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Carbon capture utilisation and storage - C C U S
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Carbon capture, utilisation and storage (CCUS) refers to a suite of technologies that can play a diverse role in meeting global energy and climate goals.
CCUS involves the capture of CO2 from large point sources, such as power generation or industrial facilities that use either fossil fuels or biomass as fuel. The CO2 can also be captured directly from the atmosphere. If not being used on-site, the captured CO2 is compressed and transported by pipeline, ship, rail or truck to be used in a range of applications, or injected into deep geological formations (including depleted oil and gas reservoirs or saline aquifers), which can trap the CO2 for permanent storage.
CCUS technologies also provide the foundation for carbon removal or "negative emissions" when the CO2 comes from bio-based processes or directly from the atmosphere. There are around 35 commercial facilities applying CCUS to industrial processes, fuel transformation and power generation.
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VALUE CHAIN
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Capture should work more efficiently with power plants, and their CO-concentrated streams than ambient air, but new direct air capture (DAC) technologies are garnering a lot of attention. Storage is done both offshore and onshore, and new storage technologies can metalize carbon oxide into rocks by keeping it underground for two years. Transportation of captured carbon dioxide has developed with the deployment of pipeline networks and ships but faces challenges of high operating costs. The use of captured or transported CO2 is done with new technologies transforming them into jet fuels, diamonds, alcohol, auto parts, lenses, chemicals, and building products, along with expanded use in oil recovery.
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Figure 5. - Progress across the CCUS value chain (Source: ADI Analytics)
Industrial Applications of CCUS
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In the cement and concrete industrial sectors, large amounts of COâ‚‚ are released during the firing of limestone and clay that splits the materials into COâ‚‚ and calcium oxide (CAO). To address this challenge, research projects are advancing worldwide to pilot new technologies that recover and recycle the COâ‚‚ generated in this process as well as develop new concrete products that actively absorb COâ‚‚ from the atmosphere and capture it inside the concrete when the concrete hardens.
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In the fuel and basic chemicals industrial sectors, there is an urgent need to promote of bio-jet fuel to help the aviation industry reduce its carbon footprint. One potential solution is new technology that produces synthetic gas from various carbon sources such as recovered COâ‚‚. When combined with chemical processes and biotechnology based on catalytic reactions and microorganismsm, this synthetic gas can now be used to produce synthetic fuels and basic chemicals that can contribute to decarbonization in these sectors.
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Although the potential for absolute COâ‚‚ emissions reduction is relatively small compared to other industrial sectors because of low production volumes, innovations in the fine chemicals sector do offer opportunities to make a meaningful environmental impact. There is a growing body of research worldwide focused on technologies that can convert COâ‚‚ and biomass into oxygenated compounds such as high-functional plastics.
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There are three basic types of COâ‚‚ capture: pre-combustion, post-combustion and oxyfuel with post-combustion.
Pre-combustion processes convert fuel into a gaseous mixture of hydrogen and CO2. The hydrogen is separated and can be burnt without producing any CO2; the CO2 can then be compressed for transport and storage. The fuel conversion steps required for pre-combustion are more complex than the processes involved in postcombustion, making the technology more difficult to apply to existing power plants.
Post-combustion processes separate CO2 from combustion exhaust gases. CO2 can be captured using a liquid solvent or other separation methods. In an absorption-based approach, once absorbed by the solvent, the CO2 is released by heating to form a high purity CO2 stream. This technology is widely used to capture CO2 for use in the food and beverage industry.
Oxyfuel combustion processes use oxygen rather than air for combustion of fuel. This produces exhaust gas that is mainly water vapour and CO2that can be easily separated to produce a high purity CO2 stream.
Direct Air Capture Direct air capture (DAC) technologies extract CO2 directly from the atmosphere, for CO2 storage or utilisation. Two technological approaches are currently being used to capture CO2 from the air: solid and liquid DAC. Solid DAC (S-DAC) is based on solid adsorbents operating at ambient to low pressure (i.e. under a vacuum) and medium temperature (80-120 °C). Liquid DAC (L-DAC) relies on an aqueous basic solution (such as potassium hydroxide), which releases the captured CO2 through a series of units operating at high temperature (between 300 °C and 900 °C).
Source: Global CSS Institute - IEA
Transporting and using CO2
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CCUS will be useful in decarbonising industries that are likely to have residual emissions to 2050. Obvious examples are heavy industries like steel making and power generation that uses natural gas or biomass. CCUS capture rates are not 100% efficient, so there will still be some residual emissions.
Today, around 5kg of CO2 can be captured per person per year across the world, to a total of around 39.5 million tonnes. Yet, global CO2 emissions are around 44 billion tonnes. So a significant gap remains. Although the current planned pipeline will double the amount that can be captured per person, a much greater scale up is needed – around a thousand times the current level per person – to sequester the global average person’s carbon emissions of five tonnes (5000kgs) per year.
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Figure 6. - Transport overview of the CCUS value chain (Source: globalccsinstitute.com)
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Transporting CO2
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Before it can be used or stored, captured CO2 must be transported, usually via pipelines. For this, it is compressed into a liquid state and can then be moved through the pipelines, by ships or in road tankers.
Sharing infrastructure such as pipelines between multiple emissions sources, creating ‘industrial clusters’, is becoming increasingly attractive. Clustering can combine emissions from power stations and industry into a single pipeline, cutting costs and providing the scale needed to make CCUS projects viable.
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Use of CO2
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Captured CO2 can be used to make a multitude of materials. It can be converted to building materials such as concrete (mineralisation), used to make plastics via polymerisation as a feedstock for microalgae that is converted to biofuels, among others.
These processes can be very energy intensive. The additional cost of using CO2, as well as the waste produced in making new materials, can impact the viability of CCU projects.
CO2 can also be used directly in commercial processes such as food and drink, horticulture and in enhanced oil recovery. In food and drink, CO2 can be used to carbonate drinks, freeze and chill food and in packaging. In horticulture, it can be added to greenhouses to enhance the production of crops that use CO2 in photosynthesis.
The main use for CO2 today is enhanced oil recovery, a process to increase the maximum amount of oil and gas that can be extracted from a site. By injecting CO2 into the reservoir, more hydrocarbons are forced out than would be otherwise. The additional revenue of these fuels imparts a value on the CO2 used to extract them; to compete other uses of CO2 will also need to produce economic value.
Overview of existing and planned CCUS facilities in Europe, showing the UK currently has the most, followed by the Netherlands. Source: IOGP.
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CCUS globally
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Globally, the International Energy Agency (IEA) has indicated that as CCUS ‘is the only group of technologies that contributes both to reducing emissions in key sectors directly and to removing CO2 to balance emissions that are challenging to avoid’, the technology is ‘a critical part of “net” zero goals.'
As countries are unlikely to be able to meet their net zero goals without abatement in tricky-to-tackle areas, investment in CCUS has rocketed in recent years. From only 18 large scale CCS facilities in operation around the world (in six countries) in 2018, there have been over 30 commercial facilities announced in the last three years.
These new plants have been deployed across the continents, including Australia, Brazil, Canada and Saudi Arabia. However, in most locations the CO2 the projects are commissioned purely for enhanced oil recovery.
Combined, these CCUS projects have received an estimated investment of around $27bn and have the potential to double the amount of CO2 captured globally to around 80MtCO2.
Although much below where the world needs to be to limit global warming to 1.5°C by the end of the century, this rapid scaling up is likely to continue to 2050 and beyond, with the abatement levels growing as the technology gets cheaper and more readily available.
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