JP2013215653A - Fresh water production apparatus and fresh water production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means which distills a diluted draw solution efficiently and separates fresh water.SOLUTION: A fresh water producing apparatus includes: a forward osmosis means in which a liquid whose solvent is water is brought into contact with a draw solution in which a prescribed amount of ammonia and carbon dioxide is dissolved in water, via a semi-permeable membrane, and then water in the liquid is moved to the draw solution via the semi-permeable membrane; a distillation column which distills a diluted draw solution which is diluted with water obtained in the above means; a cooling/regeneration means which cools a gas that comprises carbon dioxide, ammonia and water vapor which can be obtained from the top part of the column of the distillation column, and which regenerates the draw solution; and a recovery means for fresh water, which substantially does not include carbon dioxide and ammonia obtained from the top part of the column of the distillation column. The fresh water production apparatus has a water vapor generating device, which generates water vapor by making use of solar energy that is collected by a light collecting device, disposed as a heating means in the distillation column.

Description

  The present invention relates to an apparatus for producing fresh water and a method for producing fresh water, for example, by purifying seawater using solar heat and a semipermeable membrane.

  As an apparatus which desalinates seawater using solar heat, there exists a thing of patent document 1, for example. This apparatus produces fresh water by condensing water vapor obtained by flash evaporation after heating seawater with a solar pond.

  Moreover, the apparatus which manufactures fresh water using a solar heat and a semipermeable membrane is also known (patent document 2). As shown in FIG. 5, the apparatus includes a reflection unit 21 that reflects sunlight, a heat collection unit 22 that receives heat of reflected sunlight and heats mineral oil or molten smoke supplied therein. The steam generator (evaporation unit) 23 for evaporating water using the mineral oil or the molten smoke heated by the heat collecting unit 22 as a heat source, the steam turbine (turbine unit) 24 driven by the evaporated steam, and the steam turbine A fresh water is produced from a generator (power generation unit) 25 driven by 24, a reverse osmosis membrane desalination device (fresh water generation unit) 26 that produces fresh water from salt water, and exhaust heat of steam that drives the steam turbine 24. It comprises a multi-stage effect desalination apparatus (fresh water generating section) 27 for watering, and a combustion furnace (combustion section) 28 for burning biomass such as dates or wheat.

  On the other hand, if a salt solution having a higher concentration than seawater is present through the semipermeable membrane, water can be transferred to the salt solution by osmotic pressure without applying pressure. If a solution in which a volatile substance is dissolved is used as the salt solution, purified water can be obtained by evaporating and separating the volatile substance by distilling the salt solution. A method using a combination of ammonia and carbon dioxide as a volatile substance has already been developed (Patent Documents 3 and 4).

  In the method of Patent Document 3, a salt solution obtained by dissolving ammonia and carbon dioxide is passed through a semipermeable membrane on the side opposite to seawater, and water in the seawater is passed through the semipermeable membrane into the salt solution. This is a method in which the obtained diluted salt solution is sent to a distillation tower to obtain water, and a mixed gas containing ammonia, carbon dioxide and water is separated, and this mixed gas is returned to the original chamber of the semipermeable membrane. .

  In the method of Patent Document 4, a salt solution obtained by dissolving ammonia and carbon dioxide is passed through a semipermeable membrane on the side opposite to seawater, and water in the seawater is passed through the semipermeable membrane into the salt solution. The obtained diluted salt solution is separated into ammonium ions and carbonate ions individually using an ion exchange membrane or distillation tower to obtain purified water, and the separated ammonium ions and carbonate ions are dissolved to dissolve the semipermeable membrane. It is a method to return to the original room.

JP-A-2-214586 JP 2006-341165 A US Patent Application Publication No. 2005 / 0145568A1 JP 2011-83663 A

  The method of Patent Document 1 has low heat collection efficiency and is not suitable for producing a large amount of fresh water.

  Since the method of Patent Document 2 is a method of converting solar heat into electricity via a heat engine, conversion loss occurs, and the power generation efficiency with the received solar heat as 1 is generally low, about 0.1 to 0.2. is there.

  On the other hand, the conventional desalination by the forward osmosis method, as in Patent Document 3, is the total amount of the aqueous solution containing dilute ammonium carbonate and the total amount of gas composed of carbon dioxide, ammonia and water separated from the distillation tower. And the concentration of carbon dioxide and ammonia in the aqueous solution containing ammonium carbonate for taking out the water entering the distillation tower increases, and when these concentrations rise, the energy for taking out the water is increased. You will need more.

