Integration of Hydrothermal Carbonisation and Anaerobic Digestion for the Energy Valorisation of Grass

Aaron E. Brown, James M. Hammerton, Miller Alonso Camargo-Valero and Andrew B. Ross
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Aaron E. Brown: School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK
James M. Hammerton: School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK
Miller Alonso Camargo-Valero: BioResource Systems Research Group, School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK
Andrew B. Ross: School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK

Energies, 2022, vol. 15, issue 10, 1-21

Abstract: The integration of hydrothermal carbonisation (HTC) and anaerobic digestion (AD) can overcome some of the disadvantages of thermal or biological processing alone. This study aims to investigate integrated HTC-AD across a range of integration strategies and HTC processing temperatures (150 °C, 200 °C and 250 °C) to improve the energy conversion efficiency (ECE) of grass, compared to AD alone. The separation of hydrochars (HCs) for combustion and process waters (PWs) for digestion appears to be the most energetically feasible HTC-AD integration strategy, compared to HC or HTC-slurry AD. Hydrochars represent the greater energy carrier with between 81–85% of total energy output. The ECE of grass was improved from 51% to 97% (150 °C), 83% (200 °C) and 68% (250 °C) through integrated HTC-AD. Therefore, lower HTC processing temperatures yield more favourable energetics. However, higher HTC temperatures favour more desirable HC properties as a combustion fuel. The hydrochar produced at 250 °C (HC-250) displayed the highest HHV (25.8 MJ/kg) and fixed carbon: volatile matter ratio (0.47), as well as the greatest reduction in slagging and fouling potential (ash flow temperature > 1550 °C). Overall, integrated HTC-AD is an effective energy valorisation strategy for grass. A compromise exists between the quality of hydrochar and the energetic balance. However, at 250 °C the process remains energetically feasible (EROI = 2.63).

Keywords: grass; hydrothermal carbonisation; anaerobic digestion; integration; hydrochar; process water; biomethane; pre-treatment; affordable and clean energy (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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