9. Catalyst Regeneration in Fluid Catalytic Cracking

Abstract

Catalytic cracking is one of the most important refinery processes, in which a hot heavy oil feed, such as virgin gas oil, coker gas oil, or residual oil, is brought into intimate contact with catalyst particles to convert it into valuable light oil and olefinic gas products. To maintain the catalyst activity at a useful level, and to supply the heat needed for vaporizing and cracking the feed, it is necessary to regenerate the catalyst by burning off this coke with air. The fluidized catalysts are circulated continuously between a reactor and a regenerator and acts as a medium to transfer heat from the latter to the former. To maintain high equilibrium catalyst activity and to reduce fresh catalyst makeup, the trend is to increase carbon burning intensity (CBI) and to decrease carbon content of the regenerated catalyst (CRC), to minimize catalyst inventory in the reactor–regenerator system. To this end, the superiority of fast fluidized bed (FFB) regeneration has become quite evident. Reductions in residence time lead to a smaller catalyst inventory in the reactor-regenerator system, and consequently much lower catalyst deactivation rates due to hydrothermal effects. A lower catalyst inventory has also the additional operational advantage that the fluidized catalytic cracking units (FCCU) can respond more quickly to changes in catalyst management. The FFB operates with high gas velocity and high solid mass flow rate as compared to the ordinary turbulent bed. It also exhibits unique axial and radial profiles for voidage, temperature and carbon concentration.