Salt field formation

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Salt field formation

A note on Laying out a salt works

The following aspects have to be taken note of while establishing a salt works for its successful

operation.

LOCATION :- The salt works should be laid out preferably away from an estuarine area as

sudden flood or flow of copious waters inthe river will dilute the sea brine to 0 Be against itsusual 3 Be. This will render pumping from primary source impossible and practically starve the

salt works for brine when it is most needed during summer months. This will have disastrous

effect on salt production. Likewise, the salt works should be laid out over land at least a metre

higher than the high tide level, to avoid inundation particularly of the crystalliser area. This willfacilitate draining rainwater caused by unreasonable rain to resume operation andalso effectively

drain the bitterns.

2) RAINFALL:- The pattern of rainfall to be studied. The rainfall should preferably be confinedto a particular consecutivemonths, instead of spread all over the year. For instance, in Tuticorin

the rains cover during 15/10 to 15/12, and in Gujarat between June 15th to September, leavingthe other months for undisturbed production of salt.Rainfall figures for past five years, month

wise should be collected. The productivity there will be about 15 tones per acre per year, against

50 to 60 at Tuticorin and Gujarat where sea brine is used Rail fall details for past 5 years to becollected along with occurence of floods, if any, which adversely affect salt production.

MET DATA:- Meteorological data, particularly the Max/Min temperature, average relative

humidity and the wind pattern(wind rose for the year for the location) should be collected.General high ambient temperature and low humidity say nor above 55% will be helpful to salt

production as they are congenial conditions for evaporation . There is bound to be seasonalvariation in the wind direction and wind velocity. Land breeze with velocity of steady 15 to 20kmph will help to achieve good salt production.

SOIL CONDITIONS:- Salt works should be laid out over land with clayey soil which does notallow seepage of brine into the ground. Soil with at least 50% to 60% clay content can be

rendered non-percolative by wet plouing the land followed by consolidation same, preferably for

large area like reservoir and condensers. The crystallisers need more attention as seepage should

be zero in this area which handles the concentrated 25 Be brine, which is incidentally thecostliest brine.

However, sandy soil also can be used for salt works by using 600 gauage LDPE film as barrier.But the cost of such development is very high and the productivity of the area also should be

high enough to justify such expenditures so that the payback period is reasonably short.

BRINE SUPPLY:- Large salt works depend on seabrine of 3to

3.5 Be (35 ppt), as it is available in unrestricted quantities.The sea brinecan bepumped outstraight from sea by constructing a jetty (eithersteelorRCC) projecting into the sea for say 100

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meter and locating the pump shed at its end Conveyance of pumped briue either by RCC or

PVC/FRP pipes. The location of the jetty should not be

affected by floods in the rover, which will reader the sea briue 0 to 1 for considerable length of

time, depending on the duration of the flood.The other source of briue is the seeb soil

briue,preferably through borewells which yield briue of EOPPT to 100ppt, with a yield of 60 to100gpm. But borewells tend to the undependable, as the yield gets reduced over time and at

times dilution also gets in. These are ideal for areas below 100 acres as otherwise there will be

over exploitation of the B/W briue leading to failure of the borewell.

6). LAYOUT DESIGN:- a well designed salt works has definite functional areas as below;

6.1) Reservoirs Where the briue used is sea briue of 3 Be, the reservoiur forms 36% of the totalarea devided into divided into smaller chambers pumped briue is allowed to pass through these

chambers in a Zig Zag manner as shown in the accompanyingillustration. The density allowed

rise upto 10 Be in this area.

6.2) Condensers: In this area, the 10 briue is the 10 briue from reservoirs, is allowed to flow

through smaller chambers , resulting in gradual rise in density upto 25 Be(250ppt). The last stagecondensor is also known as gpysame condensor where gypsame, CaSo4;2H2O seperater from

briue into fine needle shapes crystals and builds up to into a thick layer, as a economically useful

by product. The area occupied by condensers is about 40% (=1 -%%).

6.3). Crystallisers: This area is about 10% of the total area. Individual Crystallisers are preferably

of size 15 in wide by 30 to 40 in long. In a typical layout there will be twp rows of crystallisers

side by side with the supply channel in between. On either at a land usually 30 cm below the bedlevel of the crystalliser. This is to facilitate complete drainage of better us (also known as mother

liquor) before collection of salt. There should be wall weather road between adjustment twin

rows of crystallisers where scraped salt is temporary stored before being transported and heapedon the storage yard.

6.4) Storage platform: This area, rige depending on the capacity of the salt works, should be atleast one metre above the high flood level. Salt brought from crystallision area should be stored

in well defined pyramidical heap. There should be proper road between now heaps or dispatches

of salt and heaps for avoided with shallow drains all around to rain away rainwater. 100 to 1000t

capacity heaps are common.

