JP2000288356A - Reverse osmosis membrane separation apparatus and water producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the linear velocity of fluid flowing in membrane surfaces of reverse osmosis membrane elements to suppress concentration polarization and making a reverse osmosis membrane separation apparatus sufficiently exhib capability of the reverse osmosis membrane elements by installing a reverse osmosis membrane module in which a plurality of reverse osmosis membrane elements are connected in series and specifying the cross-section surface area of a raw water flow route of the reverse osmosis membrane elements. SOLUTION: The reverse osmosis membrane part is composed of a module 3 to which a plurality of reverse osmosis membrane elements are boaded. In this case, the reverse osmosis membrane element 1 in the upstream side is made to have a wider cross-section surface area of a raw water flow route than the reverse osmosis membrane element 12 in the downstream side. The raw water passed through a raw water intake route 4 and pressurized by a pressurizing pump 5 and led to the module 3. Consequently, the raw water is subjected to reverse osmosis membrane treatment by the reverse osmosis membrane element 1 and the passed water is taken out through a passed water discharge route 7. The concentrated water which is not passed through the reverse osmosis membrane element 1 is led to the reverse osmosis membrane element 2 and treated by the element 2 and the passed water is discharged through the passed water discharge route 7 and concentrated water is discharged through a concentrated water discharge route 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel reverse osmosis for separating a high-concentration solution using a reverse osmosis membrane element, such as desalination of brackish water, desalination of seawater, and recovery of valuable resources, into a reverse osmosis membrane. The present invention relates to a membrane separation device and a fresh water producing method.

[0002]

2. Description of the Related Art There are various techniques for purifying high-concentration solutions. As an example of energy saving and resource saving processes, a membrane separation method using a reverse osmosis membrane is used.
According to the reverse osmosis method, a solution containing a solute such as a salt is allowed to pass through a reverse osmosis membrane at a pressure equal to or higher than the osmotic pressure of the solution, so that a liquid with reduced solute content (permeated water) and concentrated water Can be separated. This technology, for example, can obtain drinking water from seawater, brackish water, water containing harmful substances, and is also used for the production of industrial ultrapure water, wastewater treatment, recovery of valuable resources, etc. I have.

[0003] The reverse osmosis method is generally used in a state in which a plurality of reverse osmosis membrane elements are loaded in series in one pressure vessel as shown in Fig. 4 (this is called a module). In FIG. 4, the module 32 has a configuration in which a plurality of reverse osmosis membrane elements 10 are connected in series, and includes a raw water intake passage 40, a booster pump 50, a concentrated water discharge passage 60, a permeate discharge passage 70, and a power recovery. A reverse osmosis membrane separation device is configured together with the device 80. When raw water is introduced into the module 32 by the pressurizing pump 50, permeated water is sequentially separated from the reverse osmosis membrane element on the module inlet side, and the raw water is supplied to the element on the module outlet side while gradually increasing its concentration. . At this time, in the element disposed on the module outlet side, the raw water tends to stay due to a decrease in the membrane surface linear velocity (the rate obtained by dividing the average raw water flow rate per unit time passing through the element by the raw water flow passage cross-sectional area). In other words, the performance of the element deteriorates due to concentration polarization near the reverse osmosis membrane surface in the element. With concentration polarization, impurities in raw water are concentrated on the reverse osmosis membrane surface on the raw water side,
The phenomenon that the impurity concentration on the membrane surface becomes higher than the impurity concentration of the raw water, increasing the osmotic pressure on the membrane surface to reduce the amount of fresh water, or causing the insoluble matter such as gel or scale to precipitate on the membrane surface and lowering the element performance. This is a phenomenon that always occurs in the reverse osmosis method.

[0004] Taking the case of seawater desalination using a reverse osmosis membrane as an example, when trying to obtain permeate of 40% of the supplied seawater, the seawater concentration is increased from 3.5% to about 6%. At this time, the osmotic pressure of seawater is from about 3.0 MPa to about 4.5 MPa.
To rise. In order to satisfy the quality of the permeated water, the operation is performed at an operating pressure higher than the osmotic pressure by about 2.0 MPa (this is called an effective differential pressure). At the element on the module inlet side, a sufficient effective differential pressure is obtained, so that the permeated water quality and the amount of permeated water can be obtained commensurate with the membrane performance.However, at the module outlet side, a sufficient effective differential pressure cannot be obtained, and the membrane surface linear velocity Is about 60% of the module inlet side, so that sufficient permeated water cannot be obtained in both mass. For this reason, at present, most of the permeated water amount of the whole module is covered by the element on the module entrance side.

