Pilot-scale pyrolysis of green coconut husk pellets for biochar production and evaluation in bituminous coal–biochar blends

Coal-fired thermoelectric plants remain important for dispatchable electricity generation and supply stability, but their dependence on fossil carbon results in high greenhouse gas emissions. This study evaluated pilot-scale batch pyrolysis of green coconut husk pellets for biochar production and its incorporation into bituminous coal blends as a potential route for partial fossil-coal substitution. Pyrolysis experiments were performed in a pilot-scale pyrolysis unit using 40 kg of pellets at final temperatures of 400 and 500 °C. The products were characterized by proximate analysis, higher heating value (HHV), non-condensable gas composition, and mass and energy balances. Coal–BIO400 blends were prepared with biochar produced at 400 °C (BIO400) at 1, 5, 10, and 20 wt% and characterized for proximate, elemental, inorganic, morphological, surface elemental, and energetic properties. Pyrolysis at 400 °C favored biochar production, with a yield of 34.13%, compared with 28.05% at 500 °C. Although the 500 °C condition increased non-condensable gas yield from 15.93% to 22.57%, the 400 °C condition showed a significantly higher recoverable product-energy ratio, while no statistically significant differences were detected in gross product-energy recovery ratio or biochar energy between the two conditions. BIO400 showed low moisture content, high fixed carbon content, and an HHV of 27.42 MJ·kg⁻¹, corresponding to 96.7% of the bituminous coal HHV. The coal–BIO400 blends retained HHV values of 28.25–28.44 MJ·kg⁻¹, and no statistically significant differences in HHV were detected among BIO400, bituminous coal, and the coal–BIO400 blends under the reported analytical conditions. These results support the evaluation of green coconut husk biochar as a potential component for partial fossil-coal substitution, although combustion, emission, ash behavior, boiler compatibility, and life-cycle assessments are still required.