What Equipment Are There For Rice Bran Extruding And Oil Extraction Process?

Rice bran is a by-product of rice processing, generally accounting for 4% to 6.5% of the amount of rice and 6% to 8% of the amount of brown rice. The oil content of rice bran is 15% to 22%, which is equivalent to the oil content of soybeans. Rice bran oil is a nutritious edible oil and is recognized as a nutritional health oil at home and abroad. However, most rice bran resources are used as livestock and poultry feed, resulting in a huge waste of resources. Therefore, vigorously developing and utilizing rice bran resources has very important practical significance for alleviating the contradiction between supply and demand of edible oil and increasing the added value of rice bran.

1 Physical properties of rice bran
Rice bran is rich in lipids, proteins, minerals, vitamins, phytin, trypsin inhibitors, lipase and phytohemagglutinin (hemagglutinin), and is a valuable oil resource. Rice bran is very easy to deteriorate and has very poor storage. The main reason is that rice bran contains a variety of enzymes, and lipase and lipoxygenase are the two main enzymes that affect the stability of rice bran. Under suitable conditions, lipase can promote the decomposition of oil in rice bran into glycerol and free fatty acids, resulting in an increase in the acid value of rice bran. In addition, lipoxygenase catalyzes the oxidation and deterioration of free unsaturated fatty acids, resulting in a rancid smell. The results show that lipase exhibits strong activity at a moisture content of 12% to 15%, a temperature of 35 to 40 °C, and a pH of 7 to 8. The relationship between the freshness of rice bran and the oil yield and refining rate is shown in Table 1.

Table 1 Relationship between rice bran storage time and acid value, oil yield and refining rate

2 Stabilization pretreatment of rice bran
Since fresh rice bran is very easy to oxidize and become rancid, which in turn affects its comprehensive utilization value, it must be stabilized and pretreated first to effectively inhibit and passivate the activity of rice bran lipase and reduce the loss of nutrients. Its stabilization treatment methods include refrigeration, microwave, radiation, dielectric heating, chemical treatment, heat treatment and puffing. According to domestic and foreign data reports, the use of puffing to inhibit and passivate lipase and stabilize the acid value of rice bran has become the only feasible industrial technology and can maintain its nutritional value. The shelf life of rice bran treated by puffing can reach 1 year. When stored at room temperature for 2 to 3 months, the acid value (KOH) increases by no more than 3 mg/g. When stored at room temperature for 1 year, the acid value (KOH) is stable below 10 mg/g, and the residual enzyme activity of lipase is less than 4%. Rice bran→bran separation→magnetic separation→conditioning→puffing→drying→de-leaching workshop
Based on the physical properties of rice bran and the feasibility of the stabilization pretreatment method mentioned above, the best process route was determined through practice.
 

3 Rice bran puffing process and key points of operation
3.1 Process flow
3.2 Key points of operation
3.2.1 Bran separation

The rice bran produced by general rice mills contains 1% to 4% bran. Since the main component of bran is starch, if the material moisture is high during leaching, it will absorb water and swell and stick together under continuous warm conditions, affecting solvent penetration and feeding, and bran absorbs oil, which leads to an increase in residual oil in the meal and a decrease in oil yield, so it must be removed.
The bran separation screen is a commonly used screening method. It is a bran separation equipment specially designed for the characteristics of rice bran. The general output of a single unit is 8 to 10 t/d. The main principle is to use the difference in particle size between broken rice, rice bran and rice bran, and to use the relative movement between rice bran containing rice bran and the screen surface to separate the broken rice and rice bran through two layers of screen surfaces with different mesh sizes. Generally, the upper screen surface uses 20 mesh square holes, and the lower screen surface uses 28 mesh square holes. The cross-sectional size of the screen surface is 1 m wide, and the inclination is 8°~10°. Note that the amplitude should be slightly larger, so that the separation effect is better, and the rice bran content can be less than 1%.
3.2.2 Magnetic separation

During the processing of rice or the transportation of rice bran, some metal impurities such as iron nails, screws, and iron filings are often mixed in. These iron impurities will cause serious wear and even damage to the extruder screw in the subsequent process, and may block the pores of the extruder discharge die hole, causing the pressure of the press chamber to increase extremely, thereby affecting the extrusion effect, and in severe cases, it may also cause safety accidents. Therefore, the iron impurities must be removed before the material enters the extruder. The non-powered permanent magnet cylinder is a permanent magnet with high magnetic field strength and high iron removal efficiency. When the material enters from the feed port, the iron impurities can be automatically adsorbed to the surface of the permanent magnet, thereby achieving the purpose of separation. It is the preferred iron removal equipment in the current oil processing.
3.2.3 Conditioning

