Conceptual design of an integrated hydrothermal liquefaction and biogas plant for sustainable bioenergy production

Initial process studies carried out in Aspen Plus on an integrated thermochemical conversion process are presented herein. In the simulations, a hydrothermal liquefaction (HTL) plant is combined with a biogas plant (BP), such that the digestate from the BP is converted to a biocrude in the HTL process. This biorefinery concept offers a sophisticated and sustainable way of converting organic residuals into a range of high-value biofuel streams in addition to combined heat and power (CHP) production. The primary goal of this study is to provide an initial estimate of the feasibility of such a process. By adding a diesel-quality-fuel output to the process, the product value is increased significantly compared to a conventional BP. An input of 1000 kg h−1 manure delivers approximately 30–38 kg h−1 fuel and 38–61 kg h−1 biogas. The biogas can be used to upgrade the biocrude, to supply the gas grid or for CHP. An estimated 62–84% of the biomass energy can be recovered in the biofuels.