CCUS Basics

Understanding CCUS

What is CCUS?

Carbon capture, utilization and storage (CCUS) is a set of methods to stop carbon dioxide reaching the atmosphere or remove what is already there.

The combustion of fossil fuel and some industrial processes such as making cement or steel emit carbon dioxide that is mixed with other gases in various concentrations. A range of capture technologies are used to extract it in concentrated form. The carbon dioxide can then either be stored or utilized.

In carbon capture and storage (CCS), the captured carbon dioxide is transported predominantly by pipeline or ship to an onshore or offshore underground storage site and pumped into a suitable storage reservoir such as a deep saline aquifer or depleted oil or gas field.

In carbon capture and utilization (CCU), the captured carbon dioxide is put to use. The carbon dioxide can be permanently locked up in a product (in construction materials, for example) or go into a process (such as enhanced oil recovery, EOR) that ensures permanent storage. It can also be used and then emitted – for example, through chemical conversion to make synthetic fuels, displacing fossil-fuel use. 

Today, CCUS projects around the world are storing millions of tonnes of carbon dioxide each year. But millions need to turn into billions to meet the Paris Agreement goals. One way to accelerate CCUS scale-up is to focus on CCUS hubs, which take carbon dioxide from several sources and then transport and store it using common infrastructure.

Why is CCUS important for the energy transition?

CCUS can clean up the stubborn emissions that renewables struggle to reach.  According to the International Energy Agency, “reaching net zero will be virtually impossible without CCUS”.

Industrial cleaner. Industry accounts for about a quarter of global GHG emissions, most in the form of carbon dioxide. Some of those emissions can be eliminated easily using renewable electricity, but much cannot. For example, carbon dioxide is a by-product of some chemical processes, such as making the most common type of cement using limestone. CCUS may be the most realistic way to tackle those emissions. Many industrial processes also need intense heat, which can be difficult or expensive to provide with electricity using today’s technologies, so it usually comes from burning fossil fuels. CCUS could be the most cost-effective way to cut those emissions.

Power supporter. Future electricity generation is likely to be dominated by solar and wind power, with output that depends on the weather rather than tracking demand. On a still, grey day, backup power will be needed. In many locations, backup will be provided by natural gas – which could supply low-carbon electricity with the help of CCUS.

Hydrogen launcher. Hydrogen will be an essential part of a net zero world. It can be used to power heavy industry and long-range transport in a low carbon way. It can also replace natural gas in providing heat. It is becoming an important part of decarbonization plans. Eventually, most hydrogen will be made using surplus renewable power; in the meantime, gas-rich countries can drive the clean hydrogen market by making it from natural gas. This process generates carbon dioxide, so CCUS is needed to clean it up.

Air purifier. Just cutting down on emissions will not be enough to prevent dangerous climate change. Some carbon dioxide will need to be taken out of the air, both to balance any remaining greenhouse gas emissions and to compensate for emissions in the past. This is known as carbon removal. The storage element of CCUS will be vital in ensuring the removed carbon does not return to the atmosphere.

How much CCUS is needed to reach net zero emissions?

The International Energy Agency (IEA) has developed a scenario to show what technologies must be deployed to reach net zero emissions from the energy sector. It sees carbon storage capacity reaching 1.2 gigatonnes a year by 2030, and 7.6 gigatonnes per year by 2050. To put that into perspective, stand-alone CCUS facilities can capture around 1-2 million tonnes of carbon dioxide per year. CCUS hubs are likely to store an average of 10 million tonnes of carbon dioxide per year by 2030, so around four hubs each quarter would need to be built every year from 2024 to 2030 to meet the IEA scenario.

In the latest IPCC AR6 reports, nearly all the 97 scenarios that keep global warming below 1.5°C with no or limited overshoot include CCUS in some form – for industries, power and for carbon removals – with 665 gigatonnes of carbon dioxide cumulatively captured and stored by 2100.  That translates to around 10 gigatonnes of carbon dioxide captured and stored per year by 2070. 

How CCUS can support industrial regions and jobs

CCUS, in association with other clean technologies, can help industrial regions survive and flourish while moving to low-carbon production. As well as preserving traditional industries and the jobs and infrastructure that go with them, having access to carbon transport and storage infrastructure and clean hydrogen will help industrial regions attract new green businesses across the supply chain.

