Cotton Seed Solvent Extraction Plant

Cottonseed, as the by-product of cotton ginning operation, is covered with fibrous lint. The cottonseed is mainly made up of inner kernel, usually called "meats".


    Cottonseed, as the by-product of cotton ginning operation, is covered with fibrous lint. The cottonseed is mainly made up of inner kernel, usually called "meats". This meaty portion contains all the oil as well as proteins, and it is enclosed in the fibrous hull. The hulls stick out over the cotton fiber which escape the ginning and left on seeds. These cotton fibers are called "lint".

    The inner kernel can be planted, fed to livestock, made into cottonseed oil for human consumption, used for fertilizer, or used in products like lotions and soap. The lint we get from cotton delinting has wide application in cotton blanket, sweat shirt, paper board industry and cotton pulp, etc. Therefore, the cottonseed delinter is very essential in cotton processing.

    Cotton seed is first cleaned free from the foreign matters such as stones, shale, sticks, iron, earth, etc. The foreign matter in the seed can be anywhere between 2 to 5 % depending upon the way kapasis handled at the fields. It is essential to remove the foreign matters so as to protect the further processing machinery from damage and excessive wear and tear. Seed cleaning is carried out over reciprocating type sieves to separate unwanted matter. The seed is then pneumatically lifted to separate the heavy matters such as stones, iron, etc. The cleaned seeds are then fed into a battery fof delinting machines in which tight rolls of seed are pressed over high speed circular saws. The saws scrape off the lint from the seed and the lint is sucked pneumatically into lint beating and cleaning devices.

    The lint beating and cleaning is done to increase the cellulose content of the lint and the product is bagged. Delinting is generally done in two stages, in the first stage a light cut is taken and in the 2nd stage more severe cut is allowed. The fiber length of the first lint is much longer than the second cut lint. Long fiber is preferred for the use in paper and artificial silk industry. The recovery of lint varies from seed to seed depending on its original lint content, but generally the recovery is about 1.9% to 2.2% first cut and 3.8% to 4.5% second cut.

    The delinted seed is then Fed into Hullers wherein the outer hull of the seed is cracked by knife edge mounted on high speed rotors. The mixture of hulls and meats so produced is passed over reciprocating sieves to separate the meats from hulls. The hulls are passed through a series of separators and beaters to ensure that they are free of entrained oil and protein bearing meats and then bagged, the meats containing about 35 % oil and 35 % protein are conveyed to the expelling section for crushing. Some portion of hulls is allowed to go with meats for adjusting the protein content of the final meal to the desired level.

    In the Expelling section, meats are cooked in a tempering apparatus and fed into a series of expellers consisting of heavy screws working in strong cages. The meats are squeezed with pressure as high as 5 to 10 tonnes per sq. inch. At this pressure the oil is squeezed out through the slits in the cage and the meats pressed into oil cakes containing about 10 to 12% oil are discharged through the cage.

    The crude oil obtained from the expellers is filtered through plate and frame type filter presses and then sent to washing neutralisers before being sent to Refinery, wherein they are washed with caustic soda, which reacts with free fatty acid content of the oil and forms soap. The soap is separated from the oil and the oil is the pumped to refinery for further process.

    The cake thus obtained in the expelling section is fed to the solvent extraction plant for further extraction of oil.

    The process of Solvent Extraction involves the injection of hexane into the oil bearing materials resulting in a mix of oil and solvent, called miscella. Hexane from miscella is later evaporated using Distillation unit and resulting in unrefined oil. Hexane so evaporated is condensed and can be recycled. Our innovative design techniques in continuous extractor and desolventiser toaster have resulted in minimum hexane loss and we gained accolades from the clients. The by-products so obtained from the desolventiser toaster i.e. De-oiled Cake is an excellent ingredient for cattle and poultry feed manufacturing as De-oiled cake contains proteins and other nutrients.
    Extraction being the main section is further divided into the following subsections:

