Carbon Capture

 

Carbon capture is a process that aims to reduce greenhouse gas emissions, primarily carbon dioxide (CO2), from various industrial processes and energy production. It is a technology that involves capturing and storing CO2 before it is released into the atmosphere, thus preventing it from contributing to global climate change. Carbon capture is an essential part of the solution to mitigate climate change, as it allows us to continue using fossil fuels while reducing their impact on the environment.

In this paper, we will explore the science behind carbon capture technology, the various methods of capturing CO2, its applications, benefits, and challenges. We will also examine the current state of carbon capture technology and its potential for the future.

Carbon capture is gaining attention from governments, industries, and investors as a potential solution to the climate crisis. Several countries have set targets to reduce their carbon emissions, and carbon capture is seen as a crucial technology to help them achieve their goals. While there are still challenges to be overcome, such as the cost-effectiveness and safety of carbon capture, its potential benefits are substantial.

This article is about storing carbon so that it is not in the atmosphere. For facing the deployment of CCUS, and the future outlook of CCUS.

 

CARBON CAPTURE

Carbon Capture: is the process of trapping carbon dioxide (co2) produced by burning fossil fuels or other chemical or biological processes and storing it in such a way that it is unable to affect the atmosphere, with the aim of mitigating the effects of global warming.

"Large amounts of greenhouse gases will need to be removed from the atmosphere via carbon capture"

The use of carbon capture technology is seen as a potential solution to reduce greenhouse gas emissions and mitigate climate change. It is estimated that carbon capture could help to reduce global CO2 emissions by up to 90% by 2050.

However, the technology also has its challenges and limitations.

TYPES OF CARBON CAPTURE TECHNOLOGIES

They fall into three categories:

1.     Post-combustion carbon capture (the primary method used in existing power plants)

2.  Pre-combustion carbon capture (largely used in industrial processes), and oxy-fuel combustion systems.

3. For post-combustion carbon capture, CO₂ is separated from the exhaust of a combustion process.

1.   Post-combustion capture is the most common method of carbon capture. It involves capturing CO2 from the flue gas after the fuel has been burned. The captured CO2 is then compressed and transported for storage or utilization. This method is widely applicable and can be retrofitted to existing power plants, making it an attractive option for reducing emissions from fossil fuels.

2.   Pre-combustion capture is a process that involves converting fossil fuels into a gas before combustion. This process produces a gas stream that is mostly hydrogen and CO2. The CO2 is then separated from the hydrogen before combustion. This method is more efficient than post-combustion capture and is used in integrated classification combined cycle (IGCC) power plants.

3. Oxy-fuel combustion capture involves burning fossil fuels in an oxygen-rich environment. This produces a flue gas that is mostly CO2 and water vapor. The water vapor is condensed, leaving a stream of nearly pure CO2. This method is still in the experimental stage and is not yet widely deployed.

4.  Direct air capture: This technology involves capturing carbon dioxide directly from the atmosphere using chemical or physical processes.

5.   Biological carbon capture: This technology involves using photosynthetic organisms such as algae or plants to absorb carbon dioxide from the atmosphere. 

WHAT IS CARBON CAPTURE AND STORAGE?

Carbon capture and storage (CCS) is a way of reducing carbon emissions, which could be key to helping to tackle global warming. It’s a three-step process, involving: capturing the carbon dioxide produced by power generation or industrial activity, such as steel or cement making; transporting it; and then storing it deep underground. Here we look at the potential benefits of CCS and how it works.

HOW CAN CCS HELP PREVENT GLOBAL WARMING?

The Intergovernmental Panel on Climate Change (IPCC) highlighted that, if we are to achieve the ambitions of the Paris Agreement and limit future temperature increases to 1.5°C (2.7°F), we must do more than just increasing efforts to reduce emissions – we also need to deploy technologies to remove carbon from the atmosphere. CCS is one of these technologies and can therefore play an important role in tackling global warming.

HOW DOES CCS ACTUALLY WORK?

There are three steps to the CCS process:

1.     Capturing the carbon dioxide for storage

The CO2 is separated from other gases produced in industrial processes, such as steel and cement production or from burning of fossil fuels in power generation.

2.     Transport

The CO2 is then compressed and transported via pipelines, road transport or ships to a site for storage.

3.     Storage

Finally, the CO2 is injected into rock formations deep underground for permanent storage. 

WHERE ARE CARBON EMISSIONS STORED IN CARBON CAPTURE AND STORAGE?

Possible storage sites for carbon emissions include saline aquifers or depleted oil and gas reservoirs, which typically need to be 0.62 miles (1km) or more under the ground.

As an example, a storage site for the proposed Zero Carbon Humber project in the UK is a saline aquifer named ‘Endurance’, which is located in the southern North Sea, around 90km offshore. Endurance is approximately 1 mile (1.6km) below the seabed and has the potential to store very large amounts of CO2.

