Decentralized Thermochemical Conversion of Local Biomasses: Energy Recovery and Biochar Production in Resource-Limited Arid Regions

This study explores the utilization of local biomass through slow pyrolysis in a multifunctional domestic reactor, with a view to producing renewable energy and improving soil quality in arid regions. Four underutilized biomass sources were studied: millet stalks, cashew shells, cashew shell meal, and rumen contents. Thermal monitoring using thermocouples showed pyrolysis temperatures ranging from 270 to 350 °C, while the combustion chamber reached up to 800 °C depending on the biomass. Four thermal phases were identified (heating, devolatilization, stabilization, and cooling), confirming stable reactor operation. Gas analyses revealed a predominance of CO (approximately 1000 ppm) as well as variations in O2, H2S, and hydrocarbons, indicating a conversion process dependent on the type of biomass and interactions between chambers. Mass and energy balances show that performance depends heavily on the physicochemical properties of the feedstocks, particularly the content of volatiles, lignin, and ash. Cashew shells exhibited the highest energy efficiency (approximately 42.9%), followed by rumen contents (approximately 34.4%), while cashew shell meal showed lower performance due to prior extraction of volatiles. Biochar yields and energy distribution vary significantly depending on the biomass, highlighting the importance of feedstock selection in decentralized pyrolysis systems. Overall, household pyrolysis enables simultaneous energy recovery and biochar production under realistic, non-optimized conditions. These results provide new insights into biomass–reactor interactions and support the development of decentralized bioenergy solutions tailored to sub-Saharan regions.