WO2002024576A1

WO2002024576A1 - Device for the production of potable water by solar means from seawater or brackish water

Info

Publication number: WO2002024576A1
Application number: PCT/DE2001/003667
Authority: WO
Inventors: Olaf Hubbert; Helmut Lessing; Alexander Klomsdorff
Original assignee: Envitech Gmbh
Priority date: 2000-09-22
Filing date: 2001-09-24
Publication date: 2002-03-28
Also published as: DE10047522A1; AU2002223432A1

Abstract

The invention relates to a device for the production of potable water by solar means from seawater or brackish water, comprising a housing (2), arranged at an angle, completely enclosed and thermally well-insulated. The front surface (13) thereof, facing the sun, is enclosed by a transparent sheet. An evaporation surface (3) is situated in the housing (2), dividing the interior of the housing into an upper evaporation chamber (4) and a lower condensation chamber (5). Said evaporation chamber (4) and condensation chamber (5) are connected at the lower end of the evaporating surface such that the air mass enclosed in the housing can circulate. A brine pan (6) is arranged at the lower end of the evaporation surface (3), which catches brine (14) dropping from the evaporation surface (3) and is equipped with an overflow (7). A potable water outlet (8) is arranged at the lower end of the condensation chamber (5), in which at least one first condenser (9) is arranged. According to the invention, a feed line (20), with integrated pump (21), goes from the brine pan (6) to the inlet of the at least one first condenser (9), a line (22) goes from the outlet of the at least one first condenser (9) to the upper end of the evaporation surface (3) and an inlet for the dosed feed of salty water (26) is connected to the brine pan (6).

Description

Device for solar drinking water production from sea and brackish water

The present invention relates to a device for solar drinking water production from sea or brackish water (hereinafter, also in the claims, abbreviated to "salt water") according to the features of the preamble of claim 1.

In many regions of the world, particularly in Africa, there is a great need for drinking water that can only be met unsatisfactorily from existing natural resources. Since there is always strong solar radiation in these regions, it was and is only natural to use solar energy to produce drinking water by desalination of salt water. There is a need for self-sufficient, robust, easy-to-use, economical to erect and operate, especially decentralized, small systems due to a lack of or poorly trained infrastructure and due to a lack of specialist staff.

The previous performance ranges of small solar stills are between three to six liters of drinking water per day and square meter (L / day m ² ). This low output is disproportionate to the investment and operating costs. For this reason, such devices have so far not been able to implement solar drinking water generation in practice.

A generic device is known from DE 38 29 725 C2. It is a small, decentralized device that is also easy to use and robust. However, practical experience has shown that the desired output of up to 20 L / day m ² is far from being achievable, so that, despite the low cost of materials, the economy must also be questioned here.

In the device according to DE 38 29 725 C2, an independent circulation of the air masses builds up due to an imbalance between the hot air masses in the evaporation space and the cooler air masses in the condensation space. This enables drinking water to be obtained from the hot, water vapor-saturated air masses coming from the evaporation space and flowing past the condenser. The heat recovered by the condensation of the drinking water heats the salt water flowing through the condenser as the cooling medium, which is then heated further by a heat exchanger arranged in the brine bath and by an additional heater which is arranged in a frame of the device housing facing the sun. to be led. In this way, flow temperatures of the salt water of over 80 ° C are reached. At this temperature, the salt water flows onto the evaporation surface and evaporates there under the influence of solar radiation. The brine concentrated by the evaporation flows down on the evaporation surface and drips there into a brine pan that has an overflow. The evaporated water is carried by the heated air masses through their circulation path to the condenser. and condenses there. The drinking water obtained in this way collects in a lower point of the device and is discharged from there to the outside.

The object of the present invention is to further develop a generic device such that a substantial increase in the yield of drinking water can be achieved, so that such devices pay off economically.

According to the invention, this object is achieved with a device having the features of claim 1.

The present invention makes use of the knowledge that the brine is cooled to such an extent by the energy required for evaporation that an almost complete condensation of the evaporated water from the circulating air phase can take place solely on the basis of the resulting temperature gradient. The condenser is therefore supplied with brine from the brine tank as a coolant. The brine heats up so much in the condenser (up to approx. 90 to 95 ° C) that it can be fed directly to the evaporation surface after leaving the condenser and is available there for a cycle of water extraction.

Since water is constantly withdrawn from the system due to the condensation and brine discharge via the overflow, this water must be replaced to the same extent. This is done according to the invention in that fresh salt water is metered into the brine tank from where it returns to the circuit. Experiments with non-optimized prototypes of this device have yields of drinking water of up to 20 L / day m ² . This yield is a factor of 3 above that of previously known constructions. Even higher performance will be possible by optimizing the device.

