Preparation of pellet and pelletized torrefied fuel without a binder from Dipterocarpus alatus fruit

Abstract The increasing energy demand and environmental problems from conventional fuels require alternative renewable, eco-friendly and inexpensive energy sources, such as those derived from biomass. The combination of torrefaction and pelletization of biomass enhances the fuel quality and handling and transportation. Therefore, this study utilized Dipterocarpus alatus fruit, a seasonal waste material, to prepare solid fuel pellets and pelletized torrefied samples. The milled raw material was pelletized by a single unit press without any addition of binder. Torrefaction of the biomass was performed at 200, 250 and 300°C for 15 to 60 min, after which the torrefied samples were pelletized. The obtained pellets satisfied the standard values for diameter (6 – 8 mm) and pellet length (3.15 – 40 mm). The density of biomass pellets typically ranges from 1,000 to 1,400 kg/m 3 , and the value for the Dipterocarpus alatus fruit pellet was 1,108 kg/m 3 . There was a significant increase in bulk density from 39 kg/m 3 (feedstock) and 186 kg/m 3 (milled sample) to 484 kg/m 3 for the non-torrefied pellets. These pellets had a calorific value of 18.31 MJ/kg and torrefaction increased the values to 18.45 – 24.58 MJ/kg. The axial compressive strength (1,820 N/cm 2 ) was higher than the diametral compressive strength (196 N/cm 2 ). However, torrefaction reduced the pellet density (720 – 1,093 kg/m 3 ), bulk density (215 – 330 kg/m 3 ) and compressive strength (384 – 1,561 N/cm 2 for axial direction and 11 – 153 N/cm 2 for diametral direction). Infrared analysis revealed that torrefaction lowered the peak intensity of O–H, C=C, C=O, C–O and C–H vibrations, which indicated that structural alteration took place within the raw biomass. Overall, the study demonstrated the viability of Dipterocarpus alatus fruit for the production of fuel pellets in both standard and torrefied form.