AU2008203793B2

AU2008203793B2 - Desalination of seawater in a vacuum tube

Info

Publication number: AU2008203793B2
Application number: AU2008203793A
Authority: AU
Inventors: Oktay Karacanta
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-06-17
Filing date: 2008-08-07
Publication date: 2011-05-12
Anticipated expiration: 2028-08-07
Also published as: AU2008203793A1

Description

DESALINATION OF SEAWATER IN A VACUUM TUBE Field of the Invention The present invention relates to apparatus for extracting water from seawater and in 5 particular to apparatus for extracting water from seawater using a vacuum. The invention has been developed primarily for use in desalination and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use. Background of the Invention 10 Some existing desalination apparatus employ a vacuum in order to increase evaporation for desalination purposes, especially at lower temperatures. However, existing arrangements suffer from a number of disadvantages including being inefficient and costly to operate. As such, a need therefore exists for an apparatus for extracting water from seawater and a method for operating the apparatus that is efficient and cost effective. 15 It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country. Summary of the Invention An object of the claimed invention is to provide an apparatus for extracting water from 20 seawater and a method for operating the apparatus which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative. According to one aspect, there is provided as apparatus for extracting water from seawater, 25 the apparatus comprising a vacuum tube having an inlet partially immersed within reservoir seawater reservoir and an outlet partially immersed within a pure water reservoir, wherein the vacuum tube has a vacuum tube diameter and the inlet is dilated to form an evaporation hood having an evaporation hood diameter greater than the vacuum tube diameter and the outlet comprises a vapour condenser. 30 Advantageously, the evaporation hood increases the surface area of seawater for evaporation thereby increasing the evaporation rate. Furthermore, the evaporation hood 1 having a diameter larger than the vacuum tube reduces the amount of material required to construct the vacuum tube. Preferably, the apparatus further comprises a vacuum pump coupled to the vacuum tube operable to create a partial vacuum within the vacuum tube. 5 Advantageously, the vacuum pump may be used to create a vacuum within the vacuum tube to increase the evaporation rate. Furthermore, the vacuum pump need only be operated once to set up the initial vacuum within the vacuum tube, thereafter, the operation of the condenser, condensing the vapour within the vacuum tube maintains the vacuum within the vacuum tube. 10 Preferably, the apparatus further comprises a vacuum gauge configured to measure the partial vacuum within of the vacuum tube. Advantageously, the vapor gauge may be used to measure the vacuum within the vacuum tube so as to ascertain when the vacuum within the vacuum tube matches the saturation pressure of the water. 15 Preferably, the apparatus further comprises an inlet valve operable to seal the inlet; an outlet valve operable to seal the outlet; pure water valve operable to introduce pure water into the interior of the vacuum tube; and an overflow valve at an apex of the vacuum tube operable to control the overflow of water from the vacuum tube, wherein the inlet valve, outlet valve, pure water valve and overflow valve are operable to create a partial vacuum within of the 20 vacuum tube. Advantageously, the four valves may be used to create a vacuum within the vacuum tube without the need for a vacuum pump. Preferably, the vapour condenser further comprises a condenser chamber having a heat exchanger operably connected to a cooling unit. 25 Advantageously, the heat exchanger may be used to increase the rate of condensation within the condenser chamber. Preferably, the apparatus further comprises heat insulation about the vacuum tube. Advantageously, the heat insulation mitigates the effect of atmospheric temperature variations. 30 Preferably, the apparatus further comprises a settling bin configured to substantially collect brine from the inlet. Furthermore, the apparatus may further comprise a brine pump connected to a brine removal pipe connected to the settling bin. 2 Advantageously, brine may be removed for commercial or environmental purposes. For example, brine may be removed from the seawater reservoir and taken to a packing facility where it may be dried and packed. Preferably, the apparatus further comprises a hydroelectric generator operable to generate 5 electricity from the flow of water from the pure water reservoir. Advantageously, the hydroelectric generator may be used to offset the energy costs of running the apparatus. For example, where the apparatus is located away from a sea shore, the energy generated by the hydroelectric generator may be used to pump seawater from the seashore to the apparatus for processing. 