Solvent Oil Extraction

Solvent oil extraction is a method of making edible oil by using the principle of extraction and selecting a kind of organic solvent which can dissolve oil and grease, through contacting with the oil (soaking or spraying), so that the oil and grease in the oil can be extracted.

Applicable Raw Materials

At present, the international common practice is: vegetable oils with high oil content (such as peanuts and rapeseed, sunflower seeds, cottonseeds, etc.) are usually produced by pre-pressing and solvent extraction technology; vegetable oils with low oil content (such as soybeans) are usually produced by direct extraction. In order to make full use of oil resources and improve economic benefits, oil cakes after pressing should generally continue to be extracted to produce cooking oil.

Solvent Oil Extraction Basic Process

The basic process is to immerse oil flakes (or pre-pressed cakes) in selected solvents, dissolve oil in solvents (composing mixed oil), then separate the mixed oil from solid residues (meal), evaporate and strip the mixed oil according to different boiling points, so that the solvent vaporizes into vapor and oil separates, thus obtaining oil (extracted crude oil). The solvent vapor is recycled after condensation and cooling. The meal also contains a certain amount of solvent. After desolution and drying, the meal can be dried. The solvent vapor volatilized during desolution and drying is still recovered by condensation and cooling.

Solvent Oil Extraction Flowchart

solvent oil extraction process
 

Edible Oil Solvent Extraction Advantages

  • Solvent oil extraction method has the advantages of low residual oil rate, less than 1% residual in the cake (high oil yield), low labor intensity, good working environment and good quality of meal. The disadvantage of solvent oil extraction process is that there will be residual solvent in crude oil, but if it is strictly operated according to the standard, the residual cannot be detected in final product.
  • It can be seen that compare to oil pressing method, solvent oil extraction method is indeed an efficient way of edible oil production, which has been widely used at present.
     

Solvent Extraction Detail Introduction

1. Solvent Extraction System:
The meal(cake) or flakes comes from the pretreatment or prepressing plant is conveyed to the extraction workshop buffer bin by scraper conveyor. The buffer bin could control the meal level automatically by sealed valve at the bottom of the buffer bin. The cake is temporarily stored in the buffer bin and stacked in certain height for the purpose of keeping constant flow and sealing against solvent gas escaping from extractor during the extractor is running or shutdown. The meal is feeded into each cell, from inlet to outlet, using the different concentration miscella oil spraying, and before the miscella drains out, using the the fresh solvent spaying to exact the oil out completely from cake. Then the miscella oil sent to the temporary storage tank and go for Evaporating System, and the oil meal go for Desolventizing process.

Negative pressure in the extracting system has helped against solvent gas escaping out.

solvent extraction system


2. Wet Meal Desolventizing system:
The oil meal after oil drain we call wet meal. The Desolventizer (D.T.D.C.) is used to evaporate and separate the solvent and some moisture out from Wet Meal. The Desolventizer is made up of 7 layers.(For capacity less than 100tpd, usually 5 layers, DT-desolventizer-toaster), The 1st, 2nd layers are designed for pre-heating Wet Meal to reduce solvent and moisture contents. These trays are heated by indirect steam to remove the free solvent on the surface of Wet Meal. During this period, the temperature of Wet Meal is kept unincreased due to a large of solvent evaporating. The pre-desolventized Meal then goes down to the 3rd and 4th, layers which are designed for steam penetration and heated by direct and indirect steam. Mixture of Steam and Solvent Vapor will pass through Wet Meal, which can not only make heat exchange but also remove some Solvent in the Wet Meal. The 5th is desolventizing layer. Saturated Steam blows in directly and removes Solvent in Wet Meal completely. There is steam condensate in the direct steam, which will increase moisture content in meal. In the and 6th layer, blow in Hot Air to reduce moisture in the Meal. Subsequently blow in Cold Air in the 7th layer to reduce temperature of Desolventized Meal. After all these steps, the Meal is discharged out of Desolventizer and conveyed from the extraction workshop to Meal Storage House by Meal Conveyor. 

Hot Air used for drying extracted Meal in the DTDC- Desolventizer is supplied by Blowing Fan and heated by Hot Air Heater. 

wet meal desolventizing and miscella evaporating system

 
3. Miscella Evaporating System:
Miscella is temporarily stored in the Miscella Tank where some Meal Fine can settle down by sedimentation and then is pumped out back to Extractor. The Miscella is pumped by the Feeding Pump to the 1st Stage Evaporator. Heat source of 1st Stage Evaporator is the secondary steam coming from Desolventizer. So the heating energy from DTDC Desolventizer is significantly re-used and saved. Miscella from 1st Stage Evaporator makes heat exchange in Heat Exchanger with crude oil coming from Oil Stripper, thus temperature of Miscella when entering into 2nd Stage Evaporator is increased and temperature of crude oil is lowed. The Miscella is then pumped to the 2nd Stage Evaporator. Heat source of 2nd Stage Evaporator is indirect steam. Subsequently the Miscella is pumped to the Oil Stripper. It is negative pressure in the Oil Stripper, where total volatile in crude oil is reduced by direct steam.

Miscella Evaporating System


4. Solvent Vapour Condensing System:
Solvent Vapour Condensing System is closely connected with Evaporation System. It is negative pressure in the 1st and 2nd Evaporatorsas well as in the Oil Stripper and the related Condensers. The Mixed Vapour from shell of the Evaporators enters into the EV Condenser; and the Mixed Vapour from the Oil Stripper enters into the ST Condenser. Mixed Vapour from DTDC Desolventizer is used as heat source for 1st Evaporator and, after being used, most of it will be condensed into liquid; that un-condensed Vapour from shell of 1-Stage, Evaporator enters into DT Condenser . All Solvent Vapour from Extractor, un-condensing Vent Vapour, Free Vapour from Solvent-water Separator, Free Vapour from Solvent Working Tank, Free Vapour from Underground Solvent Storage Tanks and Free Vapour from Miscella Tank finally enters into the Vent Condenser, where the Vapour is cooled by cooling water and most of the Solvent Vapour is recovered in this way. At last, Vent Vapour with little Solvent enters into the paraffin oil recovering system.

Solvent Vapour Condensing System


5. Paraffin Oil Recovering System:
Generally the paraffin oil without Solvent is called “Lean Oil”, while the paraffin oil containing of Solvent is called “Rich Oil”). The Vent Vapour firstly enters into Paraffin Oil Absorber, where temperature should be less than 35℃. The Paraffin Oil and Vent Vapour contact with each other counter-currently. Paul Ring in the Paraffin Oil Absorber ensures ideal absorption effect. Details are as follows: the Rich oil from Paraffin Oil Absorber  is pumped into the Heat Exchanger to make heat exchange with Lean Oil. Then after being heated in the Heater by steam, the Rich Oil enters into Paraffin Oil Stripper, where vapour-liquid heat exchange is made on the surface of Paul Ring between direct steam and Rich Oil to remove Solvent in the Paraffin Oil. Then the Lean Oil enters into Paraffin Oil Absorber again for re-use. Vent Vapour, after being full absorbed by paraffin oil, is let out of the workshop by the Vent Fan.

Paraffin Oil Recovering System

The Solvent Condensate from every condensers finally is collected by the Liquid Collector  and then sent into Combined Solvent-water Separator to remove water from Solvent. Wastewater separated in Combined Solvent-water Separator flows into Boiling Tank, if there is still some Solvent Residue in the Waste Water, then boil it in the Boiling Tank before discharging. 

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