EP2219753A2

EP2219753A2 - Integrated solar collector and multiple effect distillation

Info

Publication number: EP2219753A2
Application number: EP20080851941
Authority: EP
Inventors: Tom Juul Andersen
Original assignee: Idekontoret ApS
Current assignee: Idekontoret ApS
Priority date: 2007-11-21
Filing date: 2008-11-20
Publication date: 2010-08-25
Also published as: WO2009065407A2; WO2009065407A3

Abstract

A solar powered distillation system is disclosed comprising a solar collector (210) and a multiple-effect distiller further comprising a plurality of condensation-evaporation stages. The plurality of condensation-evaporation stages further comprises a first and a last condensation-evaporation stage, and further one or more intermediate condensation-evaporation stages that are placed between the first and last condensation-evaporation stages. The distillation system further comprises a first heat exchanger (220) for heating the first condensation-evaporation stage of the multiple-effect distiller, a first conduit (222) enabling a first heat-transport fluid to flow from the solar collector (210) to the first heat exchanger (220) and back to the solar collector (210), and a second conduit (232) for supplying the multiple-effect distiller with a feed liquid. The solar collector (210), the first conduit (222), the first heat exchanger (220), and the multiple-effect distiller constitute a thermodynamically driven heat transportation system.

Description

Integrated solar collector and multiple effect distillation

Field of invention

The present invention generally concerns a integrated system for distilling a fluid, the system comprising a combination of a thermal solar collector and a multiple-effect distillation unit that is thermally connected and working be thermodynamics without mechanical help from pumps etc. and using the excess energy of the system for preheating the feed fluid going into the system resulting in a high energy reuse ratio of the system. Two additional features enhancing the initial energy input for the distillation process are a graduated preheating the feed liquid to be distilled and a controlled, or differential, heating of the feed liquid in the first stage of the multiple- effect distillation unit, resulting in a minimum overall loss of energy in the system.

Description of related art

Several solar powered multiple effect distillation solutions for freshwater production has earlier been described. US-A-4.475.988, US-A-4.402.793, US-A-4.329.205 and JP 11.156341 all describe proposed implementations of a solar distillation system. However, none of the abovementioned applications has ever been brought to the market, due to the low efficiency, high manufacturing cost and high need of maintenance of the systems.

Any of the above systems is based on a number of heat conductive sheets/foils that through a number of stages will evaporate and condensate a fluid. The sheets/foils may be placed in any angle and the initial heat for the process may be added from any side of the system and then travel through the stages to reuse the energy. It is also given in any of the systems that the stages in the multiple effect systems must be air/vapour/water tight within the system and to the ambient in order to work.

The construction of such system is amongst others troubled by the amount of energy needed for evaporation of fluids. Solar power is free, but the solar capture devices are not, so the investment versus yield is an issue restricting the commercial/practical appropriateness of such systems. Relying on solar irradiation, the amount of kWh per square meter of ground space, a such system needs to optimize the energy reuse to the utmost in order to produce enough and relatively cost effective distilled fluid e.g. water.

Thermal solar collectors with selective coatings and specialized glass coverings are after decades of development a refined technology for collecting thermal energy from the sun. The current invention is therefore related to the use of solar thermal collectors and the low tech combination thereof, with a multiple effect distillation unit, being one of the most energy effective technologies within low tech distillation.

Other factors are important. One is the rigidity of the system, another is a self circulating loop eradicating the need for pumps and sensors between the solar energy collector and the multiple-effect distillation unit. Thermal solar collectors with selective coatings and specialized glass coverings are after decades of development a refined technology for collecting thermal energy from the sun. The current invention is therefore related to the enhanced use of this energy and the low tech combination with a multiple effect distillation unit.

Thus, there is a need for a new and improved energy construction of a combination of a multiple-effect distillation system and a thermal solar collector that utilizes the advantages of each technology for a low tech and effective solar still.

Object of the invention

An object according to the present invention is to provide a self-contained solar powered distillation system requiring no other power source than solar radiation. A particular feature of the present invention is that it all the essential elements of the distillation system are supported by a common frame. A particular advantage with the present invention is that it allows for a compact distillation system that can be delivered, installed, and operated as a single module or unit.

Another object according to the present invention is to provide a self-contained solar powered distillation system having an improved efficiency. Another feature of the present invention is that it involves a multiple-effect distiller supplied with a differential heating of its first condensation-evaporation stage, i.e. the heat supplied to each finite area element of the heat-supply or lower surface of the multiple-effect distiller may vary. Another advantage of the present invention is that a larger volume of liquid can be distilled for a given energy input and period of time.

Summary/Disclosure of invention

In addition to the above objects, the above advantages and the above features, numerous other objects, advantages and features will be evident from the disclosure below. The objects, advantages and features are according to a first aspect of the present invention obtained by a solar powered distillation system comprising a solar collector, a multiple-effect distiller further comprising a plurality of condensation- evaporation stages. The plurality of condensation-evaporation stages further comprises a first and a last condensation-evaporation stage, and one or more intermediate condensation-evaporation stages that are placed between the first and last condensation-evaporation stages. The distillation system further comprises a first heat exchanger for heating the first condensation-evaporation stage of the multiple- effect distiller, a first conduit enabling a first heat-transport fluid to flow from the solar collector to the first heat exchanger and back to the solar collector, and a second conduit for supplying the multiple-effect distiller with a feed liquid. The solar collector, the first conduit, the first heat exchanger, and the multiple-effect distiller constitute a thermodynamically driven heat transportation system.

