GB2472034A

GB2472034A - Solar desalination system

Info

Publication number: GB2472034A
Application number: GB0912702A
Authority: GB
Inventors: Max Denning; Graham Murphy
Original assignee: AQUACYCLE Ltd; C Questor Group Ltd
Current assignee: AQUACYCLE Ltd
Priority date: 2009-07-22
Filing date: 2009-07-22
Publication date: 2011-01-26
Also published as: GB0912702D0

Abstract

A device for desalinating water produces fresh water for irrigation or drinking by using solar heat to evaporate saltwater within a floating enclosed structure. The top of the device may comprise a roof membrane, wherein water vapour condenses on the roof. The resultant condensation runs down the inner surface of the roof and is collected in gutters at the base of the roof. Preferably, the water in the gutters enters a small sump and is pumped to storage tanks. The roof may sit on a floating frame. Water in the enclosed structure may be aerated to enhance growth of algae and other salt water plants. The roof membrane may comprise a smooth outer surface, containing a translucent thin film photovoltaic material, whilst the underside of the roof has a capillary surface. Alternatively, the underside of the roof may comprise a hydrophobic surface.

Description

Aquacycle

Background

Globally, the number of people continues to increase, as does the amount of water used. In many of the more arid parts of the world, demand for water considerably exceeds the ability of natural systems to sustainably supply. As a result of this, underground water sources are being overexploited. We are effectively mining the water rather than harvesting it. Once this ground water is gone, there will be no further regular supply, and those people presently depending on the groundwater will face serious problems. For the rich, it is simply a case of bringing in water from more distant sources, desalinating water, or relocating to a more favoured location, however for the poor, it means failed crops, thirst, drinking dirty water, poor health, and very often a slow premature death.

Current desalination technologies are too expensive, and too energy intensive for general application, especially in the poorer arid regions. Hygiene and health, agriculture and food supply are thus compromised. Were sufficient resources made available for example using aid from developed nations, supplying adequate water using conventional distillation or reverse osmosis would still be problematic, and may ultimately result in an increased climate change pressure due to increased use of fossil fuels.

The purpose of this invention is to increase the available water supply by replicating on a small scale the hydrological cycle by which water is evaporated by the sun, condenses, and falls back to Earth as potable fresh water. The water produced by the system could either be potable, or irrigation quality depending on the purity of the pond water. In the latter case, filtration could upgrade the water from irrigation to

potable quality.

General description

The Aquacycle solar desalination device consists of a lightweight plastic roof on a set of floats which sits on a pond, estuary, marsh, or other salt or brackish water source.

The underside of said roof consists of a large surface area "capillary structure" designed to ensure that there is plenty of collecting surface on which water can condense, and that any condensation runs down the underside of the roof into gutters and is collected through a filter into a covered water container. As an alternative, the roof could be made of a hydrophobic plastic which would also result in water droplets forming, growing, and running down into gutters for collection. (A good cover on the water collector is important in tropical and sub-tropical areas to prevent mosquitoes from gaining access to the water -so risking malaria and other insect borne diseases) In this way, the Aquacycle collects water, and keeps it clean and safe for use when needed. Aquacycle therefore can make a useful contribution to providing an adequate water supply for drinking, and hygiene as well as contributing to water supplies for irrigation, so contributing to food security. As Aquacycle is a modular technology, with each unit small and light enough for a small number of people to deploy and move by hand, it lends itself to arrays of units, offering the possibility of larger scale water production, and where photovoltaic thin film devices are incorporated into the roof structure, of supplying a community with electrical power.

The Roof Structure The roof of the Heliocycle has much in common with a tent, with the support structure made up of flexible fibreglass "tent poles" or locally sourced products of equivalent function held in a curved shape by cord under tension to form an arch. An alternate would be to use similar materials or bamboo to form lightweight "A" frames, giving a fixed pitch roof rather than an arch. The frame is attached to floats which support the roof above the water. (Fig 1 C. Support Structure). The dimensions of the device are variable, but designed to facilitate easy manual handling by a small number of people. More than one section could be assembled together to make a larger structure simply by tying the sections together.

