An “in-situ binding” approach to produce torrefied biomass briquettes

Biomass-derived coal or “biocoal” produced using a torrefaction process presents a carbon-neutral option of coal for power generation. While torrefaction delivers a carbon content and hydrophobicity comparable to coal, it lowers its density and creates material handling, storage, and transportation challenges. Densification into briquettes would help mitigate these challenges. However, the torrefied biomass is difficult to densify and may require the use of binders, which are expensive and can be incompatible with respect to material and emissions. A cost-effective approach to utilize lignin in-situ of the biomass to promote binding during densification was demonstrated using a pilot-scale briquetter unit during this study. Lignin, a cross-linked polymer, tends to break down and lose its binding ability under high-temperature conditions of torrefaction. In this paper, we investigated the use of a lightly torrefied material as a binder-LTM (biomass torrefied in the transition region of non-reactive and reactive temperature ranges of torrefaction). When mixed with torrefied biomass and densified together under suitable moisture and temperature conditions, the lignin is shown to mobilize and provide binding to the briquettes. The results showed that briquettes produced using LTM as binder and 10% to 11% moisture provided in-situ binding, improved density and durability, and produced hydrophobic briquettes.