Transport

In most cases, CO2 emission sources and storage sites are located far away from each other. Transportation of CO2 from the source to the storage site ocurrs either by pipelines or by ships.

Introduction

Coal and gas power plants are often built close to industrial areas or cities where electricity is consumed to ensure the shortest possible distance for transporting electricity by cable. But appropriate storage sites for CO₂ are not necesarily located close to where power plants are built.

In most cases the storage location is located at some distance away from the emission source, meaning that an infrastructure for CO₂ transport must be established.

There are two transport options: pipelines and ships.

In the figure above there are three coal power plants with different solutions for CO2 transport. (1). A short pipeline from the power plant to the harbour, and then CO2 transport by ship to an offshore injection point. (2) A short onshore pipeline from the power plant to the coast, and then a large offshore pipeline at the bottom of the sea to the injection point. (3) An onshore pipeline from the power plant to the onshore injection point.

Pipelines are the only option for onshore transport when CCS becomes commercially available and millions or even billions of tons CO₂ will be stored annually. In theory, it is possible to transport CO₂ by truck or by train. However, the large number of trucks and trains that would be required to transport millions of tons of CO₂ render the idea completely impractical. Truck transport would be possible in the initial phases for small research or pilot projects.

If the storage site is below an ocean, which is often the case, the offshore CO₂ transport can be made via pipelines or ships. Ships are generally the cheapest alternative for transport over long distances or for small volumes, while pipelines are cheapest for large volumes and greater distances.

CO₂ transport by pipelines

Transporting CO₂ by pipelines is not a new idea. In fact, CO₂ has been transported by pipelines in the USA since the 1970s. There is a large network of pipelines for CO₂ transport in the USA. Here the CO₂ is pumped up from naturally occuring CO₂ reservoirs and transorted to oil fields where the CO₂ is injected to increase the oil production.

CO₂ is transported in ordinary steel pipelines of the same type that are used for natural gas. Yet this creates the challenge of corrosion as CO₂ is corrosive and can quickly corrode holes in a steel pipeline. However, as corrosion requires water, it can be avoided if all water is dried out of the pipeline prior to transportation.

CO₂ is always compressed to a high pressure 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.

In general, there are two types of pipelines: offshore and onshore. The pipes themselves are quite similar, but the difference is that offshore pipelines are more difficult to install and maintain, while onshore pipelines are visibile and thereby reduce the recreational value of the areas they cross.

Ship transport

CO₂ can easily be transported by ship, and today smaller volumes of CO₂ used for coooling or in food production are shiped from its producers to the consuments.

CO₂ is transported in ships as liquid, and the CO₂ must therefor be cooled to -30 oC and compressed to above 18 bar prior to the transport.

Ship transport of CO₂ is similar to transporting LNG (liquefied petroleum gas), and companies that already operates on the LNG marked are starting to modify their ships to get them classified for CO₂ transport.

Ship transport is a very good alternative to pipelines. In general, ships will be more cost effective than pipelines for small CO₂ volumes or long distances. But ships can also be a good alternatives in an initial phase of developing CCS. Building pipelines takes a long time, and ship transport can therefore be a good way to get the first few CCS projects started. Furthermore, ships can also be the prefered alternative when CO₂ is used for enhanced oil recovery (EOR), i.e. injection of CO₂ in oil fields to push out more oil. In such cases the need for CO₂ is often limited to a short time window of a few years, and no one builds a pipeline that will be in operation only a few years. 

CCS infrastructure

In the future there could be pipelines all over the world linking sources of CO₂, such as coal power plants, with safe storage locations. If the full potential of CCS is realised it could mean transporting billions of tons of CO₂ annually. However, the following questions must be raised when considering this prospect:

• Is it possible to build pipelines in densely populated areas?
• Can the large amounts of steel required for the pipelines be supplied fast enough?
• How can we ensure that no water enters the pipeline?
• What are the environmental effects of the pipelines?
• What is the optimal way of linking many CO₂ sources with many CO₂ storage sites? Is it preferable to connect all CO₂ sources and sinks, or should there be lots of pipelines linking one CO₂ source with one storage site?

Authorities and research institutions are starting to address questions like these and within a decade a pipeline infrastructure will most likely be a reality in many places around the world.

See also

• CO₂ capture
• CO₂ storage

External links

• KinderMorgan, a US company that owns interests in CO2 pipelines
• IM Skaugen, a company with ships for CO2 transport
• CO2 transport, as regarded by power company RWE