Insights into the product quality and energy requirements for solid biofuel production: A comparison of hydrothermal carbonization, pyrolysis and torrefaction of olive tree pruning. (1st January 2022)

• Record Type: Journal Article
• Authors: González-Arias, J.; Gómez, X.; González-Castaño, M.; Sánchez, M.E.; Rosas, J.G.; Cara-Jiménez, J.
• Is Part Of: Energy. Volume 238:Part C(2022)
• Publication Date: 2022-01-01
• Subjects: Hydrothermal carbonization -- Slow pyrolysis -- Torrefaction -- Olive tree pruning -- Biofuel; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Energy consumption -- Periodicals; 333.7905
• DOI: 10.1016/j.energy.2021.122022
• Languages: English
• ISSNs: 0360-5442

Abstract

Abstract: For a bio-economy establishment, understanding the energy consumption needs to produce solid biofuels is a key point. Herein, olive tree pruning was treated by both dry (pyrolysis and torrefaction) and wet (hydrothermal carbonization) thermal treatments. Product yield, solid quality and energy consumption were assessed. The solids were characterized by means of chemical and thermogravimetric analysis. For all treatments, coal-like solid products were obtained, with higher heating values (HHV) of almost 30 MJ kg −1 in most of the conditions evaluated. Chars from pyrolysis presented the greater carbon content (between 76 and 85 wt%) but also the higher ash content (ranging from 6 to 9 wt%). From an energy consumption perspective, torrefaction registered the lowest energy consumption (between 5.85 and 20.76 MJ kg −1 char). The highest energy contents per kilogram of char produced were also reflected in torrefaction samples, with values around 11 MJ kg −1 char. Although the obtained HHVs were greater for pyrolysis chars the higher mass yields obtained in torrefaction makes it more profitable. The least severe conditions allowed to obtain a positive energy balance only with the solid phase considered. Nonetheless, further room for improvement is possible since the gas and liquid phases may also be valorised. Graphical abstract: Image 1 Highlights: Pyrolysis, torrefaction and HTC were assessed regarding yield, quality and energy consumption. From both wet and dry treatments, products with HHV of ca. 30 MJ kg −1 were obtained. Pyrolysis concentrates the carbon content in the char to a greater extent (80 wt%). The highest energy content per kg of char were reflected in torrefaction samples. Torrefaction registered the lowest energy consumption from ca. 5–20 MJ kg −1 char.