Latest upgrade to GT26 said to push combined cycle efficiency beyond 60%

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At PowerGen Europe this week Alstom announced the latest upgrade to its KA26 combined-cycle power plant offerings, based on improvements to the GT26 gas turbine. The enhanced KA26 gas-fired power plant can deliver more than 500 MW, can be started up in less than 30 minutes, and ramp up to more than 350 MW in less than 15 minutes from low load, said Mark Coxon, senior VP of the company’s gas business.

The KA26 is said to deliver 500 MW of power, more than 61% efficiency, and able to avoid more than 350,000 metric tons of CO2 emissions, compared with existing combined cycle plants in EU-27. The upgraded GT26, for the 50 Hz market, provides more efficiency with lower emissions, based on sequential combustion technology. This is characterized by splitting the combustion process into two stages, separated by expansion in a high-pressure stage. In this “re-heat” process, fuel is further added part way through the expansion process, resulting in high gas turbine efficiency, high power density and low emissions.

Emissions are kept under control for the full operational range (down to 40% and at around 20% CCPP low load). The GT26 combustion system will achieve emission values below 25 vppm NOx at 15% O2 dry over a GT load range from 100% down to 40% and below, as well as a low-load parking point.

The compressor architecture is based on the 22-stage design of the current GT26 engine. This included increasing the variable vane row count from three to four. The blade design was also optimized by using Controlled Diffusion Airfoils (CDA) and improved sealing in the combustor, based on a decade-long, technology-sharing agreement with Rolls Royce.