A SEMINAR REPORT ON SOLAR POWER WATER PURIFICATION OPPORTUNITIES Submitted To The Maharaja Sayajirao University of Baroda In Partial Fulfilment for the Degree of the Degree of Bachelor of Engineering (Chemical) YEAR: 2016-17
Prepared By: SELADIYA CHETAN MAGANBHAI (EXAM NO: 32)
DEPARTMENT OF CHEMICAL ENGINEERING FACULTY OF TECHNOLOGY AND ENGINEERING THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA
“
SOLAR POWER WATER PURIFICATION OPPORTUNITIES”
A Seminar Report Submitted Su bmitted In Partial fulfilment of the Requirement For the Degree of
BACHELOR OF ENGINEERING
(Chemical Engineering) Prepared By: SELADIYA CHETAN MAGANBHAI
Guided By: MR. VISHAL THAKARE
DEPARMENT OF CHEMICAL ENGINEERING, FACULTY OF TECHNOLOGY AND ENGINEERING, THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA
DEPARTMENT OF CHEMICAL ENGINEERING FACULTY OF TECHNOLOGY AND ENGINEERING THE MAHARAJA SAYAJIRAO UNIVERSITY VADODARA
CERTIFICATE This is to certify that Mr. Chetan M. Seladiya, a student of The M. S. University of Baroda Faculty of Technology & Engineering, Chemical Engineering Department, has successfully completed his report on “SOLAR POWER WATER PURIFICATION OPPORTUNITIES ” for the degree of Bachelor of Engineering
(Chemical Engineering) for the academic year 2016-2017 This work has not been submitted elsewhere for the purpose of degree to the best of our knowledge.
Guide
Head of The Department
Mr. Vishal Thakare
Dr. B. R. Sengupta
Department of Chemical Engineering,
Department of Chemical Engineering,
The M.S. University of Baroda,
The M.S. University of Baroda,
Vadodara, Gujarat
Vadodara, Gujarat
ACKNOWLEDGEMENT
I firmly believe that no work/seminar can be completed by a single person alone. Numerous people helped me during the course of this seminar. First and foremost, I would like to take this opportunity to express my sincere regards to convey my deep sense of gratitude to my guides Mr. Vishal Thakare. I am thankful to my guides for their excellent guidance, encouragement and support throughout my seminar work. Their profound knowledge that they readily shared with me has helped me to overcome many difficulties. I cannot forget the innumerable time and effort to teaching me both in this seminar and in writing it, that my work will never be able to match. I am again very thankful to them for being very approachable with respect to this seminar. I am also extremely thankful to Dr. B. R. Sengupta as Head of Department of Chemical Engineering, for her cooperation in providing the department facilities, especially the computer laboratory and all the necessary facilities for work. I am grateful to all the faculty members of chemical Engineering Department and Library staff of M. S. University, Baroda.
CHETAN M. SELADIYA EXAM NO: 32
ABSTRACT There is almost no water left on earth that is safe to drink without purification after 20-25 years from today. This is a seemingly bold statement, but it is unfortunately true. Only 1% of Earth's water is in a fresh, liquid state, and nearly all of this is polluted by both diseases and toxic chemicals. For this reason, purification of water supplies is extremely important. Keeping these things in mind, model which will convert the dirty/saline water into pure/potable water using the renewable source of energy (i.e. solar energy).The basic modes of the heat transfer involved are radiation, convection and conduction. The results are obtained by evaporation of the dirty/saline water and fetching it out as pure/drinkable water. The designed model produces 1.5 litres of pure water from 14 litres of dirty water during six hours. The lack of clean drinking water is a problem that plagues many areas of the world today. Distillation is one of many processes available for water purification, and sunlight is one of several forms of heat energy that can be used to power that process. Water desalination is increasingly becoming a competitive solution for providing drinking-water in many countries around the world. Currently there are more than 14,000 desalination plants in operation worldwide producing several billion gallons of water per day. Fifty-seven percent are in the Middle East and Gulf region where large scale conventional heat and power plants are installed. The integration of renewable energy resources in desalination and water purification is becoming more viable as costs of conventional systems increase, commitments to reducing greenhouse gas emissions are implemented and targets for exploiting renewable energy are set. Thus, solar energy could provide a sustainable alternative to drive the desalination plants, especially in countries which lie on the solar belt such as Africa, the Middle East, India, and China. This report includes a review of water desalination and solar desalination technologies that have been developed in recent years and the recent efforts in the field of desalination by using solar energy, including the economic and environmental aspects.
