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  Nov 2006 Jan 2006
     
Solvent Extraction Plant
 
Available in following capacities:-
Solvent Extraction Plant Pictures
 
  • 100 Tones Per Day (24 hrs.)
  • 150 Tones Per Day (24 hrs.)
  • 200 Tones Per Day (24 hrs.)
  • 250 Tones Per Day (24 hrs.)
  • 300 Tones Per Day (24 hrs.)
  • 500 Tones Per Day (24 hrs.)
Suitable to process following types of seeds and oilcakes:-
 
  • Soyabean Seed and Oilcake
  • Groundnut Oilcake
  • Rapeseed Oilcake
  • Cottonseed Oilcake
  • Sunflower Oilcake
  • Castor Oilcake
  • Neemseed Oilcake
Our scope of work include from concept to commissioning on Turnkey basis.
 
Process of Extraction:

 
Solvent Extraction is basically a process of diffusion of a solvent into oil-bearing cells of the raw material, resulting in a solution of the oil in solvent. Various solvents can be used for extraction. However, after extensive research and consideration of various factors, such as commercial economics, edibility of the various products obtained from extraction, physical properties of the solvent (especially its low boiling point) etc; hexane is considered to be to be the best and it is exclusively used for the purpose. In a nutshell the extraction process consists of treating the raw material with hexane and recovering the oil by distillation of the resulting solution of oil in hexane called miscella. The hexane absorbed in the material is recovered by evaporation and condensations also from the distillation of miscella. The hexane thus recovered is reused for extraction.  The low boiling point of hexane (67 C) and the high solubility of oils and fats in it are the properties exploited in the solvent extraction process.  The entire extraction process can be divided into the following stages:-
 
  1. Preparation of raw material.
  2. Process of extraction. 
  3. Desolventisation of extracted material.   
  4. Distillation of miscella.
  5. Solvent recovery by condensation.
  6. Final solvent recovery by absorption.
  7. Meal finishing and bagging.
Because of the highly inflammable character of the normal hexane, those stages of process which involve high speed machineries, such as material preparation, finishing and bagging, are carried out at least 50 feet away from the main extraction plant wherein the remaining processing stages involving handling of the solvent are carried out.  
 
PREPARATION OF RAW MATERIAL:

For thorough and efficient extraction, it is necessary that each and every oil-bearing cell of the material is brought in contact with the solvent.  Therefore, proper preparation of materials prior to extraction is very important to ensure this contact. The smaller the material size, the better is the penetrating of the solvent into the oil-bearing cells; but too fine a size will prevent the solvent from percolating through the mass.  Therefore an optimum size is to be maintained for best extraction. Hence material preparation methods vary from material to material depending on its oil content, size and physical properties.

 The oilcakes from expellers or ghanis are first broken into small pieces in a cake sizer consisting of spiked rolls and then cracked between the two corrugated rollers into small pieces of about 3mm size. This way, the size of the cake/seed is reduced to the optimum without formation of excessive "fines" If the size reduction is carried out by hammer mills or pulverisers heavy "fines" may occur due to direct method impact of the beaters on the cake. 

For high oil content mantels (oil content 15 % or more), the following steps of preparation are recommended to make the material suitable for penetration of the solvent into the oil cells as well as for best percolation.

 
  • Passage of the seed through corrugated roller mills with 3mm flutes reduce the size to about 3mm.
  • Heating the broken material to about 80 C with open steam in  temporary and humidifying the material to raise the moisture content to about 11 to 12%.  
  • Flaking of the humidified material between a pair of plain rolls to 0.25mm thickness or below.  
  • Conveying the flakes to the extraction system after crisping  them in a current of air to make them firm.
 The Flow-chart involved the machinery for preparation of soyabean
 
PROCESS OF EXTRACTION:

 
The prepared material enter the extractor through the rotary air seal. The extractor consists mainly of a very slow moving articulated band conveyor inside a totally enclosed chamber. The band is lined with perforated sheets and porous stainless steel cloth. The mass of the material moving this band forms a slow moving bed. During the movement of the bed through the extraction is washed continuously at various points with miscella of decreasing concentrations and finally with a fresh solvent in a counter current manner by means of sprayers kept in a line over the meal bed.  The miscella percolates through the meal bed, passes through the perforated bottom and collects in various hoppers kept below the bed. The miscella from the last hopper is taken of for distillation.
 
