AU8142101A - A desalination process - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s) LIDS PTY LTD Invention Title: A DESALINATION PROCESS The following statement is a full description of this invention, including the best method of performing it known to me/us: -2- A DESALINATION PROCESS Field of the Invention This invention relates to a water desalination system involving evaporation of water from a brine by use of solar energy.

Background to the Invention Desalination of water may be a suitable option in some regions where the only source of water contains salt or brine having a higher than acceptable total of dissolved salts concentration for industrial or domestic use.

The most common desalination systems currently available involve either vacuum distillation or reverse osmosis. Where large capacity consumption of the desalinated water is used such as in conversion to potable water or for de-mineralised water used in large capacity steam boilers (such as power generation) the system of choice is the vacuum distillation process. This process makes use of the utilities available from major infra-structure processes and produces high volumes of product per day.

20 However, a drawback of this process is high operational costs both for consumables and normal maintenance and therefore the cost per unit volume desalinated water produced is high.

For smaller applications, such as on ships or offshore structures, or small capacity 25 onshore plants, reverse osmosis processes are used. The benefit of this type of process is that operational costs are lower in comparison to vacuum distillation. However, the life cycle of membranes used in reverse osmosis is directly affected by the presence of contaminants in an inlet water stream and therefore maintenance costs can vary considerably.

H:jnelson\kcp~speci\DESALINATION PLANT COMPL.doc lSAb0/01 Both types of desalination process require significant electrical power availability.

Vacuum distillation plants also require a source of steam.

It will be apparent from the above discussion that, in the ordinary course of events, the desalination of seawater or brackish water, such as bore or artesian water or geothermal source water requires significant investment. High running costs, operational costs and maintenance costs adversely affect the applicability of such desalination processes.

Summary of the Invention It is therefore the object of the present invention to attempt to provide a water desalination process that desirably avoids costs of the kind above discussed.

With this object in view, the present invention provides a water desalination system S. 1 including at least: 15 a water inlet system; an evaporation unit in fluid communication with said water inlet system and including an optical chamber having lens means for focussing solar radiation on water present within said evaporation unit for evaporating said water; and a water recovery system connected to the evaporation unit for recovery of water evaporated in said evaporation unit in desalinated form.

Preferably said lens means is of prismatic form.

Preferably said lens means includes a solar tracking system for tracking the sun to maximise solar radiation applied to said water within the evaporation unit as the position of the sun varies during the day.

Preferably said evaporation unit is configured to evaporate water in a flash process. In one embodiment, the evaporation unit further includes a flash chamber.

H:Vnelson~kccp\poci\DESALNATION PLANT COMPL.doc 18110101 -4- Preferably said optical chamber is disposed above said flash chamber. Preferably a thermal seal which is transparent to said solar radiation is disposed between said optical and flash chambers.

Preferably said evaporation unit further includes a cascade or weir assembly over which said water can flow for producing a laminar water flow.

Preferably said desalination system further includes supplemental water heating means for applying thermal energy to said water in addition to that provided by said solar radiation in said evaporation unit. In one embodiment, said supplemental water heating means includes a first heater means for heating said cascade or weir assembly.

Advantageously, said supplemental water heating means further includes a second heating means for solar preheating of said water prior to entry into said evaporation unit.

o .o 15 Preferably said flash chamber is maintained at a pressure less than atmospheric pressure.

a Preferably said water inlet system includes a pump for pumping water from a water source to said evaporation unit.

Preferably said desalination system further includes flow distribution means to distribute said water as a plurality of water flows into said flash chamber.

Preferably said desalination system further includes a mist eliminator to assist condensation of evaporated water to liquid phase water.

Preferably said mist elimination system includes one, or both of, a packed bed; and, a metallic mesh. Preferably said packed bed is packed with ceramic rings or other packing. However, condensation may be achieved by alternate means, including by use of a refrigeration system.

H:jnelson\keep\speci\DESALINATION PLANT CONIPL.doc 18110101 Preferably said water recovery system includes a storage tank which may communicate to locations where recovered water is to be used. Pumping systems may thus also form part of the water recovery system to achieve this purpose.

Concentrated salt streams or brines may be a waste product. However, storage in evaporation ponds or other evaporation means may allow recover of dried salts for other uses. Evaporation ponds may be lined with impermeable materials such as impermeable clays.

