The growth in emissions of carbon dioxide, implicated as a prime contributor to global warming, is a problem that can no longer be swept under the rug, but perhaps it can be buried deep underground or beneath the ocean.
It is hard to underestimate the importance of carbon capture and storage (CCS) technology to our aims of limiting the damage wreaked by emitting carbon dioxide into the atmosphere.
In spite of the best efforts of the international community to curtail the burning of fossil fuels, an influential new report suggests that the world will continue to rely on coal for the foreseeable future. According to the International Energy Agency (IEA), coal's share of the global energy mix will continue to rise, and by 2017 coal will come close to surpassing oil as the world's top energy source.
The lack of a commercially proven CCS solution makes this prospect even more perturbing. "CCS technologies are not taking off as once expected, which means CO2 emissions will keep growing substantially," IEA executive director Maria Van der Hoeven says. "Without progress in CCS, and if other countries cannot replicate the US experience and reduce coal demand, coal faces the risk of a potential climate policy backlash."
From the last set of figures released fossil fuels provided 81 per cent of the global energy demand as well as 85 per cent of the growth over the past decade. "For the IEA, carbon capture and storage is not a substitute, but a necessary addition to other low-carbon energy technologies and energy efficiency improvements," Juho Lipponen, head of the IEA Carbon Capture and Storage Technology Unit, recently told the 11th International Conference on Greenhouse Gas Control Technologies in Kyoto, Japan. "Fossil-fuel CCS is particularly important in a world that currently shows absolutely no sign of scaling down its fossil fuel consumption."
To achieve greenhouse gas emission reduction targets limiting a global average temperature rise to no more than 2°C, the IEA estimates that energy-related emissions must reduce very substantially. Large-scale investments in several technologies are required in order to meet this target, with CCS contributing 7 gigatonnes (Gt) of the required 42Gt emission reduction in the IEA's least-cost scenario. If CCS were to be excluded as a technology option in the electricity sector, the IEA states that investment costs over the period to 2050 would increase by 40 per cent.
CCS is used in a number of industries today, and already plays an important role in tackling climate change. Around the world, eight large-scale CCS projects are storing about 23 million tonnes of CO2 each year. With a further eight projects currently under construction (including two in the electricity generation sector), that figure will increase to over 36 million tonnes of CO2 a year by 2015. This is approximately 70 per cent of the IEA's target for mitigation activities by CCS by 2015.
But despite that optimism Brad Page, CEO of Global CCS Institute, offers a warning. "To maintain the path to the 2°C target, the number of operational projects must increase to around 130 by 2020 from the 16 currently in operation or under construction," he says. "Such an outcome looks very unlikely as only 51 of the 59 remaining projects captured in the Global CCS Institute's annual project survey plan to be operational by 2020, and inevitably some of these will not proceed."
Page insists that it is vital that there be more progress towards reducing emissions by policy that will achieve large-scale emission reductions. "It is important to recognise progress in a number of countries including the UK and China, as well as the inclusion of CCS in the United Nations Framework Convention on Climate Change (UNFCCC) Clean Development Mechanism (CDM)," he says. "The radical technological change required to decarbonise the energy system means that countries cannot rely on a carbon price alone. Governments must ensure that the necessary regulatory infrastructure is in place, and as the IEA has noted, 'policy packages should be regularly reviewed to maintain coherence over time'."
There are no surprises when it comes to the technology involved in CCS; the component technologies have been proven at demonstrator size and other industries, such as oil and gas, have experience in its use.
"Like many emerging technologies, CCS faces barriers which discourage new projects from emerging and prevent existing projects moving to construction and operation," Page continues. "Funding for CCS demonstration projects, while still considerable, is increasingly vulnerable and the level of funding support still available will service fewer projects than initially anticipated. The relatively higher-cost CCS projects require strong government support continuing into the operational phase."
Certain sectors of industry have decades of experience capturing, transporting and piping CO2 deep underground, as well as experience in understanding and monitoring its behaviour.
All the key processes of CCS have been proven over a number of years and there are currently four industrial-scale CCS projects operating worldwide storing around five million tonnes of CO2 each year. In March 2012 the Global CCS Institute had identified 75 large-scale integrated projects globally, including 15 projects in operation or under construction which are expected to capture 35.4 million tonnes per annum. What needs to happen now is to integrate CCS into projects at commercial power stations and at other major CO2-emitting processes to drive the really significant emissions reductions that are needed.
