Biomass Torrefaction for the Production of High-Grade Solid Biofuels: a Review
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Biomass Torrefaction for the Production of High-Grade Solid Biofuels: a Review Temitope Olumide Olugbade 1,2
&
Oluwole Timothy Ojo 2
# Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Torrefaction of biomass materials has received a tremendous attention over the years due to its ability to produce a high-grade solid biofuel with enhanced durability, excellent grindability, higher bulk density and calorific value, and greater energy density, as compared to the original untreated biomass material. It is a mild pyrolysis treatment technology under inert atmosphere which can improve the chemical and physical properties of raw biomass through the elimination of oxygen, reduction of moisture content, and change of chemical compositions. When raw biomass is mildly pyrolyzed in a default-oxygen or N2 atmosphere at moderate temperatures, the properties of raw biomass including low calorific value, hydrogen-carbon ratio, hygroscopicity, and grindability can be significantly enhanced. In the present review, the operating mechanism of different torrefaction processes including wet, dry, and ionic-liquid-assisted torrefaction is analyzed and discussed. More importantly, the reactor design for commercialization purpose, reaction kinetics and mechanism, economics, and sustainability of biomass torrefaction is discussed in detail. This review is extended to the torrefaction of agro-residue biomass since torrefied agro-residue-based pellets can be produced from agro-residues. The various technological applications of biomass torrefaction are also reviewed and the prospects in ensuring the continuous production of high-grade fuels are summarized. Keywords Thermochemical process . Biomass . Economics . Sustainability . Reaction kinetics . Agro-residue
Introduction Upgrading the quality of biomass by torrefaction to produce high-grade solid fuels with enhanced properties is the dream of many biofuel producers and energy specialists. This has been achieved over the years through the mild thermal pretreatment of raw biomass under inert atmosphere at optimized temperature and duration. This process is referred to as torrefaction. Torrefaction is a thermal conversion process of transforming an ordinary biomass and agro-residues into a high-grade solid biofuel which can be used for gasification and combustion purposes. Depending on the operating conditions, the different torrefaction processes in existence are wet
* Temitope Olumide Olugbade [email protected] 1
Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, SAR, China
2
Department of Industrial and Production Engineering, Federal University of Technology Akure, P.M.B. 704, Akure, Ondo State, Nigeria
torrefaction [1, 2], dry torrefaction [3–5], and ionic-liquidassisted torrefaction [6]. Several studies have been carried out on solid biomass biofuels as regards their energy and mass yield [7–10], and standard fuel analysis [11–14]. Many of the previous studies mainly focused on the possible ways of enhancing the
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