Water Desalination Idea

Prepared by: Dr Sead Spuzic Version: 9; 16th March 2008

‘Rain Farm’ Proposal Abstract Water purification, e.g. water desalting and wastewater recycling remain to be amongst the high priorities in the arid regions. Current methods of desalination present significant costs due to maintenance and energy consumption, in addition to problems with the contamination of environment. A sustainable method with significantly lower consumption of energy could be considered as an acceptable solution if a rational compromise can be accepted with regard to the lower production capacity of such type of water desalting plants, and smaller (local) water purification units. 1. Introduction Desalination processes are based on controlling pressure, temperature and brine concentrations to optimize the water extraction expense. Methods of desalination include for example reverse osmosis, pressure barrier osmosis and other filtering techniques. Nuclear-powered desalination is considered to be economical on a large scale, but the issue of environment contamination remain to be resolved. In summary, large-scale desalination typically requires significant amount of energy as well as maintaining specialized, expensive infrastructure, making it very costly compared to the use of natural sources of fresh water. [1-5] However the availability of large fields of saline water as well as the convenient climate conditions (high solar emission) along some geographic regions such as the Australian coast, suggest considering the process of evaporation [4]. Australian coastal line comprises numerous shallow bays covering large areas in vicinity of urban centres. This environment is ideal for experimenting with “rain farm”, a workplace for collecting desalinated water based on the greenhouse effect. 2. Pilot experiments Experiments were made at Mount Cook area in Wellington New Zealand. A container made of “Acrylic glass” (Polymethyl methacrylate) was filled in with sea water op to 10 % (Fig. 1a).

(b) (a) (c)

Fig. 1: Containers used in pilot experiments (drawings are not in scale) A second inverted container made of completely transparent glass was used as a cover and as a condensation module. Geometry of the container was a cylinder with base diameter of 24.5 cm and height 22.5 cm, with wall thickness of 2 mm (Fig 1b). An improvised guttering system (made of acrylic glass) was used to collect the water condensed on the walls of the glass container (Fig 1c). In some experiments, component “a” was replaced by a glass container.

Total number of pages: 12 (twelve) 1


The assembled containers were exposed to sunlight in the open space. The desalinated water vapour condensed on the upper base and the side wall. Certain quantity of collected desalinated water was lost due to the flaws in the guttering system (leakage). Relevant measurements and observations are shown in Table 1: Table 1: Observations collected

during pilot experiments

in January 2008

Friday 18th Jan.

Sunday 20 Jan

Wednesday 23rd Jan

+ Black body

Thursday 24th Jan

+ Black body

Maximum temperature °C 18 22 19 19 Wind Speed km/h 30 10 11 15 Rainfall mm 0.0 0.0 0.0 0.0 Relative Humidity % 65 55 71 55 Pressure hPa 1020 1020 1012 1022 Wind direction SSE E NNW SSE Sky cloudiness 20% 10% 50% 50% Accumulated water ml/hour 2 3 10 10 Approximate measurement of the glass cylinder temperature indicated that the temperature inside the cylinder was above 40 oC. Bearing in mind the simplicity of pilot experiments and the relatively low ambient temperatures, the effect of black-body shown in Table 1 is significant. Subsequent measurements without the use of black body were conducted at Athelstone (Adelaide, South Australia) between 10 am and 11 am on 16th March 2008. Glass container design was similar to configuration shown in Fig 1. Measurements inside the glass container showed temperatures above 90 oC. Ambient temperature was 35 oC. The greenhouse effect (glass allows the passage of sun light but holds heat inside the container by trapping warmed air) can be manipulated to rise the temperature within the cylinder significantly above 50 oC. This will create favourable chemo-physical conditions for water evaporation within the cylinder, (Fig. 2). Fig. 2: Water phase diagram. Further pilot trials were conducted by combining various geometries of glass/acrylic/black-body components in order to enhance the condensation. It was observed that inserting the black



body in the lower zone of the evaporation area favourably affects both the evaporation and the condensation on the inner surface of external walls. The geometry of the top view cross-section should be considered based on the optimisation of the packing area, evaporation area, condensation surface and the ease of manufacture. Fig. 3: Top view of hypothetical cross-sections of four containers packed in the square envelope. Packing of the same quantity (4) of square or circular cross-sections within the same envelope will provide less favourable conditions for collecting the desalinated water. Condensation surface is one of principal factors affecting the quantity of collected desalinated water. The highest quantity of condensed water was collected from the inside surface of vertical external walls. Therefore the height H of the external container should be as large as possible. In addition the cross-section of external walls can be designed to provide the longest perimeter. Cross-section geometry shown in the top view in Fig. 3 provides significantly longer perimeter compared to the same quantity (four) of rectangular or circular cross-sections that can be packed within the same square. An ideal cross-section should be selected from a homotopic set of cross-section geometries, to satisfy the following requirements:

- the largest possible condensation surface (x1 => Max.) - the largest possible evaporation surface. (x2 => Max.) - the easiest manufacture (both from the point of view of container manufacture and the

guttering system assembly). This can be measured by the cost of manufacture (x3 =>min.). However the guttering system should satisfy the requirement for the maximum amount of collected desalinated water. (x4 => Max.)

