Energy demand is continually increasing with the developing industrial processes. As anthropogenic activities are releasing enormous quantities of CO2 to the atmosphere through the conversion of terrestrial carbon (Bistline & Rai 2010).
Carbon Capture and Storage (CCS) is a technology facilitating the continuous use of fossil fuels while reducing the emissions of atmospheric CO2 through cost effective means (Styring & Jansen 2011).
CCS is the process involving capturing CO2 emitted from fossil fuel combustion or preparation, With its transport to storage sites isolated from the atmosphere in geological formations (Jansen & Styring, 2011) (IPCC, 2005). It can also be applied to industrial process, for example the production of hydrogen, iron and cement.
Concerns of the public about the effect of CO2 and climate change led to the United Nations Framework Convention on Climate Change (UNFCCC) in 1992 (Pires et al. 2011). This meeting was aimed to discuss ways of stabilizing the green house gas in the atmosphere to levels which anthropogenic activities do not intervene with the climate system.
A wide range of carbon capture and storage technologies are being developed in order to allow for the transportation of the carbon dioxide emitted from fossil fuels to safe geological storage instead of its emission to the atmosphere. The commercial deployment of certain developing technologies is expected to improve techniques for monitoring the CO2 stored and reduce costs for CO2 capture. However, projects with CCS will always require more energy than projects without. Therefore, project operators will only adopt CCS technologies if an appropriate value for CO2 reduction is achieved or if legislations are introduced.
This report is produced on carbon dioxide capture and storage technologies illustrating the subject and its current role to mitigation in climate change, taking into consideration legal issues, cost implications, and public perceptions.
2. Carbon capture technologies
(Gibbins & Chalmers 2008) Capturing CO2 allows for the production of a stream of concentrated CO2 at high pressure for the ability to transport and store at the desired sites as low concentrated gas stream transport is impractical due to cost of energy and other associated issues.
The methodologies generated for the capture of CO2 are;
2.1 Post Combustion Capture
In post combustion, the CO2 emitted from the combustion fossil fuels is isolated from the flue gases and captured with the usage of a liquid solvent, it is then removed from the solvent, dried, compressed ready for transportation (Rackley 2009).
2.2 Pre-Combustion Capture
The primary fuel is reacted with steam and air or fuel to produce syngas (carbon monoxide and hydrogen). The carbon monoxide is then reacted with steam in a shift converter to produce CO2 and hydrogen. The resultants can be separated into two streams. A hydrogen stream and a CO2 gas stream (Hunt et al. 2010). (IPCC 2005) states that cost of precombustion is higher compared to post combustion. The combustion of fuel in the pre-combustion process is more expensive however more favourable separation is achieved as the CO2 produced from the shift reactor is at higher concentration (15 to 60% by volume on a dry basis) and pressure.
2.3 Oxyfuel Combustion systems
In this method, the primary fuel reacts with oxygen to produce CO2 and water. The removal of water is done through condensing and compression of the gas stream. CO2 is then purified and transported.
The economic, commercial and technical assumptions considered are reflected through the cost range (Grimaud & Rouge 2014). Different systems have different costs according to the CO2 systems running the processes, the design of the plant and the financing carried out.
3. Carbon dioxide transportation
Transportation methods include pipeline, ship and road tanker, with pipelines being the most common; many million tonnes of CO2 are transported each year (Pires et al. 2011). In order for CO2 to be transported, it must be first compressed to lower its volume before transportation to storage sites.
Only when CO2 is dry, corrosion to pipelines is avoided, (Gibbins & Chalmers 2008) if moisture is present, it can be removed from the pipeline stream. Using Corrosion resistant material can significantly increase costs to the construction of pipelines, therefore it is not usually considered.
Using ships for transportation where applicable is economically more favourable, but are only carried over small scale as demand is limited. Road tankers are not a cost effective option in comparison to shipping and pipelines therefore are not likely to be appealing for large scale CO2 (Rackley 2009)).
4. Carbon storage
There are different types of carbon dioxide storage including; geological, ocean and mineral storage. Adding CO2 to the Ocean or forming pools of it on the ocean at industrial scales, effects the ocean causing acidification. Morality of ocean organisms was caused. Also, the effects on marine organisms will have ecosystem consequences (Rackley 2009).
