Carbon Capture and Storage

Technology basics

The CCS technology processes, costs, and potential scale for deployment are summarized in a 2007 report by the Global Energy Technology Strategy Program.¹ A more detailed review is available in an IPCC special report.² In summary, the technology consists of five components: CO2 capture, compression, transport, injection into a suitable geologic formation, and monitoring. CO2 capture is currently applied to a small portion of the emissions from some coal and gas power plants, for sale to industrial users, such as the beverage and food processing industries. Oil and gas companies currently practice CO2 pipeline transport and injection into geologic formations, for enhanced oil recovery. However, no monitoring and verification technologies currently exist for ensuring that CO2 injected underground remains underground.³

CO2 capture and compression

The capture of CO2 is generally done by either chemical absorption (with amine scrubbers), physical absorption, or flue gas recycling. Capture of CO2 can be performed on any operation that produces CO2 emissions, but economically feasible sites will be large point sources of CO2, such as electric power plants, refineries, or industrial facilities. There are about 8,100 such sites globally at present, which account for about 60% of total annual fossil and industrial CO2 emissions.⁴ While industrial facilities generally produce less annual CO2 emissions than baseload electric power plants, the processes often generate high-purity CO2 streams that would incur relatively low CO2 capture costs. CO2 capture has been explored at cement plants,⁵ oil refineries, ethanol refineries, steel factories, and chemicals factories (particularly ammonia and ethylene).⁶ While the possibility of employing CCS on a Fischer-Tropsch coal-to-liquids process has been proposed,⁷ the high CO2 emissions intensity of the conversion process (even when CCS is used) combined with the scale of liquid fuel demand make this proposal dubious.⁸  

Overview of Geologic Storage Options.

Source: Intergovernmental Panel on Climate Change (2005). IPCC Special Report on Carbon dioxide Capture and Storage, Figure SPM.4.. Author: IPCC. Permission: IPCC.

Transport and storage

Once captured and pressurized, the CO2 is then transported to a suitable geologic reservoir through pipelines. Currently, the U.S. has more than 3,000 miles of CO2 pipelines, maintained by energy companies for purposes of enhanced oil recovery.⁹ Potential storage sites include depleted oil and gas reserves, enhanced oil recovery sites, deep saline formations, deep unmineable coal seams, CO2-driven coal bed methane recovery, and deep saline-filled basalts and other formations (see figure).¹⁰ The CCS process does not involve simply filling subterranean cavities with CO2 to a certain pressure and then capping the injection well, as takes place for compressed air energy storage, for instance. Instead, injected CO2 permeates into pore spaces between grains or minerals, which are often occupied by fluid (mostly water). The CO2 displaces in situ fluids and occupies the pore spaces, and dissolves into fluids.¹¹ While leakage of CO2 is a concern, the IPCC notes that observations from engineered and natural simulations of CO2 storage indicate that the fraction of CO2 retained in appropriately selected reservoirs will likely exceed 99% for over 1,000 years.¹²

Costs

Carbon capture and storage will incur unambiguous economic costs. While linking CCS systems with enhanced oil recovery operations may offset some of these costs, this application is limited in comparison with the scale of emissions that will need to be mitigated, and would only apply to the portion of large point sources of CO2 that are near oil wells. Capture and compression costs are higher than the other components of CCS costs,¹³ so this phase is especially important for determining the whole-system cost of CCS. It is generally cheaper to capture CO2 from purer and higher-pressure CO2 streams, as they require less post-capture processing.¹⁴ Therefore, an integrated gasification combined cycle coal power plant will incur lower CO2 capture costs than a pulverized coal power plant, as the flue gases from pulverized coal combustion consist of a variety of compounds in addition to CO2. The costs of CO2 capture and compression are shown in the table below for a variety of possible facilities.

Table 1: The cost of CO2 capture for various industrial processes. Costs are in $ (USD) per metric ton of CO2. Source: GTSP 2007, p.33.

