WO2008104001A1

WO2008104001A1 - Laminar solar water purification and desalination cell and array

Info

Publication number: WO2008104001A1
Application number: PCT/US2008/054925
Authority: WO
Inventors: Gordon Rogers
Original assignee: Gordon Rogers
Priority date: 2007-02-23
Filing date: 2008-02-25
Publication date: 2008-08-28

Abstract

Methods and apparatus for the evaporation demineralization of water by utilizing latent heat of condensation and solar heating. A module floatable on a body of water includes first and second elongated liquid receiving channels, a dome, a lower chamber and an upper chamber. The first channel conducts water from the body of water to a reservoir located within the module. The second channel is in heat exchange relationship with the first liquid receiving channel and conducts water from the reservoir to the exterior of the module below the reservoir. The dome encloses the top of the reservoir and forms a vaporization chamber. An exit drain in the vaporization chamber leads to a collection channel for conducting demineralized condensate out of the module. The lower and upper chambers contain a gas insulating the first and second liquid receiving channels from the water environment below the module and the air environment.

Description

LAMINAR SOLAR WATER PURIFICATION AND DESALINATION CELL

AND ARRAY

BACKGROUND

[001] This invention relates to the production of pure water from sources such as the ocean, brackish ground, agricultural run-off and mine tailing water using readily available materials and solar power. All plants and animals need clean water to survive on a nearly daily basis. Drought on our planet has been an ongoing issue challenging the survival of humans and ecologies throughout history and in many places throughout theworld. Existing means of purification have associated high energy costs, both in terms of the energy needed to construct the facility which processes the water being purified and in the amount of energy used in the purification process itself. Desertification forces people from land that once produced food and that was hospitable. The lack of a reliable source of clean drinkable water causes poverty or loss of life. Most of the population ofthe planet lives close to an ocean or other body of non-potable water. These considerations have caused water, and the lack there of, to be the center of great public concern and potential conflict. Recent studies have shown that an estimated forty percent of the last thousand years have been droughts. Many cultures have vanished because of the lack of water. Yet unusable water sources abound, or are uneconomic to purify. Theseemingly simple evaporative and condensative properties of water, and the ubiquity of bubble-wrap products inspire this invention.

SUMMARY

[002] In general, in one aspect, the invention provides methods and apparatus for the evaporative demineralization of water to provide at least partially demineralized water byutilizing latent heat of condensation and solar heating for energy of vaporization. A multilayer module floatable or level-able on, or with respect to a body of mineral- containing water includes a first elongated liquid receiving channel, a second elongated liquid channel, and a dome. The first elongated liquid receiving channel has an entrance port and an exit port. The entrance port is in communication with the exterior of the module and is located at or below the surface of the body of water upon floating the module on the body of water. The exit port into a reservoir located within the module. The second elongated liquid receiving channel is in a heat exchange relationship with the first elongated liquid receiving channel, and has an entrance port and an exit port. The δentrance port is in communication with the reservoir at or near the bottom of the reservoir. The exit port is in communication with the exterior of the module below the reservoir. The dome sits above the reservoir and encloses the reservoir and forms a vaporization chamber having an inner domed condensation surface and a condensate- collecting surface. The condensate-collecting surface has an exit drain in communication 0with a collection channel for conducting demineralized condensate out of the module. The lower chamber contains air or gas insulating the first and second elongated liquid receiving channels from the water environment below the module. The upper chamber above the dome contains air or gas insulating the dome from the external air environment.

5[003]Advantageous implementations can include one or more of the following features. The modular apparatus can include several of the modules. The collection channel from each of the modules can be in communication with a common collection channel to collect condensate from the apparatus. At least a portion of the multilayer module can have one or more of the following properties: water insolubility, made of food-grade0materials, and capability to withstand temperatures of up to 100 degrees centigrade. The multilayer module can be placed at a maintainable height with respect to the surface of the body of mineral-containing water. A lower chamber can be provided that contains air or gas insulating the first and second elongated liquid receiving channels from the water environment below the module. An upper chamber above the dome can be provided that5contains air or gas insulating the dome from the external air environment.