Conditioning is a key process in the rice bran puffing process. Here, the rice bran is adjusted to the appropriate moisture and temperature to provide the best conditions for puffing. During the conditioning, an appropriate amount of hot water or steam should be added, and indirect steam heating should be used at the same time to make the rice bran have appropriate plasticity, so that an appropriate pressure can be established in the extrusion cavity during extrusion and puffing. When the rice bran is sprayed out from the nozzle, the cell structure can be better destroyed, the oil is released, and enough fine pores are created, which is conducive to leaching. At present, most of the conditioning is completed by continuous vertical multi-layer steaming cooker with relatively large heating areas. Direct steam is introduced into the first layer, and the moisture is generally controlled at about 13% after wetting. The temperature rises layer by layer, and the final discharge temperature is controlled at 65~70 ℃, and the moisture is about 12%.

3.2.4 Extruding

The extruding of rice bran is achieved through the extruding machine. When the rice bran enters the machine chamber, it is pushed forward with the rotation of the screw shaft, and the volume in the machine chamber is reduced and pressure is gradually generated. At the same time, the friction between the rice bran and the screw shaft and the inner wall of the machine chamber produces self-heating effect, which increases the temperature of the material. In addition, the heating effect of direct steam makes the temperature in the machine chamber reach 120 ℃, and the direct steam pressure reaches 0.8 MPa. Finally, it is squeezed out through the die hole of the nozzle. Due to the sudden decrease in pressure, the internal moisture quickly vaporizes and escapes from various parts of the rice bran, resulting in countless tiny holes in the puffed rice bran, which is conducive to the leaching and penetration of oil, thereby increasing the leaching rate and reducing the residual oil in the meal. Generally, the moisture content of the material discharged by the puffing machine is controlled at 13%~15%. Before starting the extruder each time, it is best to turn the large pulley by hand to listen for any abnormal sound. If there is no abnormality, then start the machine; the machine needs to be preheated to 80~120 ℃ before feeding; the direct steam cannot be turned off during operation to prevent the rice bran from being pressed into the metal hose and blocking the steam channel. In addition, stable and continuous feeding is also a key factor in ensuring the extrusion effect. If the feed amount is too much, the extrusion temperature will decrease, the pressure in the machine chamber will increase, and blockage will easily occur. If the feed is cut off for a long time before feeding, serious jamming or even burning of the motor will occur, causing accidents. If the feed amount is too small, sufficient machine chamber pressure cannot be formed, resulting in insufficient extrusion.

3.2.5 Drying

The rice bran coming out of the extruder has too much moisture and the temperature is too high. The moisture needs to be adjusted to 7%~9% and the temperature is 50~60 ℃ to meet the requirements of leaching. The flat dryer is currently a commonly used equipment.

4 Extraction process and operation points of expanded rice bran
4.1 Process flow

The process and equipment for leaching puffed rice bran are similar to those for other oils. The whole process is also divided into four major sections: material leaching, wet meal desolventizing, mixed oil evaporation and solvent recovery. The key points of each section are explained below.
4.2 Key points of operation
4.2.1 Leaching section Since puffed rice bran is easily ground by the chain during drying and subsequent scraper conveying, a large amount of powder is produced, which greatly reduces the permeability of the solvent and increases the residual oil rate in the meal. Therefore, when designing a horizontal rotary extractor, the material grid should not be too high, and the material layer is generally controlled at about 1.3 m, and the leaching time should be extended, generally more than 2 h. The designed processing capacity is equivalent to 1.3~1.5 times that of soybean blank processing. In addition, during the leaching process of the blank, the powder will inevitably enter the oil bucket through the gap between the grid plates. If it accumulates for a long time, it will cause the mixed oil pipe at the oil outlet to be blocked, and the mixed oil cannot be extracted, affecting the normal production. To address this problem, a recoil pipe can be installed in each oil hopper of the extractor and connected to the outlet pipeline of each circulating pump. During the production process, the control valve of the recoil pipe is often opened to flush the powder in the oil hopper and pump it into the extractor material layer through the circulating pump together with the mixed oil. The self-filtration effect of the material layer reduces the amount of powder entering the oil hopper, thereby ensuring the normal production.

