OA19938A - System and method for water purification using a solar collector - Google Patents

Abstract

A water purification assembly comprises at least one solar collector (1) powering an evaporator (2) and one condenser (5) for the evaporated purified water. Solar collector (1) has an absorber (7) for absorbing solar radiation, said absorber sealed in an upwardly extending transparent housing (8), as well as a metal tube connected for thermal conduction with absorber (7) and extending in the longitudinal direct ion of the housing, said metal tube being filled with a liquid and having its top end extending from housing (8) provided with a condenser head (11) for the condensation of the liquid evaporated inside metal tube (9). Absorber (2) comprises a vessel (13) holding the water (15) to be purified, with condenser head (11) of solar collector (1) protruding into said vessel so as to evaporate water (15) by heating it to its boiling temperature

Description

WATER PURIFICATION ASSEMBLY AND METHOD

The invention relates to a water purification assembly according to the precharacterizing 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 desalination 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 intervention is the provision of a water purification assembly and method featuring 10 high performance and low building costs.

In accordance with the invention, this object is attained by the water purification assembly recited in patent claim 1. Patent claims 2 to 12 recite preferred embodiments of the inventive water purification assembly. Patent claim 13 is directed to the inventive water purification method.

The inventive assembly and method use a solar collecter comprising a sunlight absorber sealed in 15 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 métal tube extending through the inside the housing in the longitudinal direction thereof. The absorber and the métal tube preferably are sealed inside the housing in a gastight condition so as to preclude thermal convention with the ambient air.

Each métal tube is partly filled with a liquid, preferably water. At the top, which extends from the housing, the métal tube carries a condenser head containing a cavity which communicates with the métal tube. In this cavity is condensed the water vapour or steam previously generated by évaporation of the water in the métal tube by the heat the sunlight-absorber provides to the métal tube.

For example, the absorber may be a sheet of copper or a coat of sunlight-absorbing métal or a 25 metal-ceramic material disposed inside the housing. For thermal insulation of the absorber and the métal tube from the environment, the housing preferably is evacuâted. The métal tube - including the condenser head - may be copper or a copper alloy.

Solar coliectors of this type - comprising evacuated single - or double walled glass tubing for a housing - are referred to also as vacuum tube coliectors and are used in building services engineering for 30 heating system support and for 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 head of the condensed 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 évaporation heat may raise the condenser head 35 température to 200 °C. In accordance with the invention, this température of the condenser head is used for distilling the water to be purified in the evaporator. To this end, the evaporator vessel is provided with an inwardly protruding réceptacle adapted to receive inserted 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 purification assembly may be kept low.

At the same time, the performance of the inventive assembly features is unusually 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 condenser receives much greater amounts of water vapour and, thus, of water.

The réceptacle provided in the evaporator housing to receive the condenser head of the solar collector may be designed to be sleeve-shaped, for example. Large-area contact of the condenser head with the inserted réceptacle is desired for high thermal transfer; to this end, the inner cross-sectional shape of the réceptacle is designed to match the outer cross-sectional shape of the condenser head. Further, the réceptacle preferably is made of métal so as to ensure losses as low as possible when transferring the heat from the condenser head to the water the evaporator housing holds for évaporation.

With the assembly operating, the evaporator housing is filled in its bottom portion with the water to be evaporated while the top portion accommodâtes the steam that forms. The condenser head preferably extends into the réceptacle to the top water level only, and at any rate only partly to the level of the steamfilled région of the evaporator vessel.

The evaporator housing is provided on the outside with a thermal insulation suited for the high températures that occur ïn the operation of the assembly - e.g. minerai wool covered with an aluminium-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 collectors - such as 10 to 40 in number - in a parallel side-by-side reiationship in a common plane, with the condenser heads at their top ends each inserted in a réceptacle in the evaporator vessel.

The evaporator vessel, which extends substantially horizontally across the upwardly extending tubular solar collectors, may be formed by a tube, for example. The tubular réceptacles into which the condenser heads of the solar collectors 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 réceptacles in the evaporator housing for the réception of the condenser heads of the solar collectors présent the heat transfer surfaces for transmitting the heat from the condenser heads to the water to be evaporated in the evaporator 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 région of the réceptacles only to allow the water to flow around the réceptacles, i.e. to flow through between the réceptacles and the surrounding vessel walls, while the sections of the evaporator vessel between two adjacent réceptacles hâve a smaller diameter.

To this end, the shape of the evaporator vessel may be designed to match the sleeve-like réceptacles, i.e. to hâve 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 accumulâtes the steam that forms. It is preferred for the assembly to be operated contînuously, i.e. a feed pump is provided to contînuously 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 stérile 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 tumed 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, sait deposits, sédiments 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 sait.

Of additional advantage may be pump used to draw the steam from the evaporator vessel and to conduct it to the condenser. This results in the formation of négative pressure in the evaporator vessel above the water surface, which promotes the évaporation process. The pump may be powered by the photovoltaic 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 through a riser conduit.

Preferably, pre-heating means are provided to pre-heat the water supplied to 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 condenser may be fed to the preheater. 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 collectors of the evaporator may be designed to be smaller where the water températures 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 collecter in the assembly of figurai ;

Figure 3 shows a sectional view of part of the evaporator along lines lll-lll in Figure 4 including the top ends of the solar collectera of the assembly in Figure 1, but with a thermal insulation of the evaporator vessel omitted; and

Figure 4 a sectional view along line IV-IV in Figure 3, but with the condenser heads or solar collectera omitted.

