THERMODYNAMIC EVALUATION OF ENERGY SYSTEMS FOR THE COPRODUCTION OF SYNTHETIC BIOFUELS AND ELECTRICITY

The coproduction of synthetic biofuels and electricity through the Fischer-Tropsch (FT) synthesis coupled with power generation could be a promising pathway in order to green the energy sector. We present a system based on lignocellulosic biomass gasification coupled with FT synthesis and electricity generation through a combined-cycle scheme. In addition to a base case study, three modifications of the base case are considered. These modifications include: autothermal reforming (ATR) of a fraction of the FT tail gas to increase the fuel yield; combustion of a fraction of the conditioned biosyngas to increase electricity production; ormembrane separation of the FT tail gas to increase the fuel yield. The thermodynamic evaluation of the four systems is carried out through exergy analysis. In order to obtain the data required for the analysis, the four bioenergy systems are simulated using Aspen Plus (R). Global exergy efficiencies of 23.7-28.2% are calculated, depending on the plant configuration. The membrane separation and ATR systems are identified as the best options according to thermodynamic criteria. In contrast, the biosyngas combustion system shows the least favourable results. The gasification subsystem is found to contribute more than 50% to global exergy destruction, showing an efficiency of 67.8%. The power generation subsystem also shows a high contribution to the global exergy destruction (18.5-28.4%) due to increased fuel consumption and significant irreversibilities of the combined-cycle power plant.