As is well known, a part of the waste heat of closed cycle gas turbines can be used without any reduction in power production. However, if the plant is designed for optimal power conversion, the outlet temperatures of the repeatedly intercooled compressors are so low, that only a small part of the removed heat is useful. The closed cycle gas turbine compressor behaves analogous to a heat pump, and therefore an increase of useful heat can be realized without an undue reduction in power production. A moderate increase of the cycle pressure ratio above its optimum, a temperature increase at the compressor inlet and a reduction of the number of intercoolers are good methods for this. Measures, however, which bypass heat from the heater to the precooler, such as recuperator bypass, are not of interest. As far as closed gas turbines are considered, a further degree of freedom is given by the possibility of cycle gas inventory control, as demonstrated in combined power and heat production characteristics. These explanations are not only relevant for fossil fired plants, but also for nuclear high temperature reactors with helium turbines proposed in future.

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