From Residual Biomass to Bioenergy and Biochar: A Techno-Economic and Environmental Analysis of Pistachio-Shell Gasification–Cogeneration

This study investigates the gasification of pistachio shells for the co-production of biochar and renewable energy, integrating process simulation, energy recovery, and techno-economic–environmental assessment. The investigation has been carried out by experimental tests in a 30 kg/h downdraft gasification–cogeneration system and process simulation. The zero-dimensional simulation model, validated against first-hand experimental data, was used to evaluate two operational scenarios differing in biochar yield (10% and 17%) and energy yield. The integration of the gasification–CHP system with a representative pistachio-processing facility (500 t yr−1 shell availability) demonstrated annual useful energy outputs ranging from 574 to 900 MWh yr−1 (as the sum of heat and electricity). The techno-economic analysis yielded operating profits of 96,720–117,637 € yr−1, return on investment (ROI) between 15.5% yr−1 and 18.85% yr−1, and payback periods of 6.45 and 5.3 years for the high- and low-char scenarios, respectively. The environmental assessment revealed total CO2-equivalent savings of 241–279 t yr−1, with biochar sequestration contributing up to 41% of avoided emissions. Overall, the results confirm that higher carbon conversion to syngas enhances energy, environmental and economic performance, while higher biochar yields favour fixing carbon in the soil, according to the assumed scenarios’ conditions. The proposed framework demonstrates a scalable, sustainable solution for coupling pistachio-shell gasification with industrial energy and a material valorization pathway.