DESIGN & LAYOUT OF SOLAR SALT WORKS Dr. M J. Mehta,
Delivered lecture in Training Training course cum Seminar Seminar in Salt Technology Technology at Madras Madras,, 4 – 22 Augu August st 1981 1981 1 DESIGN & LAYOUT: The process of obtaining common salt and other marine chemicals which are dissolved in sea water or natural brine is entirely by gradual evaporation and fractional separation of solids at different densities (concentration). The method by which common salts is produced by solar evaporation is very much practiced in our country even before the chemistry of salt was established. This method is utilized to different degree depending upon the prevailing climatic conditions, the geographical location of the source and the advancement of technical knowledge and its application. In western western hemisphere where where prolonged dry weather is uncommon, solar evaporation of either sea water or natural brine is not so feasible and salt is produced by dry mining of salt deposits or by artificial Evaporation of brine in tropical country like India, where long dry weather exists, manufacture of salt by solar evaporation is adopted, and salt of very good quality & quantity has been produced. The design of solar salt works has remained a rule of thumb by the persons persons experienced experienced in salt manufactur manufacture e as the demand for salt has increased due to growing population & industrial consumption. The greater purity & more yield per acre has become more important. Hence, it has become necessary to apply more basic data of evaporation of brine, soil characteristic, characteristic, climatic conditions, etc. for the layout of salt works. 2 DESIGN AND LAYOUT OF SALT WORKS IN INDIA: (1) Steps involved in establishment of a salt work: The main operations involved in the manufacture of salt are evaporation and crystallization depending on the solubility relations of the constituents constituents of sea water. The design of a solar salt work is primarily aimed at accomplishment of these operations in a most efficient manner, and calls for an
experience in the various engineering aspects of of salt manufacture. manufacture. The different steps involved in establishment of a salt work in order of their priority are:
1. Selection of a suitable site; 2. Designing Designing the layout; and 3. Construction of the salt work as per design.
3 FACTORS AFFECTING DESIGN: 1 Selection of a suitable site: The selection of a suitable site is the most important step in the establishment of a solar salt work as the ultimate success of the project depends on the proper decision in this respect. This selection is influenced by the technical factors which which includes the production of salt as well by the commercial factors which include the disposal of salt in the market. Being the cheapest commodity, a site close to the market is very very much desirable, as it helps in minimizing the cost involved involved in its transport. It is advantageous to locate a salt work in the proximity of a salt based industry or where shipping and rail transport is within reach. The next step involves in finding out the nature of soil. A soil of almost impervious nature nature is a major major requirement. This property of soil depends on its composition. Normally the soil near the sea coast is alluvial type and contains coarse sand: 0.2 to 2.0mm; fine sand 0.02 to 0.2mm; 0.2mm; silt 0.002 to 0.02 0.02 mm and clay below 0.002 mm. The fraction coarser than coarse sand is gravel having a particle size from 2 to 75 mm.
Soils containing containing gravel and coarse sand are quite unsuitable for
establishment of a salt work as they cause cause considerable percolation. The percentage of fine sand, silt and clay also varies from soil to soil and depending on these percentages they are broadly classified into three types viz. Sandy, Loamy and Clayey and each type is further sub classified as follows:
Table 1: Classification of soil
Type
Sandy
Loamy
Clayey
Class
Percentage Fine-Sand
Silt
Clay
I) Sand
92-100
0-8
0- 8
ii) Sand loam
70-92
0-12
0-20
iii) Loamy sand
62-65
5-25
8-35
iv) Sandy Clay
50-75
0-7
25-50
I) Loam
50-75
10-25
10 -25
ii) Silty loam
0-75
25-100
0-25
iii) Silty clay loam
0-50
25-75
25-40
iv) Clay loam
35-70
8-25
25-40
I) Silty clay
0-35
25-60
40-75
ii) Clay
0-64
0-25
30-100
It is found that soils containing up to 60 percent of fine sand as the largest particle size and not less than 40 percent clay and silt together afford a reasonably impervious soil. Therefore, soils of silty clay and clay class are the most suitable for establishment of solar salt works.
