Design and Off-Design Characteristics of the Alternative Recuperated Gas Turbine Cycle With Divided Turbine Expansion

Abstract

In order to fully address the characteristics of the alternative recuperated cycle with divided turbine expansion, both design and off-design analyses have been performed. Two types of mechanical design are assumed: two shaft and single shaft. In particular, optimal pressure ratio division between the high- and low-pressure turbines is evaluated for the single-shaft configuration. It is predicted that the alternative recuperated cycle hardly exhibits sensible design efficiency advantage over the conventional recuperated cycle for moderate turbine inlet conditions and with usual component performances. An advantage of the alternative cycle with single-shaft design is that thermal efficiency is less sensitive to compressor pressure ratio compared to other configurations, and we can also have flexibility in the turbine division without much efficiency loss. The part load analyses have been carried out with the aid of realistic component maps and models for off-design operation. In addition to the general fuel only control, a variable speed control is assumed as the part load operating strategy of the single-shaft configuration. Obvious advantage with the alternative cycle is observed in the variable speed operation of the single-shaft design. With this strategy, the part load efficiency of the alternative cycle is far superior to the conventional cycle. Almost constant efficiency is predicted for a wide power range.