  In addition, as disclosed in Patent Document 4, mixing a part of an aqueous solution containing thinned ammonium carbonate with a gas-separated one is obtained by distilling the entire amount of an aqueous solution containing thinned ammonium carbonate. While water can be taken out, the amount of water taken out is reduced, and power for circulating a part of the aqueous solution is applied, and piping for circulating a part of the aqueous solution is required, which complicates the structure.

  For this reason, the entire aqueous solution containing diluted ammonium carbonate is sent to the distillation column to reduce the energy required for distillation, and more water is taken out, and the structure is simplified by reducing power and piping. Was necessary.

The present inventor has developed the following method and apparatus as means for solving this, and applied for a patent as Japanese Patent Application No. 2011-238284.
(1) A liquid whose solvent is water and an induction solution in which predetermined amounts of ammonia and carbon dioxide are dissolved in water are brought into contact with each other through a semipermeable membrane, and water in the liquid is made into the induction solution through the semipermeable membrane. The infiltration step to be transferred and the dilution induction solution diluted with water obtained in the above step are adjusted to a predetermined temperature, and then sent to a distillation column to obtain a gas composed of carbon dioxide, ammonia, and water vapor from the top of the column. And the purified water manufacturing method which has the distillation process of obtaining purified water from a tower bottom part, and the cooling regeneration process which cools the said gas and reproduces | regenerates the said induction | guidance | derivation solution.
(2) A liquid whose solvent is water and an induction solution in which a predetermined amount of ammonia and carbon dioxide are dissolved in water are brought into contact with each other through a semipermeable membrane, and the water in the liquid passes through the semipermeable membrane and the induction solution. Osmotic means to be moved to the dilution, dilution induction solution temperature adjustment means for adjusting the total amount of the dilution induction solution diluted with water obtained by the means to a predetermined temperature, and dilution adjusted to the predetermined temperature by the temperature adjustment means Obtained from a distillation column for distilling the induction solution, cooling regeneration means for regenerating the induction solution by cooling a gas comprising carbon dioxide, ammonia, and water vapor obtained from the top of the distillation column, and the bottom of the distillation column A purified water manufacturing apparatus having purified water recovery means that contains almost no carbon dioxide and ammonia.

  The above invention is characterized in that a gas composed of carbon dioxide, ammonia, and water distilled and separated from an aqueous solution containing diluted ammonium carbonate is cooled as it is to obtain an aqueous solution and reused.

  An object of the present invention is to improve the above-described invention and provide means for efficiently distilling the dilution-inducing solution and separating fresh water.

  The present invention has been made for such a purpose, and is characterized in that solar heat is used as it is without being converted into electricity as a heat source for distilling the diluted induction solution.

That is, in the present invention, a liquid whose solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is passed through the semipermeable membrane. A forward osmosis means for transferring to the induction solution, a distillation column obtained by distilling the diluted induction solution diluted with water obtained by the means, and a gas comprising carbon dioxide, ammonia, and water vapor obtained from the top of the distillation tower A fresh water producing apparatus comprising: a cooling and regenerating means for regenerating the induction solution; and a means for recovering fresh water substantially free of carbon dioxide and ammonia obtained from the top of the distillation tower. As a heating means for the tower, a fresh water producing apparatus characterized in that a steam generator that generates water vapor using solar energy collected by a light concentrator is installed;
A liquid in which the solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is transferred to the induction solution through the semipermeable membrane. A forward osmosis means, a distillation column obtained by distilling the diluted induction solution diluted with water obtained by the means, and a gas comprising carbon dioxide, ammonia and water vapor obtained from the top of the distillation tower, and A fresh water producing apparatus comprising cooling and regenerating means for regenerating a solution, and carbon dioxide obtained from the bottom of the distillation tower and fresh water recovery means substantially free of ammonia, as heating means for the distillation tower, A heat collecting device that heats the heat medium by solar energy collected by the light collecting device and a steam generator that generates water vapor using the heat medium heated by the heat collecting device are installed. And fresh water production equipment,
A liquid in which the solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is transferred to the induction solution through the semipermeable membrane. The forward osmosis step and the dilution induction solution diluted with water obtained in the above step are fed into a distillation column to obtain a gas composed of carbon dioxide, ammonia and water vapor from the top of the column, and carbon dioxide and ammonia from the bottom of the column. A fresh water production method having a distillation step of obtaining fresh water substantially free of water and a cooling regeneration step of cooling the gas and regenerating the induction solution, wherein the concentrated sun is used as a heating source in the distillation step. A method for producing fresh water, characterized by using water vapor produced using energy;
The water vapor is water vapor produced using a heat medium heated by condensed solar energy, and provides the fresh water production method as described above.