[004] In general, in one aspect, the invention provides methods and apparatus for evaporative demineralization of mineral-containing water. At least one module is placed such that the module is exposed to the sun or other source of radiant energy onto a comparatively cold body of mineral-containing water to float the module. An0evaporation cycle is performed by: allowing a portion of mineral-containing water to flow into the first elongated liquid receiving channel and into the reservoir and to flow from the reservoir into the second elongated liquid receiving channel until the water level in the reservoir rises and blocks the exit port of the first elongated liquid receiving channel; allowing water in the reservoir to be heated by radiant energy radiating throughthe dome into the evaporation chamber causing water in the reservoir to evaporate, condense on the condensing surface, collect on the condensate-collecting surface and flow into the exit drain to fill the collection channel whereby condensate exits the module and the filling of the collection channel blocks exit of vapors from the evaporation chamber; higher concentration mineralized water in the reservoir during evaporationproceeding as effluent to flow into the second elongated liquid receiving channel and out of the module through the exit port in communication with the exterior of the module below the reservoir; and during flow of mineral-containing water and effluent into and from the module, the first and second elongated liquid receiving channels are continuously filled respectively with mineral-containing water and effluent in heatexchange relationship as the evaporation cycle is repeated within the module and demineralized water is continuously collected through the collection channel.

[005] Advantageous implementations can include one or more of the following features. Mineral-containing water can be pumped into the module to fill the first and second channels and reservoir and control the throughput of water. [006]The invention can be implemented to include one or more of the following advantages. The methods and devices in accordance with various embodiments of the invention are highly efficient and have a predictable and beneficial environmental impact. The devices described herein can be made from recycled materials and are recyclable themselves. They can be used by people with minimal training, the user cost is low, theyare inexpensive to manufacture and do not require any maintenance. In addition to being used for seawater desalination and water purification, various embodiments of the devices can also be used for atmospheric carbon dioxide scrubbing, industrial and mining cleanup and food production. It should also be noted that various embodiments of the devices are extremely scalable, such that they are compatible with large scale infrastructure and can be appropriately sized to be suitable for a single individual or family.

[007] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the δinvention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[008]FIG. 1 shows an exploded view of a cell in accordance with one embodiment of the invention.

0[009]FIG. 2 is a vertical cross section of a cell in accordance with one embodiment of the invention.

[001O]FIG. 3A is a top elevational view of an array of cells in accordance with one embodiment of the invention.

[001I]FIG. 3B is a vertical cross sectional view of an array of cells in accordance with 5one embodiment of the invention.

[0012JFIG. 3C is a top view of an array of cells in accordance with one embodiment of the invention.

[0013]FIG. 4D is a top elevated view of a cell mounted on a non horizontal surface in accordance with one embodiment of the invention. 0[0014]FIG. 5E is a top elevated view of a cup and mirror layer in accordance with one embodiment of the invention.

[0015] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Overview [0016] The various embodiments of the invention described herein pertain to water purification. In particular, the various embodiments of the invention relate to a scalable means for the purification, including desalination, of water by use of multiple layers of thin plastic. In various embodiments, these layers are convoluted into bubbles and manifolds δforming channels, thermal transfer interfaces and containment, as well as thermal isolation in contained gas volumes. Various implementations of the invention will now be described by way of example and with reference to the drawings. As the skilled reader will realize, the underlying principles of the various embodiments of the invention as described herein can be used not only for water desalination and purification, but also in a wide range of 0other applications, such as atmospheric carbon dioxide scrubbing, industrial and mining cleanup and food production.

Specific configuration of a single cell embodiment

[0017]FIG. 1 shows an expanded view of one embodiment of a single cell (100). FIG. 2 shows a vertical cross sectional view of the same cell assembled. As will be discussed in5further detail below, the water flow through the cell is actuated by both gravity and vacuum exerted on water flowing between the top external surfaces of neighboring domes, not covering the dome tops. A low vacuum can be provided by water flowing past the exit port on the lower layers.

