REXA recently conducted a steam turbine actuator retrofit on a Nuovo Pignone steam turbine driving a hydrogen recycle compressor at a refinery in Mexico. The OEM actuator was the original Nuovo Pignone style, which consisted of a pilot valve and power piston. This actuator required an external oil supply from the turbine oil skid (pump). One of the main issues with this actuator type is its susceptibility to oil contamination and varnishing, which causes internal stiction. The actuator exhibited poor control and “hunted” for position, ultimately leading to large and unwanted RPM swings and costly, nuisance trips.
Refinery personnel met with REXA to develop the right solution. Following review of all the issues, REXA proposed the “Rotating Equipment Total Integrated Solution” package. This all-inclusive upgrade solution includes onsite evaluation, engineered actuator mounting hardware and installation drawings, TAR supervision and support, both mechanical AND electrical integration/calibration, as well as on-site REXA product training.
By utilizing the self-contained design of Electraulic™ Actuation, the need for the external oil supply to the OEM actuator was eliminated. All segments of the REXA hydraulic circuit are positive pressure. The oil inside the actuator is never exposed to atmospheric conditions and excessive heat, ensuring no contamination or varnishing. Replacing the old flyball governor and installing our Electraulic™ actuators allowed tighter RPM control. This also enabled fully automatic startup of the machine from the control room, meaning they were able to start the unit and put it online consistently without variants in operator methods.
The implementation of the speed controller and our actuator to control the process loop enabled the capability for our customer to fully modify the setpoint from the control room from 0-100% speed – a much needed upgrade from the analog control loops of the OEM equipment.