Production of Torrefied Biomass Pellets in a Rotating Bed Thermal Reactor

Abstract

Oil palm fronds and corncobs are major agricultural residues in Thailand with high energy content. They can be used as substitutes for fossil fuels in the energy and power industry. Mild pyrolysis or torrefaction can enhance their fuel properties towards coals. The objective of this work was to improve both agricultural residues into torrefied biomass pellets for the use of high-quality solid fuels. In this work, oil palm fronds and corncobs were torrefied in a 0.15 m3 thermal reactor and subsequently compressed into densified fuels. Torrefaction temperature and time were 200 °C/40 min and 200 °C/20 min for oil palm fronds and corncobs, respectively. The torrefaction rotating torrefaction reactor was equipped with a 0.25 kW electric motor for speed control. Nitrogen was used as the carrier gas. Their chemical and physical properties were analyzed. From the results obtained, it was found that the use of a rotating torrefaction reactor was able to produce high-quality torrefied biomass with high fixed carbon and low volatile matter and moisture contents. Maximum higher heating values of torrefied oil palm fronds and corncobs achieved were above 23 and 20 MJ/kg, respectively. The physical properties of both torrefied biomass pellets obtained were found to meet the technical specifications of solid biofuels standards. Maximum of bulk density, mechanical durability, and water resistance of torrefied oil palm frond and corncob pellets were in a range of 1, 110-1, 230 kg/m3, 90.6-91.7%, and 91.9-93.0%, respectively.