Energy, exergy and mass balances of a biomass pyrolysis pilot plant

This work presents the methodology and results of the energy, exergy, and mass balances of a fixed-bed downdraft biomass pyrolysis pilot plant. The analysis covers different operating modes: pyrolysis without energy recovery, with energy recovery from products, and with combustion of non-condensable gases including exhaust-gas heat recovery. The proposed framework enables consistent comparison of energy and exergy performance under varying process configurations. Experimental results show that the external heat demand of the pyrolysis process strongly depends on the energy recovery strategy. When products are cooled to the reference state, the required heat input is approximately 1.3 MJ/kg, increasing to about 3 MJ/kg when products leave at the pyrolysis temperature. The combustion of process gases significantly reduces this demand, while integrating exhaust-gas heat recovery leads to quasi-autothermal operation. Exergy analysis reveals that gas combustion and heat recovery lower exergy efficiency due to the conversion of high-quality pyrogases into exhaust gases. Nevertheless, the methodology developed allows quantifying these trade-offs and provides a comprehensive tool to evaluate process integration strategies in biomass pyrolysis systems aimed at improved thermal performance and sustainability.