Biomass Utilization in Dual Combustion Gas Turbines for Distributed Power Generation in Mediterranean Countries

Abstract

In Mediterranean regions, such as Puglia in Italy, the supply chain constraints (i.e. local biomass availability, logistics of supply, storage and seasonality issues) limit the optimal size of a biomass fired power plant in a range of 5–15 MWe. In this scenario, innovative Dual Combustion Externally Fired Gas Turbine (DCGT) Power Plants cofired by natural gas and biomass are examined. For this purpose, biomass external firing is explored under two alternatives: direct combustion of solid biomass and atmospheric fixed bed biomass gasification with air. The proposed cycles are analyzed considering both the Net Overall Electric Efficiency and the Marginal Efficiency of biomass energy conversion, defined for the cofiring of biomass and natural gas. Since natural gas represents a quite expensive fossil fuel resource, a Marginal Efficiency higher than zero indicates the convenience to burn natural gas in this typology of power plant rather than in traditional Combined Cycle with higher efficiency. The energy analysis has been carried out by varying pressure ratio, turbine inlet temperature, heat exchanger efficiency and considering the further option of steam injection. The results of the thermodynamic assessment highlight that the gasification should be preferred to the direct combustion of biomass because of the higher marginal efficiency, although the net overall electric efficiencies of the two plants are almost the same (31%).