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

Abstract

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.