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In our refinery RFCC unit MAB was running with suction IGV mode since 2009 to 2017 AT 4350 RPM. During TA 2017, We changed the mode from IGV to speed control as suggested by OEM and the speed reduced from 4350 to 4000 and 6 to 8 tons/hr HP steam consumption reduced. Last month we try to increase the flow by 10,000 Nm3/hr we found the compressor suction side journal bearing temperature on increasing trend. After overhaul the machine in 2017 all the bearing temperatures in turbine and compressor found around 65 degC and the compressor suction journal temperature was 87degC.and maintained the same till last month. The oil analysis shows no any abnormality ( Low MPC, ISO oil cleanliness meets OEM's spec, oil colour is clear and no tracing of varnishing. RULER test given positive results) In the last one month only in compressor suction journal bearing temperature raising gradually up to 106degC ( High alarm 106, HH alarm 115)and then coming back to 96 and then raising again. This fluctuation raising and reducing is continuing. Mean time, as per OEM's recommendation we increase the oil flow to this particular bearing, reduce the oil supply temperature from 45 to 42 degC and compressor primary filters 50% replaced but no significant effects noticed,
Our doubts are if the oil quality is bad then all the bearing temperature should fluctuate but we have increase the bearing temperature only in compressor suction bearing.
Any one had similar experiences or can you share your thoughts for trouble shooting.