CN108314121B - Brackish water desalination device and brackish water desalination method - Google Patents

Abstract

The invention relates to the field of brackish water desalination technology, in particular to a brackish water desalination device and a brackish water desalination method. The brackish water desalination device includes an inner circulation structure and an outer circulation structure, the inner circulation structure and the outer circulation structure form a double-layer structure; the inner circulation structure forms the first water circulation network for desalination of the brackish water, and the outer circulation structure forms the first water circulation network for desalination The second water circulation network of brackish water; the internal circulation structure includes a solar collector, which is used to collect heat during the day and store it in the first water circulation network; the brackish water forms desalinated water through evaporation and condensation during the circulation of the first water circulation network. The heat is transferred to the second water circulation network to realize heat storage; at night, the second water circulation network condenses to form desalinated water. The brackish water desalination device uses the heat accumulated during the day to realize diurnal continuous brackish water distillation at night, which doubles the desalination efficiency; and uses natural cold and heat sources to save costs.

Description

Brackish water desalination device and brackish water desalination method

technical field

The invention relates to the field of brackish water desalination technology, in particular to a brackish water desalination device and a brackish water desalination method.

Background technique

The world's first large-scale solar desalination device was built by Swedish engineer Wilson in 1872. It is a roof-type solar distillation device in northern Chile. The total heat collection area is 4700m ² , and it can produce 23t of fresh water per day in sunny days. Its structure is simple, similar to A greenhouse, but covers a large area, the daily water production rate is generally 2-4kg/m ² , and the thermal efficiency can only reach 35%-45%. After the traditional ceiling type (pool type), solar stills have appeared in various forms such as inclined curtain core type, inclined plate type, inflatable type, and liquid-absorbing core type. On the basis of these basic forms, in order to improve the heat utilization efficiency, it has gradually developed from a single-level structure to a multi-level structure. At present, the most researched and the most mature technology is still the disc solar still, which is easy to popularize and apply because of its simple structure and convenient materials. However, the disc-type solar distiller has a serious defect of low efficiency. Generally speaking, its annual production rate is only about 1000kg/m ² , which cannot meet the requirements of users. Both theory and practice have proved that if the latent heat of condensation of water vapor is reused during the operation of the system, the heat energy required for the evaporation process will be significantly reduced. The above requirements can be achieved in a multiple effect distillation system, the main advantage of which is the successful use of the latent heat of condensation of water vapor and the sensible heat of hot brine to recycle to preheat the incoming seawater. However, their structures are usually complex, and the operating costs and fixed capital investment are relatively high.

It can be seen that the solar-powered desalination devices for distilling seawater or brackish water in the prior art can only distill and collect desalinated water during the day, which has low production capacity and high cost.

The information disclosed in this background section is only intended to enhance the understanding of the general background of the present invention, and should not be considered as an acknowledgment or any form of suggestion that the information constitutes the prior art that is already known to those skilled in the art.

Contents of the invention

The object of the present invention is to provide a brackish water desalination device and a brackish water desalination method, which alleviates the technical problems of low production capacity and high cost of solar distilled seawater or brackish water desalination devices in the prior art.

A brackish water desalination device provided by the present invention comprises: an inner circulation structure and an outer circulation structure, wherein the inner circulation structure and the outer circulation structure form a double-layer structure;

The inner circulation structure forms a first water circulation network for desalination of brackish water, and the outer circulation structure forms a second water circulation network for desalination of brackish water;

The internal circulation structure includes a solar collector, which is used to collect heat during the day and store it in the first water circulation network; the brackish water forms desalinated water through evaporation and condensation during the circulation of the first water circulation network and transfers heat transfer to the second water circulation network, so that the second water circulation network gets heat and stores it; at night, the heat stored in the first water circulation network and the second water circulation network is released, so that the brackish water Desalinated water is condensed during circulation in the second water circulation network.

As a further technical solution, the internal circulation structure includes an inner heat storage pool and an inner roof; the inner roof cover is arranged on the inner heat storage pool; the solar heat collector The water inlet communicates with the inner heat storage pool, and the water outlet communicates through the top of the inner roof so that the brackish water returns to the inner heat storage pool;

The outer circulation structure includes an outer heat storage pool and an outer top cover; the outer top cover is set on the outer heat storage pool; the outer heat storage pool and the outer top cover The top is connected, so that the brackish water in the outer layer heat storage tank enters between the outer layer roof and the inner layer roof and returns to the outer layer along the outer surface of the inner layer roof Thermal storage pool.

