The steam distillation process for extraction of essential oils from plant material consists of 4 basic parts.
The Steam Generator or Boiler.
Capable of producing saturated steam at pressures of 50 to 150 psi.The high pressure is required to raise the steam temperature above 100c (in the region of 150c.)
The Retort or Still
Contains the plant material.High pressure steam is passed in at the base into a void beneath a perforated grid wich supports the charge of plant material.The steam passes through the plant material heating and saturating it with water.The resulting vapour a mixture of steam and essential oil vapours (the oil is in the most part insoluable in water) passes out at the top and is conveyed to the condenser.
The vapours from the retort are cooled by passing down a long spiral or bundle of tubing cooled by being immersed in a flow of water.The condesate runs by gravity ino a container in which the oil and water separate by virtue of their differing specific gravities. This is the Separator
The mixture of condensed oil and water runs into the separator where the lighter insoluable oil floats on the surface and accumulates slowly and from where it is drawn off periodically.This is the Essential Oil. The water - or rather water containg the more water soluable constituents extracted by the steam, known as the hydrolat or 'floral water' - is drawn off continuously from the bottom of the separator
Images of destillers:
List of plants that you can distill: