1.1 Turbines

Combustion turbines used for electric power production are composed of two basic types. Industrial combustion turbines are usually referred to as single-shaft heavy-duty combustion turbines, with generating capacities typically of 20 MW to more than 130 MW. Industrial combustion turbines are typically dual-fuel units, operating with natural gas or distillate oil. Aeroderivativc turbines are modified aircraft engine turbines, typically of 500 kW to more than 40 MW capacity, normally operating with natural gas fuel.

The capacity of both types of turbines is rated at the International Standards Organization (ISO) specified inlet air conditions of 59 F (15 C) air temperature, 60% relative humidity, and 14.7 psia (101.325 kPa) absolute pressure (sea level) at a power factor of 0.9. Industrial turbines operate using constant combustion inlet air volume. Aeroderviative turbines typically operate with multiple compressor shafts and with inlet air volumes that vary with compressor shaft speed. The capacity of turbines is dependent upon the mass flow rate of air entering the turbine. Higher combustion air mass flow rates increase the capacity of the turbines while also increasing the fuel mass flow rate. The increase in fuel mass flow rate is smaller than the increase in power output, and heat rates (the ratio of fuel input rate to power produced) decrease at the higher air mass flow rales. Newer turbines operate at lower airflow rates per unit of power produced. The lower flow rates decrease the cooling required for CTIAC systems to increase the turbine power, therefore increasing the net benefit.