Role of Organic Additives and pH on the Wet Absorption Process for SO₂ Removal in Flue Gas

In this study, to explore the effective conditions and methods for SO2 removal from flue gas, a CaCO3 absorbent and various additives were used to investigate the pH changes and removal efficiency of SO2 from aqueous solutions. Desulfurization performance was investigated using the CaCO3 absorbent concentration and additive type as variables. CaCO3 was dissolved in an appropriate pH range to produce HCO3– ions to provide a buffering effect for the H+ ions generated via its reaction with SO2 in an aqueous solution. This process extended the absorption duration of the SO2. With a higher CaCO3 concentration, the alkalinity of the absorption solution remained longer and the SO2 removal efficiency and absorption duration were higher. Organic acids, such as acetic, adipic, and citric acids, and the organic salts of sodium acetate, magnesium acetate, potassium acetate, and calcium acetate were used as additives. The removal efficiency of the additives in the SO2 absorption reaction was as follows: citric acid < adipic acid < no addition < acetic acid < potassium acetate ≤ magnesium acetate ≤ sodium acetate ≤ calcium acetate. Organic acid additives lowered the initial pH of the absorption solution and effectively promoted CaCO3 dissolution. The chemical buffering system using metal acetate salts exhibited a high SO2 absorption performance with a gradual decrease in pH. Additionally, experiments were conducted using a simulated flue gas whose composition was similar to that of actual flue gas. The HCO3– from CO2 increased the SO2 removal efficiency and absorption duration owing to a buffering effect. This study demonstrates the potential of a system capable of long duration absorption of low-concentration SO2 and confirms that the presence of calcium acetate and CO2 enhances SO2 removal capacity in desulfurization processes.