US20040098998A1

US20040098998A1 - Solar thermal system with solar pond and method of maintaining solar pond

Info

Publication number: US20040098998A1
Application number: US10/471,244
Authority: US
Inventors: Mikio Kinoshita
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-03-12
Filing date: 2002-03-08
Publication date: 2004-05-27
Also published as: WO2002073099A1; JPWO2002073099A1

Abstract

A solar thermal system, comprising a solar pond (10) for accumulating salt water heated by solar radiation and a moisture supply device (20) allowing the vapor evaporated from the water having impurities such as sea water to be absorbed by the salt water; a method of maintaining the solar pond; and a method of forming the solar pond; the system, wherein the moisture supply device may have an absorbing heat pump for receiving the supply of the salt water and the water having the impurities, and the salt water with excellent cleanliness is circulated to the solar pond by the operation of the moisture supply device, whereby scale deposit and propagation of algae in the solar pond can be prevented.

Description

TECHNICAL FIELD

The present invention relates to a solar heat system having a solar pond, a method for maintaining the solar pond, and a method for constructing the solar pond.

BACKGROUND ART

As a kind of solar heat system, a solar pond is known. Transparent saline water having a prescribed distribution of concentration is stored in the solar pond. A lower layer of the saline water is heated to a high temperature by solar radiation. The concentration of the lower layer of the solar pond is larger than that of an upper layer. Therefore, even when the lower layer of the saline water is heated to a high temperature, the convection is not generated, and the heat transmission from the high-temperature lower layer to the upper layer is extremely small. Thus, the hot saline water is obtained in the lower layer of the solar pond.

Due to the difference between the concentrations of the saline water, the salts diffuse. In order to prevent the variation of the distribution of the concentration of the saline water due to the diffusion of salts, water is supplied to the upper part of the saline water. Further, the lower layer of the saline water is concentrated. In maintaining the solar pond in this way, it is important to properly supply water to the upper part of the saline water and to concentrate the saline water of the lower layer. In particular, when the upper part of the solar pond is opened, because the water is evaporated at the upper layer part, it is required to supply a large quantity of water.

As to the quality of water to be supplied, the purity is requested. For example, when impurities such as nutritive salts are included in the water to be supplied, because undesirable microbes or algae propagate, the transparency is decreased. In order to reduce the costs for supplying water, it is requested to supply water having prescribed purity at a low cost, in the solar pond according to the background arts.

Further, when seawater is used as such saline water, there has been the problem that scale is deposited with the concentration of the seawater.

The present invention is made in view of the above, and an object of the present invention is to solve the above-mentioned problems and the other problems. Another object of the present invention is to provide a solar pond and a method for maintaining the solar pond, in which the maintenance is facilitated. Still another object of the present invention is to provide a solar heat system having a solar pond in which the maintenance is facilitated. Still another object of the present invention is to provide a solar heat system having a solar pond capable of utilizing low-cost seawater as the source of the water to be supplied and a method for maintaining the solar pond. Still another object of the present invention is to reduce the costs in constructing the solar pond.

DISCLOSURE OF INVENTION

According to an embodiment of the present invention, a novel solar heat system is provided. The solar system includes a solar pond for storing saline water heated by solar radiation and a water providing device for allowing the saline water to absorb water vapor evaporated from impurities containing water. The water providing device may include an absorption heat pump which is supplied with the saline water and the impurities containing water. The solar heat system may further include a concentrator for concentrating the saline water.

According to another embodiment of the present invention, a novel method for maintaining a solar pond is provided. The method for maintaining the solar pond includes the steps of storing saline water having a prescribed concentration distribution in the solar pond and allowing the saline water to absorb water vapor evaporated from impurities containing water. The method for maintaining the solar pond may further include the step of concentrating the saline water.

