AU2007352929A1

AU2007352929A1 - System and method for water purification using a solar collector

Info

Publication number: AU2007352929A1
Application number: AU2007352929A
Authority: AU
Inventors: Bernd Hofler; Peter Turk
Original assignee: Turk Ges fur Produktmarketing und Werbemittel Mbh
Current assignee: TURK GESELLSCHAFT fur PRODUKTMARKETING und WERBEMITTEL MBH
Priority date: 2007-05-03
Filing date: 2007-07-26
Publication date: 2008-11-13
Also published as: CA2685895A1; MA31425B1; MX2009011765A; EP2152634A1; TN2009000415A1; ZA200907188B; WO2008134999A1; IL201540A0; DE202007018537U1

Description

19283/1 PCT WATER PURIFICATION ASSEMBLY AND METHOD The invention relates to a water purification assembly according to the pre characterizing portion of claim 1, particularly for the desalination of sea or brackish water, but also for the treatment of sewage. It also relates to a method of purifying water. In addition to reverse osmosis, the most important methods of sea water desali nation include distillation, in which the water is evaporated and then condensed. Sunlight is being used for the purpose also (see e.g. US 4,329,204 and US 6,821,395 B1). Prior sea water distillation assemblies using sunlight are poor performers, however, as they provide few liters only of fresh water per day. The object of the invention is the provision of a water purification assembly and method featuring high performance and low building costs. In accordance with the invention, this object is attained by the water purification assembly recited in patent claims. Patent claims 2 to 12 recite preferred embo diments of the inventive water purification assembly. Patent claim 13 is direct ed to the inventive water purification method. The inventive assembly and method use a solar collector comprising a sunlight absorber sealed in an upwardly extending enclosure which is transparent, i.e. transmissive of sunlight, and especially a housing of glass. The absorber, which may comprise e.g. sheet copper or a sunlight-absorbing coating disposed in the housing, is coupled for the transmission of heat with a metal tube extend ing through the inside the housing in the longitudinal direction thereof. The ab- 2 sorber and the metal tube preferably are sealed inside the housing in a gas tight condition so as to preclude thermal convection with the ambient air. Each metal tube is partly filled with a liquid, preferably water. At the top, which extends from the housing, the metal tube carries a condenser head containing a cavity which communicates with the metal tube. In this cavity is condensed the water vapour or steam previously generated by the evaporation of the water in the metal tube by the heat the sunlight-absorbing absorber provides to the metal tube. For example, the absorber may be a sheet of copper or a coat of sunlight-ab sorbing metal or a metal-ceramic material disposed inside the housing. For thermal insulation of the absorber and the metal tube from the environment, the housing preferably is evacuated. The metal tube - including the condenser head - may be copper or a copper alloy. Solar collectors of this type - comprising evacuated single- or double walled glass tubing for a housing - are referred to also as vacuum tube collectors and the heating of service water (see the folder published by RZ Solartechnik, Friedrich-von-Tieck-Str. 20, 89420 Hoechstedt, Germany). In systems of this kind, the heat of the condenser head is transferred to a carrier liquid which is conducted to a heat exchanger. It was found that condensing the water, which was evaporated in the condenser head by the incident solar radiation, and the concomitant release of the evapor ation heat may raise the condenser head temperature to 200 *C. In accord ance with the invention, this temperature of the condenser head is used for dis tilling the water to be purified in the evaporator. To this end, the evaporator vessel is provided with an inwardly protruding receptacle adapted to receive in- 3 serted therein the solar collector's condenser head for heat transfer to the water inside the evaporator. In accordance with the invention, this system makes use of a commercially available solar collector so that the prime costs of the inventive water purifica tion assembly may be kept low. At the same time, the performance of the inventive assembly features is unusu ally high. In contrast to prior distillation systems using solar radiation, which simply evaporate the water, the inventive evaporator serves to heat the water in it to its boiling point so that the system condensor receives much greater amounts of water vapour and, thus, of water. The receptacle provided in the evaporator housing to receive the condensor head of the solar collector may be designed to be sleeve-shaped, for example. Large-area contact of the condenser head with the inserted receptacle is de sired for high thermal transfer; to this end, the inner cross-sectional shape of the receptacle is designed to match the outer cross-sectional shape of the con denser head. Further, the receptacle preferably is made of metal so as to en sure losses as low as possible when transferring the heat from the condenser head to the water the evaporator housing holds for evaporation. With the assembly operating, the evaporator housing is filled in its bottom por tion with the water to be evaporated while the top portion accommodates the steam that forms. The condenser head preferably extends into the receptacle to the top water level only, and at any rate only partly to the level of the steam filled region of the evaporator vessel.

