Parametric study of rice husk torrefaction for the development of sustainable solid fuel

Author(s): Ma. Theresa A. Banta, Rizalinda L. De Leon
University of the Philippines, Diliman, Quezon City 1101, Philippines
International Journal of Smart Grid and Clean Energy, vol. 7, no. 3, July 2018: pp. 207-217
ISSN: 2315-4462 (Print)
ISSN: 2373-3594 (Online)
Digital Object Identifier: 10.12720/sgce.7.3.207-217

Abstract: Torrefaction is the thermal treatment of lignocellulosic biomass at temperatures between 200°C to 300°C under inert or low oxygen environment. This process produces a dark brown, brittle substance that is hydrophobic, has high energy density, and less prone to biological degradation. The removal of oxygen-containing compounds is the primary purpose of torrefaction. Oxygen to carbon ratio is highly correlated to the biomass heating value. An increase in oxygen to carbon ratio from 0.1 to 0.7, results to a 60% reduction in higher heating value of the biomass. Removal of oxygen-containing compounds lowers the oxygen to carbon ratio thus increasing the higher heating value of torrefied biomass. These improved properties are significant for thermochemical conversion processes such as combustion and gasification particularly for power generation purposes. This study examines the impact of residence time, temperature, and particle size on torrefied rice husk, using a bench-scale batch reactor. Simultaneous variation of temperature between 240°C and 295°C; residence time between 30 minutes and 60 minutes; and particle size between 1.19mm and 2.38mm were done. The results showed significant improvement in higher heating value of rice husk which increased by up to 25% from 13.4MJ/kg to 16.8MJ/kg. The fixed carbon increased up to 107% from 12.8 to 26.6 weight percent in dry basis. Analysis of results show that process temperature significantly affects the fuel properties of torrefied rice husk compared to residence time, particle size, and the interaction of these factors.
Keywords: torrefaction, rice husk, thermal pretreatment, biomass energy

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