The presence of fine sand in soil imparts another desirable
characteristic to it viz., increased bearing strength. The soils which can improve in bearing strength up to 1 to 1.40 Kg per square centimeter are quite suitable. This property of the soil makes the beds of the crystallizers sufficiently hard and do not get damaged during salt harvesting operations either manually or by mechanical means. In order of preference, after the clayey type of soils clay loam and silty clay loam from among the loamy type are also useful for establishment of the salt works. The soil should be devoid of any vegitatation as their roots in the soil cause voids through which heavy percolation occurs. 4 AREA REQUIREMENT: The area requirement for a solar salt work being very large, sufficient land should be available close to the source of brine for immediate use as well as for any future expansion. Further, the land should preferably display a gentle gradient of about 30 to 40 cm in a kilometer and be in a depression which gets inundated by the periodical spring tidal rise to an extent of about half to one meter. This assures a continuous adequate brine supply 5 BRINE DENSITY: The brine density is a factor that links with the economics of salt manufacture. Since brine requires a large area and solar energy for concentration, and which further requires to be exposed for longer period, the lesser the concentration of the initial brine more it is uneconomical to operate the solar salt works. The normal density of sea water is in the vicinity of 3.5 ø Be'. But it varies depending on the location of the site. Brine from sea coasts in the neighborhood of which rivers discharge their flood waters usually gets diluted. Such dilution effect is observed immediately after rainy season. It then slowly gains in density with advancement of season. It is wasteful to admit brine of the density below 1.5 ° Be'
. 6. EVAPORATION Evaporation is the chief operation involved in the manufacture of salt. A number of factors are known which affect evaporation, both meteorological and physical. These are (1) quantity of dissolved substance or substances, (2) radiation, (3) temperature, (4) humidity, (5) rainfall, (6) Wind, (7) depth of water mass, (8) soil colour and (9) size and shape of water surface. Because of the complicated relationship between these various factors, it is difficult to assess the relative importance of each individual factor and therefore the combine effect of the influencing factors on the rate of evaporation is only Taken in to consideration The manner in which each individual factor plays its role in evaporation is described bellow: 7. DISSOLVED SUBSTANCE: Since the solubility of sodium chloride is little affected with increase in temperature, it is crystallized out from Sea Water on evaporation. The rate of evaporation and consequently the concentration of a liquid solution depend on the quantities of substances or substances dissolved in it. The more the quantities of dissolved substances the lesser is the rate of evaporation. Evaporation decreases by about one per cent for every one percent increase in salinity under identical conditions and also simultaneously decreases with increasing evaporating area. 8. RADIATION: The change in state of water from a liquid to a gas involves a utilization of approximately 590 calories per gram of water. Solar radiation therefore plays a considerable part and governs the main variations in the rate of evaporation. It is now generally regarded as the most important single factor involved. 9 TEMPERATURE: .The air and the water temperatures are largely dependent on solar radiation. Since the temperature of water surface governs the rate at which the water molecules leave the surface and enter in to overlaying air, evaporation rate is increased at higher
temperatures. The ideal range of temperature is between 20 C (min) and 45 C (Max). Evaporation rate falls appreciably when the air temperature falls below 10 C. 10. HUMIDITY: Humidity is an important factor. With an increase in the relative humidity the capacity of the atmosphere to take up more water vapour from the evaporating body decreases. The regions in which the relative humidity prevails at low value are more suitable for establishment of salt works. The evaporation particularly ceases to take place when the relative humidity exceeds 80%. Relationship exists between solar energy, radiation, temperature, humidity and evaporation.
11. RAINFALL: The progress and the net evaporation rate in a particular area depend on the total and distribution rainfall during the year. To operate a successful solar salt works, it is essential that the annual rainfall should be as low as possible and its distribution restricted too few months leaving longer clear weather duration for salt manufacture. The area receiving not exceeding 600 mm of rainfall in a total spell of 100 days are considered most suitable for establishment of salt works. Solar salt plants can be successfully operated in areas even where the total annual rain fall is to an extent of 1600 mm but which is restricted to a definite duration of rainy season. Occasional showers not exceeding 15 to 20 mm in any one spell of 24 hours do not deter the salt manufacturing operations. 12. WIND VELOCITY: Wind helps in removal of the air saturated with water vapour from the surface of the evaporating body and bringing in contact with it fresh unsaturated layer of the atmosphere thus increasing evaporation. Such an increase in evaporation with wind speed is observed up to a certain critical value and any further increase in the wind speed does not further enhance the evaporation. A desirable range of wind speed which aids evaporation is from 3 Km to 15 Km per hour.
