Combined Torrefaction and Densification of Rice Husk: Effect of Process Parameters

Torrefaction and densification technologies have been reported to enhance biomass properties for efficient and effective energy production. The enormous quantity of agricultural residues generated every year globally has threatened the people and the environment due to indiscriminate dumping and burning of the residues. Therefore, this study aims to convert agricultural residues (rice husk) into usable energy through the combined application of torrefaction and densification technology. The collected and sorted rice husk was torrefied at different temperatures (220, 240, 260, and 280 °C) and 60 min as residence time. The densification process was carried out on the torrefied samples at two different pressures (5 and 10 MPa), while the dwelling time was set at 4 min. The densification products’ water resistance, shatter index, density, and drop to fracture properties were investigated following the established standards. The results showed that the outcomes of the torrefaction process were influenced by temperature and residence time, though the effect of temperature was more pronounced. Torrefaction biogas, biochar, and bio-oil yields varied between 19.23–26.28, 35.90–53.85, and 26.92–37.82%, respectively. The shatter index and drop to fracture properties increase with densification pressure and decrease with torrefaction temperature. However, the water resistance property increases with torrefaction temperature. The highest and the lowest shatter index and drop to fracture were obtained from the sample produced at 220 °C (10 MPa) and 280 °C (5 MPa), respectively. The briquettes made in this study displayed good fuel properties and can be utilized for different energy purposes.