PNNL

Abstract

Renewable, low-carbon biofuels offer the potential opportunity to decarbonize marine transportation. This paper presents a comparative techno-economic analysis (TEA) and process sustainability assessment of four conversion pathways: (1) hydrothermal liquefaction (HTL) of wet waste such as sewage sludge and manure; (2) fast pyrolysis (FP) of woody biomass; (3) landfill gas Fischer-Tropsch synthesis (LGFT); and (4) lignin-ethanol oil (LEO) from the lignocellulosic ethanol biorefinery utilizing reductive catalytic fractionation (RCF). These alternative marine biofuels have a modeled minimum fuel selling price between $1.68 and $3.98 per heavy fuel oil gallon equivalent (HFOGE) in 2016 US dollars based on a mature plant assessment. The selected pathways also exhibit good process sustainability performance in terms of water intensity compared to the petroleum refineries. Further, the O and S contents of the biofuels vary widely. While the non-HTL biofuels exhibit negligible S content, the raw biocrudes via HTL pathways from sludge and manure show relatively high S contents (> 0.5 wt%). Partial- or full- hydrotreatment can effectively lower the biocrude S content. Additionally, co-feeding with other low-sulfur wet waste such as food waste can provide another option to produce lower S-content raw biocrude to meet the target with further hydrotreating. This study indicates that biofuels could be a cost-effective fuel option for the marine sector. Marine biofuels derived from various feedstocks and conversion technologies could mitigate marine biofuel adoption risk in terms of feedstock availability and biorefinery economies.