Absorbent system and method for capturing cofrom a gas stream

Abstract

The present invention relates to an absorbent, an absorbent system and a process for removing acidic gas such as COfrom exhaust gases from fossil fuel fired power stations, from natural gas streams, from blast furnace oven off-gases in iron/steel plants, from cement plant exhaust gas and from reformer gases containing COin mixtures with HS and COS. The liquid absorbent, a mixture of amine and amino acid salt is contacted with a COcontaining gas in an absorber and COin the gas stream is absorbed into the liquid. The absorbed COforms more than one type of solid precipitate in the liquid at different absorption stages. In a first absorption stage solid precipitate of amine bicarbonate is formed and is withdrawn as slurry from the bottom of a first absorber section. In a second absorption stage solid precipitate of alkali metal bicarbonate is formed and withdrawn as slurry at the bottom of a second absorber section. The slurry withdrawn from the first absorption section is heated to dissolve the precipitate with COrelease in an amine flash regeneration tank. The slurry from the second precipitation stage is withdrawn from the bottom of the second absorber section and sent to a regenerator for desorption with COrelease. The lean amine and amino acid salt mixture from the flash regenerator and desorber are mixed and returned to the top of the absorber. This absorbent system improves carbon dioxide removal efficiency due to its higher COremoval ability per cycle when compared with conventional amine, absorbent from organic acid neutralized with inorganic base and carbonate based absorbent system. It exhibits less solvent vaporization loss because part of the absorbent is in salt form.