In an LM Extractor, the material enters through an inlet hopper and is swiftly saturated with miscella.
Solvent Extraction is a process in which oil is extracted from oil-bearing materials by treating it with solvent having low boiling point. The solvent extraction method recovers almost all the oils and leaves behind minimum oil in the raw material. The solvent extraction method can be applied directly to any low oil content raw materials. It can also be used to extract pre-pressed oil cakes obtained from high oil content materials. Because of the high percentage of recovered oil, solvent extraction has become the most popular method of extraction of oils.
Despite the seemingly complicated array of equipment, the process consists of just four major functions:
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 called Miscella. Hexane is considered to be the best solvent and it is exclusively used for this purpose. Hexane has about the best characteristics of the many solvents tried over the years with a boiling point of 69°C it is a liquid in all but the most extreme climates of the world. With a high volatility and a low sensible heat of 144 Btu/lb (335 kJ/kg) it is relatively easy to remove from the solids and oil with low energy use.
The mass of the material moving on this band forms a slow-moving bed. During the movement of the bed through the extractor it 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 perforated bottom and collects in various hoppers kept below the bed. The miscella from the last hopper, which is concentrated, is taken off for distillation.
The D.T. consists of a vertical cylindrical vessel with horizontal jacketed compartments and a central rotating vertical shaft on which are mounted sweeps in each compartment. The Material to be desolventised and toasted is fed in to the top compartment of D.T and heated with open steam. Open steam condenses a lot of moisture in the material at the same time evaporating the solvent.
The material then flows to lower compartment. In lower compartments the material is gradually heated to 115 to 120° C thus evaporating all the solvent, cooking the material and driving away extra moisture. Finally, the material, which is now completely desolventised is continuously discharged through airtight seal into a redler conveyor, which carries into the bagging section.
The vapours evolved in the desolventiser are led through a dust catcher wherein they are scrubbed with hot water spray to remove fine dust and then led to a condenser to condense the vapours.
Firstly, the solvent is separated out from the miscella by getting heated inside economiser. The concentrated miscella thus obtained from the economizer unit is rapidly heated in the first evaporator by means of low-pressure steam and enters into the series of flashers & heaters, where solvent vapours are flashed off. The oil rich miscella thus obtained is charged into the dryer & stripper. The flashed of solvent vapours are condensed into the condensers & liquid solvent is recirculated back to the process through solvent water separator.
Distillation system operates under high vacuum. Furthermore, the distillation system is coupled with a final drying of oil in final oil heater, which results in production of oil with exceptionally low volatiles in it. After that the oil is transferred to the oil storage tank by passing it through oil cooler where the temperature of oil is tried to brought down near to atmospheric temperature.
In a running plant, non-condensable gases with mostly air get into the system during the processes like Extraction and distillation. These gases can cause damage to the system, hence, have to be taken care of. For this, Recuperation system is installed through which the vent gases are passed through. In this Recuperation system, we use vegetable & Veg Mineral Oil as a media that completely absorbs and release the solvent traces in the gases. The oil has to be kept in check for the presence of volatiles.