Soya bean Solvent Extraction Plant

Soya bean Seed Solvent Extraction Plant

Soybeans are the most processed oilseed, accounting for about 56% of oilseeds processed by solvent extraction plants. Each soybean is approximately 7% hull by weight. The hull is a paper-thin shell surrounding each seed, high in fiber and low in oil. It has a very low density unless ground finely, and thus occupies a lot of space in costly processing equipment. Being low in oil, hull extraction is less profitable, and it is also low in protein. When removed early in the process, the extracted meal has a higher protein content and market value.

For these reasons, one of the initial steps in soybean processing is often dehulling. Removing about 90% of the 7% hull reduces the extraction volume, lowers desolventizing energy, increases the protein percentage of the meal, and provides a by-product with some value—the hulls.

This dehulling function is usually integrated with other preparation systems to crack, heat, and flake the material, preparing it for solvent extraction. The dehulling process and other preparation steps are outlined below:

Soybean Preparation Steps

• Cracking: Each soybean is cracked into 4-8 pieces using sharp serrated rolls. Cracks should be large enough to allow effective distortion during flaking, but not so large as to reduce flaker capacity or require excessive power.
• Dehulling: Primarily done to improve meal protein levels. It also reduces the amount going to extraction and increases density in the extractor, leading to more retention time.
• Conditioning: Material sent to flakers should be about 158°F (70°C), with final flakes at the extractor around 147-154°F (64-68°C) and 9-10% moisture.
• Flaking: Flaking breaks cell structure to release oil, easing extraction. For shallow-bed extractors, flakes should be approximately 0.012" to 0.015" (0.30-0.38 mm), and for deeper beds, around 0.013" to 0.017" (0.33-0.43 mm).
• Expanding: Flakes are heated and formed into larger, denser collets. Expanding reduces residual oil and facilitates solvent penetration during extraction.
• Cooling: The soybean collets are cooled to stabilize them before being conveyed to the extraction section, ensuring structural integrity and quality for oil extraction.With properly prepared soybean material and adequate extraction time, it is often possible to achieve around 0.35-0.60% residual oil.

Extraction Section

Horizontal continuous extractors, used worldwide, operate on gravity percolation. The prepared material is transported to the extractor via a conveyor. Solvent sprayers spray the solvent across the raw material bed, moving it from the feed to the discharge end. The extractor bed, equipped with an efficient filtration system, holds the material and provides clean miscella, which then goes to heaters to separate hexane from oil in stages. Lighted sight glasses allow viewing of the spray distribution within the extractor.

The wet meal from the extractor is de-oiled but still contains absorbed solvent. It is transported by bulk flow conveyor to the desolventizing section for hexane recovery.

Desolventization

The desolventizer-toaster (DT) consists of a series of vertically mounted heating jackets. Each jacket has a double bottom for high-pressure steam, with open steam provision to ensure the material surface is fully treated.

De-oiled material from the extractor, containing 20-35% solvent, enters from the top of the desolventizer and passes through steam-heated stages while an agitator shaft with blades rotates it. The desolventization process involves direct and indirect heating to a temperature well above the solvent’s boiling point, ensuring no residual solvent remains in the de-oiled material. The material flows from one jacket to the next via discharge chutes, while solvent vapors are sent to condensers through a wet scrubber for washing.

The de-oiled, desolventized meal, known as de-oiled bran, is an excellent ingredient for cattle and poultry feed. It is conditioned and cooled to the desired moisture level before transport to the bagging section via conveyor.

Distillation

The miscella from the extractor contains approximately 12-18% solvent (for oil cakes or rice bran) and up to 25-35% for sunflower or rapeseed. These liquids are separated by evaporating the solvent, which has a lower boiling point (64-67°C), leaving pure oil.

The distillation occurs in three stages under vacuum (zero oxygen), retaining better oil characteristics. The first stage occurs in an economizer, followed by a flasher, which evaporates the solvent, leaving only oil. The oil is further treated with open steam to remove any residual solvent.

The produced solvent vapors pass through an oil vapor separator to capture any oil particles before moving to a condenser.

Condensation of Hexane

Hexane vapors from the desolventizing and distillation sections require condensation. Floating head-type condensers with tube bundles circulate cooling water through the tubes, with vapors outside. Solvent vapors cool and condense into liquid, which is then separated from water in a solvent-water separator and returned to the extractor. Uncondensed gases are directed to a contact cooler and washed with cold water spray.

Final Solvent Recovery

Residual air in the system may contain trace solvent vapor. To recover this, a final vent air stripping column with an absorber is used, which provides ample contact surface. Mineral oil in the absorber captures solvent vapors from the air. Residual vapors are evacuated through a vent condenser cooled by water in a closed circuit. The residual air is aspirated through an absorption tower where mineral oil absorbs any remaining hexane before condensation.