In an advantageous embodiment of the invention, an auxiliary heater heated by solar energy is interposed in the supply line leading from the outlet of the at least one first condenser to the evaporation surface. This additional heater can be set up separately from the housing of the device and connected to it by correspondingly insulated pipes. However, it is more advantageous to integrate this additional heater into the housing. In this case it consists of a piping system (solar cell) arranged in the frame of the housing.

The fact that the brine is passed after the condenser over the additional heater further heats up to about 95 to 99 ° C, so that operating temperatures of the device of up to about 110 ° C can be reached. These high operating temperatures intensify the circulation of the air masses inside the housing, which further increases the yield of drinking water.

In an advantageous embodiment of the present invention, the at least one first capacitor is arranged in the region of the upper end of the condensation space, that is to say at the hottest point in this space. This measure increases the self-sufficient air mass circulation, since the "imbalance", ie the difference in density of the air masses, increases between the condensation space and the evaporation space. In a preferred embodiment of the invention, on the circulation path of the air masses, in addition to the at least one first condenser, at least one second condenser is arranged, the inlet of which is connected to a salt water reservoir by a feed line with an integrated pump and the outlet of which is integrated into the salt water reservoir by a discharge line is. Via this at least one additional condenser, salt water is therefore recirculated from the reservoir to the latter. This additional cooling helps optimize distillate production. However, it also entails a loss of energy, since it constantly dissipates heat from the system. It is therefore advisable to use this heat. This is done in a development of the invention in that this heat is layered in the salt water reservoir. For this purpose, the supply line to the condenser is integrated in the lower and the discharge line from the condenser in the upper area of the salt water reservoir. As a result, relatively cool salt water is always made available to the condenser and condensation energy is nevertheless introduced into the reservoir. It is of course expedient if the salt water reservoir is thermally insulated so that radiation losses from the stored heat are avoided, or at least greatly reduced. With the heat stored in the salt water reservoir, drinking water can be produced, even if only to a small extent, when the sun is no longer shining (night condensation) by supplying the salt water from this reservoir to the evaporation surface.

It has already been mentioned above that the water extracted from the system by distillation is compensated for by feeding fresh salt water into the brine tank. It is useful if this salt water required for filling up a bypass is branched off from the discharge line coming from the at least one second condenser, since the salt water then flows to the brine trough already warmed up.

Finally, the device is completed by further pipelines connecting its components and by switching valves for switching pipes on and off in order to be able to implement different operating modes.

The invention is explained in more detail below on the basis of exemplary embodiments. In the accompanying drawing:

1 shows in a very schematic manner ¹ a device according to the invention in its basic structure, connection pipes and valves arranged therein having been omitted from this illustration for reasons of clarity,

2 shows a flow diagram for operating a device according to the invention in optimal continuous operation,

Fig. 3 is a flow diagram for operating the device according to the invention in a start-up operation and

Fig. 4 is a flow diagram for operating a system according to the invention in night condensation operation. The device 1 shown schematically in FIG. 1 for solar drinking water production (solar still) consists of a thermally highly insulated housing 2, which is set up in an inclined position to the horizontal. On the sun's rays

11 facing the front of the housing 2 is an additional heater

12 integrated in the housing frame. This front side 13 of the housing 2 is formed in a known manner from a composite of sunlight-permeable glass panes and foils. A black evaporation surface 3 is arranged in the housing 2, which divides the interior of the housing into an upper evaporation space 4 and a lower condensation space 5, the evaporation surface 3 shading the condensation space 5 from the evaporation space 4 and to a certain extent also thermally insulating it. At the lower end of the condensation chamber 5, a brine tank 6 with an overflow 7 is arranged. Below the brine tub 6 there is an outlet 8 for the distilled water. At the other, upper end of the condensation space 5, a first capacitor 9 and a second capacitor 10 are provided.

Continuous operation of the solar still 1 described above is explained below on the basis of a flow diagram shown in FIG _. the pipeline-side connections of the assemblies of the solar still 1 emerge.

From Fig. 2 it can be seen that two circuits 15, 16 for liquid media, namely salt water 26 and brine 14 are realized in the solar still 1. In the circuit 15 is salt water 26 from a thermally insulated salt water reservoir 17, which, for. B: can be a barrel or another container and is constantly filled up with salt water 26 depending on consumption, via a Supply line 18 and a pump 19 integrated therein are supplied to the condenser 10. After flowing through this condenser 10, the salt water 26 flows back to the salt water reservoir 17 via a discharge line 27.

