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

The valorization of underexploited biomass in arid regions represents an important pathway for decentralized energy production and sustainable soil management. Although biomass pyrolysis has been widely investigated, most studies are conducted under controlled laboratory conditions, with limited assessment of low-technology systems operating under real domestic use. This study evaluates the thermochemical behavior and energy performance of locally available biomasses using a multifunctional household oven. Millet stalks, cashew nut shells, cashew nut shell cake, and rumen contents were subjected to slow pyrolysis. Temperature evolution in the pyrolysis and combustion chambers was continuously monitored using type ‘K’ thermocouples, and mass and energy balances were applied to assess product distribution and process efficiency. Pyrolysis temperatures ranged between approximately 270 and 350 °C, while combustion temperatures reached up to 800 °C depending on the biomass. Product yields varied significantly according to feedstock characteristics. Cashew nut shells showed the highest energy efficiency (about 71%), followed closely by millet stalks, whereas rumen contents presented lower performance. Thermal profiles consistently revealed four successive phases governed by biomass composition and reactor–biomass interaction. These findings confirm the technical feasibility of household-scale pyrolysis for combined energy recovery and biochar production under realistic operating conditions.