The CCUS industry itself will also bring new jobs and income. Developers of two UK hubs, HyNet NorthWest and the East Coast Cluster, predict that potential job gains could be significant: 6,000 regional jobs in the area around HyNet and 25,000 jobs per year to 2050 for the East Coast Cluster.

Imperial College London is developing a new tool for The CCUS Hub using a standardised methodology to show the economic impact of deploying CCUS technologies on a range of industries in four UK regions. The methodology can be applied to other global regions.

What are the alternatives to CCUS?

Low-carbon hydrogen is likely to be a friendly rival to CCUS in decarbonizing some areas of industry, and for backup power. When made using renewable power to split water it is known as green hydrogen. This can be burned instead of natural gas in backup powerplants; it can replace the fossil fuels used in steelmaking; and it can provide high temperatures for some other industrial processes.

Green hydrogen is expensive today and is expected to take several years at least to scale up. Until then, CCUS could give the hydrogen economy a boost, by enabling a different kind of clean hydrogen – blue hydrogen – made from natural gas with CCUS. That would scale up the market for clean hydrogen and pave the way for more green hydrogen in the future.

There are some industries where hydrogen is not a decarbonization solution. For example, it cannot decarbonize cement manufacture, the source of around 7% of global carbon dioxide emissions, which releases carbon dioxide from limestone used in the process. Alternative building materials are being explored that could eventually do away with the need for cement, but for the foreseeable future, CCUS is the primary way to cut emissions.

Is CCUS necessary for carbon removal?

To meet the Paris goal of limiting global warming to 1.5°C, negative emissions are “unavoidable”, according to the IPCC. Carbon removal is essential to balance residual emissions from aviation, shipping and heavy industry – it is the ‘net’ in net zero. It can also remove historical or legacy emissions – carbon dioxide still in the atmosphere from past industrial activity.

Nature-based solutions like planting trees and other land-use changes can address part of the challenge, but the required quantities of carbon dioxide to be removed are so vast and the need for more durable solutions so crucial that the large-scale deployment of engineered and hybrid solutions will be vital.

Some solutions, such as biochar and enhanced rock weathering, use technology to support and enhance natural solutions. While still nascent, methodologies are now available and dozens of companies in both areas are currently developing commercial-scale operations.

Two of the leading technological carbon removal solutions – bioenergy with carbon capture and storage (BECCS) and direct air capture and storage (DACS) – require the infrastructure of CCS. BECCS bolts CCS onto power plants that burn biomass – so plants suck carbon out of the air, which is then injected into saline aquifers or depleted oil and gas reservoirs, or mineralised in rock. Direct air capture and storage (DACS) captures carbon dioxide directly from the atmosphere and then permanently stores it in geologic formations.

Both technologies are in the early stages of development and expensive. DACS requires large amounts of energy, while BECCS requires a source of sustainable biomass in vast quantities, without competing for agricultural land. There is a growing consensus, however, that they are crucial options to develop at scale as part of global net zero strategies. As a result, momentum is growing and costs are projected to fall with further deployment.

CCUS infrastructure designed to decarbonize industry is often seen as preparing the infrastructure for carbon removal to be developed at scale in the future. Over the past year, however, carbon removal facilities have been touted as anchor projects for broader industrial CCUS hubs. 1PointFive expects its direct air capture facilities – including the Stratos plant under construction in Texas – to be the anchor for other companies that want to use its transport and storage infrastructure. Similarly, in Denmark, Orsted’s planned BECCS plants are expected to provide the infrastructure for decarbonizing a refinery and other companies. 

How mature is CCUS technology?

Carbon capture has been in use since the late 1930s, using carbon dioxide as an ingredient for carbonated drinks and other industrial purposes. The storage part began in 1972, when a plant in Texas started injecting captured carbon dioxide into an oilfield, in order to increase oil production from wells – a process known as enhanced oil recovery (EOR). Pure geological carbon storage, without EOR, goes back to 1996, when Norway started pumping carbon dioxide captured from natural gas production into a saline aquifer under the North Sea at its Sleipner facility. These two uses – EOR and natural gas processing – still account for most of the 40 million tonnes of carbon dioxide captured globally each year.

