Exploring the synergistic effect of NaOH/NaClO absorbent in a novel wet FGD scrubber to control SOx/NOx emissions

Escalating SOx and NOx emissions from industrial plants necessitates customized scrubbing solutions to improve removal efficiency and tackle cost limitations in existing wet FGD units. This work investigates the real-time intensified removal pathways via an innovative two-stage countercurrent spray tower configuration strategically integrating NaOH (M_a) and NaOH/NaClO (M_a/M_b) to remove SOx and NOx emissions simultaneously from the industrial stack through a comprehensive parametric study of absorbents concentration, reaction temperature, gas flow rate, liquid to gas ratio (F_L/F_G), and absorbent showering head. Flue gas stream comprising SO₂ bearing 4500 ppm, SO₃ bearing 300 ppm, 70 ppm NO, and 50 ppm NO₂ brought into contact with two scrubbing solutions as M_a, and a complex absorbent of M_a/M_b at varying respective ratios. Ninety-two percent SOx emissions were removed using 5% NaOH with double-stage scrubbing, while NO_x removal was observed below 50%. Adding NaClO facilitates additional "free radical (ClO^-)" chemical pathways for gases to react and decompose into ionic forms for easier solubilization so as to significantly enhance the removal capacities for both SOx and NOx compounds. NaClO oxidizer, along with NaOH, boosted the respective removal efficiencies of SO_x to 99.6% and 92% NO_x, proving complementary media integration advantages arising from staged exposure and bubbly interphase mass transfer phenomena. The customized synergistic effect of M_a and M_b promoted the development of an additional free radical oxidation route while sustaining the solubilization of SOx/NOx in caustic, driving toward fractional detoxification. A dimensionless emission performance model was developed along with mechanism validation through DFT in context to the successful formation of residual salts by applying the DMol3 tool in Materials Studio by exploring the convergence analysis, geometry optimization, and COSMO sigma profile.