An advantage with this solar powered distillation system is that, due to the thermodynamically driven heat transportation system, it requires no moving mechanical parts to function, such as pumps, filters and fans. Hence, it may be made robust and service be kept to a minimum when operating the distillation system. This in turn means that the distillation system can be placed at locations that are hard to reach, e.g. a slanted roof top on a multi storey building.

Additionally or alternatively, the plurality of condensation-evaporation stages may define a preferred heat-flow direction for heat supplied to the first condensation- evaporation stage by the first heat exchanger, wherein the preferred heat-flow direction is in a direction of increasing gravitational potential. This allows for a multiple- effect distiller that is heated from below, where the heat spreads upwards within the distiller by the vapour. This means that the distillate is collected above the concentrate or feed liquid, which is an advantage as it secures the separation of the distillate from the concentrate, enabling a higher purity of the distillate. If the distillate were located below the concentrate, drops of the concentrate could fall into the distillate.

Additionally or alternatively, the plurality of condensation-evaporation stages may define a preferred liquid-flow direction of the feed liquid entering the multiple-effect distiller, wherein the preferred liquid-flow direction is in a direction of decreasing gravitational potential. This means that the feed liquid or concentrate within the multiple-effect distiller will traverse the plurality of condensation-evaporation stages by the force of gravity, making it possible to maintain a thin film of the feed liquid in each stage and no tray-like arrangement with a large collection of feed liquid is necessary. In turn, this means a high surface over volume ratio of the feed liquid, which enhances the evaporation rate. The heating of the feed liquid within the distiller should be kept small or at a minimum, since then the feed-liquid can reach the desired temperature more quickly for a fixed heat input, i.e. the start-up time is shorter for the distillation system

The multiple-effect distiller may define a height, a length, and a width, wherein said length is larger than said width, and said width is larger than said height. Additionally, the length may extend in a lengthwise direction being parallel to the preferred liquid- flow direction and the width may extend in a sideways direction being horizontal. If the multiple-effect distiller is oriented so that the plurality of condensation-evaporation stages is coplanar with a horizontal plane, the height is the general vertical dimension. As the feed liquid, or concentrate, generally travels along the length of the multiple- effect distiller, these particular features allows for a larger amount of feed liquid to be evaporated. Naturally, the evaporation rate can be doubled by doubling the width and scaling the rest of the distillation system accordingly. This doubling may not work for the length, since, for a certain length, all of the feed-water may evaporate before leaving the distillation unit, which may result in unwanted depositing of material solved in the feed-liquid inside the distiller. Instead, the doubling of the evaporation rate can be achieved by having two distillation systems, where the smaller width allows for a more flexible positioning of the individual distillation systems. Further, a minimal height allows for a compact and flat construction of the distillation unit.

Additionally or alternatively, the first heat exchanger may supply more heat to the multiple-effect distiller at an upstream location than at a downstream location of the preferred liquid-flow direction. This kind of heating can be regarded as a differential heating, as the amount of heat supplied at per unit area is not constant over the whole lower side of the multiple-effect distiller. This particular feature depends on the evaporation process to distribute the heat inside the multiple-effect distiller. Thereby, direct heating by the first heat exchanger close to the outlets for the remaining feed liquid or distillate can be avoided, which otherwise result in a heat loss, as some of the heated feed liquid may not evaporate before this leaving the distiller.

Additionally or alternatively, the multiple-effect distiller may be oriented so that the preferred liquid-flow direction defines an angle to a horizontal surface in the range of approximately 5 degrees to approximately 30 degrees. It has been shown that this particular feature is favourable for the evaporation and condensation within a multiple- effect distiller.

Additionally or alternatively, the solar powered distillation system may further comprise a second heat exchanger for cooling the last condensation-evaporation stage of the multiple-effect distiller, wherein the second conduit is coupled to the second heat exchanger for removing heat from the last condensation-evaporation stage by heating the feed liquid. It has been shown that this particular feature is favourable for the evaporation and condensation within a multiple-effect distiller, since it enables a well defined temperature between the condensation-evaporation stages, as well as an additional control over of the over the operative temperatures of each stage.

Additionally or alternatively, the solar powered distillation system may further comprise a third heat exchanger for heating the feed liquid, wherein the third heat exchanger is coupled to the second conduit and to the first conduit and the feed liquid is heated by cooling the first heat-transport fluid. It has been shown that this particular feature is favourable for the evaporation and condensation within a multiple-effect distiller. Generally, the optimal temperature of the feed liquid is higher than its initial temperature. This particular feature allows for the feed liquid to reach a temperature close to the optimal temperature for the distiller, which means that the distiller needs to be optimized for inducing a phase change only, i.e. evaporation, and not for heating the feed liquid from its initial temperature.

Additionally or alternatively, the third heat exchanger may provide a graduated heating of the feed liquid, whereby the temperature of the feed liquid supplied to the first condensation-evaporation stage is larger than the temperature of the feed liquid supplied to the one or more intermediate condensation-evaporation stage, and the temperature of the feed liquid supplied to the one or more intermediate condensation- evaporation stage is larger than the temperature of the feed liquid supplied to the last condensation-evaporation stage. Generally, the temperature of the feed liquid decreases from the first to the last condensation evaporation stage. This particular feature of the distillation system allows for a temperature of the feed liquid that is supplied to the individual condensation-evaporation stages to be close to the optimal temperature for each stage. Clearly, this is an advantage as it enables more efficient evaporation.

