Carbon capture and storage (CCS) is a combination of technologies designed to prevent the release of CO2 generated through conventional power generation and industrial production processes by injecting the CO2 in suitable underground storage reservoirs. Basically, capture technology separates CO2 emissions from the process, after which the compressed CO2 is transported to a suitable geological storage location and injected. Feasible methods of transporting of CO2 include both pipelines and shipping. Appropriate geological storage locations for CO2 include abandoned oil and gas fields, deep saline formations and unminable coal seams. The dominant reason to do CCS is CO2 emission reductions from industry and power generation; without incentives for such emission reductions, little CCS can be expected. The deployment of CCS in the industrial and power generation sectors would allow fossil fuel use to continue with a significant decrease in CO2 emissions. However, a full CCS chain has yet to be implemented, and many technical, environmental and economic uncertainties remain.
There are several technologies that are employed in the capture, transport and geological storage of CO2. The majority of research and development has been directed towards efficiency improvements in the technologies used to separate CO2 from other compounds normally emitted by an industrial process. These technologies are generally referred to as ‘capture technologies’. Capture processes can be grouped in three categories, whereby the suitability of each approach depends on the industrial process or type of power plant in question.
Post-combustion: CO2 is removed from the flue gas resulting from the combustion of a fossil fuel. Post-combustion separation involves the use of a solvent to capture the CO2. Typical applications for this technology include pulverized coal (PC) plants, and natural gas combined cycle plants (NGCC). This technology is particularly suited to retrofit applications (Parliamentary Office of Science & Technology, 2009).
Pre-combustion: The primary fuel in the process is reacted with steam and air or oxygen, and is converted to a mix of carbon monoxide and hydrogen, often called a ‘syngas’. The carbon monoxide is subsequently converted to CO2 in a ‘shift reactor’. The CO2 can then be separated, and the hydrogen is used to generate power and/or heat. This technology is particularly suitable to be applied to integrated gasification combined cycle (IGCC) power plants (IPCC, 2005).
Oxy-fuel combustion: The primary fuel is combusted in oxygen instead of air, which produces a flue gas containing mainly water vapour and a high concentration of CO2 (80%). The flue gas is then cooled to condense the water vapour, which leaves an almost pure stream of CO2. Additional equipment is required for the in situ production of oxygen from air (Mckinsey & Company, 2008).
Industrial processes: The separation technologies can also be used in various industries, such as natural gas processing, and in steel, cement and ammonia production (IPCC, 2005).
Once CO2 has been effectively ‘captured’ from a process, it will be required to transport it to a suitable storage location. CO2 is most efficiently transported when it is compressed to a pressure above 7.4 MPa, and a temperature above approximately 31˚C. Under these conditions, the CO2 displays supercritical properties; it is a liquid with gas characteristics. Thus, CO2 would normally be transported at high pressures in pipelines made of carbon steel, not dissimilar to normal natural gas pipelines, or in ships if it needs to cross a great expanse of water. CO2 pipelines already exist at large scales, albeit primarily in sparsely inhabited areas, particularly in the US for enhanced oil recovery (EOR). CO2 ships have not been implemented, but are unlikely to cause technical problems.
Suitable CO2 storage locations include abandoned oil and gas fields or deep saline formations, with an expected minimum depth of 800 m, where the ambient temperature and pressures are sufficiently high to keep the CO2 in a liquid or supercritical state. The CO2 is prevented from migrating from the storage reservoir through a combination of physical and geophysical trapping mechanisms (IPCC, 2005). The technologies used to inject the CO2 are similar to those used in the oil and gas industry. In addition to well-drilling and injection equipment, measurement and monitoring technologies are essential to observe the remaining capacity of the storage site, and the behaviour of the CO2. While certain injection technologies are known, improvements specifically for CO2 storage are still under development. Once the injection phase has been completed, the well will need to be sealed by using a suitable (usually cement) ‘plug’, placed at an adequate depth to prevent the CO2 rising up the well and possibly escaping or contaminating groundwater.
The application of technologies elsewhere suggests that CCS is technically feasible in most large, stationary CO2 point sources. CO2 separation technologies are already applied in natural gas processing (NGP), where CO2 removal from natural gas is necessary to improve the heating value and/or to meet pipeline specifications. CO2 storage, combined with NGP has been successfully demonstrated at the Sleipner gas field in Norway, and in the In Salah gas fields in Algeria. There are a number of planned CCS plants globally. Within the industrial sector, the Quest CCS Project in Alberta, Canada, involves the capture of 1.2 MtCO2 per annum from an oil sands upgrader, and transportation to a deep saline formation for storage. The project is expected to be operational in 2016. Within the power sector, the Kemper County IGCC Project, in Mississippi, is a new build 600 MW integrated gasification combined cycle power station, that plans to capture 3.5 MtCO2 per annum, using the CO2 for enhanced oil recovery. This project is currently under constructions and due to be completed in late 2014. The Global CCS Institute identify 12 CCS projects currently in operation, with 8 projects undergoing construction (Global CCS Institute, 2013).
Regulatory uncertainty and public perception
Any new technology with potential risks faces regulatory uncertainty in its initial stage. For CCS, these impediments are in the process of being resolved. In recent years, there have been modifications made to international legislative provisions, namely the London Protocol (Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 and 1996 Protocol) and the OSPAR Convention (Convention for the Protection of the Marine Environment of the North-East Atlantic) to accommodate for the offshore storage of CO2. However, there remain a number of legal questions concerning issues of storage liability, monitoring responsibility and the transboundary transport of CO2. The lack of regulatory frameworks has the potential to hinder progress of CCS projects, given the associated level of risk faced by project developers. In the EU, Canada and Australia, legal frameworks for CCS have been adopted; in the United States discussions on it are ongoing.
