Capture

CO2 produced by power plants or refineries can be separated from the flue gases by means of physico-chemical processes, concentrated and compressed, and then transported by pipelines, in super-critical conditions, from the plant to the storage point, where it is injected underground in suitable deep and permanent natural deposits.
Currently available technologies can reduce CO2 plant's emissions by 85 to 95%.

During the electricity generation processes - even according to the technology and the plant power system - CO2 can be separated from the other effluents with different approaches, including:

  • pre-combustion
  • post-combustion
  • oxy-combustion


Pre-combustion

CO2 separation before combustion seems to be the most promising solution in the medium to long term. Primary fuel is subjected to a gasification process (solid or liquid fuels) or reforming (natural gas), with the production of a fuel synthesis gas (syngas) composed essentially of CO, CO2, H2 and H2O. The syngas is then subjected to different treatments of purification and subsequently to a process of conversion of CO into CO2 by reaction with water vapor (water - gas shift reaction, WGS), with further production of hydrogen. The thus obtained mixture consists essentially of carbon dioxide and hydrogen, which are then separated.

Post-combustion

Carbon dioxide separation from the flue gas is of particular interest for the retrofitting of existing plants. CO2 removal is generally based on natural gas absorption processes with chemical solvent, already experienced in the petroleum and chemical industries. The separation processes, however, are characterized by high energy absorptions and are quite expensive and complex.

Oxy-combustion

It is a technology widely studied for coal, which burns in oxygen: is thus obtained a mixture of CO2 and water vapour, which can be easily separated. With reference to the only section of CO2 removal, this is the simplest approach, but is overall affected by high energy costs for the production of oxygen which, at the moment, is almost exclusively based on cryogenic air separation processes.