As a further technical solution, the inner side of the inner roof is provided with a first water collection tank for collecting the desalinated water in the first water circulation network;

The inner side of the outer top cover is provided with a second water collection tank for collecting the desalinated water in the second water circulation network.

As a further technical solution, the internal circulation structure also includes a water distribution nozzle arranged on the top of the inner roof, and the water distribution nozzle communicates with the water outlet of the solar heat collector for The brackish water spray falls into the inner water storage tank.

As a further technical solution, the inner heat storage pool is connected to the water inlet of the solar heat collector through a first pipeline, and a first circulating pump is arranged on the first pipeline.

As a further technical solution, the outer circulation structure also includes a water distribution tank arranged on the top of the outer layer top cover, the water distribution tank communicates with the outer heat storage pool, and is used to introduce brackish water into the between the outer roof and the inner roof and along the outer surface of the inner roof back to the outer heat storage pool.

As a further technical solution, the outer heat storage pool is connected to the water distribution tank through a second pipeline, and a second circulating pump is arranged on the second pipeline.

As a further technical solution, the outer heat storage pool is connected with a replenishment pipe for introducing brackish water, and the port of the water replenishment pipe for connecting the outer heat storage pool is provided with a second float valve; The outer heat storage pool is in communication with the inner heat storage pool, and a first float valve is arranged at the connection between the two.

As a further technical solution, both the outer heat storage pool and the inner heat storage pool are buried underground.

The present invention also provides a brackish water desalination method, using the brackish water desalination device described in any one of the above technical solutions to collect desalinated water, including the following steps:

Diurnal cycle desalination: the solar heat collector in the internal circulation structure collects solar energy, and heat is stored in the first water circulation network by circulating the brackish water in the first water circulation network; the brackish water circulates in the first water circulation network; When circulating in the first water circulation network, evaporation and condensation form desalinated water, and release latent heat of vaporization, which is absorbed by the brackish water in the second water circulation network; the brackish water in the second water circulation network stores heat through circulation stored in said first water circulation network;

Circulating desalination at night: the heat stored in the first water circulation network and the second water circulation network is released, so that the brackish water circulating in the second water circulation network condenses to form desalinated water.

Compared with the prior art, the brackish water desalination device and the brackish water desalination method provided by the present invention can achieve the following beneficial effects:

The invention provides a brackish water desalination device, which includes an inner circulation structure and an outer circulation structure, the inner circulation structure and the outer circulation structure form a double-layer structure; the inner circulation structure forms a first water circulation network for desalinating brackish water, and the outer circulation structure The structure forms the second water circulation network for desalinating the brackish water; the inner circulation structure includes a solar collector for collecting heat during the day and storing it in the first water circulation network; the brackish water passes through evaporation during the circulation of the first water circulation network Condensation forms desalinated water and transfers heat to the second water circulation network, so that the second water circulation network can obtain heat and store it; at night, the heat stored in the first water circulation network and the second water circulation network is released, making the brackish water in the second water circulation network Condensation forms desalinated water during the circulation of the water circulation network.

During the day, when the brackish water circulates in the internal circulation structure, the solar collector collects heat to continuously increase the temperature of the brackish water, so that the brackish water in the first water circulation network continuously accumulates heat, and at the same time, the heated brackish water evaporates Condensation forms desalinated water. During this process, the heat released during the condensation process is collected by the brackish water in the second water circulation network, and is continuously accumulated in the second water circulation network along with the circulation of the brackish water in the second water circulation network. At night, the brackish water in the second water circulation network condenses continuously as the temperature drops during the circulation process to form desalinated water.

It can be seen that the brackish water desalination device provided by the present invention utilizes natural cold and heat sources and adopts a two-layer water circulation network. The inner layer directly uses solar energy to store heat, and the outer layer uses evaporation to generate secondary heat heat storage of latent heat of vaporization to achieve With the recovery of heat, the heat accumulated during the day is used at night to realize continuous distilling of brackish water day and night, which doubles the desalination efficiency; and the use of natural cold and heat sources saves costs.

