Total Liquids Incoming to Slops Wax Tray

[qazx]

In some vaccum towers(specially in the packed towers) total liquids incoming to Slops Wax tray(I mean the first tray above the flash zone) is too high that this tray is already full of liquids and liquids over flow from tray's down-pipes or chimneis are there.
Is it usual?Has anyone measured total liquid incoming to Slops Wax tray for a totally draw-off operation(no over flow)?If yes,what is its percentage based on the tower feed?

 

[25362]

This washdown liquid is called overflash in the refining jargon, and represents 2-5% on the feed to the column. To maximize vacuum gas oil product this stream (resulting from reflux) is minimized to the point that the VGO contains non-volatile asphaltenes (usually measured by color) that make it inadequate for further FCC processing.

This "overflash" liquid is either added to the bottom asphaltic bitumen, or the fuel oil pool, or is sent back to the heater to be recycled to "extinction" i/o to maximize the VGO offtake.

Chimney trays collecting these liquids must be carefully designed. On this subject I suggest you pay a visit to Distillation -Operation- by Henry Z. Kister (McGraw-Hill).