The position of environmental NGOs on CCS is mixed; while some support the technologies, others oppose it. A general lack of awareness and understanding among the lay public has been observed by social scientists. In several communities where CO2 storage projects were planned, local stakeholders have shown concern about the risks of CCS, and have in some cases protested. Public perception of CCS is currently seen as a significant barrier if CCS demonstration projects are not accompanied by unbiased information provision and community engagement processes.
Environmental impact and risks
CCS has the potential to significantly reduce CO2 emissions from power generation and industrial installations. The greatest risk associated with CCS is possible leakage from pipeline systems and storage sites, either temporary or permanent. CO2 is not a poisonous gas, but can lead to asphyxiation if the concentration in the air becomes high enough, for example if the leakage occurs in a closed building. The risks of CO2 leaking from a pipeline is no different to the transportation of natural gas for example, however CO2 is not flammable. Many countries have established regulatory frameworks and standards for the transport and permanent storage of CO2, which aim to ensure that such practices pose no threat to the safety of humans and the environment.
Negative environmental impacts relating to CCS are associated with additional fossil fuel demand, due to the energy penalty to operate the capture unit, and the toxicological impacts related to the use of solvents to chemically trap the CO2 (Zapp et al., 2012). The use of CCS is a trade-off between the high potential for CO2 abatement, and the moderate environmental impacts of reduced energy efficiency and environmental impacts associated with CO2 capture.
Worldwide, there are currently four examples of full-scale CCS projects, all of them in the industrial sector and not in electricity production. In addition to Weyburn, which uses CO2 from a coal gasification facility in the United States, the Norwegian oil company Statoil has been injecting around a million tonnes of CO2, separated from natural gas, per year into deep saline formation under the North Sea since 1996, and since 2008 similar technology is applied in the Snohvit project, also in Norway. A consortium of BP, Statoil and Sonatrach have been injecting CO2 at In Salah in Algeria, also with CO2 originating from gas production. Technology similar to pre-combustion capture is used in fertilizer and hydrogen production, where the CO2 captured is used in other industrial processes, or vented. Oxy-fuel combustion technology for use in power generation is still in the demonstration stage but is currently tested in Germany by Vattenfall, a European electricity company.
The global capacity to geologically store CO2 is large, with recent basin-wide potentials estimated between 8,000 Gt and 15,000Gt (IEA, 2008b). However, the level of knowledge concerning storage potentials varies on a global, regional and local scale (IPCC, 2005). Estimates of storage capacities are most advanced in Europe, North America, Japan and Australia. Depleted oil and gas reservoirs are estimated to have a global storage capacity of between 675-900 GtCO2, and this storage option appears suitable because of the existing knowledge of such locations, as well as the potential to re-use existing infrastructure from oil and gas extraction processes (IPCC, 2005). Deep saline formations are understood to have a storage capacity of at least 1000 GtCO2, and are believed to be distributed in many of the world’s sedimentary basins. It has been stressed that more information regarding storage capacities is required in areas experiencing accelerated growth in energy use, including China, India, Southeast Asia, Eastern Europe and Southern Africa (IPCC, 2005).
The level to which CCS supports sustainable development is a widely debated topic. The discussions around allowing CCS into the Kyoto Protocol’s Clean Development Mechanism exemplify the varying opinions between stakeholders. It is argued by some that no technology involving the combustion of fossil fuels can be associated with sustainable development, due to the finite nature of such resources. Others point towards the effects of fossil fuel use, beyond emissions of CO2 alone, including the environmental impacts of coal mining (Coninck, 2008).
As stated above, CCS could capture between 85-95% of the CO2 produced in a plant (IPCC, 2005), but net emission reductions are in the order of 72 to 90% due to the energy it costs to separate the CO2 and the upstream emissions (Viebahn et al., 2007)
Currently, by far most applications of CCS are not economically feasible. The additional equipment used to capture and compress CO2 also requires significant amounts of energy, which increases the fuel needs of a coal-fired power plant by between 25-40% and also drives up the costs (IPCC, 2005). CCS demonstration projects in the power sector are expected to cost $90-130/tCO2 avoided, with the cost possibly dropping to $50-75/tCO2 for full scale commercial activities taking place after 2020 (Mckinsey & Company, 2008). These costs take into account the energy penalty of CO2 capture, but not the upstream emissions, so they assume an emission reduction of 80 to 90% compared to a conventional plant.
Recently, there has been a focus on assessing the potential and costs of CCS in the industrial sector (UNIDO/IEA, 2011; ZEP, 2013). Many industrial processes, for example primary steel production, cement production and oil refining are operating at the limits of energy efficiency, and CO2 capture is the only technology that is able to reduce emissions further. Costs of apply CCS within industry vary greatly between applications, however some costs are much lower than those found in the power sector (see Figure 4).
It must be noted that although CCS applications will raise the costs of energy generation and industrial production, the IEA (2008a) has calculated that an exclusion of CCS from the global mitigation portfolio will increase the cost of achieving climate stabilization by 70%. Based on this information, inclusion of CCS in the mitigation portfolio can be justified from a long-term economic efficiency standpoint.
At the 2010 climate conference in Cancun, Mexico, the Conference of Parties to the Kyoto protocol (CMP) decided to include CCS projects under the Clean Development Mechanism (CDM).
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