The Roof Cover The roof cover is of smooth finish on the top surface, and channelled "capillary" structure on the underside. (Fig 1 A & F). An alternate is made with a hydrophobic cover and without capillary channelling. The plastic selected is rip resistant, and fibre reinforced where necessary. Plant derived plastics are a candidate for this application subject as and when they are available with sufficient durability. The cover blocks UV light, both to protect its constituent plastic, and to remove a part of the solar spectrum of no photosynthetic benefit. The roof structure offers the possibility of built in cooling equipment.

In order to avoid overheating and excessive light levels, some degree of shade is within the plastic, giving the opportunity to incorporate a thin film photovoltaic layer within the plastic structure (Fig 1 A)-This shading reduces the amount of illumination going through the plastic and shades any algal or other crop growing in the pond. The electricity generated i the photovoltaic version is sufficient to provide basic electrical services such as light and communications to several families using efficient LED lighting, radios and mobile phone chargers. A further option is the use of a photo-reactive pigment, which reduces light levels by varying degrees according to the brightness of the light. The cover is as air tight as possible to ensure very high humidity under the cover, and allow condensation to form as soon as the air above the roof is cooler than the pond.

Aeration An aerating system (Fig 1 D) is installed under the Aquacycle device to optimise the growth of algae or other salt water crops, to prevent the development of anaerobic conditions, and to enhance evaporation -so increasing the degree of desalination occurring in the Aquacycle. The system thus makes possible in seawater an enhanced form of the traditional Chinese aquaculture system in which manure is disposed of, algae grow, and fish eat the algae to provide protein in the diet of local inhabitants.

The aeration system will ensure that volatile organic carbon and nitrates will be efficiently mopped up, so simultaneously enhancing water quality. Algae or other sea water crops might also be harvested for the production of fine chemicals such as food colourings, nutritional supplements, medicines, fish / animal feed, or bio-fuels.

Floating frame The Aquacycle roof sits on a floating frame (Fig 1 H) designed to raise the roof above the surface of the "pond" sufficiently to permit drainage of condensing water through filters into gutters, (Fig 1 B) and then to drain or pump said water to insulated storage tanks outside the pond area. These tanks being deep and narrow to reduce surface area and cut evaporation.(Fig 1 C shows pipes to tank storage) The floating frame keeps the gutters sufficiently high to avoid contaminating the desalinated water when waves form on the pond. The structure sits on a manmade or natural body of water which is distilled over time by the actions of the sun (Fig 1 E) Note:-Fig 2 shows A,B,C,D,E & H jn plan view Fig 1 & 2 key to labels A. Roof membrane -smooth on outside, containing translucent thin film photo-voltaic or other shading substance, and has either "capillary" structure to underside, or hydrophobic surface to ensure condensation runs down to gutters and is collected.

B. Gutter -water runs down the roof, is collected in the gutters and pumped off to storage. Each gutter slopes down to a small sump to facilitate such collection.

C. Pipe -water collected from a number of Aquacycle devices is gathered and collected into storage tanks.

D. Aeration pipes -aeration ensures optimal growth of algae, enhances evaporation by intimate air water contact, and keeps the pond water from becoming excessively hot by evaporative cooling.

