Design and construction of water solar distillation, work by steam circulation technique

Transcription

1 Design and construction of water solar distillation, work by steam circulation technique Jaafar A. Kathum, Jamal Mohamad Hamed, Ali H. Abdul-Munaim, Eman Ali Ehsan Sheat University of technology /Baghdad/ Iraq Abstract The shortage of drinking water around the world is a great problem, facing humanity in present and the future of humans. So we must look for solutions even if they are partial solutions. Solar distillation systems can be considered as a simple solution for this problem. Solar still can produce clean water for laboratory applications, drinking, and for agricultural purposes, depending on the size of the system. These systems have been used for a long time ago; the purpose of the current research is to introduce some improvements for the system to increase the productivity of the distilled water. Three different types of desalination plants have been designed and constructed. First one is a simple conventional solar basin. It can produce about 3L/m 2 D of fresh water as a maximum capacity on summer. It has a simple shape and the cheaper type of basin solar still. The second one increased the productivity to 7L/m 2 D. In the third model the bed divide into two side hot and cold side this allow the vapor circulate from the hot sunny part to the cold shadow part of the distillation system, led to an increase of 20% of water productivity. Also, other modification was introduce that is the sun seeker device to maintain sun ray perpendicular to glass cover, this led to an increase in production by 15%. The production of new design was about 9L/m2D of pure water as a maximum capacity on summer. Index Terms Solar energy, distillation, salty water, thermal insulation, dust accumulation. C I. INTRODUCTION limate change and global warming impose new conditions and rules on the governments and peoples of the world to take into account and take their necessary reserves [1]. Human activities, especially the burning of fossil fuels for energy, have a big role in this dilemma. So to minimize their risks, we must turn to renewable energies as an alternative to energy production [2, 3]. The fluctuation of oil prices in recent years has devastated the economies of many countries of the world, whether exported or imported [4]. In Iraq, where electric power was cut for long hours, forcing citizens to rely on personal or collective generators working with gasoline and diesel and causing high pollution to the environment [5]. Solar energy in this country is very suitable in terms of the intensity of solar radiation and long duration of brightness during the year for use as a suitable alternative to the production of electric power [6, 7]. It can also be used to operate water pumps in areas far from the electrical grid and very efficiently [8]. The limit resources of drinkable water in many areas of the world are an old and seems to be also a future problem. Throughout history people had continually tried to treat salty water to use it for drinking and agriculture purposes. Fresh water resources are under heavy pressure due to population growth rates and pollution caused by industrial wastes. A very small fraction of about 1% of all world water resources is available as fresh water [9].Fresh water is water that dissolved salts below about 1000 milligrams per liter (mg/l) and is considered an acceptable water supply [10]. Desalination and water distilling is not a new process but in fact it is a very old method of cleaning and purifying of water. The old models were the still types which are composed of tank with a black floor and a transparent cover [11].It is not necessary to boil water and distil it, distillations are one of many processes available for water purification, and sunlight is one of several forms of heat energy that can be used to drive that process. Sunlight has the advantage of zero fuel cost, but it requires more space to collect the solar energy [12]. Solar distillation systems can be small system or large, They are designed either to serve a single family, which producing from 3 to 15 Liter of drinking water daily, as shown in fig.(1) or to produce much greater amounts of fresh water, for a small village or city as shown in Figure (2), [13]. These solar energy distilling plants are relatively not expensive and low technology system. Solar still is a device to desalinate impure water like brackish or saline water like sea water. It is a simple device to get potable fresh distilled water from impure water, using solar energy as fuel. which can be used for various applications as domestic, industrial and laboratory sectors it is true clean water these desalination units have the advantage of low installation cost no fuel consumption [14]. However, there are two important disadvantages: low capacity of water production, and the system required large sunshiny space. A solar still consist of shallow rectangle basin made from glass, or reinforced plastic, bottom of the basin is painted with black color to absorb solar energy effectively. This distillation still has no moving parts or filters to replace, and no requires any type of fuel [15]. The water is distilled at the highest surface of glass cover. Solar Stills have got major advantages over other industrial distillation systems. The accumulation of dust on the transparent surface causes a decrease in the solar radiation that reaches distilled water and reduces its efficiency. Fortunately, dust can be prevented from accumulating by washing the 239

