Modern large air Brayton gas turbines have compression ratios ranging from 15 to 40 resulting in compressor outlet temperatures ranging from 350 °C to 580 °C. Fluoride-salt-cooled, high-temperature reactors, molten salt reactors, and concentrating solar power can deliver heat at temperatures above these outlet temperatures. This article presents an approach to use these low-carbon energy sources with a reheat-air Brayton combined cycle (RACC) power conversion system that would use existing gas turbine technology modified to introduce external air heating and one or more stages of reheat, coupled to a heat recovery steam generator to produce bottoming power or process heat. Injection of fuel downstream of the last reheat stage is shown to enable the flexible production of additional peaking power. This article presents basic configuration options for RACC power conversion, two reference designs based upon existing Alstom and GE gas turbine compressors and performance of the reference designs under nominal ambient conditions. A companion article studies RACC start up, transients, and operation under off-nominal ambient conditions.

Because molten fluoride salts can deliver heat at temperatures above 600 °C, they can be used to couple nuclear and concentrating solar power heat sources to reheat air combined cycles (RACC). With the open-air configuration used in RACC power conversion, the ability to also inject natural gas or other fuel to boost power at times of high demand provides the electric grid with contingency and flexible capacity while also increasing revenues for the operator. This combination provides several distinct benefits over conventional stand-alone nuclear power plants and natural gas combined cycle and peaking plants. A companion paper discusses the necessary modifications and issues for coupling an external heat source to a conventional gas turbine and provides two baseline designs (derived from the GE 7EB and Alstom GT24). This paper discusses off-nominal operation, transient response, and start-up and shutdown using the GE 7EB gas turbine as the reference design.

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Water or steam injection for NOX control or power augmentation can impact turbine hot section component life and maintenance interval. This relates to the effect of added water on hot-gas transport properties. Higher gas conductivity, in particular, increases heat transfer to blade and vane, and can lead to higher metal temperature and reduced part life. Part life impact from steam or water injection is also related to the way engine is controlled. Life cycle impact of steam injection on the LM6000PC HP turbine blade has been studied. The relationship between steam injection, LP turbine inlet temperature control, blade metal temperature, and corresponding life change was analyzed. The analysis result can be used for the assessment of life cycle impact with steam injection and temperature control limit.

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