TURN-DOWN CAPABILITY OF ANSALDO ENERGIA'S AE94.3A

At an ever-faster pace, market's requirements for operational flexibility and turn-down capabilities are becoming the fundamental driver for heavy-duty gas turbine design and upgrade. This enables better compensation of the natural intermittence of renewable energy sources such as wind and solar by effectively compensating for both surpluses and shortages compared to the electric grid power request. Gas turbine-based energy plants require a lowest Minimum Environmental Load (MEL) for times when the power request is mainly covered by renewable sources and, however, need to promptly respond to green energy shortages. Ansaldo Energia has been addressing such requirements overall its gas turbine portfolio for several years, recently including further extension of MEL for GT26, as discussed in GT2021-59457. The present paper addresses the development project carried out to reduce the MEL for AE94.3A via a modular upgrade package especially intended for the wide existing Service fleet, made of more than 110 units. In order to accomplish the AE94.3A MEL reduction, several features were designed and tested including VIGV extra-closure, air bypass through compressor blow-off lines and extended use of anti-ice air recirculation. None of these require major hardware changes but only upgrades within a normal service outage, together with minor control system adaptations. The wide-ranging technical challenges attached to the MEL reduction features are discussed. Validation on field via special instrumentation focused on compressor, secondary air system and turbine for several engines is also presented. The achieved Minimum Environmental Load reduction is shown and its potential discussed together with some features already in place, such as the use of CO catalyzer or the regulation of control valves put on external cooling lines. The readiness and performance level of this MEL upgrade package, already in operation on several power plants, is here demonstrated. This makes the AE94.3A gas turbine more flexible towards current and future market requirements.