  In the present invention, solar heat is used as a heat source, so that loss in the case of conversion to electricity is eliminated, and utilization efficiency of solar heat is improved. Therefore, compared with the case where a reverse osmosis membrane apparatus is used, the installation area of a solar heat collecting apparatus can be reduced in space and cost.

  Further, the energy required for distillation is obtained by regenerating and reusing the induction solution by cooling the gas consisting of carbon dioxide, ammonia and water, which is distilled and separated from the dilution induction solution, into an aqueous solution. And more water can be taken out, and the power and piping can be reduced to simplify the structure.

  In addition, the concentration of the induction solution can be increased or decreased by a simple method, and the apparatus can be operated efficiently.

It is a block diagram which shows an example of a structure of the apparatus of this invention. It is a block diagram which shows an example of another structure of the solar energy utilization part of the apparatus of this invention. It is a block diagram which shows an example of the solar heat collection system of this invention. It is a block diagram which shows another example of the solar heat collection system of this invention. It is a block diagram which shows an example of a structure of the conventional apparatus.

  The liquid (desalination target liquid) used for obtaining fresh water (purified water) in the present invention may be water as long as the solvent is water. Examples thereof include seawater, lake water, river water, and factory waste water.

Forward osmosis means The forward osmosis means is a means for bringing the desalination target liquid and the induction solution into contact with each other through the semipermeable membrane, and moving the water in the desalination target liquid through the semipermeable membrane to the induction solution by the difference in osmotic pressure. A semipermeable membrane device is used.

  The induction solution is an aqueous ammonium carbonate solution produced by dissolving a predetermined amount of ammonia and carbon dioxide in water. The lower limit of the predetermined amount is an amount that makes the water in the desalination target liquid a concentration that allows the water to pass through the semipermeable membrane to the induction solution, and is a salt concentration that is equal to the osmotic pressure of the desalination target liquid. . The upper limit of the concentration is determined so that a salt of ammonia and carbon dioxide, that is, ammonium carbonate, ammonium hydrogen carbonate, ammonium carbamate, etc. does not precipitate on the semipermeable membrane surface or in the distillation tower, and this can be obtained by experiment. . One of the methods for confirming whether or not precipitates are generated on the semipermeable membrane surface or in the distillation column is a method of judging whether stable operation is possible by operating for a long time. The molar ratio of ammonia to carbon dioxide is about 1.5-3. This molar ratio is also taken into consideration so that the salt of ammonia and carbon dioxide does not precipitate on the semipermeable membrane surface or in the distillation column.

  The semipermeable membrane is preferably one that can selectively permeate water, and a commercially available one, particularly a forward osmosis membrane, can be preferably used. The material is not particularly limited, and examples thereof include cellulose acetate-based, polyamide-based, polyethyleneimine-based, polysulfone-based, and polybenzimidazole-based materials. The form of the semipermeable membrane is not particularly limited and may be any of a flat membrane, a tubular membrane, a hollow fiber, and the like.

  The apparatus to which this semipermeable membrane is attached usually has a semipermeable membrane installed in a cylindrical or box-shaped container, and the desalination target liquid flows into one chamber partitioned by this semipermeable membrane, and the other chamber A known semipermeable membrane device can be used, and a commercially available product can be used.

  The entrance of the chamber through which the desalination target liquid flows is connected to a desalination target liquid reservoir (this may be the sea, a river itself, or a tank). The outlet side is usually connected by piping to the outlet of the desalination target liquid reservoir. A circulation line connecting both pipes can be provided to circulate the desalination target liquid.

  The inlet of the chamber through which the induction solution flows is piped to the cooling regeneration means, and the outlet is piped to the diluted induction solution temperature adjusting means provided as necessary, thereby forming a circulation line for the induction solution.

