It’s quite strange that the bearing temperatures of the turbine–centrifugal compressor unit have decreased
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Our compression unit consists of a back-pressure turbine and a centrifugal compressor; the turbine is driven by steam at a medium pressure of 3.5 MPA. On the unit monitoring screen, temperature monitoring is carried out for the bearings on both sides of the turbine, the bearings on both sides of the compressor, as well as the thrust bearings at both ends of the unit – a total of 6 temperature points. Recently, something strange has happened: every day around 4 p.m., the temperatures at these 6 bearing points start to drop, by as much as 12°C, before returning to normal after about half an hour. It’s been over 10 days now, and it happens in such a regular pattern – every day at around 4 p.m. on time. We have been monitoring these parameters for several days, and almost none of them show any abnormalities. The parameters under observation include steam pressure, the pressure of lubricating oil entering the engine, the temperature of the lubricating oil after cooling, the compressor speed, and the vibration of the unit’s shafting – all of which are normal. Only one end of the shaft displacement is somewhat related to temperature fluctuations. The relationship between them is such that the shaft displacement gradually decreases, from 0.39 to 0.36; thereafter, the temperatures of the bearings start to drop sharply. Then the shaft displacement increases again to 0.39, and the bearing temperatures return to normal as well. Based on my current judgment, it seems that the periodic fluctuations in shaft displacement are the cause of the variations in bearing temperatures at various points. But what’s strange is why the shaft displacement fluctuates in such a regular manner It drops to a minimum of 0.36 around 4 p.m. every day, while it remains at 0.39 for the rest of the time. We invite experienced users to join the discussion and help us solve this problem; thank you all!
What is the normal bearing temperature? It’s strange; keeping an eye on it. . .
Is it due to a change in load or a problem with the instrument?
Is it after the shift change at four o’clock, and has the circulating water been adjusted? You should check the entire system
Interesting, there are such strange things out there
It should have nothing to do with loops. . You are coking units, right? . . Could it be related to the dry gas flow rate at the four-way valve, which causes changes in the compressor capacity and the inlet and outlet pressures? Which results in a decrease in the serial quantity. What about the changes in bearing bush temperature? . .
Reply to 1# 6862798: It’s indeed quite strange; the shaft displacement is only related to the temperature of the main thrust bearing pads! !
Thoroughly check for any adjustments during this period, and also look at the changes in ambient temperature; something that follows such a regular pattern should not be caused by some other issue.
All system-related issues have been checked, and no problems were found. It’s after 4 o’clock, the time for shift handover, but there are no periodic operations or adjustments related to this at that time. The instrument technicians said it wasn’t their problem. We think that since all six readings have decreased, it can’t be an issue with the instruments; it’s possible that it’s just one reading that has changed accidentally.
First, check whether there are any other events during this period that follow such a pattern. Some of these events might seem unrelated to each other, but in reality, that’s not necessarily the case. Let’s take our equipment as an example: one of our copper compressors (TA6000) has normal vibration levels of 3/8/9. However, every eight hours, the vibration level increases by one unit, reaching up to 12 at times. At first, we didn’t know why this was happening; the unit was operating stably, so it seemed like it wasn’t due to a fault within the unit itself. We removed the sensor used to measure vibration and checked it, and there was no problem with it either. Finally, it was found that the time at which the primary vibration fluctuation occurred was roughly the same as the time when the electric furnace in the device was switched over (the furnace switch-over occurred about half an hour earlier). But the electric furnace is 300 meters away from this unit, and the cables are not in contact with the unit either; moreover, the vibration extension cables are all armored and shielded. How do you explain this? So intuitively, it seems to be caused by the electric furnace, but I still can’t figure out the principle behind it. I also hope that the experts on this forum can help me think this through
“Which end is it that the shaft displacement has some relation to temperature fluctuations? Please provide the specific temperature values and load.