Abstract
Residue Fluid Catalytic cracking (RFCC) is a valuable subset of the more conventional Fluid Catalytic cracking (FCC) process that generates most of the world’s gasoline pool. The critical distinction of RFCC involves the processing of “dirty” atmospheric residue (AR) directly from crude distillation and not just the more conventional use of relatively pure gasoil feedstocks. By direct catalytic cracking of “dirty” residue the refiner benefits economically by avoiding a whole intermediate process, namely vacuum distillation. Unfortunately direct FCC processing of atmospheric residue (AR) exposes the vessel internals to geological salts naturally present in crude oil but concentrated in the residue fraction during the distillation process. Internals of regenerator vessels (cyclones, refractory anchors, hexmesh, and cross bracing) are typically manufactured in UNS(1) S30409, which is sensitive to corrosive low melting point eutectics. In the normal crude distillation process, metals are concentrated by approximately two-fold in AR. Thereafter coke formed on the catalyst particles is burnt off in a regeneration process leaving much higher quantities of metal salts in a high temperature environment between 720-800 °C. Chemical analysis of salt scabs covering deep pits show higher concentrations of Vanadium and Sodium which are consistent with low melting point eutectic corrosion. This article presents findings on type II high temperature (650-800°C) corrosion in RFCC regenerator service (alloy SS304H) and examines the possible strategies for alloy upgrade in RFCC service.
