The pretreatment of oil bearing material not only affect the permeability in the process of extracting, residual oil content in soybean meal and other indicators directly, but also affect various components in the oil, the quality and refining efficiency of the crude oil, the quality of the final product and the energy consumption in the of production, etc. Therefore, pretreating of raw material should be adjusted and optimized according to the difference of the product to meet different needs.
1. The traditional pretreatment process
The traditional pretreatment process generally includes cleaning, crushing, softening, flaking, drying, etc. For raw material with high oil content, oil plant mostly adopts single pressing or prepressing, that is, press flakes after cooking. Traditional process has been more mature and stable after many years of production practice. It has the advantages of simple process flow and less equipment investment. Deficiency of tradition pretreatment is that the degree of cell damage is lower and fines content is higher. The texture of flake is fine and tight, permeability and drip speed are slow during the process of extraction. Thus, the extraction rate is lower with much extraction solvent and concentration of mixed oil is lower, which would result in increasing evaporation system load and poor quality of crude oil. Based on this reason, the oil industry has been exploring new pretreatment process for many years.
2. The extrusion process
The extrusion technology is a new production technology suitable for a variety of oil bearing materials. It overcomes the difficulties of traditional processing technology, such as high heating temperature of material, long processing time, etc. The process of extrusion: raw material - cleaning - crushing - softening - flaking - extrusion - extraction. When using expanded material for extraction, the extraction solvent reduces greatly compared with flake extraction, approximately 0.65:1. The concentration of mixed oil is higher than 30%. The hygrothermal effect in the extrusion process passivates enzymes so that the nonhydratable phospholipids in extracted crude oil reduces, which improves the quality of crude oil. Therefore, the extrusion technology is worth promoting. At present, the technology is in its infancy, the newly built oil plant has been using this technique. We believe that it will used widely soon.
3. The peeling process
Oil seeds contain a certain amount of husk, while the crude fiber and other components in the husk would directly effect the nutritional value and palatability of cake. Thus, it should be removed in the pretreatment process. Now, peeling and shell and kernel separation technology of oil seeds are relatively mature. The technology and equipment are complete. In recent years, soybean protein and rapeseed protein receive more and more attention. The commonly used soybean peeling process is as follows: soybean - cleaning - grading - drying - tempering - crushing - peeling - softening - flaking - extracting. The cleaning process is the same with the traditional process. Soybean after drying would be tempered for 48h ~ 72h before crushing and peeling. Also some manufacturers would send the soybean after drying into fluidized bed for cooling before crushing and peeling. Single or twice air separation method would be used after crushing.
4. The microwave processing technology
Microwave heating has the features of fast speed, short time, not being limited by the shape of material, uniform heating, high thermal efficiency and guaranteed product quality. It also has certain humid heat sterilization effect. When using microwave to heat the material, protein denaturation caused by passivation antinutritional factors of enzymes and other problems can be solved. Therefore, the combination of microwave heating and pneumatic drying method can be used for raw materials with special requirements.
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