Densified and Carbonized Fuel Derived from Biomass and Municipal Solid Waste as a Vector for Energy Transition from Coal in Brazil

The transition to a low-carbon economy requires sustainable alternatives to fossil fuels. Up-recycling municipal solid waste and forestry biomass into solid biofuels presents a promising waste-to-energy strategy. This study aimed to develop a high-calorific, highly durable hybrid solid fuel without synthetic binders, utilizing the natural interlocking of lignocellulosic and plastic matrices under mild slow pyrolysis. Blends of Eucalyptus sawdust and municipal solid waste rejects (40 wt%) were densified with and without a glycerol binder. The optimal binder-free blend underwent slow pyrolysis at 400 °C and 500 °C to evaluate energy upgrading. Results showed that the binder-free formulation achieved mechanical durability of 99.67%, whereas glycerol severely compromised the dimensional stability of the pellets. Mild pyrolysis (400 °C, 30 min) increased the higher heating value to 27.75 MJ/kg—significantly outperforming local coal (18.3 MJ/kg)—while maintaining trace chloride levels, confirming the production of an environmentally safe, premium-grade energy vector.