Rice bran pretreatment is the first step in the oil extraction process. The raw rice bran may contain impurities such as dust and small particles, which are removed through a screening process. After that, the material enters the quenching and tempering system, where a small amount of steam—approximately 2% of the total raw material—is introduced to soften the bran. This softening makes it easier for the subsequent pressing and oil extraction steps to be more efficient.
The next stage is pressing. Following the pretreatment, the rice bran is directly fed into a hydraulic press, where cold pressing is used to extract most of the oil contained within the bran. This oil, known as rice bran oil, is then sent to the physical refining workshop for further purification. Meanwhile, the solid residue from the pressing process, referred to as the cake, still contains some residual oil and is transferred to the leaching section for additional oil extraction.
In the leaching process, the cake is placed into an oil leaching device, where a solvent like n-hexane is added. This solvent dissolves the fat present in the cake, forming a mixture of oil and solvent. The resulting mixed oil passes through a filter medium, which traps any solid particles, leaving behind a cleaner oil mixture.
The mixed oil then undergoes evaporation. Since the oil is nearly non-volatile while the solvent has a low boiling point, steam is used to evaporate the solvent. This increases the concentration of the oil in the mixture significantly. The process involves two stages: the first stage uses a long-tube evaporator, where the mixed oil is heated and vaporized, allowing the solvent to be separated. The concentrated oil moves to the second evaporator for further processing before being cooled and prepared for the next stage.
The long-tube evaporator is a key component of this process. It operates by preheating the mixed oil before it enters the heating tubes. As the oil rises, it forms a thin film along the tube walls, where continuous evaporation occurs. This thin-film evaporation enhances heat transfer efficiency and ensures a high-quality oil output.
After evaporation, the oil still contains trace amounts of solvent, which are removed through a stripping process. A controlled amount of direct steam is introduced into the oil, helping to lower the boiling point of the solvent and facilitating its removal. The steam and solvent vapor are then condensed and recovered for reuse, ensuring minimal waste and environmental impact.
Wet mash desolvation follows the leaching stage. The wet mash obtained from the leaching process contains residual solvent, which is removed by introducing water vapor. This step is similar to the stripping process, ensuring that the final product is clean and free of unwanted chemicals.
The stripped oil is then filtered to remove any remaining impurities. This includes natural sedimentation, where insoluble particles such as cake fragments and plant matter settle at the bottom of the tank. This step ensures the oil is clear and ready for further refinement.
Hydration degumming is another critical step. A small amount of water (1–3% of the oil weight) is added to the oil, causing phospholipids and other water-soluble impurities to coagulate and precipitate out. These impurities are then separated from the oil, improving its purity and stability.
Next, the oil is vacuum-dried to remove any remaining moisture. This is done using a continuous packing dehydrator under a vacuum of approximately -0.09 MPa. This step is essential for preparing the oil for decolorization, as excess moisture can interfere with the adsorption process.
Adsorption decolorization involves adding a small amount of bleaching clay (about 2% of the oil weight) to the oil. The mixture is stirred thoroughly to allow the clay to absorb color pigments and other impurities. Afterward, the oil is filtered to remove the clay, resulting in a clearer and more refined product.
Deacidification is performed by heating the oil to around 250°C and passing it through a structured packed tower. Saturated steam is injected from the bottom, allowing for effective stripping of free fatty acids. This process improves the oil's quality and extends its shelf life.
Deodorization follows, where the oil is again passed through a structured packed tower. At a temperature of about 230°C, steam is introduced to strip away any undesirable odors and volatile compounds. This step ensures the final product has a neutral taste and smell.
The by-product, fatty acid, is collected and cooled before being pumped back into the system for reuse. This not only reduces waste but also contributes to a more sustainable production process.
Dewaxing is the final step in the refining process. Any remaining wax in the deodorized oil is removed by cooling the oil in a crystallization tank and then filtering it through a plate and frame filter press. This separates the wax from the oil, resulting in a clear and high-quality product.
Finally, the finished oil is stored in a holding tank and transported to the packaging line. It is then filled into containers using a small filling machine and prepared for sale. This completes the entire rice bran oil extraction and refining process, producing a premium edible oil suitable for various applications.
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