Why Are We Interested in Carbon Capture and Storage?
Carbon Capture and Storage (CCS) technology enables capture and storage of CO2 emitted by fossil-fuel power plants, and is expected to play an important role in the transitional phases towards a low-carbon economy. However, there are still many obstacles to overcome before CCS may be rolled out for significant climate change mitigation. These include energy and cost efficiency, and plans for the assessment and management of the economic, health, legal and environmental issues associated with large-scale deployment of CCS.
The global challenge of achieving greenhouse gas emissions reductions necessary to mitigate climate change is enormous. This challenge is inextricably linked to how we produce and use energy, with far-reaching implications for every sector. Significant reductions must come from improvements in the efficiency of energy production and use, fuel substitution, increased use of renewable energy and increased use of nuclear power. These should be coupled to the rollout of carbon capture and storage (CCS) technologies applied to fossil-fuel power generation and energy-intensive industry. Emission reductions must also be coupled with behavioural and lifestyle changes in order to restrain demand in the developed world as the spread of electrification increases the demand in the rest of the world.
The energy sector accounts for the largest share of anthropogenic CO2 emissions, mostly as a by-product of fossil fuel combustion (including coal, gas and liquid fuels). The trajectory of global fossil fuel use and corresponding CO2 emissions is characterised by an exponentially increasing trend – a direct consequence of the rising demand for energy which accompanied the industrial revolution in the West, a trend that is now sustained by the spread of industrialisation to the rest of the world – particularly China and India.
If the world continues to follow a path of intensive fossil fuel use, then CCS technology will be essential for achieving large-scale global CO2 emissions reductions within the next 30–40 years. From an energy security perspective, CCS can play an important role by decoupling CO2 emissions from fossil fuel usage, and allowing a more diverse range of fuels and energy supply lines to meet a demand that cannot be met in the near-term by renewable or nuclear energy.
From an economic standpoint, CCS can underpin a minimum-cost mitigation pathway. For example, according to the International Energy Agency (IEA) ‘Blue Map scenario’, to achieve a 50% global CO2 reduction by 2050 – at lowest cost – about one fifth of the total reductions in CO2 emissions is required from the application of CCS to power generation, industry and fuel transformation.
What is CCS?
CCS, which is proposed as one part of the CO2 mitigation strategy, refers to a broad suite of technologies developed to capture carbon dioxide (CO2) gas produced when fossil fuel (or biomass) is used in power stations and industry. This includes the equipment to capture and purify the CO2 gas produced during combustion or gasification of fuel, the infrastructure for handling and transporting the pure CO2, and the technologies for injecting and storing it in deep geological formations.
A range of important CCS applications include CO2 sourced from the use of coal, gas and biomass for power and industry; and storage in geological forms, such as saline aquifers and depleted oil and gas fields. There is significant potential for CCS to contribute to emissions reduction outside of the power sector; for example, according to the IEA Technologies Perspectives 2010, CCS applied to industrial emitters could represent 20% of the total amount of CO2 captured using CCS technology in 20502. The major industrial emitters are cement plants and oil refineries, which, after the power sector, are ranked 2nd and 3rd highest in terms of CO2 emissions from stationery sources. Other major industrial contributors to global CO2 emissions include the iron and steel, aluminium, and pulp and paper sectors. These sources represent large sources of CO2 that are frequently difficult (or impossible) to decarbonise without fundamental and expensive changes to the underlying processes.
CCS will be essential for
achieving major emissions
reductions with continued
fossil fuel use
However, the different applications of CCS have various emission reduction outcomes. For example, a coal-to-liquid-fuel production plant with CCS will still result in CO2 emissions to the atmosphere if the fuel is burnt in the transport sector where capture may not be economically viable. On the other hand, a coal-fired power plant with CCS that substitutes some coal with biomass could potentially result in negative emissions, assuming the emissions associated with cultivating and transporting the biomass is less than the amount absorbed from the atmosphere during its growth. Life cycle assessment is therefore crucially important to benchmark the different technology options in terms of cost, efficiency and net emission mitigation potential.
