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The idea

Carbon capture and storage, also known as carbon capture and sequestration or CCS, describes a variety of ways to reduce the carbon dioxide emitted by burning fossil fuels. Most commonly it refers to methods based on capturing carbon dioxide from large point sources such as fossil fuel power plants and storing it so that it does not enter the atmosphere. It also refers to ways of removing CO₂ directly from ambient air, for example by biological methods such as biochar.

In the following paper:

• D’Alessandro et al, Carbon dioxide capture: prospects for new materials, Angew. Chemie Int. Ed. 49 (2010), 2–27.

the authors summarize two of the key issues as follows:

Two points must first be made with respect to capture materials and potential capture technologies, given the sheer magnitude of global CO₂ emissions. First, any chemical employed to capture CO₂ will rapidly exhaust its global supplies if it is used in a once-through manner; and second, any chemical produced from CO₂ as a reactant will rapidly saturate global markets for that chemical. These considerations underscore the necessity that capture materials must be regenerable. In this case the energy input for regeneration is one of the key factors in determining the efficiency and cost.

List of methods

Injection into the ground

One widely studied approach to CCS is simply injecting CO₂ into the ground. See:

• National Academy of Engineering (NAE) and Board on Energy and Environmental Systems (BEES), The Carbon Dioxide Dilemma: Promising Technologies and Policies. Franklin M. Orr, Sequestration via injection of carbon dioxide into the deep earth.

In 1991, Norway became the first country in the world to impose a federal tax on atmospheric CO₂ emissions from operations such as coal-fired power plants. Later this tax of $55 of per ton of CO₂ was extended to cover offshore oil and gas production. This motivated Norwegians to set up an operation called Sleipner which strips CO₂ from natural gas offshore in the North Sea and reinjects 0.3 megatons of carbon a year into a non–fossil-fuel–bearing formation. This is apparently the world’s largest carbon capture and storage project. However, a one-gigaton ‘wedge’ would require building 3500 Sleipner-sized projects (or fewer, larger projects).

For more details, see:

• Sleipner gas field, Wikipedia.

• James W. Johnson, A solution for carbon dioxide overload, Science and Technology , December 2000.

For safety issues, see these comments on the Sleipner project:

• Bellona, Factsheet: Security of CO2 storage in Norway.

Among other things, they write:

The injected CO₂ will potentially be trapped by geochemical processes. Solubility trapping has the effect of eliminating the buoyant forces that drive CO₂ upwards, and through time it can lead to mineral trapping, which is the most permanent and secure form of geological storage.

Solubility trapping

Solubility trapping is where the CO₂ dissolves in water. It’s harder for the CO₂ to escape the reservoir when it’s dissolved, rather than just sitting on top of water in a light buoyant phase. The solution itself sinks deeper and more securely into the reservoir, because it’s heavier with CO₂ in it. Mineral trapping is where the CO₂ chemically reacts with minerals so that carbon gets sequestered in stable, solid precipitates.

On Azimuth, John Furey? writes:

Hank Roberts writes:

Here are some further references discussing trapping mechanisms and sometimes failure modes:

• Plains CO₂ Reduction Partnership, Factors affecting the potential for CO2 leakage from geologic sinks, October 2005.

Here is the executive summary:

• Stuart M. V. Gilfillan et al., Solubility trapping in formation water as dominant CO2 sink in natural gas fields, Nature Letters 458 (2009), 614-618.

Injecting CO2 into deep geological strata is proposed as a safe and economically favourable means of storing CO2 captured from industrial point sources. It is difficult, however, to assess the long-term consequences of CO2 flooding in the subsurface from decadal observations of existing disposal sites. Both the site design and long-term safety modelling critically depend on how and where CO2 will be stored in the site over its lifetime. Within a geological storage site, the injected CO2 can dissolve in solution or precipitate as carbonate minerals. Here we identify and quantify the principal mechanism of CO2 fluid phase removal in nine natural gas fields in North America, China and Europe, using noble gas and carbon isotope tracers. The natural gas fields investigated in our study are dominated by a CO2 phase and provide a natural analogue for assessing the geological storage of anthropogenic CO2 over millennial timescales. We find that in seven gas fields with siliciclastic or carbonate-dominated reservoir lithologies, dissolution in formation water at a pH of 5–5.8 is the sole major sink for CO2. In two fields with siliciclastic reservoir lithologies, some CO2 loss through precipitation as carbonate minerals cannot be ruled out, but can account for a maximum of 18 per cent of the loss of emplaced CO2. In view of our findings that geological mineral fixation is a minor CO2 trapping mechanism in natural gas fields, we suggest that long-term anthropogenic CO2 storage models in similar geological systems should focus on the potential mobility of CO2 dissolved in water.