Storage capacity by region

Source: Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p. 25.. Author: GTSP. Permission: GTSP / Pacific Northwest National Laboratory.

Transportation and injection costs show considerable variability, as shown in the table below. Transportation costs are sensitive to the distance being transported, and to the volume of the CO2 stream in the pipeline. Injection costs are far lower for storage in terrestrial geologic sites than for ocean storage or mineral carbonation (whose costs are especially speculative¹⁵ ). However, there may be little need for these more expensive storage options for the foreseeable future. It is estimated that terrestrial geologic reservoirs could store approximately 11,000 Gt of CO2; the total fossil and industrial CO2 emissions for the upcoming century are estimated to be about 9,000 Gt.¹⁶ Moreover, the distribution of potential CO2 storage reservoirs is such that most nations have storage reservoirs with adequate capacity for future emissions (see figure); prominent exceptions include Japan and South Korea.¹⁷

 Table 2: Cost ranges for the components of a CCS system as applied to a power plant or industrial source. Costs are in $ (USD) per metric ton of CO2. Source: IPCC 2005, Table SPM.5.

Environmental considerations

The carbon capture and storage technology requires energy. Coal IGCC power plants with CCS will require between 9% and 14% more input fuel per unit of electricity produced; this figure is approximately 15% to 25% for pulverized coal power plants, and 8% to 10% for natural gas combined cycle plants.¹⁸ As well, because CCS would allow fossil energy to remain the backbone of the energy system, the range of environmental, social, and political issues associated with fossil fuel extraction, transport, and marketing would not be addressed.

CCS will also increase a power plant's water use, already a potentially problematic issue for thermal electric power plants in the future. According to a recent National Energy Technology Laboratory report, CCS retrofits on pulverized coal power plants, and CCS systems on new pulverized coal power plants will nearly double the water requirements of the plant. However, an IGCC coal power plant with CCS will actually consume less water than either a subcritical or a supercritical pulverized coal power plant without CCS. ¹⁹

Stored CO2 could also potentially leak into surrounding aquifers, where it would acidify waters and cause environmental and health-related damages. Ocean storage may lead to further acidification of oceans. For these and a variety of other reasons, a number of environmental groups oppose any state-funded research and development of CCS technology, including Greenpeace International.²⁰

Legal considerations

As noted by the IPCC report, few countries have developed legal or regulatory frameworks for long-term CO2 storage, and no emissions accounting methods have been adopted for stored CO2.²¹ Larger issues may include assessment of liability for leakage-related damages and other unintended consequences of large-scale deployment of CCS.

Footnotes

1. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage.

2. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage.

3. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.15.

4. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.8.

5. World Business Council for Sustainable Development and Battelle Memorial Institute (2002). Substudy 8: Climate Change: Toward a Sustainable Cement Industry.

6. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.33.

7. National Energy Technology Laboratory (2008). Coal-to-Liquids Status in the U.S.: Status and Activities.

8. Dooley, JJ, and RT Dahowski (2008). Large Scale U.S. Unconventional Fuels Production and the Role of Carbon Dioxide Capture and Storage Technologies in Reducing Their Greenhouse  Gas Emissions. GHGT-9, Washington, DC, November 2008.

9. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.15.

10. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.16.

11. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage, Chapter 5, p. 205.

12. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage, Chapter 5, p. 246.

13. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage, Chapter 8, p. 346.

14. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.32.

15. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.15.

16. Global Energy Technology Strategy Program (2007). Carbon Dioxide Capture and Geologic Storage, p.8.

17. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage, Chapter 8, p.358.

18. David, J., and H. Herzog (2000). The Cost of Carbon Capture. Massachusetts Institute of Technology.

19. National Energy Technology Laboratory (2008). Estimating Freshwater Needs to Meet Future Thermoelectric Generation Requirements.

20. Greenpeace International (2008). CCS is not going to solve the climate crisis.

21. Intergovermental Panel on Climate Change (2005). IPCC Special Report on Carbon Dioxide Capture and Storage, Summary for Policymakers, p.15.