KR19980702914A - Desalination of salt-containing water and apparatus for same - Google Patents

Abstract

The present invention relates to a desalination method of a hydrous or seawater using a hollow fiber-type reverse osmosis membrane, and a device therefor, and to achieve a longer life of the reverse osmosis membrane, and at the same time, a simple and economical new method and apparatus therefor. The purpose is to provide. The present invention uses a vertical cylindrical reverse osmosis membrane device in the desalination of salt-containing water using a hollow fiber reverse osmosis membrane, and pretreatment to the reverse osmosis membrane apparatus during water passage. The raw water is supplied to the fibrous layer through the inner circumferential space provided between the core tube and the inner circumferential surface of the fibrous layer of the reverse osmosis membrane device in the core tube disposed along the central axis of the reverse osmosis membrane apparatus. It is made to flow in, and it flows out through the outer peripheral space provided between the outer peripheral surface of the fiber layer, and the outer cylinder of a reverse osmosis membrane apparatus.

Description

Desalination of salt-containing water and apparatus for same

As shown in Fig. 5, in the desalination method of the conventional salt-containing water using the reverse osmosis membrane method (hereinafter, sea water is described as an example unless otherwise specified), the reverse osmosis membrane apparatus 6 When supplying salt-containing water (hereinafter referred to as raw water), it was common to adopt a pretreatment system. Here, the pretreatment includes: (1) a furnace treatment for removing suspended matter in the raw water, which is a pressure loss enhancer of the reverse osmosis membrane apparatus (usually, a coagulant such as a chemical agent such as FeCL ₃ (CL2). ), The suspended solids are coagulated and coarsened, and then filtered through a sand blasting apparatus (3) or (2) pre-chlorine treatment to prevent biocontamination of the reverse osmosis membrane. Usually, a drug such as Cl ₂ , NaC 10, etc. (CL ₁ ) is added before the furnace treatment, and in case of using a reverse osmosis membrane that avoids the drug for all chlorine, it is necessary to reduce the drug. Drugs, for example, addition of a reducing agent such as NaHSO ₃ (CL3) is required).

When such a pretreatment unit is placed in the whole system, the initial cost (including the flow control valve and the electrical measurement equipment equipment cost) to match the throughput of the pretreatment device and the reverse osmosis membrane device as well as the cost of the pretreatment device itself. Not only does it cause an increase, but the running cost (power coast of the pump 2 to overcome the cost of the injection agent and the resistance of the pretreatment device itself and the resistance of the flow control valve (not shown) installed in the line C). This leads to an increase in the production water production cost.

In addition, the pretreatment must periodically discharge the block of added flocculant (CL2) to the outside of the system to agglomerate and coarse the suspended matter and suspended matter in the raw water captured by the furnace member, and these are disposed of as a waste for environmental measures. Should be treated as

In addition, when the pressure loss of the reverse osmosis membrane apparatus 6 exceeded the predetermined value, production of fresh water was paused and the reverse osmosis membrane apparatus was washed. This cleaning is performed by using a cleaning unit installed separately from the fresh water production system shown in FIG. 5, by using a cleaning unit containing ammonium citrate or an organic detergent in a cleaning pump line (D2) → reverse osmosis membrane. It carried out by cycling in the path | route of an apparatus (raw water side)-the line F1. This washing system has to be equipped with a washing unit separately from a fresh water production system, and thus prepares a dedicated washing liquid, which is also a cost increase factor of the whole system. In addition, the object which a cleaning effect exerts is also limited to what melt | dissolves in cleaning liquids, such as a metal hydroxide.

In addition, as a new cleaning method, a method of backflowing fresh water from the treatment shrinkage by using the static osmosis phenomenon has been proposed (Japanese Patent Application No. 54-40232, Japanese Patent Application No. 63-59312, and Japanese Patent Application Laid-Open No. Hei 1-19306). The publications of the heading of the present disclosure), such proposals merely use the reverse flow of fresh water as the physical peeling force of the membrane-attached particles, the cleaning effect is not sufficient.

The present invention relates to a desalination method of a hydrous or seawater using a hollow fiber reverse osmosis membrane, and an apparatus therefor.

