Sulfur Chemistry and Its Role in Corrosion and Deposits

Sulfur in fuel oil and coal, and its resultant oxidation to SO₃ during combustion, is a recognized factor in corrosion and deposits. As a step toward controlling the formation of SO₃, and eventually controlling the conditions and rate of corrosion, a program has been undertaken under ASME support to establish, among other things, the mechanism by which sulfur compounds are oxidized to SO₂ and to SO₃ in flames. The present paper reviews some of the basic thermodynamics and reaction kinetics pertaining to the oxidation of H₂S and SO₂, and to the SO₂–SO₃ equilibrium. Included in the review are discussions of the stability of H₂S, the slow oxidation of sulfur vapor and of H₂S, the induction period (preignition) reactions leading to the fast, explosive oxidation of H₂S, and effects of additives on the explosion reaction. The heterogeneous (catalyzed) oxidation of SO₂ is discussed in terms of the effects of specific catalysts on the SO₂–SO₃ equilibrium.