The direction of the wind is an equally important consideration as its speed. The wind blowing from over the sea is normally saturated with water vapour and is incapable of taking fresh water vapour, thus reducing evaporation. Wind blowing from over the land is dry and can take up water vapour till it attains saturation and thus aids evaporation.
The direction of the wind therefore plays its own part... Usually wind blowing from NE and NW direction in India in very much useful in enhancing the rate of evaporation. The direction of the wind prevailing for most of the period of salt manufacture is made use of while laying evaporating ponds and more particularly the crystallizers. 13. PERCOLATION: Brine percolation from reservoir, condensers and crystallizers is one of the major factors which should not be ignored in designing the solar salt works. Because it affect the production and economic of unit The majority of the soil near the sea coast is alluvial in nature showing strong stratification. This property makes exact measurement of percolation. This property makes exact measurement of percolation very difficult. But a designer with some broad guidelines should be able to design a fairly reasonable plan. Typical Permeability Values The classification of soil on the bases of permeability is given below which is derived from a table by Terzaghi and Peck (1948)
Classification
of
soil
permeability is given below Table 2: Permeability of soil by Terzaghi (1948) Degree of Permeability
Range of coefficient of permeability, ‘K’ (m / s)
High
Greater then 10 Exp -3
Medium
10 Exp -3 to 10 Exp -5
Low
10 Exp -5 to 10 Exp -7
Very Low
1- Exp -7 to 10 Exp -9
according
to
Practically impermeable
Less the 10 Exp -9
Table 3: Drainage properties of soil Drainage Properties
Genera Soil Type
Permeability Co-efficient, K
Good
Gravels
K = 1, 10 e - 1, 10 e - 2,
Good
Clean sands
10 e - 3, 10 e – 4, 10 e – 5
Poor
Silt & Sands
10 e -6, 10 e -7, 10 e – 8
Impervious
Intact clays
10 e -9, 10 e -10, 10 e -11
14. RATIO OF THE SITE: The area requirement and the ratio of Reservoir and Condenser to Crystallizer vary from place to place depending on the brine density available and seepage losses. Evaporation rate is useful in calculating the appropriate area for definite brine density. These factors are inter-connected with each other. Therefore, it is very necessary to collect these data for calculating the ratio of the site; the estimation of area requirement for concentration ponds necessary to provide a sufficient supply of saturated brine to unit area of crystallizing pond 15. SOIL COLOR: The colour of the soil also plays its part in effecting evaporation because darker soils, having a low albedo absorb more residual radiation then the soils of lighter colour. The resulting increase in surface temperature may modify the rate of evaporation quite significantly.
16. SIZE AND SHAPE OF WATER SURFACE: The relationship between the size of evaporating water surface and the rate of evaporation was first study by Tomlison. It is observed that evaporation from open water surface decreases with increasing area. The reasons for this phenomenon can be explained with Dalton equation, who suggested that if other factors remain constant, evaporation is proportional to the wind speed and the vapour pressure deficit, i.e.
the difference between the saturation vapour pressure at the temperature of water surface and the actual vapour pressure of the overlying air. In practice the rate of evaporation can be directly measured by using U.S. Weather Bureau Standard "A" pan evaporimeter. It is a circular tank 120 cm diameter and 25 cm deep. A still well is placed in the tank to maintain still water surface and to support the hook-gauge for accurate measurements. The still well consists of an iron triangular base with leveling screws. A pipe of about 9 cm diameter is fixed to the base. The bottom of the pipe is closed leaving a small hole for the entry of water. Water is filled in the pan to a depth of 20cm. Daily fall in water level is recorded with the help of a hookgauge. Evaporation rates thus obtained are higher than actual rates from the larger bodies of water because of smaller area of the evaporation and therefore need correction. The correction factor varies with location, climate and season and ranges between 0.65 to 0.77 17. PLANING THE DESIGN AND LAYOUT OF SALT WORKS: Once the site for establishment of a salt work is selected, from the best compromise of several ideal factors. The next step rests in carefully preparing a layout which can fetch the maximum advantage of the climatic and other parameters prevailing in the locality which affect the yield of salt per unit area, its collection storage and transport for ultimate disposal in the market. The basic principal to be followed in planning and designing a salt work is to obtain economic production by keeping the manufacturing cost as low as possible. The first step in designing of a salt work is to decide the proper selective locations of the different components. Under the ideal conditions the total brine
