Hard on the heels of Siemens’ announcement last week that it had breached the 60% combined cycle efficiency barrier at Irsching 4 – achieving a TUV verified figure of 60.75% on 6 May – comes GE’s launch of a new 510 MWe 50 Hz combined cycle plant, the “FlexEfficiency* 50”, said to be capable of achieving over 61% efficiency. And again, like Siemens, the new plant is also designed to be extremely flexible, employing air cooling only.

Around ten years ago, when combined cycle plants were envisaged as predominantly operating in baseload duty, GE thought steam cooling (of rotating as well as stationary components) was the route to higher efficiency. But the demand from users for flexibility, exacerbated by the need to accommodate more renewables on the grid, has changed all that, coupled with advances in air cooled turbine technology itself (new alloys, increased computer power for modelling blades, etc). Steam cooling is also relatively complex and adds to capital costs.

The FlexEfficiency* 50, envisaged as the first product in what is described as the new “FlexEfficiency* portfolio”, builds on GE’s existing FB gas turbine, and is the result of an R&D investment of over $500 million.

Changes from the FB include increase of firing temp by 50 deg F (although the new GT is still described as a “1500 deg class” machine), increase in power turbine stages from 3 to 4, improved compressor design (including greater use of 3D aerodynamic blade modeling), better sealing, and increased maintenance interval.

Launching the new technology in Paris on 25 May, Paul Browning, VP, Thermal Products, GE Power & Water, described it as “a natural gas fired combined cycle plant whose purpose is to help enable greater uptake of renewable energy.”

The new plant draws on GE’s aeroengine expertise to offer a ramp rate of 51 MW/min without straying outside emissions limits (50 ppm NOx) and the ability to go from hot start to full rated power in 28 minutes. The plant will also be able to maintain high efficiency at part load and stay within emissions guarantees when turned down to 40% load.

The gas turbine will be tested in GE’s new $170 million full speed full load test facility at Greenville, with testing anticipated to start in January 2014.

Shipping of the lead combined cycle plant is anticipated for 2014, with commercial operation and first achievement of 61% efficiency expected in 2015.