Study on Sulfuric Acid Condensation on Planar and Particle Surfaces in Flue Gas by Thermodynamic Equilibrium Analysis

SO₃ in coal-fired flue gas causes equipment corrosion and sulfuric acid mist emissions. As the flue gas temperature decreases, SO₃ converts to gaseous H₂SO₄ and condenses with H₂O via binary heterogeneous condensation. Here, based on thermodynamic equilibrium theory, a model for H₂SO₄-H₂O binary heterogeneous condensation is developed and verified by comparing the calculated planar acid dew point (T_ADP,plane) with the previously reported experimental data. The equilibrium parameters of condensation on both planar and particle surfaces are investigated. On planar surface, T_ADP,plane increases with the gas concentration, while the equilibrium sulfuric acid mass fraction (ω_PE,plane) increases with H₂SO₄ concentration and decreases with H₂O concentration. For H₂SO₄ concentrations of 0.5-50 ppm and H₂O concentrations of 0.5%-15%, T_ADP,plane ranges from 356.37 to 426.67 K and the equilibrium sulfuric acid mass fraction (ω_PE,plane) ranges from 71.922% to 91.058%. The equilibrium parameters on micrometer particle surfaces are similar to those on planar surfaces, while on submicrometer particle surfaces, the acid dew point (T_ADP,particle) decreases and the equilibrium liquid film sulfuric acid mass fraction (ω_PE,particle) increases with decreasing particle diameter (d_p) due to the Kelvin effect. We found that T_ADP,particle/T_ADP,plane and ω_PE,particle/ω_PE,plane are barely unaffected by p_v,i and can be considered as a function of d_p. Based on the numerical results, formulas with good prediction accuracy for T_ADP,particle and ω_PE,particle are proposed. The results provide predictive models for acid dew points on particle surfaces, which are crucial for guiding strategies to mitigate corrosion and reduce sulfuric acid mist emissions in coal-fired power plants.