JP7587973B2 - Inorganic salt recovery device and inorganic salt recovery method - Google Patents

Description

The present invention relates to an inorganic salt recovery device and an inorganic salt recovery method for recovering inorganic salts from inorganic salt-containing water.

As a method for recovering inorganic salts as crystals from inorganic salt-containing water, a method is known in which wastewater containing inorganic salts is concentrated using a concentrating device such as a reverse osmosis membrane treatment device, or using an evaporating device such as an evaporator, and then the inorganic salts are crystallized from the concentrated liquid using a crystallizer to recover them (see, for example, Patent Documents 1 and 2).

In reverse osmosis membrane processing, for example, when concentrating a substance with low solubility in water, the solubility becomes the rate limiting factor, and there is a problem that the concentration cannot be increased. In addition, when using an evaporation device capable of high concentration such as an evaporator, the required thermal energy increases, resulting in an increase in energy costs. Therefore, there is a need for a technology that can reduce energy costs and, for example, concentrate wastewater containing substances with low solubility in water to a high concentration. In addition, installation space and thermal energy costs for the crystallization device are required.

Patent No. 6653736 Patent No. 4781374

The object of the present invention is to provide an inorganic salt recovery device and an inorganic salt recovery method that can reduce energy costs and highly concentrate inorganic salt-containing water to recover inorganic salts.

The present invention provides an inorganic salt recovery device comprising: a heating means for heating water to be treated that contains inorganic salts to a range of 30°C to 40°C to obtain heated water; and a semipermeable membrane treatment means for using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the heated water through the first space and pressurizing the first space to cause water contained in the heated water to permeate the semipermeable membrane to obtain concentrated water, and passing a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water; and a cooling means for cooling the concentrated water to a range of 15°C to 25°C to crystallize the inorganic salts, wherein the inorganic salts are substances whose solubility in water increases by 0.5 g/100 g-H ₂ O or more per 1°C of water temperature in the range of 15°C to 40°C.

In the inorganic salt recovery device, the heating means heats the water to be treated by heat exchange with a first heat medium, the cooling means cools the concentrated water by heat exchange with a second heat medium, and it is preferable that the device further includes a heat pump means for exchanging heat between the first heat medium and the second heat medium.

It is preferable that the inorganic salt recovery device further includes a solid-liquid separation means for separating the crystallized inorganic salt into solid and liquid, downstream of the cooling means.

It is preferable that the inorganic salt recovery device further includes a return means for returning at least a portion of the solid-liquid separated water obtained by the solid-liquid separation means to a stage prior to the heating step.

In the inorganic salt recovery device, the concentration of the inorganic salt in the concentrated water is preferably in the range of 70 to 95% of the solubility of the inorganic salt at the temperature of the concentrated water.

It is preferable that the inorganic salt recovery device further includes a first reverse osmosis membrane treatment means upstream of the heating means, the water to be treated is subjected to reverse osmosis membrane treatment to obtain a first RO concentrated water and a first RO permeate, and the first RO concentrated water is heated by the heating means.

It is preferable that the inorganic salt recovery device further includes a second reverse osmosis membrane treatment means downstream of the semipermeable membrane treatment means, and the diluted water is treated with a reverse osmosis membrane to obtain a second RO concentrated water and a second RO permeate.

The present invention is an inorganic salt recovery method including a heating step of heating water to be treated containing an inorganic salt to a temperature in the range of 30°C to 40°C to obtain heated water, a semipermeable membrane treatment step of using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane to pass the heated water through the first space and pressurize the first space to cause water contained in the heated water to permeate the semipermeable membrane to obtain concentrated water, and passing a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water, and a cooling step of cooling the concentrated water to a temperature in the range of 15°C to 25°C to crystallize the inorganic salt, wherein the inorganic salt is a substance whose solubility in water increases by 0.5 g/100 g-H ₂ O or more per 1°C of water temperature in the range of 15°C to 40°C.
It is a device.

In the inorganic salt recovery method, it is preferable that the heating step heats the water to be treated by heat exchange with a first heat medium, and the cooling step cools the concentrated water by heat exchange with a second heat medium, and the method further includes a heat pump step of exchanging heat between the first heat medium and the second heat medium.

In the inorganic salt recovery method, it is preferable that the method further includes a solid-liquid separation step of separating the crystallized inorganic salt into solid and liquid after the cooling step.

It is preferable that the inorganic salt recovery method further includes a return step in which at least a portion of the solid-liquid separated water obtained in the solid-liquid separation step is returned to a stage prior to the heating step.

In the inorganic salt recovery method, it is preferable that the concentration of the inorganic salt in the concentrated water is in the range of 70 to 95% of the solubility of the inorganic salt at the temperature of the concentrated water.

In the inorganic salt recovery method, it is preferable to further include a first reverse osmosis membrane treatment step prior to the heating step, in which the water to be treated is treated with a reverse osmosis membrane to obtain a first RO concentrate and a first RO permeate, and the first RO concentrate is heated in the heating step.

In the inorganic salt recovery method, it is preferable to further include a second reverse osmosis membrane treatment step subsequent to the semipermeable membrane treatment step, and to treat the diluted water with a reverse osmosis membrane to obtain a second RO concentrated water and a second RO permeate.

The present invention provides an inorganic salt recovery device and an inorganic salt recovery method that can reduce energy costs and highly concentrate inorganic salt-containing water to recover inorganic salts.

1 is a schematic configuration diagram illustrating an example of an inorganic salt recovery device according to an embodiment of the present invention. 1 is a schematic configuration diagram showing an example of a semipermeable membrane treatment device in an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a semipermeable membrane treatment device in an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a semipermeable membrane treatment device in an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a semipermeable membrane treatment device in an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a semipermeable membrane treatment device in an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of an inorganic salt recovery device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of an inorganic salt recovery device according to an embodiment of the present invention.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

An example of an inorganic salt recovery device according to an embodiment of the present invention is outlined in Figure 1, and its configuration will be described.

The inorganic salt recovery device 1 includes a heating device 10 as a heating means for heating water to be treated that contains inorganic salts to obtain heated water, a semipermeable membrane treatment device 12 as a semipermeable membrane treatment means for passing heated water through the first space using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, pressurizing the first space to cause the water contained in the heated water to pass through the semipermeable membrane to obtain concentrated water, and passing a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water, and a cooling device 14 as a cooling means for cooling the concentrated water to crystallize the inorganic salt. The inorganic salt recovery device 1 may include a solid-liquid separation device 16 as a solid-liquid separation means for separating the crystallized inorganic salt into solid and liquid, downstream of the cooling device 14.

In the inorganic salt recovery device 1, a pipe 18 is connected to the inlet of the heating device 10. The outlet of the heating device 10 and the inlet of the semipermeable membrane treatment device 12 are connected by a pipe 20. The concentrated water outlet of the semipermeable membrane treatment device 12 and the inlet of the cooling device 14 are connected by a pipe 22. The diluted water outlet of the semipermeable membrane treatment device 12 is connected to a pipe 24. The outlet of the cooling device 14 and the inlet of the solid-liquid separation device 16 are connected by a pipe 26. The recovered inorganic salt outlet of the solid-liquid separation device 16 is connected to a pipe 28, and the solid-liquid separated water outlet is connected to a pipe 30.

The inorganic salt recovery method and the operation of the inorganic salt recovery device 1 according to this embodiment will be described.