[0018]As can be seen in FIGs. 1 and 2, the illustrated embodiment of the cell (100)0includes a number of layers. An outer dome (102) provides thermal isolation for the cell (100). An inner dome (104) forms an evaporative containment vessel. The inner dome layer (104) is thermally insulated from airflow above the cell (100) by the outer dome (102) located above. Some embodiments that are used in environments where external convection is low, such as areas with typically low winds, may have no outer dome (102).5As the skilled person realizes, the insulating layer formed between the outer dome (102) and the inner dome (104) constitutes a trade-off between these effects and reflective losses due to multiple surfaces. Idealized insulation values are dictated by the type of gas that is used between the outer dome (102) and the inner dome (104). The interlayer gas volume is maintained distinct from the interior of the inner dome (104). In a sense, the

0 insulating gas can be thought of as the 'hot attic' of the dome. This may be formed by a mating array or layer above the evaporative containment cell.

[0019] The double-dome structure allows pre-heating of the inner dome (104) to preclude condensation energy losses there. This preclusion of convection cooling on the internal δsurface exacerbated by air movement in the absence of the external dome is considered herein to be a preferable trade-off against the alternative of any losses incurred by the necessitated heating of the interstitial space between the outer dome (102) and the inner dome (104). An additional feature of this approach is that it automatically changes the cell's (100) volume and thereby its natural water level. This feature can be supplemented0by similar sealed air bladders below the operating waterline not only to perform the thermal isolation of coils, as will be discussed below, but in order to flush accumulated minerals when the cell cools at night and the water level rises to above the operating height by increasing the head or by decrease in buoyancy. These terms define the long- term operability of the system. 5[002O]An evaporative structure (106) is provided below the inner dome (104)in some embodiments. In the illustrated embodiment, the evaporative structure (106) is porous, water insoluble, made of food-grade materials, and is capable of sustained temperatures approaching or slightly exceeding 100 degrees centigrade. Some embodiments use calculated target temperatures achieved substantially lower than 100 C or may use open0water approaches not involving an evaporative surface area enhancer. This reduces mineral salt deposition.

[002I]As can be seen in FIGs 1, 2, 3, and 4, an elevated cup (108) whose interior bottom is formed by the two sheet layers below (110,112) is additionally accessed by the end point of a spiral channel with incoming water located one layer below (110). The layer5(108) forming the cup is and a shaped mirror focusing on the cup to some extent in some embodiments, otherwise in contact and seals with the layer (110) below it. In the illustrated embodiment, the elevated cup layer (108) is non-porous, water insoluble and is of food-grade materials and a reflective coating in mirrored embodiments, on its upper- surface and capable of sustained temperatures above 100 degrees centigrade. The mirror0may be formed with a slot oriented toward the area of the entrance of the incoming water under the boundary of the dome and a cap and channel for steam direction toward cooler regions of the condensation surface.

[0022]Below the cup layer (108) is an incoming spiral channel layer (110). The spiral channel has a curvature that is the same as the curvature of an outgoing spiral channel inthe outgoing spiral channel layer (112) below. The incoming spiral channel is principally contained by the spiral below, except at its endpoints on the output end which terminate outside the thermal containment bubble created by layer below when present on the cellular level, and of the end closest to the center of the cell which terminates in an opening onto the bottom of the central cup (108). Since the top of the incoming waterchannel serves as the bottom of the condensation chamber (ceiling/floor relationship between layers), a thermal exchange boundary is formed. By forming a coil of input water thermally interfacing with the floor of the condensation chamber, the temperature of the cold, incoming water is raised jointly by condensation on the interface and post- process effluent temperatures exposure. [0023]Below the incoming spiral channel layer (110) is an outgoing spiral channel layer (112), which forms the outgoing channel by means of a spiral conduit where the layer (112) is otherwise in contact with the above layer (110) forming seals around the perimeter of the spiral channel and in a central depression forming the floor of the cup (108) two layers up. The role of the outgoing spiral channel layer (112) is to feed theperforation with effluent process water enriched in mineral concentration.