"All three parts of the chain have been demonstrated around the world and used around the world on a commercial scale in different industries," Judith Shapiro, of the UK's Carbon Capture and Storage Association, says. "Carbon capture already happens in gas-related industries, transport of carbon happens in the US and has for 30 years, and the oil and gas industries use injecting CO2 to use in enhanced oil recovery. The point of CCS is that we now need to put them all together in a power. The technologies themselves are understandable and everyone is very happy with them."
How it works
CCS covers three distinct phases – capture, transport and storage. It begins with the capture of CO2 released during the burning of fossil fuels. Here the CO2 is separated from gases in electricity generation using one of three competing technologies: pre-combustion capture, post-combustion capture and oxy-fuel combustion.
A pre-combustion system involves first converting solid, liquid or gaseous fuel into a mixture of hydrogen and CO2 using one of a number of processes such as gasification or reforming. The hydrogen produced by these processes may be used, not only to fuel our electricity production, but also in the future to power our cars and heat our homes with near zero emissions.
For post-combustion technologies CO2 can be captured from the exhaust of a combustion process by absorbing it in a suitable solvent. The absorbed CO2 is liberated from the solvent and is compressed for transportation and storage. Other methods for separating CO2 include high-pressure membrane filtration, adsorption/desorption processes and cryogenic separation.
In the process of oxy-fuel combustion the oxygen required is separated from air prior to combustion and the fuel is combusted in oxygen diluted with recycled flue-gas rather than by air. This oxygen-rich, nitrogen-free atmosphere results in final flue-gases consisting mainly of CO2 and H2O, so producing a more concentrated CO2 stream for easier purification.
Once the CO2 has been captured it needs to be transported to a suitable storage site. The technologies involved in pipeline transportation are the same as those used extensively for transporting natural gas, oil and many other fluids around the world.
Once it has been transported, it is stored in porous geological formations that are typically located several kilometres under the earth's surface, with pressure and temperatures such that CO2 will be in the liquid or 'supercritical phase'. Suitable storage sites include former gas and oil fields, deep saline formations – porous rocks filled with very salty water, or depleting oil fields where the injected CO2 may increase the amount of oil recovered.
At the storage site the CO2 is injected under pressure into the geological formation. Once injected, the CO2 moves up through the storage site until it reaches an impermeable layer overlaying the storage site; this layer is known as the cap rock and traps the CO2 in the storage formation. This storage mechanism is called structural storage.
Over time the CO2 stored in a geological formation will begin to dissolve into the surrounding salty water. This makes the salty water denser and it begins to sink down to the bottom of the storage site. This is known as dissolution storage. Finally mineral storage occurs when the CO2 held within the storage site binds chemically and irreversibly to the surrounding rock.
As the storage mechanisms change over time from structural to residual, dissolution and then mineral storage, the CO2 becomes less and less mobile. Therefore the longer it is stored the lower the risk of any leakage.
"Storage site selection and characterisation is a lengthy and costly process so this must begin at initial project stage," Page adds. "Indeed the majority of perceived risk in CCS projects is often associated with storage. Public understanding of CCS remains low. Early stakeholder engagement is therefore important and this must include addressing perceptions of storage."
Shapiro concedes that it is the storage stage that poses the most difficulties. "With'CO2 injection you need to know exactly what you are doing in terms of what the site looks like where you are injecting CO2; you need to know exactly what the pressure and what the temperature is, what state you are injecting into," she says. "Particularly you need to be looking at long-term liabilities because of the European CCS directive which came into force at the end of 2009."
The path to commercial-scale CCS continues to be trodden with small steps. In Norway and Canada, two projects highlight the benefits of public- and private-sector support in advancing cost-effective technology. The opening of the $1bn Technology Centre Mongstad (TCM) in Norway, an industrial-scale test centre for carbon capture, marks an important milestone in research, development and demonstration (RD&D) efforts and should demonstrate the potential for CCS costs to be reduced significantly over time.
In Canada, Shell's Quest project announced it will capture and store more than one million tonnes of CO2 per year produced at the Athabasca Oil Sands Project. It is hoped that the knowledge generated by both of these projects will drive innovation around the world.
"In the UK we are moving to a more positive situation with the electricity market reform," Shapiro concludes. "Unique actually in the world, Electricity Market Reform (EMR) creates a system where CCS is suddenly on a level footing with renewables and nuclear. The question is, is there enough money in the treasury putting forward in EMR – is there enough fund for CCS that we need? This is an interesting question and [is] under debate."