Membrane treatment method and apparatus for liquid to be treated

Abstract

To provide a membrane treatment apparatus for a liquid to be treated capable of efficiently concentrating the liquid to be treated at a high concentration.SOLUTION: A membrane treatment apparatus for a liquid to be treated includes a plurality of first membrane units 10-1, 10-2 for concentrating a liquid to be treated by increasing a pressure of the liquid to be treated in multiple stages, and a second membrane unit 20 for further concentrating the treated liquid concentrated in the plurality of first membrane units 10-1, 10-2 by contacting the recovered liquid at a lower pressure than the liquid to be treated through a semipermeable membrane to generate a concentrated liquid. The plurality of first membrane units 10-1, 10-2 produce and discharge freshwater in the first membrane units 10-1, 10-2 by feeding the non-permeate of the first membrane unit 10-1 in the first stage to the first membrane unit 10-2 in the second stage, and the liquid to be treated concentrated in the first membrane units 10-1, 10-2 is discharged, and the second membrane unit 20 uses a part of the non-permeated liquid of the first membrane unit 10-1 of the preceding stage as a recovered liquid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and apparatus for membrane treatment of a liquid to be treated, and more particularly to a method and apparatus for membrane treatment of a liquid to be treated using a reverse osmosis membrane.

Background Art

[0002] As an apparatus for membrane-treating a liquid to be treated such as seawater, Patent Document 1 discloses that seawater is supplied to a first reverse osmosis membrane module to separate fresh water and discharge concentrated brine, while low osmotic pressure water is supplied to a second reverse osmosis membrane module to separate fresh water and discharge concentrated low osmotic pressure water, and the discharged concentrated brine and concentrated low osmotic pressure water are supplied to a forward osmosis membrane module, and a water production system is disclosed in which the concentrated brine is diluted with water supplied from the concentrated low osmotic pressure water through the forward osmosis membrane.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above water production system is mainly aimed at increasing the amount of water production, and since it is configured to dilute the concentrated seawater generated by the first reverse osmosis membrane module in the forward osmosis membrane module, there is room for consideration in increasing the concentration ratio when concentrating and recovering the liquid to be treated.

[0005] Therefore, an object of the present invention is to provide a method and apparatus for membrane treatment of a liquid to be treated that can efficiently concentrate the liquid to be treated at a high concentration.

Means for Solving the Problems

[0006] The object of the present invention is achieved by a liquid treatment method comprising: a first concentration step of pressurizing a liquid to be treated and concentrating it in a plurality of stages of a first membrane unit; and a second concentration step of supplying the liquid to be treated concentrated in the first concentration step to a second membrane unit and bringing it into contact with a recovered liquid at a pressure lower than that of the liquid to be treated through a semipermeable membrane to further concentrate the liquid to be treated and generate a concentrated liquid. In the first concentration step, the non-permeate of the previous-stage first membrane unit is sequentially supplied to the subsequent-stage first membrane unit, so that fresh water permeated through the membrane is generated in each stage of the first membrane unit and discharged without being mixed with other liquids, and the liquid to be treated concentrated without permeating through the membrane in any of the first membrane units in each stage is discharged. The second concentration step is achieved by a liquid treatment method in which a part of the non-permeate of the first membrane unit other than the last stage is used as the recovered liquid.

[0007] In this liquid treatment method, it is preferable that the second concentration step includes a step of depressurizing a part of the non-permeate of the first membrane unit to be the recovered liquid. The depressurization of the non-permeate of the first membrane unit can be performed by pressure exchange with the non-permeate of the first membrane unit on the subsequent stage side of the first membrane unit.

[0008] Further, it is preferable that the first concentration step includes a step of pressurizing the liquid to be treated supplied to the first membrane unit at the foremost stage or the non-permeate of the first membrane unit other than the last stage by pressure exchange with the concentrated liquid generated in the second membrane unit.

[0009] It is preferable that the first concentration step includes a step of pressurizing the liquid to be treated supplied to the first membrane unit at the foremost stage or the non-permeate of the first membrane unit other than the last stage by a high-pressure pump or a booster pump capable of inverter control.

[0010] It is preferable that the first concentration step includes a step of merging the recovered liquid that has passed through the second membrane unit into the liquid to be treated supplied to the first membrane unit at the foremost stage.

