Appeal No. 1996-3491
Application 08/213,347
unrecovered volatile hydrocarbons typically pass with the
spent catalyst into the regeneration section wherein they are
combusted in preference to the coke on the spent catalyst, and
this results in the exhaustion of the oxygen in the air in
localized areas, e.g., where the spent catalyst and volatile
hydrocarbons enter the regeneration section. Because such
localized areas in the dense phase catalyst bed are
essentially starved of oxygen, carbon monoxide, rather than
carbon dioxide, is formed by the combustion of the coke in the
dense bed. The carbon monoxide thus formed in these localized
areas passes from the dense catalyst bed into a dilute
catalyst phase (regenerator vapor region) where it may react
with oxygen in that region to cause “afterburning” with the
concomitant generation of heat and substantial increase in
temperature in the regenerator vapor region to such an extent
that the catalyst is again deactivated. See Luckenbach at
column 2, lines 2-59. Accordingly, “afterburning” produces
undesirable regions of excess heat in regions of low catalyst
density zones and detrimentally affects the regeneration of
the catalyst and risks mechanical damage of the regenerator
vessel (specification, page 2, lines 21-24).
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