- the smallest possible packing area. (x5 => min.) - the largest possible top-view free surface beyond the containers. (x6 => Max.) - the largest possible free volume for light travel beyond the containers. (x7 => Max.)

By introducing the black body and by increasing the proportion of condensation surface, the quantity of desalinated water has increased significantly thus encouraging further research in this direction. Based on the above considerations, several potential geometries for testing configurations are anticipated in Figures 4 to 7.



Sea water

Vapour

H

D

Fig. 4: A simplified design. It is anticipated that by inserting a cylinder in a larger container, the greenhouse effect can be enhanced within the lower portion of the assembly.

External wall; condensation takes place at the inner surface, within the container.

Fig. 5: In this version, it is anticipated that the condensation zone should have an increased diameter, and a side channel is added for incorporating the guttering system. Also, it is anticipated that a base container should be added to create a steady zone within the sea bead.



Sea water

Desalinated water

Fig. 6: In this version, the geometry of the condensation module is modified to enhance collecting the condensed water.

Sea water re-filling zone: sustainable system controls the open/close gates and the sliding bottom (stepwise process); refer to Appendix 1.

Water vapour accumulation container (High pressure)

Mini-tornado generator

Evaporation cylinder (Low pressure)

Whirlpool generator

Condensation surface

Fig. 7: An enlarged water vapour accumulation container is added at the top, and the “nozzle” that can be opened and closed is envisaged. In addition, two zones – a high pressure zone and a low pressure zone – are foreseen along with adding a “whirlpool generator”.



Most successful pilot trials (conducted on 23rd and 24th January 2008) were designed with the total condensation area of which enabled collecting 10 ml/h of desalinated water. This corresponds to relative rate of (mm/h) By assuming that there will be certain correlation between the condensation area and the amount of collected water, an approximation can be made to predict the possible capacity of a real-scale configuration. Additional set of trials was made with measuring the sea water evaporation rate only (without collecting the condensed water). These approximate measurements showed the evaporation rate due to the solar radiation between 10 and 17 ml/h. Expressed in the volume per evaporation area per hour, these approximate measurements showed the rate of 2.3 mm/h. Assume that a “rain farm” is constructed on an open sea area of 60 by 60 m, thus enabling for erecting of 400 towers. If the dimensions of one tower are as shown in Fig. 8, this enables creating the total condensation area of about 13500 m2 and the evaporation area of 450 m2.

(b) (a)

∅ 2.6 m Fig. 8: (a) Tower base (top view); the side view construction is outlined in Figures 4 to 7; (b) Schematic profile shown in the perspective view. The height of the tower is anticipated to be between 3 and 4 m. By assuming the direct proportionality between the amount of the collected desalted water and the condensation area, the conservative evaluation is projected to 400 to 600 litres per one hour of the day-light time. Following the proportionality with the evaporation area, conservative estimates reach over 900 litres of the evaporated sea water per hour. The above projection should be tested by conducting the sequential experiments as per following strategy:



3. Strategy Phase 1: Conduct experiments at a selected open location (field trial) to observe the efficacy of various configurations. Containers of diameters D = 0.5 to 1 m, and height H = 1 to 2 m should be used to evaluate the rate of accumulation of desalinated water. Various materials and cylinder configuration geometries, wall materials, black body configurations and guttering systems should be tested in order to evaluate the effect of significant factors. The mathematical approach to the evaluation at this stage is statistical design of experiments based on multifactorial analysis of variance. Phase 2: If the phase 1 will show that that the significant volume of desalinated water (>0.45 mm/h) can be collected, experiments should be conducted at an open field location with high solar radiation, to analyse the performance of the narrowed variety of cross-sectional geometries. Containers of diameters D = 1 to 2 m, and height H = 2 to 3 m should be used to evaluate the rate of desalinated water accumulation. Various cylinder geometries, wall materials, black body and guttering systems will be tried based on the analysis of the phase 1 above. Aim is to achieve the rate >0.5 mm/h of desalinated water. The mathematical approach to the optimisation at this second stage is the multifactorial fractional design of experiments. Phase 3: If the above experiments confirm that a significant volume of desalinated water can be collected, the experimental “rain farm” should be constructed. At least 20 towers (cylinder diameter D between 3 and 5 m, height H between 4 and 5 m) should be erected utilising a convenient area of flat inhabited coast. A schematic of a basin utilised for such a purpose is shown in Fig. 9. Containers made of suitable transparent material will be erected with the open base submerged below the sea level. Black body grid will be designed based on previous experience. A guttering system will collect the condensed water in the central reservoir. Mathematical strategy for designing the testing configuration at this 3rd stage is based on non-linear optimisation using the mathematical functions defined during the previous two stages. (a) (b) Fig. 9: An example of basin where the “rain farm” containers can be conveniently installed and tested. (a) top view; (b) side view showing the cross-section of the basin.