[0024] The bottom layer (114) forms a dome and an upper boundary of the tube described above. In the illustrated embodiment, the layer is sealed along the sides of the tube of the outgoing spiral channel layer (112). This forms sealed regions around the features on the next layer up to provide thermal isolation of those features. The layer is perforated into aflat tube below. The lower surface is of food-grade materials. In this wide and shallow tube (not shown) water flows downhill on a slight grade to provide suction and seawater or process water to be purified for slightly saline enriched water to mix. In some embodiments, the water should preferably be at the lowest ambient temperature easily available. Finally, a collection channel (116) is provided for freshwater effluent to berouted for collection. 5

[0025] The dome formed by the bottom layer (114) thermally insulates the double coil from the surrounding water, which allows for thermal-countercurrent-gradient-flow of water coming into and going out of the processing cell and the associated recapture of the '"Heat of Vaporization" energy. Specifically, regions exchange heat when channels of δdiffering temperatures at their respective opposite ends, with a thin barrier between them, approximate physical contact while retaining channel integrity and respective opposite flow directions. The ends are considered 'opposite' because the end of the channel with the incoming flow is in close proximity to the other channel's outgoing flow. At the other end of the tubes, the channel with outgoing flow shares a reservoir with the channel 0with outgoing flow. The temperatures of the respective incoming and outgoing ends of the channels will approach equality with increasing heat exchange and better thermal contact over longer lengths of the channels. Near the incomings channel's source, the temperature of the incoming water is lower than that of the water vapor in the cell volume above the incoming channel and, as a result, water from that vapor will condense on the δcolder regions of the channel preferentially. Where the water has remained vapor, this condensation will impart the arithmetic negative of the heat of vaporization in amounts proportional to the amount of water that condenses, in the amount of the Heat of Vaporization times the amount of water. The amount of energy expended in the initial evaporation and associated distillation purification can be recaptured in this way when0multiplied by an efficiency term. The result is a cell that obtains distilled water for the energy losses required by the energy of solution of the solute concentration change and the temperature increase of the effluents, both of the fresh water product and the processed salt water, along with any inefficiencies of the configuration.

Operation of a single cell 5[0026]The water flow through a single cell (100), in accordance with one embodiment, will now be discussed. In the shown embodiment, water flows by gravity through an aperture on the top surface of the cell into the top channel (110) of the thermally- contacting spirals and circulates around the central cup (108) on a spiral of decreasing radius until it arrives at the cup (108). The water then fills, or partially fills, the cup0(108). At the cup (108), evaporation occurs at increased rate by virtue of the temperature increase both from being in thermal contact with water that has already left the cell (100) and due to condensation on to the colder regions of the spiral channels previously discussed.

[0027] The water then leaves the cup (108) through the lower channel (112) because of pressure from the incoming water, and because of vacuum created by the water flowing δahead of it. Additionally, the pressure increases with the evaporation of water exposed to solar energy. As noted above, the water will condense preferentially on the coldest available areas. Input water may be selected at the minimum temperature available to use this effect. Generally water of a lower temperature than will be achieved in the cell (100) will be available. The water that condenses is routed by gravity and cell geometry to the0lowest point in the cell (100) and to an exit port dedicated to freshwater extraction. Water condensing onto warmer areas of the chamber floor will be accordingly warm, varying flow rate can be used to dictate effluent temperatures.

