Torrefaction of Agriculture Residue To Enhance Combustible Properties

TLDR

Torrefaction improves biomass thermochemical properties relevant to combustion, co‑combustion with coal, or gasification. The study investigates torrefaction of rice husks, sawdust, peanut husks, bagasse, and water hyacinth under nitrogen. The authors varied torrefaction temperature (250–300 °C) and residence time (1–2 h) in nitrogen, measured mass and energy losses, and examined combustion behavior of raw and torrefied rice husks in a spout‑fluid bed combustor. Torrefied products were darker, drier, richer in ash, fixed carbon, and energy density; higher temperatures improved mass and energy yields, with bagasse at 300 °C/1.5 h achieving an HHV of 25.68 MJ/kg comparable to lignite, and torrefied husks ignited faster and raised bed temperatures due to low moisture, retaining up to 98 % of the original energy content.

Abstract

Torrefaction improves the thermochemical properties of biomass that are relevant to combustion, co-combustion with coal, or gasification. This study examines torrefaction of rice husks and four other agriculture residues (sawdust, peanut husks, bagasse, and water hyacinth) in nitrogen. Two main operating parameters of torrefaction, temperature and residence time for the process, were varied in the range of 250−300 °C and 1−2 h, respectively. Product evolution and mass and energy losses during torrefaction were measured. Similar to other work, the torrefied products in the present work were characterized by a more brownish color, reduced moisture content and volatile matter, and increased ash, fixed carbon content, and energy density. The difference between the mass and energy yield was shown to improve for the higher torrefaction temperatures investigated. For the biomass studied, the torrefied bagasse at 300 °C and 1.5 h resulted in the highest higher heating value (HHV) of 25.68 MJ/kg of product, which was comparable to the HHV of lignite. Dependent upon the severity of the torrefaction conditions, the torrefied fuel can contain up to 98% of the original energy content on a mass basis. The combustion behavior of both raw and torrefied rice husks was studied in a spout-fluid bed combustor by measuring its temperature history at different zones. It is observed that torrefied husks ignite faster and raise the bed temperature to a higher level because of its low moisture content.