Carbon capture and storage

CCS means removing CO2 from power station flue gases and storing it in depleted oil and gas fields, deep saline aquifers or unmineable coal seams. Technically the processes of CO2 capture, transport and storage in geological structures are known to be feasible, and are already used in the oil industry to enhance oil recovery from depleted onshore fields. Scaling these up and integrating them so as to remove CO2 from large power stations (and to sequester it) appears possible, and could make a very significant contribution to cutting emissions from electricity generation. CCS significantly increases the cost and lowers the efficiency of generation, however, and the economic barriers to investment are considerable (NERA, 2004). There are also technical and legal issues to be resolved. Public funding is required so that the various kinds of CCS technology can be demonstrated at scale as quickly as possible. This will not only show if CCS is a contender for large-scale cuts in emissions, but will also help to develop the necessary legal frameworks for this new form of waste storage.

The contribution CCS could make to cutting emissions from electricity generation is difficult to predict, but appears likely to be substantially greater than for nuclear power. This is because of the larger share of fossil fuels in global power generation and industrial sectors, particularly in rapidly growing economies like China. In principle, CO2 could be removed from the atmosphere by growing trees or other woody crops for use as fuel in power stations fitted with CCS technology. This could help to tackle non-point source emissions such as those from transport or distributed electricity generation and avoid many of the drawbacks associated with first and second generation biofuels highlighted above.

The main interest, however, is in using CCS to make coal-fired power generation more environmentally acceptable, given the vast reserves of coal around the world and its relatively low price as a fuel. This has been the main focus in national programmes for the development and deployment of these technologies, notably in the US, Germany and Australia. International initiatives such as the US-led Carbon Sequestration Leadership Forum have also been established. CCS can equally well be applied to gas-fired power stations, but the possibility of technology transfer to countries where coal-fired generation is increasing rapidly, such as China and India, has been an important factor in the focus on coal.

Developing and demonstrating CCS technologies is crucial if coal is to make a significant contribution to a low carbon energy future, but other technologies that improve the efficiency of coal-fired generation should not be neglected. Supercritical combustion and use of gas turbines are more technologically mature than CCS, having benefited from decades of public R&D funding in the US and elsewhere. A second, related consideration is that the increasing emphasis on CCS should not crowd out more incremental technology supported by public R&D (NERA, 2004). While the ultimate goal is for China, India and other emerging economies to implement advanced technologies including CCS, this will not happen in the short to medium term.

In the meantime incremental improvements can deliver significant economic and environmental benefits. Large numbers of existing power plants and industrial facilities in China have very poor efficiency by international standards, and can be upgraded (Watson, 2002). It has been estimated, for example, that in China the widespread adoption of supercritical coal fired power generation technologies that are in general use in many developed economies could result in average annual emissions savings in excess of the UK's current economy wide annual emissions (Watson et al., 2007). Furthermore, new plants can be 'future-proofed' to some extent by making them 'capture ready' - though defining this for legal and political purposes is far from straightforward.

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