According to still another embodiment of the present invention, a novel method for constructing a solar pond is provided. The method for constructing the solar pond includes the step of dissolving solid salt by unsaturated saline water, supplying the saline water in which the solid salt is dissolved to a water providing device, allowing the saline water in which the solid salt is dissolved to absorb water vapor evaporated from impurities containing water in the water providing device, further dissolving the salt by returning a part of the saline water which has absorbed the water vapor evaporated from the impurities containing water to the solid salt, and feeding the rest of the saline water which has absorbed the water vapor evaporated from the impurities containing water to the solar pond.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual view illustrating a solar heat system according to an embodiment of the present invention. [0010]
FIG. 2 is a conceptual view illustrating a layered structure of saline water stored in the solar pond illustrated in FIG. 1. [0011]
FIG. 3 is a conceptual view illustrating an example of a structure of the water providing device illustrated in FIG. 1. [0012]
FIG. 4 is a conceptual view illustrating a solar heat system according to another embodiment of the present invention. [0013]
FIG. 5 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. [0014]
FIG. 6 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. [0015]
FIG. 7 is a conceptual view illustrating an inside of a cooling container of FIG. 6. [0016]
FIG. 8 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. [0017]
FIG. 9 is a conceptual view illustrating a flow in a method for constructing a solar heat system according to still another embodiment of the present invention. [0018]
FIG. 10 is a conceptual view illustrating an inside of a water providing device provided for a solar pond according to still another embodiment of the present invention. [0019]
FIG. 11 is a conceptual view illustrating a solar heat system according to still another embodiment of the present invention. [0020]
FIG. 12 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. [0021]

