Conceptual design and techno-economic assessment of coupled hydrothermal liquefaction and aqueous phase reforming of lignocellulosic residues

Abstract

Hydrothermal liquefaction is a promising technology for producing renewable advanced biofuels. However, some weaknesses could undermine its large-scale application, such as the significant carbon loss in the aqueous phase (AP) and the necessity of biocrude upgrading. In order to deal with these challenges, in this work the techno-economic feasibility of coupling hydrothermal liquefaction (HTL) with aqueous phase reforming (APR) was evaluated. APR is a catalytic process able to convert water-dissolved oxygenates into a hydrogen-rich gas that can be used for biocrude upgrading. Two cases were proposed, based on different lignocellulosic feedstocks: corn stover (CS) and lignin-rich stream (LRS) from cellulosic ethanol production. HTL-APR plants operating with the same mass flow (3.6 t/h) at 10 wt% solid loading were herein evaluated, resulting in an input size of 20 MW (LRS) and 16.5 MW (CS). Based on experimental and literature data, the mass and energy balances were performed; subsequently, the main equipment was designed; finally, the capital and operating costs were evaluated. The analysis showed that the minimum selling prices for the biofuel (0% internal rate of return) were 1.23 (LRS) and 1.27 €/kg (CS). The heat exchangers accounted for most of the fixed capital investment, while electricity and feedstock had the highest impact on the operating costs. The implementation of APR was particularly profitable with CS, as it produced 107% of the hydrogen required for biocrude upgrading. In this case, APR was able to significantly reduce the H2 production cost (1.5 €/kg) making it a competitive technology compared to conventional electrolysis.