4 The evaporator housing is provided on the outside with a thermal insulation suited for the high temperatures that occur in the operation of the assembly e.g. mineral wool covered with an aluminum-foil or silicone. It is preferred for the housing of the solar collector to be tubular in shape. The length of the tubular housing may be 1 to 2 meters and its diameter 5 to 10 cm, for example. It Is preferred also to assemble a plurality of tubular solar collect ors - such as 10 to 40 in number - in a parallel side-by-side relationship in a common plane, with the condenser heads at their top ends each inserted in a receptacle in the evaporator vessel. The evaporator vessel, which extends substantially horizontally across the up wardly extending tubular solar collectors, may be formed by a tube, for exam ple. The tubular receptacles into which the condenser heads of the solar col lectors are inserted may extend crosswise - i.e. from the bottom up - through the elongated evaporator housing or tube and be sealed at the top by a lid, for example. The receptacles in the evaporator housing for the reception of the condenser heads of the solar collectors present the heat transfer surfaces for transmitting the heat from the condenser heads to the water to be evaporated in the eva porator vessel. For increased heat transfer area relative to the amount of water to be evaporated in the evaporator vessel, it is preferred for the evaporator vessel not to be a tube with a constant cross-sectional area. Instead, its cross sectional area should be large enough in the region of the receptacles only to allow the water to flow around the receptacles, i.e. to flow through between the receptacles and the surrounding vessel walls, while the sections of the evapo rator vessel between two adjacent receptacles have a smaller diameter.

5 To this end, the shape of the evaporator vessel may be designed to match the sleeve-like receptacles, i.e. to have upwardly extending cylindrical or prismatic sectional shapes. In operation of the evaporator vessel, its bottom portion is filled with the water to be evaporated; its top portion accumulates the steam that forms. It is prefer red for the assembly to be operated continuously, i.e. a feed pump is provided to continuously supply the evaporator vessel with new water to be purified while the steam that forms is withdrawn and condensed in the condenser to form purified distilled water. In addition, the distilled water will be sterile at least if distillation takes place at 100 "C or higher at normal pressure. To ensure the evaporator vessel being filled with water to a given level, means are provided to regulate that level in the evaporator vessel, with the feed pump being turned on or off, for example, when the actual water level is lower or higher, respectively, than the aforesaid given level. The feed pump may be powered from a photovoltaic system which may be connected to a battery. On this basis, it is possible to use the feed pump for night-time.purges of the evaporator vessel, for example. Where the assembly is used for sea water desalination, for example, salt deposits, sediments and the like contaminations may be removed from the evaporator vessel this way. It is preferred for the water purification assembly to provide tilting means making possible the emptying of the evaporator vessel of brine before it is purged (purified). The brine may be conducted to pans for the recovery of sea salt. Of additional advantage may be a pump used to draw the steam from the eva porator vessel and to conduct it to the condenser. This results in the formation 6 of negative pressure in the evaporator vessel above the water surface, which promotes the evaporation process. The pump may be powered by the photo voltaic system also. To ensure that steam only, but no water, can reach the evaporator vessel in the condenser, the evaporator preferably communicates with the condenser the evaporator. Where the condenser is cooled in counter-current fashion with water or another fluid for condensing the evaporated water, the heated fluid conducted in counter-current in the condensor may be fed to the pre-heater. Also, the pre-heater may be operated with one or several solar collectors of the kind used in accordance with the invention for the evaporator. The solar col lectors of the evaporator may be designed to be smaller where the water tem peratures are higher. In other words: instead of an exemplary solar collector unit two meters long and correspondingly wide, it would be possible to use a substantially smaller unit. The invention will now be explained in greater detail under reference to the attached drawings, which show: Figure 1 a front view of the inventive assembly; Figure 2 a view of a portion of a solar collector in the assembly of Figure 1; Figure 3 shows a sectional view of part of the evaporator along lines lil-Ill in Figure 4 including the top ends of the solar collectors of the assembly in Figure 1, but with a thermal insulation of the eva porator vessel omitted; and Figure 4 a sectional view along line IV-IV in Figure 3, but with the conden ser heads or solar collectors omitted.

