A1 Journal article (refereed), original research

Effect of hydrothermal carbonization and torrefaction on spent coffee grounds


Open Access publication

Publication Details
Authors: Sermyagina Ekaterina, Mendoza Clara, Deviatkin Ivan
Publisher: Estonian Agricultural University
Publication year: 2021
Language: English
Related Journal or Series Information: Agronomy Research
Volume number: 19
ISSN: 1406-894X
JUFO-Level of this publication: 1
Open Access: Open Access publication

Abstract

Coffee is one of the most tradable commodities worldwide with the current global
consumption of over 10 billion kilograms of coffee beans annually. At the same time, a significant
amount of solid residues, which are known as spent coffee grounds (SCG), is generated during
instant coffee manufacturing and coffee brewing. Those residues have a high potential in various
applications, yet they remain mostly unutilized. The current work presents the experimental
comparison of two pretreatment technologies - hydrothermal carbonization (HTC) and
torrefaction - for converting SCG into a valuable char. The results showed that low-temperature
torrefaction (< 250 °C) has a negligible effect on feedstock properties due to initial pre-processing
of coffee beans. However, the energy conversion efficiency of torrefaction at higher temperatures
is comparable with that of HTC. The average energy yields for high-temperature torrefaction
(> 250 °C) and HTC were on the level of 88%. Devolatilization and depolymerization reactions
reduce oxygen and increase carbon contents during both processes: chars after torrefaction at
300 °C and HTC at 240 °C had 23–28% more carbon and 43–46% less oxygen than the feedstock.
Both pretreatment methods led to a comparable increase in energy density: the highest HHV of
31.03 MJ kg-1
for torrefaction at 300 °C and 32.33 MJ kg-1
for HTC at 240 °C, which is similar
to HHV of anthracite. The results showed that both processes can be effectively used to convert
SCG into energy-dense char, even though HTC led to slightly higher energy densification rates.


Last updated on 2021-15-04 at 12:55