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Sammanfattning

This study examines the torrefaction of raw digestate (RD) to upgrade properties of product followed by thermal-pyrolysis behaviour analysis of RD and torrefied product. Results showed that key torrefaction indices mainly mass yield (MY%), energy yield (EY%), higher heating ealue (HHV), energy-mass co-benefit index (EMCI) were affected by torrefaction reaction temperature. As temperature increased 200 degrees C to 300 degrees C, MY% was decreased from similar to 95 % to similar to 69 % while EY% initially enhanced till 260 degrees C, then became constant till 300 degrees C. Torrefaction enhanced fixed carbon and HHV by 14.3-86.7 % and 15.8-35.8 % as compared to RD as temperature increased from 200 to 300 degrees C, however, ash content increased. Torrefaction of RD at 240 degrees C for 30 mins provided best results in terms of MY%, EY% and HHV with tradeoff between fixed-carbon and ash-content. Furthermore, thermal-pyrolysis behaviour of RD and TD240 was investigated by model-free and model-based kinetic models to examine the kinetics primary reactions under thermal decomposition. Estimated activation energies (Ea) reduced from 129.2-225.9 kJ/mol, 122.4-203.5 kJ/mol, and 127.3-227.4 kJ/mol for RD to 107.5-132.4 kJ/mol, 110.4-132.8 kJ/mol and 106.2-132.7 kJ/mol for TD240 using Friedman, Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) models respectively. Activation enthalpy (Delta H) obtained 123.9-190 kJ/mol and 108.4-127.6 kJ/mol for RD and TD240. Furthermore, mass and energy balance showed the process has 97.65 % self-efficient without any external energy. Overall, effectiveness of torrefaction process showed to upgrade the existing biogas plants.

Nyckelord

Digestate; Torrefaction; Mass and Energy balance; Kinetic modeling; Thermal behavior

Publicerad i

Thermal Science and Engineering Progress
2025, volym: 62, artikelnummer: 103688
Utgivare: ELSEVIER

SLU författare

UKÄ forskningsämne

Bioenergi
Energisystem

Publikationens identifierare

  • DOI: https://doi.org/10.1016/j.tsep.2025.103688

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/142091