BEST MODE FOR CARRYING OUT THE INVENTION

In order to illustrate the present invention in more detail, the present invention is explained referring to the accompanying drawings. The same reference numerals designate the same or corresponding parts throughout the several views. [0022]
A solar heat system according to an embodiment of the present invention is explained, referring to FIGS. [0023] 1-3. FIG. 1 is a conceptual view illustrating the solar heat system according to an embodiment to of the present invention.
In FIG. 1, the solar heat system includes a [0024] solar pond 10, a water providing device 20, and a concentrator 50.
[0025] Transparent saline water 70 is stored in the solar pond 10. The solar pond 10 absorbs solar radiation. FIG. 2 is a conceptual view illustrating a layered structure of the saline water 70 stored in the solar pond 10. The saline concentration of an upper layer 70A is lower than that of a lower layer 70C. The saline concentration of an intermediate layer 70B changes continuously. The distribution of the saline concentration of the intermediate layer 70B is controlled in a prescribed range so as not to generate convection due to heat. A means for adjusting the concentration distribution (not shown) maybe provided therefor. As the salts, the salt including sodium chloride, sodium magnesium, and/or sodium calcium may be used. For example, the saline concentration of the upper layer 70A and the saline concentration of the lower layer 70C may be 6 wt. % and 25 wt. %, respectively. The temperature of the lower layer 70C is higher than that of the upper layer 70A. The broken line of FIG. 2 conceptually illustrates the boundaries of the above-mentioned layers.
A [0026] water supply pipe 40 and a drain pipe 42 are provided between the water providing device 20 and a water source (not shown) Impurities containing water is supplied to the water providing device 20 through the water supply pipe 40. For example, as the impurities containing water, seawater, groundwater, river water, lake water, or processed disposal water may be supplied. The value of the molar elevation of boiling point of the upper layer 70A of the saline water 70 is larger than that of the impurities containing water.
Further, a [0027] water supply pipe 30 and a drain pipe 32 are provided between the saline water 70 and the water providing device 20. The saline water stored in the upper layer 70A is supplied to the water providing device 20 through the water supply pipe 30.
In the [0028] water providing device 20, the water vapor evaporated from the impurities containing water is absorbed by the saline water. Thus, the saline water is diluted. The diluted saline water is returned to the upper layer of the saline water stored in the solar pond 10 through the drain pipe 32. The impurities containing water which is concentrated by providing water to the saline water is drained to the outside of the system through the drain pipe 42.
FIG. 3 is a conceptual view illustrating an example a structure of the [0029] water providing device 20. In FIG. 3, the water providing device 20 is a kind of absorption heat pump. Namely, the water providing device 20 includes a plurality of plates 22, a plurality of permeation members 24, and a plurality of permeation members 26.
Each permeation member[0030] 24 is applied on a surface of the plate 22. The saline water is supplied to each permeation member24 through the above-mentioned water supply pipe 30. The saline water permeates each permeation member24.
Each permeation member[0031] 26 is applied on another surface of the plate 22. Each permeation member26 is disposed opposite the permeation member24. The impurities containing water is supplied to each permeation member26 through the above-mentioned water supply pipe 40. The impurities containing water permeates each permeation member26. The saline water does not permeate each plate 22. Namely, nonvolatile material such as the salt does not migrate between the impurities containing water and the saline water.
As mentioned above, the value of the molar elevation of boiling point of the saline water is larger than that of the impurities containing water. Therefore, the water vapor evaporated from the impurities containing water permeating each permeation member[0032] 26 defuses in an air gap, and is absorbed in the saline water permeating the opposite permeation member 24. The impurities containing water which is concentrated due to the loss of water is drained through the drain pipe 42. The saline water diluted by the absorption of water is drained through the drain pipe 32 onto the surface of the saline water 70 stored in the solar pond 10. The outlet of the drain pipe 32 may be extended to the right side of FIG. 1. Accordingly, the concentration of the upper layer of the saline water 70 is maintained in a prescribed range. Because the nonvolatile impurities in the impurities containing water does not migrate to the saline water, the purity of the saline water is maintained well. Accordingly, the purity is obtained, which is equivalent to that of the case in which the saline water is diluted using distilled water.
In order to increase the diffusion amount of the water vapor evaporated from the impurities containing water, the inside of the [0033] water providing device 20 may be evacuated into a vacuum state using the vacuum system having a vacuum container (not shown) Alternatively, the inside of the water providing device 20 may be heated to a prescribed high-temperature using a heating system with a container having heat-insulation (not shown). Further, in order to increase the efficiency in the heating, a heat exchanging means (not shown) maybe provided. Further, the plurality of plates 22 may be arranged along a closed line.
The [0034] concentrator 50 is supplied with the saline water through a water supply pipe 60. The concentrator 50 concentrates the saline water stored in the lower layer of the solar pond 10, and supplies the concentrated saline water to the lower layer of the solar pond through the drain pipe 62. Accordingly, the concentration of the saline water stored in the lower layer of the solar pond 10 is maintained in a prescribed range.
The [0035] concentrator 50 may be, for example, a multi-effect distillation device. In this case, in order to drain the generated distilled water, a distilled water drain pipe 64 is provided. Further, the concentrator 50 may distill the saline water utilizing the temperature difference between the upper layer and the lower layer of the saline water stored in the solar pond. The saline water stored in the upper layer of the solar pond 10 may be cooled by evaporation. Alternatively, the saline water may be concentrated by the cooling by a natural wind.
In the construction of the [0036] solar pond 10, saline water having a concentrated concentration may be stored to a prescribed water level first. Thereafter, by supplying the saline water to the water providing device 20, the water vapor evaporated from the impurities containing water may be absorbed in the saline water. By supplying the saline water as diluted this way to the solar pond 10, the layered saline water having the above-mentioned concentration distribution may be prepared.
FIG. 4 is a conceptual view illustrating a solar heat system according to another embodiment of the present invention, which includes, in addition to the solar heat system illustrated in FIG. 1, a [0037] desalination device 80, a high-temperature heat source pipe 90 connected to the desalination device 80, and a cooling source pipe 9 2 connected to the desalination device 80.