While these uses will continue, and can support CCUS business models, the scale-up of CCUS will focus on abating industrial and backup power emissions, as well as negative emissions. That requires adapting existing technologies for new applications and testing them on a new scale. Until recently, a commercial-scale stand-alone CCUS facility had a storage capacity of around 1-2 million tonnes per year. The average storage capacity for CCUS hubs currently under development is around 10 million tonnes per year, a figure that is likely to grow as technology is standardized and costs fall.  

How does carbon capture work?

In the exhaust from industrial processes and fossil fuel powerplants, carbon dioxide is mixed in with nitrogen, oxygen and other gases. Carbon capture separates out the carbon dioxide to get a level of purity that facilitates compression and makes the gas safe for transport and storage, avoiding risks due to corrosion and chemical reactions. 

The main method currently used to do this is amine scrubbing. Flue gas is piped into the bottom of a vertical reactor vessel, where it rises up through a mist of a carbon dioxide absorbing liquid (usually an amine solution). The scrubbed gas is released at the top, with typically 90% or more of its carbon dioxide removed. The amine then goes to another vessel where high-temperature steam takes out the carbon dioxide. Finally, the near-pure carbon dioxide is compressed ready for transport.

Other approaches are being pursued to reduce costs and improve efficiency. One option is to use solid calcium oxide that reacts with carbon dioxide in flue gas to become calcium carbonate, which is then heated to reverse the reaction and generate concentrated carbon dioxide. There are also polymer membranes that can separate gases, as well as adsorption onto the surface of porous structures such as metal-organic frameworks.

Instead of catching the carbon dioxide after combustion, fuel can be pre-treated at high temperature to turn it into a mixture of carbon dioxide and hydrogen. One capture technology separates out the carbon dioxide, leaving hydrogen that is burnt as low carbon fuel. It is also possible to burn fuel in pure oxygen to generate a stream of concentrated carbon dioxide, doing away with the need for any gas-separation technology. This technology is, however, still in development.

How do you transport carbon dioxide?

The main options are pipelines, ships, tanker trucks, barges and trains. For pipeline transport, the carbon dioxide gas is usually compressed. At a pressure of more than 74 atmospheres it enters what is known as a supercritical phase: dense like a liquid, but highly compressible and low in viscosity, like a gas. Pipeline transport is the lowest-cost option for large volumes of carbon dioxide or where pipeline infrastructure already exists. This is the solution planned for use by the East Coast Cluster in the UK and Porthos in the Netherlands, for example, and for the bulk of planned US hubs.

Where stores or pipelines are not readily available or volumes are smaller, carbon dioxide can be chilled into a liquid state to go on ships and/or tanker trucks for transport to the injection location. The transport cost per tonne is higher, but the solution offers greater flexibility for collecting multiple sources, requires less capital expenditure upfront and is lower risk in built-up areas.

Northern Lights in Norway is the first hub to develop a shipping option. It will start operations in mid-2024, collecting carbon dioxide from terminals and taking it by ship to temporary and then permanent storage. It has ordered two medium-pressure 7,500 cubic metre liquid carbon dioxide carriers from China for delivery in 2024 and two more for 2025. That will meet its initial target of 1.5 million tonnes per year. To reach its Phase 2 goal of 5 million tonnes per year, from a range of European ports, it will need many more ships of different sizes, as well as inland waterway barges, able to transport carbon dioxide safely, also at lower temperatures and pressures.

The development of more complex transport options in Europe is also leading to the development of new players in the value chain that take responsibility for elements such as compression, temporary storage, transport to terminals and the building of terminals at ports.

How does carbon storage work?

The aim of CCUS is to keep carbon dioxide permanently out of the atmosphere. The favoured method is geological carbon storage – injecting carbon dioxide into deeply buried rocks. It is injected at high pressure, in a supercritical state that is both dense like a liquid and low in viscosity like a gas.

Before injection can take place, the subsurface is studied and tested with well and geophysical data to verify that the site is suitable for storage. Suitable rock formations are porous, to accommodate the carbon dioxide, and sealed off by impermeable layers of rock above.