requirement is obtained through sluice gates at the time of spring tides is flown by gravity to the process areas and crystallizers without any aid of pumping. In the absence of such ideal conditions one has to make use of the contours of the land available and design the layout in a way that the flow of brine is regulated by gravity as far as possible and pumping is resorted to at minimum stages. Levels and surrounding contours of ground vis-à-vis the sea and its tidal rise have to be perfectly known before finalizing the site for reservoir and that of intake gates known as sluice gates. Usually the contour levels are noted at every 60 meters distance in relation to a fixed bench mark. The difference between the readings in relation to the bench mark and that as per tidal rise above the mean sea level 9 M.S.K. as predicted in the tide tables is noted at some convenient points and the readings of levels are then converted in relation to mean sea level. This affords direct relation between the tidal rise and the contours of the land. 18. SLUICE GATES FOR SEA WATER INTAKE:
In salt works, normally, following types of sluice gates are used for taking sea brine in to reservoir, during high tides, (1) Automatic sluice gates (2) Lifting type In addition to above types of gates, box type of gates with Lifting gates to be manually, are used extensively to regulate the flow of brine to one compartment of condenser to another. The use of such gate is simple and not expensive. As an alternate Hume pipes of the flow of
suitable size with suitable regulating arrangement for
brine , can also be used, with advantage automatic sluice gates. It is
misnomer to call these type of gates as automatic type of gates as these do not work automatically, however, such type of gates eliminates to great extent, human factor in admitting brine on high tide in to reservoir, as compare to lifting type of gates, at the same time, there are certain disadvantage of such types of gates is that the tide water can not availed of to any limited extent if tidal rise goes above the level of brine in reservoir close down when the level of brine in creek has gone down. Secondly these gates are only in one way in letting in the brine and no quantity of brine can be drained out of reservoir through these gates in case the bunds are threatening or similar other emergency. Some improvements
have been
proposed to be carried out over conventional pattern of automatic sluice gates which are given below : (1) Brackets fitted with cushinonery ( rubbery ) materials have been provided for returning gates with dual reason for checking the heavy
percolation after the
gates have returned and secondly the opening of gates on receiving high tidal water will be easy .present practice is to pact the side of sluice gates with mud etc .and even with this arrangement, the leakage is very heavy.. The gates do not open of their own , on high tide and on many occasions. (2) Provision has been made to operate the gates on both sides of the support so that after close of manufacturing season, these gates may operate as flood gates discharging rain water accumulated in the Reservoir and not allowing tidal brine to enter in to reservoir. (3) Normally width of sluice gates is maintained as 1.2 Mt. There appears to be no reason to restrict the width of gate as 1.2 Mt. or so. The cost of construction of sluice gate can be reduced by increasing the width of the gates. It is usually accepted as 1.9 Mt. widths of the sluice g ates. Location of sluice gates should be on main creek so that without any hindrance maximum advantage
of tidal water may
be taken
with the
view to
avail
maximum advantage of tidal rise. The overall opening for the sluice gates may be
worked out depending on height of an average tide, level of reservoir area
and
pressure and period of high tides. The idea being to obtain the maximum
advantage during high tide to let in the brine in reservoir..
