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    Prof. Abdul A Rahman
Prof. Abdul A Rahman

Project development

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Project development

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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 its usual 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 will facilitate 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 confined to 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, leaving the 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 be collected 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 seasonal variation in the wind direction and wind velocity. Land breeze with velocity of steady 15 to 20 kmph will help to achieve good salt production.

SOIL CONDITIONS:- Salt works should be laid out over land with clayey soil which does not allow 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 the costliest 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 out straight from sea by constructing a jetty (eithersteelorRCC) projecting into the sea for say 100 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 to 100gpm. 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 total area 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 stage condensor 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 bed level 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 heaped on the storage yard.

6.4) Storage platform: This area, rige depending on the capacity of the salt works, should be at least 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 of briue.

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.

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 assess the 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 to source 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 be correspondingly 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 with HDPE 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 upto this, 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.

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. The absorption 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 of tower. 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 taken to 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.

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