Formation and Characterization of Deposits in Cyclone Dipleg of a Commercial Residue Fluid Catalytic Cracking Reactor

Deposits in the cyclone dipleg of a commercial residue fluid catalytic cracking (RFCC) reactor, which are one of the primary problems causing abnormal shut-down of RFCC, were characterized using an analytical approach in order to understand the formation mechanism of the deposit. The main components of the deposits are hydrocarbons and a high portion of inorganic matter, reflecting dipleg conditions with particle flow. The deposit consists of two parts of massive bulk matter which are mainly pure Sb metal and catalyst particles surrounded by filamentous cokes and lumps of carbonaceous matters. Nickel nanopowders on the catalyst surface and from heavy oil in vapor phase catalyze the filament coke, which accelerate the increase in the amount of deposits by filtering heavy oil droplets. The Sb metals, originated from injected Ni passivator in the riser, contribute largely to deposit formation, and this is validated by a simulation of RFCC conditions and a calculation of cyclone collection efficiency. Possible mechanisms for the deposit formation and methods for the reduction of the deposits are proposed.