The CO2 absorber usually contains a wash section above an absorption section.
The absorber operates at atmospheric pressure, resulting in low gas densities and very large towers. Both sections are packed with FLEXIPAC® structured packing to minimize the tower diameter, which can be quite large based on the huge amount of flue gas to be treated.
The wash section removes any entrained amine from the treated flue gas, reducing expensive solvent make-up costs. In the lower section, CO2 is absorbed by chemical reaction with the solvent, and the packing provides surface area for this absorption to take place. The aggressive surface treatment on the structured packing helps spread the liquid and increase the mass transfer efficiency.
The solvent must be regenerated for reuse by heating to break the chemical bonds. The solvent recirculation rate is minimized to reduce the required regeneration heat load. This is also referred to as the parasitic heat load because it reduces the overall power plant efficiency. With a minimized solvent recirculation rate, any maldistribution of liquid or vapor can cause an equilibrium pinch and will result in higher CO2 slip than desired. The use of well-designed high performance INTALOX® liquid and vapor distributors will allow the use of lower solvent recirculation rates and result in less energy used for regeneration.