Alkali refining differentiates between chemical refining and physical refining process. Free fatty acids present in the oil are removed during the alkali refining process. Free fatty acids present in oils are neutralized by a strong base (alkali) followed by removal of soap stock and precipitated NHP by centrifugal separation. Overall steps involved in alkali refining are gum conditioning, alkali neutralizing, water washing or silica adsorption and vacuum drying.
Kumar offers two types of technologies for alkali refining:
In short mix degummed oil is heated and conditioned with phosphoric acid or citric acid, and caustic lye is added. This causes free fatty acids to react with the sodium hydroxide (caustic lye) forming soap stock, which is then removed by centrifugation. Neutralized oil still contains traces of soap. Water washing is carried to remove these traces of soap.
Oils with high non-hydratable phosphatides require longer residence time for reaction, especially soybean and rapeseed as well as oils with higher free fatty acids. The extended mix process is specially designed to address this problem. High FFA oils require more substantial concentrations of caustic soda and longer residence time to complete the reaction. Neutralization is effectively carried out by caustic. The soap formed also carries away other impurities including colour pigments and trace metals during centrifugation.
Controlled Flow Cavitation (CFC)
The system utilizes jet compression and decompression principles to generate cavitation in a controlled environment to separate the heavy phase from the lighter phase. The effect of cavitation is improved dispersion and decreased consumption of phosphoric acid, caustic soda and water in the degumming and neutralization processes. This CFC™ technology by Arisdyne Systems is a novel yet proven technology and added benefits of increased oil yield in refining systems.
Alkali refining is used for sunflower, rapeseed and soybean oils.
Water degummed oil is heated and conditioned with phosphoric acid or citric acid to remove non-hydratable phosphatides by providing optimum retention time and separated with soap stock. This pretreatment process is also used before bleaching of oils like palm and palm kernel oils during the physical refining process.
For low-quality oils or oils with FFA of more than 0.1%, neutralization is carried out after gum conditioning to maintain oil output quality. Gum conditioned oils are treated with caustic soda in a conditioning reactor for a short time where free fatty acid converted into soap stock & thus non-hydratable phosphatides and soap-stock form a heavy phase, and separated in a centrifugal separator.
WATER WASHING / SILICA ADSORPTION
Neutral oil from the centrifuge is mixed with hot water to remove the remaining soap from the oil. Water washing is replaced by silica adsorption in the areas having stringent environmental norms. Silica adsorption reduces the load of effluent treatment plant. It ultimately results into lower processing cost.
Washed oil is sprayed through a specially designed nozzle in a vessel which is under a vacuum of 60 torr. The oil is dried continuously in the vacuum drier and sent for further processing.
- Atmospheric reactor with variable retention time and agitation to optimize both degumming and neutralizing processes.
- Temperature control at each step of the process.
- Conditioning reactor ensures maximum precipitation of non-hydratable gums.
- Neutralization tank acts as a buffer to dampen flow fluctuation during separator discharge resulting in reduced oil loss
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