Depleted oil and gas fields fit the bill, as the geology is well known and has demonstrated ability to hold oil and gas and natural carbon dioxide underground for millions of years, trapped in microscopic rock pores and under impermeable cap rocks. Wells that have been abandoned or not plugged properly are potential leakage sites, so these conditions need to be reviewed to ensure their ability to contain high pressure carbon dioxide. Carbon dioxide storage into a depleted field was already implemented as part of the Lacq CCS demonstration pilot.

Carbon dioxide can also be injected into large saline aquifers, where brine is held within porous rocks. While some carbon dioxide gets trapped in small pores, the majority flows upwards to be trapped under the impermeable caprock. Over hundreds to thousands of years it dissolves in the brine, eventually combining chemically with the rock. (For more detail on trapping mechanisms see this 2019 review article.)

Saline aquifers have more carbon dioxide storage resources than depleted oil and gas fields, but they are less well characterized and therefore require more appraisal work upfront to support carbon dioxide storage on a large scale. Sleipner offshore Norway has been injecting carbon dioxide in a saline aquifer since 1996 in line with initial expectations.

Close monitoring, using multiple approaches including 4-D seismic data, helps to confirm that the carbon dioxide is migrating within the rock space as expected. If it does not, the operator can change the injection pressure or sites to manage its behaviour.

Another option is mineral storage: chemically reacting carbon dioxide with calcium or magnesium-based minerals to form stable carbonates. This is currently much more expensive than geological storage and uses a lot of energy, but is progressing in areas where there is plentiful geothermal energy along with suitable rock. Mineralization is being used in Iceland to store carbon dioxide from direct air capture via a facility that is currently being expanded. Pilot projects and further research are also underway in Oman, UAE, Saudi Arabia, Kenya and other countries to test the potential for large-scale storage.

How much geological storage space is available?

The Oil and Gas Climate Initiative has put together a CO2 Storage Resource Catalogue that covers 850 potential geological sites in 30 countries. The catalogue compiles carbon dioxide storage resource assessments, summing to 14,000 gigatonnes – more than enough to meet projected needs for CCUS over the coming century. Less than 600 gigatonnes is identified as ‘discovered resources’ – sites where at least one well has been drilled to establish the potential for carbon dioxide storage. Further appraisal is expected to reveal many more such sites.

The Catalogue is updated annually. The 2023 iteration will cover additional European, Middle Eastern and North African Mediterranean countries.

What is the potential of carbon utilization?

In an ideal world, carbon utilization would shift CCUS from a fee-based waste-disposal business model into a self-financing recycling one. However, while carbon utilization is starting to pick up, it will account for just a tiny fraction of the gigatonnes of carbon lock-up needed for the foreseeable future.

Several industries today use carbon dioxide as a raw input for a variety of products and processes. According to the IEA, top uses for the carbon dioxide include fertilizer and enhanced oil recovery, while applications in food and beverage, healthcare and materials also claim significant market share. Worldwide demand for carbon dioxide is predicted to grow by more than 7% per year to 2030.

The expanding range of use cases for carbon dioxide could help make the economics of CCUS hubs feasible, but the big question is whether the carbon dioxide is ultimately released back into the atmosphere once sold to a third party. Most current commercial applications of carbon dioxide are not net-positive for the climate; for carbon utilization to play a key role in the development of CCUS hubs as a climate tool, the carbon dioxide must be locked away for good.

Nevertheless, several nascent use-cases could lead to lower- or zero-emitting options to business-as-usual, particularly in hard-to-decarbonize sectors like aviation. The IEA outlines several promising areas:

  • Synthetic fuels: Captured carbon dioxide, in combination with hydrogen produced from green sources, could be used as feedstock for various types of liquid fuels. Burning these fuels in airplanes, for instance, would provide substantial climate benefits over traditional kerosene. Using synthetic fuel could also reduce greenhouse gas emissions from marine vessels.
  • Chemicals: Captured carbon dioxide could be used to substitute for fossil-derived inputs to a number of everyday materials, including plastic, fibre and synthetic rubber. Climate benefits would endure as long as the material does not degrade, ensuring that the carbon dioxide remains sequestered in the end product.
  • Building materials: Captured carbon dioxide could be used to substitute for various inputs at numerous stages of the production of different building materials, thereby sequestering it away indefinitely. One of the most promising applications could see it replace the water used in traditional concrete mixtures.
  • Biofuel: Some companies are using captured carbon dioxide to supercharge the growth of living organisms like algae, which could then themselves be burned for fuel. Climate benefits could be substantial, especially if the carbon dioxide released while burning the biofuel is, itself, captured.

