Case Study: In-situ balancing of a non-linear SYN gas compressor rotor

Haider Ali, Engro Fertilizers


Synthesis gas compressor plays a vital role in an Ammonia Urea complex (fertilizer plant). Syn gas is primarily composed of hydrogen which makes it highly flammable, thus making it a huge safety concern if not operated in defined limits.
This case study expounds In-situ balancing of SYN gas compressor train comprised of 18 MW steam turbine</strong> and three compressor cases (low pressure, intermediate pressure and high pressure). Operating at 9800 RPM the rated output of the train is 17500 ksph at 3050 PSI.
Machine operates above the 1st critical making instu-balancing more challenging. What makes this case study exceptional </strong>is the non-linear behavior</strong> of the compressor rotor. The machine is equipped with Oil seal which exhibits hang up phenomenon due to tight seal clearances. This results in oil seal acting as the third bearing, damping shaft movement hence increasing the system stiffness. With every startup, the influence vectors used for balancing drifts and special measures have to be taken to compensate for oil seal hang up.

This case study will cover the problems faced on the compressor in regards with non-linear behavior of the compressor rotor, changing system stiffness and steps taken to compensate for this change in order to balance the machine.


Haider Ali holds chancellors silver medal in mechanical engineer degree and has a combined experience of 5 years in rotating machinery diagnostics in addition to maintenance/overhaul experience of turbo machinery (centrifugal compressors and steam turbines) and retrofits of gas-turbine components. He is widely recognized for his work on BCL compressors and tandem dry gas seals installation and troubleshooting.

Haider joined Engro Fertilizer in 2013 and has since been the integral part of the diagnostics team for the World’s biggest single train Ammonia Urea complex. Haider is a VA-III certified Vibration analyst.