Techno-economic Analysis of Sustainable Biofuels for Marine Transportation

Abstract

Renewable, low-carbon biofuels offer the potential opportunity to decarbonize marine transportation. This paper presents a comparative techno-economic analysis and process sustainability assessment of four conversion pathways: (1) hydrothermal liquefaction (HTL) of wet wastes such as sewage sludge and manure; (2) fast pyrolysis of woody biomass; (3) landfill gas Fischer–Tropsch synthesis; and (4) lignin–ethanol oil from the lignocellulosic ethanol biorefinery utilizing reductive catalytic fractionation. These alternative marine biofuels have a modeled minimum fuel selling price between $1.68 and $3.98 per heavy fuel oil gallon equivalent in 2016 U.S. 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 wastes such as food waste can provide another option to produce raw biocrude with lower S content to meet the target with further hydrotreatment. 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 economics.

Desalting biocrude for improved downstream processing toward marine fuel application

“…A scale of 1000 dry tonne/day sewage sludge HTL plant in the previous work was used as the base case for the sake of comparison (UWBC). 9 Detailed process descriptions of the HTL plant without a water-washing process and TEA financial assumptions can be found in the ESI (S20†). Fig.…”

“…1,2 It is therefore unsurprising that biofuels produced by a variety of technologies including fermentation, pyrolysis, Fischer–Tropsch, and hydrothermal liquefaction (HTL) are being evaluated for marine applications. 3–10…”

“…1,2 It is therefore unsurprising that biofuels produced by a variety of technologies including fermentation, pyrolysis, Fischer-Tropsch, and hydrothermal liquefaction (HTL) are being evaluated for marine applications. [3][4][5][6][7][8][9][10] The HTL process converts biomass feedstocks to biocrudes using subcritical water at high pressure (typically 10-25 MPa) and high temperatures (typically 250-350 °C). At temperatures greater than 300 °C the ion product of water (K W ) is about three orders of magnitude higher than that under ambient conditions and the dielectric permittivity is signicantly reduced.…”

Reactive Extraction Process for Separating 2,3-Butanediol from Fermentation Broth

“…The latter's environmental footprint could include acidification and eutrophication that disrupt the natural balance of aquatic life. 37 Furthermore, sustainability metrics are not limited to environmental impacts. The economic aspect of the sustainability is also important and can be represented by the BDO product separation cost, which is $0.22/kg BDO product.…”

“…The former relates to water removal from the available supplies without returning to a water resource system by mechanisms such as evaporation and cooling tower drift. The latter’s environmental footprint could include acidification and eutrophication that disrupt the natural balance of aquatic life . Furthermore, sustainability metrics are not limited to environmental impacts.…”