R&D pays off in efficiency

Evolutionary engineering and revolutionary research have combined to allow GE Power Systems to nose ahead of its competition. GE recently announced its “G” and “H” generation systems, boasting 60-percent combined-cycle efficiency.

The G-machines will reach a 58-percent net thermal efficiency in combined-cycle operation, with the H-technology breaking the 60-percent barrier. The most efficient combined-cycle plants currently in operation hit 55-percent efficiency. An increase of a single percentage point of efficiency can reduce operating costs by (US)$15 to $20 million over the life of a typical gas-fired, combined-cycle plant of 400 to 500 MW, according to GE statistics.

“It`s a platform of combined-cycle technology that integrates the gas turbine, steam turbine and generator into a seamless system, where each component is optimized for the highest level of performance,” said David Genever-Watling, GE Power Systems president and CEO. “The centerpiece of this new technology platform is an advanced closed-loop, steam-cooling system in the gas turbine which permits higher firing temperatures while retaining combustion temperatures at levels consistent with low emissions.”

Conventional air film cooling lowers turbine temperature by injecting coolant into the hot gas stream, which quenches the hot gas stream, disrupts the flow, and reduces efficiency and output. In GE`s new system, steam from the turbine bottoming cycle is used to more efficiently cool the critical gas turbine parts, without disrupting or diluting the working hot gas stream. Benefits of this system include:

Steam turbine can operate at a higher firing temperature without an increase in bulk metal temperatures, thus increasing efficiency and output.

Reduction in first-stage nozzle air cooling permits a higher firing temperature for a given combustor discharge temperature, allowing low NOx emissions and high-efficiency standards to be met simultaneously.

Integrating the gas turbine with the bottoming cycle allows energy, added to the steam coolant, to be recovered by expanding the fluid in the steam turbine, generating more power.

The combustion system for the H-gas turbines evolved from proven GE Dry Low NOx systems which have reduced power plant emissions by more than 100 million pounds in approximately 85 installations with nearly 250,000 hours of operation.

Today`s G-technology machines can be upgraded from simple to combined cycle for 58-percent efficiency, or they can be upgraded to H-technology for 60-percent efficiency. The first 9H gas turbine will be tested in 1997, with the rest of the G and H families to follow.