DESIGN OF SLUICE GATE
FIG 1 DETAILS OF MANUALY OPERATED SLUICE GATE
FIG 2 ELEVATION OF SLUICE GATE
FIG 3 LAY - OUT PLAN OF SLUICE GATE
FIG 4 GATE WITH SPINDLE AND THREEDED HANDLE
Once the relative positions of the different process areas of a salt work in the design are decided, the next consideration rests on deciding the areas to be covered by these process areas and their orientation. The ponds should be oriented to have the short dimensioning of the same in the direction of the wind. The area requirement for a given production rate very directly with the brine feed density, seepage losses and the applicable evaporation rate it is determined in relation to the changes in volume of brine occurring with progressive evaporation. The initial concentration of the brine available and the rate of evaporation prevailing in the locality are other considerations. The design of any salt work differs from that of another as the contours of the land in each case very even in the same region. The area requirement of different compartments is arrived at with the help of an expression
A
= Q / S × E
Where A = area required in hectares Q = quantity of brine to be evaporated in kilolitres E = rate of evaporation in meter S = Sq. meter of an hector = 10,000 Similarly the loss of brine on evaporation can be determined with an expression L=A×E×S Where A = Loss of brine in kilolitres/day and the other notations have the same meaning as above. They yield then can be obtained from a known feed of saturated brine is arrived at by using an expression: Y = Q × 1.2 × P
Where Y = yield of salt per day in metric tonnes Q = quantity of saturated brine evaporated daily in kilolitres P = Percentage of salt content in saturated brine. 1.20 being specific gravity of saturated brine Further, as only 80 percent of NaCl percent in solution separates out till 29.530 Be the yield obtained thus needs to be corrected accordingly. 19. RESERVOIR AND CONDENSERS: The actual pond subdivisions largely depend on the elevation contours and geometry occurring in the pond area. These are normally worked in series though at certain points flow gates or weirs are provided to control maintenance of desired depth the division of reservoir area may be restricted to only 2 or 3 parts to fetch maximum
advantage
of
storing tidal water or fill in the same by gravity within the limited duration of tidal rise. The individual compartments in the condenser are much smaller than those in the reservoir. The brine entering the condensers from
reservoir is of about 6øBe' and
the concentration of it is to be further raised to 25øBe'. This wide range of concentration is achieved by spreading it in a number of compartments which prevent mixing of brine of different densities, Thus helping in progressive evolution of concentration The flow-path of brine in the condensers is so arranged that it is made to travel over a longer distance which aids in evaporation as brine in motion evaporates more quickly than in stagnant conditions .usually the condensing ponds with larger variation in concentrations are not located continuous to each other for fear of infiltration of brine of weaker densities into that of higher ones. However when the topography of the land does not permit this they are separated from each other by strong dikes which are well consolidated with densification of soil mass 20. CRYSTALLZERS: This is a pivotal part of a salt work due to the fact that brine which is reduced in volume practically too about one tenth of its original volume over a large area and over a long period is made to yield salt in it. From this point of view, soil of this area needs to be of
an almost impervious nature. The beds of crystallizers are necessarily well consolidated and are neatly maintained. In this area sufficient good roads are provided for haulage of salt from crystallizers to the main stacking ground. The size of an individual crystallizer is determined with reference to the operational conditions such as use of mechanical appliances for all or part of maintenance and harvesting operations, the method of irrigation system followed which in turn depends on the incidence of rain during the manufacturing period. These are constructed with due consideration to normal wind direction. The widthwise shorter dimensional area may fall in line with the direction of the wind to obtain benefit of increased evaporation. The optimum brine depth that is maintained in crystallizers is between 12 to 15 cm which stands well to diurnal variations in temperature and also to the dilution effect due to occasional incidence of rains. The maximum numbers of crystallizers are arranged in a single row to keep the length of roads less. Series feeding method for quality of Common Salt In order to improve quality and yield of common salt manufacture by solar evaporation of brine, a system known as series feeding method which followed by western country has been successfully tried out in our experimental salt farm, Bhavnagar. The data has been presented which indicate the quality and quantity of salt obtained by this method and this is compared with conventional system of manufacturing salt e.g. parallel feeding The common salt is manufactured by parallel feeding in India consist of gradual solar evaporation of brine and fractional crystallization of salt from brine. The crystallizing pans are prepared conventionally and charged with saturated brine, the salt is collected up to 29.5 Be’ and bittern at this stage is immediately discharged. This salt by and large used to meet demand for human consummation, with industrial development India in late 1960, established series feeding method was adopted by many salt manufacturers and they could as well meet the demand for industrial grade salt.