  In the present invention, since a high-concentration induction solution is used, there is a possibility of clogging of piping due to salt precipitation. To prevent this, the diluted induction solution is passed through the outlet piping of the cooling regeneration means. It is preferable to provide a dilution-inducing solution water passing means for watering.

Dilution induction solution temperature adjustment means The dilution induction solution temperature adjustment means is a means for adjusting the diluted induction solution to a predetermined temperature by extracting water from the desalination target liquid with a semipermeable membrane device, and this is performed by heating. Is called. Although a heating means is not ask | required, it is good to use a heat exchanger at the point which utilizes effectively the heat which generate | occur | produces in a system. As the heat source, heat such as gas obtained from the top of the distillation tower or fresh water obtained from the bottom of the tower can be used.

  The predetermined temperature at which the dilution induction solution is adjusted is a temperature at which the salt of ammonia and carbon dioxide does not precipitate, and this can be determined by experiment. This temperature adjustment is usually performed by heating. This heating can be performed by exchanging heat with the gas discharged from the top of the distillation tower and using the temperature, or by exchanging heat with purified water discharged from the bottom of the distillation tower. Temperature can also be used. Both can be used together, or another heat source can be used.

  The dilution induction solution temperature adjusting means is connected to the distillation column by piping.

Distillation Tower A known distillation column may be used, and any of a shelf system, a packing system, and the like may be used. A heater is provided at the lower part of the distillation tower, and the steam generated by heating the purified water at the lower part is brought into contact with the diluted induction solution falling from the upper part to exchange heat. A reboiler, a heat exchanger, etc. can be used for a heater.

  In the present invention, solar energy is used as a heat source of the heater. Specifically, water may be directly generated by a condensing device to generate water vapor, a condensing device and a steam generator are provided, a heat medium is heated by the condensing device, and a heat medium is generated by the steam generator. Steam may be generated by exchanging heat with water.

  In any case, the concentrator may be one that is generally used for the use of solar energy, and usually a heating tube placed at the focal point of a concave mirror or bowl-shaped reflector or commonly called a heliostat, For example, a reflector group that automatically tracks the position of the sun every few seconds is used.

  The heat medium may be one generally used for solar energy, such as a heat medium oil such as silicone oil, or a molten salt such as lithium carbonate or potassium carbonate that flows like water when dissolved by heat. .

  When solar energy is exclusively used as the heat source of the heater, it is desirable to provide a heat storage device to stabilize the heat supply, but an auxiliary heater may be provided to stabilize the heat supply. .

  In any case, when the temperature of the heat source is 100 ° C. or higher, distillation can be performed at normal pressure, but when it is lower than that, it is necessary to reduce the pressure.

Cooling and regenerating means Pipe connected to the tower top gas cooling and regenerating means from the top of the distillation tower via the dilution induction solution temperature adjusting means, cooling the gas consisting of carbon dioxide, ammonia and water vapor obtained from the top of the tower to prepare an aqueous solution Put it in a state. Although a cooling means is not ask | required, a heat exchanger can be used. Although it does not specifically limit as a heat source to cool, River water, seawater, air, etc. can be used.

Induction Solution Storage Tank The induction solution storage tank is a reservoir for the induction solution regenerated by the cooling regeneration means and can also serve as a storage tank for the induction solution prepared in advance.

Fresh water recovery means The fresh water recovery means is means for drawing out purified water containing almost no carbon dioxide and ammonia from the bottom of the distillation tower, and a pump is usually used. If there is a significant difference in height between the distillation tower and the storage tank for fresh water, and if the inside of the distillation tower is not depressurized, natural spillage can be used. Moreover, when the fresh water extracted from the tower bottom part contains some ammonia and carbon dioxide, a water treatment is implemented suitably according to a use.

Fresh water storage tank The fresh water storage tank is a fresh water storage tank extracted from the bottom of the distillation tower.

  The structure of an example of the fresh water manufacturing apparatus to which this invention is applied is shown in FIG.

  In FIG. 1, 1 is a container of a semipermeable membrane device, and a semipermeable membrane 4 is accommodated therein. Seawater 2, which is an example of a liquid whose solvent is water, enters the chamber on the left side of the container, where water 5 moves through the semipermeable membrane to the right side chamber due to the osmotic pressure difference with the induction solution, and is concentrated thereby. Seawater 3 is discharged from the left chamber. The induction solution 6 enters the right chamber, and the diluted induction solution 7 diluted with water that has passed through the semipermeable membrane 4 exits the right chamber.

