Carbon capture, utilisation and storage (CCUS)

[vc_section][vc_row][vc_column width=\”1/2\”][vc_column_text]What are carbon capture, utilization, and storage?

Carbon capture, utilization, and storage (CCUS) is the process of capturing carbon dioxide emissions and either using them to make things such as building materials (utilization) or permanently storing them thousands of feet below the surface (storage).

Capturing carbon dioxide from industrial operations before it has a chance to enter the atmosphere helps reduce emissions, as does removing it directly from the air. The carbon dioxide is then reused or sent through an injection well deep underground where it is locked away safely and permanently.

Where is CCUS happening?

Today, CCUS facilities around the world have the capacity to capture more than 40 MtCO2 each year. Some of these facilities have been operating since the 1970s and 1980s when natural gas processing plants in the Val Verde area of Texas began supplying CO2 to local oil producers for enhanced oil recovery operations.

How is CO2 captured?

CO2 capture is an integral part of several industrial processes and, accordingly, technologies to separate or capture CO2 from flue gas streams have been commercially available for many decades. The most advanced and widely adopted capture technologies are chemical absorption and physical separation; other technologies include membranes and looping cycles such as chemical looping or calcium looping. The various technologies are described futher below.

 

Principal CO2 capture technologies

Capture Technology	Overview
Chemical absorption	A common process operation based on the reaction between CO2 and a chemical solvent (such as compounds of ethanolamine). Chemical absorption using amine-based solvents is the most advanced CO2 separation technique.
Physical separation	Based on either adsorption, absorption, cryogenic separation, or dehydration and compression. Physical adsorption makes use of a solid surface (e.g. activated carbon, alumina, metallic oxides or zeolites), while physical absorption makes use of a liquid solvent (e.g. Selexol or Rectisol). After capture by means of an adsorbent, CO2 is released by increasing temperature (temperature swing adsorption) or pressure (pressure swing adsorption or vacuum swing adsorption).
Oxy-fuel separation	Involves the combustion of a fuel using nearly pure oxygen and the subsequent capture of the CO2 emitted. Because the flue gas is composed almost exclusively of CO2 and water vapour, the latter can be removed easily by means of dehydration to obtain a high-purity CO2 stream.
Membrane separation	Based on polymeric or inorganic devices (membranes) with high CO2 selectivity, which let CO2 pass through but act as barriers to retain the other gases in the gas stream.
Calcium looping	Involves CO2 capture at a high temperature using two main reactors. In the first reactor, lime (CaO) is used as a sorbent to capture CO2 from a gas stream to form calcium carbonate (CaCO3). The CaCO3 is subsequently transported to the second reactor where it is regenerated, resulting in lime and a pure stream of CO2. The lime is then looped back to the first reactor.
Chemical looping	Like calcium looping, a two-reactor technology. In the first reactor, small particles of metal (e.g. iron or manganese) are used to bind oxygen from the air to form a metal oxide, which is then transported to the second reactor where it reacts with fuel, producing energy and a concentrated stream of CO2, regenerating the reduced form of the metal. The metal is then looped back to the first reactor.
Direct separation	Involves the capture of CO2 process emissions from cement production by indirectly heating the limestone using a special calciner. This technology strips CO2 directly from the limestone, without mixing it with other combustion gases, thus considerably reducing energy costs related to gas separation.
Supercritical CO2 power cycles	While in conventional thermal power plants, flue gas or steam is used to drive one or multiple turbines, in supercritical CO2 power cycles, supercritical CO2 (i.e. CO2 above its critical temperature and pressure) is used instead. Supercritical CO2 turbines typically use nearly pure oxygen to combust the fuel, in order to obtain a flue gas composed of CO2 and water vapor only.

 

How is CO2 transported?

The availability of infrastructure to transport CO₂ safely and reliably is essential for deployment of CCUS. The two main options for the large-scale transport of CO₂ are via pipeline and ship, although for short distances and small volumes CO2 can also be transported by truck or rail, albeit at a higher cost per tonne of CO2.

Pipelines are the cheapest way of transporting CO2 in large quantities onshore and, depending on the distance and volumes, offshore. Transport by pipeline has been practised for many years and is already deployed at large scale. There is an extensive onshore CO2 pipeline network in North America, with a combined length of more than 8 000 km.

While CO2 is currently shipped in small quantities for use in the food and beverage industry, large-scale transportation of CO2 by ship has not yet been demonstrated but would have similarities to the shipping of liquefied petroleum gas (LPG) and liquefied natural gas (LNG). Norway’s Longship CCS project will be the first to transport large quantities of CO2 to an offshore CO2 storage site.

