dear,
What could be the reason, if the temperatures of trays below the diesel tray is reduced. and all other parameters of column is almost same making Diesel Quality slightly heavy.
In my Crude distillation column, there are 51 trays, feed tray is 6. diesel withdraw tray s 13. and tray 8 and tray12 temperature is reduced sharply one night. after facing this problem, I have emptied out diesel trays thrice in order to remove flooding if that may be the reason. During emptying out temperature becomes normal but after normallizing column that tray 8 and tray12 temperature resetted to about 10 deg less than normal temperature.
if any further information is needed plz ask.