[0005]

In the prior art, the influence of concentration polarization is increased by the decrease in the linear velocity of the reverse osmosis membrane element arranged on the module outlet side, and the reverse osmosis membrane originally has In some cases, the performance was not sufficiently exhibited, and the quality of permeated water or the amount of permeated water was reduced, or the pressure loss increased due to impurities in raw water or fouling substances or scales precipitated by microorganisms. As a result, maintenance costs, such as an increase in the number of cleaning times of the element and an increase in the amount of chemicals added to prevent fouling, are increased, and the power required for the pump is increased, resulting in an increase in power costs. Increase.

The present invention improves the linear velocity of the membrane surface of the reverse osmosis membrane element disposed on the module outlet side, minimizes the influence of concentration polarization occurring in the element, and achieves sufficient performance from the element of the entire module. An object of the present invention is to achieve energy saving, prevent a pressure loss from rising, and stably operate a reverse osmosis membrane separation device for a long period of time.

[0007]

According to the present invention, there is provided a reverse osmosis membrane module comprising a plurality of reverse osmosis membrane elements connected in series. Downstream of the reverse osmosis membrane element located on the side, at least one reverse osmosis membrane element having a raw water flow passage cross-sectional area smaller than the raw water flow passage cross-sectional area of the reverse osmosis membrane element, and The raw water flow path cross-sectional area of all the reverse osmosis membrane elements located downstream of any reverse osmosis membrane element except for the reverse osmosis membrane element located on the side is less than or equal to the raw water flow path cross-sectional area of the arbitrary reverse osmosis membrane element. It is characterized by a certain reverse osmosis membrane separation device.

[0008] Here, the reverse osmosis membrane module is configured such that 10.0 ≧ ((cross-sectional area of raw water flow path of reverse osmosis membrane element located on the upstream side) / (reverse osmosis membrane element located on the downstream side) It is also preferable to have at least one set of reverse osmosis membrane elements satisfying the following relationship:

Further, a fresh water producing method in which raw water is supplied to the above reverse osmosis membrane separation apparatus to obtain permeated water is also preferable.

Further, it is preferable that the raw water is an aqueous solution having a solute concentration of 0.5% by weight or more, and it is also preferable that the raw water is seawater or brine.

The present invention also provides a reverse osmosis membrane module comprising a plurality of reverse osmosis membrane elements connected in series,
When looking at any two reverse osmosis membrane elements, ((linear membrane velocity of raw water in the reverse osmosis membrane element located downstream) / (linear membrane velocity of raw water in the reverse osmosis membrane element located upstream) )) ≧ 0.8 The method is characterized by a method of treating raw water so as to satisfy the relationship of 0.8.

Here, when looking at any two adjacent reverse osmosis membrane elements, ((linear velocity of raw water membrane surface in reverse osmosis membrane element located on the downstream side) / (reverse osmosis membrane located on the upstream side) It is also preferable to treat the raw water so as to satisfy the relationship of the following:

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a reverse osmosis membrane separation apparatus according to one embodiment of the present invention, which comprises a raw water intake passage 4, a booster pump 5, a reverse osmosis membrane portion, a concentrated water discharge passage 6, and a permeated water discharge passage 7. The reverse osmosis membrane portion includes a module 3 loaded with a plurality of reverse osmosis membrane elements 1 and 2 provided through a raw water flow path. The reverse osmosis membrane element 1 has a larger cross-sectional area of the raw water flow path than the reverse osmosis membrane element 2. Raw water is boosted by a booster pump 5 through a raw water intake passage 4 and is introduced into the module 3. The introduced raw water is subjected to reverse osmosis treatment by the reverse osmosis membrane element 1, and permeated water is taken out through the permeated water discharge passage 7. The concentrated water that has not passed through the reverse osmosis membrane element 1 is introduced as raw water into the reverse osmosis membrane element 2 disposed on the outlet side (downstream side), and the permeated water is taken out through the permeated water discharge passage 7 described above. The concentrated water is discharged to the outside of the module 3 through the concentrated water discharge passage 6. In this example, the permeated water that has passed through the reverse osmosis membrane elements 1 and 2 is collectively taken out (joined in the elements) and taken out of the module 3.