10 According to another aspect, there is provided a method for operating an apparatus for extracting water from seawater, the water having a water saturation pressure, the apparatus comprising a vacuum tube having an inlet partially immersed within a seawater reservoir, the inlet dilated to form an evaporation hood, and an outlet partially immersed within pure water reservoir, the outlet being provided with a vapour condenser; a vacuum pump and a vacuum 15 gauge, the method comprising activating the vacuum pump to create a partial vacuum pressure within the vacuum tube; measuring the partial vacuum pressure within the vacuum tube using the vacuum gauge; and deactivating the vacuum pump when the partial vacuum pressure is less than the water saturation pressure. Advantageously, a vacuum pump may be used to create the initial vacuum within the 20 vacuum tube. The vacuum gauge may be used to determine the point at which the vacuum within the vapour vacuum tube equals the saturation pressure of the water vapor for the purposes of deactivating the vacuum pump. According to another aspect, there is provided a method for operating an apparatus for extracting water from seawater, the water having water saturation pressure, the apparatus 25 comprising a vacuum tube having an inlet partially immersed within a seawater reservoir, the inlet dilated to form an evaporation hood and an outlet partially immersed within pure water reservoir, the outlet having a vapour condenser; an inlet valve operable to seal the inlet; an outlet valve operable to seal the outlet; pure water valve operable to introduce water into the interior of the vacuum tube; and an overflow valve at an apex of the vacuum tube operable to 30 control the escape of gasses and overflow of water from the vacuum tube, the method comprising: closing the inlet valve and the outlet valve; opening the pure water valve to substantially fill the interior of the vacuum tube with water; opening the overflow valve until the water overflows; closing the pure water valve and the overflow valve; opening the inlet valve and the outlet valve, thereby creating a partial vacuum within the vacuum tube. 3 Advantageously, the four valves may be used to create a vacuum within the vacuum tube without having to use a vacuum pump. Preferably, the method further comprises activating the vapour condenser to maintain the partial vacuum pressure at the water saturation pressure. 5 Advantageously, a vacuum need only be created within the vacuum tube initially, thereafter the condensation of the vapor within the vapour condenser maintains the partial vacuum within the vacuum tube. Other aspects of the invention are also disclosed. Brief Description of the Drawings 10 Notwithstanding any other forms which may fall within the scope of the present invention, a preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 shows an apparatus for extracting water from seawater in accordance with a preferred embodiment of the present invention; 15 Fig. 2 shows an apparatus for extracting water from seawater in accordance with another embodiment of the present invention; Fig. 3 shows a method operating the apparatus shown in Fig. 1, in accordance with another embodiment of the present invention; and Fig. 4 shows a method operating the apparatus shown in Fig. 2, in accordance with 20 another embodiment of the present invention. Detailed Description of Specific Embodiments It should be noted in the following description that like or the same reference numerals in different embodiments denote the same or similar features. Figs. 1 and 2 show an apparatus for extracting water from seawater. The apparatus 25 comprises a vacuum tube 2 having an inlet 1 partially immersed within a seawater reservoir 11 and an outlet 6 partially immersed within a pure water reservoir 7. In one embodiment, the vacuum tube 2 is an inverted U-shaped vacuum tube 2 as shown in Figs. 1 and 2. However other shapes and configurations of vacuum tube 2 may be used depending on the particular application. 4 The outlet 6 comprises a vapour condenser 4 for cooling the vapour to form water. The vapour condenser may exchange heat with a cooling unit 5. As such, liquid water forms within the outlet 6 and flows into the pure water reservoir 7. In operation, water vapour evaporates from the seawater within the seawater reservoir 11. 5 The water vapour travels through the interior of the vacuum tube 2 where is condensed by the vapour condenser 4. In order to maximize the evaporation rate of the water, the interior of the vacuum tube 2 may be evacuated to provide a vacuum, as described below. In order to further maximize the evaporation rate of the water, the diameter of the inlet 1 is dilated to form an evaporation hood having an evaporation hood diameter greater than the 10 diameter of the vacuum tube 2. As such, the evaporation hood provides a larger surface area of seawater within the vacuum tube 2, thereby increasing the rate of evaporation. Furthermore, the evaporation hood allows for a relatively narrow vacuum tube 2 to be employed, thereby providing a materials saving. The evaporation hood may be configured to prevent solute from being dragged into inlet 1. 