CO2 transportation by ship offers greater flexibility than pipelines, particularly where there is more than one offshore storage facility available to accept CO2. The flexibility of shipping can also facilitate the initial development of CO2 capture hubs (regional clusters), which could later be connected or converted into a more permanent pipeline network as CO2 volumes grow. In some instances, shipping can be a cost-effective transport option, especially for long-distance transport, which might be needed for countries with limited domestic storage resources.

How can CO2 be used?
CO2 can be used as an input to a range of products and services. The potential applications for CO2 use include direct use, where the CO2 is not chemically altered (non-conversion), and the transformation of CO2 to a useful product through chemical and biological processes (conversion).

 

Utilization
In the context of flue gases, CO2 is seen as a waste product. However, there are many applications, where CO2 is utilized or considered as a valuable commodity.

Enhanced Oil Recovery
At present, CO2 is most valuable for enhanced oil recovery (EOR). In 2008, in the United States, about 80% of CO2 for EOR is obtained from natural resources and the rest is from anthropogenic sources such as coal gasification or gas processing (Advanced Resources International (ARI), 2010). The permanent storage of CO2 in depleted oil fields is definitely one of the attractive carbon storage options. The fact that there is a market for CO2 is an important incentive to develop more efficient carbon capture technologies, such that anthropogenic CO2 can compete with CO2 from natural reservoirs.

There are two practical issues. Firstly, the total amount of CO2 that can be used for EOR is much less than the total emissions of CO2, which implies that EOR can only be a partial solution. For example, CO2 used in EOR operations was limited to only 60 million tons (Advanced Resources International (ARI), 2010). Secondly, one may wonder whether EOR gives a net CO2 reduction. The argument is that because of EOR we produce more oil, and hence, further increase anthropogenic CO2 emissions. However, a better argument is to compare one barrel of oil produced with EOR compared to one barrel of oil that is produced without EOR. In this comparison, one barrel of oil with EOR gives a lower CO2 emission as a fraction of the CO2 used to recover the oil stays in the reservoir. However, here we did assume that the other barrel of oil does remain in the reservoir and that EOR does not increase the demand for oil.

CO2 to Chemicals
If we look at the current chemical industry, about 7% of all oil is used as feedstock for carbon in products ranging from plastics to soaps. Replacing oil by a renewable feedstock is an important long-term challenge of the chemical industry. The viability of using CO2 as a chemical feedstock is considerably improved if the price of carbon is sufficiently high such that CO2 can replace oil. While the carbon-free energy sources required for CO2-to-chemical technologies (e.g., solar and wind) are still expensive for such CO2 utilization schemes, the research and development of those CO2 conversion pathways should be developed now to prepare for our rapidly changing future.

CO2 to Fuels
The challenge with upgrading CO2 to fuel is that it requires energy. As it does not make any sense to use fossil fuels for this process, we assume that we will use renewable energy. The first argument is, if we have renewable energies we should primarily use this for generating electricity. However, this leaves us with two problems: storage of energy and transportation fuels.

An important advantage of fossil fuels is their high energy density. Renewable energies such as wind or solar require large-scale energy storage to ensure that electricity can be produced at times in which there is no wind or sun. Sometimes, this energy storage can be as simple as pumping water, but not all countries have this option. For example, Denmark has an excess of wind energy during the winter, but too little during the summer. The idea is to use methanol to store the excess energy in the winter and use a conventional power plant with carbon capture in the summer. In this cycle, the efficient conversion of CO2 into a fossil fuel like methanol is an essential step.

Incorporating CO2 into Construction and Building Materials
The cement industry produces about 7% of CO2 emissions and is the second largest emitter of CO2 after coal-fired power plants (International Energy Agency Greenhouse Gas R&D Programme (IEA-GHG), 2002). Replacing 10% of building materials with carbonate minerals is expected to reduce CO2 emissions by 1.6 Gt/year, which is about 5% of the global CO2 emissions as of 2011 (Sridhar and Hill, 2011). However, it is important to determine the correct composition of carbonate minerals to be included in the concrete matrix to reduce issues related to the mechanical strength of the materials.

Storage
Given the enormous amounts of CO2 we are emitting, it is difficult to imagine any form of carbon storage other than injecting into geological formations. Appropriate geological formations such as deep saline aquifers, depleted oil and gas fields, unmineable coal seams, and silicate formations (e.g., basalt) can accommodate up to 11,000 Gt CO2 (Dooley et al., 2006), which is much greater compared to the annual CO2 emissions, which are to the order of 30 Gt of CO2/year. In addition, from our experience with EOR we know how to transport and inject CO2 in geological formations. The challenge is, however, the scale. At present, only about 50 Mt CO2 has been stored today and 13 Mt CO2/year is expected by 2016 given plans in place for additional projects (Levina et al., 2013).