    * Extraction of oil from prepared raw materials
    * Desolventisation
    * Distillation/evaporation of Hexane to recover oil from miscella
    * Condensation of Hexane
    * Final Solvent Recovery Section 

    Extraction section
    Horizontal Continuous Extractors are employed around the globe and works on the principle of gravity percolation. The prepared material from the preparatory section is transported to the continuous extractor unit using conveyor system. Extractor unit comprises of a number of solvent sprayers which sprays the solvent over the entire bed of raw material transporting the material from feed to the discharge end. Extractor bed with efficient filtration system for holding the material besides providing clean miscella moves over the rails inside the extractor unit. Miscella is combination of oil and the solvent (mostly hexane) percolated through the material bed. Miscella is then subsequently taken to heaters for separating hexane from oil in three to four stages. Light and sight viewing glasses are provided to view the distribution of spray inside the extractor unit.

    The wet meal from the extractor unit is de-oiled material and absorbed solvent is transported by means of bulk flow conveyor to the Desolventising section to recover the hexane. 

    Desolventiser-Toaster (DT) consists of a series of heating jackets mounted vertically one over the other. Each jacket has a specially designed double bottom in which high pressure steam is introduced. Provision for open steam is also made such that the entire surface of the material is subjected to its action. 

    De-oiled material from the continuous extractor unit contains 20 to 35% of solvent. This material enters from the top of desolventiser toaster and passes from stage to stage of steam jacket while being rotated with an agitator shaft fitted with blades. The basic principal involved in Desolventisation is direct and indirect heating of the de-oiled material with steam to a temperature well above boiling point of the solvent and to ensure that no solvent is left over in the de-oiled material. The material flows from one steam jacket to the next through discharge chutes. Solvent vapours are sent to the Condensers via a wet scrubber where the solvent is washed for any fines. The de-oiled and desolventised meal called as De-Oiled bran is an excellent ingredient for cattle and poultry feed manufacturing is conditioned and cooled to desired moisture level before being transported to the bagging Section with the help of a conveyor.

    Miscella from the extractor unit contains nearly 12% to 18% of solvent in case of oil cakes or rice bran and up to 25% to 35% in the case of sunflower seed or rapeseed and hence the two liquids of miscella have to be separated. Separation of two liquids is done by the evaporation of solvent due to its lower boiling point of 64 to 67 degree Celsius and thus leaving clean oil behind.

    Distillation process is usually carried out in three stages under vacuum condition (zero oxygen for better efficiency of evaporation at elevated temperatures) to retain the better oil characteristics. First stage of distillation is carried out in Economizer followed by a Flasher to evaporate the solvent and thus leaving practically only oil behind. Thus obtained oil is further treated with open steam to ensure that no solvent stays behind.

    The solvent vapours thus produced passes through an Oil Vapour separator to separate out any oil particles trapped with the solvent vapours before passing on to a Condenser.

    The oil and solvent mixture is distilled later to recover the solvent. The hot oil from the evaporator is passed through a cooler to cool to room temperature, and finally transported to the storage tank.

    Condensation of hexane
    Hexane vapours from Desolventisation Section and also from Distillation Section need to be condensed. Condensers usually are of floating head type and with tube bundles to carry the cooling water. Cooled water at room temperature is circulated inside the tube bundles and with vapours outside of the tubes. Thus the solvent vapours are cooled and gets condensed into liquid. The condensate liquid so obtained is passed to solvent water separator where the difference in densities of water and solvent and their immiscibility accomplishes complete separation. The so obtained solvent from this tank is again fed 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. 

    Final solvent recovery
    The air that is being ejected out of the system contains traces of solvent. In order to recover these traces, a special final vent air stripping column has been provided. It comprises of a main Absorber to give a large contact surface. It is partly filled with mineral oil to absorb the solvent vapors from the air. 
    The residual vapours from these condensers are evacuated by ejector to a vent condenser cooled by water in close circuit. The residual air is aspirated through an absorption tower where mineral oil absorbs residual hexane in air before being condensed using vent condenser.