As per safety regulations the main Solvent Plant is located 50 ft. away from the Preparatory, Conditioning and Bagging section as highly hazardous and inflammable Normal Hexane solvent is used (50 feet is present prescribed distance around).
Rotary Air Lock
The prepared Raw materials from the Preparatory section are conveyed by Redler Conveyor to the Extractor via Rotary Valve which regulates the feed of material to Feed Bin. Level indicators are provided on the Feed Hopper to control low and high level of the materials in extractor.
Extractor is a machine with slow moving articulated band conveyor inside a totally enclosed chamber. The band conveyor is lined with perforated sheet, covered with stainless steel wire mesh for easy percolation of Miscella. The Band Conveyor moves on the rail provided inside the extractor. A series of sprays are located above the band conveyor for spraying miscella and solvent on top of the moving material bed of the extractor. During the movement of the bed through the extractor it is washed continuously at various points with miscella of decreasing concentration and finally with a fresh solvent in a counter current manner by means of sprays kept in a line over the meal bed.
The miscella percolates through the meal bed, passed through the perforated bottom and collects in various hoppers kept below the bed which ultimately flows to the miscella holding tank. The extracted meal from the band conveyor falls into the discharge bin and conveyed to the desolventising section by vapour seal chain conveyor.
Extracted material has tendency for retaining the solvent with it and this solvent has to be recovered. The retention varies from 25% to 30% on weight of material extracted. The basic principles involved in desolventisation is indirect/direct heating of material with steam to a temperature well above the boiling point of solvent and thus ensuring that no solvent is left over with the material. Vapours of solvent are then sent to the condensers via scrubber where solvent is condensed.
The D.T. consists of a vertical cylindrical vessel with horizontal jacketed compartments i.e. Double Bottoms and a central rotating vertical shaft on which blades are mounted to 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.
- Intimate contact of material with hot surface helps in properly desolventising the extracted meal i.e evaporation of hexane from the meal and there by maintaining quality of the finished product.
- Steam consumption is also reduced as steam circulates internally.
- Mechanical/Pneumatic level controlling system maintains minimum bed height for complete desolventisation within short contact time.
- Vapour outlet from DT is passed to economizer thus maintaining energy efficient process.
Mixture of oil and solvent obtained in the extractor is known as Miscella and it normally contains 15% to 25% of oil in solvent. The rich miscella from extractor is collected in tanks from where it is pumped to the distillation column. It is kept under vacuum by means of a series of steam ejector. The miscella passing through tubes of evaporator is heated by jacketed steam and thus hexane is turned into vapour immediately. The vapours are led to the condensers via separators. The concentrated miscella passes on to the Oil Preheater to raise the temperature to 100ºC and then to stripping column for final removal of the last traces of solvent from oil. The vapours from the equipments are condensed in the condenser.
Solvent Recovery System
Solvent vapours are formed both in desolventisation section as well as distillation section and these are to be condensed. Special floating head type condensers with stainless steel tubes are provided. The floating head type condenser helps quick and easy removal of tubular bundle for periodical cleaning.
The air that is being ejected out of the system contains traces of Solvent in order to recover the traces, special final vent air stripping system has been provided.
It comprises of a main absorber which is packed with a Pall Rings to give a larger surface of contact. It is partly filled with groundnut oil/ mineral oil being suitable absorbing media which absorbs the Solvent vapours from the air. The oil and Solvent mixture is distilled to recover the Solvent.