Additionally or alternatively, the solar powered distillation system may further comprise a common frame for supporting the solar collector, the multiple-effect distiller, the first heat exchanger, the first conduit, and the second conduit, the common frame defining a preferred operative orientation. This particular feature has the advantage that the distillation system may be transported and installed as a single unit.

The solar collector may have an outlet opening that is connected to the first conduit, the first heat exchanger and/or the third heat exchanger may have an inlet opening connected to the first conduit, wherein the inlet opening is located at a more elevated position than the outlet opening when the common frame is in its preferred operative orientation. This particular feature allows the first heat-transport fluid to cool at a point located higher than where it is heated. This enhances the circulation of the solar driven first heat-transport fluid, which in turn gives a more efficient transportation of heat from the solar collector to the first heat exchanger, which in turn supplies more heat to the distillation process.

Additionally or alternatively, more than half of the body of the multiple-effect distiller may be located below the body of the solar collector when the common frame is placed in the preferred operative orientation. Whit this particular feature, more than half of the multiple-effect distiller may be covered by the solar collector when viewed from the direction of the sun. This has the advantage that the uppers side of the multiple-effect distiller, which is to be cooler than its lower side, is protected from heating by the direct solar radiation. Further, this particular feature also enables a compact construction of the distillation system. The common frame in conjunction with the solar collector may define a common housing enveloping the multiple-effect distiller, the first heat exchanger, the first conduit, and the second conduit. This particular feature has the advantage that the distillation system may be transported and installed as a single unit. Simultaneously, the elements of the distillation system may be protected from direct physical wear or damage.

Additionally or alternatively, the common housing may have a lower opening and an upper opening, wherein the upper opening is located at a more elevated position than the lower opening when the common housing is in its preferred operative orientation, for enabling a thermodynamically driven airflow to remove heat from the last condensation-evaporation stage. It has been shown that this particular feature is favourable for the evaporation and condensation within a multiple-effect distiller, since it enables a well defined temperature between the condensation-evaporation stages, as well as an additional control over of the over the operative temperatures of each stage.

Additionally or alternatively, the solar powered distillation system may further comprise a fourth heat exchanger for cooling the last condensation-evaporation stage of the multiple-effect distiller and a fourth conduit for leading a second heat-transport fluid to and from the fourth heat exchanger, enabling heat to be removed from the last condensation-evaporation stage by heating the second heat-transport fluid. This particular feature has the advantage that the heat from the outer side of the last condensation-evaporation stage is not lost, but can be used for other purposes. For example, the second heat transport fluid may be water that after passing through the fourth heat exchanger is stored in an insulated hot-water tank for domestic use.

A second aspect of the present invention is a system for distilling a fluid comprising a combination of a thermal solar collector and a multiple effect distillation unit that is thermally connected and working by thermodynamics without mechanical help from pumps etc and using the excess energy of the system for preheating the feed fluid going into the system. The invention reduces the technical complexity of a high performance solar multiple distillation system by enhancing the energy reuse of the system and lowering cost of a system. The energy reuse of a distillation system is well documented and is based on various usual combinations of means e.g. multistage and vacuum. In the low tech segment the multiple effect distillation system is based on a fine balance of natural evaporation and condensation through a number of condensation-evaporation stages that in number/area mostly are determined by initial amount/type of energy, the thermal conductivity of the stages and the flow rate of the feed fluid in the stages. These essential (along with others) parameters are important for the overall system performance - measured in energy reuse and overall yield.

It is given that any system prefers as much heat energy to the first stage as possible and as cold energy to the last stage as possible. Both requirements will mean enhanced evaporation and condensation in the respective stages - but in the between stages the energy performance of a such system will be enhanced as well, because the total efficiency of a such system is the "energy difference" between the lower and upper stage.

The reuse of energy is also determined by the ratio between heating and evaporation of the feed fluid. The higher temperature for a feed fluid, and given that the temperature difference between the stages is sufficient, the higher energy efficiency and yield is possible. The evaporation ratio at a given temperature is constant and the condensation ratio at a certain temperature difference is a constant as well.

In a distillation system, heating is non-effective waste of energy, so therefore preheating of the feed fluid is important to have in such system. In the first stage of a multiple still system, temperatures should at optimum be close to boiling point and the optimum temperature differences through the stages varies, but should be in the area of 3 to 5 C. The closer distance between the stages the more effective the system. At temperatures below 50 C the evaporation ratio and vapour content in air is not interesting in non-vacuum systems. Therefore it is often seen that an 8 to12 stage - or effect - system work at app 90 C at the first stage and the last stage is about 50 to 60 C.

As an example of a multiple effect still system with 9 stages, the above figures will result in an energy reuse factor in the range of 2,5 to 4 if the system runs without cooling at the upper stage and with heat applied through a water reservoir at 90 C placed below the lower stage. Applying the inventive cooling to the upper stage and the inventive direct heating to the lower stage, the same system can achieve an energy reuse factor of up to 5. The ability to transfer the solar thermal energy to the feed fluid is essential for the energy efficiency of the system. Here, in a preferred embodiment, a thin film of fluid is the most effective way of achieving quick heating and evaporation at a higher temperature. Therefore a thermal effective construction of the fluid connection of the solar collector and the lower stage is preferred.