1 is a schematic diagram of a device of one embodiment of the method of the present invention.

Fig. 2 is a partially enlarged cross-sectional view (cutting along a core tube axis) schematically showing the relationship between the core tube and the fiber layer of the reverse osmosis membrane device which is one embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of a portion (core tube and inner space) of the apparatus shown in FIG. 2.

4 is a cross-sectional view (only one fiber layer is shown) schematically showing the water flow in the module of the reverse osmosis membrane device which is one embodiment apparatus of the present invention.

5 is a diagram illustrating a diagram of a conventional system.

Fig. 6 is a partially enlarged sectional view schematically showing the relationship between the core pipe and the fiber layer of the conventional reverse osmosis membrane device.

FIG. 7 is an enlarged cross-sectional view of a part of the apparatus shown in FIG. 6.

The present invention has been made to provide a simple and economical desalination method of a salt-containing water such as seawater and an apparatus for solving the problems of the prior art.

MEANS TO SOLVE THE PROBLEM This inventor came to complete this invention by carefully considering and verifying the deterioration factor of the whole system as well as the deterioration factor including the deterioration of the reverse osmosis membrane apparatus.

First, the pressure loss factor of the whole system cannot be ignored because the resistance of the pretreatment device itself and the resistance of the flow control valve provided between the prechamber and the reverse osmosis membrane device cannot be ignored. This is because, according to the conventional way of thinking, if the pretreatment is omitted, the reverse osmosis membrane device, including the increase in pressure loss, may occur, but the mechanical design of the reverse osmosis membrane device and the operation of the reverse osmosis membrane device are considered. This is because they found that pretreatment was not essential.

That is, the present invention, in the desalination of salt-containing water using a hollow fiber-type reverse osmosis membrane, by using a vertical cylindrical reverse osmosis membrane device, when the water is supplied, the raw sea water that has not been pretreated to the reverse osmosis membrane device The raw water is introduced into the fibrous layer through the inner circumferential space installed between the core tube and the inner circumferential surface of the reverse osmosis membrane apparatus in the core pipe disposed along the central axis of the reverse osmosis membrane apparatus, and is installed between the outer circumferential surface of the fibrous layer and the outer osmosis membrane apparatus. It is characterized by flowing through the outer space. The obstacle of the reverse osmosis membrane which is anticipated when pretreatment is omitted is as follows.

(1) and (7), in the conventional reverse osmosis membrane device, the fiber layer (the hollow fiber type reverse osmosis membrane, so that each membrane is referred to as "fiber 65" and these fibers The aggregated portion is referred to as the "fiber layer 64"), so that the inlet portion abuts on the outer circumferential surface of the core tube 61 via the inner screen 63, so that the through-hole of the raw water punched through the fiber layer inlet portion, that is, the core tube. Relatively coarse particles are trapped at the exit of the hole 62 (hereinafter referred to as a hole) to block the portion and increase the flow resistance (most of the pressure loss of the reverse osmosis membrane device itself is due to this factor). At the same time, drift occurs and performance decreases. In addition, lowering the passage flow rate of the hole 62 may reduce the possibility of blockage at the corresponding part. However, in order to do so, the opening area of the hole should be increased, and the strength of the core pipe 61 to which the supply pressure of the raw water is applied will be increased. It is unrealistic because (force to resist bending) falls.

(2) If operation continues for a long time, fine particles gradually start to accumulate in the fibrous layer, which becomes a resistance and lowers the efficiency of desalination (production volume / raw volume). Of course, the pressure loss also rises.

(3) When water penetrates the fiber, fine particles mixed into the fiber layer are deposited on the surface of the fiber to form a gel layer, which becomes a resistance, deteriorating the efficiency of desalination or generating concentration polarization, thereby increasing the amount of permeated salt on the treated water side. . Of course, the pressure loss also rises.

④ The microorganisms that started to multiply in the gel layer, especially the microorganisms in the vicinity of the fiber surface, are not completely extinguished even in Cl ₂ or NaC 10 injected into raw water for the whole chlorine. The fine particles deposited by the secretion and are deposited firmly on the surface of the fiber) are amplified.

⑤ The fiber itself is damaged by the bacteria.