One of the main negative factors of CCS is leakage from storage, geological reservoirs.The global risk of storage is that some fraction of the gas may leak to the atmosphere which will significantly contribute to climate change, and the local risk, for humans, ecosystems and ground water.
Technologies used for capturing and utilising carbon can reduce CO2 emissions to the atmosphere, but with project operators, an appropriate rate of reduction must be observed emissions or legislations that require CCS technology are introduced, the CCS will not be used as it requires extra energy compared with systems without CCS ((IPCC), 2005).
The capture stage of CCS is considered to have the greatest costs, in the region of 75-90 USD/tCO2 (Styring & Jansen 2011). (Pires et al. 2011) states that CO2 capture can range from 24 to 52 '/ton-CO2. Transport and storage can also be seen relatively significant, with the cost of 100km pipeline ranging from 1 to 6 '/ton-CO2. These costs are mainly due to the energy requirement for the processes, reducing the overall efficiency of power plants with such technologies, as it is still unclear as to how energy demand by these processes can be reduced. However, these costs may come down due to economies of scale and innovation. When the CO2 is obtained from a high purity source, the costs of capture can be low. For storage it is mainly dependent on the set techniques for monitoring the reservoirs like the infrastructure and CO2 injection capability. The significant transportation costs are mainly due to the low volumes, the environment and landscape and long distances.
(Warren et al. 2014) mentions that in the united states, if the production of CO2 from power generation persists on increasing at the current rates, the technology of CCS is capable of storing enough carbon dioxide to stabilize current emissions for another 100 years. This emphasizes the importance of CCS implementation as a geological viable climate change mitigation method at least for the next century.
(Pires et al. 2011) states that the stabilisation of the green house gas in the atmosphere can be achieved through using renewable energy resources including solar, biomass and wind energy which are non- carbon energy resources. But due to the difficulty of converting fossil fuel systems to renewable energy systems and the abundance of fossil fuels and high costs of renewable energy, fossil fuels continue to be the main source of energy for next few years. Hence, the development of CCS technologies is significant for CO2 mitigation in the atmosphere.
As well as costs, public perception also affects the development of CCS technologies. Even if the technical, geological, economical, and legal requirements are achieved, the lack of public acceptance and support may affect the implantation of the technology. Many CCS projects proposed worldwide were cancelled due to public attitudes(Styring & Jansen 2011). The cancellation of the Vattenfall CCS project in Germany for example that was due public perception. (Warren et al. 2014) learning the attitude of the public towards CCS is vital for understanding the future feasibility of CCS. (Warren et al. 2014) carried out a survey to find out public understanding of CCS in which very low awareness and understanding of the process was shown.
(Ayong Le Kama et al. 2013) studies the optimal carbon capture and sequestration policy and attempted to analyse the optimal CCS policy in a deterministic world and found that under certain conditions, CCS may be a long term solution to curb carbon emissions, however, as the current world is not deterministic, the CCS technologies currently in action are still recent and the complete environmental consequences on oceans for example are still not clear.
The CCS process is technically feasible at a commercial scale with a range of technologies, with European deployment of CCS expecting up to 12 demonstration projects to be operational by 2015 (Pires et al. 2011). In the UK, a government run competition is being held to identify a post-combustion 300-400 MW project which is able to capture carbon dioxide that is released due to a slipstream of gases in a supercritical pulverised plant, the winner of the competition will be receiving funding for any extra CCS costs. None of these projects have yet been confirmed.
The lack of funding mechanisms that are significantly large and long term are the primary barriers to deployment and the legal and regulatory frameworks which are set for the geological and for the transport of CO2.
' CCS has the potential to increase flexibility in achieving greenhouse gas emission reductions.
' Project operators will only consider CCS if the rate of reduction is observed in emissions or legislations that require CCS technology is introduced.
' Fossil fuels continue to be the main source of energy, the development of CCS technologies is significant for CO2 mitigation in the atmosphere.
' Public perception affects the development of CCS technologies. Even if all technical, economical, geological and legal requirements are achieved, the lack of public acceptance and support may affect the implantation of the technology.
' Many CCS projects proposed worldwide were cancelled due to public attitudes.
' Other mitigation options include energy efficiency.
' The leakage from storage, geological reservoirs is a major factor taken when considering CCS.
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