During the testing of the carbon dioxide unit, as the speed increased to around 5,000 revolutions per minute, the vibration of the gears increased rapidly
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During the testing of the carbon dioxide unit, vibration increased rapidly when the speed reached around 5,000 revolutions per minute; an alarm was triggered due to the vibration of the large gear. When the speed reached around 6,000 revolutions per minute, interlocks were activated because of the high level of vibration, and this happened several times without any change. On site, it was reported that there were no abnormal noises from the unit (it was also noted that the unit experienced surge at a speed of 4,500 revolutions per minute, with the surge noise disappearing once the speed exceeded 5,000 revolutions per minute)
What gas do you use as the testing medium? Is it carbon dioxide?
Reply to 1# dongdog: Based on your description, 5000 should be the critical speed of the unit. At this critical speed, the vibration of the unit reaches its peak, and it is necessary to pass through this point quickly. It’s possible that the unit stayed at this critical speed for too long; thus, it shut down as soon as it reached 6000. Professional assistance is required for this process, and this represents one of the most important issues in starting up the unit.
Is it original driving? Is the first critical speed 4900? If the vehicle is being started after maintenance, what was replaced during the maintenance? Is there a problem with the gear meshing in the speed increase gearbox? Please describe it in more detail.
During the commissioning of carbon dioxide units, it is necessary to pass through the critical speed range quickly; otherwise, the unit will experience significant vibration, which may even lead to shutdown.
When driving, one should quickly exceed the critical speed
We were conducting initial testing, and we ran another test today; the speed reached 6,300 revolutions. The high-frequency oscillations appeared again. The medium used for our testing is carbon dioxide, and its purity meets the required standards. Today, we tried the 4-3, 2-1 anti-surge strategies, and in all cases we managed to stay outside the surge zone. Everything seems to be working normally from a process perspective; I thought we might be able to overcome this issue today, but unfortunately it happened again
Additionally, the critical speeds of the turbines are 2500 and 4122 revolutions per minute
Also, when we started up today, we opened all of the relief valves for the second-stage outlet as well. We initially thought that the flow rate in the second circuit was insufficient; at 4400 revolutions per minute, the flow rate was adjusted to optimize the operating conditions, and it was reported on site that surging had completely disappeared. As the speed increased further, approaching 6000 revolutions per minute, an alarm related to the high speed of the large gear appeared again. By the time the speed reached 6300 revolutions per minute, a high-speed interlock mechanism was activated
This post was last edited by mirook on 2010-7-7 09:20. It seems that it’s not a surge issue; rather, it’s resonance or critical speed. Your critical speed value should be that of the compressor; currently, it is the large gear that is vibrating heavily, so it’s necessary to check the critical speed of that gear. Is the vibration at the large gear also the shaft vibration measured by the eddy current sensor? Do all the measurement points on the large gear exhibit high vibration levels? Have there been any changes in the vibration at other measurement points? This is a new aircraft, right? It would be best to measure the vibration spectrum to determine which frequency is causing the vibration, so as to identify the location of the problem.