Introduction of Soybean Dehulling Technology

(Last Updated On: October 31, 2022)

Soybeans contain 6 to 8% hulls, which contain 12.5% protein, 0.6% oil, and 40% crude fiber. The main purpose of soybean dehulling is to produce high-protein, low-fiber soybean meal, while soybean dehulling can improve the yield of the extracting section and reduce the consumption of steam, electricity, solvents, etc.

Usually, the pre-treatment part of the dehulling is called pre-dehulling, as opposed to the skimming of defatted soybean meal, which is called post-dehulling. Post-dehulling is based on the difference between the kernel and skin size and capacity in the meal for screening, crushing, and wind selection of the sieved material. The post-dehulling product is high protein soybean meal and low-protein soybean meal. Since post-dehulling does not require drying and temperature and humidity regulation, steam consumption is low. However, post-dehulling can only be used for the production of feed soybean meal, and with the application of extrusion expansion in soybean pretreatment, making post-dehulling quite difficult, and currently, post-dehulling technology has been virtually eliminated.

 There are three main methods of dehulling: cold dehulling, hot dehulling, and warm dehulling.

The standard process of pre-dehulling is drying, tempering, crushing, skin-kernel separation, and conditioning. Due to the advent of the hot dehulling process, the standard process is now called cold dehulling. The hot dehulling process is drying, rupture, skin-kernel separation, crushing, and tempering. Warm dehulling process: drying & tempering → crushing → kernel separation

1. Cold Dehulling Process

Extracting oil plant soybeans into the warehouse moisture is generally 11 ~ 13%, the seed skin and kernel adhesion is strong, the toughness of the skin is large, at this moisture, soybeans even if broken, the seed skin may still be attached to the broken kernel, cold dehulling through the drying of soybeans and the subsequent tempering section to reduce the adhesion of the skin and kernel.

1.1 Drying

    Soybean drying is often carried out in the drying tower, the air is heated and warmed to dry soybeans counter-current. The hot air temperature is high, the drying operation is fast. But if the temperature is too high will deepen the color of the oil and meal, and NSI decline. The General hot air temperature is 60 ~ 80 ℃, soybean temperature is 50 ~ 60 ℃.

1.2 Tempering

After drying soybeans into the tempering. In the tempering warehouse, the moisture in the warehouse soybean uniform distribution, and the skin, and kernel further shrinkage. Tempering warehouse residence time depends on the dry removal of moisture and the rate of drying, drying to remove more moisture, drying speed, moisture distribution time, and the requirement for a long residence time in the warehouse. The general residence time is 3~7 days.

1.3 Crushing

Soybean crushing with a roller crusher, crusher roller surface engraved with a certain slope of the triangular sharp tooth groove, soybean crushing into 6 ~ 8 flaps, due to drying soybeans and a certain amount of time tempering, the skin and kernel can easily be separated.

1.4 Skin and Kernel Separation

Crushed soybeans into the double-screen vibrating screen or plane rotary sieve screening.

The upper layer of the screen on the screen for coarse skin and larger bean grains. Soybean skin the suction device mounted on top of the upper screen sucks the skin away to the soybean skin system, while the beans fall from the upper screen by conveying the re-crushed.

The upper material of the lower screen is medium-sized bean skins and broken bean grains, which are sucked out of the skins by the Kice Aspirator and sent to the bean skin system, while the broken bean grains are tempered and rolled.

The lower screen through the material is fine skin and powder, accounting for about 5-10% of soybeans, this part of the separation is more difficult, usually with the bean kernel into the next process.

1.5 Condition

Due to the relatively low temperature of soybeans, in order to reduce the vibration of the rolls in the rolling process, and reduce the powder degree of the billet, while regulating the appropriate immersion moisture, must be conditioned by the conditioning process, cold dehulling conditioning is actually softening adjustment. Larger processing capacity using horizontal rotary tube bundle heater, small and medium-sized vertical steam frying pan. General tempering time of 20 minutes, the discharge temperature of 50 ~ 65 ℃, moisture 9 ~ 11%.

2. Hot Dehulling Process

Hot dehulling process simplifies the dehulling process of soybeans, mainly in two ways.

(1) soybeans by Fluidized-bed drying to about 80 ℃, hot soybeans directly to the rupture, skin, and kernel separation.

(2) soybeans after preheating to dry using a jet air dryer to dry soybeans.