21. SERIES FEEDING SYSTEM: To study Series Feeding System in field conditions 4 – 6 crystallizers’ numbers of size each having 400 * 125 Sq ft, are prepared. Feeding and discharging channel are also prepared, only difference from parallel feeding is that, in series feeding arrangement is made to charge brine from first pan to second & second to third and so on. Numbers of pans can alter depending upon the uniform supply of brine. Brine of 25,5’ Be is charged to first pan in series and rate of charging the brine and level of depth in crystallizers to be
maintained in each series of pan are to be adjusted in such a fat ion that last pan in the series gets the density of brine between 28.5’ – 29.5’ Be After about 7 to 10 cm layer of salt is deposited, harvesting can be started and flow of brine connected to next pan in order to facilitate the harvesting in previous pan The quality of salt obtained in series shows that in first two pans gave higher impurity of calcium and in last two pans gave less impurity of calcium and middle pans average calcium of first and last two pans. The level of magnesium impurity is just reversed Advantages: Continuous supply of brine of 25.5 Be to-gather with discharge of bittern at 29.5 Be helps in increasing rate of evaporation of brine, hence yield is increased Salt of different grade can be obtained Earlier discharge of bittern helps in increasing the recovery of by-products Due to lower density of brine in the earlier pans washing of salt with saturated brine is not required
Fig 5:
Fig 6
Table: 4 Analysis of Salt obtained from Series and Parallel feeding Pans Salt Ions
Parallel P
Series Feeding Pans
Ca ++ Mg ++ CaSO4 MgSO4 MgCl2 NaCl Be Range Salt in M.T obtained
0.16 0.21 0.55 0.35 0.56 98.30 25.5 – 30
620
S1 0.18 0.14 0.61 0.23 0.37 98.30 25.5 - 26
S2 0.15 0.15 0.51 0.26 0.42 98.30 25.826.3
630
700
S3 0.11 0.19 0.39 0.32 0.52 98.70 26.3 – 27 710
S4 0.11 0.27 0.37 0.46 0.74 98.30 26.527.5 715
S5 0.09 0.35 0.32 0.58 0.91 9810 27 – 28
680
S6 0.08 0.44 0.29 0.34 1.17 97.80 27.5 – 30 665
22. CHANNELS AND ROADS: Channels are provided to flow the brine in concentrating ponds to negotiate areas which are not accessible with straight gravity flow. Such channels are wide as large quantities of brine move through them.
These channels may be longer which afford more
circulating area and thus aid evaporation. Channels in crystallizer area meant to feed crystallizers with saturated brine are meant to carry the mother liquor discharged from them. The feeding channel because of the increased value of the concentrated brine needs to be shorter. Their width at the base is not more than 50 cm. They are required to be constructed just above the bed level of the crystallizers with a gentle gradient of 1 Cu M a length of every 35 meters. The bittern channels need to be located with their base level 15 cm below the bed level of crystallizers and have 1.5 Times steep gradient then the feeding channels. The feeding and bittern channels are located away from each other to avoid bitterns finding way in the crystallizers. Roads in a salt work are of necessity constructed on the embankments. Such roads mainly serve three purposes viz. (I) to facilitate transport of salt, (ii) to provide access to the chief points of operation and (iii) to provide access to different areas for maintenance work. The roads No.1 are more important and are constructed as permanent feature. Transportation planning should be integrated with all management planning to obtain more economy through increased sufficient turnover. 23. EMBARKMENTS: There are two types of embankments viz., (I) outer protective embankments and (ii) inner partition embankments. The dimensions of the various embankments in salt works differ according to their location and water level rising against it.
The outer
embankments are required to have an approximately one meter free board above the highest tidal rise in the area. These embankments may have a top width of 4 meters to permit vehicular traffic. The movements of vehicular traffic on it impart an advantage of
thoroughly consolidating the same. The internal partition embankment is usually constructed with about 60 cm free board and all embankments are provided with a slope of 1:2 to prevent erosion from wave action.
24. STORAGE GROUND: The storage ground is normally located close to the crystallizing area and is about 1.5 meter on a higher level than the surrounding ground. The storage ground should be well consolidated, properly leveled and should be desirably given a peripheral gentle gradient so that rain water does not remain stagnant near salt but is effectively drained out.
Fig 7: Section of the outer and inner bunds
25. EQUIPMENTS: In large solar ponds, pumps are used for pumping in sea water or for pumping brine at some stage or the other due to gradient variations. These are also used for discharging out bitterns from the crystallizer area; numerous types of pumps are used in different salt works. The type of pump and the material of its construction depend on the liquid to be handled and the lift required. Generally the requirement of salt works in low head and high capacity and the liquid to be handled is denser than water.
For this vertical,
centrifugal mixed flow and axial flow pumps are commonly found suitable.