CONTENTS Sr. No.
Page No. Acknowledgment
II
Abstract
III
Contents
IV
List of Figures
V
1
Introduction
1
2
Challenges
4
3
Technologies
7
3.1
Thermal desalination processes
7
3.2
Membrane desalination process
8
3.3
Integration of Desalination With Renewable Energy
9
4
Solar water desalination
11
4.1
Direct process
11
4.2
Indirect process
13
4.2.1
Solar Still coupled with Solar Collectors
14
4.2.2
Solar humidification and Dehumidification
15
4.2.3
Water desalination powered by solar photovoltaics
16
4.3
Solar water purifier
16
4.3.1
Working principle
16
4.3.2
Solar water purification system
17
4.4
Output of a solar still
18
4.5
Output per square meter of area
18
5
Summary
19
References
20
LIST OF FIGURES Figures Title
Page No.
2.1
Distribution of world water resources
04
2.2
Current and projected growth of desalination market worldwide
06
2.3
Global distribution of desalination capacities world wide
06
3.1
Water desalination technologies
07
3.2
Effective range of membrane processes and applications
08
3.3
The use of renewable energy sources in water desalination
09
3.4
Combinations of renewable energy resources with water desalination
10
technologies. 4.1
Possible configurations of solar energy resources with water desalination technologies
11
4.2
Solar still desalination unit
12
4.3
Water desalination technologies coupled with solar power sources installed worldwide.
14
4.4
Schematic diagram of single solar and multi effect solar still coupled with a solar collector.
14
4.5
Humidification and dehumidification desalination unit coupled with solar collector
16
4.6
RO desalination unit coupled with a PV generator
16
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CHAPTER 1
INTRODUCTION Water is the basic necessity for human along with food and air. There is almost no water left on Earth that is safe to drink without purification. Only 1% of Earth's water is in a fresh, liquid state, and nearly all of this is polluted by both diseases and toxic chemicals. For this reason, purification of water supplies is extremely important. Moreover, typical purification systems are easily damaged or compromised by disasters, natural or otherwise. Everyone wants to find out the solution of above problem with the available sources of energy in order to achieve pure water. Technology that is not only capable of removing a very wide variety of contaminants in just one step, but is simple, cost-effective, and environmentally friendly. That is use of solar energy. Water and energy are necessary for life on Earth and sustain the modern world. In many parts of the developed world, the control and exploitation of water and energy has driven economic development and progress. In the developing world, many regions suffer from shortages of fresh water and energy supplies. The United Nations Environment Program (UNEP) stated that one third of the world’s population live in countries with insufficient fresh water to support the population. Consequently by 2025, two thirds of the world population will face water scarcity. Drinking water of acceptable quality has become a scarce commodity. The World Health Organization estimates that over a billion people lack access to purified drinking water and the vast majority of these people are living in rural areas where the low population density and remote locations make it difficult to install traditional clean water solutions. Purification of seawater is known to be one of mankind’s earliest forms of water treatment, and it has become one of the most sustainable alternative solutions to provide fresh water for many communities and industrial sectors. This plays a crucial role in socio-economic development in a number of developing countries, especially in water stressed regions such as Africa, Pacific Asia and countries in the Middle East. Hence, the increase in population together with the industrial and agricultural development in emerging countries will accelerate rapidly the deterioration and depletion of the available freshwater resources.