2 transparent surface with specific periods in distilled water and thus reducing its harmful impact [16, 17]. The most advantages of solar distillation still are [18]: 1- Produces absolute pure water. 2- There are no moving parts. 3- No need to any energy types. 4- No skilled operator required. 5- Local manufacturing and maintenance. 6- Low investment cost. 7- Can purify highly saline water as sea water. Desalination plants of the world now produce approximately 6 billion gallons daily, enough to provide about 5 percent of the world s population [19]. The aim of this work is to enhance the distillation productivity of solar distillers by adding modification and compare the resulted performance to select the best type for Iraqi climates utilization. Figure (3), and then consider the energy and mass balances around the system. Fig. 1, Two types of small water distillation plants. Fig. 2, High number of distillation plants using seawater in USA to serve small city. II. THEORETICAL WORK To study the water distillation still as a thermal system, first the control volume must be applied as shown in 240 Fig. 3, Water distillation still as a thermal system Energy inters the system are: a. Direct radiation of solar energy. b. Ambient and surrounding reflecting radiation energy. Energy leaving the system are: a. Heat transfer from still walls by convection. b. Heat transfer to surrounding by radiation. c. Radiation lost energy to surrounding by reflection. d. Heat energy transfer to ground by conduction. e. Energy lost by clean water outlet. f. Energy lost with waste salty water. Due to the several number and complexity of the heat and mass transfer, included in the water still system it was seen that modeling the whole water still distillation system was too complex. The sun energy is not constant with the time and, also due to the change of the sun location and the existence of dust and clouds, air pollution, and etc., along the day. The unsteady state conditions are existed in all parameter of the water still distillation, so it is too difficult to get a mathematical formula with the unsteady state condition. So, depending on practical work will by better and more satisfaction in evaluation to approach the optimum system [20]. Finally important notes must be considered during this study as follow: - The size of the still must with a standard size as 1 or 2 meter square. - The quantity of brine water in basin must be kept minimum, because a lot of salty water in basin will absorb the solar radiation energy and remain the salty water temperature at low level. - The salty water basin walls must be insulated, because some heat energy will escape to ambient, that tend to redaction in still performance. - The temperature deference between glass upper surface of collector and salty water, must kept maximum as possible, it is the important parameter which defined the still performance.

3 - The transparency of glass condenser cover must be of high quality to reduce the absorption of solar radiation which tends to heat the glass. - The distance between surface of salty water and glass lower surface must be kept as minimum as possible, to shortage the vapor transfer distance. - The glass collector thickness must be minimal to increase the heat transfer of the condensed vapor to the surrounding. - Water distillation still must be placed in open space, with high wind speed, and under sun light for a long period of time. - The incident angle of the solar light on glass collector surface must be kept vertical to reduce the reflectivity of the light on the glass surface. - The upper surface of the glass collector must be kept clean, because dust will absorb the light energy and tends to increase the glass temperature, this will reduce amount of condense water on hot dusty glass. - The water distillation still system must be completely closed, to prevent any escape of the vapor to the surrounding, only small pipe for salty water inlet and small pipe for clean water outlet. The performance of the water distillation still actually is depending on the availability of solar energy. Iraq is located near the maximum rate of solar radiation energy; the amount of solar energy on Iraq is about 2500 kwh/m²/y. So that in Iraq the solar distillation still can be work effectively and it can be a good solution for fresh water leakage [21]. With an available space of about 3m², everybody can construct his own basin unit of water distillation system to product clean water [22]. The system can be placed on the building roof or in the garden or wherever the user as long as it gets enough sunshine. An average family uses approximately 20 liters of drinking water daily; with a good basin design the pure water of 7L/m2D as mean capacity, so 3.5 m 2 of distillation system is suffice to supply this family with pure water. III. STILL WATER QUALITY In principle, the water produces from a solar still should be quite pure. The slow distillation process allows only pure water to evaporate from the basin and collect on the glass cover, leaving all particulate contaminants away. In general fresh water is water that contains minimal quantities of dissolved salts, especially sodium chloride. Natural sources for freshwater are rain, lakes, streams, rivers, and underground with a salt content of less than 500 parts per million [23]. Salty water is water found naturally in the ocean or seas and which has high salinity content. Full strength seawater contains 35 parts of salt, mainly sodium chloride for each 1000 parts water, salinity equal 35 (p.p.t) equaling 3.5 %. Too much salinity in water is harmfulfor human health. Salinity up to 500 (mg/l) is normal but less is better, up to 1,000 mg/l salinity is considered the limit for long term human consumption. Any value over 1,000 (mg/l) has long term bad healthy effects [24]. The distilled water from a solar basin does not be success commercially, since the water is not boiled which lowers (PH). Solar stills use natural evaporation and condensation, which is the 241 rainwater process. This allows for natural ph level that produces excellent quality as compared to steam distillation [25]. Contamination may be taken place due to some mistake on basin construction. There are several ways to minimize the contamination from the materials in the basin itself. Preconditioning of the distiller is by adding sodium bicarbonate in the basin under the sun for several days may be sufficient to avoid most volatiles [26]. Still parts should be made of noble materials to prevent any bad effect on the water which is flowing through it, even at the high temperatures which might be occurred, polyvinyl chloride plastic pipe is commonly available at relatively low cost. Vinyl chloride has been identified as a carcinogen potentially harmful to workers in basin manufacturing, so we should be very careful about using this material in a drinking water system. So it is recommended to construct the water still distillation plants all from thermal chock resistance glass material. Solar stills is a useful device to produces fresh drinkable water, also it is important for industrial application, Hospitals, laboratories, and also for radiator and battery maintenance [27]. IV- PRACTICAL WORK To design the optimum water distillation basin three types of basin were constructed and tested, to find the best one.the first distillator was a simple type build from glassas rectangular box, the upper transparent surface is inclined with 12 from the horizon, and the base is painted with black color to absorb the sunlight radiation, as Fig. 4 shows. Table 1 listed the still diminsions and technical specifications. Fig. 4, Simple rectangular glass basin. TABLE 1 THE STILL DIMENSION AND TECHNICAL DETAILS OF THE BASIN 2 Basin cross section area 1 m Basin length Basinwidth Front height Rear height 1200 mm 834 mm 100 mm 200 mm