In one application, potable water derived from the desalination system may be used to water salinity affected areas. In this case, the water recovery system may communicate with a reticulation system to return treated water to areas of flora planted to improve the level of water table.

15 Remote operation without attention from an operator is possible. In that case, preferably the desalination system includes control systems and a telemetry system to allow remote operation of said desalination system.

S..The water desalination system of the present invention may conveniently be used, with minimal environmental impact, to provide potable water in areas such as remote communities proximate to the sea or sources of brackish or contaminated water.

Brackish water may be sourced from lagoons or bores. Water sourced from the system may also be employed for industrial purposes at expected lower cost than conventional techniques.

Brief Description of the Drawings A description of illustrative embodiments of the invention will now be made with reference to the accompanying drawings in which: H:jnelsonkepspciDESALINATION PLANT COMPL.doc 1810/01 -6- Figure 1 is a process flow diagram of the water desalination system of one embodiment of the present invention used for desalination of brackish/ground or geothermal source water showing salt recovery and distribution of product water; Figure 2 is a process flow diagram of the water desalination system of a further embodiment of the present invention used for desalination of seawater; Figure 3 is a detail side section of the prismatic chamber shown in Figures 1 and 2; Figure 4 is a detail side section of the flash chamber shown in Figures 1 and2; Figure 5 is a detail plan view of lens support means used in accordance with embodiments of the invention illustrated in Figures 1 to 5; and Figure 6 is a detail side view of lens support means upper portion showing location of a lens in the support means.

ooooe 15 Detailed Description of the Preferred Embodiments oo.

Referring now to Figures 1 and 2, in each case there is shown a water desalination system 10 including a water inlet system 20 and an evaporation unit 30. Evaporation unit 30 is in fluid communication with water inlet system 20 and includes an optical or prismatic chamber 35. The prismatic chamber 35 has lens means 40 for focussing solar radiation visible light) on water present within evaporation unit 30, and particularly within a flash chamber 36 thereof. Concentration of solar radiation on water provides heat energy for evaporation. The evaporation unit 30 is also in fluid communication with a water recovery system 50 which ultimately distributes desalinated water to end users.

Referring now more particularly to Figure 1, water desalination system 10 is used for desalination of brackish/ground contaminated or geothermal source water. Such water is recovered from a bore 11 having a lift pump 12 which pumps salty water through a filter 13 for removal of solid matter. Lift pump 12 may be of vertical turbine type and H:'nelson\kocp\apeci\DESALINATION PLANT COMPL.doc 18/10/01 may have multiple stages. This will depend upon the amount of "lift" required to provide inlet water to the remainder of the inlet water system Filter 13 which includes parallel filter elements 13a and 13b, removes solids prior to direction of water to preheater bank 14 for preheating of water prior to the evaporation stage. The water pressure at filter element 13a may be monitored, with water routed through filter 13b once pressure at filter 13a exceeds a pre-determined value. The filter 13a may then be cleaned or replaced as appropriate.

The preheater bank or preheater unit 14 may not be required in all applications. The preheater unit 14 may comprise a solar panel of conventional type in which capillary tubes 14a are set in an enclosed panel having a glass face allowing solar energy to heat water which passes through the capillary tubes.

15 A desirable and advantageous alternative preheater unit 14 may be formed in a radius selected for the line of latitude the desalination system 10 is designed for. Such a preheater unit 14 has a chamber 14a provided with a serpentine tube bank 14b. The serpentine tube bank tubes may be of titanium, inconel or other metal suitable to handle water at 60 0 C or more, with high concentrations of chloride or other contaminants. The top of the preheater bank 14 is to be angled to an optimum angle for the particular line of latitude in which desalination system 10 is located. An upper face of the chamber 14a also includes a lens system, incorporating one or more short focal length lenses that are mounted on thin thermal glass sheet. This concentrates solar radiation (and thus heat energy) on all levels of the serpentine tube bank 14b.

Serpentine tube bank 14b communicates through inlet storage tank 24 with evaporation unit 30 to which water is pumped by pump 124. Most of the water will be directed to inlet storage tank 24 but a portion may be recirculated through line 114, back to the preheater unit 14 inlet to enhance thermal efficiency. The inlet storage tank 24 is of conventional construction for a storage tank but may be rubber lined and insulated to H:jnclon\kcp\poci\DESALINATION PLANT COMPL.dc ISfl0/01 -8maintain water temperature as high as possible. Tank 24 could be provided with a heater element additional to, or substitutory for, preheater unit 14.

