A Fifty Percent Plus Efficiency Mid Range Advanced Cheng Cycle

Cheng Power Systems, Inc. following the successful Cheng Cycle development based on the Allison 501KH, is developing a 50%+ efficiency medium-power-range Advanced Cheng Cycle. The recent development work involved the selection of a candidate gas turbine which possesses the following attributes: (1) a single shaft, (2) advanced compressor and turbine aerodynamic design, and (3) F-Class firing temperature. The targeted results were a 30MW+ output and 50%+ efficient intermediate-load Advanced Cheng Cycle with the simple-cycle performance characteristics of quick startup and shutdown and a $/kW cost comparable to simple-cycle machines, but at a combined-cycle efficiency. A candidate engine was selected which has the following performance characteristics: a compressor pressure ratio of 18:1, a turbine inlet temperature of 1250°C, and a net efficiency of 35%. Cheng Power has a unique software program which predicts the energy balance at various ambient conditions. The program takes into account the massive cooling air flows incorporated into advanced gas turbines and the heat recovery boiler performance characteristics when developing our performance analyses. The uniqueness of the Cheng Cycle is that it selects a trajectory of steam-to-air ratios to maintain high efficiency for the entire operating range of the power system, while offering competitive efficiency, simple hardware, the possibility of retrofit, fast response to load change, and feasible cogeneration plant operations. The quick startup of the Advanced Cheng Cycle is suitable for variable load operation in the mid range, i.e. 8 to 10 hours per day. This paper provides the energy balance of the proposed plant and its variation with ambient temperature. The paper also addresses the emission characteristics of this engine, which provides low NO_x and CO emissions at levels that satisfy most U.S. EPA requirements without SCR or any other add-on devices.