Seeking advice on sudden shaft displacement issues in centrifugal compressors
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I would like to ask the experts: When our compressor unit was operating normally, the shaft displacement suddenly changed from -0.01 mm to 0.07 mm and has remained at that level ever since (it has not returned to its original value). This change caused a sudden increase in the leakage of air from the main seal of the dry gas seal, but the leakage level quickly returned to normal. By checking the curves, I saw that neither the suction pressure nor the discharge pressure changed (air enters from both sides, with exhaust at the middle). The temperature of the thrust bearings also showed no significant changes. What could be the cause of this phenomenon? Additionally, what parameters changing during normal operation of the compressor can lead to sudden changes in shaft displacement? I hope you will kindly share your insights!
There are no changes in the lubricating oil system
Check if there are any fluctuations in the lubricating oil and if there are any changes in vibration
1. Based on the descriptive information, there is an instantaneous change in the dry gas seal when the shaft displacement changes abruptly, indicating that such a sudden change in shaft displacement actually occurs and is not a false signal; the recovery of the dry gas seal leakage rate is attributed to the control mechanism of the sealing system. 2. The most likely factors causing changes in shaft displacement generally include: 2.1. Whether the balance pipes of the compressor are unobstructed; 2.2. Changes in the stage pressure difference, which is closely related to changes in process conditions. Some parameters that can be observed include pressure, temperature, and flow rate, while others cannot be seen, such as changes in molecular weight due to variations in composition; 2.3. Mechanical damage, with changes in the area over which pressure acts leading to abnormal vibrations ； The damage to the tilting pad thrust bearings is progressive; it would be useful to check whether there are any abnormalities in the lubricating oil return temperature at the moments of displacement changes, or to analyze the lubricating oil to observe any changes in the content of metal impurities
It might be that foreign objects on the sensor surface are causing the values to change
My view on this issue is that all the possibilities mentioned in the above analysis may apply, but the most critical problem cannot be addressed, and it is also difficult to gather evidence to determine the cause of the problem. If I were to encounter such a situation, I would handle it in the following way; see if it can serve as a reference. When such things occur, check whether interlock shutdown restrictions have been activated but the shutdown did not take place; in this case, an emergency stop is required. If it is within the normal range, it can only be maintained for now, with a plan to address it during the next maintenance session. For such issues, the area that should be checked first is the clearance of the thrust pads. There’s nothing wrong with this area; you can disregard the others as you see fit. ，，，，，。 Other possibilities besides those mentioned include a blocked return air pipe; it might be due to what is referred to as a \"water blockage\", caused by an instantaneous blockage of water. In that case, there must be a leak in the intercooler, and it’s necessary to check for leaks whenever the system is started or stopped – it’s easy to detect such issues ； Problems with the oil system are also easy to detect; as for sudden issues related to electrical signals, nothing can be identified other than checking whether the connections in the wiring are in good condition. So, based on the current analysis and judgments, it seems that focusing on that is what matters.
Is there any change in temperature between the different sections? Is the balance tube blocked?
It should first be checked what parameters were adjusted at that time. There are two points for reference: 1. A significant adjustment in speed will result in corresponding changes in inlet and outlet pressures. 2. Significant adjustment of lubricant temperature (may be substantial)