Cryogenic distillation: a promising technology for carbon capture

Carbon Capture and Storage (CCS) encompasses an integrated suite of technologies that can prevent large quantities of CO₂ from being released in the atmosphere from the use of fossil fuels. The CCS chain consists of three parts: capturing the carbon dioxide, transporting it to a storage site via ship or pipeline, and either using it as a resource to create valuable products or services or storing it deep underground in geological formations.

 

CCS technologies – which can be applied in the industrial sector and for power generation – could play an important role in meeting energy and climate goals. In the IEA Sustainable Development Scenario, CCS accounts for 7% of the cumulative emission reductions needed globally by 2040. This implies a rapid scale-up of CCS deployment, from around 30 million tonnes (Mt) of CO₂ currently captured each year to 2 300 Mt per year by 2040.^[1]

 

As of 2019, there are 17 operating CCS installations in the world – including about 70% in North America – capturing 31.5Mt of CO₂ per year, of which 3.7 Mt are stored geologically. Most of them being industrial and not power plants.^[2]

 

 

Its uses cover a variety of industrial applications, outstanding abatement of CO₂ from process or exhaust gases and in natural gas processing. In the former, depending on the technology, CO₂ is separated from H₂ (pre-combustion), N₂ (post-combustion) and H₂O (oxy-combustion, which burns hydrocarbons with pure O₂), while in natural gas processing, CO₂ is separated from CH₄ and light hydrocarbons.^[3]

 

 

CO₂capture technologies are available in the market but are costly in general, and contribute to around 70–80% of the total cost of a full CCS system.^[4]

 

 

The main CO₂ separation technologies that can be applied to isolate the CO₂ from the flue/fuel gas stream prior to transportation are absorption (the most mature process), adsorption, chemical looping, membrane separation, hydrate-based separation and cryogenic distillation.^[4]

 

 

The cryogenic distillation process is the following: flue gas containing CO₂ is cooled to desublimation temperature (-100 to -135°C) and then solidified. CO₂ is separated from other light gases and compressed to a high pressure of 100 to200 times the atmospheric pressure. The amount of CO₂ recovered can reach 90–95% of the flue gas. Since the distillation is conducted at extremely low temperature and high pressure, it is an energy intensive process estimated to be 600–660 kWh per tonne of CO₂ recovered in liquid form. Several patented processes have been developed and research has mainly focused on cost optimization. CO₂ is obtained as liquid with benefits in CO₂ transport (no compressors needed, pumps used instead). It is appropriate for high CO₂ content.^{[3] [4]}. Cryogenic carbon capture technology is a relatively young technology but is being actively developed. Furthermore, cryogenic distillation has been adopted for many years in industry for CO₂ recovery.^[4]

 

 

There are actually very few large-scale CCS projects in operation using cryogenic distillation.^[3] However, it should be noted that a facility using this technology is under construction at a fertiliser plant in Zibo City, Shangdong Province, China. Upon completion it is expected to capture 400 Mt of CO₂ per year.^[5]

 

 

^[1] IEA, Carbon capture, utilization and storage. Available following this link.

^[2] Global CCS Institute, Facilities Database. Available following this link. 

 

 

^[3] de Queiroz Fernandes Araújo O. , Luiz de Mederos J. Carbon capture and storage technologies: present scenario and drivers of innovation. Current Opinion in Chemical Engineering, Aug. 2017. Available following this link.

^[4] Leung D. Y. C. et al. An overview of current status of carbon dioxide capture and storage technologies. Renewable and Sustainable Energy Reviews , November 2014. Available following this link.  

^[5] Asia Times, China aims to capture greenhouse gases. Available following this link.