Degumming
Degumming is the first operation in refining. The Degumming process consists of a mere hydration of the crude oil. Certain impurities like phospholipids, gums and proteins are soluble in oil in their anhydrous form, but insoluble once they are hydrated. This is how the hydratable phospholipids are removed from the oil. Part of the constituents however remain in the oil, and an acid treatment is needed to remove them.
Water degumming is more generally carried out in the extraction plant rather than in the refinery, lest foots should conglomerate in the crude oil intermediate tanks.
The aqueous phase obtained after degumming separation is recirculated into the meal stream of the toaster. Should lecithin be of significant commercial value, it can be dried separately.
Bleaching
Bleaching is the process operation which is carried out before deodorisation.
In addition to colouring matters, the bleaching treatment using actived earth will remove residual phosphatides, metals, soaps and oxidation products.
Bleaching is performed in 3 stages :
Initial mixing of oil with bleaching earth under controlled conditions of temperature, acidity and humidity for a specific residence time.
Secondly the oil is heated under vacuum with sparge steam to ensure proper mixing with bleaching earth for a specific residence time.
Finally the mixture is pumped through hermetic leaf filters with stainless steel mesh elements followed by polishing filtration.
Spent cake is dried by steam blowing to remove the oil from the wet cake.