In Waste to Energy (WtE) incineration plants, SiC-containing refractory linings are commonly used to protect the first-pass waterwalls of the boiler from the high temperatures and the corrosive agents. The service life of the refractories (bricks, tiles or castables) located near the combustion area is particularly limited due to severe conditions. Besides the complex atmosphere (with among others chlorine and sulphur-containing gases, alkali-vapours, and heavy metals), an oxide slag layer is formed on the surface of the refractory linings. This slag, mainly composed of {SiO2-CaO-Al2O3}, is known for infiltrating the refractories and degrading them. 

The slag elementary composition is quite similar for all the municipal waste incineration plants, in spite of the variety of the waste input. The liquidus of the slag is typically in the range 1180-1280°C. A common practice to assess the corrosion resistance of a refractory material for the WtE industry is to perform static or dynamic corrosion tests, for which the refractory material is in contact with a synthetic or a real slag beyond 1250°C. However, operating data tend to indicate that the temperatures at the refractories surface are not so high. Moreover, a significant Na/K-enrichment near the fireside surface has been observed in post-mortem refractories, and the laboratory slag/refractory corrosion tests fail to explain this phenomenon. 

This constatation highlights the fact that the corrosion mechanisms of the refractories in the lower areas of waste incineration furnaces can not be totally reproduced without considering the complex atmosphere of these kinds of installations. Particularly, the alkali vapours seem to play an important role in the slag degradation mechanisms of refractories linings. 

For a better understanding of the possible degradation mechanisms, fifteen refractory castable references have been selected for corrosion tests. The castables were shaped into crucibles, and several corrosive reagents were introduced into these crucibles. The corrosive mixes were composed of oxides, alkali-salts or both. The composition affects the viscosity and the melting point of the mixes. After testing at 1100°C for 160 hours, the infiltration depth was measured and the refractory degradation assessed. FactSage thermochemical calculations complete the study. These tests have resulted in a ranking of the materials for the considered conditions and some typical degradation modes have been observed.