A heat exchanger positioned near the bottom of the distillation column re-heats and vaporizes liquid and reintroduces the vapor several trays higher. This improves separation by introducing more heat into the column. For effective functioning of the reboiling process, level monitoring of the reboiler is required.
In some steam reboilers, the level must be controlled so that only a percentage of tubes are covered. This allows a control scheme to regulate the heat transfer in the reboiler by controlling the percentage of the reboiler tubes covered by liquid. This is a critical control loop as heat transfer into the liquid is a strong function of the percentage of tubes covered.