Ka Lok/Joe Zmich (UOP LLC)

Assuming that the question relates to the inner screen of the chlorination zone of a UOP Atmospheric CCR regeneration section relative to the burn zone, the most likely cause of this is failing to operate the CCR regeneration section burn zone per the UOP General Operating Curve. If the catalyst circulation rate for given oxygen concentration exceeds the maximum indicated by the curve, it’s likely that catalyst with higher than desired coke will enter to the chlorination zone leading to catalyst damage. The damaged catalyst can be smaller and fracture into dust and chips in the chlorination zone leading to plugging of the chlorination zone screen.

Some licensees have observed an increased slot width in the chlorination zone after a long time in operation. An increase in slot width increases the tendency of the screen to foul with catalyst chips or smaller diameter catalyst.