JP2016190220A - Membrane distillation system and operation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane distillation system which has a compact and simplified structure and an operation method thereof.SOLUTION: A membrane distillation system 100 comprises: a membrane distillation device 10 comprising a hydrophobic porous hollow fiber membrane 1; and a flushing mechanism 6. The membrane distillation device 10 comprises: a first liquid phase part where raw water flows; a first gas phase part; an evaporation part; a second liquid phase part where cooling water flows; a second gas phase part; a condensation part formed of a coolant; and a third gas phase part 32. The shortest distance between the hydrophobic porous hollow fiber membrane 1 of the evaporation part and the coolant of the condensation part is equal to or more than 10 mm, and the pressure on the first gas phase part, on the second gas phase part and on the third gas phase part may be equal to or more than 1 kPa and equal to or less than saturation vapor pressure of the water at raw water temperature.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a membrane distillation system and a method for operating the same.

  The membrane distillation method uses a hydrophobic porous membrane that only permeates water vapor, and condenses the water vapor that has passed through the hydrophobic porous membrane due to a saturated water vapor pressure difference from heated raw water (high temperature water) to obtain distilled water. Is the method. Membrane distillation does not require high pressure and can reduce kinetic energy compared to reverse osmosis in which pressure is applied to raw water and filtered through a reverse osmosis membrane to obtain purified water. In addition, distilled water obtained by membrane distillation method has extremely high performance for separating non-volatile solutes such as salinity, and high-purity water can be obtained.

  The principle of the main membrane distillation method is shown in FIG. In FIG. 1, (a) is a DCMD method (Direct Contact Membrane Distillation) in which water vapor from the high temperature water side is directly taken into low temperature water as distilled water generated through the hydrophobic porous membrane 1 '. (B) shows that an air gap 3 'is provided between the hydrophobic porous membrane 1' and the condenser 2 ', and the condenser 2' (for example, a cooling plate made of metal such as aluminum or stainless steel having high heat conductivity). This is an AGMD method (Air Gap Membrane Distillation) in which water vapor from the high temperature water side is condensed on the surface to obtain distilled water. (C) is a VMD method (vacuum membrane distribution) in which a vacuum gap is provided on the distillation side of the hydrophobic porous membrane 1 ′ and water vapor from the high temperature water side is moved to the outside to obtain distilled water. (D) is an SGMD method (Sweeping Gas Membrane Distillation) in which a sweeping gas is allowed to flow to the distillation side of the hydrophobic porous membrane 1 ′ and water vapor from the high temperature water side is moved to the outside to obtain distilled water.

  The DCMD method is configured by a simple device in which high-temperature water and cooling water (low-temperature water) flow through a membrane, and the movement distance of water vapor is equal to the film thickness and the movement resistance is small, so the per unit area of the membrane Although the amount of distilled water (Flux) can be increased, the produced distilled water must be taken out of the cooling water. In addition, since high-temperature water and cooling water are in direct contact with each other through a membrane, heat loss occurs due to heat exchange, and the difference in vapor pressure, which is the driving force for the movement of water vapor, is reduced, resulting in thermal energy efficiency for water production There is also a disadvantage that becomes lower.

  On the other hand, the gap-type membrane distillation mainly using the AGMD method has a merit that distilled water can be directly taken out although the movement resistance is large and the flux tends to be small because the air gap 3 'moves in addition to the membrane. . Moreover, since the high-temperature water and the cooling water are not in direct contact with each other through the membrane, heat loss can be minimized, the thermal energy efficiency is high, and the water production cost can be reduced.

In addition, the membrane distillation method has a fouling problem caused by a separation target existing in membrane supply water such as raw water, as in other membrane separation methods. Fouling refers to a phenomenon in which a substance to be separated existing in a membrane supply water such as raw water adheres to and accumulates on the membrane surface or pores. The main constituents of fouling include inorganic substances such as silica, aluminum, iron, calcium, and manganese, natural organic substances (NOM), and organic substances resulting from microbial metabolites. In the membrane distillation method, when the membrane surface is contaminated, the evaporation surface of the water vapor is blocked by the contamination, resulting in functional deterioration. In particular, when the concentration of the raw water increases to increase the recovery rate of purified water relative to the raw water, or under operating conditions for the purpose of concentrating the raw water system, membrane clogging is likely to occur, resulting in a problem of reduced water permeability.
The following studies have been made as countermeasures against fouling.

