Combustion Turbines

Combustion turbines are available in a wide range of sizes (500 kW - 25 MW) with most commercial products falling in the 1 - 7 MW size range. Simple cycle turbines have efficiencies generally in the range of 20 - 45%. Heavy frame turbines have slightly lower efficiencies (20 - 34%) than the aero derivative turbines (26 - 45%). While several factors influence efficiency, it generally scales proportionately with size; the larger the turbine the higher the efficiency.

Combined cycle combustion turbines can reach efficiencies of up to 55% (LHV). However, these are larger units generally utilized in central power plant arrangements, rather that distributed generation.

Uncontrolled emission levels for combustion turbines is approximately 150 - 300 ppm NOx, but domestic regulations prevent such units from operating in the U.S. Emission control systems are used to reduce NOx emissions to approximately 6 ppm for natural gas turbines:

Other performance related items for combustion turbines include:

• Part load efficiencies (50% load) are approximately 25% lower than full-load efficiencies.
• Start up times range from 2 to 5 minutes.
• Combustion turbines require natural gas pressure range from about 160 psig up to about 610 psig, depending on the manufacturer, type, and size of turbine.
• Most combustion turbine applications require a gas compressor which reduces the plant power output by 2 - 4%.
• CTs are rated based on standard conditions at sea level. Output and fuel consumption will decrease about 3.5% for every 1000 feet above sea level.
• CTs are rated at a nominal temperature of 59°F, and their output decreases by 0.3 to 0.5% per °F increase in ambient temperature.
• Heat rate increases about 0.1 to 0.2% for every 1°F increase in turbine inlet temperature.