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Desalination is a process in which saline water is separated into two parts using different forms of energy, one that has a low con-centration of dissolved salts (fresh water), and the other which has a much higher concentration of dissolved salts than the original feed water (brine concentrate). Saline water is classified as either brackish water or seawater depending on the salinity and water source. Large commercial desalination plants that use fossil fuels are in use in most of the countries suffering from water shortages. For instance, a number of oil rich countries use fossil fuel to supplement the energy for water desalination supply. In contrast people in many other areas of the world have neither the financial nor oil resources to allow them to develop in a similar manner. The production of 1000 m 3/day of freshwater requires 10,000 tons of oil per year, which can be considered a highly significant energy consumption, as it involves a recurrent energy expense which few of the water-short areas of the world can afford. Recently, the utilization of renewable sources (e.g., solar, biomass, wind, and geothermal) to drive desalination plants has emerged as a promising sustainable solution for fresh water supply in regions lacking energy supply. This may be especially significant in regions where water is needed and renewable resources are available such as Africa and the Middle East region. The conversion of solar radiation into direct utilization has been investigated for many years. Recently, attention has been directed towards improving the conversion efficiency of solar energy systems, desalination technologies and their optimal coupling to make them economically viable for small and medium scale applications. Extensive research and development activities have been conducted to explore the opportunities for sustainable and feasible methods of producing drinking water using solar energy. Conventional desalination systems are operated using fossil fuels, resulting in increase in costs because of the rise in world energy prices, increase in environmental pollution and the emission of greenhouse gases. In spite of these problems, it is likely that seawater desalination in large scale heat and power plants will continue to play a substantial role in providing fresh water for domestic and industrial use in areas of high population density, especially in oil rich Gulf countries and parts of India and China. However, such plants are not economically viable in remote areas where electricity infrastructure is poor and sup-plies inadequate and unreliable. The key point is that efficient and environment friendly solar energy coupled with desalination technologies would be an appropriate alternative to producing fresh water on both
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small and medium scales. This solution is suitable for supplying up to a half of the rural population living in arid regions that lack conventional fossil fuels, while reaching an average of 15% in oil rich countries. Solar thermal water desalination is proving to be a viable method of producing fresh water from saline sources in remote locations; humidification and dehumidification solar water desalinations units and conventional basin solar stills with a relatively large footprint are an example of such simple technologies, but the main problems with the use of solar thermal energy in largescale desalination plants are the relatively low productivity, the low thermal efficiency and the considerable land area required. However, since solar energy utilized is “free” the operating costs are significantly reduced compared with conventional plant.
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CHAPTER 2 CHALLENGES In the next few decades, access to water for drinking, agricultural and industrial use will become an increasingly crucial challenge for many countries around the world. Currently, freshwater is becoming a scare commodity and is used unsustainably in the majority of the world’s regions. Over 70% of the Earth’s surface is covered by water but most of it is unsuitable for human
consumption. With total global water reserves of about 1.4 billion km 3, around 97.5% of it is in the oceans and the remaining 2.5% is fresh water present in the atmosphere, Ice Mountains, freshwater lakes, rivers and groundwater, as shown in Fig. 2.1. Only about 0.014% is directly available for human beings and other organisms. In spite of water scarcity, freshwater resources are also very unevenly distributed across the world.
Figure 2.1: Distribution of world water resources
The world’s water consumption rate is doubling every 20 years, and is outpacing
population growth by two times. Almost one fifth of the world’s population live in areas where water is scarce. It is projected that by the year 2025 water demand will exceed supply by 56% due to persistent regional droughts, and shifting of the population to urban coastal cities. As of today, about three billion people have no access to a potable source of water and about 1.76 billion people live in areas already facing a high degree of water shortage.
Pa ge |5 The mismatch between the need for fresh water and its availability will intensify as competing needs for water grow due to population growth, urbanization, the impact of greenhouse gases on the environment and increases in house-hold and industrial demand for water. However, most projections estimate that the world population will stabilize at between 8 and 9.50 billion by around 2050 and that most of this growth will take place in the developing world, population growth will not only increase domestic water consumption, but also impacts on the consumption of agricultural, industrial and other products, and energy use.
Recently, the rapid economic growth of many countries, particularly in China and India, has led to higher incomes stimulating greater consumption of goods and services. The production of goods and services requires huge quantities of water. Decoupling income growth from water consumption is one of the major challenges to water management. Urbanization is another demographic trend resulting in greater water use. Such rapid growth would add tremendous stress on the region’s water resources. Even today, the major cities rely on deep wells to abstract water
from aquifers. The discharge of inadequately treated wastewater in many developing countries contributes negatively in the pollution and degradation of its limited water resources.