Patent Document 1 discloses a method for regenerating a hydrophobic porous membrane in which the hydrophobic porous membrane is washed with a chemical that decomposes organic substances and dried.
Patent Document 2 discloses a membrane distillation system in which a membrane distillation apparatus is pretreated by chemical treatment or biological treatment.

JP-A-5-192543 JP 2010-75808 A

In order to expand the use of membrane distillation technology in the future of pure water production and water treatment areas, membrane distillation systems that have both stable water treatment capacity and compactness against fouling are required.
As described above, as a countermeasure against fouling, there are a method of cleaning a film using a chemical that decomposes organic matter, and a method of removing a substance causing fouling by chemical treatment or biological treatment. However, installation of pretreatment equipment and a dryer are required, and there is a problem that the system becomes large.
On the other hand, backwashing is known as a washing method for separation membranes such as microfiltration membranes and ultrafiltration membranes widely used in water purification treatment, but it is difficult to apply to hydrophobic porous membranes of membrane distillation method It is. Since the hydrophobic porous membrane of membrane distillation method is used in a dry state, it is necessary to apply high pressure to pass the inside of the membrane with a cleaning liquid, and also to dry and regenerate the membrane after cleaning. Therefore, it is very troublesome and costly.
In order to solve the above problems, an object of the present invention is to provide a cleaning system having a compact and simple configuration and an operation method thereof.

  The present inventors pay attention to the fact that dirt attached to the membrane surface in the membrane distillation method is less affected by compaction than dirt attached to a filtration membrane that is filtered by applying pressure to water. The present invention was completed by finding that the adhered dirt can be easily removed by flushing the washing water without applying it.

That is, the present invention is as follows.
(1)
A membrane distillation system comprising a membrane distillation apparatus provided with a hydrophobic porous membrane, and a flushing mechanism for flushing the hydrophobic porous membrane.
(2)
The membrane distillation apparatus according to (1), wherein the first liquid phase part through which raw water flows, the first gas phase part, the first liquid phase part and the first gas phase part are separated from each other. From an evaporation section made of a porous hollow fiber membrane, a second liquid phase section through which cooling water flows, a second gas phase section, and a cooling body that separates the second liquid phase section and the second gas phase section A condensing part, and a third gas phase part connecting the first gas phase part and the second gas phase part, the hydrophobic porous hollow fiber membrane of the evaporation part and the cooling of the condensation part The shortest distance to the body is 10 mm or more, and the pressures of the first gas phase part, the second gas phase part and the third gas phase part are 1 kPa or more and the raw water temperature water Membrane distillation system used between below saturated vapor pressure.
(3)
A method for operating the membrane distillation system according to (1), wherein a membrane distillation step in which raw water is permeated through the hydrophobic porous hollow fiber membrane and membrane distillation is performed, and washing water is supplied to the hydrophobic porous hollow fiber membrane And a flushing step for flushing, and a method for operating the membrane distillation system.
(4)
(3) The operation method of the membrane distillation system characterized by using raw water or water having lower conductivity than the raw water as the washing water.

  ADVANTAGE OF THE INVENTION According to this invention, the membrane distillation system of a compact and simple structure and its operating method can be provided.