In order to deal with such obstacles, the following measures have been adopted in the present invention.

Measures of obstacle ①

A space 68a (hereinafter referred to as an inner circumferential space) is provided between the fibrous layer 64 (exactly, the inner screen 63) and the core pipe 61 of the reverse osmosis membrane device 6, and the raw water from the hole 62 is collected. It is once drawn into this inner circumferential space and flows into a fiber layer uniformly and at low flow velocity (preferably 1-5 mm / sec) via this space. Here, the inner circumferential space 67a is inevitably formed by disposing a plurality of ribs 66 extending in the core axial direction on the outer circumferential surface of the core pipe 61. That is, the inner circumferential surface of the fiber layer 64 is in contact with the lip top surface through the inner screen 63 (see FIGS. 2 and 3). Further, the expanded spherical area of the hole 62 may be smaller than the conventional method, and the hole 62 is disposed intensively in the upper and lower portions of the core pipe 61 (as a result, raw water in the axial direction of the core pipe in the inner circumferential space 67a). Dispersion of the stimulus is promoted, and the excretion of the lip is also compatible with each other, thereby reducing the strength of the core tube itself. The smaller the opening area of the hole, the greater the pressure loss in the hole, but the inflow of raw water into the fiber layer 64 becomes uniform and the lower the flow rate. As a result, it can be ignored as compared to the pressure loss reduced.

In addition, the device of the present invention has a vertical type, that is, the core pipe is vertically excreted, and raw water flows along the core tube axis (which may be in any direction from top to bottom and bottom to top), so that the inner screen 63 and the fibrous layer 64 ) Particles that are blocked from entering the inner circumferential surface (irrespective of the inflow direction of the raw water) and large particles having a high sedimentation rate (only when the raw water flows from the top to the bottom) are placed in the inner circumferential space 67a and the lower portion of the core pipe in the water flow direction. Although it accumulates, the former can cope with backwashing and air cleaning of the fibrous layer 64 which will be described later (mechanical consideration, that is, the hole 62 is concentrated at the upper and lower portions of the core pipe 61, the inner circumferential space 67a). It is effective in that it is effectively used as a sediment delivery channel), and the latter may be treated by discharging sediment with water pressure from the drainage pipe (with valve) installed at the bottom of the system to the outside of the system or to the concentration line. ( Valves are normally open).

If necessary, the water permeation of the reverse osmosis membrane device 6 is stopped, and the raw water or the concentrated water flows to the raw water side (outside of the fiber 65) of the reverse osmosis membrane in the opposite direction to the flow at the time of water passage, thereby reverse osmosis membrane The fiber layer 64 of the apparatus is cleaned (hereinafter referred to as backwashing). This obstacle is simply attached to the fiber, so that the fine particles can be easily removed by backwashing. Although the frequency of washing | cleaning may be set suitably according to the water quality of raw water, since it is effective to cope with such an obstacle promptly, it is preferable about once every several days.

Measures of obstacle ②

Since the internal space of the fibrous layer 64 is sufficiently large, the occurrence thereof is later than that of the disturbances ① and ③. Therefore, it is inevitable to take countermeasures against obstacles ① and ③.

Measures of obstacle ③

In addition to the countermeasure of the obstacle ④, when the countermeasure (backwashing) of the above-mentioned obstacle ① is performed, production water in which Cl ₂ or SO ₂ is added to the treated water side (the hollow part of the fiber 65) of the reverse osmosis membrane, or CO ₂ The surface of the fiber 65 of the reverse osmosis membrane device is washed by supplying the production water to which the addition of the water is added in the reverse direction from the time of water passage. Since Cl ₂ , SO ₂ , and CO ₂ are gaseous substances, they easily permeate the reverse osmosis membrane. Therefore, the reverse osmosis membrane is a gaseous substance that has permeated from the treated water side to the raw water side. Kill (so that sterilization of raw water is not necessary when watering). As a result, the adhesion to the membrane surface of the gel layer is lost, and then the gel layer is subjected to the normal osmosis phenomenon of the produced water (sufficient penetration pressure even when the salt-containing water is hydrated by flowing the concentrated water to the raw water side of the reverse osmosis membrane). It peels from a film surface. This exfoliated gel layer is discharged out of the system rapidly by riding on backwater or concentrated water. Here, SO ₂ is effective in the case of using the reverse osmosis membrane which avoids Cl ₂ in a reverse osmosis membrane (6). CO ₂ acts as a solubilizer when there is a scale of CaCO _{3 or} the like. Naturally, the obstacle ④ and the obstacle ⑤ are also eliminated by taking measures against the obstacle ③.

