CO2 Capture and Storage (CCS)

Evidence of global warming and related climate changes has been accumulating over the past decades, and global warming is now recognized as a fact by the scientific community. The greenhouse effect due to the presence of small amounts of gases in the atmosphere is considered responsible for such warming. CO₂ is the primary greenhouse gas contributing to about two-thirds of any climate change. The current atmospheric concentration of CO2 is more than 360 ppm, i.e. 30% more than the pre-industrial concentration of about 280 ppm, and exhibits an unprecedented increase rate of about 1.5 ppm per year. The present carbon dioxide concentration is believed to be the highest during the past 20 million years. Human activities are considered responsible for such an increase, particularly the burning of fossil fuels that is estimated to produce three-quarters of the anthropogenic carbon dioxide emissions.

Most scenarios project that the supply of primary energy will continue to be dominated by fossil fuels until at least the middle of the century. Efforts directed toward reducing carbon dioxide emissions from the use of fossil fuels include improving energy efficiency, switching from carbon to oil, and from oil to natural gas, and exploiting renewable energy sources. All these different options should be pursued and implemented at the same time. However, fossil fuels are likely to remain a key energy source for the foreseeable future, thus motivating the increased interest in carbon management policies. Carbon Dioxide (CO₂) Capture and Storage (CCS) is a process consisting of separation of CO₂ from industrial and energy-related stationary sources (e.g. fossil fuel or biomass energy facilities, natural gas production, synthetic fuel plants and fossil fuel-based hydrogen production plants, chemical plants, and cement and metal industries), transport to a storage location, and long-term isolation from the atmosphere.

The widespread application of CCS would depend on technical maturity, costs, overall potential, diffusion and transfer of the technology to developing countries and their capacity to apply the technology, regulatory aspects, environmental issues and public perception (see at http://www.ieagreen.org.uk).

As an important recognition of its importance, the Intergovernmental Panel on Climate Change (IPCC) has prepared a Special Report on Carbon Dioxide Capture and Storage that will be published by the end of 2005 (www.ipcc.ch).

Capture

There exist several approaches to capture CO₂. Some rely on capturing CO₂ close to the source of emissions, other rely on recapturing CO₂ out of the atmosphere, possibly long after its emissions. Some need to make use of new technologies, yet to be engineered, others on exploiting and managing natural mechanisms or some combination of both. To capture CO₂ from large point sources, three engineering techniques are pursued: The first is an end-of-pipe approach whereby carbon dioxide is recovered from the flue gas by scrubbing it with an aqueous solution, e.g. of amines (post-combustion capture). The second approach is called pre-combustion, and is associated to the use of hydrogen as an energy carrier; in this case the fossil fuel is converted into hydrogen through reforming and water gas shift reaction, and CO₂ is recovered from the product stream. The last approach uses oxygen instead of air in the burner (oxy-fuel combustion), and requires air separation upstream of combustion. The post-combustion capture is the technology closest to implementation, whereas the other options require more research to achieve much higher energy efficiency, this being carried out mainly by the big oil companies.

The European Union, in the Framework Program (FP5, FP6 and FP7) has supported the CO₂ capture and storage research, including demonstration on CO₂ capture and storage co-funded by main oil and electric companies (CASTOR, ENCAP, CO₂ Capture and Storage Project).

Transport and Storage

Once captured in gas form and compressed, carbon dioxide can be transported to storage sites, which could be a suitable geological formation. Pipelines are preferred for transporting large amounts of CO₂ for distances up to around 1,000 km. For amounts smaller than a few million tonnes of CO₂ per year, or larger distances overseas, use of ships, where applicable, could be economically more attractive.

Several geological storage solutions are being tested in different countries in the world. Suitable sites are deep saline aquifers, where CO₂ slowly dissolves and reacts with the cap rock, oil reservoirs, where pumping CO₂ can enhance oil or gas production (EOR, enhanced oil recovery), or in unminable coal seams, where CO₂ displaces methane (ECBM, or enhanced coal bed methane recovery) and remains adsorbed on the coal bed. Another approach aims at mimicking natural weathering, by letting CO₂ reactastes to be fixed into carbonates. cean storage and its ecological impacts are still in the research phase.

A significant amount of resources has been, is and will be granted by governments (USA, Japan, the EU, Canada, Australia), companies (all the main oil companies, car industry, power generation industry), and research institutions for fundamental and applied research on carbon dioxide capture and storage. Examples are: the Global Climate and Energy Project of the Stanford University, the Norwegian Sleipner project in the North Sea, the European CO2Sink, the field test and research in Japan.