The CO2 collected by the CO2 capture plant is transported to a suitable storage location. Prior to transport, however, the CO2 must be dried and compressed. Drying is necessary to remove all water which can otherwise cause serious corrosion problems. Compression is necessary to increase the pressure and reduce the volume of CO2 to be transported. In practice, the CO2 is compressed prior to injection to a dense fluid state known as “dense phase” or “supercritical CO2“. Dense phase CO2 behaves like a liquid, and represents CO2 at a pressure greater than 73.9 bar.
There are two main transport options: ship or pipeline. In general, ship transport is the cheapest solution for small volumes and distances, while pipelines are cheapest for large volumes and longer distances. CO2 is preferably transported by pipeline, whereas ships may be used in the initial phase of storage characterisation when a source of CO2 is too far from a suitable storage site and greater flexibility is required. If the storage site is below an ocean, which is often the case, the offshore CO2 transport can be made via pipelines or ships.
Pipelines are the only option for onshore transport when CCS is widely rolled-out and millions or even billions of tonnes of CO2 will be transported and stored annually. In theory, it is possible to transport CO2 by truck or by train, but the large number eventually required would render the idea completely impractical.
CO2 is transported in ordinary steel pipelines of the same type that are used for gas. CO2 is always compressed to a high pressure (73.9 bar) before pipeline transportation. This is done to reduce the volume that needs to be transported and also to ensure that the CO2 is in a state in which it can be easily transported in a pipeline.
Considerable experience exists with CO2 pipeline development and operation on land and under the sea. There are 36 CO2 pipelines currently operating in the USA alone that transport 48–58 milliontonnes of CO2 each year.
There is significant potential for the development of local and regional CCS pipeline infrastructure, leading to CCS ‘clusters’ where CO2-intensive industries could locate. The development of clusters enables the sharing of infrastructure by a number of industrial sources of CO2 emissions. This in turn makes possible delivering CCS infrastructure development in the most cost-effective way and at a lower cost to consumers. Clustering and networks of CO2 capture plants will also have benefits for the operation of CO2 storage sites, as CO2 flows are less likely to be interrupted.