ZA200308662B

ZA200308662B - Device for obtaining clean fresh water by distilling contaminated primary water.

Info

Publication number: ZA200308662B
Application number: ZA200308662A
Authority: ZA
Inventors: Helmut Lessing
Original assignee: Clausthaler Umwelttechnikinsti
Priority date: 2001-04-28
Filing date: 2003-11-06
Publication date: 2004-11-08
Also published as: DE10291793D2; AU2002304898A1; ES2253532T3; DE50204956D1; EP1409411A2; WO2002087721A2; WO2002087721A3; CY1104972T1; ATE309963T1; EP1409411B1

Abstract

The invention relates to a device for obtaining clean fresh water by distilling contaminated primary water, especially saltwater. The device comprises a reaction chamber with a solar heatable evaporator surface that can be wetted with primary water, a collecting device for non-evaporated primary water, a coolable condensation surface on which water steam of the primary water is condensed, and a collecting device for the fresh water evacuated from the condensation surface. The evaporator surface and the condensation surface are mounted coaxially in the reaction chamber and are separated by a heat insulating layer. An air circulation chamber and the water steam contained therein runs upward through an outer chamber formed between the evaporator surface and the wall of the reaction chamber and outward through an inner chamber formed by the coaxial condensation surface.

Description

Device for obtaining clean fresh water by distilling contaminated primary water

The invention relates a device for obtaining clean fresh water by distilling contaminated primary water according to the precharacterizing clause of claim 1.

The problem of obtaining clean fresh water from contaminated primary water, such as salt water, brackish water, waste water or subterranean water arises everywhere where clean groundwater is absent or there 1s no widespread public water supply system with clean fresh water. This applies in particular to industrially underdeveloped countries and to tropical and subtropical regions. Here, clean fresh water has to be produced locally from sources with contaminated primary water.

Known for this purpose are mechanical filters and also devices based on the principle of reverse osmosis with semipermeable membranes or devices based on the principle of distillation. In the case of devices based on the principle of distillation, a distinction is drawn between evaporation of the primary water at atmospheric pressure or subatmospheric pressure and according to the type of energy supply for the evaporation.

In tropical and subtropical regions especially, it is opportune to obtain the energy for the evaporation of primary water from solar energy, that is to say not indirectly by generating electrical energy but by heating the primary water directly by solar power.

A device suitable for this is known from DE 37 21 072.

This device comprises an upright reaction chamber, the outer side wall of which consists of glass that is transparent to sunlight. Inside the reaction chamber there is an evaporation surface, which is wetted with primary water, and a condensation surface, on which water vapor condenses and drips off as clean fresh water. Arranged underneath the evaporation surface is a collecting device for primary water which is not evaporated and arranged underneath the condensation surface is a collecting device for clean fresh water.

The evaporation surface and the condensation surface are of a planar form and are at a distance from the side wall of the reaction chamber. Formed between the evaporation surface and the condensation surface is a circulation chamber for air and water vapor, which is also bounded by the remaining side walls and the bottom wall and top wall of the reaction chamber. In this case, air «circulates upward along the evaporation surface, 1s enriched with water vapor, deflected at the top in the reaction chamber and falls downward on the condensation surface, with water vapor condensing there and dripping off as liquid water. The air enriched with water vapor is then deflected at the bottom in the reaction chamber and rises up once again on the evaporation surface.

Since the rising and falling water-vapor-transporting air masses meet in the middle of the reaction chamber, turbulences occur at the boudary surfaces, with an adverse influence on the flow and also a resultant restriction on the yield of clean fresh water.

The invention is based on the object of improving a device of the type stated at the beginning to the extent that the yield of fresh water in relation to the irradiated evaporation surface area and the volume of the reaction chamber is improved.

This object is addressed! in the case of the device according to the precharacterizing clause of claim 1 by _ the features of claim 1.

Developments and advantageous refinements emerge from the subclaims.

