum members; thank you!

If it’s not a gauge issue, then open the cover to check it. Check whether the rotor is aligned, the coupling installation, and the bearing clearance. Check again to see if the shaft displacement is normal.

In addition to the inspection items mentioned above, it is advisable to pay attention to the compression degree of the roof tiles as well

As mentioned above, are there any other abnormalities? Please upload the spectra for comparative analysis. Is there any issue with the operation?

Check whether your pressure relief valve is functioning properly. It is designed to operate at a certain pressure level; if it fails to do so, a shutdown mechanism is activated as a form of protection for the system. Also, consider whether the air compressor has been in use for a long time without having its waste fluids removed – check if there is any blockage in related components

Please post the Bode plot, trend graph, and spectrum graph so that everyone can analyze them more effectively. Let the data speak for itself. Based on what the original poster has described, everyone can only make guesses and analyses based on experience.

Check if there is air leakage in your series valve??

Take it apart and check! Check the bearing shells

Take it apart and check! Check the bearing shells

It’s hard to tell; there are too many possibilities. It would be best to provide more information

1. Check whether it is operating in the surge flow range； If it gets too close, it cannot be shut down; the amount or speed must first be increased. 2. If the problem persists, the rotor or tilting bearing needs to be checked

Based on the poster’s description, it seems a bit like trying to pull a heavy load with a small horse – the turbine does not generate enough power as the load increases. I think the focus should be on checking the turbine, such as whether the main steam valve opens fully during load application and whether the vacuum level remains stable. Our company encountered a similar situation during the commissioning of Unit 1; it was later found that the loosening of the last-stage impeller of the turbine was responsible for the decrease in the turbine’s output power, preventing the turbine from reaching the rated pressure.

Return to Building 4#: The main steam valve of the turbine is already in the fully open position; it is regulated by the throttle valve. The vacuum level is stable as well, and the vibration of the turbine is low. It can operate at its rated speed, but this must be done under no-load conditions. It has been noted that once the turbine reaches a certain speed of operation, it is necessary to close the anti-surge valve in order to increase the pressure. As soon as the anti-surge valve in the high-pressure cylinder is closed to about 70% of its position, closing it further by even half a step causes the vibrations to fluctuate; this sensitivity makes it impossible to increase the pressure. Looking forward to continuing our communication!

Upon further thought, I realize my previous judgment was a bit arbitrary. After the speed control valve is put into use, if the rotational speed can remain stable during the pressure increase process, factors related to the turbine can be ruled out. It is able to reach the rated speed smoothly under no-load conditions, which rules out the influence of critical speed and mechanical factors. The other possible factors are oil film vibration and surge; in your case, it is likely surge. The surge mechanism of multi-stage, multi-segment turbines is highly complex, and it is related to the compression ratio of each stage, as well as the temperature and density of the medium. I would like to share some insights on these aspects: 1. Maintain stability in the gas composition during the pressure increase process. The density of hydrogen and nitrogen is greatly influenced by the hydrogen-to-nitrogen ratio; therefore, maintaining a stable gas composition ensures stable medium density. 2. Apply load strictly in accordance with the acceleration curve, adhering to the principle of increasing speed rather than pressure, and increasing speed first before increasing pressure. 3. Increase the pressure first at low pressure and then at high pressure; if the compression level in the low-pressure stage is relatively low, insufficient intake may occur during pressure increase in the high-pressure stage, leading to a surge condition. 4. Closely monitor the pressure and temperature changes at the inlet and outlet of each section. I believe what you’re describing is surge. Since there are many causes of surge, I hope my analysis will help you resolve the issue.

I think the vibration is due to mechanical issues. Our ice makers have encountered similar problems before; high rotation speeds lead to greater vibration, and after repairs, the vibration was significantly reduced.

Vibrations are generally caused by gas imbalance, resonance, and mechanical instability.

All various loading methods have been tried, but the ultimate cause has not been determined. The manufacturer collects on-site data to determine whether it may be related to the design.

Original poster, please share your experience – what happened and how was it resolved?