Proper gradual should be maintained between Reservours,condensers and crystalliseres to

encourage gravity flow. If it is not possible lift pumps may have to be used to maintain flow ofbriue.

6.5: Deep storage Ponds: Plenty of high density briue is available towards the end of the season.Just before the firstonset of rains, all briue above 15 Be should to pumped into a deep pond, say

100m*20m*5m. This briue can be used during the next season to produce additional salt, which

would otherwise have be lost,, washed away by rains. Deep Pond should form part of away salt

works.

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6.5) Better storage Pond: Bitter us discharged from crystalliing area can be stored here for sub

request recovery of bye products like bromine, potassium chloride etc.

7. TOPOGRAPHICAL SKETCH: A proper study on the feasibility of putting up a salt works on

any is dependant on the toposketch of the same. The land should be contour surveyed to assessthe ups and downs so as to route the briue flow suitably taking advantage of the gravity flow.

Depending on the contour of the land, one or more lift pumps may be formed necessary to

establish the briue flow.

To sum up the data materials to be collected are listed below;

Obtain the topo sketch of the land showing its prokiruity to sea, river, affaroach to road,

etc.

Ensure contour survey of land carried out by a returned firm of civil engineers.

Collet Met. Data for the past 5 Years

Rainfall with month-wise distribution Max. Min. Temperature and Aug. relative humidity , preferably datewise for the past 5

Years.

Wind pattern (wind Box) for the past 5 Years.

Soil condition as to the clayeyness by test pits at convenient intervals, proximity tosource of clay,etc.

Availability of electric-power, other fuels engines, sweet-nater etc.

Bromine manufacture

Bromine is available in salt works bitterus as Mg Br2 ( Magnesium Bromide) to the extent of 1.5

to 2. grams per litre in the 32 Be bitterus. At lower densities the bromine content will becorrespondingly less, and unless there is cogerrial climate conditions like dry weather with low

humidity, it will be bit difficult to get 32 Be bittern.

There a two methods commonly in rough for bromine production viz. The cold and hot process

and the steaming our process. In the cold and hot process, the betterus are acidified with

hydrochloride acid, and allowed to fall from the top of a FRP tower (Forty feet high) filled withHDPE Intellox filling material from the bottom of the tower chlorine gas is admitted. This tower

is connected to 3 or 4 absorption towers also of FRP material, filled with intellox (Raching rings)

all in series, findly to a blower. As the blower is operated, it sucks in air through all these towers.

In the absorption towers a solution of soda ash ( Sodium Carbornate) is continuously circulated.When the plant operates the chloride injected into 1st Tower ( Reaction tower) releases the

bromine from the bittern. The blower air conveys to the Devices of absorption towers where the

bromine is absorbed by the soda ash solution to form a solution of a mixture of Sodium bromide

and Sodium bromate the absorption liquor, and air going out the system is free of bromine uptothis, process is known as cold process. The towers and the connecting pipes are of FRP and all

are suitably supported by a steel frame work.

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The next stage is the air process, where the main equipment is a 30 feet high plan tower

supported in a steel frame, and filled with reaching rings, to increase the surface area. Theabsorption liquor containing sodium bromide and bromate is acidified and allowed to fall in a

their stream from the top of the tower. Steam is admitted from the bottom of then tower.The

released bromine is steamed out and outers a condenser at abmt 2/3 vd height from bottom oftower. This bromine is 99% pure as there is no contamination with chloride. Bromine is taken by

glass pipe line to the bottling section and filled in thick walled special bottles provided HDDE

screw caps with the flow gaskets.

The glass tower is assembled with 6" dia 3 feet long pyrey glass sections. Thermax packaged

boiless of 1 tph capacity are used as the steam requirement is limited.

In the second steaming out process acidified bitterus is allowed to fall from the top of 30 to 40

feet tower made with granite sections, and filled withn granite prices. Hot bitterus react with

chlorine and steam infected from below. A mixture of Bromine, chlorine and steam is taken off

flow top of tower toa gravity separator where Bromine condensers. Where pure bromine is takento a dislillation column reajected for further liberation of bromine in the granite tower.

Currents many od the bromine plants in India like DCW plant in Dhrangadhra, GHCL plant in

Vedaranyam, Southern chemical plant in Vegpalodai have ceased production as the Bromine

imported from Israel in cheaper than the cost of production in India. The bromine content in

Dead Sea in Israel is much higher, and hence their larger availability at low cost

Bromine is mainly used in the formulated of perticides and flame retandants.