The water to be treated containing inorganic salts is sent to the heating device 10 through the pipe 18, where the water to be treated is heated to obtain heated water (heating process). The heated water is sent to the semipermeable membrane treatment device 12 through the pipe 20, where the semipermeable membrane treatment device 12 uses a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane to pass the heated water through the first space, pressurize the first space, and the water contained in the heated water is permeated through the semipermeable membrane to obtain concentrated water, and at least a part of the heated water or the concentrated water is passed through the second space to obtain diluted water (semipermeable membrane treatment process). The diluted water is discharged through the pipe 24. The concentrated water is sent to the cooling device 14 through the pipe 22, where the concentrated water is cooled to crystallize the inorganic salts (cooling process). The cooling water obtained in the cooling process is sent to the solid-liquid separation device 16 through the pipe 26 as necessary, and in the solid-liquid separation device 16, the crystallized inorganic salt is separated into solid and liquid to obtain the recovered inorganic salt and the solid-liquid separated water (solid-liquid separation process). The recovered inorganic salt is discharged through the pipe 28. The solid-liquid separated water is discharged through the pipe 30.

In the inorganic salt recovery method and inorganic salt recovery device according to this embodiment, the temperature of the water to be treated is raised by a heating device 10 in the stage prior to the semipermeable membrane treatment to increase the solubility of inorganic salts in the water to be treated, and then the water is concentrated by semipermeable membrane treatment to a temperature close to the solubility of the inorganic salts at that water temperature, and the temperature of the concentrated water obtained is lowered in the stage subsequent to the semipermeable membrane treatment to recover the crystallized inorganic salts. This reduces energy costs and makes it possible to recover inorganic salts by concentrating inorganic salt-containing water to a high concentration. A solid-liquid separation process may be provided after the water temperature is lowered in the stage subsequent to the semipermeable membrane treatment to recover the crystallized inorganic salts.

In the heating step, the water to be treated is heated, for example, to a temperature in the range of 30°C to 40°C, and preferably to a temperature in the range of 32°C to 38°C. If the temperature of the heated water is below 30°C, the efficiency of recovery of inorganic salts may decrease, and if it exceeds 40°C, the semipermeable membrane module may deteriorate.

In the semipermeable membrane treatment process, the concentration of the inorganic salt in the concentrated water is preferably in the range of 70 to 95% of the solubility of the inorganic salt at the temperature of the concentrated water, more preferably in the range of 70 to 90%, and even more preferably in the range of 80 to 90%. By concentrating the inorganic salt to a range of 70 to 95% of the solubility of the inorganic salt at the temperature of the concentrated water in the semipermeable membrane treatment process, the inorganic salt becomes more likely to crystallize in the cooling process. If the concentration of the inorganic salt in the concentrated water is less than 70% of the solubility of the inorganic salt at the temperature of the concentrated water, the inorganic salt may not crystallize easily in the cooling process, and if it exceeds 95%, the inorganic salt may precipitate in the semipermeable membrane module, causing the membrane to become clogged.

The concentration of inorganic salts in the concentrated water may be monitored by installing an inorganic salt concentration measuring device as an inorganic salt concentration measuring means for measuring the concentration of inorganic salts in the concentrated water at the outlet of the concentrated water of the semipermeable membrane treatment device 12, for example, at the pipe 22. There are no particular limitations on the inorganic salt concentration measuring device, so long as it can measure the concentration of inorganic salts in the concentrated water or can measure an index that can estimate the concentration of inorganic salts. Examples of the inorganic salt concentration measuring device include a conductivity meter and a TDS (Total Dissolved Solids) meter.

In the cooling step, the concentrated water is cooled, for example, to a temperature in the range of 15°C to 25°C, and preferably to a temperature in the range of 15°C to 20°C. If the temperature of the cooling water is less than 15°C, the particle size of the precipitated inorganic salt may be non-uniform or a large amount of energy may be required for cooling, and if the temperature exceeds 25°C, the inorganic salt may not crystallize easily.

The water to be treated is not particularly limited as long as it contains inorganic salts, but examples include wastewater discharged from semiconductor factories and chemical factories.

Examples of inorganic salts contained in the water to be recovered include sodium sulfate, potassium nitrate, calcium chloride, etc. The inorganic salts to be recovered are preferably substances whose solubility in water increases by 0.5 g/100 g-H ₂ O or more per 1° C. of water temperature in the range of 15° C. to 40° C., more preferably substances whose solubility in water increases by 0.8 g/100 g-H ₂ O or more, and even more preferably substances whose solubility in water increases by 1.0 g/100 g-H ₂ O or more in the range of 15° C. to 40° C. Sodium sulfate is a substance whose solubility in water increases by 1.4 g/100 g-H ₂ O per 1° C. of water temperature in the range of 15° C. to 40° C. In this way, when recovering inorganic salts whose solubility varies greatly depending on the water temperature, the inorganic salt recovery method and inorganic salt recovery device according to the present embodiment can be suitably applied.

The solubility of inorganic salts contained in the water to be treated in water at 20° C. is preferably 70 g/100 g-H ₂ O or less, and more preferably 30 g/100 g-H ₂ O or less. The solubility of sodium sulfate in water at 20° C. is 19 g/100 g-H ₂ O. When recovering inorganic salts that are difficult to dissolve in water, the inorganic salt recovery method and inorganic salt recovery device according to the present embodiment can be suitably applied.

The heating device 10 is not particularly limited as long as it can heat the water to be treated to obtain heated water, and examples of the device include a heat exchanger that exchanges heat between the water to be treated and a heat medium, a heater, etc. A heat exchanger is preferred because it can reduce energy costs.

The cooling device 14 is not particularly limited as long as it can cool the concentrated water and crystallize the inorganic salts. For example, a heat exchanger that exchanges heat between the concentrated water and a heat medium, a cooler, etc., can be used. A heat exchanger is preferred because it can reduce energy costs.

The solid-liquid separation device 16 is not particularly limited as long as it can separate the crystallized inorganic salt into solid and liquid to obtain recovered inorganic salt and solid-liquid separated water. For example, a settling tank using natural settling, a centrifugal separator, a filter press dehydrator, a screw press dehydrator, a belt press dehydrator, a membrane filtration device (e.g., a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), etc.), a screen filtration device, etc. may be used. These solid-liquid separation devices may also be used in combination. A settling tank using natural settling is preferred from the viewpoint of reducing energy costs, etc. The cooling device 14 and the solid-liquid separation device 16 may be a device that combines a cooling device and a solid-liquid separation device that can perform both cooling and solid-liquid separation.

When the inorganic salt crystallizes with non-uniform particle size, a crushing device may be installed as a crushing means for crushing the crystallized inorganic salt. There are no particular limitations on the crushing device as long as it can crush the crystallized inorganic salt, and examples of the crushing device include a grinder.

There are no particular limitations on the semipermeable membrane treatment device 12, as long as it is equipped with a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane. Examples of the semipermeable membrane treatment device 12 are described with reference to Figures 2 and 3.

The semipermeable membrane treatment device 12 shown in FIG. 2 uses a semipermeable membrane module having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, and passes water to be treated (heated water) containing inorganic salts through the first space, pressurizes the first space, and causes the water contained in the water to permeate the semipermeable membrane to obtain concentrated water, while passing a portion of the water to be treated through the second space to obtain dilution water. The membrane module 50 has a first space 54 and a second space 56 separated by a semipermeable membrane 52. The semipermeable membrane treatment device 12 may also have a treated water tank that stores the water to be treated.

