Abstract

Today’s advanced Gas Turbine (GT) combustion systems are designed to achieve low emission limits over a wide operational range. Regular combustion tuning is usually required to ensure that emissions are kept well within the plant compliance limits and that combustion dynamics levels are low enough to meet the mechanical integrity targets of all hot gas parts. These targets must be met during the full lifetime of the power plant, regardless of ambient conditions, fuel composition or engine degradation. Considering also the recent increase of combustor inspection intervals and the change in the GT loading profile due to the intermittent nature of renewable energies, it became advantageous to develop an automated GT26 combustion tuning control.

Ansaldo Energia self-learning AutoTune system, based on the well proven product developed by Power Systems Manufacturing (PSM), tunes engine operating parameters to maintain emission and combustion dynamics within specified limits under varying ambient conditions, load ranges, gas compositions and increasing engine degradation. It increases the robustness of the operation concept by introducing dynamic set points instead of fixed settings. This results in tuning flexibility, continuous engine optimization and it helps to potentially eliminate manual engine adjustments during a major inspection cycle.

After a general introduction on the operating concept of the GT26, the interaction between AutoTune and the GT controller is described together with the set-up and tuning principles. The universal AutoTune algorithm was adapted to the unique GT26 reheat architecture and flexibility, allowing for: (i) GT26 EV and SEV tuning for emissions and pulsations during stable conditions, (ii) tuning to minimize the minimum environmental load (MEL) with changing fuel gas properties or ambient temperature with the Low Part Load (LPL) concept, (iii) handling of very reactive fuels with high C2+ concentrations, (iv) tuning during transient conditions accounting for the variation of the GT thermal state. Based on robust experience after five successful GT26 installations, tuning attempts and successful tunings are statistically analyzed on a commercial plant over a period of several weeks to demonstrate the enlarged operational flexibility and performance of the GT26 equipped with AutoTune. The data analysis focuses on the Low Part Load operation, where Autotune achieved a robust decrease of MEL of 20MW, corresponding to a reduction of 4% in terms of combined cycle relative load.

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