The schematic diagram of a membrane distillation method is shown, (a) is DCMD method (Direct Contact Membrane Distillation), (b) is AGMD method (Air Gap Membrane Distillation), (c) is VMD method (Vacuum) (D) is an SGMD method (Sweeping Gas Membrane Distribution). The schematic diagram of the membrane distillation system of this invention is shown. It is a figure which expands and shows a membrane distillation apparatus.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The hydrophobic porous hollow fiber membrane 1 is not particularly limited as long as it is produced by a conventionally known method and is a porous hollow fiber membrane made of a hydrophobic polymer as a main constituent component.
The hydrophobic polymer is a polymer having a low affinity for water, and examples thereof include polysulfone, polyethersulfone, polyethylene, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene.
The hydrophobic polymer as the main constituent component means that the component constituting the hydrophobic porous hollow fiber membrane 1 contains 90% by mass or more of the hydrophobic polymer, and 95% by mass or more from the viewpoint of the strength of the membrane. It is preferable that it is 99 mass% or more.

  The method for producing the hydrophobic porous hollow fiber membrane 1 includes a heat-induced phase separation method in which a phase separation is caused by cooling to form a porous layer, and a phase separation is caused by contact with a non-solvent to form a porous layer. Any of the dry and wet methods (non-solvent phase separation method) can be suitably used.

  The hydrophobic porous hollow fiber membrane 1 used in the present embodiment has an average pore diameter of preferably 0.2 μm or more, and more preferably 0.5 μm or more, from the viewpoint of water permeability as membrane distillation. If the average pore diameter is too high, the water repellency of the film surface decreases, and a wetting phenomenon in which water penetrates into the film occurs, leading to performance degradation.

  The hydrophobic porous hollow fiber membrane 1 used in the present embodiment preferably has a film thickness of 10 μm to 500 μm, preferably 15 μm to 300 μm, from the viewpoint of water permeability as membrane distillation and mechanical strength of the membrane. It is more preferable that it is between 20 μm and 150 μm. If the film thickness is too large, the water vapor transmission resistance is high, leading to a decrease in water permeability performance. Therefore, it is preferably less than 500 μm. If the film thickness is too small, the film may be deformed or the flow path may be blocked when used under reduced pressure. Since it becomes easy, it is preferable that it is 10 micrometers or more.

  The hydrophobic porous hollow fiber membrane 1 used in the present embodiment preferably has a porosity of 60% or more, and more preferably 70% or more, from the viewpoint of water permeability as membrane distillation. In addition, since the mechanical strength of a film | membrane will fall when the porosity becomes high too much and it will lead to the water leak in use under pressure reduction, it is preferable that it is less than 90%.

The membrane distillation apparatus 10 of the present embodiment has a first liquid phase part 11 through which raw water flows, a first gas phase part 12, and a hydrophobic property that separates the first liquid phase part 11 and the first gas phase part 12. The evaporation section 14 made of the porous hollow fiber membrane 1, the second liquid phase section 21 through which cooling water flows, the second gas phase section 22, the second liquid phase section 21 and the second gas phase section 22 are connected. A condensing unit 24 composed of a cooling body 25 that separates, and a third gas phase unit 32 connecting the first gas phase unit 12 of the evaporation unit 14 and the second gas phase unit 22 of the condensing unit 24,
The shortest distance between the hydrophobic porous hollow fiber membrane 1 of the evaporation unit 14 and the cooling body 25 of the condensing unit 24 is 10 mm or more, and the pressure of the gas phase units 12, 22, 32 is 1 kPa or more. It is a membrane distillation apparatus used between the vapor pressure and below.

The membrane distillation apparatus 10 of this embodiment includes an evaporation unit 14, a condensing unit 24, and a third gas phase unit 32.
The evaporation unit 14 is made of the hydrophobic porous hollow fiber membrane 1. More specifically, the evaporating unit 14 bundles, for example, the hydrophobic porous hollow fiber membranes 1 and stores them in a cylindrical resin or metal container 18, and at the end of the hollow fiber, the hollow fibers are connected to each other. The gap between the hollow fiber and the container 18 is filled and fixed with a fixing resin (potting resin). The end of the hydrophobic porous hollow fiber membrane 1 is open, and a head portion 16 (17) having a water flow port 16a (17a) is attached to the upper and lower ends of the container 18. In addition, a connection port (not shown) for connecting to the condensing unit 24 is provided on the side surface of the container 18. The number of connection ports is not particularly limited, and may be single or plural.

