Thermal pretreatment impact on densified biomass physical properties

Authors: GHIASI, BAHMAN - University Of British Columbia; Tumuluru, Jaya Shankar; SOKHANSANJ, SHAHAB - University Of British Columbia

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 11/18/2022
Publication Date: 6/29/2023
Citation: Ghiasi, B., Tumuluru, J., Sokhansanj, S. 2023. Thermal pretreatment impact on densified biomass physical properties. In: Tumuluru, J.S. editor. Densification Impact on Raw, Chemically and Thermally Pretreated Biomass. First Edition. Singapore: World Scientific Publishing Co. Pte. Ltd. p. 155-187. https://doi.org/10.1142/9781800613799_0006.
DOI: https://doi.org/10.1142/9781800613799_0006

Interpretive Summary: The thermal pretreatment process called torrefaction helps improve the biomass's physical properties and chemical composition. Torrefaction makes biomass brittle, helps to grind biomass easily, and creates a product with uniform particle size and shape. The challenge of the torrefied biomass is low bulk density. During torrefaction, biomasses lose moisture and other low energy content materiel and losses density. One way to overcome this limitation is by densifying the torrefied biomass. This chapter discusses the densification characteristics of torrefied biomass and its impact on the biomass physical properties and chemical composition.

Technical Abstract: Lignocellulosic biomass has low energy content and is high in oxygen content. The proximate and ultimate composition of lignocellulosic biomass is inferior compared to coal. The grinding properties of biomass are completely different compared to coal. Biomass is fibrous, whereas coal is brittle. One way to make biomass look like coal is through torrefaction. The biomass is roasted in an oxygen-free environment at temperatures of 200–300°C for different residence times. During torrefaction, the biomass loses the low energy content of volatiles and produces a solid product that is high in energy content. The solid fraction rich in carbon is torrefied biomass or ‘biocoal’. Biocoal represents a renewable energy commodity that can substitute coal. The torrefied biomass has superior biomass in terms of proximate and ultimate composition and physical properties such as grinding and particle size, but the challenge is low in bulk density. The low bulk density is primarily due to the loss of low energy content volatiles during the torrefaction process. One way to increase the density of the torrefied biomass is through densification. The densification systems commonly used today are pellet mills and briquette presses. Densification helps improve the transportation and handling of low-density torrefied biomass. The challenge is in making a durable pellet using torrefied biomass as the biomass loses its binding ability. Typically, binders are used for making torrefied and densified biomass. The challenge of adding binders is introducing foreign material to the biomass and changing the composition. In addition, adding binders can change the torrefied material properties, such as hydrophobicity. The other option to overcome this limitation is to torrefy the densified biomass. This chapter looks at the production of torrefied and densified biomass and its physical properties.