Negative CO2 Emissions: Making it Real
Nearly all projections for meeting temperature goals established in the 2015 Paris Climate agreement rely on “negative emissions,” or removing CO2 that is already in the atmosphere. So what are the best methods to achieve negative emissions, and how do we accelerate deployment of those methods?
There are several negative emissions technologies that have been talked about in the press and other venues, but the most mature is bioethanol production with carbon capture and storage (or BECCS). This is showcased by the recent start-up of a carbon capture and storage (CCS) system at the Archer Daniels Midland (ADM) bioethanol production facility in Decatur, Illinois, which will inject over one million tonnes per year (Mtpy) of CO2 7000 feet underground for permanent storage. The ADM effort was partially funded by the U.S. Department of Energy and is an important step in demonstrating that large-scale negative emissions technologies can be broadly deployed.
The production of bioethanol generates a stream of nearly pure CO2, which is ready for compression and transport after simple water removal. Negative emissions occur as follows:
- Crops absorb CO2 from the atmosphere as part of their natural growth process;
- The crops are used as a feedstock to produce bioethanol;
- The nearly-pure CO2 stream generated in the bioethanol production process is captured and permanently stored rather than being emitted to the atmosphere.
Bioethanol is ethanol that is typically produced from plants with high sugar and starch content – such as corn and sugar cane. In 2015, global bioethanol production was over 25 billion gallons. The United States and Brazil are the biggest producers, accounting for about 60% and 25% of global production respectively, followed by Europe (Spain, Germany, Sweden and France), China and Canada. Most of the bio-ethanol produced globally is used as transportation fuel.
The bioethanol production process
Bioethanol can be made from a wide range of biomass types, as noted in the Figure 1. When sugar-based plants are used, the process starts with crushing and then soaking the crop in water to dissolve sugars. The liquid part is separated from the solid and fermented using enzymes, converting the sugars into alcohol and CO2. The liquid is then distilled to produce ethanol.
Figure 1. Bioethanol production processes
When starch-based plants are used, the crop is cleaned, milled, and then converted into fermentable sugars using a targeted form of enzyme (amylase). From that point on, the process is similar to that for high-sugar crops.
Cellulosic biomass types like grass and woody crops can also be used, although this requires a different technology – biomass pre-treatment to convert cellulose into sugars – which are then fermented similarly to the conventional process. Fuel produced using this process is classified as 2nd generation bioethanol (also called advanced or cellulosic biofuel).
The fermentation step produces gases with high CO2 concentration. For each tonne of bioethanol produced, about 0.7 tonne of nearly pure CO2 is emitted from the fermentation process. After water removal, the gas can be sent for compression and transport. The costs to capture, compress, transport and store CO2 associated with this process have been estimated at approximately $30 per tonne or less – depending on the size of the facility – compared to $60 to $80 per tonne for CO2 produced from power generation.
Table 1 shows bioethanol production facilities worldwide where CO2 is captured for further use or dedicated storage. In addition to the listed operational facilities, there are projects in development planning at different scales ranging from 0.02 to 0.2 Mtpy CO2 capture.
Table 1. CCS Applications in bioethanol production
|Project||Location||Start date||Capture capacity||Characteristics/Approach|
|Arkalon||US||2009||0.31 Mtpy||EOR, Texas|
|Bonanza||US||2011||0.16 Mtpy||EOR, Kansas|
|Rotterdam||Netherlands||2012||0.3 Mtpy||CO2 supplied to greenhouses|
|Illinois Industrial||US||2017||1 Mtpy||Geological storage|
BECCS clearly represents a significant opportunity for negative emissions and moves us along the path to meeting the goals embodied in the Paris agreement. A logical question, then, is what is needed to get more of these into operation? The answer is that we need policies that promote investment in CCS. In the latter half of 2016, bills to extend and enhance tax credits for CCS – known as 45Q tax credits – were introduced in both the House and the Senate. These bills had wide, bipartisan support. The Senate bill ultimately included nearly twenty co-sponsors ranging from progressive Democrats such as Sheldon Whitehouse from Rhode Island to conservative Republicans such as Mitch McConnell from Kentucky. Similar bills are now being drafted for introduction in this new Congress.
The incentives included in the bills introduced in the previous Congress ranged from $35 to $50/tonne of CO2 stored. Incentives at that level could have a significant influence on decisions by producers and investors to deploy CCS on bioethanol and other industrial facilities.
 RFA, 2016. Renewable Fuels Association – World Fuel Ethanol Production. [Online]
Available at: http://www.ethanolrfa.org/resources/industry/statistics/#1454098996479-8715d404-e546.
 Global CCS Institute, 2016a, The Global Status of CCS: 2016 Volume 3.
 IEAGHG, 2011. Potential for biomass and carbon dioxide capture and storage, Cheltenham : IEA Environmental Projects ltd. (IEAGHG).
 NETL, 2014. Cost of Capturing CO2 from Industrial Sources. DOE/NETL-2013/1602, January 2014.
 Kemper, J., 2015. Biomass and carbon dioxide capture and storage: A review. International Journal of Greenhouse Gas Control, 40(2015), pp. 401-430.
 Global CCS Institute, 2016b. Global CCS Institute: Projects. [Online]
Available at: http://www.globalccsinstitute.com/projects/.