In the semipermeable membrane treatment device 12 of FIG. 2, the pipe 20 is connected to the inlet of the first space of the membrane module 50 via the pump 58, and the pipe 66 branching off from the pipe 20 downstream of the pump 58 is connected to the inlet of the second space of the membrane module 50 via the valve 62. The pipe 22 is connected to the outlet of the first space of the membrane module 50 via the valve 64, and the pipe 24 is connected to the outlet of the second space of the membrane module 50.

The pump 58 is, for example, a pressure pump that is driven at a rotational speed corresponding to an input drive frequency, sucks in the water to be treated, and pressurizes and discharges it to the membrane module 50. The pump 58 is equipped with, for example, an inverter 60 that outputs to the pump 58 a drive frequency corresponding to an input command signal. The valves 62 and 64 are, for example, valves whose opening and closing degree can be adjusted manually or automatically.

The semipermeable membrane treatment device 12 in FIG. 2 uses a membrane module 50 having a first space 54 and a second space 56 separated by a semipermeable membrane 52, passes the water to be treated from the first space inlet of the membrane module 50 to the first space 54 and from the second space inlet to the second space 56, and pressurizes the first space 54 to cause the water contained in the water to be treated in the first space 54 to permeate through the semipermeable membrane 52 to the second space 56, concentrating the water. That is, in the semipermeable membrane treatment device 12, the water to be treated is concentrated using the semipermeable membrane 52. The semipermeable membrane treatment device 12 is a device that performs a concentration treatment by supplying the water to be treated to both the first space 54 and the second space 56 of the membrane module 50.

In the semipermeable membrane treatment device 12, the water to be treated (heated water) containing inorganic salts is pressurized and sent from the first space inlet of the membrane module 50 to the first space 54 through the piping 20 by the pump 58 with the valve 64 open, and the water is passed through. Also, with the valve 62 open, the water to be treated is sent from the second space inlet of the membrane module 50 to the second space 56 through the piping 66 branched from the piping 20, and the water is passed through. A part of the water contained in the pressurized water to be treated permeates from the first space 54 to the second space 56 through the semipermeable membrane 52. At this time, most of the inorganic salts cannot permeate the semipermeable membrane 52, so the water in the first space 54 that did not permeate the semipermeable membrane 52 is concentrated. On the other hand, in the second space 56, a part of the water to be treated passed through the piping 66 and the permeated water with a low concentration of inorganic salts that permeated the semipermeable membrane 52 merge, and a dilution effect is produced. The concentrated water obtained in the first space 54 is discharged from the first space outlet through the pipe 22, and the diluted water obtained in the second space 56 is discharged from the second space outlet through the pipe 24. Here, in the membrane module 50, the first space 54 is pressurized and the water contained in the water to be treated in the first space 54 is permeated through the semipermeable membrane 52 into the second space 56, and concentrated water is obtained in the first space 54 (concentration process) and diluted water is obtained in the second space 56 (dilution process). The concentrated water obtained in the first space 54 is sent to the cooling device 14 through the pipe 22.

Here, the pipes 20, 66, pump 58, etc. function as a supply means for supplying treated water to both the first space 54 and the second space 56 of the membrane module 50.

The dilution water obtained in the second space 56 may be discharged to the outside of the system through the pipe 24, or may be sent to a dilution water tank and stored there, if necessary, and then discharged to the outside of the system. At least a portion of the dilution water may be further subjected to other processes, such as reverse osmosis membrane processing.

In this way, treated water (heated water) containing inorganic salts is treated to obtain treated water (concentrated water) with concentrated inorganic salts and dilution water, thereby concentrating the treated water.

By passing the water to be treated that contains inorganic salts through the first space 54 and the second space 56 of the membrane module 50, the osmotic pressure difference between the first space 54 side and the second space 56 side of the semipermeable membrane 52 is reduced, and the inorganic salts in the water to be treated can be concentrated with less energy consumption. In other words, the water to be treated that contains inorganic salts can be concentrated at low cost.

The water to be treated may be supplied to the first space 54 and the second space 56 by separate pumps. When the water to be treated is supplied by separate pumps, each pump may be provided with an inverter that controls the drive frequency.

By passing water to be treated with the same or similar concentration through both the first space 54 and the second space 56, the osmotic pressure generated by the semipermeable membrane 52 can be reduced, and the required pressure can be reduced. As a result, it is possible to concentrate water to a concentration that could not be achieved by conventional reverse osmosis membrane methods.

The semipermeable membrane treatment device 12 shown in FIG. 3 uses a semipermeable membrane module having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, and passes water to be treated (heated water) containing inorganic salts through the first space, pressurizes the first space, and causes the water contained in the water to permeate the semipermeable membrane to obtain concentrated water, while passing at least a portion of the concentrated water through the second space to obtain dilution water. The membrane module 50 has a first space 54 and a second space 56 separated by a semipermeable membrane 52. The semipermeable membrane treatment device 12 may also have a treated water tank that stores the water to be treated.

In the semipermeable membrane treatment device 12 of FIG. 3, a pipe 20 is connected to the inlet of the first space of the membrane module 50 via a pump 58. A pipe 22 is connected to the outlet of the first space of the membrane module 50 via a valve 64. A pipe 70 that branches off from the pipe 22 upstream of the valve 64 is connected to the inlet of the second space of the membrane module 50 via a valve 68. A pipe 24 is connected to the outlet of the second space of the membrane module 50.

The pump 58 is, for example, a pressure pump that is driven at a rotational speed according to an input drive frequency, sucks in the water to be treated, and pressurizes and discharges it to the membrane module 50. The pump 58 is equipped with, for example, an inverter 60 that outputs to the pump 58 a drive frequency that corresponds to an input command signal. The valves 64 and 68 are, for example, valves whose opening and closing can be adjusted manually or automatically.

The semipermeable membrane treatment device 12 in FIG. 3 uses a membrane module 50 having a first space 54 and a second space 56 separated by a semipermeable membrane 52, passes the water to be treated from the first space inlet of the membrane module 50 to the first space 54, and passes at least a part of the concentrated water discharged from the first space outlet of the first space 54 of the membrane module 50 to the second space 56 from the second space inlet of the membrane module 50, and pressurizes the first space 54, thereby causing the water contained in the water to be treated in the first space 54 to permeate through the semipermeable membrane 52 to the second space 56, concentrating the water. That is, in the semipermeable membrane treatment device 12, the water to be treated is concentrated using the semipermeable membrane 52. The semipermeable membrane treatment device 12 is a device that supplies the water to be treated to the first space 54 of the membrane module 50, and supplies at least a part of the concentrated water obtained from the outlet of the first space 54 to the second space 56 of the membrane module 50 to perform concentration treatment.

