Soybean is the crop with low oil content, which is among 11 – 20%. Solvent extraction is commonly used in soybean oil extraction under normal circumstances. Oil produced by solvent extraction has good quality and lower production cost.
Flow chart of soybean oil processing:
Soybean– cleaning– crushing– softening– flaking– extracting– evaporating– stripping– crude soybean oil (crude oil)– filtering– hydrating (degumming)– alkali refining (deacidification)– bleaching– deodorization– soybean oil
Main points of processing technology of soybean oil extraction plant:
1. Flaking is the key to pretreatment of soybean oil extraction plant, it is closely related to the oil yield and quality. While the key of flaking lies in the operation of the roller mill. In order to ensure the quality of flakes, we should strictly control the moisture and temperature of materials before flaking. The softening box is preferred too avoid excessive moisture content and temperature loss after softening. The performance of roller mill should be checked carefully before starting. If the flakes are found uneven on both ends or oil plants without flaking are mixed with flakes, the operator should stop and check the roller mill. Adjust the rolling clearance (balanced adjustment on both sides should be made and avoid to be too tight). Check whether the scraper plate is close to the surface of roller to prevent the sticking phenomenon. Pay attention to the flowing uniformity and prevent the no-load running.
From left to right: soybean, soybean flakes after expansion without leaching, soybean meal
2. The charge amount of each division in the extractor is 80-85%. The solvent temperature should be within 50 – 55 ℃. The immersion temperature of soybean flakes is 50 to 55 ℃ and the temperature of extractor is 50 ℃. The dry type large droplets spray had better be used. The liquid level of spray section should be 30-50 mm higher than the materials. When spraying fresh solvent, it shall not be spilled into the dry period. Solvent ratio (the ratio of solvent weight and the weight of leaching material) is 1：0.8-1.1. Non-toxic solvent should be used with certain volatility for oils, chemical stability, not inflammable or explosive and with narrow boiling range, small water solubility, no corrosion for the machine or react with oil meal.
3. The temperature should be controlled strictly in mixed oil processing process of soybean oil processing plant. If the concentration of mixed oil does not reach evaporation operation requirements after stripping, part of the mixed oil should continue for circular evaporation.
4. The purpose of refining of soybean oil processing plant is to make the quality of soybean oil meet the edible standard. In the refining of high temperature hydration processing, we should note that the temperature of preheating crude soybean oil is 55-75℃when adding water. Directly steam, heating water or steam and water blending can be used. The phosphatide content in crude soybean oil after leaching is 3-4%, and the amount of water added should be 2-3.5 times of phospholipid content. The temperature of water shall not be lower than the oil temperature. When phospholipid colloidal particles can be lastingly suspending in the oil and not gathering into flocs, then add water faster; otherwise, it should be slowly. At the beginning of hydration, the revolution of mixing wing (slope of 40-45 °) should be 60-70 r/min (suspension type should be 140-180 r/min). When phospholipids form, turn the revolution slowly for 20-30 r/min. Remain stable when hydrated oil temperature reaches 140 ℃ with the vacuum degree of 93325 PASCAL (700 mmHG). After deodorization, solvent content in soybean oil should be less than 50 mg/kg.
Main equipment used in soybean oil extraction plant:
Vibration sieve, stoning machine, permanent magnet drum, wind classifier, rotary dryer, softening pot, steam stirred cage, double roller mill, extruder, extractor, filter, mixing tank, evaporator, condenser, etc.
Features of finished soybean oil:
1. With yellow or brown color; refractive index (20°C) of 1.4720-1.4770; proportion (20°C / 4°C) of 0.9210- 0.9250.
2. Health standards: solvent content in the oil must not exceed 50 mg/kg. The soybean oil should have the inherent odor and taste without peculiar smell.