Combining multiple cells into scalable arrays

[0028] Once the optimal particulars of individual cells (100) are identified, arrays or δsystems of a large number of small cells (100) can be constructed with large sheets of the laminar materials to get a scalable production system with good yield. Fresh water drainage networks interconnecting several cells (100) can be constructed in both rectilinear and hexagonal packing arrangements. Any individual cells (100) considered to be leaking between fresh and saline waters can be blocked, which increases the purity0of the effluent but also decreases the amount of production. FIGs. 3A-3C show various views of an exemplary cell array (300) in accordance with one embodiment of the invention. FIG. 3 A is a top elevational view of an array (300) of cells (100) in accordance with one embodiment of the invention. FIG. 3B is a vertical cross sectional view of the array (300), and FIG. 3C is a top view of the array (300). As the skilled5person realizes, although the cells (100) in the array (300) shown in FIGs. 3A-3C are arranged in a hexagonal pattern, the cells (100) can be arranged in any suitable pattern, such as a rectilinear, a triangular pattern, an octagonal pattern or any other geometry that may provide convenient interconnections of cells and a desired yield of desalinated water. [0029] Elevated temperatures decrease the solubility of some minerals causing precipitation of mineral salts. These mineral are again soluble at the lower temperatures experienced at night. This can be exploited by a decrease in the buoyancy of the cell or array. This can be made to occur by the use of materials whose volume changes by virtue 5of the temperature. The coefficient of expansion of a gas can be used to affect the water level in the cell so as to increase the surface area of the interface and the volume available for the resolution of the salts, thus reducing the need for various conventional descaling agents.

[003O]In some embodiments, the nested spiral layers and the layer forming the ceiling of0the upper channel are physically fused at the contacting surfaces, thus providing controlled relative channel cross sections. The primary exploited mechanism of all embodiments is the exploitation of the change in concentration of the salts in the effluent solution. The associated entropy, free energy, and heats of solution changes between the three open bodies of water provide substantial offset of the terms as received from the δsun's radiation. These terms enable a dramatic increase in production in an otherwise energy conservative system.

[003I]A maximum number of cells (100) can be arrayed on a single channel of constant cross section and a given pressure, hear approximating that of the water "head" or height of the source water above the height of the systems target reservoir. The height may be0varied to accommodate different flow rates through the cellular array depending on the temperature of the interior of the cell and the current weather. The maximum number of cells under these conditions thus dictates the need for channels or ancillary plumbing periodic distances or spacing to support collection of the fresh water produced. Of special interest to both individual cells and arrays of cells, is the height of the water on5the top surface of the layer containing the cup (108). The height of the incoming water surface height must be below that of the cup (108) if no overflow drainage port exists. In this regard cell and array flooding and cross contamination of fresh water effluent is facilitated by maintaining a functional exit channel flow capacity in excess of that of the incoming channel. In suspended arrays this is compensated for by lengthening the fresh0and enriched waters' effluent tubes. [0032] In some embodiments, suitable for applications in dams and buildings and other similar contexts, the cup (108) edge may be rotated so as to operate on inclined or vertical surfaces to the. Extended lengths of this approach may need ancillary flow- control to compensate for the implicit increase in 'head' or vertical water column, but δessentially all other aspects of the geometry, as described above, can be left intact.

[0033]In one embodiment, the number of cells (100) and size of water body required to produce one million gallons of fresh water a day can be determined as follows. It is assumed that the cell diameter is approximately six centimeters, and that the production time is about 6 hours (i.e., there are 6 hours of sufficiently strong sun light for the array0of cells to work as described above. (1.2XlO ³CcZs)^"1* 1.7528X10⁵cell*cc/s = 1.46X10⁸cells. The size of the water production area would be

1.46X10⁸CeIIs *0.064m* 0. Im = 9.3X10⁵m² = 0.36sq mile = 230 acres. It should be noted that these numbers may vary depending on weather conditions, size of cells, selection of materials, and so on. In practice, about 200 Acres of water surface area is expected to be δneeded to generate a million gallons of water per day in most current embodiments.