The reverse osmosis membrane module has a plurality of reverse osmosis membrane elements housed in series in a pressure vessel. The number of elements is not particularly limited, but is preferably 4 to 8
A book element should be incorporated. A module in which these modules are arranged in parallel is called a reverse osmosis membrane module unit, and the combination, number, and arrangement can be arbitrarily determined according to the purpose.

FIG. 2 is a schematic view showing a reverse osmosis membrane separation apparatus according to another embodiment of the present invention. The reverse osmosis membrane separation device includes a raw water intake passage 4, a booster pump 5, a module 3, a concentrated water discharge passage 6, a permeated water discharge passage 7, and a power recovery device 8 such as a turbocharger. The module 3 has three reverse osmosis membrane elements 1 having the same raw water flow passage cross-sectional area, three reverse osmosis membrane elements 2 having a smaller raw water flow passage cross-sectional area, and the module inlet side (upstream side). The element having the larger cross-sectional area of the raw water flow path is arranged on the side, and a total of six elements are connected in series. Raw water is boosted by a booster pump 5 through a raw water intake passage 4 and is introduced into the module 3. The introduced raw water is subjected to reverse osmosis treatment sequentially by the reverse osmosis membrane elements 1 and 2, and permeated water that has passed through each element is taken out through the permeated water discharge passage 7. The concentrated water that has not passed through the element is sequentially introduced as raw water into the downstream element and subjected to reverse osmosis treatment, and is finally taken out of the module 3 through the concentrated water discharge passage 6. Since the extracted concentrated water has pressure energy, the energy is recovered by the power recovery device 8, used for driving the booster pump 5, and then discharged.

FIG. 3 shows the module 3 shown in FIG.
Is a schematic diagram showing a reverse osmosis membrane separation device in which three are connected in parallel to form a module unit. The reverse osmosis membrane separation device includes a raw water intake passage 4, a booster pump 5, a module 3, a concentrated water discharge passage 6, a permeated water discharge passage 7, and a power recovery device 8 such as a turbocharger. Each module has three reverse osmosis membrane elements 1 having the same cross-sectional area of the raw water flow path, three reverse osmosis membrane elements 2 having a cross-sectional area of the raw water flow path smaller than that, The element having the larger cross-sectional area of the raw water flow path is arranged on the side, and a total of six elements are connected in series. Raw water is boosted by a booster pump 5 through a raw water intake passage 4 and branched and introduced into each module. The introduced raw water is subjected to reverse osmosis treatment sequentially by the reverse osmosis membrane elements 1 and 2, and permeated water that has passed through each element is taken out through the permeated water discharge passage 7. The concentrated water that has not passed through the element is sequentially introduced as raw water into the downstream element and subjected to reverse osmosis treatment, and is finally taken out of the module 3 through the concentrated water discharge passage 6.
Since the extracted concentrated water has pressure energy, the energy is recovered by the power recovery device 8, used for driving the booster pump 5, and then discharged.

The reverse osmosis membrane element is usually a reverse osmosis membrane,
It is composed of a permeated water channel material existing on the permeation side of the reverse osmosis membrane, a raw water channel material existing on the raw water side of the reverse osmosis membrane, and a permeated water collecting pipe for collecting permeated water of the reverse osmosis membrane. Examples of the form of the reverse osmosis membrane element include a method in which a flat membrane is incorporated into a spiral, tubular or plate-and-frame element, and a method in which a hollow fiber is bundled and incorporated into an element. In the present invention, it is not limited by these forms, but a flat membrane spiral type is more effective.

