H-Class Gas Turbine in Combined Cycle

More Flexible, More Efficient Gas-Powered Electricity

H-class gas turbines, used in combined cycle power plants (CCPPs), use both a natural gas and steam turbine to achieve high efficiency and low emissions. The H-class combined cycle plant also has the operating flexibility to start up quickly and the ability to vary its electricity output in just minutes, which improves generating efficiency while supporting grid reliability.

The Technology

After World War II, the aviation industry began to leverage jet engine technology for power generation. However, it was not until 1965 that gas turbines began to be used in power generation. Following a blackout in much of the Northeast, it was discovered that gas turbines, with their flexible fuel capability and short delivery cycles, provide a reliable and flexible source of backup power. Building on decades of improvements to gas turbine designs, the H-class turbine entered the U.S. market in mid-2010 with greater efficiency due to the combined cycle design. Operation of six H-class turbines has begun in the United States in the past two years.

Like other CCPPs, the H-class combined cycle plant contains both a gas turbine and a steam turbine. The exhaust heat from the gas turbine is recovered and then used to heat water and produce steam to run the steam turbine. Using the two turbines in tandem takes advantage of the high inlet temperature of the gas turbine and the low waste-heat of the steam turbine. By combining electrical output from both turbines, the H-class system produces more than 410 megawatts of electricity at more than 60 percent efficiency. H-class turbines can also vary their output in just minutes, while maintaining higher efficiency and reduced emissions compared to other CCPPs.

The Benefits

• Increased efficiency: Compared to simple cycle gas turbine technologies, the new generation of H-class gas turbines in combined cycle consumes one-third less natural gas and emits one-third less carbon dioxide while still generating the same amount of power.
• Enabling grid flexibility and reliability: It takes H-class gas turbines just minutes to switch from full to half power (or vice versa), enabling them to optimally compensate for natural fluctuations in rapidly increasing grid feed-ins from wind and solar energy sources.

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