7 As shown in Figure 1, the inventive water purification assembly comprises a plurality of solar collectors 1 disposed in a parallel side-by-side relationship in a common plane, as well as an evaporator 2 extending above and across solar collectors 1. Evaporator 2 has connected at one end thereof a line 3 supplying the water to be purified and at the opposite end a riser conduit 4 which passes the steam generated in evaporator on to a condenser 5 in which the steam generated in evaporator 2 is condensed to form purified water or (in sea water desalination) fresh water, which exits from condenser 5 at 6. As shown .in Figure 2, solar collectors 1 each comprise an absorber 7 consist ing of a material such as sheet copper, for example, and extending from the bottom up through a tubular glass housing 8. Absorber 7 is coupled in a ther mally conductive fashion - by soldering or brazing, large-area contact or the like - to a metal tube 9 extending through the housing in the longitudinal direction thereof. The top end of metal tube 9 extends outwardly from housing 8, which is evacuated for thermal insulation. Solar collectors 1 are disposed In a position such as to be impinged as perpen dicularly as possible by the incident solar radiation. The end of metal tube 9 extending from evacuated housing 8 has thereon a condensor head 11 also of metal, In its lower portion, metal tube 9 is filled with a liquid, especially water. Incident solar radiation will heat sunlight-absorbing absorber 7, which transfers the heat to metal tube 9. This causes the water inside metal tube 9 to be eva porated, the steam so generated to condense in condenser head 11 and the 8 condensation heat of the water to be released, resulting in condensor head 11 being heated to a temperature as high as about 200 *C. The water condensed in condenser head 11 flows back into the metal tube for cyclic re-evaporation. In accordance with Figure 3, condenser heads 11 of solar collectors 1 are in serted in sleeve-like receptacles 12 extending transversely through evaporator vessel 13 of evaporator 2. Evaporator housing 13 is filled with water to be purified up to a level indicated by an arrow 14. The space 16 above top water level 14 forms the steam space. The high temperature of condenser heads 11 of solar collectors 1 causes the water 15 in evaporator vessel 13 to be heated to its boiling temperature, i.e. to more than 100 *C at normal pressure, so that major amounts thereof will eva porate. For optimum heat transfer, condenser heads 11 should be in large-area contact with the inside walls of receptacle tubes 12. In order to get the heat to move from condenser heads 11 along paths as short as possible and with losses as low as possible via the metal receptacle tubes 12 into the water 15 to be evaporated, condenser heads 11 of solar collectors 1 extend upwards about to level 14 only, i.e. not or only slightly into steam space 16. Where evaporator housing 13 comprises a simple tube having a diameter not greater than the length of a condenser head 11, that head will extend completely through sleeve-like receptacle 12, of course. As shown in Figure 1, evaporator vessel 13 is provided with a thermal insulation 10.

9 Tubes 12 receiving condenser heads 11 of solar collectors 1 present the sur face areas where heat from condenser heads 11 is transmitted to the water 15 to be evaporated in evaporator vessel 13. In order to' increase these heat-transmissing surface areas, i.e. the area of the outer surfaces of condenser heads 11, relative to the volume of the water 15 to be heated in evaporator vessel 13, the latter vessel is preferably designed to have a large cross-sectional area in the region of receiving sleeves 12 so that water 15 can flow around sleeves 12 on both sides thereof, as indicated by ar rows 18 in Figure 4. Between regions 17 holding receiving sleeves 12, evapo rator vessel 13 has portions 19 featuring a reduced width, as shown in Figure 4. In order to further increase the heat-transmitting surface area in relation to the volume of water 15 in evaporator vessel 13, regions 17 are matched in shape to receiving sleeves 12, i.e. to be cylindrical, as shown in Figure 4, or prismatic, as shown schematically for the right-hand region 17, for example. The water to be purified is fed to evaporator 2 via line 3 by means of a feed pump 21, while the steam generated in evaporator 2 is withdrawn through riser conduit 4 and condensed in condenser 5 to form purified distilled water. Addi tionally, as the water has been heated to 100 "C and more in evaporator 2, it is sterile. To ensure that evaporator 13 is filled with water 15 up to level 14 at all times, means (not shown) are provided to regulate the level of water 15 in evaporator 13, said pre-determined level 14 being maintained by turning feed pump 21 on or off, for example.