The brackish water desalination method provided by the present invention adopts the above-mentioned brackish water desalination device to distill desalinated water day and night, and has high production capacity and low cost.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic structural diagram of a brackish water desalination device provided by an embodiment of the present invention.

Icons: 11 - inner heat storage pool; 12 - inner roof; 13 - first water collection tank; 14 - water distribution nozzle; 15 - solar collector; 16 - first pipeline; 17 - first circulation pump; 18 - first float valve; 19 - inspection door; 21 - outer heat storage pool; 22 - outer top cover; 23 - second water collection tank; 24 - water distribution tank; 25 - second pipeline; 26 - second circulation Pump; 27-the second float valve; 28-cover plate of the pool; 3-water supply pipeline.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, or in a specific orientation. construction and operation, therefore, should not be construed as limiting the invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and should not be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected, or integrally connected; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediary, and it can be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Referring to Fig. 1, an embodiment of the present invention provides a brackish water desalination device, including an inner circulation structure and an outer circulation structure, the inner circulation structure is arranged in the outer circulation structure; the inner circulation structure forms the first water circulation for desalination of brackish water network, the outer circulation structure forms a second water circulation network for desalination of brackish water;

The internal circulation structure includes a solar heat collector 15, which is used to collect heat during the day and store it in the first water circulation network; the brackish water forms desalinated water through evaporation and condensation during the circulation of the first water circulation network and transfers heat to the second water circulation Network, so that the second water circulation network gets heat and stores it; at night, the heat accumulated in the first water circulation network and the second water circulation network is released, so that the brackish water condenses during the circulation of the second water circulation network to form desalinated water.

There are three reasons for the low water production of traditional solar stills: first, the latent heat of condensation of water vapor is not reused, but is lost to the atmosphere through the cover plate; second, the heat transfer mode of natural convection in traditional solar stills, It greatly limits the improvement of the thermal performance of the distiller; the third is that the heat capacity of the brackish water to be evaporated is too large, which limits the increase of the operating temperature, thereby weakening the driving force of evaporation. Therefore, in order to increase the water yield of the solar distillation system, the above-mentioned defects must be overcome.

In the brackish water desalination device provided by the embodiment of the present invention, during the day, when the brackish water circulates in the internal circulation structure, the solar heat collector 15 collects heat to continuously increase the temperature of the brackish water, so that the brackish water in the first water circulation network circulation Salt water keeps accumulating heat. At the same time, the heated brackish water evaporates and condenses to form desalinated water. The heat released during the condensation process is collected by the brackish water in the second water circulation network, and is continuously accumulated in the second water circulation network as the brackish water circulates in the second water circulation network. middle. At night, the water in the first water circulation network continuously releases heat, and the brackish water in the second water circulation network continuously condenses to form desalinated water during the circulation process.

It can be seen that the solar brackish water desalination device provided by the embodiment of the present invention utilizes natural cold and heat sources and adopts a two-layer water circulation network. The inner layer directly uses solar energy to store heat, and the outer layer uses evaporation to generate secondary heat storage of latent heat of vaporization. Heat recovery is realized, and at night, the heat accumulated during the day is used to realize continuous distillation of brackish water day and night, which doubles the desalination efficiency; and the use of natural cold and heat sources saves costs.

Moreover, when the temperature drops at night, the temperature of the brackish water in the first water circulation network continues to drop. When the salt concentration in the brackish water reaches a certain value, salt crystals are precipitated, which saves the step of drying the brackish water concentrated water, and at the same time realizes the brackish water Take advantage of it.

Wherein, the outer layer heat storage pool 21 is communicated with a replenishment pipeline 3 that introduces brackish water, and the port of the water replenishment pipeline 3 for connecting the outer layer heat storage pool 21 is provided with a first float valve 18; the outer layer heat storage pool 21 is connected with the inner layer The layer heat storage tanks 11 are connected, and a second float valve 27 is arranged at the connection point between the two.

The external brackish water first enters the outer heat storage tank 21 through the replenishment pipeline 3 , and the liquid level is adjusted by the second float valve 27 . The brackish water in the outer layer heat storage pool 21 enters the inner layer heat storage pool 11 again, and the first float valve 18 provided at the connection between the two can adjust the water intake, so that the brackish water in the inner layer heat storage pool 11 Maintain a certain fluid level.

