Comparative study of chemical absorbents in postcombustion CO2 capture

In order to reduce CO2 emissions from a power plant, CO2 can be captured either from the syngas that is to be burned or from the flue gases exiting the energy conversion process. Postcombustion capture has the advantage that it can be applied to retrofit existing power plants. In this paper the authors compare two primary amines (MEA and DGA) to ammonia with respect to their capability to capture CO2 from a flue gas stream. The ammonia process captures CO2 by formation of stable salts, which are separated from the solvent stream by filtration or sedimentation. These salts can be used commercially as fertilizers. Energy requirements are greatly reduced, since no heat is required for solvent regeneration, and no compression of the separated CO2 is necessary. Energy, however, is required for the reduction of ammonia emissions. In order to obtain the solid ammonia salts, their solubility has to be reduced by modification of the solvent and by lowering absorption temperature. With and without separation of the salt products, ammonia proved to be an alternative solvent with high CO2 removal efficiency. Simulation of all processes was carried out with Aspen Plus® and compared to experimental results for CO2 scrubbing with ammonia.