Multi-objective optimization of pelletized coffee silver skin in flue gas torrefaction for producing premium solid fuel

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Manatura, Kanit and Klinkesorn, Supaporn and Chalermsinsuwan, Benjapon and Samsalee, Namfon and Wongrerkdee, Sutthipoj and Jaojaruek, Kitipong and Pattiya, Adisak and Li, Jun (2024) Multi-objective optimization of pelletized coffee silver skin in flue gas torrefaction for producing premium solid fuel. BioEnergy Research, 18 (1). 7. ISSN 1939-1242 (https://doi.org/10.1007/s12155-024-10808-6)

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Abstract

Coffee silver skin, an organic residue from coffee production, demonstrates low solid fuel characteristics such as low bulk density and heating value, necessitating enhancements for solid fuel applications. Torrefaction in a flue gas environment (5% O2, 15% CO2, and a balance of N2, v/v) is more energy-efficient than inert torrefaction, using recovered flue gas to improve fuel quality and process efficiency. Three input factors were assessed: temperature (200, 250, and 300 °C), residence time (30, 45, and 60 min), and gas media (N2 and flue gas). Four performance metrics were evaluated: energy yield, upgrading energy index, specific energy consumption, and energy-mass co-benefit. Temperature significantly influenced most outcomes, except for energy-mass co-benefit, which was medium-dependent. Optimal torrefaction conditions achieving maximum energy yield (71.48%) and energy-mass co-benefit (5.30%) were identified at 200 °C for 30 min with flue gas. The torrefied material’s properties include moisture content, volatile matter, fixed carbon, and ash content of 3.03%, 69.24%, 27.04%, and 1.01%, respectively. Furthermore, the hydrophobicity of pelletized coffee silver skin notably increased under flue gas conditions, evident by a contact angle greater than 100°, indicating that flue gas torrefaction is a feasible approach for producing high-grade solid fuel.

ORCID iDs

Manatura, Kanit, Klinkesorn, Supaporn, Chalermsinsuwan, Benjapon, Samsalee, Namfon, Wongrerkdee, Sutthipoj, Jaojaruek, Kitipong, Pattiya, Adisak and Li, Jun ORCID logoORCID: https://orcid.org/0000-0002-7685-8543;
CORE (COnnecting REpositories)