THE COMBINED-CYCLE POWER SYSTEM USING SYNTHETIC FUELS

Whereas a typical gas turbine would operate between temperature limits of approximately 2000 degree F and 1000 degree F (1090-540 degree C) at an efficiency of 30 percent, and a steam cycle would operate between approximately 1000 degree F and 100 degree F (540-40 degree C) at an efficiency of 35 percent, in a combined cycle they operate between approximately 2000 degree F and 100 degree F (1090-40 degree C) at an efficiency of around 43 percent. If the currently used aircraft gas turbine cooling technology can be used with acceptable life of components for the hot gas path parts of industrial gas turbines, an increase in turbine inlet temperature to 2300-2400 degree F (1260-1320 degree C) could be expected. Even more advanced cooling technology, currently being developed under a DOE-supported program, will permit inlet temperatures of 2600 degree F (1430 degree C) with growth potential to 3000 degree F (1650 degree C). This will allow combined-cycle efficiencies to exceed 50 percent. There are two generic types of synthetic fuels - liquid and gaseous - that can be made from coal (or shale, for that matter) and used conveniently in the combined cycle. The production of synthetic liquid fuel does not require air or steam in the same manner as gasification and thus, close integration does not necessarily benefit the overall efficiency. The evolving ability of the gas turbine to utilize lower-grade liquid fuels and the very high efficiencies of the gas turbine steam turbine combined cycle may result in a prime candidate system for use of these synthetic liquid fuels.