The raw water flow passage cross-sectional area of the element is a cross-sectional area of the element perpendicular to the raw water flow direction, through which raw water can pass. For example, in the case of an element using a hollow fiber membrane or a tubular element, the cross-sectional area of the raw water flow path can be calculated from the inner diameter of the hollow fiber membrane or the tubular membrane, etc., on the side through which the raw water passes. . When raw water passes through the inside of the hollow fiber membrane or tubular membrane, the sum of the area of the circular cross section based on the inner diameter of each membrane may be the raw water flow passage cross-sectional area, and when passing outside, the entire element crosses The total sum of the areas of the circular cross sections based on the outer diameter of each film may be subtracted from the area. In the case of a spiral type or plate and frame type element, since the raw water flow path material is usually used for the raw water flow path, the value of the porosity of the raw water flow path material described later is used, and the cross section of the element is used. And the value calculated by multiplying the length, thickness, porosity, and number of leaves of the raw water flow path material.

In the case of a spiral type element, the length of the raw water flow path material is preferably in the range of 0.5 m or more and 1.2 m or less.

The thickness of the raw water channel material is 0.5 mm or more.
When the thickness is within the range of 0 mm or less, raw water can be uniformly supplied to the reverse osmosis membrane surface, and permeated water can be obtained efficiently while suppressing concentration polarization and pressure loss. More preferably, the effect is large when it is 0.6 mm or more and 0.8 mm or less.

The raw water flow path material generally has a network structure in which linear structures are alternately arranged. The range in which raw water can actually pass is determined by the raw water side volume of the reverse osmosis membrane in the element. It corresponds to the space excluding the volume of the slab structure. The range in which the raw water can pass is expressed as a porosity. The porosity is a ratio of a range in which raw water can flow, excluding a volume occupied by the linear structure, in a total volume obtained by the linear structure constituting the raw water flow path material, When the rate is 0.75 or more and 0.95 or less, the raw water can be sufficiently supplied to the reverse osmosis membrane surface. More preferably 0.80
It is desirably at least 0.90 and at most 0.90.

The number of leaves greatly varies depending on the diameter of the element, the diameter of the permeated water collecting pipe, and the like.
It is preferable that the raw water flow path material is contained in the range of 3 to 40 leaves per book, and it is more preferable that the raw water flow path material is contained in the range of 4 to 30 leaves per book.

The raw water flow path material is made of polyethylene,
It is preferable to use polypropylene or the like. In the present invention, any material is effective, but it is more preferable to use polyethylene which does not easily damage the film surface.

In the present invention, the membrane surface linear velocity is a value obtained by dividing the average raw water flow rate per unit time passing through the inside of the element by the above-mentioned raw water flow passage cross-sectional area. If the elements disposed in the module have the same cross-sectional area of the raw water flow path, the permeated water is extracted from each element, so that the water passes through the element as it is on the exit side of the module, that is, on the downstream side in the flow direction of the raw water. Average raw water flow rate becomes smaller. This means that the above-mentioned film surface linear velocity decreases as it goes downstream,
Element performance will be degraded, for example, concentration polarization will easily occur. In order to avoid this state, an element having a larger cross section of the raw water flow path is arranged on the module inlet side, that is, on the upstream side in the flow direction of raw water, and the upstream side element on the outlet side, that is, on the downstream side. An element having a smaller cross-sectional area of the raw water flow path than that of the element is arranged.
Thereby, the membrane surface linear velocity of the element arranged on the downstream side is improved as compared with the case where the reverse osmosis membrane element having the same raw water flow passage cross-sectional area is used, and it is possible to prevent the performance of the element from deteriorating. . Specifically, for example, in the case of a module in which six elements are connected in series, assuming that the raw water flow path cross-sectional area of the element located at the most upstream side is S, the raw water flow path cross-sectional area of the six elements is S, S, S, S in order from the upstream side in the flow direction of raw water
/ 2, S / 2, S / 2. Also, S,
S, S, S, S, S / 2, and S,
S, S / 2, S / 2, S / 3, and S / 3 can also be used. Of course, S, (5/6) × S, (4/6) × S, (3/6) so that the cross-sectional area of the raw water flow passage decreases gradually.
× S, (2/6) × S, S / 6. That is, at least one reverse osmosis membrane element having a raw water flow path cross-sectional area smaller than the raw water flow path cross-sectional area of the reverse osmosis membrane element is arranged on the downstream side of the reverse osmosis membrane element located at the most upstream side, Further, for any reverse osmosis membrane element except the most downstream reverse osmosis membrane element, the cross-sectional area of the raw water flow path of all the reverse osmosis membrane elements located downstream thereof is the same as that of the above-mentioned arbitrary reverse osmosis membrane element. What is necessary is just to be less than the water flow path cross-sectional area.