E. Water evaporates into the air bubbles released by the aeration system.

F. Tent like frame material holding up roof.

G. "Capillary" or hydrophobic surface to enhance rundown of condensing water.

H. Float maintaining the buoyancy of the device.

Claims

Claims 1. The Aquacycle is a floating desalination system which produces fresh water for irrigation or drinking using the energy of the sun.
2. The Aquacycle takes into account the risk of mosquito or other insect vectors, and covers stored water to prevent their propagation.
3. The Aquacycle avoids excess evaporation from storage by moving water quickly to insulated containers with only a small surface area.
4. The Aquacycle roof contains a capillary structure to increase surface area and so enhance condensation and ensure efficient collection of condensed water.
5. As an alternate, the Aquacycle roof ensures high levels of condensation and run down of condensed water into storage using a hydrophobic coating.
6. The roof of the structure allows for the possibility of built in thin film photovoltaic power generation using translucent modules which simultaneously provide partial shade.
7. The Roof structure if not containing thin film photovoltaic shading will in any case block UV light and will contain Potassium Iodide or other substances as needed to regulate light levels.
8. The roof structure contains an optional photo-reactive agent by which admission of light is adjusted according to its brightness.
9. Using UV blocking substances in the Aquacycle roof will reduce UV inhibition, allowing more algae or other sea water plants to grow.
10. The use of a transparent cover will trap heat, so increasing the volume of water evaporated, and available to condense within the system.
11. The addition of an aeration system under the Aquacycle will enhance evaporation by bringing many small air bubbles into intimate contact with water, so increasing the volume of humidified air.
12. Shade provided by the Aquacycle will enhance the growth of algae or alternative salt water plants, boosting the production of products derived from them, and or the yield of farmed fish.
13. By using an aeration system, the Aquacycle can ensure very efficient removal of volatile organic carbon -so boosting water quality.
14. By using an aeration system, the Aquacycle can ensure very efficient removal of nitrates -so boosting water quality.
15. The Aquacycle system boosts production of food by enhancing the growth of algae on which fish feed.
16. The Aquacycle system will contribute to the decontaminate of water containing sewage, animal manure, man made fertilizer or other unwanted nutrients so offering protection to rivers, estuaries, coral reefs, sea grasses and other vulnerable coastal and near coastal habitats.Amendments to the claims have been made as follows: Claims 1. The Aquacycle is a floating solar desalination system comprised of a lightweight plastic shading roof with a large surface area capillary structure to its underside, the shading having in addition the option of taking the form of a translucent photovoltaic material delivering electrical power, the structure designed so that water runs down the roof to floating gutters and then into insulated filtered containers preventing propagation of mosquitoes, and keeping the water clean, the device having optional additional filtration capability to deliver potable water, and for an integral pump moving water to an onshore container, to the underside optional aeration equipment to facilitate growth of marine plants, and to enhance evaporation.2. The device according to claim 1 that uses filters and covers water to avoid accessible standing water and to avoid facilitating mosquito propagation 3. The device according to claim 1 that avoids excess evaporation from storage by moving water quickly to insulated containers with only a small surface area.4. The roof of the device in claim 1 that contains a capillary structure to increase Q surface area and to enhance condensation and ensure efficient collection of condensed water.5. As an alternate, the roof of the device according to claim 4 that ensures high levels of condensation and run down of condensed water into storage using a (0 hydrophobic coating.C\J 6. The roof of the structure according to claim 4 that allows for the possibility of built in thin film photovoltaic power generation using translucent modules which simultaneously provide partial shade.7. The roof structure if not containing thin film photovoltaic shading according to claim 6 will in any case block liv light and will contain Potassium Iodide or other substances as needed to regulate light levels.8. The roof structure according to claim 4 that contains an optional photo-reactive agent by which admission of light is adjusted according to its brightness.9. Use of liv blocking substances in the roof of the device according to claim 7 to reduce UV inhibition to allow more algae or other sea water plants to grow.10. The use of a transparent cover on the device in claim ito trap heat and increase the volume of water evaporated, and available to condense within the system.11. The addition of an aeration system under the device in claim 1 to enhance evaporation by bringing many small air bubbles into intimate contact with water to increase the volume of humidified air.12. A desalination device incorporating a float and designed to sit on a body of salt water.13. The device in claim 1 that uses modular technology, resulting in scalability of the invention. (0 (\J