Turboexpander Booster Compressor (TEBC) - Radial bearing temp sensor/element damaged

[engrjalbani]

We have recently commissioned Booster Compressor driven by Turbo-expander with active magnetic bearings, everything went pretty fine during commissioning, however, after few days operation, unit was kept standby for more than three months. later, upon restart-up, unit experienced hard landing due to trip caused by mal-function of compressor radial bearing temperature (high high, set-point 130oC), in real the temperature was much lower, around 45oC. We found that main temperature element of radial bearing was faulty and sent trip signal to machine. Now it is established that temp elements (both main and spare) needs to be replaced. The replacement of temperature elements requires to dismantle complete plug-in unit of TEBC, since these elements are glued on magnetic lamination, meaning that complete machine has to undergo overhaul.

Just to share, the plug-in unit contains all rotating components including bearing cartridge, wheels etc of the turbo expander/compressor, expander and compressor wheels are mounted on a single rigid shaft, supported by 2 radial magnetic bearings and one axial magnetic bearing. TEBC speed 11500rpm.

Guys so what do u suggest whether it is safe to continue TEBC operation without radial bearing (compressor side) temperature monitoring!! since temperature elements PT100(both main and spare) of radial bearing are faulty and replace temp sensor later during machine's overhaul or otherwise. I will definitely opt the first one.


Thanks

 

[rotw]

What I dont understand is why do you have a trip specified on journal bearing temperature when journal bearing purpose is for emergency landing in your case. I dont understand the design philosophy because if bearing temperature increases it means that the shaft has already landed and bearing started to operate but you are normally then shuting down the machine, so why having a trip then on these ? I am not specialist of magnetic bearing, so I might be missing something ?

For one of my project with centrifugal compressors, we dont trip on journal bearing temperature ; these are operating continuously and essential to machine operation (means we dont have magnetic bearings).

 

[engrjalbani]

rotw(mechanical),

Machine has separate dedicated auxiliary (landing) anti-friction bearings, magnetic bearings holds machine while running,being levitated,therefore temperature of magnetic bearings is important parameter to be monitored/controlled. Besides just to share, machine has permanent gas cooling line to keep temperature of magnetic bearings within limit.

Thanks