REDUCTION OF COMBUSTION IRREVERSIBILITY IN A GAS-TURBINE POWER-PLANT THROUGH OFF-GAS RECYCLING

Combustion in conventional fossil-fueled power plants is highly irreve rsible, resulting in poor overall energy conversion efficiency values (less than 40 percent in many cases). The objective of this paper is t o discuss means by which this combustion irreversibility might be redu ced in gas turbine power cycles, and the conversion efficiency thus im proved upon. One such means is thermochemical recuperation of exhaust heat. The proposed cycle recycles part of the exhaust gases, then mixe s them with fuel prior to injection into a reformer. The heat required for the endothermic reforming reactions is provided by the hot turbin e exhaust gases. Assuming state-of-the-art technology, and making a nu mber of simplifying assumptions, an overall efficiency of 65.4 percent was attained for the cycle, based on the lower heating value (LHV) of the methane fuel. The proposed cycle is compared to a Humid Air Turbi ne (HAT) cycle with similar features that achieves an overall efficien cy of 64.0 percent. The gain in cycle efficiency that can be attribute d to the improved fuel oxidation process is 1.4 percentage points. Com pared to current high-efficiency gas turbine cycles, the high efficien cy of both cycles studied therefore results mainly from the use of sta ged compression and expansion with intermediate cooling and reheating, respectively.