Biofuel-based Poligeneration Energy System for Electricity, Heat and Mobility Demands: Plant Design and Energy Streams Management

Polygeneration systems represent a novel concept for the transition to sustainable low-carbon future energy systems. The plants based on this concept can use multiple energy sources (renewable and non-renewable) providing multiple energy services (heating, cooling, electricity) and other products such as fuels or water. In this way, a substantial increase in overall efficiency is achieved, and thus, indirectly, a reduction of pollution and greenhouse gas emissions. In this paper the design of a biomass-based polygeneration system generating electricity heat and hydrogen for small refilling stations is proposed. The polygeneration system is fed by biogas, obtained from an anaerobic digester where the biomass conversion is made. It consists of i) a biogas processing unit, based on autothermal reforming technology, in which a hydrogen-rich gas is generated, ii) a power unit based on SOFC technology, iii) a hydrogen separation unit based on membrane technology and iv) a hydrogen compression and storage unit based on ionic compressor technology. The analysis has been carried out by using a numerical approach. The system behavior has been investigated by varying the SOFC electric load from 100% to 30% (the minimum load that permits to sustain the electric power consumption of the hydrogen separation and compression units). The calculated system performance in terms of overall efficiency range from 67.5% (60% SOFC load) to 71.4% (30% SOFC load). The energy saving with respect to the separate production of electricity, heat and hydrogen ranges from 6% to 26%