The brackish water adopts the method of replenishing water from the external water supply pipeline 3-the outer heat storage pool 21-the inner heat storage pool 11 in order to ensure that the outer heat storage pool 21 has a large amount of water replenishment and a small evaporation, and is always in an unsaturated state, reducing the Maintenance workload due to salt precipitation or scaling.

Natural heat insulation function It should be noted that both the outer layer heat storage pool 21 and the inner layer heat storage pool 11 are buried, and the double-layer heat storage pool has the function of natural heat insulation and heat preservation, which is beneficial to heat storage and heat preservation, and can Reduce construction costs.

Specifically, the internal circulation structure also includes an inner layer heat storage pool 11 and an inner layer top cover 12; the inner layer top cover 12 is covered on the inner layer heat storage pool 11; the water inlet of the solar collector 15 and the inner layer heat storage The water pool 11 is connected, and the water outlet is connected through the top of the inner layer top cover 12, so that the brackish water returns to the inner layer heat storage pool 11, thereby forming a first water circulation network.

Specifically, the internal circulation structure also includes a water distribution nozzle 14 arranged on the top of the inner layer top cover 12, and the water distribution nozzle 14 is connected with the water outlet of the solar collector 15 for spraying brackish water into the inner layer storage. Hot pool11.

Here, the solar heat collector 15 is preferably a vacuum glass tube heat collector, and the inner top cover 12 is preferably made of a 0.3 mm thick stainless steel plate of type 316, which can obtain a relatively ideal condensation heat transfer effect while ensuring corrosion resistance .

The inner heat storage pool 11 communicates with the water inlet of the solar heat collector 15 through a first pipe 16 , and a first circulation pump 17 is arranged on the first pipe 16 .

Further, a first water collection tank 13 is provided inside the inner roof 12 for collecting the desalinated water in the first water circulation network.

In at least one embodiment of the present invention, the outer circulation structure includes an outer heat storage pool 21 and an outer top cover 22; the outer top cover 22 is set on the outer heat storage pool 21; The top of the layer top cover 22 is connected, so that the brackish water in the outer layer heat storage pool 21 enters between the outer layer top cover 22 and the inner layer top cover 12 and returns to the outer layer storage along the outer surface of the inner layer top cover 12. The hot water pool 21 forms the second water circulation network.

Specifically, the outer circulation structure also includes a water distribution tank 24 arranged on the top of the outer layer top cover 22, and the water distribution tank 24 communicates with the outer layer heat storage pool 21 for introducing brackish water into the outer layer top cover 22 and the inner layer top cover. 12 and return to the outer heat storage pool 21 along the outer surface of the inner roof 12.

Here, the outer layer top cover 22 is preferably made of transparent white glass, which can maximize the use of solar energy and simultaneously play the role of heat insulation.

The outer layer heat storage tank 21 is in communication with the water distribution tank 24 through the second pipeline 25, and the second circulation pump 26 is arranged on the second pipeline 25.

Further, the inner side of the outer top cover 22 is provided with a second water collection tank 23 for collecting the desalinated water in the second water circulation network.

It should be noted that the first circulation pump 17 and the second circulation pump 26 preferably use plastic self-priming pumps or diaphragm self-priming pumps, which is beneficial to equipment maintenance.

In addition, the brackish water desalination device provided by the embodiment of the present invention also includes an inspection door 19 and a pool cover 28, the inspection door 19 is arranged on the inner roof 12, and the water pool cover 28 is arranged on the outer heat storage tank 21 . The inspection door 19 and the pool cover 28 are used for cleaning and maintenance of the inner heat storage pool 11 and the outer heat storage pool 21 respectively

In combination with the specific structure of the brackish water desalination device provided in the above embodiments, the working process of the brackish water desalination device is described in detail.