When water is passed, the recovery rate of the entire module (percentage of permeated water relative to the amount of raw water supplied to the module)
Changes, the film surface linear velocity of the raw water at the element on the outlet side of the module changes even if the raw water flow rate is the same at the inlet of the module. In consideration of the balance between the recovery rate of the entire module and the linear velocity of the membrane surface, in order to maintain a stable water quality of the permeated water, in order to maintain the linear velocity of the element on the outlet side of the module, the adjacent reverse For the osmosis membrane element, the value obtained by dividing the cross-sectional area of the raw water flow path of the element on the module inlet side (upstream side) by the cross-sectional area of the raw water flow path on the module outlet side (downstream side) (the ratio of the cross-sectional area of the raw water flow path) is 1 It is preferable to exceed 10 and 10 or less,
More preferably, it is 1.25 or more and 5 or less. This relationship only needs to be satisfied for any one set (two) of elements in the module, but it is preferable that this relationship is satisfied for any two elements.

In order to obtain a permeated water having a stable water quality, when two arbitrary reverse osmosis membrane elements in the module are viewed, the membrane surface of the reverse osmosis membrane element located on the module exit side (downstream side) is viewed. The value obtained by dividing the linear velocity by the membrane surface linear velocity of the reverse osmosis membrane element located on the module inlet side (upstream side) is set to 0.8 or more. This can be achieved, for example, by changing the cross-sectional area of the raw water flow path of the reverse osmosis membrane element as described above.
In the case of an element using a hollow fiber membrane or a tubular membrane, the cross-sectional area of the raw water flow path can be changed by adjusting the inner diameter of each membrane or the number of membranes used per element, and the spiral type or plate・ When using and frame type elements, the number and length of raw water flow path materials,
It can be performed by adjusting the porosity and the like.

Further, it is preferable that the above-mentioned value be 0.9 or more for any two adjacent reverse osmosis membrane elements.

It is also preferable that the above-mentioned value exceeds 1, that is, the film surface linear velocity increases toward the downstream side. By treating the raw water while maintaining these relationships, it is possible to obtain permeated water having stable water quality.

As the reverse osmosis membrane, a polymer material such as a cellulose acetate polymer or polyamide is often used. The membrane structure includes an asymmetric membrane and a composite membrane. Membrane forms include hollow fibers and flat membranes. However, the method of the present invention can be used irrespective of the material, structure, and form of the reverse osmosis membrane, and all are effective. Among them, a cellulose acetate-based asymmetric membrane and a polyamide-based composite membrane are effective for the present invention, and the aromatic polyamide-based composite membrane is more effective.

When a spiral type reverse osmosis membrane element is used, the permeated water collecting pipe has strength enough to withstand the operating pressure, can easily join members such as a reverse osmosis membrane, and is used when permeated water flows. It is preferable that there is almost no eluate from the collecting pipe. Any material that satisfies this condition is effective in the present invention, but preferably uses a noryl resin or FRP to provide a large effect. The diameter of the water collection pipe is 10 mm from the number of reverse osmosis membrane leaves that can be used for the element and the durability.
It is desirably at least 80 mm. More preferably 25 mm
It is preferably at least 40 mm and at most 40 mm.

As a pressure increasing pump for pressurizing raw water, a centrifugal pump, a turbine pump, a plunger pump and the like are often used. In the present invention, any type of pump may be selected.

The water to be treated in the reverse osmosis membrane separation apparatus of the present invention, that is, the raw water is not particularly limited in view of the gist of the present invention, but the solute concentration in the solution is 0.5% by weight or more. If the solution is used, the element performance in the reverse osmosis membrane separation device is greatly reduced due to the impurities contained in the water to be treated and the osmotic pressure. More preferably, the raw water is seawater, brackish water, or high-concentration brackish water.

[0033]

The present invention will be described below with reference to specific examples. In the embodiments, only the case where the spiral reverse osmosis membrane element is used is described, but the present invention is not limited to these embodiments.

