Reboiler and Condensers (i) Reboiler temperatures should be kept low enough to avoid bottoms degradation and/or fouling. (ii) Common temperature differences used for heat exchange across reboiler and condensers are shown in the following Table . The liquid mixture that is to be processed is known as the feed and this is introduced usually somewhere near the middle of the column to a tray known as the feed tray. The feed tray divides the column into a top (enriching or rectification) section and a bottom (stripping) section. The feed flows down the column where it is collected at the bottom in the reboiler.