LAUSR

Abstract Polygeneration systems, designed for providing multiple energy services like hydrogen, heat and electricity, represent a possible solution for the transition to sustainable low-carbon energy systems, thanks to a substantial increase in the overall efficiency. A further step to reach zero-carbon energy systems can be done by using renewables as primary sources. In this study a biogas-based polygeneration system for the combined hydrogen, heat and electricity production is designed and analyzed from energy and economic points of view. The system consists of four sections: a biogas processing unit consisting in an autothermal reactor and a water gas shift reactor, an SOFC power unit, a hydrogen separation unit and a hydrogen compression/storage unit. The syngas generated in the autothermal reforming reactor is split in two fluxes: the first one is sent to the SOFC power unit for generating electricity and heat, the second one is sent to the water gas shift reactor to increase the hydrogen content. The hydrogen rich gas exiting the shifter, purified in the hydrogen separation unit (hydrogen quality is equal to 99.995%), is then compressed up to 820 bars and stored. The system behavior and the energy performances have been investigated by using the numerical simulation based on thermo-electrochemical models. Four operating conditions, related to different SOFC loads (from 30% to 100%), have been analyzed. The evaluated overall efficiencies range from 68.5% to 72.3% and the energy saving, calculated with respect to the separate production of hydrogen, heat and electricity, ranges from about 8% to 26%. The economic assessment, carried out by estimating the total capital investment and the plant profitability, has been performed by analyzing different management strategies (Base Load, Peaker, Ancillary Service and Mobility) and accounting for different technological development levels and market scenarios. Results show that the hydrogen production is the main contributor to the system economic sustainability thanks to the highest prices of hydrogen with respect to the electricity ones.