However, the scientific challenge is to ensure that the CO2 remains safely in these storage sites for thousands of years. Development of technologies for monitoring, verification, and assessment (MVA) to entire that the CO2 remains trapped underground is essential. While the process of injecting CO2 is well understood, the cost of monitoring the fate of injected CO2 over many years may be too prohibitive unless the cost of deploying MVA technologies is substantially reduced. In addition, key questions related to long-term safety such as induced seismicity and the potential for forming fractures need to be addressed, which constitute an important aspect of risk assessments of geologic storage.

Ideally, mineralizing CO2 into the form of carbonate (e.g., limestone, magnesite) will reduce the amount of mobile CO2 that needs to be monitored. However, the kinetics of this natural process may be on the order of geological timescales. An active area of research is to enhance this mineralization process (Gadikota et al., 2014).

How is CO2 stored – and is it safe?

Storing CO2 involves the injection of captured CO2 into a deep underground geological reservoir of porous rock overlaid by an impermeable layer of rocks, which seals the reservoir and prevents the upward migration or “leakage” of CO2 to the atmosphere. There are several types of reservoirs suitable for CO2 storage, with deep saline formations and depleted oil and gas reservoirs having the largest capacity. Deep saline formations are layers of porous and permeable rocks saturated with salty water (brine), which are widespread in both onshore and offshore sedimentary basins. Depleted oil and gas reservoirs are porous rock formations that have trapped crude oil or gas for millions of years before being extracted and which can similarly trap injected CO2.

When CO2 is injected into a reservoir, it flows through it, filling the pore space. The gas is usually compressed first to increase its density and the reservoir typically must be at depths greater than 800 metres to retain the CO2 in a dense liquid-like state. The CO2 is permanently trapped in the reservoir through several mechanisms: structural trapping by the seal, solubility trapping where the CO2 dissolves in the  brine water, residual trapping where the CO2 remains trapped in pore spaces between rocks, and mineral trapping where the CO2 reacts with the reservoir rocks to form carbonate minerals (mineralisation). The nature and the type of the trapping mechanisms for reliable and effective CO2 storage, which vary within and across the life of a site depending on geological conditions, are well-understood thanks to decades of experience in injecting CO2 for EOR and dedicated storage.

CO2 storage in basalts (igneous rocks) that have high concentrations of reactive chemicals is also possible, but is in an early stage of development. The injected CO2 reacts with the chemical components to form stable minerals, trapping the CO2.

Global CO2 storage resources are considered to be well in excess of likely future requirements. In many regions, however, significant further assessment work is required to convert theoretical storage capacity into “bankable” storage to support CCUS investment.

The role of CCUS in net-zero pathways

In the IEA Sustainable Development Scenario, in which global CO2 emissions from the energy sector fall to zero on a net basis by 2070, CCUS accounts for nearly 15% of the cumulative reduction in emissions compared with the Stated Policies Scenario. The contribution of CCUS grows over time and extends to almost all parts of the global energy system.

1)     Tackling emissions from existing infrastructure

CUS technologies play four strategic roles in the transition to net zero

CCUS can be retrofitted to existing power and industrial plants that could otherwise emit 600 billion tonnes of CO2 over the next five decades – almost 17 years’ worth of current annual emissions.

In the Sustainable Development Scenario, an initial focus of CCUS is on retrofitting fossil fuel-based power and industrial plants. By 2030, more than half of the CO2 captured is from retrofitted existing assets.

2)     A cost-effective pathway for low-carbon hydrogen production

CCUS can support a rapid scaling up of low-carbon hydrogen production to meet current and future demand from new applications in transport, industry, and buildings. CCUS is one of the two main ways to produce low-carbon hydrogen.

Global hydrogen use in the Sustainable Development Scenario increases sevenfold to 520 megatonnes (Mt) by 2070. The majority of the growth in low-carbon hydrogen production is from water electrolysis using clean electricity, supported by 3 300 gigawatts (GW) of electrolysers (from less than 0.2 GW today). The remaining 40% of low-carbon hydrogen comes from fossil-based production that is equipped with CCUS, particularly in regions with access to low-cost fossil fuels and CO2 storage.

3)     A solution for the most challenging emissions

Heavy industries account for almost 20% of global CO2 emissions today. CCUS is virtually the only technology solution for deep emissions reductions from cement production. It is also the most cost-effective approach in many regions to curb emissions in iron and steel and chemicals manufacturing. Captured CO2 is a critical part of the supply chain for synthetic fuels from CO2 and hydrogen – one of a limited number of low-carbon options for long-distance transport, particularly aviation.

In the IEA’s Sustainable Development Scenario, CCUS accounts for between one quarter and two-thirds of the cumulative emissions reductions in heavy industry (cement, steel and chemicals production). By 2070, nearly half of global energy demand for aviation is met by synthetic fuels, requiring the capture of around 830 Mt of CO2 for use as feedstock.

