JPH0271891A - Solar still containing heat storage tank - Google Patents

Abstract

PURPOSE:To operate the title still day and night by using a heat storage tank contg. a heating medium for cooling instead of seawater, and utilizing the heat storage tank as a heat source at night. CONSTITUTION:A heat collecting plate 3 is provided so that a substantially closed distillation chamber 2 is formed between the outer surface of the heat storage tank 1 and the plate 3. A seawater supply means 4 is furnished respectively in the vicinity of the outer surface of the tank 1 and inner surface of the plate 3, and fluid recovery means 5 and 6 are provided at the respective bottoms. The tank 1 consists of a vessel made of a material having relatively high heat conductivity and inert to the heating medium such as titanium, stainless steel, a corrosion-resistant coating material, an industrial heat-resistant synthetic resin, and the heating medium contained in the vessel. Alternatively, the distance between the tank 1 and the plate 3 is increased, and a heat-transfer plate 25 can be provided in between. By such a constitution, solar heat energy is absorbed in the one tank 1 in the daytime, the heat is liberated at night, seawater can be respectively evaporated and condensed in the process, the pipeline is simplified, and the whole still is also simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solar still with a built-in heat storage tank. More specifically, the heat required for heating seawater and condensing water vapor is exchanged during the day and through cold and hot heat that are alternately stored in one heat storage tank by taking advantage of the day and night cycles that exist on Earth. Concerning solar stills performed throughout the night.

[Prior Art] Various types of solar stills for desalinating seawater have been known. This kind of solar still is
Because we rely on solar heat, which is thermal energy that cannot be controlled and has a relatively small amount of heat per unit area,
The most important issue is to create a structure that can utilize that thermal energy as efficiently as possible.

One of the basic technologies for these devices is to provide a distillation chamber in which an evaporation plate and a condensation plate face each other, and heat the evaporation plate with solar heat while keeping the distillation chamber essentially closed. The seawater flowing down the inner surface is evaporated and concentrated to produce water vapor.
It is known that this is condensed on the inner surface of the condensing tube facing each other to produce distilled water.

As a further development of this technology, one or more heat transfer plates are inserted between the evaporation plate and the condensation plate, and the water vapor generated on the evaporation plate is condensed on the heat transfer plate to produce distilled water. There is a system in which the heat exchanger plate is heated by the condensation latent heat given during the process to perform the next stage of evaporation, and the heat is radiated at the final stage of the condensation plate, which is called a multi-effect solar still. This multi-effect solar still achieves high thermal efficiency by directly using the latent heat of condensation of water vapor for the next stage of heating.

As such a multi-effect solar still, the
Those described in JP-A-41314 and JP-A-57-184442 are known.

An important factor for increasing thermal efficiency in such solar stills is the release of latent heat of condensation, which is ultimately given to the condensing plate. In other words, if heat is not dissipated appropriately, the temperature of the condensing plate will rise too much, making it impossible to change the temperature difference necessary for condensation.

Therefore, in many cases, the condensing plate is air-cooled or liquid-cooled. An example of this is the solar still proposed by Oltra ("Solar Energy Utilization Handbook", pp. 859-880, published by the Japan Solar Energy Society (1985)).

In Ordra's device, a circular tube is also welded to the outside of the condensing plate, and seawater is passed through it from the bottom to the top. Seawater is preheated as it rises in the tube and then supplied to the distillation chamber.

Originally, seawater is heated by the evaporator plate to a high temperature, and then discharged as concentrated water outside the system, which generates heat in a normal water-cooled distillation system, but in this Ordra device, the condensation plate Apply the heat recovered from the
Ideally, all of the heat received from the heat source is used for evaporation.

[Problems to be Solved by the Invention] In the Aldra device mentioned above, heat is recovered for preheating seawater, but in order to achieve sufficient cooling of the condensing plate, the released latent heat must be 5 BQkcal per 1 kg of water vapor. Therefore, a large amount of low-temperature seawater is required, which exceeds the amount used for distillation. Furthermore, because there are more parts of the equipment through which seawater passes, problems such as scale formation and corrosion will also increase.

Furthermore, all conventional devices tend to require large-scale power equipment such as piping equipment and pumps.

The purpose of the present invention is to improve such a water-cooled distillation method, and to use a heat storage tank containing a heat medium instead of seawater for cooling, and to use the heat storage tank as a heat source at night. The purpose of this project is to provide a solar still that can be operated throughout the day and at night.