[0011] Further, the object of the present invention is achieved by a membrane treatment apparatus for a liquid to be treated, which includes a plurality of first membrane units that pressurize the liquid to be treated and concentrate it in multiple stages, and a second membrane unit that further concentrates the liquid to be treated concentrated by the plurality of first membrane units by bringing it into contact with a recovery liquid at a lower pressure than the liquid to be treated through a semipermeable membrane to generate a concentrated liquid. The plurality of first membrane units sequentially supply the non-permeate liquid of the previous-stage first membrane unit to the subsequent-stage first membrane unit, thereby generating fresh water that has permeated through the membrane in each stage of the first membrane units and discharging the fresh water without mixing it with other liquids. At the same time, the liquid to be treated that has been concentrated without permeating through the membrane in any of the first membrane units in each stage is discharged. The second membrane unit uses a part of the non-permeate liquid of the first membrane units other than the last stage as the recovery liquid.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a membrane treatment method and apparatus for a liquid to be treated that can efficiently concentrate the liquid to be treated at a high concentration.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a membrane treatment apparatus for a liquid to be treated (hereinafter simply referred to as a "membrane treatment apparatus") according to an embodiment of the present invention. As shown in FIG. 1, the membrane treatment apparatus 1 mainly includes two-stage first membrane units 10-1 and 10-2 for concentrating the liquid to be treated, a second membrane unit 20 for further concentrating the liquid to be treated concentrated by the first membrane units 10-1 and 10-2 to generate a concentrated liquid, and an energy recovery device 30 for recovering the pressure energy of the concentrated liquid.

[0015] The first membrane units 10-1 and 10-2 each consist of a membrane module having RO membranes (reverse osmosis membranes) 11-1 and 11-2 in a casing, and the liquid to be treated is supplied in series. The non-permeate liquid that does not pass through the RO membrane 11-1 in the first-stage first membrane unit 10-1 is supplied to the second-stage first membrane unit 10-2, and the non-permeate liquid that does not pass through the second-stage RO membrane 11-2 is supplied to the second membrane unit 20. The shapes of the RO membranes 11-1 and 11-2 are not particularly limited, and flat membranes, hollow fiber membranes, etc. can be exemplified.

[0016] The second membrane unit 20 has a high-pressure chamber 22 and a low-pressure chamber 23 formed by partitioning the inside of the casing with a semi-permeable membrane 21. The liquid to be treated concentrated by the first membrane units 10-1 and 10-2 is introduced into the high-pressure chamber 22, while a part of the non-permeate liquid discharged from the first-stage first membrane unit 10-1 is supplied as a recovered liquid to the low-pressure chamber 23 after being depressurized by a pressure reducing device 40 such as a pressure reducing valve. The liquid to be treated and the recovered liquid introduced into the high-pressure chamber 22 and the low-pressure chamber 23 respectively come into contact through the semi-permeable membrane 21 and are then discharged to the outside. The semi-permeable membrane 21 may be a hollow fiber membrane in addition to a flat membrane. The semi-permeable membrane 21 can preferably use an RO membrane (reverse osmosis membrane), but other semi-permeable membranes such as an FO membrane (forward osmosis membrane) may also be used.

[0017] The energy recovery device 30 consists of a turbocharger, which rotates a turbine with the concentrated liquid discharged from the second membrane unit 20, and uses this power to boost the pressure of the liquid to be treated supplied from the first-stage first membrane unit 10-1 to the second-stage first membrane unit 10-2. The configuration of the energy recovery device 30 is not particularly limited as long as it can recover the energy of the concentrated liquid and boost the pressure of the liquid to be treated. For example, other energy recovery devices such as a rotor type or a piston type other than the turbine type may be used.

[0018] Next, a method for membrane treating a liquid to be treated using the membrane treatment device 1 having the above configuration will be described. First, a liquid to be treated such as seawater is pressurized to about 4 MPa by a high-pressure pump 2 and then supplied in series to the two-stage first membrane units 10-1 and 10-2 for the first concentration step of concentration. In the first membrane units 10-1 and 10-2, fresh water (produced water) is generated as the liquid to be treated permeates through the RO membranes 11-1 and 11-2, and the liquid to be treated concentrated without permeating through any of the RO membranes 11-1 and 11-2 in each stage is discharged.

