Towards better understanding of temperature gradients in superheater corrosion

This paper presents a novel laboratory method for superheater corrosion experiments in which a temperature gradient is applied over the deposit and steel. Experiments using salt mixtures of NaCl/Na₂SO₄ or KCl/K₂SO₄ show alkali chloride transport (NaCl, KCl) within the salt layer, and to the steel surface. The alkali chloride is vaporized from the salt grains, transported down the temperature gradient, and deposited on surfaces with lower temperature. Mathematical model predictions show the governing transport process to be temperature gradient induced concentration diffusion, not thermal diffusion. The transport rate is species-dependent, with a greater transport rate of KCl as compared to NaCl. Further work is needed for a better understanding of the implications of temperature gradients for superheater corrosion in boiler environments.