There is a renewable energy boom worldwide. The Levelized Cost of electricity for wind and solar energy technologies has dropped by 66 and 85%, respectively. Renewable energy share in electricity production is increasing, but we still rely heavily on fossil fuels. In 2017 in the US transportation and electricity generation contribute to 57% of the country’s total greenhouse gas emissions (EPA).

While waiting for renewable energy technologies to fully mature and replace fossil-based fuel across the industry, carbon capture storage and utilization of fossil-based emissions are crucial to facilitate a quick transition. For instance, integrated gasification combined cycle (IGCC) is a common approach. It allows the implementation of carbon capture and storage in coal power plants. To facilitate this challenge we need important investments and new developments of commercial-scale facilities. But what is carbon capture?

Carbon capture – basics

Carbon capture or carbon sequestration is a suite of technologies that can keep or retain carbon dioxide (CO2) emissions from entering the atmosphere. CCS technologies are essential to limit climate crisis effects. Being key to decarbonize the industrial sector to meet the climate change target set at COP21.

During the last few decades, Carbon Capture and Storage (CCS) or Carbon Capture Utilization and Storage (CCUS) was best suited for large point sources of CO₂ such as power plants. The gas and oil industry used the technology to improve oil extraction, by also improving the fuel quality. But newer technologies are emerging, such as direct air capture. The process involves three main steps:

• The capture of CO2.
• Transportation to an injection sink.
• Underground storage.

As an alternative to storage, CO2 can be utilized in the industry. This post includes a review of the main technologies used, including real examples of plants that are in operation, as well as the current state of technology.

Carbon Capture technologies

Several CO2 capture systems are already available on a smaller scale, but generally, they can be divided into four groups:

• Pre-combustion capture
• Post-combustion capture
• Oxy-fuel combustion
• Direct Air capture

Source generation carbon sites, such as power plants, use pre- and post-combustion and oxyfuel combustion CCS technologies. This review offers the most up-to-date advancements in carbon capture, storage, and utilization technologies to help mitigate climate change. It outlines the advantages and disadvantages of each route with its readiness for commercialization to decarbonize the industrial sector.

Each of these technologies have some advantages and disadvantages.

CO2 capture strategy	Advantages	Disadvantages
Pre-combustion	High CO2 concentration (35-40%); commercially applied	Energy drop and special operating conditions. Only for new plants.
Post-combustion	Mature technology that can be retrofitted into existing plants High (10-15%)	Energy efficiency drop.
Oxyfuel-combustion	Low capital cost ; high CO2 concentration (85%)	High efficiency drop.
Direct air capture	High CO2 capture capacity potential, CO2 neutral	Energy consumption, and immature technology, Low CO2 concentration 0,04%.

Then what is the downturn, what are the disadvantages of carbon capture? If the technology exists and there is a positive impact on climate change, why is it not used everywhere? The two main barriers are the costs and the energy required in the process. Direct air capture is expensive because the CO2 percentage in the atmosphere is only 0.4%. The process of removing carbon dioxide from gas is more expensive as the concentration of CO2 in the gas is lower. There are different solutions and new developments that try to avoid these issues, e.g. this is why carbon capture from the factory stack is more cost-efficient, as the percentage of CO2 in the gases are higher, at around 10-15%. Typically, in these sites, the heat of the gases is recovered, reducing the need for additional energy.

Source separation technologies

The three main technologies used in source separation carbon capture are pre-combustion, post-combustion, and oxyfuel combustion technologies. These technologies are critical to reducing CO2 emissions from the power sector. CO2 capture technologies can be installed into new coal and gas-based power plants. Some systems such as post-combustion technology can be retrofitted into existing plants.

Globally, there are 22 demo projects for carbon capture and storage based on power generation with the majority share of pre- and post-combustion projects. There are a few demo projects based on oxyfuel combustion projects. Pre-combustion and post-combustion technologies used solvents (liquids), solid sorbents, and membrane systems to separate CO₂ from other gases.

Absorbers in pre- and post-combustion technologies use liquid solvents to capture CO₂ from the flue gases. The CO₂ is then separated from the solvent, which is sent back to the absorber reactor. Then, the captured CO2 undergoes a compression process to facilitate its transport. Oil and gas recovery, agriculture, food industry, and production of chemicals and fuels all use CO₂. The alternative is the storage of CO₂ in geological reservoirs or saline aquifers.

Pre-combustion

Pre-combustion capture removes CO₂ from fossil fuels before combustion is completed. For example, in gasification processes, a fuel, such as coal, is partially oxidized in steam and oxygen under high temperature and pressure to form syngas. This syngas is a mixture of hydrogen, carbon monoxide (CO), CO₂, and smaller amounts of other gases, such as methane (CH₄). The syngas undergoes the carbon capture process where CO and water react producing a H₂ and CO₂-rich gas mixture. The concentration of CO₂ in this mixture can range from 15-50%. While the H₂ fuel is combusted, the CO₂ can then be captured and separated, transported, and ultimately sequestered.

