Proximity to energy consumers and fuel sources largely determines the placement of new electric power plants. Only some of these facilities are located in areas with ready access to geological formations or deep waters that might provide long-term CO₂ storage. Widespread adoption of CO₂ capture and storage therefore hinges on the ability to transport CO₂ from where it is produced to where it will be stored.

Several chemical properties of CO₂ influence its transport.

• CO₂, if kept dry, is noncorrosive and compatible with pipes and storage vessels made of regular steel. In the presence of water, CO₂ forms carbonic acid, which is corrosive and must be contained in resistant alloys that are several times more expensive than regular steel.

• At standard temperature and pressure (0°C, 0.1 MPa), CO₂ is a colorless, odorless gas that is heavier than air. (CO₂ has a density of 1.98 kg m^–3; air has a density of 1.229 kg m^–3.) Thus, CO₂ that leaks out during transport tends to accumulate in depressions and may endanger people if its concentration exceeds 22%.

• Liquid CO₂ has a density of 929 kg m^–3 at 0°C and 3.5 MPa, and so moving CO₂ as a liquid transports 500 times more CO₂ per unit volume than as a gas. Most systems, therefore, transport liquid CO₂ despite the high pressures, low temperatures, and extra energy required for maintaining CO₂ in this state. Unfortunately, the high pressures and low temperatures of the liquid make it more dangerous than the gas.

Given the risks from leaks, facilities for CO₂ transport should be located as far as possible from densely populated areas.

Two major modes of CO₂ transport are pipelines and tanker ships. Pipelines operate at ambient temperatures and high pressures (10 MPa to 80 MPa), conditions under which CO₂ becomes a supercritical fluid, and so its density varies continuously with pressure without a distinct phase change. Tanker ships are more economical than pipelines for CO₂ transport over long distances. Ships carry liquefied CO₂ at low temperatures (approximately -50°C) and several atmospheres pressure (approximately 0.7 MPa), using technology similar to that for transport of liquefied natural gas (LNG). Perhaps in the future, ships will transport LNG from gas fields to power plants and return with loads of liquefied CO₂ for injection into the gas wells for long-term storage.

This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.

©2010 Sinauer Associates and UC Regents