Comparative Study of Sorbents for Spray Dry Scrubbing of SO₂ from Flue Gases

This study presents the findings of an investigation involving the absorption of SO₂ from flue gases, using three different sorbents, in a spray dryer. Experimentation involved the evaluation of three sorbents, i.e., hydrated lime (Ca[OH]₂), limestone (CaCO₃), and trona (Na₂CO₃·NaHCO₃·2H₂O), and their relevant properties, for flue gas desulfurization by spray dry scrubbing. Experiments were conducted to explore the effects of spray characteristics in the spray drying scrubber on SO₂ removal efficiency using the selected sorbents. The ranges of various operating parameters were considered, including the stoichiometric molar ratio of (1.0-2.5), the inlet gas phase temperature of (120-180 °C), and an inlet SO₂ concentration of 1000 ppm. The use of trona gave better SO₂ removal characteristics; a high SO₂ removal efficiency of 94% was recorded at an inlet gas phase temperature of 120 °C and a stoichiometric molar ratio of 1.5. Under the same operating conditions, Ca[OH]₂ and CaCO₃ gave 82 and 76% SO₂ removal efficiency, respectively. Analysis of the desulfurization products by X-ray fluorescence (XRF) and Fourier transform infrared (FTIR) spectroscopy revealed the presence of CaSO₃/Na₂SO₃, a product of the semidry desulfurization reaction. A significant proportion of unreacted sorbent was observed when Ca[OH]₂ and CaCO₃ sorbents were used at a stoichiometric ratio of 2.0. Trona also gave the highest degree of conversion (96%) at a stoichiometric molar ratio of 1.0. Ca[OH]₂ and CaCO₃ gave 63 and 59%, respectively, under the same operating conditions.