Directly
coupled pumps are more efficient due to less friction loss. The material of construction for pumps used for pumping sea brine of specific gravity 1.03 may be usual cast iron impeller, and 2 percent nickel cast iron causing suction flare for those used for pumping brine of higher concentrations the impeller of bronze and stainless steel shaft are recommended. These pumps meet with special problems like high corrosive action or brine and bitterns and precipitation of gypsum and salt. For this reason it is necessary to provide a hand hold to facilitate cleaning the same. 26. PUMPING: Pumping is mostly done with centrifugal pumps. These pumps are generally low head, high capacity type. Material of this pump is generally of cast iron. Impellers are also made of Cast Iron. Bronze impeller with cast iron body is not recommended because of galvanic action between the two dissimilar metals which increases corrosion of impellers. Worthhite impellers and rings have no such drawbacks. This type of impeller and the rings have service record of 10 – 15 years. Worthhite is complex alloys containing 46 – 47 % Fe, 20 % Cr, 24 % Ni, 3 % Mo, 3.25 % Si, Cu, Mn, and 0.70 % C. The impellers are made of Ni – Resist and Monel metals. Nickel is suitable for hot brine circulation pumps.
Ejecto type pumps can be used where suction lift is more then 7 meters. Use of submersible pumps for under ground brine pumping is mostly used. The pumps used in salt works are driven by electric motor or by diesel or petrol engines
27. PUMP SPECIFICATION: Vertical axil flow pumps single stage having discharge feature with elbow construction are normally used for brine pumping depending upon capacity requirement. They are highly efficient and large volume of water are Pumped. These pumps are ideal for permanent installation having good sump design. Proper sump design is of almost importance since uniform movement of water is essential for good performance of pumps. Sumps should be so design and constructed for affecting a short and straight flow of water to the pump with flow speed of not more then 2 ft per second, more over pump should be mostly of square or even rectangular construction without any attempts being made to bevel the corners. For optimum performance the distance from the suction bell diameter the distance from centre line of the pump to the side was equal to one suction Bell diameter and the distance from centre line of the pumps on the back well be two third of the suction bell diameter. If two or more pumps are installed at the same station each should have its own separate compartments Sea water pumps are mainly of Mild Steel material of construction and can also be manufactured in Cast iron as a material of construction to the specification requirement of the customer
Table 4: Axial flow pumps specifications for different size for salt farms with 2.0 meter head range Capacity: M³ / hr
500
1000
1500
2500
4000
HEAD
2
2
2
2
2
HP
7.5
15
25
45
65
RPM (PUMP)
960
960
960
960
960
Discharge in MM
250
300
350
400
500
Bowl in MM
250
300
350
400
500
One such Salt Works having 5000 acres had used the below mentioned pump specifications for successful operation of the unit
1. SPECIFICATION OF PUMP Centrifugal pump of standard company should be preferred from a point of view of availability of the spares. 1. Flow rate
1600 K L per Hr
2. Net Head.
11 meters
3. Suction / delivery zone.
15” – 15”
4. Efficiency
80 %
5. Speed
980 RPM
6. NPSH (Req)
5.4 meters
7. Power absorbed (kW)
55
8. Type of drive.
Motor
9. Driving Rating
75 kW.
10. Casting
Cast Iron
11. Impeller
Bronze
12. Shaft.
316 SS
13. Sealing arrangement.
Clad packing.
14. H.P
100
28. VEHICLES FOR TRANSPORT OF SALT: Usually a well laid traction line may be provided centrally in the crystallizers with bifurcations to serve all the crystallizers on either side. But where initial expenditure is considered prohibitive, a substitute transport facility can be provided by tractor and trailer
29. BELT CONVEYORS: It is desirable to have sufficient number of stackers to meet with all the requirement of storage of salt during the harvesting season. They need to be light in weight so that their movement from place to place is facilitated. They are however required to be sufficiently strong. Normally M.S. tubular frame satisfies both the requirements. 30. CONVEYOR FOR SALT:
Galvanized radial stacker for salt application is now available which is resistance to corrosion for considerable time The conveyor 90 CMS belt Width driven by 150 hp electric motor where function is to elevate the salt to sufficient height to permit feeding into the ship at the point of jetty. 31. BELT CONVEYOR SPECIFICATION: Belt conveyors should mean for Atomization of Industrial product to convey the required material from one place to another by means of various systems to feed, store, process depending on the application. 32. SCREW CONVEYOR: A Screw Conveyor is also known as flexion flexible screw conveyor, a special conveyor, a spiral conveyor, screw conveyor, helix conveyor or center less auger conveyor. How ever simple design reduce maintenance cost and some of the feature of screw conveyor is given below
Diameter Range: 75MM to 1000 MM Pitch Range: 75MM pitch to 600MM pitch Thickness: up to 12MM Application Area: In Inclined / Straight / Vertical lifts, feeders and flexible type Use: To convey sand crescent or any material in powder, granular or cake form in mild steel and stainless steel. Depending on needs, ONE CAN use rubber, PVC, Oil grade, Polyethylene, nylon sandioitc etc. The structure of the conveyor is made in mild steel or stainless steel. The conveyor solutions vary from light duty to heavy duty conveying. Application Areas: In the Food Industry, Package Handling, Sand & Gravel, Cement, coal, packs, etc. Pipe Thread Conveyor: It is a hydraulic operated conveyor that is used for threading of pipe, from 4 ½" diameters to 13 3/8" diameter and of 13 meter length. These pipe thread conveyors are used for off shore plane oil exploration with the following types of rollers:
"V" roller for to and fro motion driven by hydrometers
Guide rollers for turn motion for threading on oil country laths
Turn table "V" roller having rubber coating complete with power pack 10 Hp. Motor
(1) Reddle Conveyor: They are available in both forms, straight as well as bend and convey the material up to 90%. They have the ability to handle a bulk mass of up to 200 T.P.O.
