Modeling of cost optimized process integration of HTL fuel production
Christina Penke, Leonard Moser, Valentin Batteiger
Abstract
Hydrothermal liquefaction (HTL) is an advanced biomass conversion process for biocrude production from a broad variety of organic feedstock, including wet waste streams. The intermediate biocrudes can be further upgraded to liquid hydrocarbon fuels and thereby contribute to the mitigation of greenhouse gases from the transport sector. This work investigates an optimized sub-system integration of transportation fuel production via sub-critical HTL of primary sewage sludge. The plant design integrates HTL conversion, biocrude upgrading via hydrotreatment, and an energetic valorization of the residual aqueous phase from HTL conversion via catalytic hydrothermal gasification (cHTG). The option of on-site hydrogen production via reforming of cHTG gas is examined for the purpose of biocrude upgrading. The modeling results show that the hydrogen demand for hydrotreatment could be covered by the valorization of the HTL by-products. The thermal management of an integrated biofuel plant is optimized with respect to subsystem cost based on in-depth process modeling to quantify mass and energy flows and principles of pinch analysis to design a heat exchanger network. The cost optimized configuration results in an overall process energy efficiency of 40.5%. The results provide a basis for design choices for future HTL plants.