In addition, in the present invention, in addition to the countermeasures described above, the fiber layer 64 is washed with air (this operation cannot be performed in the horizontal reverse osmosis membrane device), thereby ensuring perfect cleaning. Specifically, after the above-mentioned forward osmosis bottle cleaning, at the appropriate point of the air cleaning process, the retained water in the reverse osmosis membrane apparatus 6 module is once removed, and reversed to the raw water side of the reverse osmosis membrane apparatus. While injecting the shrinkage, air is injected from the bottom of the fibrous layer 64. In this case, since the apparatus of the present invention is longitudinal, the vicinity of the surface of the module of the reverse osmosis membrane apparatus 6 moving upward from the bottom becomes a gas-liquid mixture flowing violently, and the fibrous layer 64 pulsates. Particles attached to each fiber surface are peeled off from the fibers in order and easily from bottom to top. Here, in order to prevent the air of the cleaning vessel from penetrating the outer circumferential space 67b of the reverse osmosis membrane apparatus 6 directly from the bottom to the upper side, a spacer (67) for closing the flow path in the outer circumferential space. ) Are arranged at least two at predetermined intervals in the axial direction of the reverse osmosis membrane device. In addition, in order to effectively use the peeling force of the adherent particles due to the prevention of drying of the fiber 65 and the forward osmosis phenomenon, the production water added Cl ₂ or SO ₂ to the reverse osmosis membrane treated water during this process, or The supply of the production water to which CO ₂ was further added is continued (as a result, the fiber surface is always wet, so that the adherent particles easily slide downwards). The retained water in the reverse osmosis membrane apparatus 6 after the completion of the air cleaning contains a large amount of particles that have been peeled off. Therefore, once the retained water has been taken out of the system, the forward osmosis membrane service cleaning is performed again to reverse osmosis membrane apparatus 6. The exfoliation particle which remain | survives in is wash | cleaned.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Shown in FIG. 1 is the basic flow of the present invention (the flow for the original purpose of obtaining fresh water from salt-containing water, ie, the flow at the time of passage). In the method of the present invention, the salt-containing water (raw water) to be treated is supplied to the reverse osmosis membrane apparatus 6 without performing pretreatment such as sand furnace. However, in order to prevent the inflow of foreign substances causing physical damage to the high pressure pump 5a and the reverse osmosis membrane device, the filter 4b is installed in front of the high pressure pump 5a. May be used). If you indicate the flow of water in a line,

(Raw water) → A → B → D 1 → D 2 → D 3 → [number of production] → E → G

↘ [concentrated water] → F1 → F2 → F3

to be.

The apparatus of the present invention has the structure shown in Figs. As can be seen in comparison with Figs. 6 and 7, the apparatus of the present invention is a vertical type (conventionally, in the horizontal type, Figs. 6 and 7, the left side is left in the longitudinal direction and the right side is in comparison with Figs. In FIG. 3, the upper left side is the upper side and the right side is the bottom side). In addition, in the apparatus of the present invention, an inner circumferential space 67a is provided between the core pipe 61 and the fiber layer 64 (exactly, the inner screen 63), and at the same time, a hole 62 through which water can pass is provided. The main difference is that the concentrated water is installed at the lower and lower portions of the raw water (pressure: about 65 kg / cm ² ) introduced in the axial direction of the core pipe 61 by being pressurized by the high pressure pump 5a. The inner screen 63 flows into the inner circumferential space 67a and flows downward through the inner circumferential space (some flows downward in the core tube and then enters the inner circumferential space 67a through the lower hole 62). Flows into the entire inner circumferential surface of the fibrous layer 64 at a low flow rate, and most of it is desalted while flowing radially (some flows in the axial direction of the core tube 61). From the top of the permeation membrane device 6, the concentrated water is discharged from the outer screen 68. It enters the main space 67b and exits the lower part of the reverse osmosis membrane apparatus (see Fig. 4. Here, it is shown as an example of flowing raw water from the top of the core tube 61 to the bottom). The reverse osmosis membrane apparatus 6 stops passing water and enters the washing operation (divided into steps. The number indicates the process sequence).

