Putting Power on Ice
by Michael Valenti,
Associate Editor 		Operators of cogeneration plants are boosting gas- turbine output during peak summer demand by making ice at night and using it to cool turbine-inlet air during the day.
Cogeneration plants, which convert turbine exhaust into additional steam and/or electricity, need to boost performance during the peak demand periods in the summer. Gas-turbine output drops in the summer, however, because the air is hotter. One solution, known as refrigerative cooling, is to cool the air entering the gas-turbine inlet, which increases turbine power output by 25 to 30 percent during peak periods. The cooler the air, the higher its density and mass. Because turbine output depends on mass flow, the cooler the air, the higher the output.

A study of evaporative, absorption, and refrigerative cooling found that refrigerative cooling, particularly when combined with off-peak chilling and storage, is the most effective inlet-air-cooling technique. Refrigerative-cooling systems freeze water at night, when electrical demand and costs are low, and store the ice to cool inlet air during daylight hours, when electrical demand and costs are high.

Henry Vogt Machine Co.'s Turbo Refrigerating Group in Denton, Tex., has developed a commercially available technology, thermal-energy storage for gas- turbine technology engine inlet air cooling (TESTIAC). The company says they can equip a 1,000-megawatt plant with TESTIAC to meet power demand that grows 10 percent annually for three years for less than half the cost of adding gas turbines. The TESTIAC system is relatively easy to install because it is not integrated into the gas turbine itself but instead functions as a stand- alone system.

Three TESTIAC systems have been installed in U.S. cogeneration plants. Thermal-storage inlet cooling is not limited to cogeneration schemes; TESTIAC systems are used in some simple-cycle utility plants in the United States.

A sidebar to the article discusses the benefits of an turbine air cooling method in Italy that integrates absorption and evaporative cooling systems.

The above was adapted from an article by Michael Valenti, Associate Editor. The full text can be found in the October 1996 issue of Mechanical Engineering magazine.©1996 ASME International. To obtain a copy of this issue, click here.

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