1. Extraction System

• Extractor: This is the heart of the plant. The prepared material (flakes) is conveyed through the extractor where it comes into counter-current contact with the solvent (typically food-grade hexane), dissolving the oil. Common types include:
  • Rotary Extractor: Compact and known for smooth, efficient operation. A modern standard.
  • Loop Extractor: Another highly efficient and continuous design.
  • Belt Extractor: Features a perforated belt to carry the feedstock.
• Solvent Circulation System: Includes pumps, pipes, and tanks that circulate fresh solvent and miscella (the oil-solvent mixture) throughout the system.

2. Post-Extraction Recovery Systems

• Evaporation System:
  • First & Second Stage Evaporators: Use indirect heating (steam) to evaporate and recover the majority of the solvent from the miscella.
  • Stripping Column/Desolventizer: Uses direct steam under vacuum to remove the last traces of solvent and moisture from the oil, producing the final Crude Oil.
• Meal Desolventizing System:
  • DTDC (Desolventizer-Toaster-Dryer-Cooler): Processes the wet meal (the extracted flakes saturated with solvent). It uses steam to vaporize the solvent, toasts the meal to deactivate anti-nutritional factors, and then dries and cools it to produce a stable, high-quality Animal Feed Meal.
• Solvent Recovery System:
  • Condensers: Cool the solvent vapor from the evaporators and DTDC, turning it back into liquid.
  • Solvent-Water Separator: Uses gravity to separate the condensed solvent from water, allowing the clean solvent to be recycled back to the extractor.
  • Mineral Oil Scrubber/Vapor Recovery Unit: Captures solvent vapors from vent gases, ensuring minimal solvent loss and meeting environmental standards.

3. The Solvent Extraction Process Flow

The entire process can be summarized in three main stages: Pretreatment → Extraction → Recovery.

Stage 1: Pretreatment
Oilseeds → Cleaning → Dehulling → Flaking → Cooking → Prepared Flakes

Stage 2: Extraction

• The prepared flakes enter the Extractor.
• Inside, a counter-current flow is established: fresh solvent washes the nearly exhausted flakes, while the strongest miscella (rich in oil) washes the fresh incoming flakes. This maximizes efficiency.
• This stage produces two streams:
  • Miscella: The oil-solvent mixture, sent to evaporation.
  • Wet Meal: The de-oiled flakes full of solvent, sent to the DTDC.

Stage 3: Recovery & Finishing

• Miscella Processing: Miscella → 1st Evaporator → 2nd Evaporator → Stripper → Crude Oil.
• Wet Meal Processing: Wet Meal → DTDC (Desolventizing, Toasting, Drying, Cooling) → High-Quality Meal.
• Solvent Recycling: Solvent vapor from all stages is condensed, separated from water, and returned to the extractor in a closed-loop system.

Advantages of Solvent Extraction

Compared to mechanical pressing, solvent extraction offers significant advantages:

1. Exceptionally High Oil Yield
   • This is the primary advantage. Solvent extraction can reduce the oil content in the meal to less than 1%, compared to 5-8% or more in expeller pressing. This dramatically increases overall oil production and economic return, especially for large-scale operations.
2. Superior Quality Meal (By-product)
   • The process occurs at relatively low temperatures, preserving the nutritional value of the protein in the meal. The resulting product is a high-quality, valuable ingredient for the animal feed industry.
3. High Automation and Low Labor Intensity
   • The plant operates as a continuous, automated system. It requires fewer operators and has lower labor costs compared to batch-based pressing methods.
4. High Adaptability
   • It is the only economically viable method for efficiently extracting oil from low-oil-content materials like soybeans and rice bran.
5. Lower Production Cost per Unit
   • While the initial capital investment is high, the combination of superior oil yield, high automation, and efficient energy use in modern plants results in a lower cost per ton of oil produced.