[0019] Then, a second concentration step is performed to generate a concentrated liquid by supplying the liquid to be treated concentrated in the first concentration step to the second membrane unit 20 for further concentration. The high-pressure chamber 22 of the second membrane unit 20 is supplied with the liquid to be treated concentrated in the second-stage first membrane unit 10-2, which is the last stage, while the low-pressure chamber 23 is supplied with the liquid to be treated concentrated in the first-stage first membrane unit 10-1 as a recovered liquid.

[0020] The liquid to be treated supplied to the high-pressure chamber 22 is pressurized by the energy recovery device 30 in the process of being supplied from the first-stage first membrane unit 10-1 to the second-stage first membrane unit 10-2. On the other hand, the recovered liquid supplied to the low-pressure chamber 23 is depressurized by the pressure reduction device 40, so that the high-pressure chamber 22 has a higher pressure than the low-pressure chamber 23. Further, as the recovered liquid supplied to the low-pressure chamber 23, by using the liquid to be treated during the concentration by the plurality of stages of the first membrane units 10-1 and 10-2 (that is, the liquid to be treated concentrated by the first-stage first membrane unit 10-1 and before being concentrated by the second-stage first membrane unit 10-2), the osmotic pressure difference from the liquid to be treated supplied to the high-pressure chamber 22 is reduced. As a result, due to the pressure difference between the high-pressure chamber 22 and the low-pressure chamber 23, the movement of water from the high-pressure chamber 22 to the low-pressure chamber 23 through the semipermeable membrane is promoted. Therefore, the liquid to be treated can be further concentrated without particularly increasing the performance or number of the high-pressure pump 2. For example, even in the case of a liquid to be treated with a low salt concentration (for example, about 0.5%), it can be concentrated to a high concentration with energy savings. The concentrated liquid generated by the second membrane unit 20 is depressurized by the energy recovery device 30 and then discharged out of the system, and can be used in other processes such as forward osmosis power generation and desalination by evaporation concentration for salt production.

[0021] The recovered liquid from which water has been recovered from the concentrated liquid in the second membrane unit 20 is merged with the liquid to be treated, then pressurized by the high-pressure pump 2, and supplied again to the first-stage first membrane unit 10-1. Thereby, the production efficiency of fresh water in the first membrane units 10-1 and 10-2 can be increased, and since the liquid to be treated is diluted and the osmotic pressure decreases, it can be supplied to the first membrane units 10-1 and 10-2 at a low pressure. From this point as well, energy savings of the high-pressure pump 2 can be achieved. When it is necessary to pressurize the liquid to be treated supplied to the high-pressure chamber 22 of the second membrane unit 20 due to energy savings of the high-pressure pump 2, a booster pump or the like may be provided in the pipe for supplying the liquid to be treated from the second-stage first membrane unit 10-2 to the second membrane unit 20. The recovered liquid is preferably merged with the liquid to be treated upstream of the high-pressure pump 2, but may also be merged with the liquid to be treated downstream of the high-pressure pump 2.

[0022] The membrane treatment apparatus 1 shown in Fig. 1 is configured to concentrate the liquid to be treated by two-stage first membrane units 10-1 and 10-2. However, the number of stages of the first membrane unit is not particularly limited as long as it is plural, and it may be configured to concentrate in three or more stages. Fig. 2 is a schematic configuration diagram of a membrane treatment apparatus according to another embodiment of the present invention, which includes three-stage first membrane units 10-1, 10-2, and 10-3, each of which includes RO membranes 11-1, 11-2, and 11-3. In Fig. 2, the same reference numerals are given to the same components as those in Fig. 1 (the same applies to the following figures).

[0023] In the membrane treatment apparatus 101 shown in Fig. 2, the non-permeate of the first-stage first membrane unit 10-1 is supplied to the second-stage first membrane unit 10-2, and the non-permeate of the second-stage first membrane unit 10-2 is supplied to the third-stage first membrane unit 10-3. In this way, by sequentially supplying the non-permeate of the previous-stage first membrane unit to the subsequent-stage first membrane unit, a first concentration step is performed in which the liquid to be treated is supplied to the first membrane units 10-1, 10-2, and 10-3 in series and concentrated. Next, a second concentration step is performed in which the liquid to be treated concentrated in the first concentration step is further concentrated in the second membrane unit 20. The concentrated liquid generated in the second concentration step is supplied to the energy recovery device 30 to boost the pressure of the liquid to be treated supplied from the first-stage first membrane unit 10-1 to the second-stage first membrane unit 10-2.

