CO2 Removal Process

Carbon Dioxide Capture and Re-Use

CCS, alternatively referred to as Carbon capture and sequestration, is a means of mitigating the contribution of fossil fuel emissions to global warming, based on capturing carbon dioxide (CO2) from large point sources such as fossil fuel power plants, and storing it in such a way that it does not enter the atmosphere. It can also be used to describe the scrubbing of CO2 from ambient air as a geoengineering technique.
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 IPCC estimates that the economic potential of CCS could be between 10% and 55% of the total carbon mitigation effort until year 2100 (Section 8.3.3 of IPCC report.)
Capturing and compressing CO2 requires much energy and would increase the fuel needs of a coal-fired plant with CCS by 25%-40%. These and other system costs are estimated to increase the cost of energy from a new power plant with CCS by 21-91%. These estimates apply to purpose-built plants near a storage location; applying the technology to preexisting plants or plants far from a storage location will be more expensive. However, recent industry reports suggest that with successful research, development and deployment (RD&D), sequestered coal-based electricity generation in 2025 will cost less than unsequestered coal-based electricity generation today.

Capturing CO2 might be applied to large point sources, such as large fossil fuel or biomass energy facilities, industries with major CO2 emissions, natural gas processing, synthetic fuel plants and fossil fuel-based hydrogen production plants. Air capture is also possible. But air away from the point source also contains oxygen, and so capturing air, scrubbing the CO2 from the air, and then storing the CO2 could slow down the oxygen cycle in the biosphere.
Concentrated CO2 from the combustion of coal in oxygen is relatively pure, and could be directly processed. In other instances, especially with air capture, a scrubbing process would be needed.
Broadly, three different types of technologies exist: post-combustion, pre-combustion, and oxyfuel combustion.

  • In post combustion capture, the CO2 is removed after combustion of the fossil fuel - this is the scheme that would be applied to fossil-fuel burning power plants. Here, carbon dioxide is captured from flue gases at power stations or other large point sources. The technology is well understood and is currently used in other industrial applications, although not at the same scale as might be required in a commercial scale power station.
  • The technology for pre-combustion is widely applied in fertilizer, chemical, gaseous fuel (H2, CH4), and power production. In these cases, the fossil fuel is partially oxidized, for instance in a gasifier. The resulting syngas (CO and H2) is shifted into CO2 and more H2. The resulting CO2 can be captured from a relatively pure exhaust stream. The H2 can now be used as fuel; the carbon dioxide is removed before combustion takes place. There are several advantages and disadvantages when compared to conventional post combustion carbon dioxide capture.
  • Plants that produce ethanol by fermentation generate cool, essentially pure CO2 that can be pumped underground. Fermentation produces slightly less CO2 than ethanol by weight. World ethanol production in 2008 is expected to be about 16 billion gallons or 48 million tonnes.

CO2 re-use
Making Jet fuel by scrubbing CO2 from the air would allow aviation to continue in a low carbon economy
Recycling CO2 is likely to offer the most environmentally and financially sustainable response to the global challenge of significantly reducing greenhouse gas emissions from major stationary (industrial) emitters in the near to medium term. This is because newly developed technologies, such as Bio CCS Algal Synthesis value captured, pre-smokestack CO2 (such as from a coal fired power station, for example) 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 stockfeed 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, the oil rich biomass to double in mass every 24 hours.
Another potentially useful way of dealing with industrial sources of CO2 is to convert it into hydrocarbons where it can be stored or reused as fuel or to make plastics. There are a number of projects investigating this possibility.
Carbon dioxide scrubbing variants exist based on potassium carbonate which can be used to create liquid fuels. Although the creation of fuel from atmospheric CO2 is not a geoengineering technique, nor does it actually function as greenhouse gas remediation, it nevertheless is potentially very useful in the creation of a low carbon economy, as transport fuels, especially aviation fuel, are currently hard to make other than by using fossil fuels. Whilst electric car technology is widely available, and can be used with renewable energy for carbon neutral driving, there are no electric jet airliners available, nor are there likely to be in the foreseeable future.

Single step methods: methanol
A proven process to produce a hydrocarbon is to make methanol. Methanol is rather easily synthesized from CO2 and H2 (See Green Methanol Synthesis). Based on this fact the idea of a methanol economy was born.

Single step methods: hydrocarbons
At the department of Industrial Chemistry and Engineering of Materials at the University of Messina, Italy there is a project to develop a system which works like a fuel-cell in reverse, whereby a catalyst is used that enables sunlight to split water into hydrogen ions and oxygen gas. The ions cross a membrane where they react with the CO2 to create hydrocarbons.

Two step methods
If CO2 is heated to 2400°C, it splits into carbon monoxide and oxygen. The Fischer-Tropsch process can then be used to convert the CO into hydrocarbons. The required temperature can be achieved by using a chamber containing a mirror to focus sunlight on the gas. There are a couple of rival teams developing such chambers, at Solarec and at Sandia National Laboratories, both based in New Mexico. According to Sandia these chambers could provide enough fuel to power 100% of domestic vehicles using 5800 km², but unlike biofuels this would not take fertile land away from crops but would be land that is not being used for anything else. James May, the British TV presenter, visited a demonstration plant in a programme in his 'Big Ideas' series.