Void properties in dense bed of cold-flow fluid catalytic cracking regenerator

Abstract

Fluid catalytic cracking (FCC) processes have been used widely in petroleum refineries. FCC regenerators play important roles for maintaining catalyst activity and supply the reaction heat. The regenerator efficiency is mainly connected to the hydrodynamics of the fluidized bed, because the gas and solid behaviors are very important factors in mass and heat transfer. The void properties, such as chord length, rising velocity, frequency, and fraction, have been determined in a large cold flow model (0.48 m-ID × 6.4 m-high) of the FCC regenerator, which was geometrically scaled down from a commercial FCC unit. The local void chord length, rising velocity, frequency, and fraction exhibit their maximum value along the radial direction of the bed. The cross-sectional mean void chord length, rising velocity, and fraction increase and the cross-sectional mean void frequency decreases with height in the bed. The variation of void properties in the FCC regenerator with turbulent fluidized bed exhibit similar trends to those in a bubbling fluidized bed. The void properties in the FCC regenerator have been correlated with the experimental parameter on the basis of bubbling bed concept. The predicted void velocities based on the correlations agreed well with the experimental data from present and previous studies. A modified bubbling fluidized bed model could describe the void properties in the regenerator operated in turbulent fluidized bed regime.