Process Modelling and Pinch Analysis for an Integrated System of Anaerobic Digestion with Digestate Recycling via Hydrothermal Gasification

Anaerobic digestion (AD) of low-grade biomass materials is one of the strategical technologies to achieve the climate-neutral target. Its implementation is however limited due to problems related to digestate management and feedstock scarcity. Digestate recycling to the AD process via hydrothermal gasification (HTG) may be an answer to the problems. This work develops and analyzes thermodynamically a novel integrated process including among others AD, HTG, and power generation unit for energy recovery from the HTG, using Aspen Plus software, with a focus on the HTG block. Effects of HTG process parameters on biogas production and energy recovery are investigated. In addition to that, a Pinch analysis was performed. The result shows that higher energy efficiency is obtained at higher temperature and higher D/W ratio. The syngas recycling to the AD increases biomethane production by 26.10%, power production by 21.42%, and total energy efficiency by 20.05%, compared to the process without syngas recycle. © 2023 Elsevier B.V. Author keywords Anaerobic digestion; hydrothermal gasification, Aspen Plus; Pinch analysis; process integration