A pressurized tubular loop connection may connect the solar collector's internal tube and the lower side of the distillation unit. This thermal connection can be enhanced by welding e.g. copper tubes to the outside/inside of the lowest stage, i.e. the first stage of the multiple-effect distiller. The tubes should stretch over the whole of the stages surface and tilted so that thermodynamics will circulate the fluid from the solar collector to the distillation unit by itself. Dimensioning and construction of the tubes should be optimized so that the water will flow and should be fitted with security components e.g. high pressure release valves and expansion vessels.

A lower stage, e.g. profiled for strength and better thermal capabilities, may be filled with the hot fluid from the solar collector. The principle is known from a flat plate heat exchanger. This will of course demand a pressure tight structure in order to withstand the forces of fluid ranging in the area of 100 C or more. Providing cooling and preheating of the feed fluid is in a preferred embodiment achieved through a thermal connection between the upper stage of a multiple effect still and the feed fluid before the feed fluid enters the still. The upper stage would normally be app 50 to 60 C and the water from the ambient can be anything from 5 to 35 C under normal conditions and depending on feed fluid source. Lowering the temperature in the upper condensation-evaporation stage with say 10 to 2OC by active cooling of the outer upper side of the stage, will more than double the yield in that stage through the bigger temperature difference obtained.

Internally, the distillation unit may be smaller in area than the solar collector allowing room for necessary technical components. A system comprising a multiple effect distillation unit of app 1m2 with 7-12 evaporation-condensation stages will depending on configuration, type of collector and local solar irridation need 1,5 to 2,5 m2 of thermal solar collector The system as a whole would then in size be approximately 200x125x40 cm (length x width x height). The fluid connection may be of the same type/form as above mentioned or in any other form. The tube may be welded to the outer upper stage of the still. The pressurized loop could be made of copper tubes of 10 to 22 mm in diameter. The solar collector and the solar still may be one unit in one casing. When the distillation unit needs maintenance, the solar collector should be disconnected from the below placed multiple effect solar still. This could be achieved through a hinged construction connecting the solar collector with the distillation unit, allowing access to the still by tilting the solar collector.

To preserve energy the still is insulated all around. Glass of Rockwool may be placed in the common casing. The compact construction and a perfect insulation are highly important for the optimized energy efficiency. The thickness of insulation should be in the range of 50 to 100 mm both over and under the still.

In most cases, when the still is a tilted still, the optimum angle between the sun and the solar collector differ from the optimum angle of still. The solar collector is most likely to be at a steeper angle than the still. This can be integrated in the common casing of the system, so that the still internally is at the optimum angle.

Internally the distillation unit may be firmly attached to the bottom structure of the system. This can or may be done either via an integrated structure in the bottom structure or via attachments (threaded, glued, pressed etc) or simply held in place by the underlying insulation material. Also, it is within the preferred embodiment that all other components may be placed in the same casing, such as tube connections in/out of the casing monitoring equipment, pumps, expansion vessels etc so that the system is contained and easy to install onto roofs, special stands, sun tracking stands or simply placed on the ground. The systems outside may therefore be fitted with brackets, feet or other means for fixation.

Further, a system may comprise an internal or external storage tank for collection of excess heat energy during daytime for usage during overcast/night time. The system may also be fitted with electric heating for supplement and/or night time production. In addition, the system's self circulating heat energy tubes can or may comprise an integrated/external heat storage tank for hot water usage (domestic hot water for bathing). The second aspect of the present invention may be summarized as an integrated solar powered multiple effect system for distilling a fluid, the system comprising a thermal solar collector integrating on the lower side hereof a number of flat plate stages of a multiple effect distillation unit. An internal liquid and by thermodynamics self-circulating connection from the solar collector to the lower side of the first stage of the multiple effect distillation unit and back to the solar collector for provision of the thermal energy supply for the distillation process and a separate liquid feed fluid connection to the multiple effect distillation unit that is thermally connected to the upper side of the last stage to provide cooling of the last stage of the distillation unit and preheating of the feed fluid. Additionally, the system may comprise thermal insulation between the solar collector and the multiple effect distillation system and between the multiple effect distillation system and the ambient. Alternatively or additionally, the thermal fluid connections to the lower side of the distillation unit or multiple-effect distiller, i.e. the first heat exchanger, is made of heat conductive tubing. Alternatively or additionally, the thermal fluid connection to the upper side of the distillation unit or multiple-effect distiller, i.e. the second heat exchanger, is made of heat conductive tubing. Alternatively or additionally, the fluid connection to any of the sides, i.e. the first or the second heat exchanger, is made as heat conductive separate stage(s) in the distillation system. Additionally or alternatively, the solar collector and the multiple effect distillation system can be individually disconnected for maintenance purposes. Additionally or alternatively, the solar collector, the multiple effect distillation unit and the fluid connections are shielded and placed inside a common outer structure or housing. Alternatively or additionally, the system inside the common outer structure comprises further mandatory components e.g. tube connections, dosing apparatus for feed fluid, monitoring equipment and expansion vessels. Alternatively or additionally, the system comprises a heat energy storage tank. Alternatively or additionally, the solar collector and the multiple-effect distillation unit are not in the same common structure, but thermally connected in two or more separate outer structures.