In the semipermeable membrane treatment device 12, the water to be treated (heated water) containing inorganic salts is pressurized and sent from the first space inlet of the membrane module 50 to the first space 54 through the piping 20 by the pump 58 with the valve 64 open, and the water is passed through. A part of the water contained in the pressurized water to be treated permeates from the first space 54 to the second space 56 through the semipermeable membrane 52. At this time, most of the inorganic salts cannot permeate the semipermeable membrane 52, so the water in the first space 54 that did not permeate the semipermeable membrane 52 is concentrated. On the other hand, in the second space 56, a part of the concentrated water passed through the piping 70 and the permeated water with a low concentration of inorganic salts that permeated the semipermeable membrane 52 merge, so a dilution effect works. The concentrated water obtained in the first space 54 is discharged through the piping 22 from the first space outlet, and at least a part of the concentrated water is sent through the piping 70 branched from the piping 22 with the valve 68 open, and sent from the second space inlet of the membrane module 50 to the second space 56. The diluted water obtained in the second space 56 is discharged from the second space outlet through the pipe 24. Here, in the membrane module 50, the first space 54 is pressurized, and the water contained in the water to be treated in the first space 54 is permeated through the semipermeable membrane 52 into the second space 56, and concentrated water is obtained in the first space 54 (concentration process), and diluted water is obtained in the second space 56 (dilution process). A portion of the concentrated water obtained in the first space 54 is sent to the cooling device 14 through the pipe 22. At least a portion of the concentrated water is sent and passed through the pipes 22 and 70 to the second space 56 of the membrane module 50 as described above.

Here, the pipes 20, 22, 70, the pump 58, etc. function as a supply means that supplies the water to be treated to the first space 54 of the membrane module 50 and supplies at least a portion of the concentrated water obtained from the outlet of the first space 54 to the second space 56 of the membrane module 50.

The dilution water obtained in the second space 56 may be discharged to the outside of the system through the pipe 24, or may be sent to a dilution water tank and stored there, if necessary, and then discharged to the outside of the system. At least a portion of the dilution water may be further subjected to other processes, such as reverse osmosis membrane processing.

In this way, treated water (heated water) containing inorganic salts is treated to obtain treated water (concentrated water) with concentrated inorganic salts and dilution water, thereby concentrating the treated water.

In the semipermeable membrane treatment device 12, a multi-stage semipermeable membrane module connected in series may be used. Examples of semipermeable membrane treatment devices with such a configuration are shown in Figures 4, 5, and 6. The semipermeable membrane treatment devices shown in Figures 4, 5, and 6 have a structure in which three stages of semipermeable membrane modules are combined in series.

The semipermeable membrane treatment device 12 shown in FIG. 4 uses semipermeable membrane modules connected in multiple stages, each having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, and passes water to be treated (heated water) containing inorganic salts through the first space of the first-stage semipermeable membrane module, pressurizes the first space, and causes the water contained in the water to permeate the semipermeable membrane to obtain concentrated water. The concentrated water is further obtained using the semipermeable membrane module of the next stage or later, and is provided with, for example, a first-stage membrane module 50a, a second-stage membrane module 50b, and a third-stage membrane module 50c as semipermeable membrane treatment means for passing a part of the water to be treated or a part of the concentrated water through the second space of the semipermeable membrane module of each stage to obtain dilution water. Each membrane module has a first space 54 and a second space 56 separated by a semipermeable membrane 52. The semipermeable membrane treatment device 12 may include a dilution water tank for storing dilution water from the first-stage membrane module 50a, a dilution water tank for storing dilution water from the second-stage membrane module 10b, and a dilution water tank for storing dilution water from the third-stage membrane module 10c. The semipermeable membrane treatment device 12 is a device that supplies the water to be treated to the first and second spaces of the first-stage membrane module, and sequentially supplies the concentrated water to the first and second spaces of the next-stage membrane module to perform concentration treatment.

In the semipermeable membrane treatment device 12 of FIG. 4, the pipe 20 is connected to the first space inlet of the first-stage membrane module 50a via the pump 58. The pipe 66a branched from the downstream side of the pump 58 of the pipe 20 is connected to the second space inlet of the membrane module 50a via the valve 62a. The pipe 24a is connected to the second space outlet of the first-stage membrane module 50a. The first space outlet of the first-stage membrane module 50a and the first space inlet of the second-stage membrane module 50b are connected by the pipe 82. The pipe 66b branched from the pipe 82 is connected to the second space inlet of the second-stage membrane module 50b via the valve 62b. The pipe 24b is connected to the second space outlet of the second-stage membrane module 50b. The first space outlet of the second-stage membrane module 50b and the first space inlet of the third-stage membrane module 50c are connected by the pipe 84. The pipe 66c branched from the pipe 84 is connected to the second space inlet of the third-stage membrane module 50c via the valve 62c. A pipe 24c is connected to the second space outlet of the third-stage membrane module 50c. A pipe 22 is connected to the first space outlet of the third-stage membrane module 50c via a valve 64.

The semipermeable membrane treatment device 12 uses a multi-stage membrane module having a first space 54 and a second space 56 separated by a semipermeable membrane 52, supplies the water to be treated to the first space and the second space of the first stage membrane module, sequentially supplies the concentrated water to the first space and the second space of the next stage membrane module, and concentrates the water by pressurizing the first space 54 of each stage to permeate the water contained in the first space 54 through the semipermeable membrane 52 into the second space 56. That is, in the semipermeable membrane treatment device 12, the water to be treated is concentrated using the semipermeable membrane 52, and the concentrated water is further concentrated using the semipermeable membrane 52 of the next stage.

Specifically, in the semipermeable membrane treatment device 12, the water to be treated (heated water) containing inorganic salts is pumped through the pipe 20 by the pump 58 with the valve 64 open to the first space 54a of the first-stage membrane module 50a, and the water to be treated branched from the pipe 20 is pumped through the pipe 66a to the second space 56a of the first-stage membrane module 50a with the valve 62a open. In the first-stage membrane module 50a, the first space 54a is pressurized and the water contained in the first space 54a is permeated through the semipermeable membrane 52a to the second space 56a (concentration process (first stage)), and dilution water is obtained in the second space 56a (dilution process (first stage)). The dilution water obtained in the second space 56a of the first-stage membrane module 50a may be discharged outside the system through the pipe 24a, or may be pumped to a dilution water tank and stored therein as necessary, and then discharged outside the system. At least a portion of the dilution water may be further subjected to other treatments, such as reverse osmosis membrane treatment.

The concentrated water obtained in the first space 54a of the first-stage membrane module 50a is sent to the first space 54b of the second-stage membrane module 50b through the pipe 82, and the concentrated water branched off from the pipe 82 is sent to the second space 56b of the second-stage membrane module 50b through the pipe 66b with the valve 62b open. In the second-stage membrane module 50b, the first space 54b is pressurized and the water contained in the first space 54b is permeated through the semipermeable membrane 52b into the second space 56b (concentration process (second stage)), and dilution water is obtained in the second space 56b (dilution process (second stage)). The dilution water obtained in the second space 56b of the second-stage membrane module 50b may be discharged outside the system through the pipe 24b, or may be sent to a dilution water tank and stored therein as necessary, and then discharged outside the system. At least a portion of the dilution water may be further subjected to other processes such as reverse osmosis membrane treatment.

The concentrated water obtained in the first space 54b of the second-stage membrane module 50b is sent to the first space 54c of the third-stage membrane module 50c through the pipe 84, and the concentrated water branched off from the pipe 84 is sent to the second space 56c of the third-stage membrane module 50c through the pipe 66c with the valve 62c open. In the third-stage membrane module 50c, the first space 54c is pressurized and the water contained in the first space 54c is permeated through the semipermeable membrane 52c into the second space 56c (concentration process (third stage)), and dilution water is obtained in the second space 56c (dilution process (third stage)). The concentrated water obtained in the first space 54c of the third-stage membrane module 50c is sent to the cooling device 14 through the pipe 22. The dilution water obtained in the second space 56c of the third-stage membrane module 50c may be discharged to the outside of the system through the pipe 24c, or may be sent to a dilution water tank and stored there, if necessary, and then discharged to the outside of the system. At least a portion of the dilution water may be further subjected to other treatments, such as reverse osmosis membrane treatment.

