Sorption Behaviors of SO₂ and NH₃ Gases on Sewage Sludge Char

Abstract

The sorption behaviors of SO₂ and NH₃ gases on sewage sludge char were investigated using a commercial thermodynamic equilibrium calculation software and lab-scale fixed-bed reactor in order to develop the desulfurization and deodorization technologies in the new energy saving sludge treatment system combining with bio-drying and carbonization technologies. The enthalpy change of the neutralization reaction of SO₂ with NH₃ (SO₂ + 2NH₃ + H₂O + 1/2O₂ = (NH₄)₂SO₄) was calculated to result in being a lower enthalpy change with a lower temperature. The results show in the thermodynamic equilibrium state of 2SO₂, 4NH₃, 2H₂O, and O₂ to form (NH₄)₂SO₄ as solid-phase species under the conditions from 0 to 200 °C. The gas activation of the char and a longer space time of SO₂ and NH₃ gases in the char increased the sorbed amounts of the gases into the char. The molar ratio of NH₃ to SO₂ in a feed gas to be 2, which is the stoichiometric molar ratio for the formation of ammonium sulfate, was the better condition for the gas-phase reaction and gas sorption of SO₂ and NH₃ gases into the char.