Located in the preheat train of the distillation column, a preflash drum system separates the vapors generated by preheating before entering the heater or main column. This prevents higher heater firing or pressure drops and reduces vapor loading of the column to avoid flooding.
Preflash drums create moderate foam that can affect measurement accuracy of liquid levels and decrease distillate production in the atmospheric column. Too low of a preflash drum level will cause pump cavitation of the flashed crude. Too high of a level will cause liquid carryover to the distillation column.