The hollow lumen of the hydrophobic porous hollow fiber membrane 1 provided in the evaporation part 14 becomes the first liquid phase part 11 through which raw water flows. The outer membrane side of the hydrophobic porous hollow fiber membrane 1 becomes the first gas phase portion 12 in the container 18 constituting the evaporation portion 14.
The raw water passed through the hollow lumen of the hydrophobic porous hollow fiber membrane 1 passes through the membrane wall of the hydrophobic porous hollow fiber membrane 1 as water vapor and moves to the first gas phase portion 12. At that time, non-volatile solutes such as salt that cannot move on the membrane wall are separated by the hydrophobic porous hollow fiber membrane 1.

  In this embodiment, the raw water is water that needs to be purified or concentrated for some purpose. For example, tap water, industrial water, river water, well water, lake water, seawater, industrial wastewater (food factories, chemical water) Waste water from factories such as factories, electronics industry factories, pharmaceutical factories, and cleaning factories), and associated water discharged during the production of oil and natural gas.

The raw water has a water temperature of preferably 50 ° C. or higher, more preferably 80 ° C. or higher, from the viewpoint of water permeability.
The water temperature of the raw water may be controlled by using heat sources such as heat exchangers and heaters, but using solar heat or exhaust heat from industrial processes, etc., does not require the heat energy cost required for heating. Or more preferable because it can be reduced.

The condensing unit 24 includes a cooling body 25. More specifically, the condensing unit 24 stores, for example, the cooling body 25 in a cylindrical resin or metal container 28, and a gap between the cooling bodies 25 at the end of the cooling body 25 and the cooling The gap between the body 25 and the container 28 is formed by filling and fixing with a fixing resin (potting resin). An end portion of the cooling body 25 is open, and a head portion 26 (27) having a water passage 26a (27a) is attached to both upper and lower ends of the container 28. Further, a connecting port for connecting to the evaporation unit 14 is provided on the side surface of the container. The number of connection ports is not particularly limited, and may be single or plural.
The shape of the cooling body 25 may be hollow or flat, but a hollow tube can be used preferably.

The cooling body 25 is provided in the condensing part 24, and the internal area | region of the cooling body 25 becomes the 2nd liquid phase part 21 through which cooling water flows. The external region of the cooling body 25 becomes the second gas phase unit 22 in the container 28 constituting the condensing unit 24.
The raw water that has been passed through the hollow lumen of the hydrophobic porous hollow fiber membrane 1 passes through the membrane wall of the hydrophobic porous hollow fiber membrane 1 as water vapor, moves to the first gas phase portion 12, and the third water The second gas phase portion 22 is cooled by the cooling body 25 and becomes distilled water.
The condensing unit 24 having the cooling body 25 is connected to the water sampling container 26 by a pipe 29, and distilled water is discharged from the condensing unit 24 and collected in the water sampling container 26.

  In the present embodiment, the cooling water is not particularly limited as long as it is a liquid that can flow through the second liquid phase portion 21 that is the internal space of the cooling body 25 and cool the water vapor. For example, tap water, industrial water , River water, well water, lake water, seawater, industrial wastewater (wastewater from food factories, chemical factories, electronics industry factories, pharmaceutical factories, cleaning factories, etc.), accompanying water discharged during oil and natural gas production, etc. Is mentioned. In the present embodiment, water used as raw water may be used as cooling water.

From the viewpoint of condensation efficiency, the cooling water preferably has a water temperature of 30 ° C. or lower, and more preferably 20 ° C. or lower.
The water temperature of the cooling water may be controlled by utilizing a heat source such as a heat exchanger or a heater.

  In the present embodiment, the evaporator 14 and the condenser 4 are provided as independent containers 18 and 28, respectively, and the third gas phase part 32 is provided so as to connect the evaporator 14 and the condenser 24. Although preferable, the evaporation unit 14 and the condensing unit 24 may be an integrated membrane distillation apparatus in the same container.

