Regeneration protocols for fixed bed reactors deactivated by coke

Coked catalyst in fixed bed reactors is regenerated by passing hot air mixed with a non-reacting diluent (like steam). The concentration of oxygen in the regenerating stream is increased from the beginning of the regeneration following a so called regeneration protocol, in order to minimize the regeneration time but still maintaining the maximum temperature within the reactor below permissible level. In this paper, we have modelled the low temperature regeneration in fixed bed reactors and have suggested general regeneration protocols, suitable for wide range of process conditions. A pseudo-homogeneous model is developed to simulate regeneration of fixed bed reactors. The model accounts for major industrially important issues like, non-uniform coke deposition along the reactor length, hydrogen content (with faster burning of hydrogen) of coke and incomplete combustion of coke. Detailed qualitative understanding of the regeneration process and the role of protocol is developed. Specific guidelines were evolved and discussed to aid process engineers to select better regeneration protocol. One worked example of regeneration of fixed bed reactors is included.