As indicated above the evaporation unit 30 includes an optical or prismatic chamber disposed above a flash chamber 36. These chambers are separated by a thermal seal which is transparent to the solar radiation and may be of thermal glass. Evaporation unit 30 is of generally circular shape in plan view and may have a structural steel support structure 31. The support structure may be coated to prevent corrosion.

Prismatic chamber 35, as shown in Figure 3, has at its upper end a lens or lens array The lens array 35a is of area suitable for evaporation of water at the desired rate. It may vary with the amount of available sunlight. The lens array 35a is configured to provide concentration of the solar radiation sufficient to evaporate water present within flash chamber 36. Desirably, the internal temperature of flash chamber 36 should reach 15 the range of 150 0 C to 3000C.

A suitable lens array 35a incorporates a series of prismatic lenses 35aa, one construction of which may be as follows. At the upper surface, each lens 35aa is convex to form a primary lens. The convex lens is bonded to a sheet or block of glass which acts as a secondary lens.

The focal length of the lenses 35aa which may be fixed relative to position of the lenses in prismatic chamber 35, is selected to achieve desired flash chamber 36 e.

temperature. It may be dependent on the application. The lenses are supported by lands 135a of a lens support or carrying cage 135 as shown in Figure 5, one lens 35aa being shown in dashed outline. The angle of inclination of the prismatic chamber 35, lens array 35a and/or each constituent lens 35aa therein is set at an optimum angle to catch available sunlight/solar radiation. This angle may be selected to accord with the latitude of location of desalination system 10. Seasonal adjustment may also be necessary. The angle may affect manufacture of the lens 35aa and is a design parameter therefor.

H:Vnezon\keeapeci\DESAL1NATION PLANT COMPL.doc 1811001 -9- Alternately as part of a solar tracking system the lens 35aa may be mounted in a manner which allows for individual automatic orientation to the optimum angle.

Solar radiation is focussed through each lens 35aa in lens array 35a down through prismatic chamber 35 through thermal sealing glass 70 into the flash chamber 36.

Prismatic chamber 35 is mounted for rotation on a drive ring assembly 37, being part of a solar tracking system, driven by drive motors 37a to rotate while tracking the sun to maximise evaporation efficiency. Such rotation occurs at low speed so motors 37a may be geared down to suit the speed required. It may be constructed of suitable material such as marine grade anodised or other aluminium, which is highly reflective to enhance thermal efficiency and which provides acceptable strength while reducing the size of the drive motor 37a for the drive ring assembly 37.

15 Although the drawings show only one evaporation unit 30, a number may be provided either in parallel or in series.

Flash chamber 36, as shown in Figure 4, is provided with a cascade or weir assembly comprising a number of weir plates 40a over which water flows or cascades during operation of desalination system Water inlet 136 is arranged above top weir plate 40aa to inlet 136. It may incorporate a nozzle or other flow distribution means such as one or more nozzles or a manifold to distribute water over the weir assembly. Each weir plate 40a has an edge lip 40b to provide residency of water within the system and provide a laminar water flow. The height of the edge lip 40b dictates the depth of water at each weir plate 40a. A shallow depth promotes evaporation. Preheater elements 39 may be located proximate the constituent plates 40a of weir assembly 40, conveniently in the air gaps below plates H:Vnelson\kecp\speci\DESALtNATION PLANT COMPL.doC 1/10/01 The elements 39 may be operated at start-up. The flash chamber 36 may have an external wall of carbon steel boiler plate. The flash chamber 36 and weir assembly may be lined with titanium or other chloride or contaminant resistant material. Flash chamber 36 is sized to desired recovered water capacity and may be insulated to reduce effect of temperature drop. It is sealed to prevent condensate loss. Further, the flash chamber 36 can be operated at a sub atmospheric pressure a partial vacuum) to further promote evaporation.

The pre-heating unit 14 and the elements 39 taken individually or in combination for a supplemental heating system for applying thermal energy heating) to the water in addition to that provided by the solar radiation acting in the evaporation unit.

An exit throat 137 makes connection of flash chamber 36 to a mist eliminator or extraction unit 38 which could comprise a packed bed, perhaps packed with ceramic 15 prill rings. The mist extractor unit 38 promotes water condensation though other forms of condenser may be used. For example, a shell and tube heat exchanger, which may be single pass; or a refrigeration system may be used in addition to, or alternatively to, mist extractor 38.