4)     Removing carbon from the atmosphere

For emissions that cannot be avoided or reduced directly, CCUS underpins an important technological approach for removing carbon and delivering a net-zero energy system.

When net-zero emissions is reached in the Sustainable Development Scenario, 2.9 gigatonnes (Gt) of emissions remain, notably in the transport and industry sectors. These lingering emissions are offset by capturing CO2 from bioenergy and the air and storing it.

Barriers to Deployment
Cost of Implementation
One of the most significant barriers to widespread deployment of CCS technologies is high cost. Although cost estimates vary widely, the greatest costs are typically associated with the equipment and energy needed for the capture and compression phases. Capturing the CO₂ can decrease power and industrial plants’ efficiencies and increase their water use, and the additional costs posed by these and other factors can ultimately render a CCS project financially nonviable. (Increased water use may also pose problems for plants in areas that already face water scarcity.)

Additionally, since CCS deployment is in its early stages, financial returns on a CCS project are riskier than normal operations. Consequently, investors impose higher risk premiums (the minimum amount of expected return required to attract investment), which further increases the private cost of the investment. Therefore, mitigating risk for investors is vital for incentivizing investment and development of CCS. Research, Development and Deployment (RDD) policies that can de-risk such investments are thus highly desirable, along with policies that can stimulate innovation and bring costs down and scale up deployment. Presently, the Department of Energy’s Carbon Capture Program is exploring these issues.

Transportation Challenges
In addition to high costs of capture technology, there are also challenges associated with transporting CO₂ once it is captured. Significant energy is required to compress and chill CO₂ and maintain high pressure and low temperatures throughout pipelines, and the pipelines themselves are expensive to build. In order to safely carry the condensed, highly pressurized CO₂, pipelines must be specially designed: existing oil and gas pipelines cannot be used. Impurities in the CO₂ stream (including water) can cause damage to pipelines and lead to dangerous leaks and explosions as the compressed fluid rapidly expands to a gas. The exceedingly cold temperatures can cause pipe and equipment to become brittle.  Finally, each source of CO₂ must be connected to an appropriate storage site via pipeline, which can make CCS more difficult and expensive to implement in areas at a distance from geological formations that are appropriate to use for storage.

Storage Considerations
Limitations on the availability of geologic storage is generally not considered a barrier to widespread CCS deployment—at least not in the short to medium term. Indeed, there is probably plenty of storage worldwide for at least the next century, specifically in the United States. While some researchers have expressed concerns about the long-term ability of storage sites to sequester carbon without significant leakage, a 2018 IPCC report concludes that “current evaluation has identified a number of processes that alone or in combination can result in very long-term storage” (pg. 245). There is also some potential for seismic activity caused by underground injection of CO₂; researchers continue to look at ways to minimize this risk, including considering above-ground carbon dioxide mineralization as an alternative to underground storage.

Uncertain Public Support
Public support is increasingly recognized as critical to the widespread implementation of CCS. Although there are few indications of public perception regarding CCS, a 2020 poll conducted by Resources for the Future, Stanford University, and ReconMR notes that most Americans have consistently favored federal government efforts to reduce air pollution from coal-fired power plants. At the same time, siting pipelines for fossil fuels is highly contentious – both from affected and nearby landowners and for groups opposed to greater use of and access to fossil fuels.

Several considerations probably play a role in public opinion about CCS: the benefit of mitigating CO2 emissions; the implication that use of CCS prolongs use of fossil fuels; the role of pipelines in impairing landscape and fragmenting ecologically sensitive areas; the perceived and actual safety of transportation and storage of CO₂; the extent to which other climate solutions are implemented in addition to CCS. Further research is needed to better understand how the public thinks about and would react to substantial deployment of CCS.[/vc_column_text][/vc_column][vc_column width=\”1/2\” is_sticky=\”yes\” sticky_min_width=\”767\” sticky_top=\”130\” sticky_bottom=\”0\”][vc_custom_heading text=\”CARBON CAPTURE, UTILISATION AND STORAGE | कार्बन अवशोषण | TIMETEA | SHIELD IAS\” font_container=\”tag:h2|font_size:24PX|text_align:center|color:%23ffffff|line_height:34PX\” use_theme_fonts=\”yes\” css=\”.vc_custom_1670070299934{margin-top: 0px !important;margin-bottom: 0px !important;padding-top: 10px !important;padding-right: 10px !important;padding-bottom: 10px !important;padding-left: 10px !important;background-color: #434a9b !important;}\”][vc_video link=\”https://youtu.be/RzXjqCAmoqE\” css=\”.vc_custom_1670070313391{margin-top: 0px !important;padding-top: 0px !important;}\”][/vc_column][/vc_row][/vc_section]