DESALINATION OF SALINE WATER USING IMPROVED SOLAR STILL

DESALINATION OF SALINE WATER USING IMPROVED SOLAR STILL

ABSTRACT:-

Solar still is a very simple solar device used for converting available brackish water into distilled water. Solar distillation uses the heat of the directly in a simple piece of equipment to purify water. The equipment, commonly called a solar still consists primarily of a shallow basin with a transparent glass cover. The sun heats the water in the basin, causing evaporation. Moisture rises, condenses on the cover and runs down into a collection through, leaving behind the salts, minerals, and most other impurities, including germs. In our project the main objective is to increase productivity of water by increasing the condensation rate by using steel balls and lenses.

Keywords:  solar still, distillate, solar energy, purification, desalination

INTRODUCTION:

Ninety seven percent of the earth’s water lies in oceans. Of the remaining 3 percent, 5/6 is brackish, leaving a mere 0.5 percent as fresh water. As a result, many people do not have access to adequate and inexpensive supplies of portable water. This leads to population concentration around existing water supplies, marginal health conditions and a generally low standard of living.

           There is an important need for clean, pure drinking water in many developing countries. Often water sources are brackish (i.e. contain dissolved salts) and contain harmful bacteria and therefore cannot be used for drinking. In addition, there are many coastal locations where seawater is abundant but potable water is not available. Pure water is also useful for batteries and in a hospital or schools.

          Distillation is a one of many processes that can be used for water purification. This requires an energy input, as heat, solar radiation can be the source of energy. In this process, water is evaporated, thus separating water vapor from dissolved matter, which is condenses as pure water.

Solar water distillation is a solar technology with a very long history and installations were built over 2000 years ago, although to produce salt rather than drinking water. Documented use of solar still began in the sixteenth community century. An early large-scale solar still was built in 1872 to supply a mining community in Chile with drinking water. Mass production occurred for the first time during the Second World War then 200,000 inflatable plastic stills were made to be kept in life-crafts for the US Navy.

          Solar distillation uses the heat of the directly in a simple piece of equipment to purify water. The equipment, commonly called a solar still, consist primarily of a shallow basin with a transparent glass cover. The sun heats the water in the basin, causing evaporation. Moisture rises, condenses on the cover and runs down into a collection through, leaving behind the salts, minerals, and most other impurities, including germs.

         Although it can be rather expensive to build a solar still that is both effective and long-lasting, it can be produce purified water at a reasonable cost if it is built, operated, and maintained properly.

SOLAR STILL OPERATION:

          The main future of operation is the same for all solar stills. The incident solar radiation is transmitted through the glass cover and is absorbed as heat by a black surface in contact with the water to be distilled. The vapor condenses on the glass cover, which is at a lower temperature because it is in contact with the ambient air, and runs down into a gutter from where it is fed into the storage tank.

NEEDS SERVED BY SOLAR DISTILLATION:

Ø Solar distillation could benefit developing countries in several ways:

Ø Solar distillation can be a cost effective means of providing clean water for drinking, cooking, washing, and bathing—four basic human needs.

Ø It can improve health standards by removing impurities from questionable water supplies.

Ø It can help extend the usage of existing fresh water in location where the quality or quantity of supply is deteriorating. Where sea water is available, it can reduce a developing countries dependence of rain fall.

Ø Solar still operating on a sea or brackish water can ensure supplies of water during a time of drought.

Ø Solar distillation generally uses less energy to purify water than other methods.

Ø It can foster cottage industries, animal husbandry, or hydroponics for food production in areas where such activities are now limited by inadequate supplies of pure water. Fishing could become important on desert seacoast where no drinking water is available for fisherman.

Ø Solar still permits settlement in sparsely-populated locations, thus relieving population pressures in urban areas.