4 Salty water capacity Angle of glass collector Salty water maximum depth Constricted material 70 liter 12 degree 70 mm all from glasses The second distiller is the wick type still, as Fig. 5 represents. The third distillation system has been constructed with technical specification as the water vapor can move from the hot part, which is facing the sun to the cold part in opposite face of the system or we can say in shadow face, and the collector bed covered by charcoal to absorb the water and form the sun as shown in Fig. 6. Table 3 listed the dimensions and technical details of the third distiller. The latest design has some advanced technology as rotation of the system to track the sun light, also to maintain water of a good amount in the basin bed and the most important thing is to make water evaporates in the sunny face while the process of steam condensation on the other side shadow face. Fig. 5, Variable directional system wick type still. Table 2 illustrates the dimensions and technical details of the still. TABLE2 DIMENSION AND TECHNICAL DETAILS OF THIS TYPE Collector length Collector width Collector thickness Add a solar radiation reflector Collector bed covered by Collector supplied with Solar cell supplied the System by from aluminum foil charcoal water washing cycle 36W 12V Water pump 12V, 1.5A Drinking water tank Salty water tank 20 liters 80 liters Fig. 6, Third type of distillation system with vapor circulation technology. TABLE 3 DIMENSION AND TECHNICAL DETAILS Collector length 1200 mm Collector width Collector thickness Collector bed covered by Make the bed as graduate surface to keep the water Introduce sun-tracking system 834 mm 120 mm Charcoal in all side of the bad to keep the sun radiation fall vertically along the day 242

5 All of the additions used in this design are important and realistic, although the model is more complex than the above, but it can be implemented easily. Experimental Procedure Experiments were conducted to verify the effect of the following factors: a) The effect of salty water depth on distillation production rate. b) Influence of thermal insulation to basin on over all still performance. c) The effect of dust or dirty glass covers on still performance. V-RESULT AND DISCUSSION The practical tests were conducted above the roof of the Energy and Renewable Energies Technology Center, University of Technology, Baghdad-IRAQ. These tests were conducted in summer starting from sunshine till the sunset to evaluate the system performance. The distiller production rate each hour was taken as an indicator to the distiller performance. Fig. 7 shows the tested distillers daily productivities variation with the salt water depth varied from low to high. The results reveal that reducing the height of salty water increased the distiller productivity relatively. Reducing the height of the brackish water means less water to be heated and faster heating process can be achieved in this case. All distillate system's production increased slightly with lower depth of the salty liquid. Besides, the results show that the maximum production of simple still type was about 3L/m2.D, it is not small quantity, it is sufficient for one person daily, especially if we know that it is not expensive, simple to maintain and easy to construction. The second type had a new design, many recommendations are applied to approach more performance, the main modification, which introduced on the new model are, using the charcoal, it behaves as absorbing medium and as a wick, this tends to 22% of water production rise. Using of aluminum foil to reflect solar radiation has less effect, the system productivity was about 7L/m2D. The third model achieved optimum productivity, about 120% of the first model and 50% more than the second model, the overall a distillation capacity was about 9L/ m 2 D. The effect of thermal insulation is relatively small, as Fig. 8 declares. The distillate performance improves slightly with use the insulate material on the bottom and wall sides. Experiments are carried out under solar irradiation at summer, which makes the heat transfer between the basin and the outside atmosphere relatively slow and the thermal loss is expected to decrease in the winter. The results indicated the improvement in the distiller productivity didn't exceed 30% in this case. Fig. 7, The effect of the salty water height in the distillers' basement on its productivities. Fig. 8, the effect of the thermal insulation in the distillers' basement on its productivities The improvement in the simple solar distiller No. 1 reflected on the amount of water produced, as Fig. 9 reveals. The aluminum foil reflector position of the sun led to an increase in productivity by 3%.The use of wood charcoal inside the distillate led to a significant increase in productivity up to 25%. The use of water to cool the upper surface of the transparent cover, tend the surface to be cold and lack of sun radiation transference, and this led to overall effect of an increase productivity up to 10%. 243

