What is Carbon Capture, Utilisation and Storage (CCUS)?

Carbon capture, utilisation and storage (CCUS), also called sequestration, refers to systems that capture carbon dioxide (CO2) generated by energy-intensive, industrial processes run on either fossil fuels or biomass. CCUS prevents the CO2 from entering the atmosphere where it contributes to climate change. CO2 sequestration does not necessarily have to be technological but can also be biological.

A brief history of carbon capture, utilisation and storage (CCUS)

Technology to remove CO2 from raw natural gas was first used in the 1930s by the natural gas industry. However, it wasn’t until 1972 that American oil companies discovered that large quantities of CO2 could be used for enhanced oil recovery (EOR) to increase profits. Natural gas companies in Texas then started capturing CO2 produced in their processing plants and selling it to local oil producers for EOR. In 1977, the Italian physicist Cesare Marchetti proposed that carbon capture and storage (CCS) technology could be used to reduce emissions from coal power plants and fuel refineries. Subsequently, the first large-scale CO2 capture, storage and monitoring project was commissioned at the Sleipner offshore gas field in Norway in 1996. 

In 2005, the Intergovernmental Panel on Climate Change (IPCC) produced a report on CCS which served to increase government support for CCS in several countries, resulting in a rise in commercial CCS facilities. Subsequently, the Global Status of CCS Report 2023 identified 40 companies in operation worldwide, in countries such as the USA, China, Canada, Norway, Australia, Brazil and the UAE, with facilities ranging from the production of hydrogen, ammonia and fertiliser, through to CO2 separation from natural sources such as natural gas, and the generation of electricity and heat.

How does carbon capture, utilisation and storage (CCUS) work?

CCUS systems are dependent on the innovation and development of new technologies that can help mitigate CO2 emissions. Currently, the main methods for capturing CO2 are:

• Pre-combustion – prior to combustion, hydrocarbons are converted into a mixture of hydrogen and CO2 that can be separated before use, following which the CO2 is stored, and the resulting hydrogen-rich mixture used as fuel with only steam as a by-product
• Oxy-fuel technology – hydrocarbons are burnt in virtually pure oxygen producing CO2 and releasing steam as the by-product, after which the released CO2 is subsequently captured and stored
• Post combustion – after hydrocarbons are burnt, CO2 is separated from the other by-products in the flue gas and stored
• Atmospheric capture – air is drawn from the atmosphere and the CO2 content separated and stored

 The volume of CO2 in the atmosphere, at approximately 420 ppm (0.04%), is far lower than the CO2 concentration found in the by-products of pre-combustion, oxy-fuel technology and post-combustion. This low concentration of CO2 in the air makes atmospheric capture energy intensive and, therefore, more expensive than the other processes.

 Issues can arise if the CO2 contains impurities such as sulphur or water, as these can lead to corrosion of the pipeline, storage vessel or well during transportation and storage. To mitigate this, combustion gases are generally scrubbed prior to the separation process.

 Captured CO2 can either be recycled or stored. Typically, captured CO2 is used as feedstock in the manufacture of fertiliser, synthetic fuels and plastics. For storage, the CO2 is injected into deep, underground geological formations at depths of >1km, such as depleted oil and gas reservoirs or saline aquifers. These are then sealed with a layer of impermeable rock to prevent the CO2 from escaping back into the atmosphere.

Pros and cons of carbon capture, utilisation and storage (CCUS) systems

The value of CCUS systems to industry and the environment, relative to the aim of tackling global warming and achieving net zero emissions, lies in their ability to:

• Support the production of low-carbon electricity and hydrogen, which can be used to decarbonise different activities
• Remove CO2 from waste gases, helping to balance out emissions that are unavoidable or technically difficult to stop
• Increase economic value by recycling CO2 into new products
• Reduce emissions and provide cleaner operation of heavy industries such as cement, steel and chemicals by retrofitting to existing power and industrial plants

However, areas of concern include:

