Removal of CO₂ from flue gas with ammonia solution in a packed tower

Ammonia was used for the major absorbent while sodium hydroxide was used as a reference in either a bubble column (semi-batch reaction) or a packed tower (continuous reaction) to absorb CO₂ in this study. In the bubble column, bubbling time as a function of temperature, pH, and dissolved inorganic carbon concentration in the solution was measured to see the characteristics of the reaction and the capacity of ammonia with regard to CO₂ absorption. Its CO₂ removal efficiency (RE) and/or absorbent utilization (AU) in the packed tower were quantified as a function of packing type, concentration/pH of absorbent, concentration of simulated flue gas (CO₂, O₂, SO₂, NO), gas flow rate, and liquid/gas ratio. Additionally, an empirical formula obtained, via the analysis of a multiple regression, was used to relate CO₂ RE and the major operation parameters. In the bubble column, the capacity of ammonia on CO₂ absorption is 1.4 kg CO₂ kg⁻¹ NH₃ in an exothermic reaction. In the packed tower, the optimum number of packing layers is 21 layers in an orderly arrangement with a reaction length of 220 mm. In addition, the optimum CO₂ RE and AU are 93 and 19%, respectively, at a given condition. After a multiple regression, the empirical formula indicates four major parameters responsible for CO₂ removal, namely ammonia concentration, CO₂ concentration, gas flow rate, and initial pH of ammonia solution. The results of this work are feasible for practical application with regard to CO₂ absorption with ammonia in a packed tower.