Lack of fresh water reduces economic development and lowers living standards. Clearly, there is a critical worldwide need to improve the management of this increasingly valuable resource. Consequently, desalination of saline water can be used to augment the increasing demand for fresh water supplies. However, desalination is a very energy intensive process, often using energy supplied from fossil fuel sources which are vulnerable to volatile global market prices.
Due water scarcity and limited available freshwater resources, the growth of the desalination market in the world is rapidly developing to meet the increasing water demand utilizing seawater, brackish water, river water, and brine. The installed capacity was 60 Mm 3/day in 2010 and is expected to be doubled by 2015. 38 Mm 3/day of these plants are planned to be installed in the Gulf region and 59 Mm 3/day in the rest of the world as shown in Fig. 2.2.
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Figure 2.2: Current and projected growth of desalination market worldwide
Seawater desalination technology, available for decades, made great strides in many arid areas of the world, such as the Middle East, the Mediterranean, and the Caribbean. Fig.2.3. shows the location of the existing desalination plants worldwide. The vast majority of high production capacity plants are installed in the Middle East. Seawater desalination in the Gulf region represents 65% of global water desalination capacity due to abundance of the world’s largest oil reserves, with an acute shortage of potable water resources as shown in Fig. 2.3. Saudi Arabia, UAE, U.S., Spain and China have the highest desalination capacity, but India and Israel have seen a significant growth since 2002.
Figure 2.3: Global distribution of desalination capacities world wide
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CHAPTER 3 TECHNOLOGIES The majority of water desalination processes can be divided into two types: phase change thermal processes and membrane processes, as shown in Fig. 3.1, both encompass a number of different processes. In addition, other alternative technologies of freezing and ion exchange, but they are not widely used. All are operated b y either a conventional or renewable energy sources to produce fresh water.
Figure 3.1: Water desalination technologies
3.1 Thermal desalination processes Thermal desalination is based on the principles of evaporation and condensation. Water is increased in temperature until it reaches its saturation temperature, beyond which evaporation occurs. The salt is left behind while vapor is taken away and condensed in another heat exchanger to produce fresh water. The thermal energy is produced in steam generators, waste heat boilers or by the extraction of back-pressure steam from turbines in power stations. The most common thermal desalination processes are: Multi-stage flash distillation (MSF); Multiple-effect distillation (MED); Vapor-compression evaporation (VC); Solar water desalination.
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3.2 Membrane desalination processes Membrane technology was originally limited to municipal water treatment such as microfiltration and desalination, but with the development of new membrane types, uses have expand ed to cover not only the water industry, but also high return processes such as chemical separations, enzyme concentration and beverage purification. This technology uses a relatively permeable mem-brane to move either water or salt to induce two zon es of differing concentrations to produce fresh water. A membrane is a thin film of porous material that allows water molecules to pass through it, but simultaneously prevents the passage of larger and undesirable molecules such as viruses, bacteria, metals, and salts. Membranes are made from a wide variety of materials such as polymeric materials that include cellulose, acetate, and nylon, and non-polymeric materials such as ceramics, metals and composites. Two of the most successful membranes are spiral wound and hollow fine fiber (HFF) and both of these are used to desalt brackish water and seawater. Fig. 3.2 shows the effective range of membrane processes and applications.
Figure 3.2: Effective range of membrane processes and applications
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3.3 Integration of desalination with renewable energy The desalination systems that use renewable energy sources can be divided into three categories: wind, solar (photovoltaics or solar collectors) and geothermal energy. These renewable energy sources can be coupled with thermal distillation or membrane desalination systems to produce water. The decision on which energy source is used should be made on the basis of economic, environmental and safety considerations. Due to its desirable environmental and safety advantages, it is widely believed that where possible, solar energy should be utilized instead of energy derived from fossil fuels, even when the cost s involved are slightly higher. Currently, solar energy is the most widely used among the renewable sources, as shown in Fig. 3.3. So that by the utilization of solar energy for fresh water production, three main problems can be addressed: fresh water scarcity, fossil energy depletion and environmental degradation due to greenhouse gas emissions and hydrocarbon pollution.
Figure 3.3: The use of renewable energy sources in water desalination
Solar energy can be identified as a viable energy source to be utilized in producing freshwater from saline water, especially in many African and Asian countries, and region which are located in semiarid and sunny climates with average global solar irradiation of 6 – 7 kWh/m2/day. A further advantage of solar water desalination technology is that peak solar energy harnessed in summer seasons coincides with high water dem and in semiarid areas.