The coaxial arrangement of the evaporation surface and . the condensation surface in the case of the device according to the invention has the effect of forming two separate chambers, in which the circulating air can be enriched with and depleted of water vapor. At the respective edges at the ends of the evaporation surface and the condensation surface, the circulating air is deflected. The coaxial arrangement also produces enlarged surface areas, in relation to the volume of the reaction chamber, ‘on which primary water can evaporate and water vapor can condense again. .. Turbulence at boundary surfaces between rising and falling air enriched with water vapor is avoided.

According to a development, the side wall of the - reaction chamber is at least partially transparent to thermal radiation. -

As a result, thermal radiation can reach the evaporation surface directly and heat it.

The evaporation surface may in this case be formed as a black absorber.

As a result, reflections from the evaporation surface ———— are significantly reduced and the input of energy from ) . thermal radiation into the evaporation surface is increased.

According to a development, the primary water is passed via a heat exchanger, which is arranged in the upper

Amended 14 September 2004 region of the condensation surface, to outlet openings in the upper region of the evaporation surface.

The heat exchanger serves the purpose on the one hand of pre-heating the primary water, and so using the thermal energy introduced via the evaporation surface only for additional heating, but on the other hand of also cooling the upper region of the condensation surface, in order to deplete the water vapor content of the circulating air as quickly as possible by condensation as it flows past the condensation surface.

As a supplementary measure, a heat exchanger for cooling medium may be additionally arranged in the upper region of the condensation surface.

This can assist the cooling of the condensation surface, which is expedient for example in the case of high temperatures in the interior of the reaction chamber and already very greatly heated primary water.

The cooling medium is preferably primary water which is flowing in an external circuit.

As a result, there is sufficient thermal capacity to achieve appropriate cooling of the condensation surface over a sustained period of time.

The primary water present in the collecting tray for unevaporated primary water can be fed once again to the evaporation surface.

By reusing the unevaporated, but heated primary water that has flowed off from the evaporation surface, the thermal energy still present in the primer water is utilized, whereby the heating up via the heat exchanger on the condensation surface and via the evaporator does

- 5 = . not have to take place from scratch, but from an elevated temperature level.

In this case, the primary water located in the collecting device can be compensated by supplying external primary water continuously or when the solubility of contamination products falls below limit values.

In this case, the thermal energy already contained in the collected primary water is largely retained, but the concentration is prevented from changing unfavorably, which could lead to contamination products precipitating if the solubility of these contamination products falls below limit values. : Furthermore, a heat accumulator for primary water may be provided and used for supplying heated primary water if the solar irradiation falls below a limit value.

This allows a continuation of the distillation to be achieved even when, although there is still adequately heated primary water available, the solar irradiation is no longer sufficient for additionally increasing the temperature and consequently effecting evaporation, for example when there 1s extensive cloud coverage or during the night.

According to a development, a heat transfer medium can be externally supplied via a heat exchanger coupled to the evaporation surface.

This makes it possible also to use other heat sources to supplement the solar irradiation, for example the waste heat of power generating plants, sewage treatment plants or heating stations.

Reflectors which direct solar radiation concentrically onto the evaporation surface are preferably arranged outside the walls of the reaction chamber.

These reflectors help to accomplish irradiation of the entire circumferential casing of the evaporation surface and consequently the achievement of an optimum input of solar energy.

In the case of a preferred configuration, the side walls of the reaction chamber as well as the condensation surface and the evaporation surface are aligned vertically.

As a result, as they rise and fall, the air and vapor masses can follow the gravitational field, whereby an optimum circulation is achieved.

In one configuration of the device, the ratio between the axial length and the diameter of the reaction chamber is made to be between 3 and 8, preferably 5, and the cross section on the one hand of the outer chamber, formed between the evaporation surface and the side wall of the reaction chamber, and the cross section on the other hand of the inner chamber, enclosed by the coaxial condensation surface, are approximately equal.

In the case of a prototype, the length-diameter ratio has proven to be particularly favorable for the yield of fresh water per irradiated unit area. The equal cross-sectional areas permit a constant circulation flow of the air enriched with water vapor.

