How is catalyst regenerated in fixed bed and fluid bed processes?

Fixed bed regeneration: In-situ (reformer, hydrotreater) - controlled combustion of coke with dilute oxygen/nitrogen mixture at 400-500C, followed by redispersion and reduction. Sulfur removed by oxidation to SO2. Sequence: deoiling, coke burn, oxychlorination (reformer), reduction. Ex-situ - catalyst removed and sent to regenerator facility for severe treatment. Fluid bed (FCC): Continuous regeneration - spent catalyst flows to regenerator where coke burned with air at 650-730C, heat released heats catalyst for reactor. Two-stage regeneration: full combustion in second stage for low carbon on regenerated catalyst. Regenerator variables: temperature (higher = lower carbon but potential damage), air rate, catalyst circulation. Catalyst loss from attrition replaced by fresh catalyst addition.