This paper describes the current status and anticipated improvements in the Cascaded Humidified Advanced Turbine (CHAT) technology. With these improvements, CHAT will provide an alternative approach to achieving the goals of the Department of Energy’s Advanced Turbine Systems (ATS) project of a 60% thermal cycle efficiency for natural gas fired combined cycle power plants.

The traditional approach to increasing the efficiency of simple cycle and combined cycle power plants was to increase the firing temperature and pressure of the basic Brayton cycle. However, every increase in the CT firing temperature required progressively higher development cost, associated with new materials and cooling techniques, and increased NOx control challenges.

CHAT is a gas turbine based cycle with intercooling, reheat, recuperation and humidification. It is based upon the integration of an existing design heavy duty combustion turbine with an additional high pressure shaft comprised of industrial compressors and expander. The current CHAT plant design includes an HP expander inlet temperature of 871 C (1600 F), which represents the level of the combustion turbine technology of the late 1960’s – early 1970’s. The expander on the power generation shaft (LP) is based upon current combustion turbine technology with turbine inlet temperature of 1400 C (2550 F). One of the most effective ways to increase the CHAT plant efficiency is to increase the HP expander inlet temperature. By increasing this temperature to a relatively low 1150 C (2100 F), and maintaining the current inlet temperatures on the LP expander, the CHAT plant could achieve the ATS program target efficiency.

The paper presents the current CHAT plant’s performance and cost characteristics, and the initial findings of a project co-sponsored by the Electric Power Research Institute (EPRI) and Energy Storage and Power Consultants, (ESPC) for the development of an HP expander with increased inlet temperatures.

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