Existing and planned ethanol biorefineries, saline aquifers, candidate CO2 pipeline rights of way and candidate injection sites in the U.S. Lack of adequate sequestration capacity near existing biorefineries necessitates construction of a CO2 transportation network to achieve high levels of abatement. Source: Sanchez, Johnson, et. al./CC BY-NC-ND

There are more than 200 existing U.S. biorefineries that emit 45 million metric tons (Mt) of carbon dioxide annually from fermentation. The near-term commercial prospects for capturing and storing this gas at U.S. ethanol biorefineries were analyzed by an international team of researchers. The modeling framework applied 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.

An assessment of CO₂ capture costs, and not including pipeline construction or sequestering the gas, concludes that about 60 percent of current emissions, or 27 Mt/year, could be captured for less than $25 per metric ton.

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. This is estimated to 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.

Bioenergy with carbon capture and sequestration (BECCS) is a promising means for CO₂ removal, involving the capture and permanent sequestration of biogenic CO₂ produced during energy conversion. However, most BECCS technologies today, such as gasification with pre-combustion CO₂ capture, have not yet been demonstrated at commercially relevant scales.

But capture of biogenic CO₂ from fermentation is unique, because unlike many other BECCS methods, 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 percent) gaseous CO₂ stream consisting only of CO₂, water and small amounts of organic and sulfur compounds. In fact, a U.S. Department of Energy supported project is capturing and storing around 1 Mt per year of CO₂ in Illinois.

Scientists from Carnegie Institution for Science, California; International Institute for Applied Systems Analysis, Austria; Lawrence Livermore National Laboratory, California; Carnegie Mellon University, Pennsylvania; and Stanford University participated in this research, which is published in Proceedings of the National Academy of Sciences.