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The solvent extraction plants are used to extract oil from various oil seeds or from pre-pressed expeller cake. The extraction of oil is done by normal Hexane, which acts as solvent. Solvent and extracted oil is then separated during the distillation process.
DAS Industries has supplied many Solvent Extraction Plants and they process varieties of material including groundnut, mustard seed, soyabean, palm kernal, sunflower, rice bran, copra, cottonseed, minor oil seed like neem, mahua, watermelon seed, castor seed, etc.
Special preparatory equipment is supplied to suit individual characteristic of the raw material.
The solvent extraction plants have following sections:
In the preparatory section the raw material (Oil seed or pre-pressed expeller cakes) is prepared for processing. If the raw material is rice bran, small pellets are prepared using pelleting machine for further processing. Similarly if the raw material is Soyabean, the flakes are prepared using cracker and flaker machines. The raw material is then fed to the extraction section of the plant.
In the extraction section, the raw material is fed to the extractor and treated with hexane and the oil is recovered. The mixture of oil and hexane is called Miscella.
The extractor is horizontal in construction with specially designed conveying system, running at extremely slow speed; it is based on counter current principle. The design has universal acceptance and majority of plants working throughout the world has accepted this designing principle.
We have a special feature where we tilt the extractor at a certain angle to improve its efficiency. The results have been marvelous and our customers have seen exceptional outcome.
The de-oiled material discharged from the extractor contains 25% to 30% solvent (Hexane). This solvent is removed in the Desolventiser Toaster. In the Desolventiser Toaster we use high pressure Jacket heating along with low pressure spurge steam through blades of Desolventiser Toaster. During this process the Desolventiser Toaster pressure is slightly below the atmospheric pressure to minimize solvent loss. The solvent vapors are used in the heat exchanger to heat the Miscella and the remaining vapors are condensed in the condensers for recycling.
The Miscella discharged from Extractor has 18% to 22% content of oil. Firstly, the solvent is separated out from the Miscella by carrying out distillation inside heat exchangers, maintaining vacuum conditions. After heating, the Miscella is fed to a flasher where the content of solvent is reduced to 2%- 3%. In the stripper, from the top, hot oil is sprayed and an open steam is injected at the bottom for further processing. After cooling the hexane vapors in condensers the liquid hexane is recycled back to the Extractor.
Solvent Recovery Section
Non-condensable gases mostly air gets into the system during the processes like extraction and distillation. These gases can cause damage to the system, and thus, have to be vented out. For this, an absorption system is attached through which the vent gases are passed through. In this absorption system, the gases are passed through vegetable oil that completely absorbs the solvent traces from the gases.
We add a special feature to pass the outgoing air and vapors from the plant through water as well where the hexane vapors are absorbed and fed back to the extractor. This ensures that no hexane leaves the plant from vent.