Post-combustion capture

Post-combustion capture refers to the removal of carbon dioxide (CO2) from a power station flue gas prior to its compression, transportation and storage in suitable geological formations, as part of carbon capture and storage. A number of different techniques are applicable, almost all of which are adaptations of acid gas removal processes used in the chemical and petrochemical industries. Many of these techniques existed before World War II and, consequently, post-combustion capture is the most developed of the various carbon-capture methodologies.

Post-combustion capture plant should aim to maximise the capture of CO2 emissions from combustion plant and delivery it to secure sequestration in geological strata. Typically, a plant will aim to achieve a CO2 capture rate of >95%. To meet the required specification, the following should be monitored:


 * CO2 mass balance
 * CO2 in fuel combusted
 * Total CO2 capture level (as a percentage)
 * CO2 released to the environment
 * CO2 quality

CO2 can be transported either as gas phase at about 35 barg or as dense phase at 100 barg. The CO2 stream should meet or exceed gas quality standards.

CO2 absorbents include primary amines which require more heat for regeneration than secondary amines However, secondary amines may form nitrosamines with Nitrogen oxides NOx in the flue gases. All non-solvent constituents must be removed from the solvent. Pilot or full-scale tests using actual flue gases and solvents may be performed.

Calcium looping is a promising second generation post-combustion capture technology in which calcium oxide, often referred to as the "sorbent", is used to separate CO2 from the flue gas. The ANICA project focuses on developing a novel indirectly heated carbonate lopping process for lowering the energy penalty and CO2 avoidance costs for CO2 capture from lime and cement plants.