At the top of flash chamber 36 is located the drive ring assembly 37 which supports the prismatic chamber Flash chamber 36 includes temperature probes 110 to sense the temperature in the flash chamber 36. Three such probes, located at 900 intervals from exit throat 137, may be employed.

Mist extractor unit 38, or other condenser means is connected to the water recovery system 50 and, in particular, to a recovered water tank 52 which may be rubber lined but generally of conventional water storage tank design. The tank 52 may be sealed, for example with a vacuum seal such as a vacuum breaker 52a. Such a valve allows water vapour to be retained within tank 52. The valve also allows air into the tank once the H:Vncson\LkepzpeiWESALINAT1ON PLANT- CONPL.doc 18/10/01 11 sun has gone down and tank 52 temperature has fallen. This assists in prevention of tank 52 buckling due to correspondent pressure drop. Such a valve may be used on all system 10 tanks that are affected by thermal gradient during the day. Tank 24 is provided with vacuum breaker 24a.

Tank 52 may be communicated with a reticulation system 54 through which product desalinated water may be pumped through lines 55 to end users 56 by pump 154. Such water may be subjected to conventional sterilisation treatment if it is to be used for potable water.

A concentrated salt solution is the other product of the desalination system 10. A brine recovery system 60 is used to deal with this. The brine recovery system 60 may take concentrated brine through the small bore hot well 36c at the bottom of flash chamber 36. Pump 61 is used to pump the brine solution for disposal or other treatment. In this 15 case, salt is crystallised in evaporation pond 64 and may be recovered as a commercial product. Disposal will be dependent upon preference. Possibilities are described further below.

Figures 2 and 3 show desalination systems 10 generally similar to that described above.

The system of Figure 2 is suitable for seawater desalination where concentrated brine is returned to the sea. This is expected to be acceptable because the flowrate is low.

Figure 2 shows a desalination system 10 suitable for desalination of seawater. Other than taking water from a seawater source, and the water recovery/brine recovery system (not shown) there are no differences with the system shown in Figure 2. Similar strategies may however, be followed in the case of seawater desalination.

Electrical or other sources of energy may be used to power the pumps and other systems. Solar, wind or other energy may be harnessed in remote areas. Control systems may be operated by battery, as necessary.

H:jnehon\kmp\zpcci\DESALINATION PLANT COMPL.doc 18/10/01 -12- In all cases, the method of operation of desalination system 10 is generally similar. In the case of a remotely telemetrically controlled system the method of operation may be described as follows.

When temperature probes 110, located in flash chamber 36 detect start-up temperature, that is sufficient to heat, or allow heating of flash chamber 36, a power generator may be started to provide power to desalination system 10. If preheater elements 39 are installed at weir plates 40, these are turned on to heat water flowing or cascading over weir plates 40 to about boiling point. Inlet pump 124 starts and provides water flow through filters 13, preheater unit 14 and on into inlet water bulk storage tank 24 or directly to evaporation unit 30. Residence time of water in inlet storage tank 24 depends on the inlet pump 124 capacity and the required recovered water flowrate from the evaporation unit o 15 When water level in inlet storage tank 24 has reached the required level, water is then pumped by pump 124 to flash chamber 36 of evaporation unit 30. The prismatic chamber 35 is inclined toward the sun at an angle suitable for the line of latitude at which desalination system 10 is located. The collector lenses concentrate solar radiation into heat energy for evaporation of water in flash chamber 36 as follows.

Beams of solar radiation (including visible sunlight) are focussed through thermal seal 70 into flash chamber 36 raising the internal temperature to allow water therein to be flashed off to steam. The internal temperature of flash chamber 36 will be within the range of 150°C to 300 0 C, well in excess of the boiling point of water at atmospheric pressure at sea level. At these temperatures, preheater elements 39 are no longer needed, they may be switched off at a pre-selected cut-off temperature which may be 100 0

C.

With a thin layer of water on first weir plate 40aa, the concentrated beam of solar radiation preheats the metal of that weir plate 40aa. Convective and radiant heat transfer H:Vnelson\koep\pcci\DESALINATION PLANT COMPL.doc 1/1001 -13to water causes the water to "flash off'. Remaining brine passes to subsequent weir plates 40ab in succession, allowing further flash stages.

