Transcript CULTIVATION OF SALT - Welcome to GHCL Connect

Salt 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.
Salt 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.
CULTIVATION OF SALT
Introduction
The 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.
Process Flow Up Chart
Solar salt process
It can be divided
in to four stage.
1.
2.
3.
4.
Brine management
Crystallization
Salt harvesting
Up gradation
Brine management
The other salts which crystallize from
concentrated brine along with sodium
chloride are
1. Iron oxide - 3 deg to 10 deg Be
2. Calcium carbonate – 10 deg to 17 deg
3. Calcium sulphate ( Gypsum ) - 17 deg
to 24.5 deg Be
4. Sodium chloride -24.5 deg to 29 deg Be
5. Magnesium Bromide – 29 deg to 31 deg Be
6. Magnesium Sulphate - 31 deg to 35 deg Be
7. Potassium chloride - 35 deg to 37 deg Be
8. Magnesium chloride – 37 deg to 39 deg Be
Stage 5 to 8 salt called as bittern salts.
Initial stage
The 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.
Second stage
This 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.
Third Stage
When 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.
Fourth Stage
At 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/ ( 100 + 36.5 ) = 26.74 % by
weight. Thus every 100 grams of
saturated brine solution contain
26.74 grams of salt and 73.26
grams of water.
Crystallizers.
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.
Crystallizers
Normally density 25.5
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.
Salt Bed Formation
Our 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 22000
tons. This quantity is lost. Only
for edible salt manufacturing to
improve the quality parameter.
Harvesting
The 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.
Up gradation by Screw washery
Up gradation
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.
Up gradation by Hose washing
Hose washing with
brine, impurities are
removed partly by 70%,
before supplying chloralkali 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.
Veda Salt Screw Washery
Performance
Parameter
Input
Output
Ca (%)
0.147
0.120
Mg (%)
0.334
0.195
WIR (%)
0.064
0.035
WI (gm/cc)
34.63
45.83
The 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.
Meteorological Factors Influencing Salt
Production
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Vapor pressure and
Temperature
Dissolved solids
Wind velocity
Surface of exposure
and
Impermeability
Vapor 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.
Dissolved Solids
The 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.
Wind Velocity
The 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.
Surface Exposure
Evaporation 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.
Impermeability
Reservoirs 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.
Rain Fall Disturbance
The 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 .
Usage of salt
Salt 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.