  The third gas phase part 32 is connected by a connection port that connects the first gas phase part 12 and the second gas phase part 22. The volume of the third gas phase portion 32 is preferably large from the viewpoint of water vapor transmission. The number of connection ports is not particularly limited, and may be single or plural. The shape of the connecting portion may be cylindrical or square. The member of the connecting portion is not particularly limited, and resin or metal can be used, but a highly heat-insulating material may be used so that water vapor does not condense at the connecting portion, and heat treatment is performed as necessary. Also good.

The third gas phase part 32 is provided so that the shortest distance between the hydrophobic porous hollow fiber membrane 1 of the evaporation part 14 and the cooling body 25 of the condensation part 24 is 10 mm or more.
Here, the shortest distance between the hydrophobic porous hollow fiber membrane 1 and the cooling body 25 means the closest distance between the outer peripheral portions of the hydrophobic porous hollow fiber membrane 1 and the cooling body 25 as a linear distance.
By setting the shortest distance to 10 mm or more, the evaporating unit 14 and the condensing unit 24 can be easily designed, and the shortest distance may be 30 mm or more.
In this embodiment, the shortest distance is 10 mm or more, so that the design of the evaporation unit 14 and the condensation unit 24 can be facilitated, but the pressure of the gas phase units 12, 22, and 32 is 1 kPa or more of the raw water temperature. By performing membrane distillation while controlling it to below the saturated vapor pressure of water, high vacuum and sweep gas are not required, and the use of the hydrophobic porous hollow fiber membrane 1 despite being compact It can be set as the membrane distillation apparatus which can implement | achieve high Flux.

In this embodiment, the gas phase parts 12, 22, and 32 form a continuous space, and the pressure of the gas phase parts 12, 22, and 32 is controlled to be between 1 kPa and the saturated vapor pressure of water at the raw water temperature. The
By setting the pressure to 1 kPa or more, it is possible to suppress energy consumption required for depressurization of a decompression device (not shown) that depressurizes the pressure of the gas phase parts 12, 22, 32, and below the saturated vapor pressure of water at the raw water temperature. By doing so, high water permeability can be realized.
From the viewpoint of energy consumption, the pressure is preferably 1 kPa or more, and more preferably 10 kPa or more.
From the viewpoint of water permeability, the pressure is preferably equal to or lower than the saturated vapor pressure of water at the raw water temperature, and is 10 kPa or lower than the saturated vapor pressure of water at the raw water temperature (difference from the saturated vapor pressure of water at the raw water temperature). Is more preferably 10 kPa or more).

Examples of the pressure reducing device 41 for reducing the pressure in the gas phase sections 12, 22, and 32 include a diaphragm vacuum pump, a dry pump, an oil rotary vacuum pump, an ejector, and an aspirator.
Examples of the method for controlling the pressure include a method using a vacuum regulator and a leak valve, and a method using an electronic vacuum controller and an electromagnetic valve.

  A membrane distillation system 100 of this embodiment will be described with reference to FIG. As shown in FIG. 2, the membrane distillation system 100 includes a membrane distillation apparatus 10, an evaporation unit 14, a condensing unit 24, and gas phase units 12, 22, and 32, and a water collection container 26, a decompression device 41, and a pressure regulator 42. Etc. For example, raw water is heated by a heat source (not shown) such as a heat exchanger or a heater, and stored as high-temperature water in a raw water tank (not shown). The high-temperature water in the raw water tank is passed through the hydrophobic porous hollow fiber membrane 1 in the evaporation section 14 by a liquid feed pump (not shown), and when passing through the hydrophobic porous hollow fiber membrane 1, a part of it is hydrophobic. The porous porous fiber membrane 1 passes as water vapor and moves to the first gas phase portion 12. The water vapor passes through the third gas phase part 32 and is stored in the condensing part 24 when the second gas phase part 22 is controlled by the decompression device 41 while the pressure is not less than the saturated vapor pressure of water at the raw water temperature. Move to the second gas phase unit 22. The water vapor that has passed is condensed on the cooling body 25 of the condensing unit 24 by the cooling water facing the lumen of the cooling body 25 in the condensing unit 24 to obtain distilled water. The cooling water is passed through the cooling body 25 from a cooling tank (not shown) by a liquid feed pump (not shown). Distilled water obtained by condensation on the cooling body 25 is collected in a water collection container 26. The pressure of the second gas phase unit 22 is adjusted to be constant by the decompression device 41 and the pressure regulator 42.