A third aspect according to the present invention is primarily, but not restricted to, intended for a tilted multiple-effect distillation system for distilling a fluid comprising a number of flat sheets with constant dosing of feed liquid. On the sheets a wick is placed to ensure slow feed water flow and a thin water film. As an example, the distillation unit may be approximately 0.6 m² in floor space and 20 to 30 cm in height. The third aspect according to the present invention may enable 1 ) a combination of a thermal solar collector and a multiple effect distillation unit that is thermally connected and where the energy transport between the solar collector and the first heat exchanger is working by thermodynamics, without mechanical means of moving heat energy from the solar collector to the distillation unit.

Further, the third aspect according to the present invention may enhance the way of transferring the energy from the solar collector to the feed liquid in said system, so that the loss of the initial energy input is reduced to a minimum and thereby enhancing the price and compactness of said system. This is done by 2) a graduated preheating of the feed water before entering said system and 3) a differential heating of the lowest, first stage in said system.

In addition, the third aspect according to the present invention may reduce the technical complexity of a high performance solar multiple distillation system and enhances the energy efficiency of such a system.

It is important for the optimized energy transfer and speed of said system that the distillation unit is placed at the lower very top end of the tilted solar collector. The distillation unit may even extend from the upper frame of the solar collector, as this is important for the transfer of maximum heat from the solar collector to the preheating and the upper half of the distillation unit. When a solar collector's self circulation loop is constructed in off balance, the said system will not start to circulate before the temperature is high enough to create movement by the upward push of hot water in the solar collector and the downward pull in the first heat exchanger. This mechanism depends on the temperatures, angles and pressure losses in the construction. As an example, by placing the distillation unit some 20 to 40 cm higher than the internal top of the solar collector an efficient thermosiphon may be obtained.

The heat exchange between the solar collector loop and the lower outer stage may be such that most of the energy is transferred at the top end of the surface area of the outer, lower stage. The speed and effectiveness of the system may be improved by having a heat transfer at the top of the stages that is larger than at the outlet at the opposite end. This means that the wanted temperature in the first condensation-evaporation stage of such system quickly will be at maximum temperature at the upper end and will gradually get colder as the fed fluid stream gets closer to the exit at the lower end of the stage. Therefore the construction of the lowest stage is to be such that the most of the evaporation is taking place at the upper half of the area by adding the most heat energy there - and less at the lower half of the area. Vapour will seek downwards to condense on the coldest surface possible. Here, this will be the second stage's condensation area, which is desired. The feed water in the first stage is not heated on its way over the last half of the area and will therefore leave the system colder than if the whole of the area was heated evenly - which also is desired.

The fluid and heat exchanging connection between the solar collector and the distillation unit may be a simple S-bent copper tube welded to the outer upper stage of the still. The pressurized loop may be made of copper tubes of 10 to 22 mm in diameter. Further, thermal conductive wings may be employed for better heat exchange to the outer lower side of the first stage. It is essential for water quality and corrosion issues that the heat is added on the outside of the lower stage. However, since this also means energy loss, an internal tubular construction may be employed. To comply with the abovementioned differential heating of the first condensation- evaporation stage according to the other aspects of the present invention, the spacing between said copper tubes may be small at the top end and gradually larger towards the lower end.

The lowest stage, or the first condensation-evaporation stage, of the multiple-effect distiller may be filled with the hot fluid from the solar collector. This principle is known from a flat plate heat exchanger with O-ring tightening between the sheets. This will of course demand a pressure tight structure in order to withstand the forces of fluid ranging in the area of 100 C or more. Again, to comply with the differential heating discussed above, the heat transfer area should mostly be at the upper half of the first condensation-evaporation stage.

Alternatively or additionally, a fresh water tank may be placed internally at the low end of said system to present a complete solution for producing and storing fresh water. A fresh water tank may be detachable, fitted with overflow, big enough for days of production etc. Further, the fresh water tank may be fitted with means for remineralisation/ other post treatment contraptions and a pressure pump for grid connection.

To enhance the energy profile a graduated feed water preheating may be incorporated in the system. The optimum temperature difference through stages differs from case to case, but is typically in the range of 3-5 degrees C. Therefore, it is an advantage to have a preheating close to this optimum. By this the heating of the feed liquid is done before entering the distillation apparatus and so the distillation starts immediately at close to optimum energy balance.

The solar collector's heat transfer tube, or first conduit, may pass through the means for feed water inlet (a double wall tube solution with the solar heated fluid in the inner tube and the feed water in the outer tube) and thereby transferring most energy at the lowest stage's feed water inlet and gradually less up to the upper stage's inlet.

It is understood that any single feature or element of an aspect according to the present invention may be employed in any another aspect according to the resent invention.

