Syngas Compressor High Vibration Diagnosis and Resolution

This case study is focused on accurately identifying the root cause of the gradual vibration rise and intermittent vibration excursions leading to potential unavailability of a compressor train. The subject machine train is a Synthesis gas compressor used in a fertilizer plant in middle east, and it consists of a LP and HP compressors driven by a Steam turbine in a single shaft configuration. This is a high critical compressor delivering 215,800 kg/hr of syngas at a rated speed of 9370 rpm, suction and discharge conditions are 30.4 bar(g), 40°C and 200 bar(g), 40°C respectively. The machine was in continuous operation since last start up in April-2022 following a major overhaul. LP Compressor NDE bearing vibration trend plots showed rising trend since late 2022, mainly due to synchronous 1X vibration gradual increase resulted from suspected rubbing. LP Compressor bearings vibration trend plots also showed multiple intermittent vibration excursion events and the amplitude during one of vibration excursion events crossed OEM Alarm limit at NDE bearing with symptoms of potential flow turbulence. LP Compressor DE vibration trends also showed similar symptoms with less amplitudes. Based on the vibration data diagnosis it was concluded that change in rotor dynamic stiffness condition caused the change/increase in 1X amplitudes whereas the flow turbulence at particular operating conditions was driven by suspected changes in seals clearances. Thus, the decision was taken to shut down the machine train to inspect LP compressor rotor internals and inspect the compressor seals condition (interstage, center labyrinth, dry gas, and balance drum seals) and clearances for signs of deterioration. The inspection revealed significant damage to the balance drum seal.