Oil is extracted from the seeds
by using press and expeller. However this method leave too much of the
high value oil in the seed cakes. To avoid this loss of oils, solvent
extraction method for oil was developed. The solvent extraction process
is a complex process and great precaution need to be taken during the
process.
The capacity and the size of plant depends upon the volume of
extraction. The extraction of solvent is done by using two process :
- Batch Solvent Extraction
The features of batch solvent extraction plant are :
- Batch solvent extraction is suitable for small scale
extraction.
- The extraction plant has enclosed steel tank with bottom
made up of screen or metal.
- The flakes are placed in the bottom where they are flooded
with solvent.
- Solvent remains in contact with the seed for few minutes.
The drain valve at the bottom finally completes the extraction.
- The introduction of steam in the bottom evaporates the
solvent out of flakes.
- Both steam and solvent is transferred into the condenser in
form of vapor.
- Solvent are lighter than water hence it is easily separated
from water.
- The wet flakes which are nearly solvent free are dried and
processed further to make it a solvent free.
- Continuous Solvent Extraction
The features of continuous solvent extraction plant are :
- Continuous extraction process uses either conveyors inside
vapor-tight housings or vertical columns filled with solvent.
- Using vapor lock or seal, flaked seeds are conveyed
continuously into the extractor. Vapor lock prevents solvent
vapors from escaping out of the extractor into the flake
conveyor.
- As the flakes enter the extractor they are sprayed with
miscella, and receive several washes with successively more
dilute miscella.
- The miscellas after being drained out of the flakes and
sieves go into into pans, which drain into pumps.
- The solvent miscella with the highest oil content, contacts
the fresh incoming flakes. The final wash uses oil-free hexane.
The flakes are then drained and dropped from the belt or the
basket into a spent-flake hopper.
- Mass-flow conveyor lifts the still solvent-wet flakes from
here and delivers them into a desolventizer-toaster. Here the
moisture content is brought down.
- As in the batch extractor system, the solvent vapors flow to
a condenser with water-cooled tubes, and the liquid solvent is
separated from the water by decanting.
- The next stage involves series of processing like drying,
washing, etc to obtain solvent free extraction.