Here, the pump 58, piping 20, 82, 84, 66a, 66b, 66c, etc. function as a supply means for supplying treated water or concentrated water to the first spaces 54a, 54b, 54c and second spaces 56a, 56b, 56c of the membrane modules 50a, 50b, 50c of each stage.

In this way, treated water (heated water) containing inorganic salts is treated to obtain treated water (concentrated water) with concentrated inorganic salts and dilution water, thereby concentrating the treated water.

The semipermeable membrane treatment device 12 shown in FIG. 5 uses semipermeable membrane modules connected in multiple stages, each having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, and passes water to be treated (heated water) containing inorganic salts through the first space of the first-stage semipermeable membrane module, pressurizes the first space, and causes the water contained in the water to permeate the semipermeable membrane to obtain concentrated water. The concentrated water is further obtained using the semipermeable membrane module of the next stage or later, and at least a portion of the concentrated water is passed through the second space of the semipermeable membrane module of each stage to obtain dilution water. For example, the first-stage membrane module 50a, the second-stage membrane module 50b, and the third-stage membrane module 50c are provided as semipermeable membrane treatment means. Each membrane module has a first space 54 and a second space 56 separated by a semipermeable membrane 52. The semipermeable membrane treatment device 12 may include a dilution water tank for storing dilution water from the first-stage membrane module 50a, a dilution water tank for storing dilution water from the second-stage membrane module 50b, and a dilution water tank for storing dilution water from the third-stage membrane module 50c. The semipermeable membrane treatment device 12 is a device that supplies the water to be treated to the first space of the first-stage membrane module, and sequentially supplies the concentrated water to the first space of the next-stage membrane module and its own second space to perform concentration treatment.

In the semipermeable membrane treatment device 12 of FIG. 5, the pipe 20 is connected to the first space inlet of the first-stage membrane module 50a via the pump 58. The first space outlet of the first-stage membrane module 50a and the first space inlet of the second-stage membrane module 50b are connected by the pipe 82. The pipe 70a branched from the pipe 82 is connected to the second space inlet of the membrane module 50a via the valve 68a. The pipe 24a is connected to the second space outlet of the first-stage membrane module 50a. The first space outlet of the second-stage membrane module 50b and the first space inlet of the third-stage membrane module 50c are connected by the pipe 84. The pipe 70b branched from the pipe 84 is connected to the second space inlet of the membrane module 50b via the valve 68b. The pipe 24b is connected to the second space outlet of the second-stage membrane module 50b. The pipe 22 is connected to the first space outlet of the third-stage membrane module 10c via the valve 64. Pipe 70c, which branches off from pipe 22 upstream of valve 64, is connected to the second space inlet of membrane module 50c via valve 68c. Pipe 24c is connected to the second space outlet of the third-stage membrane module 50c.

The semipermeable membrane treatment device 12 uses a multi-stage membrane module having a first space 54 and a second space 56 separated by a semipermeable membrane 52, supplies the water to be treated to the first space of the first stage membrane module, sequentially supplies the concentrated water to the first space of the next stage membrane module and its own second space, and by pressurizing the first space 54 of each stage, the water contained in the first space 54 is permeated through the semipermeable membrane 52 into the second space 56 to concentrate the water. That is, in the semipermeable membrane treatment device 12, the water to be treated is concentrated using the semipermeable membrane 52, and the concentrated water is further concentrated using the semipermeable membrane 52 of the next stage.

Specifically, in the semipermeable membrane treatment device 12, the water to be treated (heated water) containing inorganic salts is sent to the first space 54a of the first-stage membrane module 50a through the piping 20 by the pump 58 with the valve 64 open. In the first-stage membrane module 50a, the first space 54a is pressurized and the water contained in the first space 54a is permeated through the semipermeable membrane 52a into the second space 56a (concentration process (first stage)), and dilution water is obtained in the second space 56a (dilution process (first stage)). The concentrated water obtained in the first space 54a of the first-stage membrane module 50a is sent to the first space 54b of the second-stage membrane module 50b through the piping 82, and the concentrated water branched off from the piping 82 is sent to the second space 56a of the first-stage membrane module 50a through the piping 70a with the valve 68a open. The dilution water obtained in the second space 56a of the first-stage membrane module 50a may be discharged to the outside of the system through the pipe 24a, or may be sent to a dilution water tank and stored there, if necessary, and then discharged to the outside of the system. At least a portion of the dilution water may be further subjected to other treatments, such as reverse osmosis membrane treatment.

In the second-stage membrane module 50b, the first space 54b is pressurized, and the water contained in the first space 54b is permeated through the semipermeable membrane 52b into the second space 56b (concentration process (second stage)), and dilution water is obtained in the second space 56b (dilution process (second stage)). The concentrated water obtained in the first space 54b of the second-stage membrane module 50b is sent to the first space 54c of the third-stage membrane module 50c through the pipe 84, and the concentrated water branched off from the pipe 84 is sent to the second space 56b of the second-stage membrane module 50b through the pipe 70b with the valve 68b open. The dilution water obtained in the second space 56b of the second-stage membrane module 50b may be discharged outside the system through the pipe 24b, or may be sent to a dilution water tank and stored therein as necessary, and then discharged outside the system. At least a portion of the dilution water may be further subjected to other processes such as reverse osmosis membrane processing.

In the third-stage membrane module 50c, the first space 54c is pressurized, and the water contained in the first space 54c is permeated through the semipermeable membrane 52c into the second space 56c (concentration process (third stage)), and dilution water is obtained in the second space 56c (dilution process (third stage)). The concentrated water obtained in the first space 54c of the third-stage membrane module 50c is sent to the cooling device 14 through the pipe 22. The concentrated water branched off from the pipe 22 is sent to the second space 56c of the third-stage membrane module 50c through the pipe 70c with the valve 68c open. The dilution water obtained in the second space 56c of the third-stage membrane module 50c may be discharged outside the system through the pipe 24c, or may be sent to a dilution water tank and stored therein as necessary, and then discharged outside the system. At least a portion of the dilution water may be further subjected to other processes such as reverse osmosis membrane processing.

Here, the pump 58, piping 20, 82, 84, 22, 70a, 70b, 70c, etc. function as a supply means for supplying treated water or concentrated water to the first spaces 54a, 54b, 54c and second spaces 56a, 56b, 56c of the membrane modules 50a, 50b, 50c of each stage.

In this way, treated water (heated water) containing inorganic salts is treated to obtain treated water (concentrated water) with concentrated inorganic salts and dilution water, thereby concentrating the treated water.