  The dilution induction solution 7 exiting the chamber is heated by exchanging heat in the heat exchanger 16 and enters the distillation column 11.

  In the distillation column 11, the dilution induction solution 7 is distilled, and a gas composed of carbon dioxide, ammonia, and water vapor is discharged from the top of the column. This gas is cooled by exchanging heat in the heat exchanger 16, further exchanged with cooling water in the next heat exchanger 17, returning to the induction solution 6, and passing through the pump 18 in the container 1 of the semipermeable membrane 4. Recycled.

  On the other hand, fresh water 12 substantially free of carbon dioxide and ammonia is discharged from the bottom of the tower, and is exchanged with cooling water in the heat exchanger 20 and then discharged out of the system.

  The solar energy is condensed by the condensing device 13 to heat the water in the heating pipe (not shown), and the water becomes water vapor in the steam generator 14, and the reboiler in the distillation column 11. 15 is sent.

  FIG. 2 shows an example in which the heat medium is heated by the light collecting device 13 and is sent to the heat collecting device 19 to heat the water therein, which is converted into water vapor in the steam generator 14.

Example 1
An aqueous solution containing ammonium carbonate was used as the induction solution, and ammonia containing 8.5 mol / L and carbon dioxide containing 5.6 mol / L was used. The rest was all water, and the inflow rate of the induction solution inlet of the semipermeable membrane device was 20 kg / hr. Artificial seawater containing 35,000 mg / L of sodium chloride was used as the purification target liquid, and the inflow rate at the inlet was 200 kg / hr. The amount of water transferred to the induction solution through the semipermeable membrane was 100 kg / hr, the amount of the diluted induction solution flowing out from the outlet with the induction solution was 120 kg / hr, and the temperature was 28 ° C.

  This diluted induction solution was heated to 38 ° C. by exchanging heat with the gas coming out from the top of the distillation column, and injected into the upper stage of the distillation column.

  The distillation tower is of a 30-stage shelf type, with a reboiler on the 30th lowest stage. The temperature at the 30th stage was set to 100 ° C., and the pressure in the distillation column was set to atmospheric pressure.

Steam generated by collecting solar heat was used as the reboiler heat source. Condensing solar heat uses a concave mirror with a parabolic cross-section in the axial direction of the mirror surface, supplying water to the inside of the heating tube arranged at the focal point, and heating the collected solar thermal energy and water. By exchanging, saturated steam at 120 ° C. and 20 kg / hr was generated. The effective mirror area of the light collecting device used for collecting solar heat is 17.5 m ² . The solar heat collection system of a present Example is shown in FIG.

  In this state, the purified water coming out from the bottom of the distillation tower was 100 kg / hr, and the concentrations of carbon dioxide and ammonia contained in the purified water were 1 ppm or less.

  The gas coming out from the top of the distillation column had a temperature of 39 ° C., a molar fraction of water 0.68, carbon dioxide 0.13, and ammonia 0.19.

  This gas was heat exchanged with the diluted induction solution coming out of the semipermeable membrane device, further heat exchanged with seawater at 25 ° C., cooled to 29 ° C., converted into an aqueous solution, and returned to the semipermeable membrane device.

(Example 2)
An aqueous solution containing ammonium carbonate was used as the induction solution, and ammonia containing 8.5 mol / L and carbon dioxide containing 5.6 mol / L was used. The rest was all water, and the inflow rate of the induction solution inlet of the semipermeable membrane device was 20 kg / hr. Artificial seawater containing 35,000 mg / L of sodium chloride was used as the purification target liquid, and the inflow rate at the inlet was 200 kg / hr. The amount of water transferred to the induction solution through the semipermeable membrane was 100 kg / hr, the amount of the diluted induction solution flowing out from the outlet with the induction solution was 120 kg / hr, and the temperature was 28 ° C.

  This diluted induction solution was heated to 38 ° C. by exchanging heat with the gas coming out from the top of the distillation column, and injected into the upper stage of the distillation column.

  The distillation tower is of a 30-stage shelf type, with a reboiler on the 30th lowest stage. The temperature at the 30th stage was set to 100 ° C., and the pressure in the distillation column was set to atmospheric pressure.

