What is carbon capture and storage and how does it work?

Carbon capture and storage (CCS) is the process of capturing and storing carbon dioxide (CO2) before it is released into the atmosphere. The technology can capture up to 90% of CO2 released by burning fossil fuels in electricity generation and industrial processes such as cement production.

CO2 can be captured using different methods. The main ones are: post-combustion, pre-combustion and oxyfuel. Post-combustion technology removes CO2 from the flue gases that result from burning fossil fuels. Pre-combustion methods – carried out before burning the fossil fuel – involve converting the fuel into a mixture of hydrogen and CO2. Oxyfuel technology produces CO2 and steam by burning fossil fuels with almost pure oxygen. Post-combustion and oxyfuel equipment can be fitted to new plants or retrofitted – in other words, added to existing power stations that were originally built without it. Pre-combustion methods require large modifications to existing plans to be retrofitted, and are therefore more suitable to new built.

Once the CO2 has been captured, it is compressed into liquid state and transported by pipeline, ship or road tanker. CO2 can then be pumped underground, usually at depths of 1km or more, to be stored into depleted oil and gas reservoirs, coalbeds or deep saline aquifers, where the geology is suitable.

CO2 could also be used to produce commercially marketable products. This is commonly known as carbon capture storage and utilisation (CCSU). The most well-established form of CO2 utilisation is enhanced oil recovery (EOR), where CO2 is injected into oil and gas reservoirs to increase their extraction. Other forms of CO2 utilisation are still under investigation. These include using CO2 in concrete or plastic materials or converting it into biomass – for example, by feeding CO2 to algae, which are then harvested and processed into biofuel for transport.

What is the current scale of carbon capture and storage use, globally and in the UK?

The first large-scale CCS project began operating at Sleipner in Norway in 1996. There are now 18 large-scale CCS facilities in operation globally, with five more under construction. According to the independent Global CCS Institute (GCCSI), existing installations have the capacity to capture about 31 million tonnes of CO2 per year.

In the UK, a £1 billion competition to develop CCS was dropped in 2015, but the Government’s Clean Growth Strategy of October 2017 appears to renew a commitment to the technology, with promised investments of up to £100 million. The Scottish government is to fund a feasibility study into CCS in the North Sea, while in NE England, Tees Valley’s proposal to build a transportation and storage network to store CO2 from across Europe was approved by the European Commission in November 2017. The Government has also said that by 2025 it will phase out ‘unabated coal’ – coal burnt in power plants not fitted with CCS.

What is CCS’s potential for tackling climate change?

At the moment, CCS is the only technology that can help reduce emissions from large industrial installations. It could be an essential technology for tackling global climate change. When combined with bioenergy technologies for power generation (so-called BECCS – bioenergy with carbon capture and storage), CCS has the potential to generate ‘negative emissions’, removing CO2 from the atmosphere. Many scientists and policymakers argue that this is crucial if the world is to limit temperature rise to under 2°C, the goal of the Paris Agreement. The International Energy Agency states that a tenfold increase in capacity is needed by 2025 to be on track for meeting that target and the Global CCS Institute estimates that 2,500 CCS facilities would need to be in operation by 2040 worldwide, each capturing around 1.5 million tonnes of CO2 per year.

Are there any drawbacks to carbon capture and storage?

Overall, the capture process is expensive due to high deployment and energy costs. A plant with CCS uses more fuel than one without, to extract, pump and compress the CO2. The cost of CCS varies significantly between processes: where CO2 is already produced separately in concentrated streams, for example in fertiliser manufacturing, the cost is lower, but for processes that don’t do this, such as cement production and power generation, the cost is much higher. However, research and development efforts are trying to reduce the cost, and the price of avoiding a tonne of CO2 has already declined significantly. In the UK, the Government-commissioned Oxburgh Review argued that ‘CCS is essential for lowest cost decarbonisation’.

Possible environmental and climate change damages could be caused by CO2 leakages from storage sites if they are not adequately selected, managed and monitored. A Princeton University study, however, considers this risk to be low.

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