One. Unbalanced feeding and discharging, too much pallet material, and the temperature of the tower kettle can't go up. Top pressure drop, top temperature drop.
Two. Poor heat control, large evaporation, and a lot of materials condensed on the tray are also the results.
Solution: Stop feeding, or stop heating and add it back, or just put it once.
It's not always the fog. Or is the defoamer not effective enough? There is still a big gap between design and operation, so we should explore more.
Seeing that the liquid level in the bottom of your tower has changed so much, the change of heat exchange can be determined.