LITERATURE REVIEW

ENERGY REQUIREMENT FOR WATER DISTILLATION

          The energy required to evaporate water is the latent heat of vaporization of water. This has a value of 2260 kilojoules per kilogram (kJ/kg). This means that to produce 1 liter (i.e. 1kg since the density of water is 1kg/liter) of pure water by distilling brackish water requires a heat input of 2260kJ. This does not allow for the efficiency of the heating method, which will be less than 100%, or for any recovery of latent heat is rejected when the water vapor is condensed. It should be noted that, although 260kJ/kg is required to evaporate water to pump a kg of air through 20m heads requires only 0.2kJ/kg. Distillation is therefore normally considered only where there is no local source of fresh water that can be easily pumped or lifted.

DESIGN OBJECTIVES FOR AN EFFICIENT SOLAR STLL

 For high efficiency the solar still should maintain:

·        A high feed (undistilled) water temperature.

·        A large temperature difference between feed water and condensing surface.

·        Low vapor leakage.

A high feed water temperature can be achieved if:

·        Heat loss from the floor and walls are kept low.

·        The water is shallow so there is not so much to heat.

·        A high proportion of incoming radiation is absorbed by the feed water as heat.

Hence low absorption glazing and a good radiation absorbing surface are required.

A large temperature difference can be achieved if:

Ø A high proportion of incoming radiation is absorbed by the feed water as heat. Hence low absorption glazing and a good radiation absorbing surface are required.

Ø Condensing water dissipates heat which must be removed rapidly from the condensing surface by, for example, a second flow of water or air, or by condensing at night.

The cost of pure water produced depends on:

Ø The cost of making still

Ø The cost of the land

Ø The life of the still

Ø Operating cost

Ø Cost of the feed water

Ø The discount rate adopted

Ø The amount of water produced.

Test:1

Test:2

.

Test:3

OUTPUT OF A SOLAR STILL

          An approximate method of estimating the output of a solar still is given by:

Q = (E x G x A)/ 2.3

Where,

Q = daily output of distilled water (liters/day)

E = overall efficiency

COMPARISON OF DISTILLATE YIELD FOR TWO MATERIALS

='margin-bottom:0in;margin-bottom:.0001pt;text-align: justify;line-height:normal;mso-layout-grid-align:none;text-autospace:none'>MODE OF OPERATION AND TEST PROCEDURE:

ü Brackish water is fed into the Still through the top window on the side of the Still. The water occupies a portion of the basin.

ü The Still is exposed to solar energy from (900 - 1700) hours and as the water is heated by the sun’s heat, evaporation takes place.

ü The vapor rises and condenses on the underside of the glass cover and the condensed water runs down into the u-shaped channel which is collected in the distillate trough.

ü Two different materials were used as an absorber. The first material, black leather, was used as test I. The second material is Aluminum which was painted black and was used for test II.

ü A measuring cylinder (graduated) was used to measure the daily collection (distillate). A thermometer (10⁰ – 600⁰C) was used at every hour to measure the outer and inner glass surface and water temperatures respectively.

ü Some quantity of brackish water was collected and the salinity determined. After the distillation process, salinity of the distillate was determined.

The procedure for this method is as follows:

Ø 10ml of the distilled water was taken and

Ø 3 drops of potassium chromate as indicator was added.

Ø It was titrated with silver nitrate and

Ø The titer value was calculated after a color change was attained.

 PYRAMID SHAPED SOLAR STILL

PYRAMID SHAPED GLASS

ALUMINIUM TRAY

CONCLUSION:

                            

                             The performance evaluation carried out on the fabricated     Solar still has shown that it can be used for the desalinization of salty water. The results have shown that a high enough temperature was attained which produced evaporation and the distillate produced was confirmed fit for drinking by the salinity test conducted. The Still has a capacity of 1m³ and produces an average yield of 0.51 liter per day. The daily temperature and type of absorber materials are factors that can influence the distillate yield. The cost of production for the still is ten thousand rupees. The low cost of production is as a result of the materials employed in the fabrications..

Posted in: IEEE papers,PROJECT PAPERS,projects in 2013