Life-cycle assessment of renewable fuel production via hydrothermal liquefaction of manure in Germany

Abstract

Hydrothermal liquefaction (HTL) is a promising option for transforming wet feedstock into liquid fuels. In this work, the Global Warming Potentials (GWP) of HTL fuels obtained from manure have been analyzed for different process configurations using life-cycle assessment (LCA). The GWP of the baseline case amounts to 1.18 kg CO₂-eq. per kg_{fuel mix}, which equals to an emission reduction of about 70% compared to conventional jet fuel. Key emission drivers are H₂ production via steam methane reforming (SMR) and process heat provision from natural gas. Improvements are observed when the H₂ demand is covered by reforming of internally produced biogas or water electrolysis. The latter option is highly sensitive to the carbon intensity (CI) of the electricity input. As a consequence of different CIs, the best performing HTL process configuration strongly depends on the respective local electricity supply. Moreover, the potential emission savings from reduced manure storage durations are analyzed and quantified as −0.38 kg CO₂-eq. per kg manure. Integration into a consequential LCA approach leads to carbon negative fuel production via the HTL pathway in most of the investigated scenarios.