[0024] The membrane treatment apparatus 101 shown in Fig. 2 includes a pressure reduction device 40 that reduces the pressure of the liquid to be treated supplied as a recovered liquid to the second membrane unit 20. The pressure reduction device 40 is an energy recovery device having the same configuration as the energy recovery device 30. A part of the non-permeate of the first-stage first membrane unit 10-1 is depressurized by exchanging pressure with the non-permeate of the second-stage first membrane unit 10-2 in the pressure reduction device 40, and then supplied to the second membrane unit 20 as a recovered liquid. On the other hand, the non-permeate of the second-stage first membrane unit 10-2 is pressurized by the pressure reduction device 40 and supplied to the third-stage first membrane unit 10-3.

[0025] When the first membrane unit is arranged in multiple stages of three or more stages, the non-permeate of the first membrane unit used as the recovered liquid does not necessarily have to be the non-permeate of the first-stage first membrane unit, which is the frontmost stage. It can be the non-permeate of the first membrane unit other than the last stage. For example, the membrane treatment apparatus 201 shown in FIG. 3 includes three-stage first membrane units 10-1, 10-2, and 10-3. A part of the non-permeate of the second-stage first membrane unit 10-2 is depressurized by a pressure reducing device 40 composed of a pressure reducing valve and then supplied as the recovered liquid to the second membrane unit 20. In the configuration shown in FIG. 3, a part of the non-permeate of each of the first-stage first membrane unit 10-1 and the second-stage first membrane unit 10-2 can also be used as the recovered liquid.

[0026] The depressurization of the non-permeate of the first membrane unit used as the recovered liquid can be performed by pressure exchange with the non-permeate of any other first membrane unit in the pressure reducing device 40. However, it is preferable that the recovered liquid is depressurized by pressure exchange with the non-permeate of the first membrane unit on the subsequent stage side of the said first membrane unit.

[0027] In the membrane treatment apparatus in each of the above embodiments, the recovery of the pressure energy of the concentrated liquid by the energy recovery device 30 is performed by pressure exchange with the non-permeate of the first-stage first membrane unit 10-1. However, when the first membrane unit is arranged in multiple stages of three or more stages, it may also be performed by pressure exchange with the non-permeate of the first membrane unit from the second stage onward other than the last stage. For example, in the membrane treatment apparatuses 101 and 201 shown in FIGS. 2 and 3, the non-permeate of the second-stage first membrane unit 10-2 may be pressurized by pressure exchange with the concentrated liquid generated in the second membrane unit 20.

[0028] FIG. 4 is a schematic configuration diagram of a membrane treatment apparatus according to still another embodiment of the present invention. In the membrane treatment apparatuses shown in FIGS. 1 to 3, the energy recovery device 30 boosts the non-permeate liquid of the first membrane unit (for example, the first membrane unit 10-1 in the first stage) other than the last stage by pressure exchange with the concentrate generated in the second membrane unit 20. In contrast, in the membrane treatment apparatus 301 shown in FIG. 4, the energy recovery device 30 composed of a turbocharger or the like is arranged to further boost the liquid to be treated that is boosted by the high-pressure pump 2 and supplied to the first membrane unit 10-1 in the foremost stage by pressure exchange with the concentrate generated in the second membrane unit 20. According to the membrane treatment apparatus 301 shown in FIG. 4, since the energy recovery device 30 supplements the boosting of the liquid to be treated, the motor capacity of the high-pressure pump 2 can be reduced, so that miniaturization is possible and the manufacturing cost and running cost can be reduced.

[0029] Further, the membrane treatment apparatus 301 is provided with a booster pump 4 for boosting the non-permeate liquid of the first membrane unit 10-1 in the first stage between the first membrane unit 10-1 in the first stage and the first membrane unit 10-2 in the second stage. The booster pump 4 is a pump capable of inverter control, and can easily control the flow rate and pressure of the non-permeate liquid supplied to the first membrane unit 10-2 in the second stage by controlling the motor rotation speed, and energy saving can be achieved because a throttle in the flow path is not required. When three or more stages of the first membrane units are arranged, booster pumps with inverter control may be provided for all between the first membrane units of each stage, or booster pumps with inverter control may be provided only at necessary locations between the first membrane units of each stage.