10 The water condensed in condenser 5 exits at 6. As shown in phantom in Figure 1, condenser 5 is cooled in counter-current fashion with water entering conden ser 5 at 23 and exiting at 24. The water to be purified may be fed via line 26 to pre-heating means 25 con nected to water supply 3. The heated water used for cooling in counter-current in condenser 5 and leaving it 24 in a heated condition may be fed into means 25 for pre-heating.

Claims

1. A water purification assembly comprising at least one solar collector (1) feeding an evaporator (2), as well as a condenser (5) communicating with eva porator (2) and providing the evaporated purified water, characterized in solar collector (1) comprising a sunlight absorber (7) sealed in an upwardly extending transparent housing (8) as well as a metal tube (9) connected in a thermally conductive relationship to absorber (7) and extending in the longitudinal direct ion of said housing, said metal tube being filled with a liquid and having at its top end and extending from housing (8) a condenser head (11) adapted to con dense the liquid evaporated in metal tube (9), and in evaporator (2) comprising a vessel (13) holding water (15) to be evaporated and having condenser head (11) of solar collector (1) protruding thereinto in order to evaporate the water (15) to be purified in evaporator vessel (13) by heating it to its boiling tempera ture.

2. Water purification assembly as in claim 1, characterized by evaporator vessel (13) comprising an inwardly protruding receptacle (12) adapted to re ceive inserted therein condenser head (11) of solar collector (1) for the trans mission of heat into the water (15) to be purified in evaporator (2).

3. Water purification assembly as in claim 1 or 2, characterized by housing (8) of solar collectors (1) being designed to be tubular.

4. Water purification assembly as in any of claims 1 to 3, characterized by comprising a plurality of solar collectors (1) and by evaporator vessel (13) com prising a plurality of receptacles (12) adapted to receive inserted therein con denser heads (11) of solar collectors (1). 12

5. Water purification assembly as in claim 4, characterized by evaporator vessel (13) having in the region (17) of said receptacles (12) a larger cross sectional erea than in region (19) between two adjacent receptacles (12) so as to allow water (15) to be purified to flow around receptacles (12).

6. Water purification assembly as in any of the preceding claims, character ized by means for regulating the level (14) up to which evaporator vessel (13) is filled with water (15).

7. Water purification assembly as in claim 6, characterized by the means for regulating the water level (14) in evaporator vessel (13) including a feed pump (21) adapted to provide the water to be purified to evaporator vessel (13).

8. Water purification assembly as in claim 5 or 6, characterized by a photo voltaic system for operating said water level regulating means.

9. Water purification assembly as in any of the preceding claims, charact erized by evaporator (13) communicating with condensor (5) through a riser conduit (4).

10. Water purification assembly as in any of the preceding claims, character ized by pre-heating means (25) adapted to pre-heat the water (15) fed to eva porator (2).

11. Water purification assembly as in claim 10, characterized by condenser (5) being cooled by a fluid in counter-current fashion and by the fluid heated in counter-current fashion in condenser (5) being input to pre-heating means (25). 13

12. Water purification assembly as in claim 10 or 11, characterized by said pre-heating means (25) co-operating with at least one solar collector (1) de signed in accordance with claim 1.

13. A method of purifying water, especially of desalinating sea water by the evaporation thereof under the effect of solar radiation and by condensation of the water so evaporated, characterized in that the water (15) to be purified is heated to its boiling temperature using at least one solar collector (1) designed in accordance with claim 1.