(1) backwashing

The path (by flow), which is the path (H1 → F1 → D3 → H2), bypassed the resistance of the high pressure pump 5a, the recovery turbine 5b, and the back pressure valve (not shown) installed in the line F3. Actual pipes do not necessarily need to be shared in the same way.) The raw water or concentrated water is flowed to clean the inside and the inlet of the fibrous layer 64 (using a separate washing pump (not shown)). Here, since the concentrated water contains particles that have passed through the fiber layer 64 at the time of passage, a cartridge filter (not shown) is provided at the outlet of the cleaning pump to prevent the particles from reintroducing into the fiber layer.

At the same time, the production water stored in the production tank 7 is supplied via the line E from the production water pump 8 to the treatment contraction (hollow part of the fiber 65) of the reverse osmosis membrane device 6. [Measures of obstacle ③-⑤]. Since the high water pressure is not applied to the raw water side as in the case of passing water, fresh water penetrates from the treated water side of the reverse osmosis membrane to the raw water side by the penetration pressure of raw or concentrated water (precipitation osmosis phenomenon). Since the raw water also has an infiltration pressure of 27 kg / cm ₂ (for seawater), a sufficient driving force for forward penetration is obtained even if the concentrated water pressure for flushing is 1 kg / cm ² . As a matter of course, the amount of fresh water to be supplied may be an amount that replenishes the amount of permeate transmitted to the raw water side. Here, Cl ₂ or SO ₂ (for reverse osmosis membranes avoiding Cl ₂ ) is used instead of CL ₄ , and in some cases CO ₂ (when scale deposition of CaCO ₃ is expected) is used in combination. Although the usage amount is not specifically defined, it may be a saturation concentration in order to avoid the complicated operation. The place for addition may be sufficient as the production tank 7, and when the capacity of this production tank is too large, a dedicated tank may be provided and added to this dedicated tank. In addition, an emitter may be provided in a line for conveying the production water, and the required amount may be sucked and mixed with the production water.

(2) air cleaning

① Drainage

Air is introduced from the lower portion of the fibrous layer 64 to drain a portion of the water in the reverse osmosis membrane apparatus together with air from the upper portion of the reverse osmosis membrane apparatus 6 (when raw water flows from the top to the bottom when the raw water is passed through). A bubble layer is formed in the reverse osmosis membrane device. In this process, some degree of cleaning effect is obtained. However, since the flow of air in the fibrous layer 64 is not uniform, cleaning by this is insufficient.

② pressurization

The drainage port is closed to continue supply of air, and the inside of the reverse osmosis membrane device 6 is pressurized (2kg / cm ² ).

③ discharge

After stopping the flow of air, a blow valve (not shown) provided in the lower part of the reverse osmosis membrane apparatus 6 is opened, and the water in the reverse osmosis membrane apparatus is discharged out of the system at once. The surface of each fiber 65 is discharged from the inside of the fiber to the treated water side of the reverse osmosis membrane apparatus 6 at all times during the air cleaning process following the backwashing process. Since the adherent particles are in a slippery state, a considerable amount of adherent particles are removed and discharged by the rapid wave of the discharged water.

④ Air cleaning

Into the module of the hollow reverse osmosis membrane device 64, air is blown from the lower part of the module (outlet of the concentrated water) as in raw water or concentrated water (as in the backwashing process, similarly through the cartridge filter). In this process, although the flow of air in the fibrous layer 64 is uniform, the water surface rises violently. Therefore, the particles replenished and filled in the fiber layer 64 also fall easily. Further, during this process, a difference in density occurs between the water in the fiber layer 64 and the water in the core pipe 61, so that a circulation flow occurs, thereby contributing to the floating of the first fallen particles. Here, the injected water flows out from the inlet of the raw water as in the above process (drainage). In the apparatus of the present invention, the spacer 69 is provided in the outer circumferential space 67b to prevent direct flow in the axial direction of the core pipe 61, that is, the vertical direction of the outer circumferential space. There is no penetration.

