Gas/Steam Combined Cycles Fueled by Various Energy Sources for Large-Scale Power Production

This article will consider large-scale power generation by means of combined cycles, that is, a gas turbine engine coupled to a heat recovery steam cycle. After an introduction (outlining the fundamental role of combined cycles in today's generating systems), the thermodynamic aspect of heat recovery steam cycles are addressed. Therefore, the main components of combined cycles are described: the gas turbine (an update of large heavy-duty units), heat recovery steam generators, steam turbines, and heat rejection devices. General considerations on the performance and flexibility are addressed, with reference to combined cycle fed by natural gas, by far the most frequent situation. The final part will provide an overview of the gasification process, necessary to make combined cycles a viable option also for heavy feedstocks (such as coal, refinery residues, and biomass) and to gas turbine adaptability to operate with synthetic low-Btu gaseous fuel.