Brief description of the drawings

Additional objects and features according to the present invention will be more readily apparent from the following detailed description and appended claims, where the former is presented in conjunction with the drawings, where:

Fig.1 illustrates a sideway cross-sectional view of a preferred embodiment of a solar powered distillation system,

Fig.2 illustrates, due to symmetry, both the upper and lower sides of the multiple effect distillation unit with cooling/heating tubes attached

Fig.3 illustrates a sideway cross section view of another preferred embodiment of a solar powered distillation system, Fig.4 illustrates a particular embodiment of the lower side of a multiple effect distillation unit with heating tubes attached with varying distance between parallel and neighbouring tube segments, i.e. a first heat exchanger,

Fig.5 illustrates a particular embodiment of the upper side of a multiple-effect distillation unit with cooling tubes attached for either hot water production or preheating of the feed water for the distillation system, i.e. a second heat exchanger,

Fig.6 illustrates a particular embodiment for preheating of the feed water, i.e. via a third heat exchanger,

Fig.7 illustrates an alternative embodiment for heat transfer between the solar collector and the lower stage of the multiple-effect distillation unit, i.e. a first heat exchanger,

Fig.8 illustrates the same alternative embodiment as in Fig.7, but from a different perspective,

Fig.9 illustrates the same alternative embodiment as in Figs.7 and 8, but from yet another perspective,

Fig.10 illustrates yet another alternative embodiment for heat transfer between the solar collector and the lower stage of the multiple-effect distillation unit, i.e. a first heat exchanger, and

Fig .11 illustrates the same alternative embodiment as in Fig.10, but seen from a different perspective.

Detailed description

In addition to the disclosure above, additional objects, advantages and features of the present invention will be evident from the detailed description.

Fig 1 shows a cross section of a conceptual construction of a preferred embodiment of a system. The system comprises of a solar collector with a glass cover 210, an absorber 211 , a pressurized hot fluid tube loop connection 212 insulation 213 and a frame 215. Under the solar collector, but inside the same outer casing 231 is a still placed that is heated by the looped tube connection 212, 220, 222 and 223 allowing the liquid from the solar loop transfer the energy to the still by self circulation.

The multiple effect still unit comprises a lower initial heat transfer structure shown in Fig 2 with welded tubes 220 to the heat receiving first stage 221 of the still. The upper connection 222 between the solar collector and the still is for the hottest fluid in the system and at the lower end the relatively cooler fluid returns via tubing 223 to the solar collector.

On the opposite side of the still a similar structure, as shown in Fig 2 comprising welded tube 214 to the outer side of the still, leads the feed fluid for the still through the tubes 214.

The fluid is then at the same time preheated and the last stage of the still is cooled for optimized condensation production. Connections for feed water fluid 232 are shown on the same end as the outlet connections for excess feed fluid 233 and distilled water 234. For ease all connection can be gathered to the bottom outer frame 231 , also allowing a hinged 230 disconnecting of the two bodies.

Inside the system's outer casing 231 is shown an expansion vessel 235 for the pressurized solar collector loop and a feed fluid distribution structure 236.

Fig.3 shows a cross section of a conceptual construction of a preferred embodiment of the proposed system. The system comprises of a solar collector 101 with a glass cover 128, an absorber 129, a pressurized hot fluid tube loop connection (or first conduit) 107, insulation 123 and a common frame 115. Under the solar collector 101 , but inside the same outer casing, or common frame, 115 is a multiple-effect distillation unit 102 is placed that is heated by the looped tube connection 107 allowing the heat transfer fluid or liquid from the solar loop to transfer energy to the distillation unit by self circulation.

Connections for the distillation unit are feed water fluid 108 - or second conduit - and a waste water outlet for excess feed liquid 120 and distilled water 121 , i.e. a concentrate conduit 120 and a distillate conduit 121. All connections are placed in the outer (or common) frame 115 and a primary hinge 124 enables a hinged disconnecting of the two bodies. Further, two or more ventilation openings 118 and 119 are placed at the bottom and the top of the outer casing (or common frame) 115, allowing free flow of air trough the system, primarily past the last condensation-evaporation stage 105. On the upper end of the bottom, outer structure (or common frame) 115 a service hatch 126 pivotally supported by a secondary hinge 125 allowing easy access to the internal components.

The preferred heat-flow 109 and liquid-flow 110 directions are shown as arrows. This means that the preferred heat-flow direction is generally perpendicular to the first 104, the one or more intermediate 103, and the last 105 flat condensation-evaporation stages. Additionally, this also means that the preferred heat-flow direction is generally parallel to the flat condensation-evaporation stages 103 to 105.

The solar collector 101 has an outlet opening 116 located slightly below the inlet opening 117 of the third heat exchanger 114. This relative positioning defines a column in which a heated fluid can move upwards, which induces a circulation of the heat-transfer fluid in the first circuit 107.

The system further comprises an expansion vessel 127 for the pressurized solar collector loop and the feed liquid distribution structure (or third heat exchanger) 114. At the low end of the inside structure a water or storage tank 122 is fitted.

Fig.4 shows the outer, lower side of a multiple effect distillation unit comprising a lower initial heat transfer structure, i.e. a first heat exchanger, with tubes 106 attached to the heat receiving first stage 104 of the multiple-effect distiller. The upper - in relation to the preferred operative orientation - connection 130 between the solar collector and the still is for allowing the hotter fluid into the first heat exchange, while the lower connection 131 at the lower end is for allowing the fluid to continue to the solar collector. The connections are made in standard fittings and are insulated. The tube 106 is bent so that the distance between two neighbouring and parallel tube segments is smaller at an upstream location 111 than at a downstream location 112, thereby providing a differential heating of the first condensation-evaporation stage 104 as described above.

Fig.5 shows the upper, outer side of the multiple effect distillation units last stage with an upper final heat transfer structure 113 connected to the outside of the last condensation-evaporation stage 105, i.e. to the upper side of the multiple-effect distiller. The tube 113 is used for preheating of the feed water, i.e. corresponding to a second heat exchanger. In an alternative embodiment, the tube 113 may be employed for heating water for bathing/heating, i.e. corresponding to the fourth heat exchanger described above. The final stage 105 of the distillation unit is cooled in both of these embodiments. These particular embodiments may, in yet another embodiment, be replaced by, or used in conjunction with, the ventilation structure as shown and described in relation to in Fig.3.