Steam generated by collecting solar heat was used as the reboiler heat source. For concentrating solar heat, a concave mirror having a parabolic parabolic cross-sectional shape was used, and heat transfer oil was supplied into the heating tube disposed at the focal point. The heat medium oil used is a fluorine-based heat medium oil and has a boiling point of 350 ° C. The heat transfer oil supplied to the inside of the heating tube exchanged heat with solar heat through the heating tube while flowing through the heating tube, heated to 130 ° C. at the outlet of the light collecting device, and then stored in the heat collecting device. The stored heat transfer oil was passed through a steam generator to exchange heat with water, thereby producing saturated steam at 120 ° C. and 20 kg / hr. In this example, solar energy was collected using a condensing device having an effective mirror area of 100 m ² in order to enable stable generation of steam by solar heat stored during the daytime even when the sun goes down. The solar heat collection system of a present Example is shown in FIG.

  The purified water coming out from the bottom of the distillation column in this state was 100 kg / hr, and the concentrations of carbon dioxide and ammonia contained in the purified water were 1 ppm or less.

  The gas coming out from the top of the distillation column had a temperature of 39 ° C., a molar fraction of water 0.68, carbon dioxide 0.13, and ammonia 0.19.

  This gas was heat exchanged with the diluted induction solution coming out of the semipermeable membrane device, further heat exchanged with seawater at 25 ° C., cooled to 29 ° C., converted into an aqueous solution, and returned to the semipermeable membrane device.

  According to the present invention, since fresh water can be stably and reliably obtained from a desalination target liquid such as seawater, the present invention can be widely applied to a method and an apparatus for obtaining fresh water from seawater or the like.

DESCRIPTION OF SYMBOLS 1 Container 2 Seawater 3 Concentrated seawater 4 Semipermeable membrane 5 Water which moves through a semipermeable membrane 6 Induction solution 7 Dilution induction solution 10 Gas which consists of carbon dioxide, ammonia, and water which emerges from the top of a distillation tower DESCRIPTION OF SYMBOLS 11 Distillation tower 12 Fresh water 13 Condensing apparatus 14 Steam generator 15 Reboiler 16 Heat exchanger (dilution induction solution temperature adjustment means)
17 Heat exchanger 18 Pump 19 Heat collector 20 Heat exchanger

Claims (4)

  A liquid in which the solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is transferred to the induction solution through the semipermeable membrane. A forward osmosis means, a distillation column obtained by distilling the diluted induction solution diluted with water obtained by the means, and a gas comprising carbon dioxide, ammonia and water vapor obtained from the top of the distillation tower, and A fresh water producing apparatus comprising a cooling and regenerating means for regenerating a solution, and a means for collecting fresh water substantially free of carbon dioxide and ammonia obtained from the top of the distillation tower, the heating means for the distillation tower, An apparatus for producing fresh water, wherein a steam generator for generating water vapor using solar energy collected by a light concentrator is installed.   A liquid in which the solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is transferred to the induction solution through the semipermeable membrane. A forward osmosis means, a distillation column obtained by distilling the diluted induction solution diluted with water obtained by the means, and a gas comprising carbon dioxide, ammonia and water vapor obtained from the top of the distillation tower, and A fresh water producing apparatus comprising cooling and regenerating means for regenerating a solution, and carbon dioxide obtained from the bottom of the distillation tower and fresh water recovery means substantially free of ammonia, as heating means for the distillation tower, A heat collecting device that stores a heat medium heated by solar energy collected by the light collecting device and a steam generator that generates water vapor using the heat medium stored in the heat collecting device are installed. Fresh water production apparatus according to claim.   A liquid in which the solvent is water is brought into contact with an induction solution in which a predetermined amount of ammonia and carbon dioxide is dissolved in water through a semipermeable membrane, and water in the liquid is transferred to the induction solution through the semipermeable membrane. The forward osmosis step and the dilution induction solution diluted with water obtained in the above step are fed into a distillation column to obtain a gas composed of carbon dioxide, ammonia and water vapor from the top of the column, and carbon dioxide and ammonia from the bottom of the column. A fresh water production method having a distillation step of obtaining fresh water substantially free of water and a cooling regeneration step of cooling the gas and regenerating the induction solution, wherein the concentrated sun is used as a heating source in the distillation step. A method for producing fresh water, characterized by using water vapor produced using energy.   The fresh water production method according to claim 3, wherein the water vapor is water vapor produced using a heat medium heated by concentrated solar energy.

Images