The value chain of CCUS

CO₂ capture plays a crucial role in various industrial processes, with technologies for separating or capturing CO₂ from flue gas streams being commercially available for many decades. The most advanced and widely used methods are chemical absorption and physical separation.

CO₂ is separated from the output stream using appropriate technology as for example chemical solvents, or membranes based on the type of stream. It is also separated from other gases or air, also called as Direct Air Capture, or a concentrated source. Depending on the production sources, the CO₂ will have different characteristics which can be categorized into:

• High purity CO₂ streams production (e. g. from bioethanol or beer production processes) that directly produce an output stream of 96 to 100 % CO₂ purity
• Medium purity CO₂ streams production (e. g. from iron & steel or cement production processes) that directly produce an output stream of 20 to 50 %. CO₂ from Hydrogen production out of Syngas or refinery processes is considered to be within the 30 to 45 % purity range
• Low purity CO₂ streams production (e. g. from paper and pulp or glass production processes) that directly produce an output stream of < 20 %. In refineries, process heating and FCC unit produce low purity (3 to 20 %) streams of CO₂

CO₂ capture plays a crucial role in various industrial processes, with technologies for separating or capturing CO₂ from flue gas streams being commercially available for many decades. The most advanced and widely used methods are chemical absorption and physical separation.

CO₂ is separated from the output stream using appropriate technology as for example chemical solvents, or membranes based on the type of stream. It is also separated from other gases or air, also called as Direct Air Capture, or a concentrated source. Depending on the production sources, the CO₂ will have different characteristics which can be categorized into:

• High purity CO₂ streams production (e. g. from bioethanol or beer production processes) that directly produce an output stream of 96 to 100 % CO₂ purity
• Medium purity CO₂ streams production (e. g. from iron & steel or cement production processes) that directly produce an output stream of 20 to 50 %. CO₂ from Hydrogen production out of Syngas or refinery processes is considered to be within the 30 to 45 % purity range
• Low purity CO₂ streams production (e. g. from paper and pulp or glass production processes) that directly produce an output stream of < 20 %. In refineries, process heating and FCC unit produce low purity (3 to 20 %) streams of CO₂

For efficient storage and a re-use of the captured CO₂ purification and liquefaction processes are beneficial. The purification step includes a cleaning process to receive high purity CO₂ streams. The liquefaction process step includes several compression and cooling stages. As a result, the CO₂ is available as cooled liquid (now also named liquified CO₂ / LCO₂) and can now easily be transferred to a storage tank.

The availability of infrastructure to transport LCO₂ safely and reliably is essential for deployment of CCUS. The most common options for the large-scale transport of CO₂ are via onshore / offshore pipeline and ship. Although, for short distances and small volumes, it can also be transported by truck or rail, but at higher cost per ton of CO₂.

Transport by pipeline has been practiced for many years and is already deployed at large scale. While LCO₂ is currently transported via trucks or ships in small quantities for use in the food and beverage industry, large-scale transportation of LCO₂ by ship has not yet been experienced much but seems to have similarities to liquefied petroleum gas (LPG) and liquefied natural gas (LNG) shipping.

Biogenic liquified CO₂ can be used in many applications. We have selected 3 potential ones.

Food and beverages
The worldwide food and beverage industries consume about 11 Mt CO₂ annually. It is one of the most established and common end uses of LCO₂.

Some applications could be soft drinks, water, beer carbonation or the production of deoxygenated water. These industries require very high CO₂ purity.

Greenhouses
In this application, CO₂ is used in the artificially air renewing system. The CO₂ can help to increase the plants growth rate by 15 to 40 %. The CO₂ consumption depends on the crop type and on lighting control.

Another important use in agriculture is pest control, where CO₂ is considered an alternative to products such as methyl bromide, phosphines and insecticides. It has the advantage of leaving no residues after treatment. The fumigating effect of carbon dioxide allows post-harvest treatment, especially in organic agriculture, increasing food safety and reducing production residues.

Fertilizers
The industrial production of fertilizers in the EU-27 accounted for 18,100 kt in 2019. Approximately 72 % of this production corresponds to nitrogenous fertilizers, which include urea and ammonium nitrate.

To minimize the total carbon footprint from global biomass production, it is crucial to use land efficiently by adopting modern and more sustainable agricultural practices.

Urea is one of the most known chemical products. It can be used as a chemical fertilizer in urea resins, urea – melamine resins and as an animal feed additive. The most common urea production method is reforming natural gas, producing carbon dioxide and ammonia. Comparing to the nitrates production, urea emits less CO₂, but upon spreading, the situation is reversed, since urea releases the CO₂ contained in its molecule.

Urea also often releases more N₂O. Therefore, the life cycle carbon footprint is higher for urea than for nitrates. As CO₂ is used during urea production, biogenic LCO₂ represents an environmentally friendly alternative.

LCO₂ is stored by injecting the captured LCO₂ into a deep underground geological reservoir of porous rock. These reservoirs are sealed by an impermeable layer of rocks, preventing any upward migration or leakage to the atmosphere. Various types of reservoirs are suitable for CO₂ storage, with deep saline formations and depleted oil and gas reservoirs having the largest capacity. These formations consist of layers of porous and permeable rocks saturated with salty water (brine) and are found 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 extraction.

The injected LCO₂ fills the pore space of the reservoir. The gas is usually compressed first to increase its density. The reservoir must be at depths greater than 800 meters to retain the CO₂ in a dense liquid state. The LCO₂ 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
• mineral trapping where the CO₂ reacts with the reservoir rocks to form carbonate minerals (mineralization)

The trapping mechanism depends on the sites’ lifespan and geological conditions. Decades of experience in the LCO₂ injection and storage help to better understand the characteristics and select the right trapping method.

It is also possible to store CO₂ in basalts (igneous rocks) that have high concentrations of reactive chemicals. However, this method 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. Nevertheless, in many regions, significant assessment work is required to convert theoretical storage capacity into effective storage.