Fig.6 shows a suggested embodiment of a third heat exchanger 114 comprising a inner, heat conductive tube 341 for the heated fluid from the solar collector, which may constitute a segment of the first conduit described above. The heat conductive tube 341 is surrounded by a tube shaped manifold 340 with a slightly larger diameter allowing feed water to enter through a single inlet 342 and exit via a plurality of outlets 343. The flow of the heat-transport fluid within the heat conductive tube 341 defines an upstream position 344 and a downstream position 345. The single inlet 342 for the feed water is located at an upstream position 344 relative to the plurality of outlets 343. As the plurality of outlets are arranged in sequence along the flow of the heat-transport fluid, the temperature of the feed water from an outlet of the plurality of outlets increases with an increased distance from the single inlet 342 during operation. In this suggested embodiment, each of the plurality of outlets leads to a single condensation- evaporation stage (not shown in Fig.6).

Figs.7 to 9 show a particular embodiment of the heat transfer between the solar collector and the lower stage of the multiple-effect distillation unit, i.e. corresponding to the first heat exchanger, in the form of a profiled fluid filled chamber welded to a frame. The drawings are shown in front, back and in profile, where Fig.7 shows the front, Fig.8 the back, and Fig.9 a perspective view of this particular embodiment.

The front of the frame 451 is attached to or constitutes the outside wall of the first condensation-evaporation stage, i.e. the lower side of the distillation unit. The frame 451 is fitted by way of fastening holes 453. Further, the frame 451 has a hole 433 for the passage of the rest fluid or concentrate from the distillation unit, and another hole 434 for the passage of the distillate from the distillation unit. A profiled chamber 452 is connected to the frame structure 451 for allowing the heat-transport fluid from the solar collector to heat the distillation unit by conduction through the frame 451. The profiled chamber 452 constitutes a segment of the self circulate in the loop, or the first conduit. In each corner of the chamber 452 a connections is placed, two 454 for the inlet of the heat-transport fluid and two 455 for the outlet of the cooled fluid. The connections 454 and 455 may be fitted with sensors, electric heating devices etc. The profiled chamber 452 covers less than half of the frame 451 , making it suitable for a differential heating of the distillation unit as discussed above.

Figs.10 and 11 show yet another particular embodiment of the heat transfer between the solar collector and the lower stage of the multiple-effect distillation unit, i.e. corresponding to the first heat exchanger, in the form of a profiled fluid filled chamber welded to a frame. The drawings are shown in front, back and in profile. Fig.10 shows a perspective view of this particular embodiment, while Fig.11 shows the front.

The front of the frame 551 is attached to or constitutes the outside wall of the first condensation-evaporation stage, i.e. the lower side of the distillation unit. The frame 551 is fitted by way of fastening holes 553. Further, the frame 551 has a hole 533 for the passage of the rest fluid or concentrate from the distillation unit, and another hole 534 for the passage of the distillate from the distillation unit. A profiled chamber 552 is connected to the frame structure 551 for allowing the heat-transport fluid from the solar collector to heat the distillation unit by conduction through the frame 551. The profiled chamber 552 constitutes a segment of the self circulate in the loop, or the first conduit. In each corner of the chamber 552 a connections is placed, two 554 for the inlet of the heat-transport fluid and two 555 for the outlet of the cooled fluid. The connections 554 and 555 may be fitted with sensors, electric heating devices etc. The principal difference between this particular embodiment and the embodiment described in relation to Figs.7 to 9 is that the profiled chamber 552 covers a significant portion of the area of area of the frame 551, i.e. it is not optimized for a differential heating of a distillation unit. Item list

101 solar collector

102 multiple-effect distiller 103 intermediate condensation-evaporation stage

104 first condensation-evaporation stage

105 last condensation-evaporation stage

106 first heat exchanger

107 first conduit 108 second conduit

109 preferred heat-flow direction

110 preferred liquid-flow direction

111 upstream location

112 downstream location 113 second heat exchanger

114 third heat exchanger

115 common frame

116 outlet opening

117 inlet opening 118 lower opening

119 upper opening

120 concentrate conduit

121 distillate conduit

122 storage tank 123 insulation

124 primary hinge

125 secondary hinge

126 service hatch

127 expansion vessel 128 glass cover

129 absorber

130 upper connection

131 lower connection

132 upper end 133 lower end

210 glass cover 211 absorber

212 first conduit or looped tube connection

213 insulation

214 second heat exchanger or welded tube 215 frame

230 hinge

231 outer casing or frame

232 connection for feed water

233 outlet for excess feed water or concentrate conduit 234 outlet for distilled water or distillate conduit

235 expansion vessel

236 fluid distribution structure

220 first conduit or looped tube connection

222 first conduit or looped tube connection 223 first conduit or looped tube connection

340 tube-shaped manifold

341 heat conductive tube

342 single inlet 343 plurality of outlets

344 upstream position

345 downstream position

433 hole for concentrate passage

434 hole for distillate passage 451 frame

452 profiled chamber

453 fastening holes

454 heat-transport fluid inlet

455 heat-transport fluid outlet 533 hole for concentrate passage 534 hole for distillate passage