In the following Examples and Comparative Examples, the ratio of the cross-sectional area of the raw water flow passage means the cross-sectional area of the raw water flow passage of the element arranged on the module inlet side (upstream side) on the module outlet side (downstream side). Divided by the cross-sectional area of the raw water flow path of the element, and the ratio of the linear velocity on the membrane surface means the linear velocity on the membrane surface of the element arranged on the module outlet side (downstream side) on the module inlet side (upstream side). Means the value obtained by dividing by the linear velocity on the film surface of the element arranged at (Example 1) Desalination rate of 99.75% and membrane water permeability of 0.72 (m ³ / m ² ) · d around a permeated water collecting pipe having a diameter of 30 mm.
A raw water flow path material made of polyethylene having a width of 0.9 m, a thickness of 0.7 mm and a porosity of 0.85 is placed on the functional layer side of the polyamide reverse osmosis membrane having the above performance, and the permeated water flow is placed on the support membrane side of the reverse osmosis membrane. Each of the path materials is arranged with 24 leaves, and a reverse osmosis membrane element 1 having a diameter of 0.2 m and a length of 1 m, which is spirally surrounded, is provided on the module inlet side, and a permeated water collecting pipe similar to the above,
A reverse osmosis membrane element 2 having a diameter of 0.1 m and a length of 1 m and spirally enclosing six leaves using a reverse osmosis membrane, a raw water flow path material, and a permeate flow path material, one on the module exit side, a total of 2
The book was loaded into the module 3 in series through a raw water passage, and a reverse osmosis membrane separation apparatus shown in FIG. 1 was manufactured which was connected to the inlet of the module and comprised a booster pump 5 for increasing the pressure of the raw water. Module inlet pressure is 6.5MPa,
The experiment was performed with the raw water salt concentration set to 3.5% and the raw water temperature set to 25 ° C.

As a result of continuous operation in a steady state for 100 hours, the desalination ratio was 99.70%, and the raw water amount was 115.0 m.
^The permeated water amount was 25.0 m ³ / d with respect to ³ / d. The pressure loss during operation is constant at 0.03 MPa, and
^{3 The} energy required for production was about 2.00 L in terms of crude oil.

