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rupture under compressive forces generated by the contact between adjacent tiles (Figure 6).


Burnout material (wax, bitumen or plastic cap)


Tube Wall


Tapered Edge: For easy backfilling


Threaded bolt with round washer


Straight Joints: Allow for easy cleaning


Wide Anchore Groove: For fast


adjustment when installing


Figure 3: Typical tile design – Saint-Gobain T-Clip Pro


Backfilling mix (Refrax® PLUS flow)


Fibre gasket


In the case of SiC refractories, 3


main types


: 1) Passive oxidation, 2) Active oxidation 3) Deposit-induced corrosion by molten salts. Other mechanisms probably also exist, but are not yet well understood due


widely in the literature [3], [4], [5], [6], [8]


to their complexity and


sensitivity to random variation from incinerator to incinerator.


In oxidizing atmospheres, SiC and Si3


N4 process, are known to form a


protective scale of silica or silicon oxy-nitride. This


called


passive oxidation, corresponds to the following reactions:


[a] SiC(s) + 2O2(g) [b] Si3 [c] 2Si3


N4(s) N4(s) → SiO2(s) + 3O2(g) + 3/2O2(g) + CO2(g)


→ 3SiO2(s) → 3 Si2


+ 2N2(g) N2


O(s) + N2(g)


However, depending on the environment temperature, the silica formed can be found as amorphous or crystalline (cristoballite, quartz or tridymite) phases. The formation of silica inside the material microstructure can lead to non-negligible volume expansion of the refractory (Figure 7). As a consequence, tiles may touch each other and fail due to cracking or to anchoring system fatigue.


Figure 4: Refrax® PRO tiles with mortar - 8000 eoh 1


Figure 6: Typical expansion issues in WtE units


of corrosive degradations have been reported


Technical Paper


Figure 5: Refrax®


PRO tile without mortar - 8000 eoh Refractories corrosion issue in WtE units


Flue gases and ashes produced under several forms during the process condensate and/or penetrate the refractories through the porosity and can cause reactions with its constituents. In most of the cases, these reactions lead to a significant volume expansion. Combined with thermal stresses caused by temperature fluctuations or thermal gradient; an excessive expansion of the refractory parts would lead to material failure, cracking or


1 Eoh = equivalent operational hours January 2019 Issue ENGINEER THE REFRACTORIES 19


Figure 7: Thermal expansion of Silicon Carbide, amorphous SiO2 SiO2 as a function of the temperature


and crystalline


In atmospheres with low oxygen partial pressure and possibly with high velocity gas flows, active oxidation may occur by forming volatile silicon components [5]


via the following reactions: [d] SiC(s)


+ 2H2 [e] Si3 N4(s) O(g) + 3H2 → SiO(g) O(g) + CO(g) → 3SiO(g) + 2H2(g) + 2N2(g) + 3H2(g)


. In this case, the material microstructure can be weakened


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