The flushing mechanism 6 of the present embodiment includes a washing water discharge line 61 that discharges washing water after flushing the hydrophobic porous hollow fiber membrane 1, an on-off valve 62 installed in the middle of the washing water discharge line 61, including.
The washing water discharge line 61 is connected to the washing water outlet of the membrane distillation apparatus 10.
As the on-off valve 62, a valve normally used in a water purification system such as an electromagnetic valve can be used. The on-off valve 62 is controlled to open and close based on a control command from a control unit (not shown), and switches between discharge and stop of cleaning water. The on-off valve 62 can be manually opened and closed to switch between discharge and stop of the washing water.
Hereinafter, an example of the operation method of the membrane distillation system 100 of the present invention will be described according to the operation using the membrane distillation system 100 shown in FIG.
In the membrane distillation step, the on-off valve 58 of the raw water discharge line 57 is opened and the on-off valve 62 is closed. The raw water supplied from the raw water supply line 51 flows into the evaporator 14 from the raw water inlet of the membrane distillation apparatus 10 and is discharged from the raw water outlet through the hydrophobic porous hollow fiber membrane 1 in the evaporator 14. At that time, water vapor that has passed through the membrane moves to the condensing unit 24, is condensed on the cooling body 25, and becomes purified water. Nonvolatile substances such as ionic components contained in the raw water cannot be permeated through the membrane and are removed from the purified water. Purified water is discharged from the purified water outlet. The discharged purified water is supplied as purified water.
Next, after performing the membrane distillation step for a predetermined time or after passing a predetermined amount of raw water, the hydrophobic porous hollow fiber membrane 1 of the membrane distillation apparatus 10 is flushed (membrane washed) as follows.
In the flushing step, the opening / closing valve 62 of the cleaning water discharge line 61 is opened, and the opening / closing valve 58 of the raw water discharge line 57 is closed. In the flushing step, the opening / closing valve 58 and the opening / closing valve 62 are switched as described above, and the washing water is supplied from the raw water supply line 51 to the membrane distillation apparatus 10 as shown in FIG. The discharge (that is, the drain of the raw water) is stopped, and the hydrophobic porous hollow fiber membrane 1 is flushed to discharge the washing water.
The washing water flows from the raw water inlet of the membrane distillation apparatus 10 and passes through the hydrophobic porous hollow fiber membrane 1 in the membrane distillation apparatus 10. At this time, the inner surface of the hollow fiber membrane is flushed, so that dirt or the like adhering to the membrane surface is washed away by the raw water.
The raw water containing dirt becomes washing water and is discharged from the washing water outlet. The washing water passes through the washing water discharge line 61 and is discharged out of the system.
The cleaning water of the present embodiment can use raw water as it is as cleaning water, but when water having lower conductivity than the raw water is used, dirt components such as inorganic substances are easily dissolved and a high removal effect is obtained. preferable. From this point of view, a part of purified water may be used as washing water.
After the flushing process is completed, the process can be directly transferred to the membrane distillation process.
In the operation method of the membrane distillation system 100 of the present invention, the means for controlling the switching from the membrane distillation process to the flushing process (that is, the opening / closing of the on-off valves 58 and 62) is not particularly limited. Alternatively, the membrane distillation system 100 may be provided with an automatic control means (control unit) and switched by automatic control.
Since the flushing requires only minor equipment changes such as the addition of a line, the membrane distillation system 100 of the present invention that restores the water permeability by flushing can be made compact and simple.

  Hereinafter, examples and the like that specifically illustrate the configuration and effects of the present invention will be described. However, the present embodiment is not limited to the following examples.