[0030] Also, the high-pressure pump 2 of the membrane treatment apparatuses shown in FIGS. 1 to 4 may be a pump capable of inverter control, and energy saving can also be achieved thereby. In particular, in the membrane treatment apparatus 301 shown in FIG. 4, since the motor capacity of the high-pressure pump 2 can be reduced by the energy recovery device 30 as described above, in combination with the high-pressure pump 2 capable of inverter control, the cost of the inverter device can be reduced and the installation hurdle can be lowered.

[0031] In each of the above embodiments, the pressure reducing device 40 uses a pressure reducing valve or an energy recovery device, but other devices that can effectively utilize pressure energy may also be used. For example, by using a turbine having a power generation function as the pressure reducing device 40, the recovered electrical energy can be used for the above high-pressure pumps, booster pumps, etc., so that further energy savings can be achieved.

Explanation of Signs

[0032] 1,101,201,301 Membrane treatment device 10-1,10-2,10-3 First membrane unit 20 Second membrane unit 30 Energy recovery device 40 Pressure reducing device

Claims

1. a first concentration step of boosting the liquid to be treated and concentrating it in a plurality of stages of a first membrane unit; a second concentration step of supplying the liquid to be treated concentrated in the first concentration step to a second membrane unit and bringing it into contact with a recovered liquid at a pressure lower than that of the liquid to be treated through a semipermeable membrane to further concentrate the liquid to be treated and generate a concentrated liquid; in the first concentration step, the non-permeate of the previous-stage first membrane unit is sequentially supplied to the subsequent-stage first membrane unit, so that fresh water permeated through the membrane is generated in each stage of the first membrane unit, and the fresh water is discharged without being mixed with other liquids, and the liquid to be treated concentrated without permeating through the membrane in any of the first membrane units in each stage is discharged; a method for membrane treatment of a liquid to be treated, wherein the second concentration step uses a part of the non-permeate of the first membrane unit other than the last stage as the recovered liquid.

2. The method for membrane treatment of a liquid to be treated according to claim 1, wherein the first concentration step includes a step of combining the recovered liquid that has passed through the second membrane unit with the liquid to be treated supplied to the first membrane unit at the frontmost stage and concentrating the combined liquid in the plurality of stages of the first membrane unit.

3. The method for membrane treatment of a liquid to be treated according to claim 1, wherein the first concentration step includes a step of boosting the liquid to be treated discharged from the first membrane unit at the frontmost stage and supplying it to the subsequent-stage first membrane unit.

4. The method for membrane treatment of a liquid to be treated according to claim 1, wherein the second concentration step includes a step of depressurizing a part of the non-permeate of the first membrane unit that becomes the recovered liquid.

5. The method for membrane treatment of a liquid to be treated according to claim 4, wherein the depressurization of the non-permeate of the first membrane unit is performed by pressure exchange with the non-permeate of the first membrane unit on the subsequent stage side of the first membrane unit.

6. The method for membrane treatment of a liquid to be treated according to any one of claims 1 to 5, wherein the first concentration step includes a step of boosting the liquid to be treated supplied to the first membrane unit at the frontmost stage or the non-permeate of the first membrane unit other than the last stage by pressure exchange with the concentrated liquid generated in the second membrane unit.

7. The method for membrane treatment of a liquid to be treated according to any one of claims 1 to 6, wherein the first concentration step includes a step of boosting the liquid to be treated supplied to the first membrane unit at the frontmost stage or the non-permeate of the first membrane unit other than the last stage by a high-pressure pump or a booster pump capable of inverter control.

8. a plurality of first membrane units for boosting the liquid to be treated and concentrating it in a plurality of stages; A second membrane unit that further concentrates the liquid to be treated concentrated by the plurality of first membrane units by bringing it into contact with a recovered liquid at a lower pressure than the liquid to be treated through a semipermeable membrane to generate a concentrated liquid. The plurality of first membrane units generate fresh water that has permeated through the membrane in each stage of the first membrane units by sequentially supplying the non-permeate liquid of the previous-stage first membrane unit to the subsequent-stage first membrane unit, and discharge the fresh water without mixing it with other liquids. At the same time, the liquid to be treated that has been concentrated without permeating through the membrane in any of the first membrane units in each stage is discharged. The second membrane unit is a membrane treatment apparatus for the liquid to be treated that uses a part of the non-permeate liquid of the first membrane units other than the last stage as the recovered liquid.

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