During the day, the brackish water in the inner heat storage tank 11 enters the water inlet of the solar heat collector 15 along the first pipeline 16 under the drive of the first circulation pump 17, and flows out from the water outlet of the solar heat collector 15. During this process, the brackish water absorbs solar energy and increases in temperature. The brackish water flowing out from the water outlet of the solar heat collector 15 reaches the top of the inner roof 12 , and is sprayed downwards by the water distribution nozzle 14 , and the brackish water falls into the inner layer heat storage pool 11 . In the process of spraying the brackish water downward, due to the high temperature of the brackish water, part of the brackish water will evaporate into water vapor and condense on the inner wall of the inner roof 12, and this part of the water vapor will form desalinated water along the inner layer. The inner wall of the top cover 12 flows downwards and is collected by the first sump 13 . Circulating successively, the temperature of the brackish water in the inner layer heat storage pool 11 continues to rise. It should be noted that when the brackish water evaporates and condenses on the inner wall of the inner roof 12, latent heat of vaporization will be released.

The brackish water in the outer heat storage pool 21 is driven by the second circulation pump 26 to reach the top of the outer roof 22 along the second pipeline 25, and is evenly distributed downwards by the water distribution tank 24. Since the inner roof 12 is located Inside the outer roof 22, the brackish water spilled from the water distribution tank 24 enters between the outer roof 22 and the inner roof 12, and falls on the outer surface of the inner roof 12 under the action of gravity, along the inner roof. The outer surface of the cover 12 flows down into the outer heat storage tank 21 . During the process of the brackish water flowing downward along the outer surface of the inner roof 12 , the latent heat of vaporization released by the water vapor condensed on the inner side of the inner roof 12 is absorbed by the part of the brackish water. Circulating successively, the temperature of the brackish water in the outer layer heat storage pool 21 continues to rise. It should be noted that, when the brackish water flows along the outer surface of the inner roof 12, part of the brackish water evaporates and condenses on the inner wall of the outer roof 22, and this part of water vapor forms desalinated water along the outer roof. The inner wall of 22 flows down and is collected by the second sump 23.

At night or when the sun sets, the solar heat collector 15 no longer collects heat, and the heat storage of the brackish water in the inner heat storage tank 11 stops. In the continuous circulation of the brackish water in the first water circulation network, the inner heat storage tank The temperature of the brackish water in 11 keeps dropping, and when the salt concentration in the brackish water reaches a certain value, salt crystals are precipitated.

As night falls, the ambient temperature continues to decrease, and the brackish water in the outer heat storage pool 21 is continuously circulated in the second water circulation network, part of the brackish water condenses on the inner wall of the outer roof 22, The condensed water is collected in the second water collection tank 23 and used as desalinated water.

The present invention also provides a brackish water desalination method, using any brackish water desalination device provided in the above embodiments to collect desalinated water, including the following steps:

Diurnal cycle desalination: the solar collector 15 in the internal circulation structure collects solar energy, and the heat is stored in the first water circulation network through the circulation of brackish water in the first water circulation network; when the brackish water circulates in the first water circulation network Evaporation and condensation form desalinated water, and release latent heat of vaporization, which is absorbed by the brackish water in the second water circulation network; the brackish water in the second water circulation network stores heat in the second water circulation network through circulation;

Night circulation desalination: the heat accumulated in the first water circulation network and the second water circulation network is released, so that the brackish water circulating in the second water circulation network condenses to form desalinated water.

In summary, the brackish water desalination device and the brackish water desalination method provided by the embodiments of the present invention have the following technical advantages:

1. It adopts the design of double-layer heat storage pool and the design of secondary utilization of evaporation latent heat. The inner layer directly uses solar energy to store heat, and the outer layer uses evaporation to generate secondary heat storage of latent heat of vaporization, which realizes heat recovery and utilizes the accumulated heat during the day at night. The heat realizes continuous distilling of brackish water day and night, and doubles the desalination efficiency;

2. Utilizing natural cold and heat sources, without the need for additional complex equipment and power, distributed in-situ desalination and utilization of brackish water can be used to save costs;

3. The brackish water adopts the method of replenishing water from the external water supply pipeline 3-outer heat storage pool 21-inner heat storage pool 11 in order to ensure that the outer heat storage pool 21 has a large amount of water replenishment, a small amount of evaporation, and is always in an unsaturated state. The inner hot water storage pool 11 realizes continuous concentration, saves the step of drying brackish water concentrated water, and at the same time maximizes the use of brackish water, reducing the maintenance workload due to salt precipitation or scaling;

4. The whole device adopts the buried double-layer structure, which has the function of natural heat insulation;

5. It is used in the central and western regions where water is scarce in my country. It can make full use of the abundant solar energy resources and the characteristics of large temperature difference between day and night to meet the huge demand for desalination of brackish water in the central and western regions.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (6)

