CO2 Transport Specification, Purification and Dehydration Solutions

CCUS is one of the key solutions to reduce emissions like carbon dioxide (CO2) in the atmosphere and minimize the effect on global warming. CO2 is separated from other gases at large industrial facilities like refineries, natural gas power plants, steel mills, and cement plants, or from the atmosphere. The two most common technologies for CO2 capture are membranes using physical separation and amines using chemical absorption. The bulk CO2 that is separated must go through additional purification steps to be ready for transportation. Once the CO2 meets pipeline specification, the CO2 is further compressed using high pressure to change the CO2 from a gas to a supercritical liquid. Pipelines are the most common mode of transport. After being transported to the well-characterized and permitted geological storage site, the CO2 is injected underground into deep rock formations where it is safely and permanently stored. Geologic formations have safely contained a variety of liquids and pressured gases such as oil, natural gas and naturally occurring CO2. It is expected that several CCUS projects are coming live, and it is also expected that they are connected through a CO2 transportation network. Such a network will be a combination of ship, trailer, train, and pipelines. Carbon steel is a natural choice as construction material for the CO2 transportation system since it has excellent strength, is relatively cheap and is readily available in large quantities. Carbon steel corrodes when exposed to CO2 and water and/or glycol, therefore it is crucial that the transportation systems are operated in a manner that prevents formation of aqueous phases (Müller et al., 2023). Although treatment specifications vary by project, some specifications are commonly accepted. First, water in the treated CO2 typically needs to be less than 50 ppmv. The water content of <50 ppmv is well below that suggested to avoid the risk of corrosion for transport in pipelines and is set to avoid the risk of formation of ice in the liquefaction process equipment, rather than for any issues with transport containers. Second, for liquefaction, water specification in the treated gas can be as high as 50 ppmv. This is due to the higher liquefaction temperature of CO2 compared to other gases, like natural gas or nitrogen. Finally, glycol needs to be completely removed. This last point often disqualifies triethylene glycol (TEG) units for CO2 dehydration service.