A heat transmitting medium is circulated in the high-temperature [0038] heat source pipe 90. The high-temperature heat source pipe 90 supplies the thermal energy included in the saline water stored in the lower layer of the solar pond 10 to the desalination device 80.
A heat transmitting medium is circulated in the [0039] cooling source pipe 92. The cooling source pipe 92 releases the heat emitted from the desalination device 80 into the saline water stored in the upper layer of the solar pond 10. The upper layer is cooled by the evaporation cooling, radiation cooling, and the cooling by a natural wind, and so forth.
As the [0040] desalination device 80, a multi-effect distillation device or a multi-stage flash evaporation device and so forth may be used. The desalination device 80 may desalinate the saline water supplied by the water providing device 20.
The [0041] desalination device 80, the high-temperature heat source pipe 90, and the cooling source pipe 92 are moved in the direction illustrated by an arrow of FIG. 4.
FIG. 5 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. In FIG. 5, the solar heat system includes a [0042] solar pond 10, a first water providing device 20, a second water providing device 120, a flash evaporation container 210, a steam power generator 220, and a cooling container 230.
The saline water is stored in the [0043] solar pond 10. An upper layer of the solar pond 10 is opened, and the saline water in the upper layer is cooled by the evaporation cooling and so forth. The solar pond 10 may be plural.
Seawater is supplied to the first [0044] water providing device 20 from the sea 310. In the water providing device 20, the saline water absorbs the water vapor evaporated from the seawater. Thus, the saline water is diluted. The seawater concentrated after providing the water is stored in a salt precipitation field 320. The seawater stored in the salt precipitation field 320 is further concentrated so that solid salts are precipitated in the salt precipitation field 320. Such solid salts may be used for constructing a new solar pond.
The high-temperature saline water stored in the lower layer of the [0045] solar pond 10 is introduced into the flash evaporation container 210. Accordingly, the saline water is flash-evaporated in the flash evaporation container 210 to emit the water vapor. The water vapor is introduced into the steam power generator 220. The condensed water after passing the steam power generator 220 and the water vapor are cooled in the cooling container 230. With this cooling, the water vapor is condensed into water. The cooling is performed by cooling water supplied to the cooling container 230. As the cooling water, the saline water in the upper layer of the solar pond 10 is used. The condensed water, as the freshwater, is drained into the freshwater tank 260. Namely, that solar heat system simultaneously generates the power and the freshwater.
An [0046] evacuation device 240 evacuates the space in the cooling container 230, thereby the non-condensation gas remaining in the cooling container 230 is evacuated.
With the flash-evaporation of the saline water, the saline water is concentrated. The saline water after the flash-evaporation is returned to the lower layer of the [0047] solar pond 10. By controlling the saline concentration of the returned saline water, the saline concentration of the lower layer is maintained at the prescribed value. When it is required to dilute the saline water after the flash-evaporation, a valve 128 open is opened. The saline water is diluted by absorbing the water vapor evaporated from the seawater through the operation of the second water providing device 120 which is supplied with the seawater from the sea 310. When the valve 456 is opened, the saline water is just returned to the solar pond. Further, in order to prepare for the case when it is required to concentrate the saline water, a concentrator (not shown) may be provided.
FIG. 6 in is a conceptual view illustrating the flow of a solar heat system according to still another embodiment of the present invention. In FIG. 6, the solar heat system includes a [0048] solar pond 10, a first water providing device 20, a second water providing device 120, a flash-evaporation container 210, a steam generator 220, and a cooling container 232. Further, a valve 456, a valve 128, and an evacuation device 240 are provided.
FIG. 7 is a conceptual view illustrating an inside of the cooling [0049] container 232. The saline water in the upper layer of the solar pond 10 is directly introduced into the cooling container 232. The height of a saline water drainage part 610 and a saline water introduction part 620 are in the positions lower than that of the cooling container 232. Therefore, the Torricelli's vacuum state is realized inside the cooling container 232. A shelf-like fluid path 234 is installed in the cooling container 232, and the saline water flows in the direction illustrated by an arrow in the cooling container 232. The saline water directly absorbs the water vapor, and is drained. The evacuation device 240 evacuates the space in the cooling container 232.
FIG. 8 in a conceptual view illustrating the flow of a solar heat system according to still another embodiment of the present invention. In FIG. 8, the solar heat system includes a [0050] solar pond 10, a first water providing device 20, a second water providing device 120, a flash-evaporation container 210, a steam power generator 220, a cooling container 232, a heat exchanger 250, and a concentrator 50. Further, a valve 56, a valve 456, a valve 128, and an evacuation device 240, and a freshwater tank 260 are provided.
The [0051] heat exchanger 250, which is supplied with the saline water in the upper layer of the solar pond 10, cools the freshwater which is circulated between the heat exchanger 250 and the cooling container 232, utilizing this. The freshwater which is cooled by passing the heat exchanger 250 is directly introduced into the cooling container 232. The freshwater absorbs the water vapor in the cooling container 232. The freshwater having the amount corresponding to the amount of the introduction is returned to the heat exchanger 250. The surplus freshwater is drained into the freshwater tank 260. Accordingly, the solar heat system simultaneously generates the power and the freshwater.
When the [0052] valve 56 is opened, the saline water is further concentrated by the concentrator 50, and is returned to the lower layer of the solar pond 10. When the valve 128 is opened, the saline water is diluted by the water providing device 120, and is returned to the lower layer of the solar pond. When the valve 456 is opened, the saline water is just returned to the lower layer of the solar pond 10. In order to control the distribution of the concentration of the saline water stored in the solar pond 10, a controller (not shown) may be provided. In this case, the controller controls the operations of the valve 56, the valve 128, the valve 456, the first water providing device 20, the second water providing device 120, and the concentrator 50.
FIG. 9 is a conceptual view illustrating a flow in the method for constructing a solar pond according to still another embodiment of the present invention. In FIG. 9, a saline [0053] water dissolving container 330 is provided for storing saline water in the solar pond 10. Solid salts and a small amount of saline water are stored in the saline water dissolving container 330. The saline water that is in the saturated state is supplied to the water providing device 20.
