Bio-Briquettes Derived from Fibrous Agricultural and Softwood (FAS) Residues: A Review on Production Methods, Effects of Chemical Components, Utilization Potential, and Future Outlooks

Fibrous Agricultural and Softwood (FAS) residues represent abundant lignocellulosic resources for bio-briquette production, yet their potential is strongly influenced by feedstock characteristics, chemical composition, processing conditions, and application requirements. A structured narrative review of 106 publications was conducted to synthesize these interrelationships and identify development prospects. FAS bio-briquette performance is governed by interactions between feedstock composition and processing conditions, with lignocellulosic fractions and ash-forming minerals determining the balance among mechanical integrity, energy performance, and combustion behavior. Various FAS residues, including rice husk and straw, corn cob, sugarcane bagasse, coconut and oil palm residues, cocoa pod shell, fruit and nut residues, pine residues, and softwoods have been investigated under diverse processing conditions. Reported properties varied widely with densities of 0.30–1.32 g/cm3, calorific values of 12.41–31.51 MJ/kg, moisture contents (MC) of 0.3–29.72%, ash contents of 0.1–59.2%, volatile matter (VM) of 0.9–90.7%, fixed carbon (FC) of 22.97–81.73%, compression strength of 0.004–21.75 MPa, ignition times of 10.25–106 s, burning rates of 0.119–5.85 g/s, and burning times of 23.88–84 min, while shatter resistance >99% and shatter indices 0.56–2.49%. Beyond domestic cooking and heating, FAS bio-briquettes show potential for coal co-firing, metallurgical reduction, and construction-material applications through ash utilization, although suitability depends on application-specific trade-offs. Future development should prioritize feedstock-specific optimization, scalable production, techno-economic and life-cycle assessment, and standardized quality and sustainability criteria for reliable commercialization.