Numerical Analysis of Particle Uneven Distribution at Riser and Deposit Phenomenon at Cyclone in RFCC Reactor

Abstract

One of the main problems associated with reactors in commercial Residue Fluidized Catalytic Cracking (RFCC) process in refinery plant is that each of six outlets of the riser has different particle mass flow rates. This phenomenon causes particle uneven distribution and catalyst loss. High conversion of cracking reaction requires uniform catalyst distribution in the riser. The riser termination device (RTD) is installed to reduce product gas residence time and achieve rapid separation between catalysts and product gas. RTD is made up of six close-coupled cyclone sets at the top of riser. Also, particle deposit formation in the cyclone duct has caused shutdown problems as well as a decrease of the cyclone efficiency. This study analyzes flow pattern of catalyst particles in the riser and the cyclone. Moreover, particle mass flow rates are investigated at each outlet by the number of feed injector. The cracking reaction is taken into account in the simulation scheme and its conversion is evaluated in the riser by employing multiphase-particle in cell (MP-PIC) method, one of computational particle fluid dynamics (CPFD) methodologies. It applies both a stochastic particle model and Lagrangian method for particle phase, and Eulerian method for fluid phase, respectively. Mass flow rates at the outlets of riser are different from each outlet from 107.8 kg/s to 144.1 kg/s, which means solid loading ratio for certain cyclones increased. The solid loading ratio affects the cyclone separation efficiency. As a result, particle uneven distribution flow was identified. Standard deviations of particle mass flow rate at the 4-injector riser case and 6-injector riser case represent respectively 11.3 and 8.8. So, this article suggests that particle uneven distribution will be alleviated by using 6-injector riser than 4-injector riser.