Exergy analysis of groundnut shell (arachis hypogaea) pyrolysis: thermodynamic performance assessment for biochar and syngas production in Senegal

Groundnut shell (Arachis hypogaea), a major agricultural residue in Senegal with an estimated annual availability exceeding 700,000 tonnes, represents a significant yet underutilised bioenergy resource in West Africa. While the thermochemical conversion of this feedstock has received growing attention, rigorous exergy-based assessments under conditions representative of the sub-Saharan African context remain scarce. This study presents a comprehensive energy and exergy analysis of groundnut shell slow pyrolysis for simultaneous biochar, bio-oil, and syngas production. Using proximate and ultimate analysis values alongside empirical yield data from recent experimental literature, thermodynamic simulations were performed across a pyrolysis temperature range of 400–600°C. Results indicate that the overall exergy efficiency of the pyrolysis system ranges from 75.8% to 79.3%, with maximum efficiency achieved at lower temperatures (400°C) where biochar yield is optimal. The exothermic char formation stage was identified as the dominant source of irreversibility, accounting for 42.1% of total exergy destruction. The chemical exergy of the produced syngas fraction (H₂, CO, CH₄) increased from 4.82 to 7.31 MJ/kg of dry feedstock as pyrolysis temperature rose. Comparison with energy efficiency values (80.5–84.3%) confirms that conventional energy analysis systematically overestimates system performance by masking thermodynamic quality losses. These findings provide a critical thermodynamic benchmark for groundnut shell pyrolysis, with direct implications for the design and optimisation of decentralised biochar production facilities within Senegal's Plan Sénégal Émergent renewable energy framework.