2.1 Preheating

Soybean preheating in the tempering tower, usually tempering tower includes 6 to 9 layers of built-in horizontal steam heating flat pipe independent heating unit, 2 to 3 layers of air intake devices, and 1 to 2 layers of air outlet devices. Soybeans contact the heating flat pipe from top to bottom due to their own gravity, the temperature rises, the internal moisture gradually gathers to the surface, and the bean skin is softened. Water vapor, part of the soybean skin by the suction device sucked out. If the soybean moisture is high, the air is heated by the heater, through the air intake device into the heater, direct contact with soybeans, and the right amount of soybean drying. Heating steam pressure generally does not exceed 0.1Mpa, soybeans in the heater for a residence time of 20 ~ 30 minutes.

2.2 Drying

2.2.1 Fluidized-bed drying

Fluidized-bed dryer, through the hot air heating and drying of soybeans, hot air temperature of about 120 ℃, when the material through the Fluidized-bed, and through the perforated plate bed of hot air contact, soybean surface moisture is brought out by the hot air, soybean skin and surface burst due to high temperature, the skin of the beans loose, cracked. Fluidized-bed discharge air contains a small amount of soybean hulls, the discharge air is divided into two Shakelong unloading soybean hulls after the reuse of all the way, all the way to the atmosphere. By Fluidized-bed drying, soybean temperature 75 ~ 92 ℃, moisture 10% or so.

2.2.2 Spray air drying

The use of specially designed jet air dryer (Jet Dryer) for soybean heating and drying, JetDryer belongs to the crawler type air dryer. Preheated soybeans are evenly distributed to the crawler by the feeding device, the crawler movement speed of about 0.05m / s, the hot air from the jet fan through the air spray device from the bottom of the crawler through the material bed, soybeans are boiling, the hot air temperature 121 ~ 149 ℃, the soybean surface moisture is removed.

Spray air dryer soybean residence time of 1 ~ 3 minutes, the discharge temperature of about 88 ℃.

2.3 Crushing

Usually hot dehulling process using a single roller crusher to split the soybean into two flaps along the crack, and then into the hammer-blade crusher, half of the flap beans by the high shear force of the hammer blade impact, so that the skin from the bean kernel on the separation.

2.4 Hull-kernel separation

After cracking, the skin and kernel are separated in the wind separator apparatus, which has a regular arrangement of horizontal steel pipes inside the wind separator, and the broken material enters through the feeder, falls in a waterfall, and impacts with the steel pipes, and the kernel falls down and is broken, and the skin is sucked out by the wind in the shakelong to unload out for screening.

2.5 Crushing

Same as the cold dehulling process, the bean kernel is crushed into 6~8 flaps in the crusher, as the bean kernel is hot, therefore, little powder is produced when crushing.

2.6 Conditioning

Since the bean kernel is hot, conditioning is actually the cooling of the hot beans. Usually, the air is fed at room temperature, and the outgoing air brings out part of the skin and kernel chips to be unloaded and screened in the cyclone. After conditioning, the temperature of the bean kernel is about 65℃.

3. Process comparison of cold dehulling and hot dehulling

By comparing the various processes of hot dehulling and cold dehulling, it is obvious that the hot dehulling process has the following advantages.

Continuous processing hot dehulling process eliminates the need for several consecutive days of tempering section time for soybeans of different moisture can be processed continuously.

3.1 High dehulling efficiency  

In the cold dehulling process hull separation is the screening of the entire broken material, while the hull separation in the hot dehulling process is the screening of the broken aspirate (about 10-15% of the yield).

3.2 Less exhaust gas emission 

The hot air is recycled and less exhaust gas is discharged. At present, the hot dehulling process is used more often, but there is a risk of spontaneous combustion in the hot air drying in the hot dehulling process. After 2002, new press manufacturers choose to use the warm dehulling process, increase the number of layers of the tempering tower in the hot dehulling process, improve the de-watering capacity of the tempering tower, and eliminate the drying part of the Fluidized-bed or jet dryer. Some of the original cold dehulling processes has also been modified one after another to warm dehulling.

The soybean dehulling process currently used by Chemsta is neither cold nor hot dehulling and is similar to warm dehulling in that it can remove 90% of the soybean skin and effectively provide the protein content of soybean meal while effectively protecting the NSI.

Especially for soybean white flake, high protein is very important, higher protein in white flake, higher protein in soybean protein (SPC or SPI) produced by soybean white flake.

It has been successfully applied in a number of projects at home and abroad, and we will subsequently introduce Chemsta’s unique soybean dehulling technology in detail.

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