CO2 transport

CO2 can be transported in a number of different ways, including by road tankers and railway, but for the volumes involved in carbon capture and storage, pipeline and ship are the most practical and economical options.

Extensive experience exists in transport of CO2 by pipeline, while transport of CO2 by ship and other carriers is still in its infancy, so far only applied for small quantities of food grade CO2. However, natural gas, petroleum gas and condensates are routinely transported by all of the mentioned carriers under a wide variety of conditions - including through deserts, mountain ranges, heavily populated areas, arctic areas and in deep sea. Transport of CO2 is similar to and not more challenging than the transport of hydro carbon gases.

Pipeline is the most economical method of transport of CO2 for distance up to 1000 - 1500 km, depending on specific conditions and the volume transported. Beyond this distance transport by ship may be more economical (IPCC, 2005). No planned CCS projects today are based on marine transport of CO2 from the capture site to the storage site, but future projects mat require marine transport, particularly in the case that no suitable storage site is found within the vicinity of a large emission source or a cluster of many large emission sources.

Contents

1. Transporting CO2 by pipeline
2. Transporting CO2 by ship
3. CO2 infrastructure and transport in the North Sea
4. Risks and safety
5. Challenges
6. References

Transporting CO2 by pipeline

Main articles: Transporting CO2 by pipeline

Natural gas pipeline in Alaska (Source: sxc.hu)

Typical annual emissions from a fossil fuel power plant range from about 1 MtCO2 to 4 MtCO2 or more. Industrial process emissions fall within a wider range, with the majority of viable sources for CO2 capture typically emitting more than 0.5 MtCO2 pr year (IPVV, 2005). At this scale, pipelines are the the most economical way of transporting CO2 over distances up to 1000 km or more, depending on specific conditions. Offshore pipelines are generally more expensive to build and maintain than onshore pipelines, but are still more economical than ship transport up to hundreds of kilometers, depending upon specific conditions. Costs are subject to increase in mountainous terrain and in heavily populated areas, as well as when numerous obstacles such as freeways or rivers must traversed, or through nature reserve areas or other areas where extra precautions must be taken in construction and maintenance.

Dry CO2 does not corrode the steel pipelines generally used for pipelines unless they contain large fractions of corrosive contaminants such as hydrogen sulphide. It would also be possible to design a corrosion resistant pipeline to carry CO2 contains water or other corrosive contaminants. This could be an attractive option if removing such contaminants significantly increases capture costs, as may be the case with some capture technologies.

CO2 has been used extensively for enhanced oil recovery (EOR) in the USA for decades, and several long distance pipelines for CO2 are in operation. These pipelines transport 50 MtCO2 pr year, over a total distance of more than 2500 km.

CO2 becomes liquid at about 5.7 MPa at room temperature. As a liquid CO2 has a density close to water and is easily transported by pipeline. Increasing pressure also reduces volume. Gas pipeline systems typically operate at 10 to 80 MPa.

Transporting CO2 by ship

Main articles: Transporting CO2 by ship

Transporting CO2 by ship is a practical solution when volumes are too small or the distance of transport too far for pipeline transport to be an economical or practical solution. As a commercial commodity in food production, cooling and for other industrial purposes, CO2 is often transported by ship today. The market for CO2 in Europe is almost 3 million tons a year. A large part of this is transported by ship.

Liquified natural gas and petroleum gases are routinely transported by marine tankers, at a very large scale. CO2 is transported in the same way, but only on a small scale, because of limited demand. The  properties of liquified CO2 are similiar to those of petroleum gases, so no major technology advancements are required to transport CO2 by ship on a large scale.

Some net CO2 loss must be expected in long distance transport by ship. This results partly from boil-off and partly from the exhaust from the ship's engines. The total loss to the atmosphere from ships is between 3 and 4% per 1000 km. This figure can be reduced by recapturing some of the lost CO2 and by changing to low or zero emission fuels in the ship's engines (IPCC, 2005).

CO2 infrastructure and transport in the North Sea

Main article: CO2 infrastructure and transport in the North Sea

Proposed CO2 infrastructure in the North Sea (Source: ZERO)

In 2007 the EU Commission presented an energy and climate policy package, mandating the 27 member states to cut emissions of carbon dioxide and other greenhouse gases by 20 per cent in 2020 compared with 1990 emission levels. The Commission suggests carbon storage as a main solution to achieve this goal. Storage in the North Sea will therefore be of considerable importance to enable Europe to reach its emission goals.

In 2005 The Norwegian and British governments formed the North Sea Basin Task Force, a work group whose aim is to investigate and plan for the possible joint regulation of carbon capture and storage in the North Sea. A report finished in November 2007 establishes that a yearly capture and storage of between 200 and 350 million tons CO2 is possible in the period 2030-2040. Such an amount requires necessary infrastructure to be installed and will vary with the establishment of new fossil energy production and post-fitting of capture equipment on existing power plants. This all means that emissions from all large point sources in Norway and the UK can be captured and stored permanently underneath the North Sea (Element Energy et al 2007).

In 2005 the CO2 emissions from stationary sources in the UK was close to 270 million tons, while the Norwegian emissions totalled about 43 million tons, of which 60 per cent come from stationary sources. The storage capacity in the North Sea is large enough for storing emissions from other countries around the basin.  

Risks and safety

Land pipelines are built to defines standards and are subject to regulatory approval to assure a high level of safety, particularly in populated areas. Pipelines in operation are monitored internally by pigs (piston-like inspection devices that are driven through the pipeline by gas pressure) and externally by corrosion monitoring and leak detection systems. In the event of a leak, transport of gas is shut down automatically.

The risks involved in transport by ship is low. New tankers are generally well designed to avoid loss of cargo in the  case of a collision, stranding or fire. There has been no accidental losses of cargo from LNG tankers. Should an accident happen to a liquid CO2 tanker, liquified CO2 might be released onto the surface of the sea. The environmental effects of such an event are not fully known, and requires further study. However, the long-term effects are anticipated not to have the long-term environmental impacts of crude oil spills.

Challenges

There are few technical challenges in large scale CO2 transport. Extensive experience in pipeline transport of CO2 has been gained in connection with use of CO2 in EOR in the USA and Canada. Further, experiences from transport of natural gas pipeline are closely related to transport of CO2.

There is less experience with large scale transport of CO2 by ship. Some further development of large transport vessels is needed, but as with pipeline transport, analogues experience with transport of liquid natural gas provides very useful knowledge and experience. 

References

IPCC, 2005: IPCC Special Report on Carbon Dioxide Capture and Storage