Stupid question. Have you tried to blow it back into the column with steam? And I question the safety of performing that task as it could potentially cause problems with your bottoms pump if you sluff off a big chunk of coke. I would guess a six month window. . .but guessing is exactly all you can do. You could proactively reduce charge rate and reduce the amount that you fill the drum so as to reduce the amount of particles entrained. Or, you could reduce cycle time at the same charge rate to reduce the amount the drum is filled. Perhaps these options could buy you more time.