Vibration issues of CRYOSTAR nitrogen expander
Thread Content
The nitrogen expander in the 64000 Air Liquide air distribution unit operates in a nitrogen circulation mode. At 23:30, the vibration at the pressure-boosting end suddenly increased from 16 um to 23 um, and it fluctuated around this level until 4:30 a.m., when it rose to 35.32 um, triggering an shutdown (the shutdown threshold is 35 um). After the shutdown, inspections of the instruments showed no problems, and the expander was restarted at 6 a.m.; however, vibration levels remained high, around 24 um. As the load on the expander increased, the return valve at the pressure-boosting end was fully closed, and once stability was achieved, the vibration levels fluctuated around 17 um. But whenever adjustments were made to the expander, the vibration levels became more sensitive and higher. The vibration amplitude at the expanded end did not change significantly and remained relatively stable, around 13 um. Please analyze what possible reasons could be causing this?
If it is confirmed that the equipment is fine, then check the piping on site. I think it’s still the piping system that causes the issues; the fluctuations in gas flow lead to vibrations, in addition to the vibrations inherent in the equipment itself.
If it’s a piping issue, having been in use for two years, if the vibration level suddenly increases, could it be a problem with the pipes?
If it’s not during the test drive phase, then still 1) check the instrument issues, and once it’s confirmed that the instruments are fine. 2) Verify that the bellows expansion joints on the pipeline are installed properly. 3) Is there any fluctuation in oil pressure during vibration?
It is recommended to 1. shut down the machine to check the filter; this may be due to a damaged filter that allows foreign objects to enter the expander, or it could be that the foreign objects puncture the filter, potentially damaging the impeller and causing severe vibration. 2. Check the moving vanes of the nozzle; it is possible that one or more of these vanes do not move, resulting in flow deviation and excessive vibration.
Agreed; after all, it’s been in use for two years, so it’s possible to take apart the filter screen for inspection. Disassemble the expansion joint at the pressure-boosting inlet to check if there is a problem with the impeller. During the disassembly process, check whether the pipes are under high stress.
Please check again and tighten all the positioning and fastening points on your return line. If that still doesn’t work, realign the expander once more. It’s been two years; according to standard practices abroad, a comprehensive inspection of the torque on the bolts of moving equipment is required once a year.
During maintenance a few days ago, I encountered a similar situation; it was caused by leakage in the primary cooler of the circulating nitrogen compressor (the water inside is difficult to remove). When the outlet dew point dropped to -55 degrees Celsius, the high- and low-temperature expanders were started. The vibration at the pressure-increasing end of the high-temperature expander gradually increased, eventually reaching a level 1 um away from the value that triggers shutdown. What’s your situation? Please provide more details. It seems that foreign objects may be stuck to or have fallen off the impeller. If you discovered this issue during operation, then first check whether there could be any moisture that has entered, and secondly analyze whether any foreign objects might have stuck to the components during previous startups
The analysis of the phenomenon you described is as follows: the reason for the first jump out of the vehicle is unknown, and therefore it cannot be analyzed. After the second start-up, the vibration level was high before the anti-surge valve closed completely; it returned to normal once the valve was fully closed. However, it experienced significant fluctuations as soon as the operating conditions were adjusted. In my opinion, the main reasons are as follows: First, the initial trip may have been caused by an opening in the anti-surge valve. Under normal operating conditions, the booster should not have any opening; the anti-surge valve is only used when starting the expander while it is hot. There are precedents of trips or turbine damage occurring due to an opening in the anti-surge valve. II. It is recommended that you pay attention to whether there are any signs of fluctuation in the anti-surge valve during the turbine adjustment process; even slight fluctuations can lead to large variations in vibration levels. III. It is possible that the components of your turbine are already damaged; it is recommended to carry out a thorough overhaul as soon as possible, otherwise there is a risk of the machine becoming unusable
It is recommended to shut down the machine and disassemble the expander for inspection