• High associated costs due to CCUS facilities being capital-intensive to deploy and energy-intensive to operate
• Renewable energy combined with electrification can be more cost effective in reducing emissions, raising the issue of what to invest in when changing to alternative operations
• Levels of risk and uncertainty around the technological performance of CCUS operations
• Potential CO2 leakage from storage sites, resulting in environmental damage and the reversal of emission savings
• The possible requirement for large amounts of water, depending on the technology used, for the CCUS system operation

About biological carbon sequestration

Biological / natural sequestration, also known as indirect or passive, happens when CO2 is stored in the natural environment in ‘carbon sinks’ such as forests and woodlands, soil and large bodies of water:

• Forests and woodlands – CO2 is bound within a plant or tree during photosynthesis. On average, forests store twice as much carbon as they emit and an estimated 25% of global CO2 emissions is sequestered in other vegetative forms, such as grasslands.
• Soil – in bogs, peatbogs and swamps, CO2 mixes with minerals such as calcium or magnesium and, over thousands of years, is transformed and stored as carbonates. CO2 is eventually released from the earth but, in some cases, after more than 70,000 years
• Large bodies of water – an estimated 25% of emitted CO2 is held in the upper layers of oceans.

Forest and soil carbon sinks are under threat due to deforestation, intensive agriculture and new construction whilst excessive CO2 can acidify bodies of water and pose a threat to biodiversity. Practises such as reforesting and rewilding can help to address these issues.

The future for carbon capture, utilisation and storage (CCUS)

CCUS development and deployment has recently gained substantial momentum as a result of a strengthened focus on climate-related targets, increased global policy support for technological innovation, and a robust regulatory framework for the management and monitoring of CO2 storage sites. This has led to market expansion and associated reduction in costs due to scale. The application of CCUS is helping energy-intensive industries, such as chemicals, petroleum, iron and steel, cement and paper, to meet their net zero obligations, thus safeguarding both their future and jobs. The future challenge is to continue scaling up CCUS activities in order to help global industry achieve net zero emissions.

Examples of CCUS-related TWI projects

COCACO21A – Conversion of captured CO2 to store industrial chemicals. This collaborative project aims to assist the drive towards net zero by converting CO2 to ethylene (C2H4) using flexible, tuneable CO2 electrolysers. Based on a nanostructured copper catalyst, the electrolysers will be powered using excess renewable energy at times of low or negative energy prices, such as when the power grid is overloaded. The converted ethylene will effectively act as energy store at times of high-energy production and can be later used for subsequent processes such as the production of polyethylene.

FORGE – Innovative coatings for energy intensive industries. FORGE, funded by Horizon 2020, targets the development of cost-effective, protective coatings that are impervious to gas, and have chemical stability and hardness. The new coatings will be demonstrated in applications such as CO2 capture and waste heat recovery, with smart monitoring used to assess the effectiveness of the coatings and deterioration.

Enhanced understanding of degradation environments that develop at metal/non-metal interfaces for CCS environments – Thermoplastic composite pipes can be reinforced with steel, enabling extremely high pressure applications such as CCUS. However, the static environment which develops locally on the reinforcement wire is unknown, requiring further research and study. This TWI Core Research Programme (CRP) project seeks to develop an understanding of the effect of CCS environments on the reinforced steel within composite pipes, and will create a system capable of determining the chemical species that permeate through the thermoplastic and their flux, as well their influence on the corrosion behaviour on typical carbon steel and zinc coated, carbon steel reinforcement wires.

MASCO2T II – Materials assessment for supercritical CO2 transport. This is a TWI Joint Industry Project (JIP) that will generate the data required for material selection relative to the design, build and re-rating of existing metallic components in CCS applications. In CCS, liquid CO2, often containing contaminants, is transported though pipelines and the contaminant can cause and/or enhance corrosion, reducing the pipeline’s working life. This project aims to study the interaction between the contaminant and the pipe material under CCS operating conditions to understand the effects on working life.