15 The apparatus may further comprise heat insulation 3 about the vacuum tube 2 to mitigate atmospheric temperature fluctuations that may affect the operation of the vacuum tube 2. In one embodiment, the apparatus comprises a settling bin 12 located below the inlet 1 and configured to substantially collect brine from the inlet. Furthermore, a brine pump 14 may be connected to a brine removal pipe 13 connected to the settling bin 12 for removing the brine. 20 The settling bin 12, brine pump 14 and brine removal pipe 13 may be used for the purposes of collecting the brine for a salt drying and packing facility or return to the sea. The apparatus may comprise a pure water delivery pipe 8 for delivering water from the pure water reservoir 7 to a delivery pond 9. In one embodiment, the apparatus further comprises a hydroelectric generator 19, connected in-line with the pure water delivery pipe 8, operable to 25 generate electricity from the flow of water from the pure water reservoir 7. The hydroelectric generator 19 may be used to meet the energy requirements of the apparatus to reduce cost. For example, where the apparatus is located away from a sea shore, a seawater supply pump, powered by the energy generated by the generator, may be used to bring seawater from the sea shore to the apparatus. 30 In one embodiment, the apparatus further comprises vacuum pump 18 coupled to the vacuum tube 2 operable to create a partial vacuum within of the vacuum tube 2. The apparatus further comprises a vacuum gauge 16 to measure the partial vacuum within of the vacuum tube 2 and a vacuum valve 17 operable to isolate the vacuum pump 18 from the vacuum tube 2. 5 As such, Fig. 3 shows a method 300 for operating the apparatus. The method 300 is used for creating a partial vacuum within the vacuum tube 2 using the vacuum pump 18. The method starts at step 305 where the vacuum valve 17 is opened and the vacuum pump 18 is activated to create a partial vacuum within the vacuum tube. At step 310, the vacuum gauge 5 16 is used to measure the partial vacuum pressure within the vacuum tube 2. At step 315, the vacuum pump 18 is deactivated when the partial vacuum pressure within the vacuum tube 2 is less than the water saturation pressure. At this stage, a column of seawater will form in the inlet 1 and a column of water will form in the outlet 6, as shown in Fig. 1. For water, each of the columns may have a height of about 10,000 mm height. The height of the 10 columns may be measures in-lieu of reading the vacuum gauge 16. Once the pump 18 has been deactivated, evaporation will start in both columns until the vapor within the vacuum tube 2 becomes saturated. As such, the pressure within the vacuum tube 2 will increase until the pressure equals the saturation pressure of the water in the reservoirs 1, 7. 15 As a numerical example, for water, if the temperature of the reservoirs 11, 7 is 23'C, the pressure within the vacuum tube 2 will reach 0.0281 bar = 291 mm w.g., which is the saturation pressure of water at 23'C. The saturation pressure within the vacuum tube 2 will resist the atmospheric pressure by 291 mm such that the height of water columns will be 10,353-291=10,062 mm w.g. Furthermore, when the cooling unit 5 of the condenser 4 is 20 activated, the saturated vapor within the condenser is cooled such that the vapor inside the condenser condenses and condensed water forms in the water tank 7. If the lower temperature of condensation is fixed at 3'C (above freezing point), for example by setting the thermostat of the cooling unit, the saturated vapor within the vacuum tube will be 0.0076 bar = 79mm mm w.g. 25 Now, a pressure differential between the evaporation hood and the condenser of 0.0281 0.0076 = 0.0205 bar = 212 mm w.g. will exist. As such, the saturated vapor within the evaporation hood will to flow from evaporation hood to the condenser and condensed water will run down through the outlet 6, into the pure water tank 7 and onwards to the water pipe 8, hydroelectric generator 19, and the delivery pond 9. And delivery pipe 10 may be used to 30 deliver pure water to customers. In another embodiment, the apparatus further comprises an inlet valve 22 operable to seal the inlet 1, an outlet valve 23 operable to seal the outlet 6, pure water valve 20 operable to introduce water into the interior of the vacuum tube 2 and an overflow valve 21 at an apex of the vacuum tube 2 operable to control the overflow of water from the vacuum tube. In the 6 manner described below, the inlet valve 22, outlet valve 23, pure water valve 20 and overflow valve 21 are operable to create a partial vacuum within of the vacuum tube 2. As such, Fig. 4 shows a method 400 for operating the apparatus. The method 400 starts at step 405 where the inlet valve and the outlet valve are closed to seal the inlet and the outlet. 