31a.3 Functional role of various processes (Figure 31.1) :

(a)  Cleaner and dehulling:

• • Mechanical cleaning is done to remove stones and other undesirable material.

• Dehulling remove hulls, dry outer covering of seed.

(b)  Cracking rolls:

• • Crushing rolls crush the oil seeds and gets flacked seeds.

(c)  Digester:

1. • 100 parts of flaked seeds are thoroughly mixed with 5-10 parts of water by rotating blades.

• Softening by means of heat and moisture is done here.

• Steam is added for heating purpose.

• Acid is formed by hydrolysis of ester.

• The seeds get swollen up.

(d)  Expeller:

• • The swollen seeds are crushed under great pressure.

• Cells of seeds get ruptured and oil is released.

• The tapering shape ensures more application of pressure on the seeds.

• The oil depleted cake is either sent for solvent extraction or used as animal feed.

• Oil is sent for purification.

(e)  Mix tank:

• • The extracted oil is treated with alkali like NaOH or Na₂CO₃ to remove fatty acids.

• It also removes heavy metals, which can start oxidation of oil.

(f) Centrifuge:

• • Acids are separated in centrifuge separator.

• These separated acids are used as foots for soap manufacturing.