The invention is explained below on the basis of the drawing, in which:

- 7 = figure 1 shows a schematic longitudinal section through a device of the invention, figure 2 shows a structural diagram of the mass conductions of primary water, figure 3 shows a representation of the mass conduction of an outer circuit and figure 4 shows a representation of the mass conduction of an inner circuit.

The device shown in figure 1 comprises a reaction chamber 10 with transparent side walls 12, in which a cylindrical evaporation surface 18 and a cylindrical condensation surface 20 are arranged and separated from each other by a heat insulating layer 22. The reaction chamber 10 is aligned vertically, and the side walls 12 as well as the evaporation surface 18 and the condensation surface 20 are likewise aligned vertically. Underneath the condensation surface 20 there is a collecting device 30 for dripping-off clean fresh water and underneath the evaporation surface 18 there is a collecting device for unevaporated dripping- off primary water.

A circulation chamber for air that is thermally induced to circulate and water vapor contained therein is formed on the one hand by an outer chamber 32 between the evaporation surface 18 and the side wall 12 and on the other hand by an innner chamber 34 of the circumferential condensation wall 20. These two chambers 32, 34 are flow-connected between the upper edge of the evaporation surface 18 and the condensation surface 20 on the one hand and the upper side 16 of the reaction chamber 10 on the other hand and between the lower edge of the evaporation surface 18 and the condensation surface 20 on the one hand and the bottom side 14 of the reaction chamber 10 on the other hand, whereby the circulation flow of the air and of the water vapor present in the air is enforced in the direction of the arrows represented by dashed lines. :

Arranged in the upper region of the condensation surface 20 1s a first heat exchanger 26, which is flowed through by contaminated primary water from the collecting device 30, and a further heat exchanger 24, which is flowed through by external primary water. The heat exchanger 26 is additionally connected to outflow openings 36 at the upper edge of the evaporation surface 18. For enlarging the surface area, the evaporation surface 18 has a structure which increases the path of the primary water introduced via the outlet openings 36. The surface of the evaporation surface 18 "is also formed as a black absorber.

Outside the reaction chamber 10 there 1s a reflector 38, which directs incident solar radiation concentrically in the direction of the circumferential evaporation surface 18.

The device operates as follows:

Solar radiation incident via the reflector 38 passes through the transparent side walls 12 of the reaction chamber 10 from the outside onto the evaporation surface 18. The evaporation surface 18 is then heated.

Primary water which leaves from the outlet openings 36 and runs down on the outside of the evaporation surface 18 is heated and partially evaporates. Depending on the temperature of the evaporation surface 18, part of the water vapor goes over into the circulating air and follows the circulation flow represented by rising arrows upward in the outer chamber 32. A remaining portion of non-evaporated primary water drips off into the collecting device 28 for remaining primary water.

The rising air stream with the water vapor contained in it is deflected after passing the upper edge of the evaporation surface 18 and condensation surface 20 and falls in the inner chamber 34 formed by the condensation surface 20. Since the condensation surface 20 is cooled by the heat exchangers 24 and 26, part of the water vapor condenses on the condensation surface 20 and finally drips off into the collecting device 30 for clean fresh water. The remaining non- condensed water vapor is deflected outward after passing the lower edge of the evaporation surface 18 and the condensation surface 20 and rises once again upward in the outer chamber 32 formed between the evaporation surface 18 and the side wall 12 of the reaction chamber 10, where an enrichment with water vapor takes place once again by the primary water evaporating on the surface of the evaporation surface 18. The circulation is maintained by the temperature difference between the heated evaporation surface 18 and the cooled condensation surface 20.

The «clean fresh water collected in the collecting device 30 can be passed on to consumers, for example a public water supply system. The primary water stored in the collecting device 28 is topped up from external sources, so that its level and the concentration of contamination products, salt for example, remains within predetermined limit values.

Figure 2 shows a representation of the mass conductions for the outer and inner circuits of the primary water.

In an outer circuit, primary water is sent from an external reservoir 42 through the heat exchanger 24 and returned again into the external reservoir 42 by means of a pump 44. It is assumed that the temperature level of this reservoir 42 is lower than the internal temperature of the reaction chamber. Used primary water in the collecting device 28 is topped up via a bypass 46.