Alternative uses of the cells and arrays

[0034] The described embodiments avail many other uses than for direct water production. Greenhouse designs using arrays allow for the growth of plants in the interior of the green house for either food production. Systems meant for carbon dioxide0(CO2) scrubbing can be placed in areas of high CO2 concentration and flow with large volumes of atmospheric gases blown by fan action into the greenhouse to allow the botanical filtration of the gas by the plants. Additionally, closed cell embodiments where the outgoing enriched effluent spiral tube is omitted allow for mineral capture in applications such as mine or agricultural wastewater clean-up. 5[0035]A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the materials that were used in the above examples are merely suggestions and other materials may be more suitable for other applications. Such modifications to the above description fall within the skill of the ordinary artisan. The incoming and outgoing spiral channels do not have to be spirals. There are a number of other geometrical patterns that may be used. Accordingly, other embodiments are within the scope of the following claims.

Claims

25CLAIMS

1. A modular apparatus for the evaporation demineralization of water to provide at least partially demineralized water by utilizing latent heat of condensation and solar δheating for energy of vaporization, comprising: a multilayer module whose height with respect to that of a body of mineral- containing water is controllable, the module comprising: a first elongated liquid receiving channel having an entrance port in communication with the exterior of the module, the entrance port being located at 10 or below the surface of the body of water upon floating, the module on the body of water, and an exit port into a reservoir located within the module; a second elongated liquid receiving channel in heat exchange relationship with the first elongated liquid receiving channel, the second elongated liquid receiving channel having an entrance port in communication with the reservoir at 15 or near the bottom of the reservoir and an exit port in communication with the exterior of the module below the reservoir; and a dome above the reservoir enclosing the reservoir and forming a vaporization chamber having an inner domed condensation surface and a lower condensate-collecting surface, the condensate-collecting surface having an exit 20 drain in communication with a collection channel for conducting demineralized condensate out of the module.

2. The modular apparatus of to claim 1 comprising a plurality of the modules.

253. The apparatus of claim 2 wherein the collection channel from each of the modules is in communication with a common collection channel to collect condensate from the apparatus.

4. The modular apparatus of claim 1 , wherein at least a portion of the multilayer 30module has one or more of the following properties: water insolubility, made of food- grade materials, and capability to withstand temperatures of nearly 100 degrees centigrade.

5. The modular apparatus of claim 1 , wherein the multilayer module further is δoperable to be placed at a maintainable height with respect to the surface of the body of mineral-containing water.

6. The modular apparatus of claim 5, wherein the multilayer module further is operable to be suspended above an effluent stream. 0

7. The modular apparatus of claim 1 , wherein the multilayer module further comprises: an upper chamber above the dome containing air or gas insulating the dome from the air environment. 5

8. The modular apparatus of claim 1 , wherein the multilayer module further comprises: a lower chamber containing air or gas insulating the first and second elongated liquid receiving channels from the water environment below the module. 0

9. A process for the evaporative demineralization of mineral-containing water comprising: placing at least one module according to any one of claims Al to A4 exposed to the sun or other source of radiant energy onto a comparatively cold body of mineral-5containing water to float or level the module, whereby an evaporation cycle is performed by: allowing a portion of mineral-containing water to flow into the first elongated liquid receiving channel and into the reservoir and to flow from the reservoir into the second elongated liquid receiving channel until the water level0 in the reservoir rises and blocks or reaches the exit port of the first elongated liquid receiving channel; allowing water in the reservoir to be heated by radiant energy radiating through the dome into the evaporation chamber causing water in the reservoir to evaporate, condense on the condensing surface, collect on the condensate- collecting surface and flow into the exit drain to fill the collection channel whereby condensate exits the module and the filling of the collection channel blocks or is assists in exiting exit of vapor's flow by virtue of its flow, from the evaporation chamber; higher concentration mineralized water in the reservoir during evaporation proceeding as effluent to flow into the second elongated liquid receiving channel and out of the module through the exit port in communication with the exterior of the module below the reservoir; and during flow of mineral-containing water and effluent into and from the module, the first and second elongated liquid receiving channels are continuously filled respectively with mineral-containing water and effluent in heat exchange relationship as the evaporation cycle is repeated within the module and demineralized water is continuously collected through the collection channel.

10. The process of claim 9, wherein mineral-containing water is pumped into the module to fill the first and second channels and reservoir and control the throughput ofwater.