Corrosion of oxide bonded silicon carbide refractories by molten salts in solid waste-to-energy facilities

Oxide bonded silicon carbide refractories are used successfully in solid waste-to-energy facilities (WtE). They are submitted to severe thermo-chemical stresses that limit their performance. Even if the corrosion resistance of silicon carbide is high, wear and failure of refractory lining are currently observed.For a better understanding of corrosion mechanisms, oxide bonded silicon carbide refractories, collected in the combustion chamber of several WtE facilities, were examined. The main mechanisms of corrosion, according to the environment of refractories, were determined. The chemical composition and the nature of the corrosive agents were calculated from the thermo-chemical modeling. They are mainly condensed phases of sulfates and chlorides (CaSO₄, K₂SO₄, Na₂SO₄, KCl, and NaCl). In service conditions, these molten salts react with the SiC aggregates and the matrix of the refractories to form low melting compounds.The post-mortem analyses showed the formation of para-wollastonite in the porosity and around the SiC grains, on the hot face of refractory tiles. Other phases such as cristobalite and microline (KAlSiO₈) were also formed down to the core of refractories. The volume expansion created by the formation of new mineral phases (cristobalite, para-wollastonite) causes the formation of micro cracks in the refractory lining.In this paper, the degradation mechanisms of oxide bonded silicon carbide refractories are presented and the main research developments for the future are discussed.