As the sun moves east to west during the day, prismatic chamber 35 drive motor 37a enables the prismatic chamber 35 to be aligned toward the sun to maximise flash chamber 36 efficiency.

Process efficiency is also affected by the intensity of solar radiation reaching the prismatic chamber 35. That is, higher temperatures may be achieved in flash chamber 36 when the sky is clear rather than when there is a cloud cover. Accordingly, inlet pump 124 may be driven at variable speed to increase flow into flash chamber 36 when flash chamber temperature or sensed sunlight is high, perhaps as measured by a photovoltaic sensor. Flow may correspondingly be decreased when flash chamber temperature or sensed sunlight is low.

Resultant saturated steam/condensate at or about atmospheric pressure is then drawn from flash chamber 36 through exit throat 137. Mist eliminator unit 38 acts as a water collector, high surface area and temperature drop promoting condensation Recovered °eeo° water may also be collected from the lower portion of flash chamber 36 by directional drains and sent to bulk water storage 54 for distribution to end users as above described.

Other condensers could be used.

Concentrated brine is disposed of or treated as above described. Desalination system offers a way to provide desalinated water to remote communities for industrial and domestic use.

Modifications and variations to the above described water desalination system as would be apparent to the skilled reader of this disclosure are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims. Such modifications and variations fall within the scope of the present invention.

H:'jneonUkaep\speci\DESALINATION PLANT COMPL.doc 18/10/01

Claims (20)

1. a water desalination system including at least: a water inlet system; an evaporation unit in fluid communication with said water inlet system and including an optical chamber having lens means for focussing solar radiation on water present within said evaporation unit for evaporating said water; and a water recovery system connected to the evaporation unit for recovery of water evaporated in said evaporation unit in desalinated form.

2. The desalination system according to claim 1 wherein said lens means is of prismatic form.

3. The desalination system according to claim 1 or 2 wherein said lens means 15 includes a solar tracking system for tracking the sun to maximise solar radiation applied to said water within the evaporation unit as the position of the sun varies during the day.

4. The desalination system according to any one of claims 1 to 3 wherein said evaporation unit is configured to evaporate water in a flash process.

5. The desalination system according to claim 4 wherein the evaporation unit further includes a flash chamber.

6. The desalination system according to claim 5 wherein said optical chamber is disposed above said flash chamber.

7. The desalination system according to claim 6 wherein a thermal seal which is transparent to said solar radiation is disposed between said optical and flash chambers. H:Mnclson\kcp\spoci\DESALINATION PLANT COMPL.doc 18/10/01

8. The desalination system according to any one of claims 1 to 7 wherein said evaporation unit further includes a cascade or weir assembly over which said water can flow for producing a laminar water flow.

9. The desalination system according to any one of claims 1 to 8 further including supplemental water heating means for applying thermal energy to said water in addition to that provided by said solar radiation in said evaporation unit.

The desalination system according to claim 9 wherein said supplemental water heating means includes a first heater means for heating said cascade or weir assembly.

11. The desalination system according to any one of claims 1 to 10 wherein said flash chamber is maintained at a pressure less than atmospheric pressure.

12. The desalination system according to any one of claims 1 to 11 wherein said water inlet system includes a pump for pumping water from a water source to said evaporation unit. o

13. The desalination system according to any one of claims 1 to 12 further including flow distribution means to distribute said water as a plurality of water flows into the flash chamber.

14. The desalination system according to any one of claims 1 to 13 further including a mist eliminator to assist condensation of evaporated water to water.

The desalination system according to claim 14 wherein said mist elimination includes one, or both of, a packed bed; and, a metallic mesh.

16. The desalination system according to claim 15 wherein said packed bed is packed with ceramic rings or other packing. H:\nelson\keepspcci\DESALINATION PLANT COMPL.doc 18/10/01 -16-

17. The desalination system according to any one of claims 1 to 16 wherein said water recovery system includes a storage tank which may communicate to locations where recovered water is to be used.

18. The desalination system according to any one of claims 1 to 17 further including control systems and a telemetry system to allow remote operation of said desalination system.

19. The desalination system substantially as herein described with reference to and as illustrated in the accompanying drawings. DATED this 18 t day of OCTOBER 2001 LIDS PTY LTD By Its Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark S

20 Attorneys of Australia. H:\jnelson\kccp\poci\DESALNATION PLANT- COMPL.doc 18/10/01