According to Siemens, more than 80 percent of global industrial gasification capacity is already capturing CO2 as part of the manufacturing process. Today’s commercially available pre-combustion carbon capture technologies generally use physical or chemical adsorption processes and will cost around $60/tonne to capture CO₂ generated by an integrated gasification combined cycle (IGCC) power plant. 

However, big setbacks have occurred such as the Kemper Mississipi coal plant initially designed to capture about 65% of the plant’s CO2 using a pre-combustion system. After starting the design in 2010, and spending as much as $3.4 billion to build “clean coal” the project was canceled in 2017 due to higher than expected costs.

Post-combustion

Back in 2013, Saga City, Japan launched a two-year biomass energy utilization project, to study how to adapt carbon capture technology for a waste-to-energy plant. The CO2 capture technology at the Mikawa pilot plant, based on the chemical absorption method in a post-combustion capture process, enables the extraction of CO2 at very high purity. After developing a pilot plant successfully they developed with Toshiba the world’s first commercial-use plant of this type. This proved to be the optimal solution for Saga City’s biomass energy utilization. The CCU plant built by Toshiba started commercial operation in August 2016. It is capturing 10 tons of CO2 per day, fueling the cultivation of algae at a neighboring algae farm.

There is currently a project trying to demonstrate that CO2 capture can be done almost at zero energy cost, as the process is basically very energy-intensive. After generating electricity and using the energy to capture all CO2 that the plant generates the heat will be used in Copenhagen’s district heating system. The Amager Bakke combined heat and power (CHP) facility designed by BIG has been built in the outskirts of Copenhagen (Denmark). It is one of the largest waste-to-energy plants in northern Europe. The complex also serves as a recreational and environmental education center and has a ski slope on its roof. The Amager Bakke waste-to-energy plant burns waste collected from 500,000 – 700,000 inhabitants and 46,000 companies in and around Copenhagen. Designed to utilize 100% energy content of the waste, the plant achieved an energy efficiency of 107%.

Post combustion coal projects

Since 2014, the 115 MW Unit#3 Boundary Dam Power Station in Saskatchewan, Canada, became the first coal power station in the world to successfully use Carbon Capture and Storage (CCS) technology. During the month of March 2021, the Boundary Dam Power Station captured 75,385 tonnes of CO₂. Averaging 2,431 tonnes of CO2 captured per day, the CCS facility has reached 4 million tonnes of CO2 captured since operations began. Once captured, CO2 is transported by pipeline 50 kilometers to nearby oilfields, to be used for Enhanced Oil Recovery (EOR) purposes. Therefore the usage is far from sustainable.

This process of EOR utilizes CO₂ to maximize the removal of oil from reservoirs. The post-combustion technology uses amine-based capture units to consume electricity and heat in operation.  The economics of the project is uncertain, following the high investment cost, and energy consumption of the CCS process, no financial return is expected.

In Texas, the NRG’s Petra Nova carbon capture project was closed in 2020, the coal-based project which was the world’s largest installation of CO2 capture on a power plant relied on using CO2 for EOR. Hugely impacted by low oil prices caused by COVID-19. From the start-up in December 2016 to the end of 2019, the facility captured 92.4% of CO₂ from the post-combustion flue gases.

Oxyfuel combustion

The oxyfuel combustion process uses oxygen rather than air for fuel combustion. This process creates a mix of water vapor and CO2. The mix can be easily separated to produce a high purity CO₂ stream.

Direct air capture

Another alternative is Direct air capture (DAC), a technology that captures CO2 from ambient air. DAC can provide a carbon-neutral loop or allow for carbon negative. The concept of direct air capture is defined as the extraction of carbon dioxide from ambient air. Since 1930, technologies that allow capturing CO₂ from ambient have been developed. Space shuttles are equipped with Carbon Dioxide Removal Assembly (CRA) to allow astronauts to breathe.

Climeworks and Carbon Engineering are two companies that have built commercial-scale DACS plants. It is a very flexible solution that can be implemented widely capturing carbon dioxide that has already been emitted. First, ambient air goes through a filter process where CO₂ is separated from the air. The filter acts as a sorbent that separates the CO₂, air is ejected with 80% less CO₂. In order to separate the CO₂ from the sorbent, there are different options using heat, pressure, or humidity.  After the sorbents are regenerated, they are used again.