In this experiment, the ratio of the cross-sectional area of the raw water flow passage of each of the module inlet side element and the outlet side element was 4.0, and the ratio of the membrane surface linear velocity was 3.5. (Example 2) The same reverse osmosis membrane element 1 as in Example 1 is provided on the module inlet side through the raw water passage, and three reverse osmosis membrane elements 2 are provided on the module outlet side through the raw water passage.
A reverse osmosis membrane separator having the form shown in FIG. 2 was prepared using the module 3 in which a total of six modules were loaded in series, and an experiment was performed under the same operating conditions as in Example 1. As a result of continuous operation for 500 hours in a steady state, the desalination rate was 99.72% and the raw water volume was 20.
A permeated water amount of 75.0 m ³ / d was obtained with respect to 0 m ³ / d. The pressure loss during operation was about 0.055 MPa. Also,
The energy required to produce 1 m ^{3 of} permeated water was about 1.72 L in terms of crude oil. In this experiment,
The ratio of the cross-sectional area of the flow passage between the module inlet side element (the element at the most upstream side) and the outlet side element (the element at the most downstream side) is 4.0, and the membrane surface linear velocity between any two elements. Is 0.83 to 3.7, and the ratio of the film surface linear velocity between two adjacent elements is 0.90 to 3.7.
3.7. (Example 3) The same reverse osmosis membrane element, raw water flow path material as in Example 1, and three reverse osmosis membrane elements 1 as in Example 1 were provided on the module inlet side through the raw water passage and the diameter of the permeated water collecting pipe was 60 mm. A reverse osmosis membrane element having a diameter of 0.2 m and a length of 1 m, in which a permeated water flow path material is spirally wound around a 12-leaf water collecting pipe, is passed through a raw water passage to the module outlet side.
A total of six tubes were loaded in series in the module 3, and the operation was carried out under the same reverse osmosis membrane separation device and operating conditions as in Example 2 except for the above. As a result of continuous operation for 500 hours in a steady state,
Salt rejection 99.74%, to obtain a permeated water 78.0m ³ / d with respect to the raw water quantity 200m ³ / d. The pressure loss during operation was about 0.063 MPa. The energy required to produce 1 m ^{3 of} permeated water is approximately 1.65 in terms of crude oil.
L. In this experiment, the ratio of the cross-sectional area of the raw water flow passage between the module inlet side element (the element at the most upstream side) and the outlet side element (the element at the most downstream side) was 2.0, and two arbitrary The ratio of the film surface linear velocities between the elements was 0.82 to 1.8, and the ratio of the film surface linear velocities between two adjacent elements was 0.90 to 1.8. (Example 4) A reverse osmosis membrane separation apparatus of the form shown in Fig. 3 having the same configuration as that of Example 2 was prepared, except that three module units 3 similar to those of Example 2 were arranged in parallel. The operation was performed under the same operating conditions as in Example 1. 500 hours of continuous operation result in a steady state, salt rejection 99.72%, to obtain a permeated water 225.0m ³ / d with respect to the raw water quantity 600m ³ / d. The pressure loss during operation is about 0,0.
It was 055 MPa. The energy required to produce 1 m ^{3 of} permeated water was about 1.56 L in terms of crude oil. Example 5 Three reverse osmosis membrane elements 1 identical to those of Example 1 were placed on the module inlet side through a raw water passage, with a porosity of 0.8 and a width of 0.6.
The same reverse osmosis membrane, permeated water collecting pipe, and permeated water collecting pipe as in Example 1 were spirally wound around the 30-leaf collecting pipe using the same raw water flow path material as in Example 1 except that m was used. Three reverse osmosis membrane elements having a diameter of 0.2 m and a length of 1 m are loaded in series on the module outlet side through the raw water passage, three in total, and the rest is the same as in Example 2. The operation was performed under the operating conditions. As a result of continuous operation for 500 hours in a steady state, the desalination rate was 99.73%, and the permeated water amount was 80.0 m ³ / d against the raw water amount of 200 m ³ / d. The pressure loss during operation was about 0.068 MPa.
The energy required to produce 1 m ^{3 of} permeate is
It was about 1.62 L in terms of crude oil. In this experiment, the ratio of the cross-sectional area of the raw water flow passage between the element on the module inlet side (the element on the most upstream side) and the element on the outlet side (the element on the most downstream side) was 1.3.
The ratio of the film surface linear velocity between the two elements is 0.82 to 1.
2. The ratio of the film surface linear velocity between two adjacent elements was 0.90 to 1.2. (Comparative Example 1) Six reverse osmosis membrane elements 1 of Example 1 were loaded in a module 3 in series to produce a reverse osmosis membrane separation apparatus having the form shown in FIG. 4 under the same experimental conditions as in Example 2. I drove. As a result of continuous operation of 500 hours, salt rejection poor and 99.68%, a water permeation rate 79.0m ³ / d with respect to the raw water quantity 200 meters ³ / d, less difference was observed as in Example 3 Did not. The pressure loss at the start of operation is about 0.07
It was 2 MPa, and the pressure loss gradually increased from 300 hours after the start of operation. Also, the energy required to produce 1 m ^{3 of} permeated water was about 1.86 L in terms of crude oil, which was higher than Examples 2 and 3. In this experiment, the ratio of the cross-sectional area of the raw water flow passage of each of the module inlet side element (most upstream side element) and the outlet side element (most downstream side element) was 1.0, and the ratio between the two adjacent elements was Was 0.90 to 0.94, and the ratio of the film surface linear velocities between any two elements was 0.66 to 0.94. (Comparative Example 2) A reverse osmosis membrane separator having the same configuration as that of Example 4 except that three modules 3 used in Comparative Example 1 were loaded in parallel was operated under operating conditions. As a result of continuous operation for 500 hours in a steady state, the desalination rate was 99.68.
%, Permeated water amount 235.0 for raw water amount 600 m ³ / d
m ³ / d, the water quality was worse than in Example 4, and no significant difference was observed in the amount of permeated water obtained. The pressure loss during the operation was about 0.072 MPa, which was higher than that of Example 4, and the pressure loss gradually increased 300 hours after the start of the operation as in Comparative Example 1. The energy required to produce 1 m ^{3 of} permeate was about 1.78 L in terms of crude oil.

