Thermo-Economic Analysis and Fluid Selection of the Bottoming ORC Cycle Coupled with an Externally Fired Gas Turbine

This paper is focused on the energy analysis of a bottoming Organic Rankine Cycle (ORC) coupled to a topping 1.3 MW. Externally Fired Gas Turbine (EFGT) with direct combustion of biomass. In particular, in this paper the ORC evaporation pressure and superheating temperature are ranged in order to examine different bottoming cycles, including supercritical ones. Different organic fluids are also examined, such as siloxanes and toluene, aiming to analyze how the fluid choice influences both the plant performance and important features for the ORC turbine design. On the basis of the results of the thermodynamic simulation, a thermo-economic assessment is proposed, to investigate the relative profitability of the bottoming ORC in comparison to only topping EFGT. For this purpose, the Italian bioenergy subsidy framework is assumed, and a sensitivity assessment is proposed, comparing the options of only electricity and CHP, and varying the biomass cost, thermal energy demand and heat selling price.