How Carbon Capture Works

Transporting Carbon Dioxide

After carbon dioxide (CO2) is captured, the next step is transporting it to a storage site. The current method of transporting CO2 is through a pipeline. Pipelines have been in use for decades, and large volumes of gases, oil and water flow through pipelines every day. Carbon dioxide pipelines are an existing part of the U.S. infrastructure -- in fact, there are more than 1,500 miles (2,414 km) of CO2 pipelines in the U.S. today, mostly for enhancing oil production [source: IPCC]. You can put a pipeline just about anywhere -- underground or underwater -- with depths ranging from a few feet to a mile.

A CO2 pipeline usually begins at the source of capture and travels directly to the storage site -- although, in some cases, it might travel as far as it can in the pipe, then transition to a tanker or ship to finish off its journey. It all depends on where the source, pipeline and storage site are located. Both the public and private sector can own pipelines.

Pipelines can transport CO2 in three states: gaseous, liquid and solid. Solid CO2 is commonly known as dry ice, and it's not cost-effective to transport CO2 as a solid. Pipelines commonly transport carbon dioxide in its gaseous state. A compressor "pushes" the gas through the pipeline. Sometimes a pipeline will have intermittent compressors to keep the gas moving. The CO2 must be clean (free of hydrogen sulfide) and dry. Otherwise, it can corrode a typical pipeline, which is made of carbon manganese steel. As of yet, there are no standards in place for "pipeline quality" carbon dioxide, but experts say that pipelines built from stainless steel would have a lowered risk of corrosion. This, however, may not be economical, since we would have to build brand new pipelines just for CO2.

Accidents with pipelines are rare, as we've found in decades of use. Only 12 CO2 pipeline leaks occurred from 1986 to 2006, with no human injuries reported. Contrast that with natural gas and hazardous liquid pipelines, which had more than 5,000 accidents and 107 fatalities in the same period [source: Parfomak]. Of course, one reason carbon dioxide pipeline accidents are rare is because we don't really have that many CO2 pipelines in use. Accidents will likely increase as the number of pipelines rises. As CO2 is odorless and colorless, though, adding an odor to the gas could help to detect leaks. Regardless, experts recommend construction of pipelines in low-population areas to minimize any impact.

Pipeline costs fluctuate depending on the route of the pipeline (through heavily congested areas, mountains, offshore). It's also possible to transport carbon dioxide as a liquid, using ships or tanker trucks. Liquid CO2 requires low pressure and a constant low temperature, so cargo tanks need to be both pressurized and refrigerated. You might be wondering what happens if a ship or truck carrying a tank of CO2 gets into an accident. Unfortunately, there isn't much data on the subject, but we do know there is an asphyxiation risk if a massive amount of CO2 escapes into the atmosphere. As with tanks that transport natural gas and other hazardous materials, good construction is key. That, and good driving.

Continue reading to learn how carbon dioxide can be stored underground or underwater.