DESOLVENTISTATION OF EXTRACTED MATERIAL:

 
After the fresh solvent each the material in discharged into an air- tight chain conveyor which conveys it to a Desolventiser/Toaster (DT).  The DT is acknowledged to be the most modern equipment for desolventising the march and manufacturers of repute all over the world have switched over to the DT in performance to the obsolete horizontal steam jacketed driers.  The DT is essentially a series of heating pans mounted vertically one over the other. Each pan has a specially designed double bottom in which high pressure steamor Thermic Fluid is introduced. The cylindrical part is also heated by means of special half round coils. Provision is made for the injection of live steam in such a manner that the entire surface of the material is subjected to its action. The material is transferred from pan to pan downwards by a heavy agitator assembly with rotating arms in every pan.  Special level control mechanism ensures the maintenance of the desired level in each pan synchronize the feed into and discharge out of the unit.
 
DISTILLATION OF MISCELLA:

 

The final miscella (solution of oil in hexane) obtained from the extractor is collected in tank, from where it is pumped to the distillation column kept under vacuum by means of a series of steam ejectors. The miscella is heated by jacket steam in the distillation column and thus the hexane is turned into vapour immediately. The vapors are led to the condenser through an entrainment separator. 

The concentrated miscella from distillation column is pumped into a similar secondary distillation unit to raise the temperature to about 100-110 C and then into the final stripper kept under high vacuum. Open steam is injected in the latter to strip the last traces of hexane from the oil.  The vapors both from the secondary still and the hyvac are condensed in the condenser.

 
SOLVENT RECOVERY BY CONDENSATION:

 
All the condensers are of floating head type with tube-bundles to carry the cooling water. The cooled water at 30 C or below is circulated inside the tubes in all the condensers and the vapors are passed outside the tubes.  Thus the vapors are cooled and condensed into liquid. The condenser condenses the vapors from the secondary distillation and final hyvac still.  The condensor condenses the vapors from the primary distillation. The condensor condenses vapors from desolventiser. The uncondensed vapour from are pushed into by ejector. All the condensate liquid (hexane+water) from these condensers is led to a solvent is searated from water by settling the difference in densities of water and the solvent and their immiscibility accomplishes complete separation. The fresh pure solvent from this tank is pumped to the extractor continuously for the final washing of the meal bed.  The uncondensed gases from the condensor are led to contact cooler where they are washed with cold water spray. The condensers and the water from here are led to the same water solvent separator.
 
FINAL SOLVENT RECOVERY BY ABSORPTION:

 

The vapour and gases from the contact cooler are led to absorbed and where they come into intimate contact with an absorbing oil (vegetable oil or mineral oil). The solvent vapors, if any, are absorbed in this oil and non-condensible gases are let out into the atmosphere. While theoretically these gases leaving the plant are expected to be free from hexane, in practice a small amount of the solvent is lost with these gases.  

The oil containing the absorbed solvent is led into an evaporater kept under vacuum and heated to 100 C. The solvent is vaporized and these vapors are led into condensor and recovered. The hot oil from the evaporator is passed through a cooler to cool to room temperature, and having been freed from hexane it is sprayed back into the absorb.  

 
MEAL FINISHING AND BAGGING:

 

The de-oiled meal from the main extraction plant is led pneumatically in a current of air to the bagging room. The draft of air is maintained by fan. 

The meal is not only conveyed but also cooled to about 45-50 C due to contact with the conveying air. The meal collects in cyclone and drops to the humidifier through an air lock feed. In the humidifier the meal is mixed with enough moisture to bring up the moisture content, thus replacing the amount loss during the extraction and desolventisation steps. The humidified meal is then bagged at the discharge of the humidifier. The bag filter collects the meal dust going with the conveying air.

 
   
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