As shown in Figure 1, the inventive water purification assembly comprises a plurality of solar collectera 1 disposed in a parallel side-by-side relationship in a common plane, as well as an evaporator 2 extending above and across solar collectera 1

Evaporator 2 has connected at one end thereof a line 3 supplying the water to be purifîed 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 purifîed water or (in sea desalination) fresh water, which exits from condenser 5 at 6.

As shown in Figure 2, solar collectera 1 each comprise an absorber 7 consisting 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 thermally conductive fashion - by soldering or brazing, large-area contact or like-to a métal tube 9 extending through the housing in the longitudinal direction thereof. The top end of métal tube 9 extends outwardly from housing 8, which is evacuated for thermal insulation.

Solar collectera 1 are disposed in a position such as to be impinged as perpendicularly by the incident solar radiation.

The end of the métal tube 9 extending from evacuated housing 8 has thereon a condenser head 11 also of métal. In its lower portion, métal tube 9 is filled with a liquid, especially water.

Incident solar radiation will heat sunlight-absorbing absorber 7, which transfera the heat to métal tube 9. this causes the water inside métal tube 9 to be evaporated, the steam so generated to condense in condenser head 11 and the condensation heat of water to be released, resulting in condenser head 11 being heated to a température as high as about 200 °C. The water condensed in condenser head 11 flows back into the métal tube for cyclic re-evaporation.

In accordance with Figure 3, condenser heads 11 of solar collectera 1 are inserted in sleeve-like réceptacles 12 extending transversely through evaporator vessel 13 of evaporator 2. Evaporator housing 13 is filled with water to be purifîed up to a level indicated by an arrow 14. The space 16 above top water level 14 forms the steam space.

The high température of condenser heads 11 of solar collectors 1 causes the water 15 in evaporator vessel 13 to be heated to its boiling température, i.e. to more than 100 °C at normal pressure, so that major amounts thereof will evaporate.

For optimum heat transfer, condenser heads 11 should be in large-area contact with the inside walls of réceptacle 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 métal réceptacle tubes 12 into the water 15 to be evaporated, condenser heads 11 of solar collectors 1 exténd 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 length of a condenser head 11, that will extend completely through sleeve-like réceptacle 12, of course.

As shown in Figure 1, evaporator vessel 13 provided with a thermal insulation 10.Tubes 12 receiving condenser heads 11 of solar collectors 1 présent the surface areas where heat from condenser heads 11 is transmitted to 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 hâve a large cross-sectional area in the région of receiving sleeves 12 so that water 15 can flow around sleeves 12 on both sides thereof, as indicated by arrows 18 in Figure 4. Between régions 17 holding receiving sleeves 12, evaporator 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, régions 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 righthand région 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. Additionally, as the water has been heated to 100°C and more in evaporator 2, it is stérile.

To ensure that evaporator 13 is filled with water 15 up to level 14 at ail times, means (not shown) are provided to regulate the level of water 15 in evaporator 13, said pre-determined level 14 being maintained by tuming feed pump 21 on or off, for example.

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 condenser 5 at 23 and exiting at 24.

The water to be purified may be fed via line 26 to pre-heating means 25 connected 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.

PATENT CLAIMS

Claims (13)

1. PATENT 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 evaporator (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 métal tube (9) connected in a thermally conductive relationship to absorber (7) and extending in the longitudinal direction of said housing, said métal tube being filled with a liquid and having at its top end and extending from housing (8) a condenser head (11) adapted to condense the liquid evaporated in métal 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 therinto in order to evaporate the water (15) to be purified in evaporator vessel (13) by heating it to its boiling température.
2. 2. Water purification assembly as in claim 1, characterized by evaporator vessel (13) comprising an inwardly protruding réceptacle (12) adapted to receive inserted therein condenser head (11) of solar collector (1) for the transmission of heat into the water (15) to be purified in evaporator (2).
3. 3. Water purification assembly as in claim 1 or 2, characterized by housing (8) of solar collectors (1) being designed to be tubular.
4. 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) comprising a plurality of réceptacles (12) adapted to receive inserted therein condenser heads (11) of solar collectors (1).
5. 5. Water purification assembly as in claim 4, characterized by evaporator vessel (13) having in the région (17) of said réceptacles (12) a larger cross-sectional area than in région (19) between two adjacent réceptacles (12) so as to allow water (15) to be purified to flow around réceptacles (12).
6. 6. Water purification assembly as in any of the preceding claims, characterized by means for regulating the level (14) up to which evaporator vessel (13) is filled with water.
7. 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. 8. Water purification assembly as in claim 5 or 6, characterized by a photo voltaic System for operating said water level regulating means.
9. 9. Water purification assembly as in any of the preceding claims, characterized by evaporator (13) communicating with condenser (5) through a riser conduit (4).
10. 10. Water purification assembly as in any of the preceding claims, characterized by pre-heating means (25) adapted to pre-heat water (15) fed to evaporator (2).
11. 11. Water purification assembly as in claim 10, characterized by condenser (5) being cooled by a fluid in counter-current fashion in condenser (5) being input to pre-heating means (25).
12. 12. Water purification assembly as in claim 10 or 11, characterized by said pre-heating means (25) cooperating with at least one solar collecter (1) designed in accordance with claiml.
13. 13. A method of purifying water, especially of desalinating sea water by the évaporation thereof under the effect to solar radiation and by condensation of the water so evaporated, characterized in that water (15) to be purified is heated to its boiling température using at least one collector (1) designed in accordance with claim 1.