Torrefaction of almond and walnut byproducts

Authors: McCaffrey, Zachariah - Zach; Torres, Lennard; Chiou, Bor-Sen; FERRIER, SAULO - Federal University Of Lavras; SILVA, LUIZ - Federal University Of Lavras; Wood, Delilah - De; Orts, William

Submitted to: Frontiers in Energy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2021
Publication Date: 3/22/2021
Citation: McCaffrey, Z., Torres, L.F., Chiou, B., Ferrier, S., Silva, L., Wood, D.F., Orts, W.J. 2021. Torrefaction of almond and walnut byproducts. Frontiers in Energy Research. 9. Article 643306. https://doi.org/10.3389/fenrg.2021.643306.
DOI: https://doi.org/10.3389/fenrg.2021.643306

Interpretive Summary: While the US nut industry is growing, markets for nut byproducts, particularly nutshells and tree prunings, have not kept pace. Torrefaction is a thermochemical process used to improve physical and chemical properties of biomass for energy and other applications. The goal of the paper was to characterize the effects of a range of torrefaction conditions on the properties of nut byproduct feedstock. The paper extends available literature in properties of torrefied biomass and will be useful to groups interested in producing bioenergy products, as well as other products and applications, from agricultural feedstocks.

Technical Abstract: Torrefaction is a process used to improve physicochemical properties of biomass for energy applications. The goal of the paper was to analyze the effect of torrefaction on the properties of nut byproducts. The process consists of thermal treatment of biomass at a temperature between 200 and 300 °C in the absence of oxygen, where final material properties of the torrefied biomass depend on the temperature, heating rate, and residence time. Torrefied biomass exhibits higher hydrophobicity and calorific value with reduced moisture absorption compared to untreated biomass, making it an ideal fuel source for energy applications compared to raw biomass. Almond shells of soft, semi-soft, and hardshell varieties, as well as walnut shells and almond wood, were torrefied at two different temperatures (230 and 290 °C) and three different residence times (20, 40, and 60 minutes) in order to optimize the physicochemical properties. The thermal behavior of raw and heat-treated biomass was investigated by TGA analysis, elemental analysis, pH, helium pycnometry, FTIR spectroscopy, and dynamic vapor sorption analysis.