A further object of the present invention is to provide a solar still that requires less piping equipment, has a simple structure, and minimizes scale and corrosion problems.

[Means for Solving the Problems] The solar still incorporating a heat storage tank of the present invention has a space between the heat storage tank and the outer surface of the heat storage tank to form a substantially sealed distillation chamber. A heat collecting plate provided, a seawater supply means provided near the top of each of the outer surface of the heat storage tank and the inner surface of the heat collecting plate, and a liquid flowing down along the outer surface of the heat storage tank and the inner surface of the heat collecting plate. and collection means for separately collecting the.

At least one heat transfer plate is provided to partition the space between the heat storage tank and the heat collection plate, and further seawater supply means is provided near the top of each of the inner and outer surfaces of the heat transfer plate,
In addition, when other collection means are provided near the bottom, a multi-effect solar still can be used.

[Operation] During the day, seawater is supplied from the seawater supply means on the heat collecting plate side. As a result, the seawater flowing down the inner surface of the heat collecting plate heated by the sun evaporates, and the concentrated seawater is collected from the collecting means on the heat collecting plate side and discharged. Further, the evaporated water vapor condenses on the surface of the heat storage tank, flows down, and is taken out as fresh water by the recovery means on the heat storage tank side.

During operation during sunlight, the heat storage tank acts as a cold source,
itself gradually accumulates heat of condensation and its temperature rises.

Next, at night, seawater is supplied from the seawater supply means on the heat storage tank side. Thereby, the seawater flowing down on the outer surface of the heat storage tank is evaporated by the heat stored in the heat storage tank, and the concentrated seawater is recovered by the recovery means on the heat storage tank side and discharged.

Further, the evaporated water vapor condenses on the inner surface of the heat collecting plate, which is cooled by the outside air at night, flows down, and is taken out by the recovery means on the heat collecting plate side.

Therefore, at night, the heat storage tank acts as a heat source,
Since it is cooled and its temperature drops by removing latent heat of vaporization, it is effectively used as a cold heat source during daytime operations.

As described above, the apparatus of the present invention desalinates seawater by utilizing the opposite temperature difference between the heat storage tank and the heat collecting plate during the day and night.

In other words, in the conventional desalination method using solar heat, a high-temperature heat source generated by daytime sunlight is used directly or is generally stored and used, but the present invention uses a rhythmic day and night heat source generated by sunlight. The desalination equipment was constructed by combining a heat source cycle of one heat storage tank with a half-cycle delay.

Note that when one or more heat transfer plates, for example n heat transfer plates, are interposed between the heat storage tank and the heat collection plate, the latent heat of vaporization LV of water in an ideal state is apparently reduced to l/n, so as mentioned above, As a multi-effect, energy-saving solar still, seawater can be desalinated more efficiently.

[Example] Next, a solar still (hereinafter referred to as an apparatus) of the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the device of the present invention, FIG. 2 is a sectional view showing another embodiment of the device of the present invention, and FIG. 3 is a sectional view showing another embodiment of the device of the present invention. 4 is a longitudinal sectional view showing another embodiment of the device of the present invention, and FIG. 5 is a sectional view of main parts.
6 is a graph showing the effects of the device of the present invention.

FIG. 1 shows a basic embodiment of the device of the invention.

The device consists of a heat storage tank (1) and a heat collection plate (3
). A seawater supply means (4) is provided near the top of each of the outer surface of the heat storage tank (1) and the inner surface of the heat collection plate (3), and a recovery means (5) is provided at the bottom of each. (6) is provided.

The heat storage tank (1) is made of a material such as titanium, stainless steel, cupronickel-containing metal, corrosion-resistant coating material, industrial heat-resistant synthetic resin, etc., which has a relatively high heat transfer effect and is not corroded by the heat medium, and is substantially sealed. It consists of a container and a heating medium housed inside the container. The outer periphery of the heat storage tank (1) except for the distillation chamber side is covered with a heat insulating material (1a), and the upper part of the heat storage tank (1) has an opening (1b) for introducing a heat medium.
is provided. Furthermore, the opening (1b) is provided with an automatic air vent valve (lc).

The type and amount of heat medium can be selected based on thermal stability and heat capacity, but it must have a high heat transfer coefficient, be less corrosive to equipment, be nonflammable, inexpensive, harmless, and It is also required to be anti-freeze. Specifically, an aqueous solution in which an antifreeze agent is dissolved, glycerin, propylene glycol, or a mixture of these and water is preferably used. Especially in the case of high temperatures, oil-based media can also be used.