When a multi-stage membrane module is used, the water may be passed through the second space side in series. An example of a semipermeable membrane treatment device having such a configuration is shown in FIG. 6. The semipermeable membrane treatment device 12 shown in FIG. 6 uses semipermeable membrane modules connected in multiple stages, each having a first space (concentrated side) and a second space (permeation side) separated by a semipermeable membrane, and passes the water to be treated (heated water) containing inorganic salts through the first space of the first-stage semipermeable membrane module, pressurizes the first space, and causes the water contained in the water to permeate the semipermeable membrane to obtain concentrated water, and the concentrated water is further obtained using the semipermeable membrane module of the next stage or later to obtain concentrated water, and at least a part of the concentrated water or at least a part of the dilution water obtained from another semipermeable membrane module is passed through the second space of the semipermeable membrane module of each stage to obtain dilution water. For example, a first-stage membrane module 50a, a second-stage membrane module 50b, and a third-stage membrane module 50c are provided as semipermeable membrane treatment means. Each membrane module has a first space 54 and a second space 56 separated by a semipermeable membrane 52. The semipermeable membrane treatment device 12 is a device that supplies the water to be treated to the first space of the first membrane module, and then sequentially supplies the concentrated water to the first space of the next membrane module to perform concentration treatment.

In the semipermeable membrane treatment device 12 of FIG. 6, the pipe 20 is connected to the first space inlet of the first-stage membrane module 50a via the pump 58. The first space outlet of the first-stage membrane module 50a and the first space inlet of the second-stage membrane module 50b are connected by the pipe 82. The first space outlet of the second-stage membrane module 50b and the first space inlet of the third-stage membrane module 50c are connected by the pipe 84. The pipe 22 is connected to the first space outlet of the third-stage membrane module 50c via the valve 64. The pipe 86 branched from the pipe 22 upstream of the valve 64 is connected to the second space inlet of the membrane module 50c via the valve 68. The second space outlet of the third-stage membrane module 50c and the second space inlet of the second-stage membrane module 50b are connected by the pipe 88. The second space outlet of the second-stage membrane module 50b and the second space inlet of the first-stage membrane module 50a are connected by the pipe 90. A pipe 24 is connected to the second space outlet of the first-stage membrane module 50a.

The semipermeable membrane treatment device 12 uses a multi-stage membrane module having a first space 54 and a second space 56 separated by a semipermeable membrane 52, supplies the water to be treated to the first space of the first-stage membrane module, passes the concentrated water in series to the first space of the membrane module of the next stage, supplies at least a portion of the concentrated water of the membrane module of the final stage to its own second space, passes the resulting diluted water in series to the second space of the membrane module of the previous stage, and pressurizes the first space 54 of each stage to permeate the water contained in the first space 54 through the semipermeable membrane 52 to the second space 56, concentrating the water. That is, in the semipermeable membrane treatment device 12, the water to be treated is concentrated using the semipermeable membrane 52, and the concentrated water is further concentrated using the semipermeable membrane 52 of the next stage.

Specifically, in the semipermeable membrane treatment device 12, the water to be treated (heated water) containing inorganic salts is pumped through the piping 20 by the pump 58 with the valve 64 open to the first space 54a of the first-stage membrane module 50a. Meanwhile, the dilution water pumped through the second space 56c of the third-stage membrane module 50c and the second space 56b of the second-stage membrane module 50b described later is pumped through the piping 90 to the second space 56a of the first-stage membrane module 50a. In the first-stage membrane module 50a, the first space 54a is pressurized and the water contained in the first space 54a is permeated through the semipermeable membrane 52a to the second space 56a (concentration process (first stage)), and dilution water is obtained in the second space 56a (dilution process (first stage)). The concentrated water obtained in the first space 54a of the first-stage membrane module 50a is pumped through the piping 82 to the first space 54b of the second-stage membrane module 50b. The dilution water obtained in the second space 56a of the first-stage membrane module 50a is discharged through the pipe 24.

In the second-stage membrane module 50b, the dilution water sent via the second space 56c of the third-stage membrane module 50c described later is sent to the second space 56b of the second-stage membrane module 50b through the pipe 88. The first space 54b is pressurized, and the water contained in the first space 54b is permeated through the semipermeable membrane 52b into the second space 56b (concentration process (second stage)), and dilution water is obtained in the second space 56b (dilution process (second stage)). The concentrated water obtained in the first space 54b of the second-stage membrane module 50b is sent to the first space 54c of the third-stage membrane module 50c through the pipe 84. The dilution water obtained in the second space 56b of the second-stage membrane module 50b is sent to the second space 56a of the first-stage membrane module 50a through the pipe 90.

In the third-stage membrane module 50c, the concentrated water obtained in the first space 54c of the third-stage membrane module 50c is sent to the second space 56c through the pipes 22 and 86 as described below. The first space 54c is pressurized, and the water contained in the first space 54c is permeated through the semipermeable membrane 52c into the second space 56c (concentration process (third stage)), and dilution water is obtained in the second space 56c (dilution process (third stage)). A part of the concentrated water obtained in the first space 54c of the third-stage membrane module 50c is sent to the cooling device 14 through the pipe 22. The concentrated water branched from the pipe 22 is sent to the second space 56c of the third-stage membrane module 50c through the pipe 86 with the valve 68 open. The dilution water obtained in the second space 56c of the third-stage membrane module 50c is sent to the second space 56b of the second-stage membrane module 50b through the pipe 88.

Here, the pump 58, piping 20, 82, 84, 22, 86, 88, 90, etc. function as a supply means for supplying treated water, concentrated water, or diluted water to the first spaces 54a, 54b, 54c and second spaces 56a, 56b, 56c of the membrane modules 50a, 50b, 50c of each stage.

The dilution water obtained in the second space 56a of the membrane module 50a may be discharged to the outside of the system through the pipe 24, or may be sent to a dilution water tank and stored there, if necessary, and then discharged to the outside of the system. At least a portion of the dilution water may be further subjected to other processes, such as reverse osmosis membrane processing.

In this way, treated water (heated water) containing inorganic salts is treated to obtain treated water (concentrated water) with concentrated inorganic salts and dilution water, thereby concentrating the treated water.

When using a multi-stage membrane module, the number of stages of the membrane module can be determined based on the concentration of the target treated water, etc. For example, if you want to obtain treated water with a higher concentration from treated water with a lower concentration, you can simply increase the number of stages of the membrane module unit.

A membrane module unit having multiple membrane modules connected in parallel may be used as the membrane module for each stage. The number of membrane modules in each membrane module unit may be determined based on the flow rate of the water to be treated, etc.

A concentrated water tank and a dilution water tank may be provided in one or more stages of the membrane module, or a concentrated water tank and a dilution water tank may be provided in each stage of the membrane module.

The semipermeable membrane 52 provided in the membrane module may be, for example, a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), or a nanofiltration membrane (NF membrane). The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. When a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of the water to be treated in the first space 54 is preferably 0.5 to 10.0 MPa.

The material constituting the semipermeable membrane 52 is not particularly limited, but examples include cellulose-based resins such as cellulose acetate-based resins, polysulfone-based resins such as polyethersulfone-based resins, polyamide-based resins, etc.

The shape of the semipermeable membrane 52 can be a flat membrane, a hollow fiber membrane, a spiral membrane, etc. A hollow fiber membrane is preferred because it allows the surface area of the semipermeable membrane to be increased.

In the inorganic salt recovery method and inorganic salt recovery device according to this embodiment, a heat exchanger is used as the heating device 10 and the cooling device 14, and a heat pump may be further provided. In addition, at least a portion of the solid-liquid separated water obtained in the solid-liquid separation device 16 may be returned to the previous stage of the heating process. An example of such a configuration is shown in FIG. 7.

In the inorganic salt recovery device 2 shown in FIG. 7, the heating device 10 is a device that heats the water to be treated by heat exchange with a first heat medium, and the cooling device 14 is a device that cools the concentrated water by heat exchange with a second heat medium. The inorganic salt recovery device 2 further includes a heat pump 32 as a heat pump means for exchanging heat between the first heat medium and the second heat medium.