Auxiliary enhancements It is anticipated that sources of natural energy, such as offshore wind turbines, permanent magnet rotors* and tidal (stream) power can be added to the solar energy to provide hybrid energy for the “rain farm” plant [8, 9]. Special effects such as focused lenses can radically increase temperatures in the evaporation zone. Adding a funnel on the top of the vapour accumulation container may help in continuous transport of vapour to a location where the condensation is desired. *) One concept of magnet supported rotation is shown in Appendix 2. Summary of foreseen advantages 1) Proposal aims to contribute to remedy of a world-level problem of high significance, especially important for Australia and in particular for South Australia. Other methods alone did not resolve this issue satisfactorily. 2) This method is highly self-sufficient with regard to the energy consumption, compared to the other existing processes. 'Rain farm' requires significantly lower specific energy input (per litre of fresh water) compared to other desalination methods. In its industrial version 'rain farm' will be driven by a combination of solar and wind energy. I conducted some improvised attempts to add the effects of other natural sources of energy, and these free-sources of clean energy, combined together, should be sufficient to enable collecting the purified water in a central reservoir. 3) This method is highly environmentally sustainable, compared to other methods, with regard to the pollution of the ambient. (Wind-mills could prove to be efficient sea-bird repellents). 4) This method is based on hybrid utilisation of several natural sources, while the other methods aimed at high capacity, neglected the natural (“renewable”) sources such as wind, solar energy, tidal fluctuations, permanent magnets, etc. 5) This method cane be used for wastewater purification (e.g. domestic recycling). Summary of foreseen disadvantages 1) The production rate (capacity) of the 'rain farm' will be lower compared to most of the other existing methods industrially used today. 2) The full-scale plant will require larger area compared to the other existing methods. 3) Construction components for the "rain farm" will be made out of advanced and costly engineering materials (this adds yet another concern: the issue of security protection may require additional investment). 4) Contamination: (i) The amount of the salt returned to the ocean can cause the local increase in the salinity of sea water. This should be controlled by the appropriate utilisation of tidal streams, and tidal ‘rinsing’ the plant sea zone. (ii) Growth of the fungi and other bio-contaminants in the system. The quality of the collected water must be controlled and eventually filtered “downstream” at the main reservoir level. This however is an issue common to all methods of fresh water supply. Techniques such as bioretention should be considered. (iii) Contamination of the evaporation and condensation translucent surfaces by the precipitation of substances that hinder translucency. This should be controlled by the appropriate selection of materials, (use of removable translucent screens) and by appropriate maintenance schedules.



Conclusions About 20 % of the Earths population have no access to clean water and this proportion is increasing. Only 2.5% of the Earths 1.4 billion km3 of water is fresh water, and 70% of that is locked up in polar icecaps. As less than 1% of the world's freshwater is available as a renewable resource it becomes obvious that water is a very precious substance. Water consumption is usually higher in developed economies than it is in poorer lands. Industry and commodity demands use water without realising that this too is a finite, life sustaining resource. The detrimental effects of melting ice and pollution reduce the available water. [5] Exploring new sustainable methods of desalination belongs to high-priority research topics. There are very limited studies on the evaluation of solar desalination systems in the open literature. Number of institutions [10 - 13] developed purification system, however these systems do not utilise synergistic effects that will result from the hybrid renewable energy sources. Availability of new translucent materials, hybrid renewable energy sources as well as the novel “black body” solid coatings opens the perspective for substantial increase in the capacity of desalination based on the evaporation. Technical configurations for the initial experiments conducted in January 2008 were relatively simple. This improvised assembly still allowed for collecting a measurable quantity of desalinated water, and the evaporation and condensation processes were very much observable. After the short exposure of the configuration to the sunlight the inner zone would become strongly befogged with the vapour. The condensation surface was covered with the large droplets of the desalinated water, sliding into the guttering system. Inserting the black-body at the lower level of the evaporation zone increased the amount of collected water significantly. Recent advances in solar-cell, wind-turbine and other energy generators encourage idea of combining desalination plant with these sources. Pilot trials with evaporative desalting indicate that the modifications in the geometry of the evaporation and condensation zones combined with introducing special materials can radically increase the capacity of this technique alone. These plants can be installed as stand-alone systems; however, by combining them together, additional profit can be obtained due to savings in initial investments and energy usage, compared to the sum of profits from the stand-alone systems. Idea of hybrid plants is already exploited elsewhere [4, 6, 7]. This approach is especially feasible for the regions that have exceptionally high solar radiation and wind speed most of the year. Key point is that such