The heat collection plate (3) is also made of the same material as the heat storage container (1), but its outer surface is coated with black paint or coated with a selective absorption film to enhance heat collection and heat dissipation effects. It is preferable to leave it there.

In the apparatus shown in FIG. 1, a glass cover (8) is provided on the outside of the heat collecting plate (3), and a heating chamber (9) is formed between the heat collecting plate (3) and the cover (8). Ventilation dampers (9a) are provided above and below the heating chamber (9), respectively.

The outer surface of the heat storage tank (1) and the inner surface of the heat collecting plate (3) act as both an evaporation surface and a condensation surface alternately during the day and at night, and the seawater supplied and flowing down from the top acts Hydrophilic wick adhesive (II) and corrosion-resistant adhesive (III) are used to ensure effective evaporation and water vapor condensation.
It is pasted as shown in the figure. That is, the hydrophilic wick is used to control the flow state and speed of seawater and distilled water, and to facilitate the exchange of heat.

The seawater supply means (4) includes a piping route (141) provided at the top of the stone and distillation chamber (2) that is alternately connected to a seawater tank or a seawater supply pump via a switching valve 03 such as a four-way valve. Consists of a guide plate (le, etc.).Guide plate (18 is the piping route Q41.(
It is inclined so as to guide the seawater flowing down from E9 to the outer surface of the heat storage tank (1) and the inner surface of the heat collecting plate (3).

The recovery means (5) and (6) separate the heat storage tank (1) side and the heat collection plate (3) side on the bottom plate of the distillation chamber (2) and mix distilled water and concentrated water. There is a partition plate erected to prevent
It is composed of 9 and ■. The outlet Og, (2) is also preferably connected to the distilled water tank via a four-way valve or the like.

Next, we will explain how to use and function of the solar still, which is constructed in a diagonal manner.

First, during the day, seawater is guided through the piping route surface shown by the solid line, and the hydrophilic wick I on the inner surface of the heat collecting plate (3)
Let seawater flow down from the top of HI).

In that case, the inner surface of the heat collector plate (3) acts as an evaporation surface,
The seawater that descends through the hydrophilic wick layer 01) on its inner surface receives heat from the heat collecting plate (3), which is heated by direct solar heat and indirect radiant heat such as diffused reflection in the heating chamber (9), and evaporates. As it descends, the salt concentration increases and is discharged from the outer outflow head.

The water vapor in the distillation chamber (2) condenses on the outer surface of the heat storage tank (1) facing the inner surface of the heat collecting plate (3). The condensed distilled water descends through the hydrophilic wick (T) on the surface of the heat storage tank, passes through the inner outlet passage □□□, and is stored in the distilled water tank.

The above evaporation and condensation effects are due to the existence of a temperature gradient in which the outside of the device is hot and the inside is cold during sunlight.
As will be described later, since the heat storage tank (1) is cooled at night, the steam condensation action is performed efficiently.

During daytime operation, the heat medium in the heat storage tank (1) absorbs condensation heat from water vapor and stores heat, gradually raising its own temperature. Therefore, it is preferable that the heat capacity of the heat storage tank (1) is as large as possible. Next, at night,
First, switch the switching valve 03 and the like. As a result, seawater is guided through the nighttime piping route 0Φ shown by the broken line, flowing down along the outer surface of the heat storage FfI (11), and concentrated water is discharged from the inner outlet Og. The heat of the heat medium in the heat storage tank is used as the heat of evaporation of seawater, and the heat medium itself is cooled.

In addition, the steam in the distillation chamber (2) condenses on the inner surface of the heat collecting plate (3), which is cooled by the outside air at night, and the heat collecting plate (3)
is recovered via the hydrophilic wick layer 01) and the outer outflow channel head.

As described above, the heat medium in the heat storage tank (1) cooled at night is used as a cold source for condensation during the day.

In the device of the present invention, the outer surface of the heat storage tank (1) and the heat collecting plate (3)
The inner surface of the tube is used alternately as the evaporation surface and the condensation surface. Therefore, when switching between day and night, the seawater supply to the hydrophilic wick on the side previously used as an evaporation surface is discontinued, it is self-cleaned for a short period of time with fresh water that has begun to condense, and then drained into distilled water. It is preferable to prevent salt from being mixed into the water. Note that such cleaning has the advantage of dissolving scale from seawater and preventing it from being constantly deposited in the hydrophilic wick.