551 frame

552 profiled chamber

553 fastening holes 554 heat-transport fluid inlet 555 heat-transport fluid outlet

Claims

1. A solar powered distillation system comprising a solar collector (101 ), a multiple- effect distiller (102) further comprising a plurality of condensation-evaporation stages, said plurality of condensation-evaporation stages further comprising a first (104) and a last (105) condensation-evaporation stage, and one or more intermediate condensation-evaporation stages (103) that are placed between said first (104) and last (105) condensation-evaporation stages, said distillation system further comprising a first heat exchanger (106) for heating said first condensation-evaporation stage (104) of said multiple-effect distiller (102), a first conduit (107) enabling a first heat-transport fluid to flow from said solar collector (101) to said first heat exchanger (106) and back to said solar collector (101), and a second conduit (108) for supplying the multiple- effect distiller (102) with a feed liquid, wherein said solar collector (101), said first conduit (107), said first heat exchanger (106), and said multiple-effect distiller (102) constitute a thermodynamically driven heat transportation system.

2. A solar powered distillation system according to claim 1 , wherein said plurality of condensation-evaporation stages define a preferred heat-flow direction (109) for heat supplied to said first condensation-evaporation stage (104) by said first heat exchanger (106), wherein said preferred heat-flow direction (109) is in a direction of increasing gravitational potential.

3. A solar powered distillation system according to any of the claims 1 to 2, wherein said plurality of condensation-evaporation stages define a preferred liquid-flow direction (110) of said feed liquid entering said multiple-effect distiller (102), wherein said preferred liquid-flow direction (110) is in a direction of decreasing gravitational potentiai.

4. A solar powered distillation system according to claim 3, wherein said first heat exchanger (106) supplies more heat to said multiple-effect distiller (102) at an upstream location (111) than at a downstream location (112) of said preferred liquid- flow direction (110).

5. A solar powered distillation system according to any of the claims 1 to 4, wherein said multiple-effect distiller (102) defines a height, a length, and a width, wherein said length is larger than said width, and said width is larger than said height.

6. A solar powered distillation system according to claim 5, wherein said length extends in a lengthwise direction being parallel to said preferred liquid-flow direction (110) and said width extends in a sideways direction being horizontal.

7. A solar powered distillation system according to any of the claims 3 to 6, wherein said multiple-effect distiller (102) is oriented so that said preferred liquid-flow direction (110) defines an angle to a horizontal surface in the range of approximately 5 degrees to approximately 30 degrees.

8. A solar powered distillation system according to any of the claims 1 to 7 further comprising a second heat exchanger (113) for cooling the last condensation- evaporation stage (105) of said multiple-effect distiller (102), wherein said second conduit (108) is coupled to said second heat exchanger (113) for removing heat from said last condensation-evaporation stage (105) by heating said feed liquid.

9. A solar powered distillation system according to any of the claims 1 to 8 further comprising a third heat exchanger (114) for heating said feed liquid, wherein said third heat exchanger (114) is coupled to said second conduit (108) and to said first conduit (107), and said feed liquid is heated by cooling said first heat-transport fluid.

10. A solar powered distillation system according to claim 9, wherein said third heat exchanger (114) provides a graduated heating of said feed liquid, whereby the temperature of the feed liquid supplied to said first condensation-evaporation stage (104) is larger than the temperature of the feed liquid supplied to said one or more intermediate condensation-evaporation stages (103), and the temperature of the feed liquid supplied to said one or more intermediate condensation-evaporation stages (103) is larger than the temperature of the feed liquid supplied to said last condensation-evaporation stage (105).

11. A solar powered distillation system according to any of the claims 1 to 10 further comprising a common frame (115) for supporting said solar collector (101), said multiple-effect distiller (102), said first heat exchanger (106), said first conduit (107), and said second conduit (108), said common frame (115) defining a preferred operative orientation.

12. A solar powered distillation system according to claim 11, wherein said solar collector (101) has an outlet opening (116) that is connected to said first conduit (107), said first heat exchanger (106) and/or said third heat exchanger (114) has an inlet opening (117) connected to said first conduit (107), wherein said inlet opening (117) is located at a more elevated position than said outlet opening (116) when said common frame (115) is in its preferred operative orientation.

13. A solar powered distillation system according to any of the claims 11 to 12, wherein more than half of the body of the multiple-effect distiller (102) is located below the body of the solar collector (101) when said common frame (115) is placed in said preferred operative orientation.

14. A solar powered distillation system according to any of the claims 11 to 13, wherein said common frame (115) in conjunction with said solar collector (101) defines a common housing enveloping said multiple-effect distiller (102), said first heat exchanger (106), said first conduit (107), and said second conduit (108).

15. A solar powered distillation system according to claim 14, wherein said common housing has a lower opening (118) and an upper opening (119), wherein said upper opening (119) is located at a more elevated position than said lower opening (118) when said common housing is in its preferred operative orientation, for enabling a thermodynamically driven airflow to remove heat from said last condensation- evaporation stage.

16. A solar powered distillation system according to any of the claims 1 to 15 further comprising a fourth heat exchanger for cooling the last condensation-evaporation stage (105) of said multiple-effect distiller and a fourth conduit for leading a second heat-transport fluid to and from said fourth heat exchanger, enabling heat to be removed from said last condensation-evaporation stage (105) by heating said second heat-transport fluid.