(2)
Roller Conveyor: Roller conveyors are used in industries in which a continuous process is carried on. Hence, it finds its applications in packing industries, pharmaceutical industries, steel foundries for mould filling etc. Some of the features of roller conveyors are: (A) They are used to convey the “poured mould” of any desired length, to stake out table. (B) They are available in mild steel construction, stainless construction or aluminum construction.
(C) They can be manually operated and motor driven. (D) Bucket Elevator: A bucket elevator, also called a grain leg, is a mechanism for hauling flow able bulk materials like salt, grain or fe rtilizers.
(E) They convey the material in vertical or inclined position. (F) They are used to convey the “poured mould” of any desired length, to stake out table. (K) They can be manually operated and motor driven. (L) They are available in mild steel construction, stainless construction or aluminum construction. (M) Have the capacity to handle materials from 1 tonne to 200 T.P d. (N) The buckets available can be in-pressed buckets, fabricated buckets or PVC buckets; as per your requirements. (O) They can be built to the desired height and are duly mounted on chains in mild steel, alloy steel or simply belt mounted. (P) Slate Conveyor: These overhead conveyors are used to convey bags or for packing. We manufacture and export slate conveyors in: (Q) Three wheel or towhead pillar type drive or (R) Wheel construction with cater pillar type drive
33. ROLLERS: Cast iron drum rollers of 1.2 m diameter and 1.8 m width having an initial dead weight of about 1200 to 1400 Kegs is suitable for rolling operations of crystallizers. This can be provided with an arrangement to fill in with water so as to increase its weight to 3 tonnes. Such a roller is found useful in consolidating the embankments, roads and like wise also. Road roller is a vehicle often equipped with heavy wide smooth rollers for compacting roads and pavements & Soil of different textures The systems adopted easily operated mechanical steering comprising of worm shaft and gear. They are designed to give jerk free movement to the front rolls. The adjustable and reversible scrapers are fitted to cover the entire width of all rolls. The rolls are fabricated out of mild steel plate and electrically welded and tested.
The brakes provided with fully self-wrapping and external contracting type, fitted with replaceable brake lining and adjustable. They often controlled by a foot-pedal or handwheel independently. The sprinklers and the water tank provided with a fixed pump that feed water into the water tank. They are provided with a heavy clutch and gearbox. Some clutches work double types and often controlled by a single hand lever. They are often provided with differential locking arrangement, which is operated from the driver's seat.
34. VIBRATING ROLLER:
This roller has articulated frame, the vibrating roller keeps on the ground and vibrates horizontally getting the required compact thickness more quickly; It can protect and press those subject to vibration. Scraper and sprinkling devices on drums and Compacting force up to 13 tonnes Roller is used for compaction of hot asphalt, soil, course aggregate and Mix materials in Road making and for sports ground. Main feature is the driving power that would be provided by an engine mounted on front frame. Moving transmission and vibration drives with reliable performance. Frame and drum hydrostatic drive. The vibratory roller keeps on the ground and vibrates horizontally, getting the required compacted thickness more quickly. Automatic disengage system is activated when the traveling d irection changed. Roller should have double amplitude and frequencies in order to allow optimum compaction. Scraper and sprinkling devices on Drum. Hydrostatic articulated center joint for good mobility for hydraulic steering system.
