Thermal Characterisation and Pyrolysis Kinetics of Agricultural Biomass Wastes from North East Nigeria for Bioenergy Production

Agricultural biomass wastes represent an underutilised renewable energy resource across North East Nigeria, where access to electricity is limited and biomass residues from groundnut, cotton, and millet production are typically burned in the field. This study characterises the thermal properties and investigates the pyrolysis kinetics of five agricultural biomass wastes, including groundnut shell, cotton stalk, millet straw, rice husk, and sugarcane bagasse, collected from farms and processing sites in Borno, Yobe, and Adamawa States. Proximate and ultimate analyses characterise the elemental composition and fuel properties of each biomass. Thermogravimetric analysis and differential scanning calorimetry were performed under nitrogen atmosphere at heating rates of 5, 10, 20, and 40 degrees Celsius per minute from room temperature to 900 degrees Celsius. Activation energies were calculated using three model-free iso-conversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, and Friedman methods. Distributed activation energy model analysis was applied to assess reaction complexity. Results show that groundnut shell and rice husk exhibit the highest calorific values among the studied materials, with higher heating values of 18.2 and 16.8 megajoules per kilogram respectively. Pyrolysis occurs in three distinct stages corresponding to moisture evaporation, primary devolatilisation, and char formation. Activation energies estimated by model-free methods ranged from 148 to 215 kilojoules per mole. The study provides thermochemical data essential for design of biomass pyrolysis reactors tailored to North East Nigerian waste streams and contributes to bioenergy feasibility assessments in the region. Keywords: pyrolysis kinetics, biomass waste, thermogravimetric analysis, bioenergy, North East Nigeria