Pretreatment is necessary for efficient oil extraction from raw palm kernel. In palm kernel oil industrial production, oil raw materials are usually palm kernel or pressed cake. If the material is palm kernel, the main pretreating steps are palm nut cleaning, shelling and separation, crushing, flaking and steamed frying. If your raw material is a press cake from palm oil press workshop, you need to do this: The material cake should be cracked by a screw conveyor and conveyed into a fiber separator drum for fiber separation. After these simple treatment, you can get cleaner palm kernel, the rest of the process is the same:
Palm Nut Cleaning
The raw palm nut’s impurity should be cleaned firstly otherwise it would cause damage to the screw press machine. The magnetic selector is installed for removing metal debris, while the vibrating sieve is used for removal of sand, fines or other undesirable impurities. And the stones could be removed by gravity stoner.
Palm Nut Shelling and Separation
By palm kernel husking and separating system, the clean palm nut is cracked and divided into palm kernel and shell. First of all, the palm nut is husked by our high-quality palm nutcracker with a husking rate of 85-95%. Next, the cracked shell and kernel are separated by air separator machine, through the air duct, shell and kernel could be firstly separated onto V-shaped screen’s upper layer and the lower layer, finally, the rest kernel on the upper layer could be dropped from the screen holes by screen vibrating. After separating, the kernel content in the shell and the shell content in the kernel are less than 5%. Shelling can increase the oil yield, improve the quality of crude oil & cake, reduce abrasion of equipment and increase the effective production of equipment. The palm shells are always sent to the boiler room for fuel use.
Since palm kernel is relatively large and hard, in order to better improve the oil yield, the palm kernel needs to be secondary crushing after husking. The main crushing equipment is rolling crusher, which can break kernels into small pieces and easy to produce oil. It has a simple structure, stable performance and easy to operate.
Flaking machine is mainly made up of two or more opposite rotating rolls (high nickel chrome molybdenum alloy). When the kernel pieces are in the middle of the two rollers, they are squeezed by instantaneous pressure to form flakes, meanwhile, the crude oil is rolled out firstly. This machine is widely used in oil plants and individual oil processing mill, easy to operate and maintain. After flaking, the palm kernels are easy to be steamed.
The purpose of steamed cooking is to completely destroy the oil cells by high temperature and moisture, so that the protein is denatured, the oil is steamed out and collected, the viscosity and the surface tension of the oil are reduced, the elasticity and plasticity of the material are adjusted, and the enzymes are passivated. Steamed cooking equipment is a steam frying pan, which can process the raw palm kernel flakes into matured flakes by heating, spraying and steaming. The equipment can also be used as a softening pot, softening can improve the quality of rolled flakes, thereby increasing the oil yield, and can improve the quality of crude oil. It is the necessary equipment for vegetable oil factory.
The pretreated palm kernel is then screw-pressed and filtered into crude oil.
Put the pre-treated palm kernel flakes into double shaft screw press machine for pressing. The working principle of double shaft screw press is through the impelling action which is generated by two intermeshing screws rotating in opposite direction in the chamber, palm kernel is compressed and the oil in it is squeezed out. Then, the expressed oil flows out of the gap in the squeezed cage. At the same time, the residue would be pressed into cakes, and constantly discharged from the end of the squeeze shaft. The palm kernel oil expeller has specially designed double shaft structure, strictly heat-treated steel fittings, vertical squeezing cage with hinge support at both ends and unique material cake discharge device, which is specially designed for pressing palm kernel oil.
The palm kernel oil obtained from pressing is generally not very clean, it contains many impurities, the clarification or filtration equipment can remove impurities and extract relatively clean palm kernel oil.
Through the steps of degumming, deacidification, decoloring and deodorizing, the way of removing solid impurities from crude palm kernel oil such as free fatty acids, phospholipids, gum, wax, pigment, and the odor is commonly known as “oil refining“. The purpose of refining palm kernel oil is removing impurities, improving product quality for safe storage.
Palm kernel oil degumming
Applying physics and chemistry methods to remove gum soluble impurity in crude oil is degumming, the common gum soluble impurities are phospholipids, some protein, and gum. The high phospholipids content in edible oil would cause oil foaming, smoke, and odor when heating, and the phospholipid at high temperatures would cause oxidization and make the oil become brown, affecting the flavor of fried foods. Degumming is based on the principle of phospholipids and some proteins containing the hydrophilic group. Pour a certain amount of hot water or dilute acid, alkali, salt and other electrolytes aqueous solution into crude oil and stir the mixture at 50℃, so that the gum soluble impurity is condensed with the water molecule and removed from the oil by centrifugation or sedimentation separation.
Palm kernel oil deacidification
Free fatty acids affect the stability and flavor of the oil. Alkaline neutralization method can remove free fatty acids which are also known as the alkali refining. The alkali refining could further remove most of the free fatty acids, phospholipids, pigments and some sulfur-containing compounds. First of all, add 0.02%~0.5% phosphoric acid into the deacidification pot and heat at 60~90℃, after 15~30 minutes’ reaction time, add 8%~12% NaOH into the pot, after 30 minutes’ saponification, the FFA is neutralized with alkali and discharged as soapstock.
Palm kernel oil decoloring
Crude oil contains chlorophyll, carotenoids, and other pigments, chlorophyll is a photosensitizer, affecting the stability of the oil, and other pigments affect the appearance of fat, which can be removed with the adsorbent. Adsorption decolorization principle is using strong adsorption characteristics of adsorbent in hot oil can absorb pigments and other impurities, then the adsorbent also with adsorbed pigment and impurities are filtered, so as to achieve the purpose of bleaching and purification.
Palm kernel oil deodorizing
The smell of crude oil will affect the oil storage and sale price, so we usually use the direct steam stripping method to remove the smell of crude oil, that is, using high vacuum, high temperature steam stripping and other measures to distill off the odor of the oil; Oil also contains 0.5% moisture, which could be removed by high temperature dehydrating technique in deodorization tower.