(Example)
Tap water was purified using the membrane distillation system 100 shown in FIG. Purified water obtained in the membrane distillation process was used as the washing water used for flushing, and electromagnetic valves were used as the on-off valves 58 and 62.
A PVDF porous hollow fiber membrane (outer diameter 1.22 mm, inner diameter 0.66 mm, average pore diameter 0.27 μm) was used. An evaporation module (evaporation part 14) containing 20 hollow fiber membranes in a polysulfone case with an inner diameter of 20 mm and 20 stainless steel tubes with an inner diameter of 1 mm and an outer diameter of 2 mm are accommodated in the same case as that used in the evaporation part 14. The condensation module (condensation part 24) was prepared, and the evaporation part 14 and the condensation part 24 were connected so that the shortest distance between the outer surface of the hollow fiber membrane in the evaporation part 14 and the outer surface of the stainless steel tube in the condensation part 24 was 30 mm (see FIG. 2, see FIG. The outlet of the condensing unit 24 is connected to the water sampling container 26 by piping, and a vacuum pump and a vacuum control device are arranged from the water sampling container to adjust the pressure in the system as shown in FIG.
65 ° C. tap water is allowed to flow through the lumen of the hollow fiber membrane of the evaporator 14 at a flow rate of 600 mL / min, and 30 ° C. tap water is allowed to flow through the lumen of the stainless steel tube of the condenser 24 at a flow rate of 600 mL / min. Then, the pressure in the module system was adjusted to 10 kPa with a vacuum pump, and the membrane distillation step was performed.
The operation of the membrane distillation system was started, and water collected in the water collection container after 30 minutes was collected. As a result, it was found that the flux was 45 kg / m ² / h. The conductivity of the water obtained was 1.0 μS / cm. Then, after 25 hours from the start of operation, when the flux gradually decreased to 15 kg / m ² / h, the flushing process was switched (that is, the opening / closing of the on-off valves 58 and 62 was switched). And after flushing, it changed to the membrane distillation process again and refine | purified tap water.
As a result, it was confirmed that the flux recovered to 45 kg / m ² / h.
(Comparative example)
The same operation was performed except that the flushing step was not performed in the operation method of Example 1. After 25 hours from the start of operation, the flux gradually decreased and continued to decrease even after dropping to 15 kg / m ² / h, and the distillation stopped eventually.

  ADVANTAGE OF THE INVENTION According to this invention, the membrane distillation system of a compact and simple structure and its operating method can be provided.

DESCRIPTION OF SYMBOLS 1 Hydrophobic porous hollow fiber membrane 6 Flushing mechanism 10 Membrane distillation apparatus 11 1st liquid phase part 12 1st gas phase part 14 Evaporation part 21 2nd liquid phase part 22 2nd gas phase part 24 Condensing part 25 Cooling Body 32 third gas phase section 100 membrane distillation system

Claims (4)

  A membrane distillation system comprising a membrane distillation apparatus provided with a hydrophobic porous hollow fiber membrane, and a flushing mechanism for flushing the hydrophobic porous hollow fiber membrane. The membrane distillation apparatus includes a first liquid phase part through which raw water flows, a first gas phase part, and the hydrophobic porous hollow fiber membrane separating the first liquid phase part and the first gas phase part. An evaporating part, a second liquid phase part through which cooling water flows, a second gas phase part, a condensing part comprising a cooling body separating the second liquid phase part and the second gas phase part, A third gas phase part connecting the first gas phase part and the second gas phase part,
The shortest distance between the hydrophobic porous hollow fiber membrane of the evaporating part and the cooling body of the condensing part is 10 mm or more, and
The pressure of the first gas phase part, the second gas phase part, and the third gas phase part is used between 1 kPa and a saturated vapor pressure of water at a raw water temperature. The membrane distillation system described. A method for operating the membrane distillation system according to claim 1,
A membrane characterized by repeating a membrane distillation step in which raw water permeates through the hydrophobic porous hollow fiber membrane to perform membrane distillation, and a flushing step in which washing water is supplied to the hydrophobic porous hollow fiber membrane and flushed. How to operate the distillation system.   The operation method of the membrane distillation system according to claim 3, wherein raw water or water having lower conductivity than raw water is used as the washing water.

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