ybrid plant will be environmentally sustainable. h Industry experts say that after 2010 the necessary greenhouse gases emissions reductions require major technological changes as the mere improvement of existing processes will not be sufficient. The climate change prompts for considering these radical changes that will be significantly amplified by greenhouse gas emission constraints. Limits of the socio-technical system and the climate change challenge will induce reductions in the production, distribution and consumption patterns. The concept of systems innovation and transitions to sustainability has increasingly gained attention over the past years in academic and policy arenas. The proposed innovation offers sustainable solution to strategically important issues and requires granting the funds for more detailed testing of pilot stages.



References [1] Karagiannis I. C. and Soldatos P. G. (2008) “Water desalination cost literature: review and ssessment” Desalination, Volume 223, Issues 1-3, 1 March 2008, Pages 448-456 a

[ 2] The International Desalination Association; http://www.idadesal.org/

[3] European Desalination Society; http://www.edsoc.com/ [4] Mahmoudi H., Abdul-Wahab S.A., Goosen M.F.A., Sablani S.S., Perret J., Ouagued A. and Spahis N. (2008) “Weather data and analysis of hybrid photovoltaic–wind power generation systems adapted to a seawater greenhouse desalination unit designed for arid coastal countries”, Desalination, Volume 222, Issues 1-3, 1 March 2008, Pages 119-127 [5] William F. Gaughran, Stephen Burke and Patrick Phelan (2007) “Intelligent manufacturing and environmental sustainability” Robotics and Computer-Integrated Manufacturing, Volume 23, Issue 6, December 2007, Pages 704-711 [6] Omer E., Guetta R., Ioslovich I., Gutman P.O. and Borshchevsky M. (2008) “Energy Tower combined with pumped storage and desalination: Optimal design and analysis" Renewable Energy, Volume 33, Issue 4, April 2008, Pages 597-607 [7] Deshmukh M.K. and Deshmukh S.S. (2008) “Modeling of hybrid renewable energy systems”, Renewable and Sustainable Energy Reviews, Volume 12, Issue 1, January 2008, Pages 235-249 [8] Renewable energy http://en.wikipedia.org/wiki/Renewable_energy Sustainable energy http://en.wikipedia.org/wiki/Sustainable_energy Wikipedia; the free encyclopedia; Wikimedia Foundation, Inc., (Accessed 7th March 2008) [9] “Magnet Motors” http://freeenergynews.com/Directory/MagneticMotors/ (Accessed 7th March 2008) [10] Arif Hepbasli (2008) "A key review on exergetic analysis and assessment of renewable energy resources for a sustainable future", Renewable and Sustainable Energy Reviews, Volume 12, Issue 3, April 2008, Pages 593-661 [11] L. Garcia-Rodriguez and C. Gomez-Camacho, “Exergy analysis of the SOL-14 plant (Plataforma Solar de Almeria, Spain)”, Desalination 137 (2001), pp. 251–258. [12] Akili D. Khawaji, Ibrahim K. Kutubkhanah and Jong-Mihn Wie “Advances in seawater desalination technologies” Desalination, Volume 221, Issues 1-3, 1 March 2008, Pages 47-69 [13] SolAqua (U.S. PATENT 6,767,433) http://www.solaqua.com/


http://www.idadesal.org/

http://www.edsoc.com/

http://en.wikipedia.org/wiki/Renewable_energy

http://en.wikipedia.org/wiki/Sustainable_energy

http://freeenergynews.com/Directory/MagneticMotors/


APPENDIX 1 The sea water re-filling container (zone) positioned below the evaporation cylinder (see Figure 7, page 5). Sea water refreshing stage (open position; whirl is active – blade is spinning) Temperature maintenance stage (closed position; whirl is passive – blade is at a rest)




APPENDIX 2 Open non-scientific sources [9] report development of “magnetic motors” - devices which convert magnetic force into mechanical force (usually rotation), with no other input. If this principle can be used to support rotation, rather than generating it independently “with no other input”, this would already present a significant saving. For example, wind turbine rotation can be made more efficient by combining it with a device shown in Figure below. In the figure, the blue colour represents one magnetic pole (e.g. south), while the red colour represents the opposite magnetic pole. The stator has a number of permanent bar-magnets installed in fixed positions (eight magnets are shown in the sketch tentatively). Small prototypes should be produced for the purpose of pilot trials.

Stator Rotor

Water Desalination Idea

Technology

water evaporation

desalinated water vapour

glass container fig

glass cylinder temperature

glass container design

accumulated water mlhour23

water phase diagram

water extraction expense