How much does CCUS cost?

CCUS is costly, but both scientists and politicians have calculated that it is the most cost-effective way to decarbonize industry. The IPCC found that excluding CCS from the portfolio of technologies doubled the cost of remaining within 2°C, the largest cost increase from the exclusion of any specific technology.

More recently, policymakers in the Netherlands and Norway have selected CCS as the most affordable way to mitigate industrial carbon dioxide emissions at scale. In the Netherlands, the government held an auction in 2021 to identify the cheapest price per tonne of industrial carbon dioxide reduction. CCS solutions were the most cost-effective by far, taking 40% of the available subsidy budget to achieve 60% of the government’s targeted emission reduction. In Oslo, the City Council identified CCS on waste-to-energy as the most cost-effective option for decarbonizing such hard-to-abate facilities, and cities across Europe are now working on this solution.

For most sectors, capture is by far the most expensive part of the process, with the exact cost depending largely on the mixture of gases it has to deal with. If there is a high proportion of carbon dioxide, at high pressure and on a large scale, it is relatively easy to capture, making costs lower than for dilute or low-pressure exhaust gases. In 2022, the US Department of Energy’s NETL report calculated that for industries with high-purity carbon dioxide streams such as those making fertilizers or ethanol, capture cost ranges from $19 to $32 per tonne of carbon dioxide. For cement the capture cost is around $60 per tonne and for steel around $65.

Transport and storage costs depend on the distance to cover and the infrastructure available. In 2017, the Global CCS Institute calculated the cost of pipeline transport and storage to be $7 to $12 per tonne for onshore and $16 to $37 per tonne for offshore. In Europe, where pipelines are less prevalent, the Clean Air Taskforce (CATF) estimates transport and storage costs to fall from a range of $75-270 per tonne, depending on location, to less than $65 everywhere as new storage sites are identified.

Overall, CCUS costs are expected to fall rapidly as the industry grows and more cost-effective capture technologies mature. The capture costs above are already substantially lower than earlier cost calculations reflecting closer work on actual facilities. CCUS hubs are expected to accelerate this process through economies of scale on transport and storage, as well as standardization effects as new industries deploy and develop new capture technologies.

How secure is CCUS?

It is vital that stored carbon dioxide stays stored, rather than leaking into the atmosphere. Leakage risk is extremely low in a well-managed reservoir, but can occur in small volumes through ill-maintained abandoned wells or rock fractures. The risk of carbon dioxide leaks decreases significantly once the injection stops, wells are sealed, and longer-term trapping mechanisms lock in a growing proportion of the carbon dioxide. As the IPCC AR6 report concludes: “If the geological storage site is appropriately selected and managed, it is estimated that the CO2 can be permanently isolated from the atmosphere.”

The industry has had almost 20 years’ experience, starting with Sleipner in Norway, of observing actual carbon storage projects that closely monitor what happens to the carbon dioxide once it is injected. These projects have provided reams of data and the chance to use learnings to make guidelines for future storage sites.

A new study, published in 2023, uses a new methodology to assess the possibility of basin-wide carbon dioxide leakage where billions of tonnes of carbon dioxide are injected underground in aquifers with caprocks. It finds that even in the worst-case scenario, where rocks present a large number of fractures, the carbon dioxide would be contained deep in the subsurface for millions of years.

What is the risk of industrial accidents?

Transporting large amounts of any gas holds the potential for accidents. A sudden pipeline failure could release a cloud of gas, and because carbon dioxide is denser than air it would stay close to the ground and settle in any depressions, possibly leading to asphyxiation. But the risk assessment and safety measures deployed by the industry are well developed, with CCUS projects running safely for decades. As part of innovations, such as carbon dioxide shipping, engineers have developed tanks with thick walls made of special high-tensile nickel steel alloy to cope with the high pressure and density.

A 2009 IEA study concluded that “the industry has sufficient experience…to conduct CCS operations safely”. The UK’s Health and Safety Executive comes to a similar conclusion: “where the risks are properly controlled the likelihood of a major hazard incident is expected to be very low, as in other similar processes in the energy, chemical and pipeline industries.”

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