2Salt Production In India India is the 3rd largest salt producer in the World with an average production of 18 million tons per annum, first and second place are USA and China respectively. In India the contribution of Gujarat is 75%, Tamil Nadu 12%, Rajasthan 9%, Andhra Pradesh 1.6% and remaining 2.4% are contributed by Karnataka, Goa, Maharashtra, Orissa, Himachal Pradesh, West Bengal and Diu & Damon.
3Salt Production In Tamil Nadu Thuthukudi, Ramanathapuram, Ngapattinam, Viluppuram and Kancheepuram are the major salt produced districts. Thuthukudi district constitutes 70% of the total salt production of Tamil Nadu and 30% of that India. Tuticorin is the second largest producer of salt in India next to Gujarat. Vedaraniam following close on its heels. Salt is produced in as much as 9000 acres of land amounting to an estimated 3.5 million tonnes.
4CULTIVATION OF SALTIntroductionThe history of solar salt, sea water evaporated in pits, formed white layer and it is called solar salt. The precipitation of salt from sea water consists of progressive evaporation of brine in large ponds using solar heat and natural wind. As the brine evaporates its concentration rises and starts the fractional crystallization in order. During the process, the sodium chloride fraction is separated from the brine appropriate concentration in crystallizer ponds and deposits crust. The salt crust is harvested by variety of methods from simple hand labour to mechanical harvester.
6Solar salt process It can be divided in to four stage. 1. Brine management2. Crystallization3. Salt harvesting4. Up gradation
7Brine managementThe other salts which crystallize from concentrated brine along with sodium chloride are1. Iron oxide - 3 deg to 10 deg Be2. Calcium carbonate – 10 deg to 17 deg3. Calcium sulphate ( Gypsum ) - 17 degto 24.5 deg Be4. Sodium chloride deg to 29 deg Be5. Magnesium Bromide – 29 deg to 31 deg Be6. Magnesium Sulphate deg to 35 deg Be7. Potassium chloride - 35 deg to 37 deg Be8. Magnesium chloride – 37 deg to 39 deg BeStage 5 to 8 salt called as bittern salts.
8Initial stageThe pond size is big and known as reservoir. Lots of shrimps and silt come along with sea water. The silt settles in ponds and there after clean brine flows further. This will not only give more clean brine but it will allow more concentration of shrimp in first stage ponds only. By gradual evaporation the sea water original volume reduced to 37% when density reaches to 10 deg Be.
9Second stageThis stage ponds is called condenser. The size of the ponds is smaller than initial stage. The original volume reduced 20%. The brine remain unsaturated till 17 deg Be, some times it is noticed that a portion of Gypsum, calcium and magnesium carbonate separates out at 12 deg Be.
10Third StageWhen concentration reached 17 deg Be the calcium sulphate (CaSo4 2H2O) starts to separate out in from of thin layer first it float thereafter settled down at bottom. The major portion of Caso4 separated out at 17 deg Be to 25 deg Be.
11Fourth StageAt this stage rate of evaporation reduces less than 50% of sea water. Here separation of sodium chloride start along with other salt impurities of sodium chloride. Every 100 grams of water evaporated from saturated solution, 36.5 grams of sodium chloride precipitate. The percentage of salt present in saturated solution would be: 36.5/ ( ) = % by weight. Thus every 100 grams of saturated brine solution contain grams of salt and grams of water.
12Crystallizers.The crystallizers are the heart of the salt works. Hence it best utilization is most important for a salt works. The crystallizers should be having minimum permeability, maximum yield with quality salt. Before and after charging the brine to crystallizers depth and density / specific gravity and also Ca and Mg should be determined.
13CrystallizersNormally density to 28.5 deg Be maintained in crystallizers. In deep charging of crystallizers, the formation of crystal is cubical where as in shallow charging crystal formation in hallow type. Removal of impurities in cubical crystal is easy in washing plant.
14Salt Bed FormationOur raw salt manufacturing process at crystallizer pans are totally different from other salt works. we used to form salt bed thickness of 16 mm above the soil bed. Normally It takes more than 30 days to form such salt beds. The total salt required for the formation is about tons. This quantity is lost. Only for edible salt manufacturing to improve the quality parameter.
15HarvestingThe salt forming over and above the salt bed is racked continuously for 10 to 15 days(It’s depending up on the prevailing weather condition ). The salt is scrapped, loaded manually and intercarted in to the storage yard. Heaping the salt by belt conveyors.
16Up gradation by Screw washery Harvested salt, has impurities derived from sea water. By screw washing insoluble residue can be removed and chemical impurities also reduced significantly. By using screw washed salt in refinery goes down the cost of production in all parameters.
17Up gradation by Hose washing Hose washing with brine, impurities are removed partly by 70%, before supplying chlor- alkali industries. By using washed salt the caustic industries save on chemicals, minimize the generation of sludge, and also reduce consumption of raw materials. The life of membrane cell increase the power consumption also goes down.
18Veda Salt Screw Washery Performance ParameterInputOutputCa (%)0.1470.120Mg (%)0.3340.195WIR (%)0.0640.035WI (gm/cc)34.6345.83The raw salt is washed in the washery to enhance the white index and reduce the other chemical impurities to ensure quality supply to Tirupporur unit.
19Meteorological Factors Influencing Salt Production Vapor pressure and TemperatureDissolved solidsWind velocitySurface of exposure andImpermeability
20Vapor Pressure And Temperature Sea water is a certain amount of its vapor the pressure. It depends upon the temperature and its rises with temperature. The tendency of the sea water to evaporate is gauged by its vapor pressure and the factors influencing vapor pressure have similar effect on the evaporation of the sea water. Atmospheric air has always a certain amount of water vapor in it. At any given temperature there is a limit beyond which air will not absorb more water vapor till the limit for the temperature is reached. The extent of evaporation depends on the vapor contend or relative humidity, the higher vapor content, lesser the evaporation.
21Dissolved SolidsThe rate of evaporation decreases with rise in concentration of the salt solution. Low concentrate brine evaporates and loses water more quick than higher concentrate brine.
22Wind VelocityThe wind is blowing over brine, the layer of air in contact with liquid surface changes constantly and more and more water evaporates to attain an equilibrium with each fresh layer of air with which it comes in to contact. 3Kmph to 15 Kmph velocity wind is ideal for salt production.
23Surface ExposureEvaporation takes place only from the surface. The larger the exposed surface of the brine, the greater is the rate of evaporation. Evaporation of brine thus increases with, rise in temperature, wind velocity and surface exposure. Evaporation decreases progressively with the rise of humidity of the atmospheric air and concentration of brine.
24ImpermeabilityReservoirs and condensers should be prepared impermeable nature to prevent percolation by ploughing, leveling and consolidation. In final condensers and crystallizer pans the soil bed should prepared impermeable by artificial treatment with clay, sand, well gravel and lime powder with propionate blending.
25Rain Fall DisturbanceThe occurrence of rainfall is vital role in the solar salt production. If it occurs frequently during the manufacturing season, it interferes by diluting the brine and reducing evaporation. If there is any heavy downpours on few occasions can be managed by allowing the rain water to over flow from the pans and its pumping out immediately .
26Usage of saltSalt is using of both industrial and edible purposes. Salt is often used in the preservation of meat , fish and other food products. As well as seasoning food and preserving it. Salt is used in large quantity for the curing of hides, the making of brines for using refrigeration and ice factories, the making of dyes. Large quantities of salts are used for making of soda ash and caustic soda. Industries which use large quantities of the salt are: Oil refining , Hard Soap , Ceramic , various Metallurgical, paper works and textiles.