In an inner circuit, primary water from the collecting device 28 is sent via the heat exchanger 26 to outlet openings 36, and a non-evaporated portion flows down on the evaporation surface 18 and returns into the collecting device 28 for primary water.

The representations according to figure 3 and figure 4 shows the inner circuit and the outer circuit once again separately on the basis of a schematic representation of the evaporation surface 18, the condensation surface 20 and the heat exchangers 24 and

Claims

Patent claims

1. A device for obtaining clean fresh “water by distilling contaminated primary water.

5. comprising a reaction chamber with a solar-heatable evaporation surface that can ~ be wetted with primary water, a collecting device for wunevaporated primary water, a coolable condensation surface , on which water vapor of the primary water condenses, and a collecting oo device for fresh water removed from the condensation surface, with the evaporation surface and the condensation surface having an ~ alignment in a vertical component, characterized in that the evaporation surface and the condensation surface are arranged coaxially in the reaction chamber and are separated from ) each other by a heat insulating layer and there is formed a circulation chamber for air and water vapor contained in it, in whith a thermally enforced flow of air and water vapor passes upward between an outer chamber formed by the : evaporation surface and a side wall of the reaction chamber , is deflected from an upward direction into a downward direction at the edges at the upper end of the evaporation surface and the condensation surface , passes downward through an inner chamber formed by the coaxial condensation surface and is Co 30 deflected from a downward direction into an upward direction at the edges at the lower end of the condensation surface and the evaporation surface . So Amended 14 September 2004

-1la-

2. The device as claimed in claim 1 wherein the contaminated primary water is salt water.

. 3. The device as claimed in either claim 1 or claim 2 characterized in that the side wall of the reaction chamber is at least partially transparent to thermal radiation. I 4, The device as claimed in any one of claims 1 to 3, characterized in that the evaporation surface is formed as a black absorber. Amended 14 September 2004

5. The device as claimed in any one of claims 1 to 4, : characterized in that primary water is passed via a Heat exchanger ; which is arranged in .the uppér . region of the condensation surface , to outlet openings in the upper region of the evaporation surface . oT 6. The device as claimed in any one of claims 1 to 35, h characterized in that a heat exchanger for ~~ cooling medium is additionally arranged in the : upper ‘region of the condensation surface . . 7. The device as claimed in claim 6, characterized in that the cooling medium is primary water which is flowing in an external circuit.

8. The device as claimed in any one of claims 1 to 7, characterized in that, from the collecting device : for unevaporated primary water, the latter can be fed once again to the evaporation surface . oo 9. The device as claimed in any one of claims 1 to 8, 7 characterized in that the primary water located in the collecting device can be compensated by . supplying external primary water continuously or ) when the solubility of contamination products falls below limit values. . 10. The device as claimed in any one of claims 1 to O. characterized in that a heat accumulator for primary water is provided and used for supplying heated primary water if the solar irradiation falls below a limit value. ’ Amended 14 September 2004 i

11. The device as claimed in any one of claims 1 to 10, characterized in that a heat transfer medium can be : externally supplied via a heat exchanger coupled to the evaporation surface ;.

12. The device as claimed in any one of claims 1 to 11, characterized in that reflectors : which direct solar radiation concentrically onto the evaporation surface are arranged outside the walls of the reaction chamber .

13. The device as claimed in any one of claims 1 to 12, characterized in that side walls + of the reaction chamber | as well as the condensation : surface and the evaporation surface are : aligned vertically.

14. The device as claimed in any one of claims 1 to 13, characterized in that the ratio between the axial length and the diameter of the reaction chamber is between 3 and 8 and the ~ cross section on the one hand of the outer chamber , formed between the evaporation surface and the side wall of the reaction chamber +, and the cross section on the other hand of . the inner chamber , enclosed by the coaxial * condensation surface ©, are approximately equal.

15. The device as claimed in claim 14 wherein the ratio between the axial : length and the diameter of the reaction chamber is 5. Amended 14 September 2004 )