Production and optimization of bio-briquettes from tea twig waste (Camellia sinensis) through pyrolysis and response surface methodology (RSM)

This study optimized the production of bio-briquettes from tea twig waste (Camellia sinensis) by integrating controlled pyrolysis, damar resin as a binder, and post-moulding immersion in used cooking oil using a Design of Experiment (DoE) integrated with Response Surface Methodology (RSM). The investigated responses included moisture content, ash content, volatile matter, fixed carbon, calorific value, and compressive strength. The optimum conditions predicted by the model were a biochar particle size of 520 µm, a damar resin concentration of 20%, and an oil immersion time of 3 min. Validation experiments under these conditions produced bio-briquettes with a moisture content of 3.14%, ash content of 3.68%, volatile matter of 13.23%, fixed carbon of 79.95%, calorific value of 8422.66 cal/g, and compressive strength of 11.24 N/cm². The results confirm that the optimized bio-briquettes met the relevant requirements of SNI 01–6235–2000 and Japanese quality standards, demonstrating their potential as a higher-value solid fuel derived from tea plantation residues.