5 At step 410, the pure water valve is opened to substantially fill the interior of the vacuum tube 2 with water. At step 415, the overflow valve is opened until the solute overflows. At step 420, the pure water valve and the overflow valve are closed. At step 425, the inlet valve and the outlet valve are opened, thereby creating a partial 10 vacuum within the vacuum tube. As such, once the vacuum within the vacuum tube 2 has been created, the vapour condenser 4 may be activated to condense the vapour so as to maintain the partial vacuum pressure at the water saturation pressure. Numeric example of the amount of pure water that can be obtained 15 Since sonic velocity exists in the examples given below, a modified Darcy formula will be applied: W =1891YD 2 K= f L /D Kv Where 20 W - Mass flow rate, lb/h Y - Expansion factor for pipe D - Pipe inside diameter, in AP - Pressure drop in psig K - Resistance coefficient 25 L - Pipe length, in f - Darcy friction factor v- Specific volume of steam at inlet pressure ft/ lb Pi Inlet pressure = 0.0281 bar = 0.413 psi = 788 m 3 /lb 30 AP/P and Y values are taken from table 4.6 of the Pipong Calculations Manual, written by E.S. Menon. Equivalent length of fittings are the same for all examples below. Two 90 elbows: K = 0.02 x 2 x 30 = 1.2 7 One entrance: K = 0.5 One increaser: K = 1.0 Total K for fittings: K = 2.7 5 As such: D-in L-in K AP/P Y A P-psi W-m 3 / day H-m 1 340 mm 10,000 mm 3.3 0.653 0.662 0.653x0.413 25 30 13.39 in 393.7 in =0.270 2 1,000 mm 50,000 mm 3.7 0.667 0.666 0.667x0.413 207 75 39.37in 1,968.5 in =0.275 3 10,000 mm 150,000 mm 3 0.648 0.658 0.648x0.413 22,326 260 393.7 in 5,905.5 in =0.268 4 10,000 mm 900,000 mm 4.5 0.689 0.674 0.689x0.413 19,255 1,020 393.7 in 35,433 in =0.285 5 20,000 mm 900,000 mm 3.6 0.664 0.665 0.664x0.413 83,306 1,110 787.4 in 35,433 in =0.274 Numeric example amount of the cost of energy for cooling unit Enthalpy of saturated vapour at 23'C = 2,543.6 KJ/Kg Enthalpy of saturated vapour at 3C = 2,506.9 KJ/Kg 10 Cooling load of 1 Kg condensed vapour: 2,543.6 - 2,506.9 = 36.7 KJ/Kg = 8.77 Kcal/Kg Cooling load of 1 m 3 condensed water: 8.77 Kcal/Kg x 1.000 Kg = 8,770 Kcal Assuming that the energy that needs to run the cooling unit is half the cooling load of the condenser. Energy consumption in cooling unit for 1 m 3 condensed water: 15 8,770 / 2 = 4,385 Kcal = 5.1 Kwh Cost of 1 m 3 water = 5.1 Kwh x $AUO.17128149 / Kwh = $AUO.87 / m 3 Numeric example amount of the amount of salt that may be obtained Assuming sea water has %3.5 salt content, for each m 3 of pure water there can be obtained 20 1,000 x 35 / 965 = 36.23 Kg salt. Interpretation Embodiments: Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment 8 is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any 5 suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. Similarly it should be appreciated that in the above description of example embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and 10 aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description of Specific 15 Embodiments are hereby expressly incorporated into this Detailed Description of Specific Embodiments, with each claim standing on its own as a separate embodiment of this invention. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant 20 to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. Specific Details In the description provided herein, numerous specific details are set forth. However, it is 25 understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. Terminology In describing the preferred embodiment of the invention illustrated in the drawings, specific 30 terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "forward", "rearward", "radially", "peripherally", "upwardly", "downwardly", and the like are used as words of convenience to provide 35 reference points and are not to be construed as limiting terms. 9 Different Instances of Objects As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described 5 must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. Comprising and Including In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, 10 i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. Any one of the terms: including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising. 15 Scope of Invention Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, 20 any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention. Although the invention has been described with reference to specific examples, it will be 25 appreciated by those skilled in the art that the invention may be embodied in many other forms. Industrial Applicability It is apparent from the above, that the arrangements described are applicable to the desalination industry. 30 10

