Bloomberg News recently published another article about a Carbon Capture project that is going to be shelved (full article, thanks David). It is still very expensive, it will add between 20 and 90% to the price of electricity from coal. So we are looking at two technologies that have to come together: separating carbon from a emission pipe and then storing it somewhere, long enough to matter. Below you can read a short primer on carbon capture and subsequent carbon sequestration.

What is carbon capture and sequestration (CCS)?

Carbon capture and storage (CCS), (carbon capture and sequestration), refers to technology attempting to prevent the release of large quantities of CO2 into the atmosphere from fossil fuel use in power generation and other industries by capturing CO2, transporting it and ultimately, pumping it into underground geologic formations to securely store it away from the atmosphere.

What is the potential impact on climate change of CCS?

Huge! CCS applied to a modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80-90% compared to a plant without CCS. The International Panel on Climate Change, IPCC, estimates that the economic potential of CCS could be between 10% and 55% of the total carbon mitigation effort until year 2100. This is huge. (We could stop burning coal as well, that would be just as effective).

Can we store enough?

We do not know, but possibly. Storage of the CO2 is envisaged either in deep geological formations, in deep ocean masses, or in the form of mineral carbonates. Deep ocean storage risks greatly increasing the problem of ocean acidification, an issue that also stems from the excess of carbon dioxide already in the atmosphere. Geological formations are currently considered the most promising sequestration sites.[7] The National Energy Technology Laboratory (NETL) reported that North America has enough storage capacity for more than 900 years worth of carbon dioxide at current production rates.[8] A general problem is that long term predictions about submarine or underground storage security are very difficult and uncertain, and there is still the risk that CO2 might leak from the storage into the atmosphere.

For ocean storage, the retention of CO2 would depend on the depth. The IPCC estimates 30–85% of the sequestered carbon dioxide would be retained after 500 years for depths 1000–3000 m. Mineral storage is not regarded as having any risks of leakage. The IPCC recommends that limits be set to the amount of leakage that can take place. This might rule out deep ocean storage as an option.

How much does it cost?

Capturing and compressing CO2 may increase the fuel needs of a coal-fired CCS plant by 25%-40%. These and other system costs are estimated to increase the cost of the energy produced by 21-91% for purpose built plants. Applying the technology to existing plants would be more expensive especially if they are far from a sequestration site. Recent industry reports suggest that with successful research, development and deployment (RD&D), sequestered coal-based electricity generation in 2025 may cost less than unsequestered coal-based electricity generation today.

Another way of storing it is to inject it into the ground for the CO2 to react with the minerals. This is called Mineral storage
In this process, CO2 is exothermically reacted with available metal oxides, which in turn produces stable carbonates. This process occurs naturally over many years and is responsible for a great amount of surface limestone. The idea of using Olivine has been promoted by the geochemist Prof. Schuiling. The reaction rate can be made faster, for example by reacting at higher temperatures and/or pressures, or by pre-treatment of the minerals, although this method can require additional energy. The IPCC estimates that a power plant equipped with CCS using mineral storage will need 60-180% more energy than a power plant without CCS.

What projects exist?

As of mid 2011, there were eight large-scale integrated CCS projects in operation. The Global CCS Institute identified 74 large-scale integrated projects in its 2011 Global Status of CCS report. For more information see Global CCS Institute website. For information on EU projects see Zero Emissions Platform website.

Can we do useful things with capture CO2?

Yes we can. If we clean it well enough, we can use it to grow stuff. Recycling CO2 may offer a response to the global challenge of significantly reducing greenhouse gas emissions from major stationary (industrial) emitters in the near to medium term[citation needed], but is usually considered a different technological category from CCS. Technologies under development, such as Bio CCS Algal Synthesis, utilises pre-smokestack CO2 (such as from a coal-fired power station) as a useful feedstock input to the production of oil-rich algae in solar membranes to produce oil for plastics and transport fuel (including aviation fuel), and nutritious stock-feed for farm animal production. The CO2 and other captured greenhouse gases are injected into the membranes containing waste water and select strains of algae causing, together with sunlight or UV light, an oil rich biomass that doubles in mass every 24 hours.

CO2 is sometimes injected into declining oil fields to increase oil recovery. Approximately 30 to 50 million metric tonnes of CO2 are injected annually in the United States into declining oil fields. This option is attractive because the geology of hydrocarbon reservoirs is generally well understood and storage costs may be partly offset by the sale of additional oil that is recovered. Disadvantages of old oil fields are their geographic distribution and their limited capacity, as well as the fact that subsequent burning of the additional oil so recovered will offset much or all of the reduction in CO2 emissions.

If you want to read more about carbon capture and sequestration, have a look here.

Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a coal-fired plant. Rendering by LeJean Hardin and Jamie Payne.