• CO2 Capture Project, website.

• NETL Simulation/Risk Assessment Best Practice Manual (draft, 17 June 2010), Appendix 1: brief summary of CO2 trapping mechanisms.

• Kjetil Haugen and Abbas Firoozabadi, CO2 injection in the subsurface.

Direct capture from the air

In capturing CO₂ from point sources, the dominant cost is supposedly the cost of capture rather than storage. However, David Keith has argued that direct capture from the air could be viable:

• David Keith, Direct capture of CO2 from the air, February 2009.

• David Keith, Why capture CO₂ from the atmosphere? Science, 325 (September 2009), 1654–1655.

Enhanced weathering

One of the main long-term mechanisms that removes carbon dioxide from the ocean and atmosphere is the natural weathering of rocks. We can vastly accelerate this process by digging up suitable rocks, crushing them into powder and spreading them around. The rock dust then ‘weathers’ by reacting with carbon dioxide. This method of carbon capture and storage is called enhanced weathering. In principle it can also serve as a source of carbon negative energy.

For more details, see Enhanced weathering.

Using natural materials for products

Plants are more or less carbon neutral over liftime. In particular during growth they on average capture more CO2, while upon decay they on average release more CO2. If one thus prevents natural materials from decaying, like by using them for products (like wood for housing) then one postpones CO2 release and thus may be able to capture some CO2 for a while. It should however be remarked that decomposition is important for maintaining a nutricious soil.

Cement manufacture

The manufacture of ordinary Portland cement uses a large proportion of limestone. This is heated in a kiln, driving off the CO₂. By replacing the calcium from limestone with magnesium from minerals such as serpentine it is possible to make the manufacture low- or even negative-carbon, producing a cement which has similar properties. Annual world production of cement, 2010, is around 2 billion tonnes.

See:

• Celtic Cement, Cenin.

Making methanol

This is not exactly a form of carbon capture and storage, but related. See Methanol economy.

Making plastics

Carbon dioxide can be used to make plastics. Unfortunately, the amount of CO₂ to be dealt with exceeds worldwide plastic demand by about 2 orders of magnitude. In 2007, worldwide production of plastic was 260 megatonnes, while 29.3 gigatonnes of CO₂ was emitted by production of energy and cement manufacture. Plastic production is expected to reach 365 megatonnes by 2015.

Coal bed methane extraction

Disused and uneconomic coal mines continue to emit methane. They can also be used to sequester carbon dioxide. Coal has a stronger affinity for CO₂ than methane. So, putting CO₂ in mine shafts displaces the methane, which can be captured and used as it rises to the surface. This idea is called coal bed methane extraction. It may constitute a source of carbon negative energy.

See:

• Coalbed methane, Wikipedia.

• Coal bed methane extraction, Wikipedia.

• Virginia Center for Coal and Energy Research.

Methane hydrate reactions

Another idea, due perhaps to ‘Uncle Al’ of internet fame, is to pump liquid CO₂ into methane hydrate formations. He claims that the recovered natural gas plus sequestered CO₂ has net zero carbon footprint. The reactions involved are

CH₄ + $n$H₂O(s) $\to$ CH₄(g) + $n$H₂O(l) + 54.44 kJ/mol gas

CO₂ + $n$H₂O(s) $\to$ CO₂(g) + $n$H₂O(l) + 63.6 kJ/mol gas

For more on the chemistry of methane hydrates (also known as methane clathrates), see

• John J. Carroll, An introduction to gas hydrates

• Methane clathrate, Wikipedia.

Algae photosynthesis

The general idea is to remove carbon dioxide from the atmosphere by growing algae, and then somehow fixing the algae in a form where the carbon that it contains will not be returned to the carbon cycle (at least for a long time).

There is a known technique called “iron fertilization,” which can be used to seed the growth of ocean algae blooms. Experiments have been conducted with the aim of carbon sequestration in mind. Although the idea has not reached practical fruition, there is a lot of potential carbon capture that can be produced by these abundant organisms. See the page Iron fertilization for further details.

Carbon capture and storage for coal-fired power plants

See the page Carbon capture and storage for coal-fired power plants.

References

For starters, try:

• Carbon capture and storage, Wikipedia.

• The Carbon Capture Report — daily reports, daily newspaper and analytics from the University of Illinois.

• ICO2N — the Integrated CO2 Network, a group of Canadian companies representing multiple industries, including coal and the oil sands. All ICO_2­N member companies claim to have a strong interest in developing carbon capture and storage.

Other references:

• Interagency Task Force on Carbon Capture and Storage, Final report, 2010, USA — a series of recommendations on overcoming the barriers to the widespread, cost-effective deployment of CCS within ten years.