Mechanisms of Hot Spot and Erosion Occurring in FCC Reactor and Regeneration Units

Abstract In Fluid Catalytic Cracking (FCC) Reactor (Rx) and Regeneration (Rg) units, hot spot and erosion of shell, cracking and erosion of refractory lining are widely known as typical mechanical damages. In a refinery plant, hot spot and through-hole rupture of shell, cracking and erosion of refractory lining were detected in the flue gas line of FCC unit. It was found that several hot spots and severe erosion occurred around variable orifice valves. This suggests that those valves may lead to the change of flow in the flue gas line, which causes hot spots and erosion. CFD analyses were performed to investigate flow pattern around variable orifice valves in flue gas line for finding the causes of those damages. CFD analysis results show that a large low-pressure area is generated in the wake of variable orifice valve due to flow separation. Hence, a large secondary flow (vortex) is formed in the wake. As a result, catalyst particles from the upstream are also sucked into the large secondary flow and then impinge against the refractory lining. Consequently, refractory lining is eroded. Also, it was found that cracks through refractory lining were generated at low-pressure secondary flow area and the downstream high-pressure area. Thus, it is suggested that a bypassing flow path is formed through the cracks and the narrow gap between shell and refractory lining. The hot gas accompanied by catalyst particles flows near the shell. Therefore, both hot spot and erosion of shell occurs. Based on the mechanisms of occurrence of hot spot and shell erosion, it is important to suppress cracking through refractory lining around orifice valves and enhance the resistance of refractory lining to erosion. The understanding of the mechanisms is very useful for planning the monitoring, inspection and taking the mitigation measures.