In the circuit 16, brine 14 is conveyed from the brine tub 6 via a pump 21 integrated in the feed line 20 to the inlet of the condenser 9. After leaving the condenser 9, the brine 14 flows via a feed line 22 into the auxiliary heater 12 and from there to the upper end of the evaporation surface 3, which is given up at a very high flow temperature, as can be seen from the explanations below ,

The strongly preheated brine 14 flows downward on the black evaporation surface 3 and is evaporated in this way by the solar radiation 11, which is indicated by the arrows 23 in FIG. 1. At the lower end of the evaporation surface 3, the brine 14 flows or drips into the brine tub 6 and is available for another cycle. The described evaporation process always leads to a significant cooling of the brine 14 despite the sun, so that it flows into the brine tub 6 at a temperature of about 7.0-75 ° C.

Due to the density differences of the air masses in the evaporation space 4 (hot, a lot of water in the gas phase) and in the condensation space 5 (cool, a little water in the gas phase), an air mass circulation builds up in the housing 2 of the solar still 1, which is shown in FIG Arrows 24 is indicated. These arrows 24 are drawn with hatching, with a tightening hatching symbolizing higher temperatures of the air masses. This symbolism shows that the air masses after the If the capacitors 9 and 10 are swept coolest, then first warm up when sweeping the brine 14 in the brine tub 6. A further heating then takes place in the evaporation space 3, so that the air masses at the upper transition from the evaporation space 4 to the condensation space 5 have their highest temperature. These hot air masses are heavily enriched with water vapor and flow due to the automatic circulation into the condensation chamber 5. There they meet the brine-cooled condenser 9, where the evaporated water condenses due to the temperature gradient between the relatively cool brine 14 and the heated air masses. After the condenser 9, the now cooled air masses flow to the salt water-cooled condenser 10. Since the salt water 26 is cooler than the brine 14, there is still a sufficient temperature gradient for further condensation despite the cooling of the air masses at the condenser 9. In addition to the condensation on the condensers 9 and 10, condensation naturally also takes place on the relatively cool underside of the evaporation surface 3 and on the housing walls of the condensation space 5. The condensed drinking water flows down on the lower housing wall and on the underside of the evaporation surface 3 and is discharged to the outside there via the outlet 8. On the underside of the evaporation surface 3, a drip web 25 is arranged in front of the brine tank 6 (FIG. 1), which ensures that condensation water which has not yet dripped from the underside of the evaporator surface 3 drips off to the lower housing wall.

As already mentioned above, the brine 14 flows to the condenser 9 at a temperature of approx. 70-75 ° C. The brine 14 is further heated in the condenser 9 and leaves it at approximately 90 ° C. A further heating then takes place in the additional heater 12 approx. 95-99 ° C, so that the brine 14 is already shortly before evaporation, the evaporation surface 3 is given up.

The salt water 26 conducted in the circuit 15 is heated in the condenser 10. This heat of condensation is withdrawn from the system and must be compensated for by solar radiation 11. In order to use this heat energetically, it is layered in the heat-insulated salt water reservoir 17. There it is available for night condensation, as will be explained further below. This stratification is realized simply by integrating the supply line 18 leading to the condenser 10 into the lower region and the discharge line 27 coming from the condenser 10 into the upper region of the salt water reservoir 17. This also ensures that the condenser 10, based on the heat content of the salt water reservoir 17, is always charged with relatively cool salt water 26.

Since water is constantly withdrawn from the internal circuits of the solar still 17 due to the distillation, water must be supplied to the system to the same extent. This is done in that the brine tank 6 is supplied with salt water 26 via a bypass 28 branched off from the discharge line 27 coming from the condenser 10.

In the mode of operation described above, the solar still has its most powerful operating state.

With regard to other modes of operation of the solar still 1, it should be mentioned at this point that in the feed line 18 from the salt water reservoir 17 to the condenser 10 and in the discharge line 27 after the capacitor 10 solenoid valves 29 and 30 are arranged. For the same reason, solenoid valves 31 to 34 are present in the feed line 20 from the brine tub 6 to the condenser 9.

Another mode of operation is preferred for starting up the solar still 1, which is explained below with reference to the flow diagram shown in FIG. 3.

The solar still 1 enters this operating state as soon as sufficient solar radiation 11 is registered by a photosensor (not shown), provided the solar trough 6 is sufficiently filled.

