Development of a Temperature-Controlled Biochar Kiln Using Macadamia Shells for Community-Level Waste Utilization
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Abstract
Objectives: This study aimed to design and develop a temperature-controlled biomass carbonization system for producing biochar from macadamia nutshells, enhancing production efficiency and promoting waste utilization in community-level circular economy applications.
Method: The developed kiln integrated temperature and airflow control systems, using waste engine oil as the main fuel (heating value 40–42 MJ/kg). The internal temperature was maintained at 500 ± 10 °C through dual thermocouples (T1 and T2) monitored in real-time. Three carbonization durations (2, 3, and 4 h) were tested. The resulting biochar was characterized using Brunauer–Emmett–Teller (BET) analysis to determine surface area and porosity, and an economic evaluation was conducted to assess cost and profitability.
Results: The system maintained stable temperatures within ±10 °C, achieving an average biomass-to-biochar conversion ratio of 30–35 % wt. The 3-hour condition yielded the highest surface area (225.65 m²/g) and total pore volume (0.106 cm³/g), indicating optimal carbon structure formation. Economic analysis revealed a payback period of 3 months, with an annual net profit of approximately 101,442 THB. The results confirm the system’s effectiveness in enhancing waste-to-value processes and supporting sustainable community-level biochar production.
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