Fuel control valve upgrade in gas turbine eliminates problems of wear

In April 2012, Turbine Technology Services was involved in the conversion project of two legacy GE Frame 5001 gas turbines at a Mississippi area power station. The units, which were originally installed with the GE Fuel Regulator Turbine Control System, supply power and steam via a heat recovery systems generator.

Originally retrofitted in the early 2000s with a more modern PLC-based turbine control system, it offered turbine owners increased flexibility in turbine control thanks to its enhanced instrumentation and diagnostic capabilities–effectively extending its operational lifetime. However, the fuel control instrumentation was not upgraded and left in its original configuration.

The only modification made at that time in the fuel control instrumentation was a conversion device, which translated the modern turbine control system command signal to a traditional hydraulic command signal that the installed fuel control instrumentation used for fuel flow control into the gas turbine.

Communication with the original turbine fuel control system communication involved a hydraulic pressure signal, which was fed to the fuel control valve for positioning. The accuracy of this control loop required the use of precisely-calibrated hydraulic-to-mechanical positioning devices. These devices are highly reliable in a clean turbine lube oil environment with proper service and maintenance.

The shortcoming in this configuration is that due to the devices’ mechanical wear characteristics, as well as the need to manually calibrate these devices in the field; these devices have become obsolete in their application. In addition, the weaning of technical knowledge on the proper procedures and settings also contributes to the limitations on this procedure.

The fuel conversion update involves the installation of modern electrically-driven servo motor actuators, mounted on fuel control valves provided by Young & Franklin, Inc.

The solution was completed by TTS who updated the way in which the PLC-based turbine control system meters the fuel flow to the gas turbine by eliminating the unnecessary pre-control valve pressure regulation, which has been a gas turbine standard.

The upgraded system is commanded via standard electrical signals generated by a single device without affecting the performance of all other systems of the gas turbine, such as lube oil.