Ansaldo Energia’s GT26 MXL3 Service Upgrade

Abstract The GT26 from Ansaldo Energia’s product portfolio is an F-class engine featuring a sequential combustion system. The GT is optimised for combined cycle applications. Over the past 25 years, the engine has undergone continuous evolutionary development, improving plant performance, operational flexibility, and maintenance costs. The GT26 MXL3 upgrade is the latest enhancement for the GT26 (2006) platform, which is the most widely deployed version in the GT26 fleet. This paper provides an overview of the development project, focusing on its objectives, design modifications, validation, and initial field performance. A key goal of the MXL3 upgrade was to strike a balance between design improvements, associated hardware costs, and the achievement of technical targets. These targets include increasing combined cycle efficiency, reducing the carbon footprint by enhancing hydrogen combustion capability, and lowering maintenance costs through extended inspection intervals. One of the primary challenges of plant upgrades is ensuring compatibility with existing components, such as the heat-recovery steam generator (HRSG), gas and steam turbine generators, or step-up transformers, which may have limited capacity to handle additional power output or exhaust energy. To address this, the GT26 MXL3 is designed to boost combined cycle efficiency by +1.6% points over the GT26 (2006) baseline while capping the increase in combined cycle power output. Power limitations introduce additional design constraints, which are discussed in this article. The GT26 MXL3 leverages the SEV burner from the GT26 (2011) version, capable of burning hydrogen-blended fuels with a maximum H2 content of 45 vol.%. Both the burner and the combustion chamber are equipped with acoustic dampers, providing a wide operating window. The combustion system is also characterized by low emissions and high fuel flexibility. Additionally, the upgrade is compatible with other operational flexibility features, including extended Low Load Operation (eLLO), extended Low Part Load (eLPL) operation, fast load gradients, and power augmentation. eLPL and eLLO improve the engine’s turn-down capability by selectively deactivating individual burners in the second combustor (eLPL) or ensuring emission compliance at low loads by operating with only the first combustor ignited. Upgrade costs are optimized by limiting the redesign scope of gas turbine components, ensuring compatibility with existing plant equipment, and extended maintenance intervals. The first GT26 MXL3 upgrade was implemented in a combined cycle plant in the Netherlands in summer 2023. Extensive validation testing, including a dedicated thermal paint test and the installation of additional validation instrumentation such as temperature and pressure sensors, tip timing, strain gauges, and rub pins, was conducted. The validation results aligned with design expectations. A routine visual inspection of the gas turbine was carried out in summer 2024 after one year of commercial operation, and all components were found to be in excellent condition.