Read more: “Instant Expert: Carbon capture and storage“
Transporting and then storing carbon dioxide below ground are the final stages of carbon capture and storage (CCS). The safe and secure burial of CO2 is the most difficult part of the process – and prompts the greatest public concern.
Yet scientists and engineers are confident that safe transport and storage is possible. Natural CO2 has been securely trapped underground for many tens of millions of years, for example, under large swathes of Italy, central France, south-east Germany and the south-western US. And the expertise and technology required for transporting, injecting and monitoring the gas can be directly derived from the oil and gas industries.
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Challenges of storage
After capture, CO2 is stored kilometres beneath Earth’s surface. Microscopic pores in reservoir rock, such as sandstone, can be filled with dissolved or liquid CO2. Above this reservoir, layers of impermeable rock, such as shale and clays, prevent the CO2 migrating to the surface. As a guide, a storage site is expected to operate with less than 1 per cent CO2 loss to the surface over the next 10,000 years.
Most countries have potential storage capacity for many decades-worth of CO2. Europe has vast storage potential offshore beneath the North and Baltic seas. The rocks beneath the UK seabed account for 35 per cent of all European Union storage capacity.
Though capacity is not a problem, finding storage sites is not easy, due to the general public’s concern about safety. Very few communities have agreed to host an onshore CO2 storage site, because there are few obvious incentives to do so, and they are nervous about the impact of leaks. However, a number of CO2 injections have already been safely carried out around the world. For now, it may be easier to develop a few, much larger sites offshore.
Combining stringent storage site selection with detailed monitoring during and after injection allows tracking of the CO2 under the surface. The most difficult part is to construct licensing and liability legislation that is both sufficiently rigorous to protect the public and state, and yet attractive enough for commercial investment.
Piped in
Very few large sources of CO2 are lucky enough to sit above a suitable storage site, so the gas needs to be transported. If carbon capture and storage (CCS) reaches full scale this will be a huge undertaking – with a daily movement of fluids comparable to the volumes of all oil and gas transported today. This rules out using trucks or rail; pipelines and shipping are the only option.
Piping CO2 is an established technology – in the US, hundreds of kilometres of pipes carry CO2 to oilfields, where it is pumped underground to enhance oil recovery. These pipelines have been operating for 30 years with an excellent safety record.
In Europe, onshore power plants and factories will, where possible, be connected to local storage destinations, but if storage is not accessible or acceptable then long-distance pipelines to the coast will be needed. Building such a pipe is not cheap – up to £1 million per kilometre – but the cost would be recovered by charging the CO2 producer a small fee for every tonne of CO2 transported.
Pipelines or ships can carry CO2 to offshore storage sites. Commercially, undersea pipes are generally cheaper if used for at least 30 years. Yet shipping wins out if the plan is to transport less than 5 million tonnes of CO2 per year, or if the distance from a single source on the coast to the offshore injection site is greater than around 500 kilometres.
Like the pipelines, CO2 shipping has a good safety record. Today, tankers continually criss-cross the North Sea carrying CO2. These ships supply the gas for everything from fizzy drinks and coffee decaffeination to dry-cleaning.
“Tankers continually criss-cross the North Sea carrying carbon dioxide for fizzy drinks and dry cleaning”
Helping hand required
To accelerate deployment, governments are subsidising early carbon capture projects.
For example, the UK government has committed up to £1 billion for the UK’s first large-scale project. Member governments of the European Union have also introduced several supporting policies. As part of the European Economic Recovery Plan, €1 billion has been split between six CCS demonstration projects to help pay for their design.
The EU also operates the world’s first emissions trading scheme, where CO2 producers purchase the right to emit CO2 from a fixed total of emissions. From 2013, almost all commercial power plants in Europe will have to purchase an emissions permit for each tonne of CO2 they release. By 2020, the permit price could rise to around €40 per tonne, which would be high enough to encourage industry investment in CCS.
Around €4 billion from the sale of EU emission permits is also being used to support the first generation of large-scale CCS validation projects.
Through these measures, the EU hopes to encourage industry to invest in up to 12 large-scale CCS demonstration projects during 2012. These projects will use different capture and storage processes, to explore the technical feasibility of each approach. Each project will also require considerable investment from the operating company, or the national government of the host country. These contributions are proving difficult to extract, and the speed at which demonstration plants are being built remains too slow and uncertain. Still, if these demonstrations succeed, the EU will lead the world in the design, deployment and financing of CCS.
Nations outside the EU are also subsidising CCS development. In the US, Canada and Australia, governments have awarded grants to support CCS projects, as well as guaranteeing loans and tax breaks. In the future, large carbon trading markets may be introduced to encourage investment. Alternatively, if the demonstration plants prove that CCS is technologically and economically viable, governments might simply make CCS mandatory for fossil power plants and CO2 intensive industry.
The country where carbon capture is perhaps most advanced is Norway. In 1991 the country introduced a high tax on CO2 emissions, which has resulted in the application of CCS to two large offshore natural gas extraction and processing facilities: Sleipner, operational since 1996; and Snohvit, operational since 2007. To date, these projects have safely stored a combined total of over 12 million tonnes of CO2, deep beneath the bed of the Norwegian Sea.