4.2.2 Desolventization Section

Under normal circumstances, the wet meal coming out of the extractor contains 25% to 35% solvent. Due to the large powder content in the wet rice bran meal, the wet meal contains up to about 40% solvent. In addition, the rice bran contains impurities such as starch. During the desolventization process of the wet rice bran, the starch in the rice bran will absorb water and swell. When the gelatinization temperature is reached, it will be gelatinized and produce adhesion, which is not conducive to the volatilization of solvent and water, causing difficulties in the desolventization section. Considering the influence of the above factors, the desolventization of the rice bran wet meal adopts a multi-layer DT-C structure to complete the desolventization, drying and cooling of the wet rice bran in one device. When designing the equipment, it is also necessary to enlarge the output of soybean slabs by 13 to 15 times, and the material layer should be thinner, which is conducive to the volatilization of the solvent and the residual solubility of the meal can meet the requirements. Since direct steam is added to the meal for desolventizing, the moisture content increases, and indirect steam heating is required to adjust the moisture to about 13%. Finally, it is cooled to below 45 ℃ by cold air and can be directly sent to the meal warehouse for packaging. Since the rice bran meal has a large powder degree, the shakron used to collect the broken pieces should also be enlarged accordingly to ensure the collection effect.
4.2.3 Mixed oil evaporation section

The rice bran concentrated mixed oil from the extractor generally contains 3% to 5% of solid impurities (mainly meal powder). These solid impurities will form dirt on the tube wall of the evaporator, reduce the heat transfer effect, and easily generate a large amount of foam during the evaporation and stripping process, causing flooding. At the same time, due to the effect of high temperature, it is easy to carbonize, which makes the crude oil darker and reduces the refining rate. Therefore, the meal powder in the mixed oil should be removed as much as possible before evaporation. At present, two vertical mixed oil tanks are usually connected in series, and the density difference between meal and mixed oil is utilized to separate them by natural sedimentation under gravity. The sedimentation time is generally greater than 40 minutes. After sedimentation separation, the mixed oil is pumped into a continuous filter for further separation, thereby ensuring that the impurity content of the mixed oil meets the requirements. Since the extractor for extracting rice bran is larger than that for processing other oils of the same scale, the corresponding circulation volume should also be increased, which requires an increase in the amount of fresh solvent sprayed, thereby reducing the concentration of the mixed oil accordingly. Therefore, when designing the evaporator, its area should also be increased accordingly. In addition, it is very important that since the concentration of the mixed oil is relatively thin, when heated, the solvent will evaporate and expand rapidly and rise rapidly. Therefore, the tubes of the evaporator should not be too long, generally 4~5 m, otherwise it will not be conducive to film rising and affect the evaporation effect. During the specific evaporation operation, the continuous and stable flow of the mixed oil should also be guaranteed, and the temperature of the mixed oil entering the evaporator should be close to the temperature when boiling and bubbles begin to form (i.e., the bubble point), which is conducive to film pulling, enhancing the evaporation effect, and making the evaporation system reach the best working condition.
4.2.4 Solvent Recovery

Section Solvent recovery is an important part of the leaching workshop. The quality of solvent recovery is not only directly related to the level of production costs, but also has a very important significance for the safe production of the workshop and the improvement of the workshop environment and sanitation. At present, most leaching workshops use shell and tube condensers, and the shell and tube materials are mainly aluminum alloy or stainless steel. It should be noted that carbon steel shell and tube condensers should not be used in leaching workshops. Mainly because: ① In the presence of solvent gas, the surface of the shell and tube wall corrodes quickly; ② After the carbon steel tube wall corrodes, the surface is rough and rust is generated. The meal entrained in the mixed gas of the desolventizer, the mud and sand entrained in the cooling water, and the scale layers of calcium and magnesium salts precipitated after the unsoftened cooling water is heated are all easy to deposit, which seriously affects the heat transfer effect; ③ Carbon steel tubes are not corrosion-resistant. When the scale layer is cleaned with a descaling agent after scaling, it is easy to cause damage to the tube wall. When processing rice bran, a large amount of fresh solvent is added during the leaching process, so the total configuration area of ​​the condenser should be increased by 10% to 15%, and the corresponding effective volume of the water distribution tank should also be increased by 10% to 15%, so as to ensure the condensation effect of the solvent and the water distribution effect of the solvent, and effectively reduce the loss of the solvent. According to the size of the scale, the connection method of the circulating cooling water can be selected in parallel or series. Generally, small-scale ones mostly use parallel connection, and large-scale ones mostly use series connection. In the configuration of the circulating water pump, the flow rate should be slightly larger and the head should be slightly higher, so as to ensure that each condenser is allocated with sufficient flow of water, and the water flow rate can also be appropriately accelerated, which is conducive to heat transfer, thereby achieving a good condensation effect and ensuring the maximum recovery of solvent gas. In addition, free gas must also be discharged into the atmosphere after recovery. Generally, small-scale leaching workshops use groundwater with relatively low temperature for direct absorption, while large-scale leaching workshops use edible grade paraffin oil for absorption.

5 Conclusion
This expansion and extraction process designed based on the analysis of rice bran characteristics produces qualified rice bran crude oil, and all economic and technical indicators meet the requirements, creating considerable economic and social benefits for the enterprise, and providing technical guarantee for oil processing enterprises to develop and utilize rice bran resources.