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Consequently, the development of affordable, inexhaustible and clean solar energy technologies will have a significant long term benefits. It will increase energy security throu gh the use of a localized indigenous, inexhaustible and mostly import independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower. Fig. 3.4 shows the integration of renewable energy resources with desalination technologies.
Figure 3.4: Combinations of renewable energy resources with water desalination technologies.
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CHAPTER 4 Solar Water Desalination Solar water desalination has a long history. The first documented use of solar stills was in the sixteenth century and, in1872, the Swedish engineer, Carlos Wilson, built a large-scale solar still to supply a mining community in Chile with drinking water. The solar energy can be captured for use either by photovoltaic (PV) devices and direct absorption using solar collectors or solar ponds as thermal energy. Solar powered desalination processes are generally divided into two categories, direct and indirect systems as shown in Fig. 4.1.
Figure 4.1: Possible configurations of solar energy resources with water desalination technologies.
4.1 Direct Process The direct systems are those where the thermal desalination processes take place in the same device and it is mainly suited to small production systems, such as solar stills, in regions
P a g e | 12 where the fresh water demand is less than 200 m 3/day. Solar still distillation represents a natural hydrologic cycle on a small scale. The simple solar still is shown in Fig. 4.2. The solar still is working as a trap for solar radiation that passes through a trans-parent cover it consists of a basin containing salt water, a pair of glass or plastic panels sloping at an angle above the basin and meeting at the apex, creating a structure much like a greenhouse. The basin is generally painted black to maximize the absorption of longwave radiation falling on the surface. Solar radiation falls on the sloping panels and the greenhouse effect that is produced in the inside raises the temperature of the salt water held in a basin.
Fig. 4.2: Solar still desalination unit
Water at the surface is evaporated, the water vapor rises in the still and reaches the sloping panels, where it condenses to liquid water and runs down the sides of the panels. The water is collected and drawn off to provide fresh water. Solar stills can produce 3 – 4 liter of fresh water per day per square meter. Because of low production rates, it is important to minimize capital costs by using very inexpensive construction materials. Efforts have been made by various researchers to increase the efficiency of solar stills by changing the design, by using additional effects such as
P a g e | 13 multi-stage evacuated stills and by adding wicking material, and these modifications have increased production per unit area. In the simple solar still shown in Fig. 4.2, the latent heat of condensation is dissipated to the environment. However, the latent heat of condensation can be used to pre-heat the feed-water, and this leads to an improvement in the efficiency. Solar still technology requires a large area for solar collection so it is not viable for large-scale production, especially near cities where land is scarce and expensive. The comparative installation costs tend to be considerably higher than those of other systems. Solar stills are also vulnerable to damage by the weather. Labor costs are likely to be high due to the need for routine maintenance to prevent scale formation and to repair vapor leaks and damage to the glazing panels. However, they can be economically viable for small-scale production for house hold sand small communities, especially where solar energy and low cost labor are abundant.
4.2 Indirect Process In these systems, the plant is separated into two subsystems, a solar collector and a desalination unit. The solar collector can be a flat plate, evacuated tube or solar concentrator and it can be coupled with any of the thermal desalination processes types which use the evaporation and condensation principle, such as multistage flash distillation (MSF), vapor compression (VOC), multiple effect evaporation (MED), and membrane distillation (MD) for possible combinations of thermal desalination with solar energy. Systems that use photovoltaic (PV) devices tend to generate electricity to operate reverse osmoses (RO) and electro dialysis (ED) desalination processes. Fig. 4.3 shows the world-wide use of the various desalination technologies using solar power sources.
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Figure 4.3: Water desalination technologies coupled with solar power sources installed worldwide.
4.2.1 Solar still coupled with solar collectors In order to increase still productivity many small-scale system configurations have been examined such as coupling single stills or multi-effect stills with solar collectors, as shown in Fig. 4.4. Coupling more than one still with such solar collectors produces an increase in efficiency by utilizing the latent heat of condensation in each effect, which is then delivered to the next stage.
Figure 4.4: Schematic diagram of single solar and multi effect solar still coupled with a solar collector.
