ABB has approximately 200 GT11N and GT11D type gas turbines currently operating in simple cycle and combined cycle power plants. Most of these machines are fairly mature with many approaching the end of their economic life. In order that the power producer may continue to operate a fleet with improved performance, Advanced Air Cooling Technology and Advanced Turbine Aerodynamics have been utilized to uprate these engines with the implementation of a completely new turbine module.

The objective of the uprating program was to implement the advanced aero/cooling technology into a complete new turbine module with:

• Improved power output for the gas turbine

• Increase the GT cycle efficiency

• Maintain or improve the gas turbine RAM (Reliability, Availability & Maintainability)

• Reduce the Cost of Electricity

• Maintain or reduce the emissions of the gas turbine

The GT11NM gas turbine has been developed based on the GT11N which has been in operation since 1987 and Midland Cogeneration Venture (MCV-Midland, Michigan) was chosen to demonstrate the uprated GT11NM. The upate/retrofit of the GT11N engine was conducted in May/June 1997 and the resulting gas turbine - GT11NM has met and exceeded the performance goals set at the onset of the development program.

The next sections detail the main changes to the turbine and the resulting performance improvements as established with the demonstration at Midland, Michigan.

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