All of the individual elements of CCS are in use today in the oil, gas and chemical processing sectors and there are more than a hundred sites worldwide where CO2 is injected underground. Most of these sites inject CO2 into depleted oil reservoirs allowing more oil to be recovered and the cost of injection and storage to be off-set (enhanced oil recovery, EOR).
However, there are a number of major challenges facing the widespread implementation of these technologies. In particular, it is a challenge to integrate all the elements of CCS and scale-up for CO2 capture from power plants and industry in the very near term, i.e. the next two decades. Closest to market technology for CO2 capture (i.e. amine-based solvents) is very energy intensive which means that about 20% more fuel must be burned at the power station to produce the same amount of power and capture the CO2. Equally, the storage of giga-tonnes of CO2 deep under ground raises new issues of liability and risk that remain unresolved. Suitable storage locations in depleted oil and gas reservoirs are not evenly distributed around the globe, and so much of the anthropogenic CO2 is proposed to be stored in deep saline aquifers; these locations are broadly distributed, but have less well characterised geology and do not offer the potential to generate revenue from enhanced hydrocarbon recovery.
The capital investment for new plant and operating costs for separating, compressing, transporting and storing the CO2 will impose a considerable economic burden on the power sector, or industrial processes. Thus, CCS deployment in these sectors will only occur with policy and regulatory frameworks designed to provide an incentive for investment, or which introduce a penalty associated with emitting CO2. Currently, the lack of a defined cost for CO2 emissions means that the commercial deployment of CCS is dependent on unique economic conditions, i.e., where the opportunity exists for EOR, or where specific policy and regulatory frameworks exist. The latter is exemplified by projects in Norway, where a CO2 emission tax has led to the Sleipner and Snøhvit projects that inject and store CO2 separated from natural gas in saline aquifers.
A number of governments, including the UK, are developing CCS policies. For example, the UK government’s new Energy Act 2010 promotes the application of CCS to coal-fired power stations using post-combustion or oxy-fuel technology, with a commitment to provide funding towards up to four CCS demonstrators via the UK CCS competition. Scottish Power’s Longannet power station is the first project likely to be funded via the UK CCS competition, with the government promising £1 billion towards capital costs for capture and storage off-shore of 90% of the CO2 produced from the equivalent of a 300 MWe generation capacity3. Recently, responding to recommendations from the UK Committee on Climate Change, the government’s commitment to fund CCS demonstrators has been extended to include gas-CCS.
A Transitional Technology
CCS is a transitional technology, offering a near-term way of mitigating climate change consistent with continued extensive fossil fuel use, while progress is made towards establishing a truly sustainable low-carbon energy system in the medium to longer term. The costs of mitigation are expected to be considerably higher if CCS is not included in future low carbon energy technology portfolios. The deployment of CCS in countries with very large indigenous fossil fuel reserves could also reinforce energy security, while not compromising climate mitigation goals. It is therefore extremely important to have early demonstration and deployment of this technology to test the system on a large scale and to iron out problems prior to its projected global rollout in the next couple of decades.
Legislative and policy clarity and consistency is needed, otherwise the large capital costs of the technology and long payback time will hold back investment in CCS. The general public are justifiably concerned about the potential risks of CO2 storage, particularly near to populated areas. Research, consultation and dialogue will be needed to help make clear the potential risks and how these will be managed to address concerns.
This article is an excerpt from a briefing paper titled: ‘Carbon capture technology: future fossil fuel use and mitigating climate change’ recently published by the Grantham Institute for Climate.
Dr Nicholas Florin is a Grantham Institute for Climate Change Junior Research Fellow based in the Chemical Engineering Department. His research interests include the development of solid sorbents for CO2 capture, and the integration of CO2 capture systems in advanced energy and industrial systems.