A Steam-Augmented Gas Turbine with Reheat Combustor for Surface Ships

Abstract

The steam-augmented gas turbine (SAGT) concept has attracted attention because of its benign level of NOx emission, its increased fuel efficiency, and significant, cost-effective increments of output power, particularly when moisture injection is increased to levels approaching 50% of air flow. Such high levels of moisture consumption distinguish the SAGT engine from commercial steam-injected gas turbines where steam flow may be less than 15% of air flow. At the high 50% levels, the SAGT burner would operate near stoichiometric combustion ratios with specific powers exceeding 570 hp-sec/lb. In a previous study, an intercooled, steam-augmented, gas-turbine concept was examined for its applicability in the Navy's DDG-51 class ship environments, which achieves efficiencies approaching the Navy's intercooled regenerative (ICR) engine, and an impressive compactness that arises from the high specific power of steam and low air consumption. A newer SAGT engine concept, described herein, dispenses with the intercooler, but adds a low-pressure reheat combustor. At the most efficient operating points, the efficiency of this new reheat SAGT engine at 43% exceeds the efficiency of the ICR engine, while exhibiting the compactness of the previous SAGT concept. Tabular and graphical simulation data comparing the baseline engine, with the ICR and other engine simulations, show that the maximum efficiency of the new SAGT engine occurs at powers required for cruising speeds. Since a DDG operates near cruise conditions for the majority of its mission time, a SAGT plant uses less fuel than the ICR plant. Moreover, since it eliminates the intercooler, developmental work on member elements, largely derivable from off-the-shelf components, is reduced. Even with conservative cost estimates, the SAGT plant is quite competitive on a first-acquisition cost basis with the current gas turbine in the fleet.