Solvent extraction is a process of diffusion of solvent into the oil bearing cells of the raw material, resulting in a solution of the oil in the solvent." Hexane" is chosen to be appropriate and the best for the use considering its viability with reference to commercial economics, edibility of various products being obtained after extraction, characteristic mainly its low boiling point and other factors. The entire process is largely divided into three main sections as follows : Preparatory Section Main Extfiaction Section Meal Bagging Section The main extraction section is again divided into following subsections Extraction of oil from prepared raw materials, Desolventisation Distillation to recover oil from solvent Condensation Final solvent recovery section The finishing section includes conveying, cooling and bagging PREPARATORY SECTION An efficient extraction would need that every oil-bearing cell of the material is in contact with solvent. In other words, the smooth preparation prior to main extraction is very vital to comply with this contact. Smaller the material size, better the penetration of the solvent into the oil bearing cells, but too fine a size will prevent the solvent from percolating through the mass. Hence an optimum size is absolutely essential for efficient extraction. The method of material preparation does vary from material depending upon its oil content and physical properties. we group them as follows: Oil cakes High OiI Content Material Floury material In the case of oil cakes, being big pieces, have to be reduced to proper size and without fail, ensuring that there are no 'fines'. Cake sizer and cake crackers are the finest to this process. In the case of high oil content seeds like sunflower, mustard, rapeseed, safflower etc. for a good extraction, it passes through the well proven expander after flaking with a squeezomatic arrangement where part of oil will be squeezed in the preparatory and balance collets will o to the plant through the latest updated drier cooler. you will find here cake cracker, cooker, flaker, expander with squeezomatic arrangement, drier cooler. In case of floury material like rice bran, etc. any of above preparation equipments are workable hence a pelletiser with conditioning screw. The prepared material is transported to the main extraction section via an chain conveyor. MAIN EXTRACTION The prepared material has above is received into extraction plant by an chain conveyor via an rotary air seal in the raw material receiver. an arrangement for controlling the level of material is fed into the extractor continuously from the receiver. The design of extractor is such that it can transport the material through the solvent spraying chambers and the speed of transportation can be varied easily. the chamber consist of number of solvent sprayer which in uniform sprays the solvent over the entire bed of raw material. The length and breadth in designed to give sufficient time for intimate contact and penetration and percolation of solvent into the raw material. To view the distribution of spray, provided on the extractor are light and sight viewing glasses. The material coming out of the spraying chamber is deoiled material, which is to recovered in the desolventising section. While the mixture of the oil and solvent called "miscella" is pumped into the miscella tank, from where it will be transported by means of a special chain conveyor to the desolventation. DESOLVENTATION The extracted material usually has a tendency for retaining the solvent with it, and this solvent has to be recovered. the retention varies from 20% to 35% weight of the material extracted. the basic principle involved in Desolventsation is indirect heating of material with the steam to a temperature well above boiling point on solvent and thus ensuring no solvent is left over with the material vapours are sent to condensers via scrubber where the solvent is condensed. As in the case of soyabean or cottonseed, an desolventiser toaster is recommended where the heating operation can be better controlled and higher rate of heating is possible to destroy unwanted enzymes present in the material. The rotary seals are provided at inlet and outlets of desolventisers to ensure an airtight arrangement. This is essential to keep the solvent loss figure down. The deoiled and desolventised meal thus obtained is then transported of finishing section with the help of a chain conveyor. A cooling arrangement consisting of meal cooler (Optional) thus ensuring proper cooling of the material for easy bagging in the finishing section and to add and hold moisture 1O to 12%. DISTILLATION Mixture of oil and solvent obtained in the extractor is known as "misceI|a" and it normally contains 12 to 18% of oil in the solvent in case of oilcakes/rice branlsoyabean and 25 to 35% in case of sunflowerseed I rapessed. During distillation, solvent evaporates first due to its low boiling point (65 to 75 degrees cen.) thus leaving clean oil behind. Distillation is performed in three stages under vacuum to ensure that no oxygen is present when the oil is heated to a high temperature. Presence of oxygen will exercise the oil making it unsuitable. First evaporation takes place in prime Miscella Flasher and concentrates in the second Flasher leaving practically only oil behind. This oil is further treated with open steam to ensure that the solvent finds its way along with the oil. The solvent vapour thus produced passes through oil vapour separator to separate out any oil particles trapped with solvent vapours and are then passed on to condensor for condensation. Vacuum in distillation is maintained with the help of evacuators. CONDENSATION Solvent vapours are formed both in desolventation section as well as in distillation section and these are to be condensed. Special floating head type condensor with tubes are provided. The floating head type condensers for complete condensation of solvent vapours. FINAL SOLVENT RECOVERY In spite of providing adequate Condensors, the air that is being injected out of the system contains traces of solvent. In order to recover the traces, a special final vent air-stripping column has been provided. It comprises of a main absorber which is fitted with stainless steel corrugated sheets to give a large surface of contact and its rotating. It is partly filled with groundnut oil being suitable absorbing media, which absorbs the solvent mixture, is distilled to recover the solvent. FINISHING SECTION The extracted and desolventised meal is transported to finishing section by means of a chain conveyor fitted with cooling arrangement. The material received has lots its inbuilt moisture, hence on a special hydrator; moisture is added to the cake thus increasing its weight.
Bardi, Nagpur, Maharashtra 
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