(28a) Impacts of CO2 Supply Systems for Algal-Based Biorefineries on Biofuel Life Cycle Assessments

Authors: 
Realff, M. J., Georgia Institute of Technology
Chance, R. R., Georgia Institute of Technology and ExxonMobil Research and Engineering
Yuan, Y., Georgia Institute of Technology
Fishbeck, T., Algenol Biofuels
Thomas, V., Georgia Institute of Technology
Varma, S., Georgia Institute of Technology
Biofuels have great potential as low-carbon alternatives to fossil-based transportation fuels. This talk will focus on utilization of CO2 in an advanced biofuel system and the integration of that system with CO2 generation sources. The biofuel system is the Algenol Direct to Ethanol®technology, which provides an efficient, cyanobacteria-based system for producing ethanol and bio-crude. The Algenol process consumes CO2 in a process that yields a biofuel with much lower greenhouse gas emissions than gasoline.1-3 In this talk, different options for CO2 capture and utilization (CCU) are considered and their impact on the overall system operation evaluated in terms of carbon footprint reduction. The boundary of the life cycle analysis includes the CO2 source. Overall 13 scenarios are described including an artificial reference case with CO2 arriving at the boundary limits of a 2000 acre, model biorefinery with zero carbon footprint burden and zero CO2 cost at a 10% IRR. Most scenarios involve combined heat and power (CHP) systems with no power supplied from the grid. Both natural gas and cellulosic fuel sources are considered for the CHP system. Five of the scenarios are “stand-alone” in that they do not require co-location with an anthropogenic CO2 source. This is achieved by generating enough CO2 on site to supply the needs of the biorefinery and selling excess power back to the grid. Four of the five stand-alone systems have carbon footprints and economics that are fully competitive with the commonly considered coal flue gas case. Overall carbon footprint reductions range from 23% to 116%. Equivalent CO2 costs (based on comparisons to the reference case) range from $35/-$96/tonne with coal flue gas being $45/tonne.

1D. Luo et al, “Lifecycle Energy and Greenhouse Gas Emissions from Ethanol Produced by Algae”, Environmental Science and Technology 44, 8670 (2010).

2Notice of EPA pathway approval: http://epa.gov/otaq/fuels/renewablefuels/new-pathways/approved-pathways.htm

3R. P. Lively et al, “Anthropogenic CO2 as a feedstock for the production of algal-based biofuels”, Biofuels, Bioproducts, and Biorefining  9, 72-81 (2015)