Climerworks DAC

Climeworks has plants in operation in Switzerland and Iceland. Their Zurich plant uses the excess heat from a waste to energy plant to capture carbon dioxide. Once capture, CO₂ is then transported to a nearby greenhouse to be used as a fertilizer. Climeworks has developed another plant in Hellisheidi, Iceland, as part of the CarbFix2 project with EU funding. The captured CO₂ dissolved in hot water is then injected into the underground rock foundations, where it is permanently stored. Climeworks DAC has been operating since 2017 with the capacity to capture about 50 tons of CO₂ annually. A new project is underway to increase the capture capacity to ~4,000 tons of CO₂.

However, the main CO₂ capture at the Hellisheidi Geothermal Power Plant comes from a post-combustion capture. The absorption process captures CO2 and H2S and separates them from the other geothermal gases from the plant. After being dissolved in condensed steam and injected into the subsurface for permanent mineralization. According to CarbFix, the cost of industrial-scale operations at Hellisheidi are less than $25/ton of CO2, which is comparable with the current price of the ETS carbon quota and far cheaper than conventional CCS methods.

In their website, you can support Climeworks in their storage capture, at a costs of 1090 USD per metric tonne of CO2 extracted and stored.

Carbon Engineering

Carbon Engineering Direct Air Capture (DAC) technology uses a similar process. Atmospheric air undergoes their process, and through a series of chemical reactions, then extracts the carbon dioxide (CO2) from it while returning the rest of the air to the environment. Back in 2015 Carbon Engineering built a $9-million pilot plant in Squamish, B.C., that captures about one tonne of CO2 per day, which is the equivalent of taking about 100 cars off the road annually. Recently, Shopify announced the purchase of 10,000 tonnes of permanent carbon removal capacity from a large-scale DAC project. 

Generally, the lower the concentration of CO2, the more energy is required to capture the CO2. This is why most carbon capture engineering efforts do not focus on direct air capture. It is harder to separate CO₂ from ambient air with a CO2 concentration of 0.004% than from flue gases of an industrial plant, with a concentration of 15% CO₂.

Carbon transport

Following the capture process, the CO₂ needs to be transported to storage or to facilities to be reutilized. CO₂ transport technologies are mature and commercially available. The CO₂ is compressed and transported by ships, tanks, and even pipelines to a suitable site for geological storage or utilization. To reduce the costs, reducing transportation is key.

Carbon storage

Carbon storage is typically considered permanent storage that in the best case allows carbon negative solutions. In order to be carbon negative, atmospheric CO₂ must be captured and permanently stored in the underground or in materials. Typically, CO₂ is injected into deep underground rock formations, at depths over one kilometer or more.

• Enhanced oil recovery carbon consists of the injection of CO2 in depleted oil reservoirs to improve oil extraction. This process allows permanent CO₂ storage in the depleted reservoir.
• Aquifer CO2 storage consists of the injection of CO2 in large underground aquifers, over 1 km deep. As the CO2 is stored, water is extracted.
• Salt cavern CO2 storage – typical in the USA and Europe. Salt caverns are artificial cavities made in salt bed deposits, for example.

Carbon utilization

After capture, the CO2 undergoes a compression stage. The main use is used in enhanced oil recovery (EOR), engineers discovered that injecting carbon dioxide into mature oil fields increases oil production. The process traps carbon dioxide underground. Carbon dioxide is a commodity for the oil industry.

What is coming?

Globally, coal is the largest energy source for electricity generation and the second-largest feedstock source of primary energy. Even though Europe and Canada are closing down fossil fuel plants, China and India are still building new coal plants. With the current rate of CO2 emissions and with CO2 level in the atmosphere higher than 409 ppm, human activities have caused more than 1∘C global warming than that of the pre-industrial level. To limit global warming to 2∘C by 2100, limiting the increase to 1.5∘C, investigating carbon capture technologies is key. As it is one of the key short-term solutions to reduce emissions by 50% by 2050. Deployment of renewable energy and energy efficiency measures alone are not sufficient.

For carbon capture technologies to become economically feasible, having adequate carbon pricing is crucial either in carbon tax or carbon allowances. Today, carbon tax significantly varies from one country to another, with values ranging from a few dollars to one hundred $/tonne of CO₂. The EU emissions trading system (EU ETS) is the world’s first major carbon market and remains the biggest one.

The EU ETS works on a cap and trade principle. A cap limits the number of certain greenhouse gases that can be emitted by installations covered by the system. Over time, the cap is reduced so total emissions fall.

Even with COVID-19 pandemic effects, the cost of emitting a ton of CO₂ hit €35.42 a record in January 2021 in the EU ETS. It is expected that the prices will reach €40 in 2021 (close to $50). This value of carbon allowance started at $5/tonne CO₂ equivalent back in 2017. Including a cost to CO₂ emissions is considered as one of the most effective ways to sustain the development of CCS technologies. If the trend continues, there will be more incentives to use CCS technologies.

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