Claims

1. An apparatus for extracting water from seawater, the apparatus comprising: a vacuum tube having an inlet partially immersed within a seawater reservoir and an outlet partially immersed within pure water reservoir, wherein: 5 the vacuum tube has a vacuum tube diameter and the inlet is dilated to form an evaporation hood having an evaporation hood diameter greater than the vacuum tube diameter, and the outlet comprises a vapour condenser. 10

2. An apparatus as claimed in claim 1, further comprising a vacuum pump coupled to the vacuum tube operable to create a partial vacuum within the vacuum tube.

3. An apparatus as claimed in claim 2, further comprising a vacuum gauge configured to measure the partial vacuum within of the vacuum tube. 15

4. An apparatus as claimed in claim 1, further comprising: an inlet valve operable to seal the inlet; an outlet valve operable to seal the outlet; pure water valve operable to introduce water into the interior of the vacuum tube; and 20 an overflow valve at an apex of the vacuum tube operable to control the overflow of water from the vacuum tube, wherein the inlet valve, outlet valve, water valve and overflow valve are operable to create a partial vacuum within of the vacuum tube.

5. An apparatus as claimed in claim 1, wherein the vapour condenser comprises a 25 condenser chamber having a heat exchanger operably connected to a cooling unit.

6. An apparatus as claimed in claim 1, further comprising heat insulation about the vacuum tube. 30

7. An apparatus as claimed in claim 1, further comprising a settling bin configured to substantially collect brine from the inlet.

8. An apparatus as claimed in claim 7, wherein the apparatus further comprises a brine pump connected to a brine removal pipe connected to the settling bin. 35 11

9. An apparatus as claimed in claim 1, further comprising a hydroelectric generator operable to generate electricity from the flow of water from the pure water reservoir. 5

10. A method for operating an apparatus for extracting water from seawater, the water having water saturation pressure, the apparatus comprising a vacuum tube having an inlet partially immersed within a seawater reservoir, the inlet dilated to form an evaporation hood, and an outlet partially immersed within pure water reservoir, the outlet being provided with a vapour condenser; a vacuum pump and a vacuum gauge, the method comprising: 10 activating the vacuum pump to create a partial vacuum pressure within the vacuum tube; measuring the partial vacuum pressure within the vacuum tube using the vacuum gauge; and deactivating the vacuum pump when the partial vacuum pressure is less than the water 15 saturation pressure.

11. A method for operating an apparatus for extracting water from seawater, the water having water saturation pressure, the apparatus comprising a vacuum tube having an inlet partially immersed within a seawater reservoir, the inlet dilated to form an evaporation hood 20 and an outlet partially immersed within pure water reservoir, the outlet having a vapour condenser; an inlet valve operable to seal the inlet; an outlet valve operable to seal the outlet; a pure water valve operable to introduce water into the interior of the vacuum tube; and an overflow valve at an apex of the vacuum tube operable to control the escape of gasses and overflow of water from the vacuum tube, the method comprising: 25 closing the inlet valve and the outlet valve; opening the pure water valve to substantially fill the interior of the vacuum tube with water; opening the overflow valve until the water overflows; closing the pure water valve and the overflow valve; 30 opening the inlet valve and the outlet valve, thereby creating a partial vacuum within the vacuum tube.

12. A method as claimed in claim 10 or 11, further comprising: activating the vapour condenser to maintain the partial vacuum pressure at the water 35 saturation pressure. 12

13. An apparatus being substantially as herein described with reference to the accompanying drawings.

14. A method being substantially as herein described with reference to the accompanying 5 drawings. 13