The circulating heated water outlet of the heating device 10 and the circulating heated water inlet of the condenser 42 of the heat pump 32 are connected by a pipe 34. The circulating heated water outlet of the condenser 42 and the circulating heated water inlet of the heating device 10 are connected by a pipe 36. The circulating cooling water outlet of the cooling device 14 and the circulating cooling water inlet of the evaporator 44 of the heat pump 32 are connected by a pipe 38, and the circulating cooling water outlet of the evaporator 44 and the circulating cooling water inlet of the cooling device 14 are connected by a pipe 40. The refrigerant outlet of the condenser 42 and the refrigerant inlet of the evaporator 44 are connected by a pipe 47 via an expansion valve 45, and the refrigerant outlet of the evaporator 44 and the refrigerant inlet of the condenser 42 are connected by a pipe 48 via a compressor 46. In addition, the solid-liquid separation water outlet of the solid-liquid separation device 16 and the pipe 18 are connected by a pipe 30.

The circulating heated water is sent through piping 34 to the condenser 42 of the heat pump 32, where it exchanges heat with the high-temperature, high-pressure refrigerant sent from the compressor 46, becoming heated water with an increased water temperature, which is sent through piping 36 to the heating device 10. In the heating device 10, the water to be treated is heated by the circulating heated water (heating process). The circulating heated water heats the water to be treated and exchanges heat to become heated water with a lowered water temperature, which is sent through piping 34 to the condenser 42 of the heat pump 32, and the circulating heated water is circulated.

On the other hand, in the heat pump 32, the refrigerant whose temperature has been reduced by heat exchange with the circulating heating water is sent to the expansion valve 45 through the pipe 47. In the expansion valve 45, the high-pressure refrigerant sent from the condenser 42 is decompressed, and the refrigerant expands and its temperature further decreases, changing into a low-temperature, low-pressure liquid. The refrigerant whose temperature has been further decreased by expansion is sent to the evaporator 44 through the pipe 47. In the evaporator 44, the refrigerant sent from the expansion valve 45 is heat exchanged with the circulating cooling water sent from the cooling device 14 through the pipe 38, and is evaporated and changes into a low-temperature, low-pressure gas. The circulating cooling water whose temperature has been reduced by heat exchange with the refrigerant is sent to the cooling device 14 through the pipe 40. In the cooling device 14, the concentrated water is cooled by the circulating cooling water (cooling process). The circulating cooling water cools the concentrated water and exchanges heat with it, becoming cooling water whose water temperature has increased, and is sent to the evaporator 44 of the heat pump 32 through the pipe 38, and the circulating cooling water is circulated. The refrigerant that has been converted into a gas through heat exchange with the circulating cooling water is sent to the compressor 46 through piping 48. In the compressor 46, the refrigerant is compressed and changes into a high-temperature, high-pressure gas. The high-temperature, high-pressure refrigerant is sent to the condenser 42 through piping 48, where the cycle of condensation → expansion → evaporation → compression is repeated.

By combining a semipermeable membrane module with a heat pump, the system reduces the amount of external heating energy required and can recover inorganic salts from treated water that contains inorganic salts in a small space.

At least a portion of the solid-liquid separated water obtained in the solid-liquid separator 16 is returned through the pipe 30 to the pipe 18, which is the upstream stage of the heating device 10 (return process). Here, the pipe 30 functions as a return means for returning at least a portion of the solid-liquid separated water obtained in the solid-liquid separator 16 to the upstream stage of the heating process.

By returning at least a portion of the solid-liquid separated water to the upstream stage of the heating device 10 (heating process), the recovery rate of inorganic salts can be improved.

In the inorganic salt recovery method and inorganic salt recovery device according to this embodiment, a first reverse osmosis membrane treatment means may be further provided in front of the heating device 10. Also, a second reverse osmosis membrane treatment means may be further provided in the rear of the semipermeable membrane treatment device 12. An example of such a configuration is shown in FIG. 8.

The inorganic salt recovery device 3 shown in FIG. 8 includes a first reverse osmosis membrane treatment device 71 as a first reverse osmosis membrane treatment means that performs reverse osmosis membrane treatment on the water to be treated that contains inorganic salts to obtain a first RO concentrated water and a first RO permeate. It also includes a second reverse osmosis membrane treatment device 72 as a 21st reverse osmosis membrane treatment means that performs reverse osmosis membrane treatment on the dilution water to obtain a second RO concentrated water and a second RO permeate.

In the inorganic salt recovery device 3, a pipe 74 is connected to the inlet of the first reverse osmosis membrane treatment device 71. A pipe 76 is connected to the RO permeate outlet of the first reverse osmosis membrane treatment device 71. The RO concentrated water outlet of the first reverse osmosis membrane treatment device 71 and the inlet of the heating device 10 are connected by a pipe 18. The outlet of the heating device 10 and the inlet of the semipermeable membrane treatment device 12 are connected by a pipe 20. The concentrated water outlet of the semipermeable membrane treatment device 12 and the inlet of the cooling device 14 are connected by a pipe 22. The dilution water outlet of the semipermeable membrane treatment device 12 and the inlet of the second reverse osmosis membrane treatment device 72 are connected by a pipe 24. A pipe 80 is connected to the RO permeate outlet of the second reverse osmosis membrane treatment device 72. The RO concentrated water outlet of the second reverse osmosis membrane treatment device 72 and the pipe 18 are connected by a pipe 78. The outlet of the cooling device 14 and the inlet of the solid-liquid separation device 16 are connected by a pipe 26. A pipe 28 is connected to the recovered inorganic salt outlet of the solid-liquid separation device 16. A pipe 30 connects the solid-liquid separated water outlet of the solid-liquid separation device 16 to the downstream side of the connection point of the pipe 78 on the pipe 18.

The circulating heated water outlet of the heating device 10 and the circulating heated water inlet of the condenser 42 of the heat pump 32 are connected by piping 34. The circulating heated water outlet of the condenser 42 and the circulating heated water inlet of the heating device 10 are connected by piping 36. The circulating cooling water outlet of the cooling device 14 and the circulating cooling water inlet of the evaporator 44 of the heat pump 32 are connected by piping 38, and the circulating cooling water outlet of the evaporator 44 and the circulating cooling water inlet of the cooling device 14 are connected by piping 40.

The water to be treated containing inorganic salts is sent to the first reverse osmosis membrane treatment device 71 through the pipe 74, where the water to be treated is subjected to reverse osmosis membrane treatment to obtain the first RO concentrated water and the first RO permeate water (first reverse osmosis membrane treatment process). The first RO permeate water is discharged through the pipe 76. The first RO concentrated water is sent to the heating device 10 through the pipe 18, where the first RO concentrated water is heated to obtain heated water (heating process). The heated water is sent to the semipermeable membrane treatment device 12 through the pipe 20, where the semipermeable membrane treatment device 12 uses a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane to pass the heated water through the first space, pressurize the first space to cause the water contained in the heated water to permeate the semipermeable membrane to obtain concentrated water, and pass a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water (semipermeable membrane treatment process). The concentrated water is sent to the cooling device 14 through the pipe 22, where the concentrated water is cooled and the inorganic salt is crystallized (cooling process). The cooling water obtained in the cooling process is sent to the solid-liquid separation device 16 through the pipe 26 as necessary, where the crystallized inorganic salt is separated into solid and liquid to obtain the recovered inorganic salt and the solid-liquid separated water (solid-liquid separation process). The recovered inorganic salt is discharged through the pipe 28. At least a portion of the solid-liquid separated water is returned through the pipe 30 to the pipe 18, which is the upstream of the heating device 10 (return process).

