Properties of Pinus sp. pellets prepared after in-line pre-compaction with torrefaction

Abstract

Pelletizing and torrefaction increase biomass energy density, generating a more homogeneous fuel with lower moisture, enabling it to burn in equipment with high energy efficiency. This work evaluated the quality of pellets made from wood particles that had been densified and torrefied in an extruder-type system. Particles of the Pinus sp. wood were torrefied at 200, 250, and 300 °C for six minutes and then compacted to produce pellets. The physical, chemical, and mechanical properties of these pellets were evaluated and compared with standard ones. Torrefaction modified the pellets properties by increasing ash, fixed carbon, higher heating value, and the energy density, while reducing the volatile matter and equilibrium moisture content. The mechanical durability of the pellets was lower than that defined by the European, German, and American standards. The torrefaction pre-compaction route with torrefied particles at a temperature of 300 °C was the most efficient for energetic use, compared to the in natura biomass. The latter has negative aspects such as great variation in size (length and diameter) and density besides high moisture content.