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4.2.2 Solar humidification and dehumidification This process, saline water is evaporated by thermal energy and the subsequent condensation of the humid air that is generated (normally at atmospheric pressure) produces freshwater. Air has the capability to hold large quantities of water vapor and its vapor carrying capability increases with temperature. Many studies on desalination using humidification – dehumidification have been conducted with a variety of fabricated devices. The principle of this process is based on the evaporation of water and the condensation of steam from humid air. The humid air flows in a clockwise circuit driven by natural convection between the condenser and the evaporator, as shown in Fig. 4.5. In this example, the evaporator and condenser are located in the same thermally insulated box. Seawater is heated in the evaporator and distributed slowly as it trickles downwards. The air moves in a counter-current flow to the brine through the evaporator and the air reaches saturation. Partial evaporation cools the brine that is left in the evaporation unit, leaving it at a higher concentration, while the saturated air condenses on a flat plate heat exchanger. The distillate runs down the plates and trickles into a collecting basin. The heat of condensation is mainly transferred to the cold seawater flowing upwards inside the flat plate heat exchanger. Thus the temperature of the brine in the condenser rises from 40 ◦C to approximately 75 ◦C. In the next step, the brine is heated to the evaporator inlet temperature, which is between 80 and 90 ◦C. The salt content of the brine as well as the condenser inlet temperature can be increased by a partial reflux from the evaporator outlet to the brine storage tank. Then distillate can be collected in a vessel and the brine goes also to saline water tank to recover a portion of the heat.
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Fig. 4.5: Humidification and dehumidification desalination unit coupled with solar collector
Fig. 4.6: RO desalination unit coupled with a PV generator
4.2.3 Water desalination powered by solar photovoltaics (PV) Solar photovoltaic (PV) systems directly convert sunlight into electricity by using solar cells made from silicon or other semiconductor materials and are connected together to form a PV module, which can then supply power to the desalination unit. The PV generator can be connected either with RO or ED water desalination technology, as described previously. Fig. 4.5 shows the assembly of a RO desalination plant coupled with a photovoltaic generator. This configuration includes a set of battery blocks to stabilize the energy input to the RO unit and to compensate for solar radiation variations, a charge controller to protect the battery block from deep discharge and overcharge, and a RO unit to desalinate the water.
4.3
Solar water purifier-Solar still
4.3.1 Working Principle The basic principles of solar water distillation are simple yet effective, as distillation replicates the way nature purifies water. The sun’s energy heats water to the point of evaporation.
As the water evaporates, purified water vapor roses, condensing on the glass surface for collection. This process removes impurities such as salts and heavy metals, as well as destroying microbiological organisms. Is a passive solar distiller that only needs sunshine to operate; There are no moving parts to wear out. The distilled water from a still does not acquire the “flat” taste of
commercially distilled water since the water is not boiled (which lowers pH). Solar stills use
P a g e | 17 natural evaporation, which is the rainwater process. This allows for natural pH buffering that produces excellent taste as compared to steam distillation. Solar stills can easily provide enough water for family drinking and cooking needs. Solar distillers can be used to effectively remove impurities ranging from salts to microorganisms and are even used to make drinking water from seawater. Stills have been well received by many users, both rural and urban, from around the globe. Solar distillers can be successfully used anywhere the sun shines. The solar stills are simple and have no moving parts. They are made of quality materials designed to stand- up to the harsh conditions produced by water and sunlight. Operation is simple: water should be added (either manually or automatically) once a day through the stills supply fills port. Excess water wool drain outs of the overflow port and this will keep salts from building up in the basin. Purified drinking water is collected from the output collection port
4.3.2. Solar water purification System Solar water purification is of the simplest and most effective methods of purifying water. Solar water distillation replicates the way nature purifies water. The sun’s energy beats water to
the point of evaporation. As the water evaporates purified water vapor rises, condensing on the glass surface for collection. This process removes impurities such as salts and heavy metals, as well as destroying microbiological organisms. The end result is water cleaner than the purest rainwater. Only solar energy is required for the still to operate. There are no moving parts to wear out. The number of systems designed to fitter or purity water has increased dramatically in recent years. As water supplies have increased in salinity, have been contaminated or have experienced periods of contamination, people have lost trust in their drinking water supply. Water filtration systems can be as simple as a filter for taste and odor to complex water treatment systems can remove more impurities but they are also the most expensive to operate and required increased maintains. Following are the different parts of the system Still Basin: It is the part of the system in which the water to be distilled is kept. It is therefore
essential that it must absorb solar energy. Hence it is necessary that the material have high absorptivity or very less reflectivity and very less transitivity. These are the criteria’s for selecting
the basin materials. Kinds of the basin materials that can be used are as follows: 1. Leather sheet, 2. Ge silicon, 3. Mild steel plate, 4. RPF (reinforced plastic) 5. G.I. (galvanized iron).