The diluted water obtained in the semipermeable membrane treatment process is sent through pipe 24 to the second reverse osmosis membrane treatment device 72, where the diluted water is subjected to reverse osmosis membrane treatment to obtain second RO concentrated water and second RO permeate (second reverse osmosis membrane treatment process). The second RO permeate is discharged through pipe 80. The second RO concentrated water is sent through pipe 78 to pipe 18, which is the upstream stage of the heating device 10.

The circulating heated water is sent through piping 34 to the condenser 42 of the heat pump 32, where it exchanges heat with the high-temperature, high-pressure refrigerant sent from the compressor 46, becoming heated water with an increased water temperature, which is sent through piping 36 to the heating device 10. In the heating device 10, the water to be treated is heated by the circulating heated water (heating process). The circulating heated water heats the water to be treated and exchanges heat to become heated water with a lowered water temperature, which is sent through piping 34 to the condenser 42 of the heat pump 32, and the circulating heated water is circulated.

On the other hand, in the heat pump 32, the refrigerant whose temperature has been reduced by heat exchange with the circulating heating water is sent to the expansion valve 45 through the pipe 47. In the expansion valve 45, the high-pressure refrigerant sent from the condenser 42 is decompressed, and the refrigerant expands and its temperature further decreases, changing into a low-temperature, low-pressure liquid. The refrigerant whose temperature has been further decreased by expansion is sent to the evaporator 44 through the pipe 47. In the evaporator 44, the refrigerant sent from the expansion valve 45 is heat exchanged with the circulating cooling water sent from the cooling device 14 through the pipe 38, and is evaporated and changes into a low-temperature, low-pressure gas. The circulating cooling water whose temperature has been reduced by heat exchange with the refrigerant is sent to the cooling device 14 through the pipe 40. In the cooling device 14, the concentrated water is cooled by the circulating cooling water (cooling process). The circulating cooling water cools the concentrated water and exchanges heat with it, becoming cooling water whose water temperature has increased, and is sent to the evaporator 44 of the heat pump 32 through the pipe 38, and the circulating cooling water is circulated. The refrigerant that has been converted into a gas through heat exchange with the circulating cooling water is sent to the compressor 46 through piping 48. In the compressor 46, the refrigerant is compressed and changes into a high-temperature, high-pressure gas. The high-temperature, high-pressure refrigerant is sent to the condenser 42 through piping 48, where the cycle of condensation → expansion → evaporation → compression is repeated.

By having a first reverse osmosis membrane treatment device 71 (first reverse osmosis membrane treatment process) that performs reverse osmosis membrane treatment on the water to be treated that contains inorganic salts upstream of the heating device 10 (heating process), the number of membranes required for the semipermeable membrane treatment process can be reduced.

By having a second reverse osmosis membrane treatment device 72 (second reverse osmosis membrane treatment process) that performs reverse osmosis membrane treatment on the diluted water downstream of the semipermeable membrane treatment device 12 (semipermeable membrane treatment process), the water recovery rate can be improved, and the inorganic salt recovery rate can also be improved.

1, 2, 3 inorganic salt recovery device, 10 heating device, 12 semipermeable membrane treatment device, 14 cooling device, 16 solid-liquid separation device, 18, 20, 22, 24, 24a, 24b, 24c, 26, 28, 30, 34, 36, 38, 40, 47, 48, 66, 66a, 66b, 66c, 70, 70a, 70b, 70c, 74, 76, 78, 80, 82, 84, 86, 88, 90 piping, 32 heat pump, 42 condenser, 44 evaporator, 45 expansion valve, 46 compressor, 50, 50a, 50b, 50c membrane module, 52, 52a, 52b, 52c semipermeable membrane, 54, 54a, 54b, 54c First space, 56, 56a, 56b, 56c Second space, 58 Pump, 60 Inverter, 62, 62a, 62b, 62c, 64, 68, 68a, 68b, 68c Valve, 71 First reverse osmosis membrane treatment device, 72 Second reverse osmosis membrane treatment device.

Claims (8)

A heating means for heating the water to be treated containing inorganic salts to a temperature in the range of 30°C to 40°C to obtain heated water;
a semipermeable membrane treatment means for using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the heated water through the first space, pressurizing the first space, and causing water contained in the heated water to permeate through the semipermeable membrane to obtain concentrated water, and passing a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water;
a cooling means for cooling the concentrated water to a temperature in the range of 15° C. to 25° C. to crystallize the inorganic salt;
Equipped with
The inorganic salt recovery device is characterized in that the inorganic salt is a substance whose solubility in water increases by 0.5 g/100 g-H ₂ O or more per 1° C. of water temperature in the range of 15° C. to 40° C. The inorganic salt recovery apparatus according to claim 1,
The heating means heats the water to be treated by heat exchange with a first heat medium,
The cooling means cools the concentrated water by heat exchange with a second heat medium,
The inorganic salt recovery apparatus further comprises a heat pump means for exchanging heat between the first heat medium and the second heat medium. The inorganic salt recovery apparatus according to claim 1 or 2,
The inorganic salt recovery apparatus further comprises a solid-liquid separation means for performing solid-liquid separation of the crystallized inorganic salt downstream of the cooling means. The inorganic salt recovery apparatus according to any one of claims 1 to 3,
The inorganic salt recovery apparatus further comprises a first reverse osmosis membrane treatment means upstream of the heating means, the water to be treated is subjected to reverse osmosis membrane treatment to obtain a first RO concentrated water and a first RO permeate, and the first RO concentrated water is heated by the heating means. The inorganic salt recovery apparatus according to any one of claims 1 to 4,
The inorganic salt recovery apparatus further comprises a second reverse osmosis membrane treatment means downstream of the semipermeable membrane treatment means, and is characterized in that the dilution water is treated with a reverse osmosis membrane to obtain a second RO concentrated water and a second RO permeate. A heating step of heating the water to be treated containing inorganic salts to a temperature in the range of 30°C to 40°C to obtain heated water;
a semipermeable membrane treatment step of passing the heated water through a first space using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, pressurizing the first space to cause water contained in the heated water to permeate through the semipermeable membrane to obtain concentrated water, and passing a part of the heated water or at least a part of the concentrated water through the second space to obtain dilution water;
a cooling step of cooling the concentrated water to a temperature in the range of 15° C. to 25° C. to crystallize the inorganic salt;
Including,
The inorganic salt recovery method is characterized in that the inorganic salt is a substance whose solubility in water increases by 0.5 g/100 g-H ₂ O or more per 1° C. of water temperature in the range of 15° C. to 40° C. The method for recovering inorganic salts according to claim 6,
In the heating step, the water to be treated is heated by heat exchange with a first heat medium,
In the cooling step, the concentrated water is cooled by heat exchange with a second heat medium;
The method for recovering an inorganic salt further comprises a heat pump step of exchanging heat between the first heat medium and the second heat medium. The method for recovering inorganic salts according to claim 6 or 7,
The method for recovering an inorganic salt further comprises, after the cooling step, a solid-liquid separation step of separating the crystallized inorganic salt into solid and liquid.