Seawater is supplied to the [0054] water providing device 20 from the sea 310. The value of the molar elevation of boiling point of the saline water in the saturated state is higher than that of the seawater. Therefore, the water vapor evaporated from the seawater is absorbed into the saline water in the water providing device 20. In this case, the saline water increases its volume. A part of the saline water that is diluted to a prescribed concentration by the operation of the water providing device 20 is supplied to the solar pond 10, thereby the saline water having a prescribed concentration is stored. The rest of the saline water which is caused to be unsaturated by the supply of water is returned to the dissolving container 330. The solid salt is dissolved into the unsaturated saline water in the dissolving container 330, and the saline water which is caused to be saturated at the outlet of the dissolving container 330 is again supplied to the water providing device 20. By repeating this, the accumulation of the saline water having a prescribed distribution of concentration in the solar pond is realized. Because the nonvolatile impurities included in the seawater are not mixed into the saline water, the saline water is pure. Thus, the method for constructing the solar pond is provided, in which the water source is the low-cost seawater.
The seawater which is concentrated by providing the water may be drained into a [0055] salt precipitation field 320. The solid salts precipitated in the salt precipitation field may be supplied to the dissolving container 330. Further, the solid salts may be used for storing saline water in another solar pond.
FIG. 10 is a conceptual view illustrating an inside of a water providing device provided in a solar pond according to still another embodiment of the present invention. The [0056] water providing device 120 includes a closed fluid path 440, a wind providing means 470, a plurality of shelves 460 in which saline water flows down, a plurality of the shelves 450 in which impurities containing water flows down.
The impurities containing water is supplied from an upper part of each [0057] shelf 450, the impurities containing water flows down the shelf, and is drained to the outside of the system from a lower part thereof.
The saline water of the lower layer of the solar pond is supplied from the upper part of each [0058] shelf 460, the saline water flows down the shelf, and is returned to the solar pond from the lower part thereof. The plurality of shelves 450 and the plurality of shelves 460 are alternately disposed in the closed fluid path 440.
A circulative air current illustrated by a plurality of arrows of FIG. 10 is generated by the wind providing means [0059] 470 in the closed fluid path 440. When the air current passes through the shelf 450, the air current is humidified by the water vapor evaporated from the impurities containing water. Then, when the air current passes through the shelf 460, the air current is dehumidified by the saline water. In this process, the water vapor evaporated from the impurities containing water is absorbed in the saline water. Accordingly, the saline water is diluted.
FIG. 11 is a conceptual view illustrating a solar heat system according to still another embodiment of the present invention. In FIG. 11, the solar heat system includes a [0060] solar pond 10, a water providing device 20, a solar radiation concentrating apparatus 900, and a reflector 910. The solar radiation concentrating apparatus 900 concentrates solar radiation toward the reflector 910. The solar pond 10 is irradiated with the solar radiation reflected by the reflector 910. The plurality of arrows of FIG. 11 illustrates the propagation direction of the solar radiation. This increases the energy density of the solar radiation for the irradiation of the solar pond 10. Thus, the thermal energy at a high temperature is supplied.
FIG. 12 is a conceptual view illustrating a flow of a solar heat system according to still another embodiment of the present invention. In FIG. 12, the solar heat system includes a [0061] solar pond 10, a water providing device 20, a plurality of vapor-transmitting water-repellent pipes 810, and a solar heat power generation apparatus 820.
Water does not permeate the plurality of vapor-transmitting water-[0062] repellent pipes 810 which transmits the vapor. The plurality of vapor-transmitting water-repellent pipes 810 are installed in an upper part of the lower layer of saline water stored in the solar pond. A vapor fluid path for serially connecting the plurality of vapor-transmitting water-repellent pipes 810 is formed. The water vapor is circulated in the vapor fluid path. The pressure in the vapor fluid path may include a value near the pressure of the saline water in the plurality of vapor-transmitting water-repellent pipes. In this case, nonvolatile gas may be contained in the vapor fluid path. Alternatively, an evacuation device (not shown) for evacuating the nonvolatile gas may be provided so that such nonvolatile gas is not included in the vapor fluid path. The upper surface of the vapor fluid path may be colored black so as to absorb the solar radiation. The vapor fluid path supplies the heat to the solar heat power generation apparatus 820.
In the above, the solar heat system having the solar pond, the method for maintaining the solar pond, and the method for constructing the solar pond according to the present invention are explained in detail. Besides, the present invention may be reduced into practice with a supplemental means for preferably operating the solar heat system having the solar pond, the method for maintaining the solar pond, and the method for constructing the solar pond according to the present invention, for example, a solar heat collecting means, heat accumulating means, a vacuum system, a thermo sensor, a saline concentration sensor, an aeration devices a filter, a transparency sensor, a heat pipe, a wind prevention sidewall, a wave extinguishing means provided on the surface of the saline water, a container for housing the water providing device, a liquid feeding means, a flow amount controlling means, and/or a heat exchanging means, or the like. [0063]
The present invention disclosed herein provides a solar heat system having a novel solar pond, a method for maintaining the solar pond, and a method for constructing the solar pond, wherein in view of the detailed teachings disclosed in the above-explanation, the practice of the present invention is not limited to the above examples for explaining the best mode of the present invention, and wherein the present invention may be practiced as another embodiment with variations within the scope of the claims as follows or may be practiced without supplemental forms or constituting elements which are appended for explaining the best embodiment of the above examples. [0064]
Industrial Applicability [0065]
According to the present invention as constituted above, the solar heat system having a novel solar pond in which the impurities containing water is the water source, and a method for maintaining the solar pond is provided. The solar heat system may be used as the heat source for a solar system, the heat source for a solar heat power generation system, the heat source for desalinating seawater, or the heat accumulating means for accumulating waste heat of a solar heat power generation system. [0066]