Similarly, in the US there are multiple large-scale carbon sites such as the Citronelle Project in Alabama. This saline reservoir injection site is about 1.8 miles (2.9km) deep.

Carbon sequestration (or carbon storage) is the process of storing carbon (in wall 1 atmospheric carbon dioxide) in a carbon pool: 2248 Carbon sequestration is a naturally occurring process but it can also be enhanced or achieved with technology, for example within carbon capture and storage projects. There are two main types of carbon sequestration, namely: geologic and biologic (also called bio-sequestration) carbon sequestration.

Schematic showing both geologic and biologic carbon sequestration of the excess carbon dioxide in the atmosphere emitted by human activities.

Carbon dioxide (CO2) is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land use and agricultural practices, such as converting crop land into land for non-crop fast growing plants. Artificial processes have been devised to produce similar effects, including large-scale, artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers or aging oil fields. Other technologies that work with carbon sequestration include bio-energy with carbon capture and storage, bio char, enhanced weathering, direct air carbon capture and sequestration (DACCS).

Forests, kelp beds, and other forms of plant life absorb carbon dioxide from the air as they grow, and bind it into biomass. However, these biological stores are considered volatile carbon sinks as the long-term sequestration cannot be guaranteed. For example, natural events, such as wildfires or disease, economic pressures and changing political priorities can result in the sequestered carbon being released back into the atmosphere. Carbon dioxide that has been removed from the atmosphere can also be stored in the Earth's crust by injecting it into the subsurface, or in the form of insoluble carbonate salts (mineral sequestration). These methods are considered non-volatile because they remove carbon from the atmosphere and sequester it indefinitely and presumably for a considerable duration (thousands to millions of years).

To enhance carbon sequestration processes in oceans the following technologies have been proposed but none have achieved large scale application so far: Seaweed farming, ocean fertilization, artificial upwelling, basalt storage, mineralization and deep sea sediments, adding bases to neutralize acids. The idea of direct deep-sea carbon dioxide injection has been abandoned.

Carbon capture and utilization (CCU) is the process of capturing carbon dioxide (CO2) to be recycled for further usage. Carbon capture and utilization may offer a response to the global challenge of significantly reducing greenhouse gas emissions from major stationary (industrial) emitters. CCU differs from carbon capture and storage (CCS) in that CCU does not aim nor result in permanent geological storage of carbon dioxide. Instead, CCU aims to convert the captured carbon dioxide into more valuable substances or products; such as plastics, concrete or biofuel; while retaining the carbon neutrality of the production processes.

Carbon dioxide removal (CDR), also known as carbon removal, greenhouse gas removal (GGR) or negative emissions, is a process in which carbon dioxide gas (CO2) is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in products.

2221 Planting trees is a nature-based way to temporarily remove carbon dioxide from the atmosphere.

In the context of net zero greenhouse gas emissions targets, CDR is increasingly integrated into climate policy, as an element of climate change mitigation strategies. Achieving net zero emissions will require both deep cuts in emissions and the use of CDR. CDR can  counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.114  CDR methods include afforestation, reforestation, agricultural practices that sequester carbon in soils (carbon farming), wetland restoration and blue carbon, bioenergy with carbon capture and storage (BECCS), ocean fertilization, ocean alkalinity enhancement, and direct air capture when combined with storage,: 115  To assess whether negative emissions are achieved by a particular process, comprehensive life cycle analysis of the process must be performed.

As of 2023, CDR is estimated to remove around 2 giga tons of CO2 per year, which is equivalent to 4% of the greenhouse gases emitted per year by human activities. There is potential to remove and sequester up to 10 giga tons of carbon dioxide per year by using those existing CDR methods which can be safely and economically deployed now.

Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide directly from the ambient air. If the extracted CO2 is then sequestered in safe long-term storage (called direct air carbon capture and sequestration (DACCS)), the overall process will achieve carbon dioxide removal and be a "negative emissions technology" (NET). As of 2022, DAC has yet to become profitable because the cost of using DAC to sequester carbon dioxide is several times the carbon price.

Flow diagram of direct air capture process using sodium hydroxide as the absorbent and including solvent regeneration

What is Carbon Capture, Utilization and Storage (CCUS)? What is the difference between CCUS and CCS?

The carbon dioxide (CO2) is captured directly from the ambient air; this is contrast to carbon capture and storage (CCS) which captures CO2) from point sources, such as a cement factory or a bioenergy plant. After the capture, DAC generates a concentrated stream of CO2 for sequestration or utilization or production of carbon-neutral fuel and wind gas. Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent or sorbents. These chemical media are subsequently stripped of CO2 through the application of energy (namely heat), resulting in a CO2 stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.

