Palm Oil Pressing Process Introduction
Palm oil is obtained by crushing fresh palm fruit. Bunches of palm fruit grow in bunches, each weighing about 20-30kg and containing 1500-2000 fruits. Farmers pick bunches of palm fruit on a regular basis and have to transport them to factories for processing on the same day. The quality of crude palm oil depends on the good condition of palm fruit bunches. Once damaged, palm fruit will quickly deteriorate, which will affect the quality of crude palm oil.
The main products of the palm fruit crushing plant are crude palm oil and palm kernels, and the processing capacity is about 60~100 tons of palm fruit bunches per hour. For crude palm oil, the general to sterilization, threshing, cooking, pressing, washing, purification, drying and other processes.
For palm kernel, after pressing and separating, there are technologies such as kernel/fiber separation, kernel tempering and tempering, kernel crushing, kernel separation and kernel drying. The dried kernels are sold to a palm kernel press to extract the oil.
Sterilization:
Sterilization, as the first step in palm fruit press, is critical to the quality of the final product palm oil. The main purpose of sterilization is as follows:
1) Passivation of lipase activity to prevent the rise of free fatty acids
2) Make palm fruit earlier to peel off from fruit bunches
3) Soften the pericarp and make it easier for oil separation
4) Nucleolus modulation reduce the crushing of nucleolus in the subsequent process.
The sterilization process uses a horizontal sterilizer, through about 3bar of steam, cooking 60~90 minutes. In recent years, with the development of technology, the sterilization process has gradually developed from intermittent to continuous sterilization process, which improves the operation efficiency and reduces the consumption of labor and energy.
Threshing:
The main effect of threshing is to separate the palm fruit from fruit bunches. The germicidal palm fruit bunches are fed into a drum thresher and as the drum rotates the palm fruit detachs from the stem. The stem is a component that does not contain any oil, so the loss of threshing process mainly comes from palm fruit still attached to the stem after threshing. Too short or too long sterilization time will affect the loss of threshing, too short time palm fruit is difficult to get rid of. Over time, the stem will absorb palm oil. The stalks are usually burned, and the ash is used to make potash, biofuel or fertilizer for plantations.
Steam and pressing:
The threshed fruit is piped into a cooking pot and reheated by direct or indirect steam. A central shaft with agitating wings is installed in the cooking pot, which agitates the palm fruit, and the high temperature makes the pulp become soft and peel away from the core. The mixture is then fed into the press. Hot water is added to help the oil flow. The mixture of crude oil and hot water is collected in a clarifying tank for clarification. Palm kernel, fiber and other impurities are discharged from the filter cake into the preparation process of palm kernel oil. The press process requires maximum extraction of palm oil from the pulp without crushing the kernels, as the crushed kernel oil will contaminate the crude oil and affect the quality. The crushing rate of nuts can be effectively reduced by using the secondary or multiple pressing process.
Purification & clarification:
The mixture in the clarifier is crude palm oil, water and a small amount of solid particles. The traditional method of clarification is gravity separation. Mixture will settlement of heating to 85 ~ 90 ℃ and then let stand for 1 ~ 3 hours. The oil on the surface is sent to a centrifuge to further remove impurities from the oil and then to vacuum drying. The slag at the bottom of the clarifying tank will be also into the inside of the centrifuge to recycle crude palm oil, eventually after vacuum drying, cooling and about 45 ℃ storage.
Wastewater from the palm oil mill:
Each ton of palm-fruit bunches treated by the plant will produce about 0.65 tons of waste water. These wastewater will affect the environment due to its high acid value, high BOD value and high COD value. In general, anaerobic or aerobic reactions in the treatment pool can bring the BOD below 100mg/L. In more environmentally sensitive areas, more advanced processes will be used to treat the sewage.
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