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Top Cover: The passage from where irradiation occurs on the surface of the basin is top cover.
Also, it is the surface where condensate collects. So, the features of the top cover are: 1) Transparent to solar radiation, 2) Nonabsorbent and Non-adsorbent of water, 3) Clean and smooth surface. The Materials Can Be Used Are: 1. Aluminum frame, 2. Glass, Glass thickness is around 8 mm. Channel: The condensate that is formed slides over from the inclined top cover and falls in the
passage, this passage which fetches out the pure water is called channel. The materials that can be used are: P.V.C., Galvanized Iron, and Reinforced Plastic Fiber. Side Walls: It generally provides rigidness to the still. But technically it provides thermal
resistance to the heat transfer that takes place from the system to the surrounding. So, it must be made from the material that is having low value of thermal conductivity and should be rigid enough to sustain its own weight and the weight of the top cover. Different kinds of materials that can be used are: wood, concrete, M.S. sheet, RPF (reinforced plastic).
4.4. Output of a solar still -
Q= [E*G*A]/2.3
Where Q=daily output of distilled water (lit/day) E=overall efficiency G=daily global solar irradiation (MJ/m2) A=aperture area of the still
4.5. Output per square meter of areaThe average daily global solar irradiation is typically 18.0 MJ/m2 A simple basin still operates at an overall efficiency of about 30% Daily output-[0.30*18*1]/2.3=2.3lit/square meter
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CHAPTER 5 Summary
:
Water and energy are the most essential pillars for a sustainable life. The scarcity of water limits the socio-economic development of many countries in the world especially in developing countries. The majority of desalination plants installed in most of the world’s countries suffering from water shortages are operated by fossil fuel, however, since the desalination processes are energy intensive, they are becoming expensive to run and the environ-mental pollution they produce is increasingly recognized as very harmful to the environment. The thermal desalination process is exclusively used for desalination of seawater in the most of oil rich countries and the RO process becomes the second on a global scale. Currently RO is considered the first choice in many industrialized and developing countries where conventional energy resources are scarce. Thermal cogeneration facilities pre-dominate in oil-rich countries of the Middle East. The desalination of brackish and seawater will increase rapidly as technologies develop and demand for freshwater grows. The use of renewable energy for desalination is becoming are liable and technically mature alternative to the conventional systems, especially in regions with poor infrastructure, lack of access to conventional forms of energy, and abundant renewable resources available. The recent developments and improvements in both solar and desalination technologies have made them mature technologies. Thus the use of solar energy for water desalination in countries in the Middle East region and Africa which lie on solar energy. . The collected distillate from solar water purification system is very much suitable for modern engineering applications like in chemical laboratories, pharmaceutical industries, maintenance of vehicle batteries and domestic purpose. Solar water purification system is portable and maintenance free, doesn’t cause any pollution.
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References:
Omara, Z. (June 2016). Solar still with condenser. Renewables and sustainable energy reviews (Vol. 59, pp. 839-857). Science Direct.
Solaqua, (2015). Solar powered Water Purification Equipment . September, 2016, http://www.solaqua.com/solstilbas.html
Menninger, F. A Solar powered Water Purification System at Goldstone. DSS Engineering Section (pp. 42-66).
Sharma, M. (2004). Engenious design to inspire. Shaastra (pp.1-2). IIT Madras.
Shatat, M. Worall, M. (2013). Opportunities for solar water desalination worldwide: Review. Sustainable Cities and Society (Vol. 9, pp. 67-80). Science Direct.
G.D.Rai. (2011). Non Conventional energy resources. Khanna Publishers.
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