When combined with long-term storage of CO2, DAC is known as direct air carbon capture and storage (DACCS or DACS). It would require renewable energies to power since approximately 400kJ of energy is needed per mole of CO2 capture. DACCS can act as a carbon dioxide removal mechanism (or a carbon negative technology), although as of 2022 it has yet to be profitable because the cost per ton of carbon dioxide is several times the carbon price.

DAC was suggested in 1999 and is still in development. Several commercial plants are planned or in operation in Europe and the US. Large-scale DAC deployment may be accelerated when connected with economical applications or policy incentives.

In contrast to carbon capture and storage (CCS) which captures emissions from a point source such as a factory, DAC reduces the carbon dioxide concentration in the atmosphere as a whole. Typically, CCS is recommended for large and stationary sources of CO2 rather than distributed and movable ones. On the contrary, DAC has no limitation on sources.

As well as CCS, there is a related concept, CCUS, which stands for Carbon Capture Utilization (or sometimes this is termed ‘usage’) and Storage. The idea is that, instead of storing carbon, it could be re-used in industrial processes by converting it into, for example, plastics, concrete or biofuel.

Comparison between sequestration and utilization of captured carbon dioxide

IS STORING CARBON AS PART OF CCS SAFE?

According to industry body the Global CCS Institute, CCS is ‘a proven technology that has been in safe operation for over 45 years’. It adds that all components of CCS are proven technologies that have been used for decades on a commercial scale.

WHERE IS CCS BEING USED ALREADY AND WHAT'S IN DEVELOPMENT?

According to the Global CCS Institute’s 2022 report, there were 194 large-scale CCS facilities globally at the end of the year – compared to 51 in 2019 – 61 of which were new CCS facilities added to the project pipeline in 2022. 30 of these projects are in operation, 11 under construction and the remainder in various stages of development.

Of the total number of projects, 94 were in the Americas (80 in the U.S.), 73 in Europe (27 in the UK), 21 in Asia-Pacific and 6 in the Middle East.

The CO2 capture capacity of all CCS facilities under development grew to 244 million tons per annum in 2022 – an impressive increase of 44% over the year.

WHERE WAS THE FIRST CCS FACILITY?

CCS has been in operation since 1972 in the US, where several natural gas plants in Texas have captured and stored more than 200million tons of CO2 underground.

Some of the main sources of carbon dioxide are:

●      Sources of Greenhouse Gas Emissions

●      Overview.

●      Electric Power.

●      Transportation.

●      Industry.

●      Commercial/Residential.

●      Agriculture.

●      Land Use/Forestry.

ADVANTAGES OF CARBON CAPTURE

●      There are several benefits to using carbon capture technology. First and foremost, it can significantly reduce greenhouse gas emissions. By capturing and storing or utilizing the CO2, it prevents it from being released into the atmosphere and contributing to global warming. Additionally, the technology can help to extend the use of fossil fuels, which are still a major source of energy worldwide.

●      Significant reduction in greenhouse gas emissions: Carbon capture technology can capture and store or utilize up to 90% of the CO2 emissions from industrial processes and power plants. This can significantly reduce greenhouse gas emissions and help mitigate climate change.

●      Extension of fossil fuel use: Carbon capture technology can help extend the use of fossil fuels, which are still a major source of energy worldwide. This can provide a transitional solution as the world moves towards cleaner energy sources.

●    Production of clean energy: The captured CO2 can be used to produce hydrogen, which is a clean energy source that can be used in various industries. The captured CO2 can also be used to produce synthetic fuels, chemicals, and materials.

●      Economic benefits: Carbon capture technology can create new jobs and economic opportunities in industries such as EOR, hydrogen production, and synthetic fuel production.

DISADVANTAGE OF CARBON CAPTURE

●    High cost: One of the main challenges of carbon capture technology is its cost. The technology is currently expensive and requires significant investment in infrastructure and equipment. The capture process can also require a large amount of energy, which can further increase costs. The transportation and storage of captured CO2 can also be expensive, especially for long-term storage.

●   Energy consumption: Carbon capture technology requires a significant amount of energy to operate, which can reduce the overall efficiency of the industrial process or power plant. This can increase the cost of energy production and reduce the overall economic feasibility of the technology.

● Limited storage capacity: The availability of suitable storage sites for CO2 is limited, which could limit the effectiveness of the technology. This could also lead to an increase in transportation costs if suitable storage sites are located far from the source of CO2 emissions.

●     Scalability: While carbon capture technology has been demonstrated at small-scale demonstration projects, scaling it up to the level needed to make a significant impact on global emissions is still a challenge. This requires significant investment in infrastructure and equipment, which can be costly.

● Overall, carbon capture technology has the potential to significantly reduce greenhouse gas emissions and mitigate climate change. However, there are still several challenges that need to be addressed, including cost, energy consumption, storage capacity, and scalability. Ongoing research and development is needed to improve the technology and reduce its costs.