1. A brackish water desalination apparatus, comprising: an inner circulation structure and an outer circulation structure, the inner circulation structure and the outer circulation structure forming a double-layer structure;

the inner circulation structure forms a first water circulation network for desalting the brackish water, and the outer circulation structure forms a second water circulation network for desalting the brackish water;

the internal circulation structure comprises a solar heat collector (15) for collecting heat in the daytime and storing the heat in the first water circulation network; the brackish water forms desalted water through evaporation and condensation in the circulation process of the first water circulation network and transfers heat to the second water circulation network, so that the second water circulation network obtains and stores the heat; when the night arrives, the heat accumulated by the first water circulation network and the second water circulation network is released, so that the brackish water is condensed to form desalted water in the circulation process of the second water circulation network;

the inner circulation structure comprises an inner layer heat storage water tank (11), an inner layer top cover (12) and a water distribution spray head (14) arranged at the top of the inner layer top cover (12); the inner layer top cover (12) is covered on the inner layer heat storage water tank (11); the water inlet of the solar heat collector (15) is communicated with the inner layer heat storage water tank (11), and the water outlet passes through the top of the inner layer top cover (12) and is communicated with the water distribution nozzle (14), so that brackish water returns to the inner layer heat storage water tank (11);

the external circulation structure comprises an external heat storage pool (21) and an external top cover (22); the outer layer top cover (22) is covered on the outer layer heat storage water tank (21); the outer layer heat storage water tank (21) is communicated with the top of the outer layer top cover (22) so that brackish water in the outer layer heat storage water tank (21) enters between the outer layer top cover (22) and the inner layer top cover (12) and returns to the outer layer heat storage water tank (21) along the outer surface of the inner layer top cover (12);

a first water collecting tank (13) is arranged on the inner side of the inner layer top cover (12) and is used for collecting desalted water in the first water circulation network;

a second water collecting tank (23) is arranged on the inner side of the outer layer top cover (22) and is used for collecting desalted water in the second water circulation network;

the outer layer heat storage water tank (21) is communicated with a water supplementing pipeline (3) for leading in brackish water, and a second ball float valve (27) is arranged at a port of the water supplementing pipeline (3) for connecting the outer layer heat storage water tank (21); the outer-layer heat storage water tank (21) is communicated with the inner-layer heat storage water tank (11), and a first ball float valve (18) is arranged at the communication position of the outer-layer heat storage water tank and the inner-layer heat storage water tank.

2. The brackish water desalination device according to claim 1, characterized in that the inner layer heat storage water tank (11) is communicated with the water inlet of the solar heat collector (15) through a first pipeline (16), and a first circulating pump (17) is arranged on the first pipeline (16).

3. The brackish water desalination plant according to claim 1, characterized in that the outer circulation structure further comprises a water distribution tank (24) arranged at the top of the outer layer top cover (22), the water distribution tank (24) being in communication with the outer layer heat storage water tank (21) for guiding brackish water between the outer layer top cover (22) and the inner layer top cover (12) and back to the outer layer heat storage water tank (21) along the outer surface of the inner layer top cover (12).

4. A brackish water desalination plant according to claim 3, wherein the outer heat storage water tank (21) is connected to the water distribution tank (24) through a second pipe (25), and a second circulation pump (26) is arranged on the second pipe (25).

5. The brackish water desalination device according to claim 1, wherein the outer layer heat storage water tank (21) and the inner layer heat storage water tank (11) are both arranged in a buried manner.

6. A method for desalinating brackish water, characterized in that the method for collecting desalinated water by using the brackish water desalination apparatus according to any one of claims 1 to 5 comprises the steps of:

day cycle desalination: the solar heat collector (15) in the internal circulation structure collects solar energy, and heat is stored in the first water circulation network through the circulation of brackish water in the first water circulation network; evaporating and condensing brackish water to form desalted water when the brackish water circulates in the first water circulation network, releasing vaporization latent heat, and absorbing the brackish water in the second water circulation network; the brackish water in the second water circulation network stores heat in the second water circulation network through circulation;

and (3) circularly desalting at night: and releasing heat accumulated by the first water circulation network and the second water circulation network, so that brackish water circulating in the second water circulation network is condensed to form desalted water.

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