The basic structure and operation of the present invention have been explained above based on FIG. It is preferable to interpose a plurality of heat exchanger plates between the heat storage tank (1) and the heat collecting plate (3) to increase the number of effects and create a multiple effect type energy-saving solar still.

In the apparatus shown in FIG. 2, the distance between the heat storage tank (1) and the heat collecting plate (3) is increased, and two heat exchanger plates are provided between them, so that the number of distillation effects approaches three. The inner and outer surfaces of the heat exchanger plate are respectively provided with hydrophilic wick layers (g) and 01) similar to those described above.

The heat transfer plate is preferably one that does not transmit water vapor and has a high heat transfer rate, such as titanium, stainless steel, etc.
01~1mm thick metal sheet or foil, or 50~2mm thick
Polyester, nylon or polyvinylidene halide films with a thickness of 0.00 Alm are suitable.

This device has the advantage of the conventional multi-efficiency type in that the outer surface of the heat exchanger plate acts as a condensing surface during the day, and the inner surface acts as an evaporation surface using the heat of condensation. Conversely, at night, the inner surface of the heat exchanger plate acts as a condensation surface, and the outer surface acts as an evaporation surface. However, in other respects, the basic structure is the same as that shown in FIG.

In any of the above devices, it is better to have the evaporating surface and the condensing surface as close as possible, but if they are too close, they tend to come into contact with each other due to a slight external force. Therefore, as shown in Figure 3, a water-repellent air-permeable membrane and a mesh spacer are inserted between the wicks 00) and 00) to allow only water vapor to pass through but prevent seawater and distilled water from coming into contact with each other. is preferred.

The devices shown in Figures 1 and 2 all have flat heat collecting plates (3).
, a heat exchanger plate, and a distillation chamber (2), but the present invention is not limited to such a case, and various shapes can be adopted, such as the cylindrical shape shown in FIGS. 3 to 5, for example.

In the cylindrical device shown in Fig. 3, (8) is a cylindrical glass cover, and the heating chamber (9) is located between the heat collecting plate (3) and the heating chamber (9).
is for holding high temperature air.

Further, (7) in FIG. 3 is a rectifying plate for smoothing the convection of the heat medium, and facilitates convection in the direction of the arrow (P), for example, during the day when the heat storage tank (1) is a source of cold heat.

When the thermal energy absorbed in the heat storage tank (1) during daytime distillation is released to the outside at night, distillation is performed again.
- Distillation is carried out one round trip during the day and night.

Therefore, the utility number of the device in Figure 3 is 4 in the ideal state.
It becomes X2”-8.

The device shown in Figures 3 to 5 has a cylindrical heat storage tank (1) in the center, and two or three similarly cylindrical heat exchanger plates are arranged concentrically on the outside of the tank, and a cylindrical heat storage tank (1) is arranged concentrically on the outside of the tank. shaped heat collecting plate (3)
It has been established. Even more heat storage! (A cylindrical current plate (7) is provided inside 11. The function and effect of this plate are substantially the same as those of the flat plate-like device shown in FIG. 1.

Next, the operation of the multilayer solar still will be explained in detail according to the daily sunlight cycle.

The following explanation and experimental data are based on the three layers shown in Figure 2 (
This is for a flat solar still with two heat exchanger plates.

Using the solar still shown in Figure 2, seawater desalination experiments were conducted in Hyogo Prefecture from August 24th to August 25th, 1985 (Sunny Weather). The measurement results of the temperature cycle of the heat collecting plate (A), the temperature cycle of the heat medium in the heat storage tank (B), and the outside temperature cycle (C) at that time are shown in FIG. Note that for the heat collecting plate temperature and the heat storage tank temperature, the values measured at the top position are respectively displayed.

At dawn, when the later solar radiation begins to pass through the glass cover (8) and heat the heat collecting surface (3), the temperature of the heat collecting plate (3) begins to rise along the cycle (A). Therefore, seawater was supplied through a seawater supply means during the day and distillation was performed.

During that time, the solar thermal energy absorbed by the heat collecting plate passes through three layers of distillation chambers, repeating evaporation (latent heat absorption) and condensation (latent heat release) three times in total for each layer, and finally the heat storage tank ( 1
), and the temperature of the heat storage tank is increased along cycle (B).

