Liquefaction

DESCRIPTION

CO₂ liquefaction is the process of converting the gaseous CO₂ into its liquid form. This transformation is achieved through a series of compression and cooling stages, allowing CO₂ to be stored and transported more efficiently.¹ Liquefaction approach uses liquid pumps that require significantly less power to raise pressure and are considerably less expensive than gas compressors.² The CO₂ is compressed in the compression train in several stages to reach liquefaction pressure. When CO₂ is available at atmospheric pressure, 3-4 stages are required as opposed to high-pressure CO₂, where compression may not even be required. Between stages, intercooling and flash separators are used to remove condensed water. The CO₂ stream enters an impurity removal unit after the compression train, where any impurities are eliminated. It passes through a liquefier that is chilled by a refrigeration loop and a pre-cooler before condensing. The stream is totally condensed and slightly sub-cooled after passing through the liquefier if it is pure CO₂ or if all impurities are condensed at a high enough liquefaction pressure. The CO₂ stream may partially condense in the liquefier in cases when the inlet gas contains contaminants. To attain the desired delivery pressure level, the condensed liquid passes through a valve. The stream next passes through a separator, which recovers liquid CO₂ and sends it to buffer storage before being transported by ship. Before the pre-cooling phase, the outlet gas of the separator is compressed and recycled to be combined with the mainstream.

REMOVED COMPONENTS

• Water is removed as condensate after every compression stage.
• Other impurities, if any, are also removed before the liquefaction step.

FUNCTION IN CCU VALUE CHAIN

• Liquefy CO₂ for transportation either by shipping, truck, rail or pipelines. For shipping, the CO₂ may be compressed between 6.5-15 bar (low to medium pressure shipping, but requires sub-zero temperatures (-50 to -30 °C).³ The typical transport temperature and the corresponding pressure in Northern lights project is -30 °C and 15-21 bar.⁴

LIMITATIONS

• The liquefaction approach necessitates CO₂ transportation at sub-zero temperatures.
• Careful assessment of the refrigeration process is critical in the liquefaction approach for accurate system power accounting.

ENERGY

• Electricity is consumed by the initial CO₂ compressors and the recycle compressor.
• Electricity is also consumed by the refrigeration cycle compressors.

CONSUMABLES

Cooling water is used for cooling in the CO₂ compression train and refrigeration cycle. It is generally recycled and not consumed.

COSTS

The cost of CO₂ liquefaction is also variable depending upon the captured CO₂ purity and target transport pressure. The cost to liquefy at a scale of 1 MtCO₂/yr of pure CO₂ ranges from €14 – €15 per tonne CO₂ at target transport pressures 8 – 16 bar.⁵ For high-pressure liquefaction, mild cooling temperatures are sufficient. The cost to liquefy CO₂ at 66 bar at 20 °C using a flash and a distillation column was reported to be €12 – €18  and €16 – €17 per tonne CO₂, respectively.⁶

TECHNOLOGY PROVIDERS

• CO₂ liquefaction by Linde, Ireland.
• Cryocap™ LQ by Air Liquide, France.
• CO₂ liquefaction by Baker Hughes, USA.
• CarboPac-L by Bright Renewables, Netherlands.
• CO₂ liquefaction by GEA, Germany

ALTERNATIVE TECHNOLOGIES

Compression: CO₂ is compressed up to 80 bar and cooled to obtain the supercritical phase, and then pumped to pressures up to 150 bar. This CO₂ phase is more suitable for pipeline transport and does not require a refrigeration cycle.

CONTACT INFO

Mohammed Khan (mohammednazeer.khan@vito.be)

Miet Van Dael (miet.vandael@vito.be)

ACKNOWLEDGEMENT

This infosheet was prepared as part of the MAP-IT CCU project funded by VLAIO (grant no. HBC.2023.0544).

REFERENCES

1.    Linde. CO₂ purification and liquefaction. Published online 2017:8.

2.    Powermag. Capturing CO2: Gas Compression vs. Liquefaction. June 1, 2009. Accessed October 29, 2024. https://www.powermag.com/capturing-co2-gas-compression-vs-liquefaction/

3.    NOV. CO2 Dehydration Product Offerings.; 2024. https://www.nov.com/-/media/nov/files/capabilities/carbon-capture-utilization-and-storage-solutions/co2-dehydration-product-offerings-brochure.pdf

4.    Northern Lights. Northern Lights’ first CO2 transport ship ready for delivery. November 25, 2024. Accessed May 12, 2025. https://norlights.com/news/northern-lights-first-co2-transport-ship-ready-for-delivery/

5.    Roussanaly S, Deng H, Skaugen G, Gundersen T. At what Pressure Shall CO2 Be Transported by Ship? An in-Depth Cost Comparison of 7 and 15 Barg Shipping. Energies. 2021;14(5635):1-27.

6.    Kim S, Jung PG, Lim Y Il, Kim H, Moon HM. CO2 Compression and Liquefaction Processes Using a Distillation Column for the Flexible Operation of Transportation. Process 2024, Vol 12, Page 115. 2024;12(1):115.