Claims

What is claimed is:

1. A solar heat system, comprising:

a solar pond for storing a saline water which is heated by a solar radiation; and

a water providing device which allows the saline water to absorb a water vapor evaporated from an impurities containing water.

2. The solar heat system according to claim 1, wherein the water providing device includes an absorption heat pump which is supplied with the saline water and the impurities containing water.

3. The solar heat system according to claim 1, further comprising a concentrator for concentrating the saline water.

4. The solar heat system according to claim 3, wherein the concentrator is a distillation device.

5. A method for maintaining a solar pond, comprising the steps of:

storing a saline water having a prescribed distribution of concentration in a solar pond; and

allowing the saline water to absorb a water vapor evaporated from an impurities containing water.

6. The method for maintaining solar pond according to claim 5, further comprising the step of concentrating the saline water.

7. A method for constructing a solar pond, comprising the steps of:

dissolving a solid salt by a saline water which is unsaturated;

supplying the saline water in which the solid salt is dissolved to a water providing device;

allowing the saline water in which the solid salt is dissolved to absorb a water vapor evaporated from an impurities containing water in the water providing device;

further dissolving the solid salt by returning a part of the saline water which has absorbed the water vapor evaporated from the impurities containing water to the solid salt; and

feeding the rest of the saline water which has absorbed the water vapor evaporated from the impurities containing water to the solar pond.