6 Fig. 9, the effect of the improvements made in the distiller No. 1 on its productivities The effect of the accumulated dust on the transparent cover surface studied by leaving the three distills in the atmosphere for two weeks to give dust a chance to accumulate on its transparent surfaces. Fig. 10 represents this effect for the tested distillers. Dust has a significant negative effect as the tests results have shown a decrease in the production of the concentrate with thick dusty layer. Although the results of the study showed that the highest productivity is for the still No. 3, but from experience and the practical work our recommendation is to construct three simple systems of basin stills, which are better than of one complex one, or construct the third model without sun tracer. Fig. 10, the effect of the accumulated dust on the tested stills productivities 244 VI- CONCLUSION The recent work investigated the use of small distillation stills with suitable solutions for supplying a family by fresh water. High intensity of solar radiation in Iraq makes this country a viable environment for this application. The study evaluated the performance of the three types of water distillers that were constructed and tested as follows: The first type is simple and cheap, it does not require skilled workers to build it, low maintenance required with low fresh water production. The maximum production of this type was about 3L/m2.D. It is not small quantity, so a collection of two or three units is sufficient to supply clean water for drinking and cooking purposes of one small family. The second distillation system is more complex, it modified wick still type and required experience to construct and maintain it. However, this type has high fresh water production reach to about (7L/m2.D) on summer production. The third model is the most advanced and higher productivity than the other tested stills. The disadvantages of this still are it is more complex in construction; but it produced about 9L/m2D throughout the testing period. However, when neglect the solar tracker system of this model, it will be easier to build and maintenance, in this case it can produce 7L/m2D of pure water. REFERENCES [1] H. M. S. Al-Maamary, H. A. Kazem, M. T. Chaichan, "Climate change: the game changer in the GCC region," Renewable and Sustainable Energy Reviews, vol. 76, pp , [2] H. M. S. Al-Maamary, H. A. Kazem, M. T. Chaichan, "Renewable energy and GCC States energy challenges in the 21st century: A review," International Journal of Computation and Applied Sciences IJOCAAS, vol.2, No. 1, pp , [3] H. M. S. Al-Maamary, H. A. Kazem, M. T. Chaichan, "Changing the energy profile of the GCC States: A review," International Journal of Applied Engineering Research (IJAER), vol. 11, No. 3, pp: , [4] H. M. S. Al-Maamary, H. A. Kazem, M. T. Chaichan, "The impact of the oil price fluctuations on common renewable energies in GCC countries," Renewable and Sustainable Energy Reviews, vol. 75, pp , [5] A. A. Al-Waeely, S. D. Salman, W. K. Abdol-Reza, M. T. Chaichan, H. A. Kazemand H. S. Al-Jibori, "Evaluation of the spatial distribution of shared electrical generators and their environmental effects at Al-Sader City-Baghdad-Iraq," International Journal of Engineering & Technology IJET-IJENS, vol. 14, No. 2, pp , [6] H. A. Kazem, S. Q. Ali, A. H. Alwaeli, K. Mani and M. T. Chaichan, "Life-cycle cost analysis and optimization of health clinic PV system for a rural area in Oman," Proceedings of the World Congress on Engineering 2013, vol. II, WCE 2013, London, U.K., July 3-5, [7] M. T. Chaichan&K. I. Abaas, "Practical investigation for improving concentrating solar power stations efficiency in Iraqi weathers," Anbar J for Engineering Science, vol.5, No. 1, pp , [8] A. H. Al-Waeli, A. H. Al-Kabi, A. Al-Mamari, H. A. Kazem, M. T. Chaichan, "Evaluation of the economic and environmental aspects of using photovoltaic water pumping system," 9th International Conference on Robotic, Vision, Signal Processing and Power Applications, Springer Singapore, pp , [9] S. Al-Kharabsheh, D. Yogi Goswami,"Analysis of an innovative water desalination system using low-grade solar heat", 2000.

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