Study Suggests “Flexible Carbon to Liquid” Fuel Process Could Displace 15-20% of Transportation Fuels in the US

Jose Michael

A preliminary analysis of a feedstock-flexible biomass waste/residue thermochemical pathway for liquid fuel production by researchers at Purdue University suggests that such a “flexible carbon to liquid” fuel (FCTL) process could replace 15%-20% of transportation fuels consumed in US and reduce greenhouse gas emissions by more than 50% compared with petroleum-derived gasoline.

At the same time, it could be more environmentally sustainable since few changes would be needed in agricultural and forestry practices, and may be more resilient against external disturbances such as feedstock supply shocks and market demand changes, they say.

This technique is more flexible than conventional methods because we can process a wider range of very different feedstocks and, at the same time, we can generate a wider range of end products—not just gasoline and diesel but ethanol and hydrogen. Or we could generate electricity directly from the gas produced.

—Professor Fu Zhao

In a paper presented on 29 September during the 6th Global Conference on Sustainable Product Development and Life Cycle Engineering in Busan, Korea, Zhao and his colleagues divide the FCTL process into two sub-processes: biomass gasification and FT synthesis.

The FT synthesis subsystem in an FCTL plant is identical to that in a CTL plant and has been well investigated. The main challenges facing the development of FCTL lie in the gasification part.

—Zhao et al. (2008)

Gasifiers fall into three main categories:, based on the means of supporting the feedstock in the reactor vessel; the direction of flow of both the feedstock and oxidant; and the way heat is supplied to the reactor: fixed/moving bed, fluidized bed, and entrained flow. Of the three, the fluidized bed gasifier supports a wide range of feedstock and particle sizes and can be operated under a wide range of conditions.

In their analysis, Zhao and his team selected a fluidized bed gasifier, and noted that plant availability could be further improved by using low rank coal as the backup feedstock.

In addition to concluding that liquids derived from an FCTL process could replace 15-20% of transportation fuel in the US, the study suggests that:

  • The cost of the derived fuels is in the range of $1.50-$2.00/gallon gasoline equivalent—i.e., competitive with other biofuels;

  • Lifecycle water withdrawal and land use of fuels derived from FCTL process are less than other biofuels;

  • A FCTL plant may generate local but intensive water supply and water quality challenges and the development of integrated water management strategies within the plant is critical;

  • A FCTL system is more resilient against external disturbances—e.g. feedstock supply shocks and market demand changes than other biofuel technologies.

The paper calls for the development an integrated process simulation model of a FCTL plant and a complete life cycle assessment in order to achieve a better picture of the economic and environmental performance of such a process.

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