In order to be able to operate this mode of operation, the solenoid valves 33 and 34 in the feed line 20 to the capacitor 9 and the magnets 29 and 30 in the circuit 15, which is thereby prevented, are closed. Instead, a solenoid valve 35 is opened in a bypass 42 from the feed line 20 to the condenser 10. The brine 14 conveyed from the brine trough 6 by the pump 21 first flows through the condenser 10, then the condenser 9 and then the additional heater 12 due to this circuit and reaches the evaporation surface 3 in this way. This operating state is maintained until the brine temperature is so has become high that the capacitor 10 is charged with a too high brine temperature (> 55 ° C) to still achieve an effective condensation. Then the solar still 1 switches over to the continuous operation described above according to the flow diagram according to FIG. 2. The described starting operation has the advantage that the solar still 1 is brought to its optimal operating temperature very quickly. In order to use the thermal energy stratified in the salt water reservoir 17, the solar still 1 can be operated in a night condensation mode. This mode of operation is illustrated by the flow diagram according to FIG. 4. As soon as a light sensor (not shown) indicates that the solar radiation 11 is too low for evaporation, the solar still 1 switches to night condensation operation. Here, the temperature of the salt water 26 in the salt water reservoir 17 should be above 50 ° C. In this operating state, the salt water 26 is passed from the salt water reservoir 17 over the evaporation surface 3, so that condensate formed can precipitate on the cold glass panes on the front side 13 of the housing.

In this operating state, the condensation energy stored in the salt water 26 is to be recovered almost completely and the salt water 26 in the salt reservoir 17 is to be cooled again as a condensation agent for the coming day. Night operation is stopped as soon as the salt water 26 has reached a temperature which is too low for effective evaporation.

In order to be able to operate this mode of operation, additional lines 40, 37 and 38 as well as solenoid valves 41, 36 and 39 blocking or opening them are provided. When the solar still 1 switches to night operation, the solenoid valves 41, 32, 33, 36 and 39 are opened and the valves 35 and 34 are closed. The salt water ^'26 is then pumped by the pump 21 via the lines 40 and 37 to the evaporation surface 3 and from there passes 6. in the brine bath from the brine bath 6 flowing the cooled salt water 26 via line 38 back to the salt water reservoir 17 to ,

Claims

P a t e n t a n s r u c h e

Device for producing solar drinking water from salt water with the following known features: a housing (2) which is closed on all sides, thermally highly insulated and set up at an angle, the front surface (13) of which faces the sun is formed from at least one thermally insulating, sunlight-permeable pane and / or film, one Evaporation surface (3), which runs essentially parallel to the front surface (13), and divides the interior of the housing into an upper evaporation space (4) and a lower condensation space (5), the evaporation space (4) and the condensation space (5) are on Upper and lower ends of the evaporation surface (3) are connected on the flow side, so that the enclosed air masses can circulate in the housing, at the lower end of the evaporation surface (3) there is a brine trough (6) which brings brine (14) dripping from the evaporation surface (3) ) catches, the brine tub (6) is provided with an overflow (7), at the un lower end of the condensation chamber (5) a drinking water outlet (8) is provided, in the condensation chamber (5) at least one first condenser (9) is arranged, and with the following, characteristic features: a feed line (20) with an integrated pump (21) leads from the brine trough (6) to the inlet of the at least one first condenser (9), and a feed line leads from the outlet of the at least one first condenser (9) (22) to the upper end of the evaporation surface (3), a feed line for metered filling with salt water (26) is integrated into the brine tank (6).

2. Apparatus according to claim 1, characterized in that in the from the outlet of the at least one first condenser (9) leading to the evaporation surface supply line (22) a solar energy-heated auxiliary heater is interposed.

3. Apparatus according to claim 2, characterized in that this additional heater (12) consists of a pipe system arranged in the frame (2).

4. Device according to one of the preceding claims, characterized in that the at least one first capacitor (9) is arranged in the region of the upper end of the condensation space (5).

5. Device according to one of the preceding claims, characterized in that at least a second condenser (10) is arranged on the circulation path of the air masses after the at least one first condenser (9), the inlet of which is through a feed line (18) with an integrated pump (19th ) is connected to a salt water reservoir (17) arranged outside the housing (2), and its outlet via a Derivation (27) opens out into the salt water reservoir (17).

Apparatus according to claim 5, characterized in that the feed line (18) integrates in the lower region and the discharge line (27) in the upper region of the salt water reservoir (17).

Apparatus according to claim 5 or claim 6, characterized in that the salt water reservoir (17) is thermally insulated.

Device according to one of claims 5 to 7, characterized in that a bypass (28) leads from the discharge line (27) to the brine tank (6), via which the brine tank (6) is filled in a metered manner with salt water (26).

Device according to one of the preceding claims, characterized in that it comprises further pipelines (37, 38, 40, 42) connecting its components (3, 6, 9, 10, 12, 17) and switching valves (29-36, 39 , 41, 43) for switching the pipes (18, 20, 22, 27, 37, 38, 40, 42) on and off is completed in order to be able to implement different operating modes.