Carbon Capture and Storage
Carbon capture and storage (CCS) captures the CO2 emitted from industrial processes and stores it deep underground. It is critical in preventing the rise in atmospheric CO2 since much CO2 emitting industrial activity is likely for decades to come despite essential developments in areas such as renewables for electricity generation and plants and algae in biofuel/chemical production.
One method of capture is outlined here. During combustion, fossil fuel reacts with oxygen of the air, producing CO2 and H2O. The product, which also contains nitrogen (from the air), is added to a solvent that only dissolves CO2. Heating the solvent boils off the CO2. This is compressed to a liquid and transported via pipeline or tanker to a site for injection deep underground into a porous rock layer containing a saline aquifer. This resembles a solid sponge with absorbed salty water. (See figure Principle of CCS.) Sometimes present is a depleted oil or gas reservoir‑‑a local region within saline formations where hydrocarbons fill most of the pore space between the rock grains. Injected CO2 dissolves in the saline or displaces the oil/gas, which can be pumped to the surface, offering a means of recovering oil and gas in a carbon-neutral way. An impermeable cap layer covers the porous rock, preventing leakage of CO2. Various methods are under research to prevent leakage through cracks that may develop in the cap rock. Some rock formations contain metal oxides that combine with CO2 to form carbonates, permanently locking in the carbon.
Globally, four commercial-scale storage projects involving oil/gas reservoirs are in operation—two in the North Sea. No significant leakage of CO2 has been detected in the monitoring of these sites (Myer, 2011). Durham Energy Institute is researching the prospect of using CO2 from industrial processes on Teesside to extract the remainder of the oil from depleted North Sea reservoirs, leaving behind the CO2 in the process.
BELLONA CCS WEB: Introduction to CCS http://bellona.org/ccs/. The five-minute video provides a clear explanation of CCS principles.
Myer L (2011) Global Status of Geologic CO2 Storage Technology Development. The US Carbon Sequestration Council. http://www.iea-coal.org.uk/publishor/system/component_view.asp?LogDocId=82579&PhyDocID=7892
Durham Energy Institute: http://www.dur.ac.uk/dei/research/geoenergy/
11 September 2011