(3) backwashing

After repeating process (2) and (3) of the said process (2) (air washing) again, the said process (1) (back washing) is performed again. This is for the washout of particles remaining in the system.

Since the apparatus of the present invention is a vertical type, the particles remaining in the system peeled off by the washing operation gradually move downward when passing through. As a result, the lower part of the pressure loss always exists in the upper part of the fiber layer, so that the increase in the pressure loss becomes a totally curved shape. In addition, since the downflow due to density occurs in the fiber layer, it prevents the color of the upper part and at the same time reduces the concentration polarization, which is advantageous in permeation of water. Of course, there is also a significant benefit, including the extension of the operational time, which is directly possible by air cleaning. As a specific benefit, the construction cost can be reduced to about 60% of the conventional system and the power consumption can also be reduced by about 10%. In addition, the cost of fresh water produced in the system of the present invention was reduced to about 75% of the conventional system. In addition, inferred from the rise of pressure loss, the method and apparatus of the present invention can expect a long life of the membrane module of 2 to 4 years without pretreatment, and a simple and economical desalination method of new salt-containing water. Can provide.

Claims (8)

In the desalination of salt-containing water using a hollow fiber reverse osmosis membrane, a vertical cylindrical reverse osmosis membrane apparatus is used, and when water is supplied, raw water is supplied to the reverse osmosis membrane apparatus without pretreatment, and the raw water is reverse osmosis membrane. It enters into the fibrous layer from the core pipe disposed along the central axis of the device through the inner circumferential space provided between the core pipe and the inner circumferential surface of the fibrous layer of the reverse osmosis membrane device, and flows out through the outer circumferential space installed between the outer circumferential surface of the fibrous layer and the outer cylinder of the reverse osmosis membrane device. Characterized in that the method. The method according to claim 1, wherein water in the outer circumferential space flows linearly in the outer circumferential space in a vertical direction. 2. The supply of raw water to the inner circumferential space according to claim 1, wherein the inner circumferential space is formed by a plurality of ribs installed on the outer circumferential surface of the core pipe and the outer circumferential surface of the core pipe in the axial direction of the core pipe and the inner circumferential surface of the fibrous layer. Method carried out through a hole that allows the passage of water intensively perforated in the upper and lower parts. The product water according to any one of claims 1 to 3, wherein the product water to which Cl ₂ or SO ₂ is added to the treated water side of the reverse osmosis membrane or the product water to which CO ₂ is additionally added after stopping the water passage. A method comprising the step of supplying concentrated water in the reverse direction and when passing through the raw water side of the reverse osmosis membrane while feeding in the reverse direction. 5. The production water according to claim 4, wherein the water retained in the reverse osmosis membrane apparatus is followed by the above-mentioned step, and Cl ₂ or SO ₂ is added to the treated water side of the reverse osmosis membrane, or CO ₂ is further added thereto. And supplying the concentrated water in the reverse direction when passing through, such as air, to the raw water side of the reverse osmosis membrane while supplying the reverse direction when passing through. In a hollow fiber reverse osmosis membrane apparatus, a core tube is disposed along a central axis of a longitudinal cylindrical reverse osmosis membrane apparatus, and an inner circumferential space in which raw water or concentrated water is axially moved between the core tube and the inner circumferential surface of the fiber layer of the reverse osmosis membrane apparatus And installing a space between the outer circumferential surface of the fibrous layer and the outer cylinder of the reverse osmosis membrane apparatus, wherein a space capable of moving the raw water and the concentrated water in the axial direction. 7. The apparatus according to claim 6, wherein at least two spacers capable of closing the passage in the outer circumferential space are arranged at predetermined intervals in the axial direction of the reverse osmosis membrane apparatus. According to claim 6, wherein the inner circumferential space is formed by the plurality of ribs and the fiber layer inner circumferential surface is formed as extending in the axial direction to the outer circumferential surface of the core tube and the core tube, the hole through which the water can pass through the core wall and intensively concentrated Perforated device.