The amount of solar radiation reaches its maximum value from around 12:00, and then gradually begins to decrease, reaching 0 around 199:00. Therefore, the temperature of the heat collecting plate also changes as in cycle (A), and 19
Around 9 o'clock the temperature becomes equal to the outside temperature, and in the morning (around 6 o'clock)
The temperature remains the same as the outside temperature until

On the other hand, cycle (B) of the heat storage tank temperature does not drop immediately even when the amount of sunlight decreases, but gradually drops from around 166:00 until the morning (around 5:00).

Therefore, the heat collection plate temperature cycle (A) and the heat storage tank temperature cycle (B) intersect at 3:00 p.m. From then until morning, the heat storage tank temperature cycle (B) is the heat collection plate temperature cycle ( Cycle (B) and Cycle (C) approach the outside temperature almost at the same time until after the 5th cycle in the morning.

As can be understood from the explanation above, the solar still of the present invention has a built-in suitable heat storage tank, so that during the day (A
) - (B) is distilled using the temperature difference, and during the day (B) -
It can be said to be a solar still that makes distillation possible again by applying the temperature difference in (A).

Next, we will use the widely known basin-type solar still (see "Solar Energy Utilization Handbook", Chapter 10, No. 2, page 851, published by the Japan Solar Energy Society) as a comparative example, and use it and the implementation of Figure 5. A comparative experiment of distilled water collection conducted simultaneously with the example device will be explained. In addition, for both devices, the distilled water yield etc. are based on the heat collecting area l111'
The values were compared. Table 1 shows the results of measurements taken over a 24-hour period from 6 a.m. on August 24, 1985 to 6 a.m. on August 25, 1985.

The total efficiency listed in Table 1 is the amount of latent heat energy required to evaporate the yield of distilled water divided by the amount of solar radiation energy, that is, the latent heat of vaporization is calculated as 5BOkcal/
kg, ((distilled water yield x O,560)/solar radiation f
f1) xto.

It is calculated by

It can be seen from Tables 1 to 5 that the solar stills shown in FIG. 5 have an energy efficiency about 5 to 6 times that of the basin type solar still.

E Effects of the Invention] The device of the present invention uses a heat storage tank as a refrigerant during the day, and releases the thermal energy stored during the day at night to use it for evaporation of seawater. In other words, the device of the present invention absorbs solar thermal energy into a single heat storage tank during the day and radiates it at night, acting like a storage battery that repeatedly charges and discharges. It repeats condensation. As a result, in the device of the present invention, the piping system is simplified compared to indirect heating type or water cooling type.
The whole device is simple.

Moreover, it has the advantage of being easy to maintain because scale in seawater does not accumulate easily. Furthermore, since the distillation action is carried out throughout the day and night, the recovery efficiency of distilled water per projected area is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the device of the present invention, FIG. 2 is a sectional view showing another embodiment of the device of the present invention, and FIG. 3 is a sectional view showing another embodiment of the device of the present invention. 4 is a longitudinal sectional view showing another embodiment of the device of the present invention, and FIG. 5 is a sectional view of main parts.
6 is a graph showing the effects of the device of the present invention. (Main symbols in the drawing) (1): Heat storage tank (a: Distillation chamber (3): Heat collection plate (4): Seawater supply means (5), (6): Recovery means (to): Heat transfer plate Figure Figure 3 Figure 4/ Figure 5

Claims (1)

[Scope of Claims] 1. A heat storage tank, a heat collecting plate provided with a space between the outer surface of the heat storage tank and the outer surface of the heat storage tank to form a substantially closed distillation chamber; A heat storage tank consisting of a seawater supply means provided near the top of each of the inner surfaces of the heat plates, and a recovery means for separately collecting the fluid flowing down along the outer surface of the heat storage tank and the inner surface of the heat collection plate. Solar still with built-in. 2. At least one heat transfer plate is provided to partition the space between the heat storage tank and the heat collection plate, and another seawater supply is provided near the top of each of the inner and outer surfaces of the heat transfer plate. 2. Apparatus according to claim 1, further comprising means and further retrieval means near the bottom. 3. The device according to claim 1, wherein a hydrophilic wick layer is formed on the outer surface of the heat storage tank and the inner surface of the heat collecting plate, respectively. 4. The apparatus according to claim 2, wherein a hydrophilic wick layer is formed on the outer surface of the heat storage tank, the inner and outer surfaces of the heat transfer plate, and the inner surface of the heat collecting plate. 5. Claim 3 or 4, wherein a water-repellent air-permeable membrane and a spacer are interposed between the hydrophilic wick layers facing each other.
The device described.