Edible oils that have very high content of fatty acids needs to be refined before using as cooking oil. The foremost propose of refining process is removing extra fatty acids and preventing the oils from oxidation. However, the refinery process isn’t only limited to remove fatty acids, it also removes the undesired components, color and odor which otherwise may have a negative impact on the taste, odor, and appearance of the product. The resultant oil is thinner without fatty acids, colorless and odorless. The following processes are followed in edible oil refinery plants.
Neutralization of crude oil by removing fatty acids: In this process the oil is neutralized in the neutralizer to remove the fatty acids by agitation with caustic soda (NAOH). Oil is heated up to about 60C by thermic fluid coils and oil is stirred by stirrer. The fatty acids are settled at the bottom as alkali soaps which is called soapstock from where it is taken out into soap pan.
Removal of impurities and color: Neutralized oil is passed through the second vessel called bleacher where color of oil is removed by bleaching process with the help of chemicals such as carbon black and bleaching clay. Oil is usually heated up to 110C by thermic fluid coils. Stirring is also carried on. Bleaching process is done under vacuum. Bleached oil then goes to filtration process where bleaching clay and chemicals are removed and cleaned.
Removal of unpleasant smell: Bleached oil is then passed through deodorizer where oil is heated above 110C through thermic fluid coils and then live steam clean is used to the oil from the bottom steam nozzles. The temperature of oil is raised up to 200 to 220C through thermic fluid coils. Entire process is done under high vacuum. Thus smell is removed from the oil in the deodorizer. Then it goes to cooler where cold water circulating coils take away heat and oil is cooled.
Micro filtration: Micro filtration is performed afterward cooling down oils temperature in cooler. This operation is carried out in a micro filter closet which makes the final edible oil that is termed as refined edible oil. This micro filtration process is especially designed for more effective filtration and best quality of final refined edible oil.
Additional Process for palm oil refinery: Besides usual refinery process palm oil requires additional process, fractionation process, where palm olene and palm sterene are isolated by cooling the refined palm oil in chilling plant. For this function crystallizing vessel is used in which chilling pipe coils cool the oil for fractionation. Palm sterene crystals are formed due to chilling which are separated in the filtration process and pure liquid of palm olene is obtained and palm sterene cake is retained in the filtration process.