Nano-bonded fused silica castable for application on fluid catalytic cracking unit riser

Fused silica aggregate shows interesting properties for the development of castables for the riser section of fluid catalytic cracking units (FCCU). Its low apparent density and reduced thermal conductivity can lead to a lightweight refractory structure and a higher thermal efficiency of the process, respectively. The fused silica linear expansion coefficient is very low (0.55 x 10^-6/ºC), allowing an excellent thermal shock resistance. Nevertheless, for the riser environment, these characteristics must be coupled with a low erosion loss. Therefore, a fused silica nano-bonded castable was developed in order to attain a high-erosion resistance. Two compositions containing fused silica and tabular alumina aggregates were evaluated. It was found out that the stress generated by the thermal expansion mismatch between the two sorts of aggregates induced the crack formation, decreasing the material materials' thermomechanical properties. A lower mechanical damage was attained by adding tabular alumina in the finer aggregates grain size. Adding a sintering additive, that induces a higher densification at low temperatures, the erosion and thermal shock resistances were also improved. The mean value of erosion loss obtained after firing at 815 ºC was 4.8 cm³. This result was very promising in comparison with the erosion loss specified by the Brazilian petrochemical industry (6 cm³⁾ for high-alumina refractory products with apparent density higher than 2.60 g/cm³. The developed fused silica nano-bonded castable seems to be an excellent choice for the riser section of fluid catalytic cracking unit application.

fused silica; thermal expansion mismatch; nano-bonded castables