To better understand the near-term commercial potential for capturing and storing atmospheric carbon dioxide, researchers from the Carnegie Institution for Science, International Institute for Applied Systems Analysis, Lawrence Livermore National Laboratory (LLNL) and Stanford University have mapped out how CO₂ might be captured from existing US ethanol biorefineries and permanently stored (or sequestered) underground.

The analysis combines process engineering, spatial optimization, and lifecycle assessment to consider the technical, economic, and institutional feasibility of near-term carbon capture and sequestration (CCS). An open-access paper on the work is published in Proceedings of the National Academy of Sciences (PNAS).

Contour plot of modeled abatement costs and scales for CO2 capture and compression for biorefineries (n = 216); 60% of fermentation CO2 emissions are available for pipeline transport for under $25/tCO2. Sanchez et al. Click to enlarge.

There are more than 200 existing US biorefineries that emit 45 million metric tons (Mt) of CO₂ annually from fermentation. Looking only at the cost of capturing the CO₂—not including building pipelines or sequestering the captured CO₂—the team found that 60% of current CO₂ emissions (i.e., 27 Mt per year) could be captured for less than $25 per metric ton.

Ethanol production is one of the least costly known applications of CO2 capture and, to date, the cost of capturing CO2 has been cited as one of the major barriers to CCS.

—LLNL scientist Sean McCoy, co-author

A credit of $60 per metric ton of CO₂ sequestered would be sufficient to cover the costs of capture, transport and sequestration for about 30 million metric tons of CO₂ per year. The team estimates this would result in the construction of 4,300 miles of pipelines.

In another scenario, a credit of $90 per metric ton to reduce emissions from ethanol production would result in the capture, transport and sequestration of 38 million tons of CO₂ and drive construction of a comparably large pipeline network.

The team’s modeling framework evaluates least-cost source-sink relationships and aggregation opportunities for pipeline transport, which can reduce the cost of transporting small CO₂ volumes to suitable sequestration sites.

Proposed modifications to the California Low Carbon Fuel Standard and recent revisions to existing federal tax credits create a substantial near-term opportunity to permanently sequester biogenic CO₂. This financial opportunity could not only spur the growth of Carbon Capture and Sequestration (CCS), but also reduce the lifecycle impacts of biofuels we use today, help fulfill mandates for low-carbon fuels in the US and elsewhere, and support development of new carbon-negative fuels.

—Sean McCoy

A promising class of technologies for carbon dioxide removal is known as bioenergy with carbon capture and sequestration (BECCS), which involves the capture and permanent sequestration of biogenic CO₂ produced during energy conversion. However, most BECCS technologies today, for example gasification with pre-combustion CO₂ capture, have not yet been demonstrated at commercially relevant scales.

Capture of biogenic CO₂ from fermentation is unique, because unlike many other BECCS technologies, it doesn’t require a costly separation of CO₂ and can be applied at existing biorefineries.

Practiced commercially for several decades, fermentation of sugars and starch produces more than 26 billion gallons per year of ethanol worldwide. Fermentation also produces a high-concentration (99%) gaseous CO₂ stream consisting only of CO₂, water and small amounts of organic and sulfur compounds. A US Department of Energy supported project is capturing and storing around 1 Mt per year of CO₂ from an Archer Daniels Midland Company (ADM) plant in Illinois. (Earlier post.)

The role for CO₂ removal envisioned in stringent climate change mitigation scenarios cannot be overstated. Deploying CCS at existing biorefineries is an important step toward large-scale deployment of BECCS and other removal technologies.

—Sean McCoy

The research was funded by the David and Lucile Packard Foundation, the Alexander von Humboldt Foundation and the US Department of Energy, Office of Fossil Energy.

Resources

• Daniel L. Sanchez, Nils Johnson, Sean T. McCoy, Peter A. Turner, Katharine J. Mach (2018) “Near-term deployment of carbon capture and sequestration from biorefineries in the United States” PNAS doi: 10.1073/pnas.1719695115