[0037]

According to the reverse osmosis membrane separation device and method of the present invention, the linear velocity of the reverse osmosis membrane element disposed on the module outlet side is improved, and the influence of concentration polarization occurring in the element is minimized. Because of this, it is possible to prevent an increase in pressure loss due to fouling or the like. Therefore, while realizing energy saving, the reverse osmosis membrane separation device can be stably operated for a long time, and stable water quality and permeated water amount can be obtained. In particular, an aqueous solution having a solute concentration exceeding 0.5% by weight,
When seawater or brackish water is used as raw water, high-quality permeated water conforming to various drinking water standards can be stably obtained.

[Brief description of the drawings]

FIG. 1 shows a reverse osmosis membrane module loaded with two reverse osmosis membrane elements according to an embodiment of the present invention, in which a raw water flow passage cross-sectional area of a module inlet side element is larger than a raw water flow passage cross-sectional area of an outlet side element. It is the schematic of the reverse osmosis membrane separation device which has.

FIG. 2 is a reverse osmosis membrane module loaded with six reverse osmosis membrane elements having a raw water flow path cross-sectional area of a module inlet side element larger than a raw water flow path cross-sectional area of an outlet side element according to another embodiment of the present invention. It is a schematic diagram of a reverse osmosis membrane separation device having a.

FIG. 3 is a schematic view of a reverse osmosis membrane separation device having three reverse osmosis membrane modules similar to FIG. 2 according to still another embodiment of the present invention.

FIG. 4 is a schematic view of a conventional reverse osmosis membrane separation device having a reverse osmosis membrane module loaded with six identical reverse osmosis membrane elements.

[Explanation of symbols]

1: Reverse osmosis membrane element (having a large cross section of raw water passage) 2: Reverse osmosis membrane element (having a small cross section of raw water passage) 3: Reverse osmosis membrane module 4: Raw water intake passage 5: Boost pump 6 : Condensed water discharge passage 7: Permeated water discharge passage 8: Power recovery device 10: Reverse osmosis membrane element 31: Reverse osmosis membrane module 32: Reverse osmosis membrane module 40: Raw water intake passage 50: Boost pump 60: Concentrated water discharge passage 70 : Permeated water discharge passage 80: Power recovery device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 HA01 HA17 HA21 HA42 HA61 HA65 MA01 MA02 MA03 MA06 MA24 MA25 MA28 MB20 MC18 MC22 MC54 PB03

Claims (7)

[Claims] 1. A reverse osmosis membrane module comprising a plurality of reverse osmosis membrane elements connected in series, wherein the reverse osmosis membrane module is provided on the downstream side of the most upstream reverse osmosis membrane element. At least one having a raw water flow path cross-sectional area smaller than the raw water flow path cross-sectional area of the permeable membrane element
Has the number of reverse osmosis membrane elements, and the cross-sectional area of the raw water flow passage of all the reverse osmosis membrane elements located on the downstream side of any reverse osmosis membrane element except the reverse osmosis membrane element located on the most downstream side is as described above. A reverse osmosis membrane separation device having a cross-sectional area equal to or smaller than a raw water flow path cross-section of an arbitrary reverse osmosis membrane element. 2. The reverse osmosis membrane module is configured so that, for adjacent elements, 10.0 ≧ ((cross-sectional area of raw water flow path of reverse osmosis membrane element located on the upstream side) / (reverse osmosis membrane element located on the downstream side) The reverse osmosis membrane separation device according to claim 1, wherein the reverse osmosis membrane separation device has at least one set of reverse osmosis membrane elements satisfying the following relationship: 3. A fresh water producing method comprising supplying raw water to the reverse osmosis membrane separation device according to claim 1 or 2 and obtaining permeated water. 4. The fresh water producing method according to claim 3, wherein the raw water is an aqueous solution having a solute concentration of 0.5% by weight or more. 5. The fresh water producing method according to claim 3, wherein the raw water is seawater or brackish water. 6. When using a reverse osmosis membrane module comprising a plurality of reverse osmosis membrane elements connected in series, and looking at any two reverse osmosis membrane elements, Wherein the raw water is treated so as to satisfy the following relationship: linear velocity of raw water on the membrane surface / linear velocity of raw water on the reverse osmosis membrane element located on the upstream side) ≧ 0.8. Method. 7. When looking at any two adjacent reverse osmosis membrane elements, ((the membrane surface linear velocity of raw water in the reverse osmosis membrane element located on the downstream side) / (the reverse osmosis membrane element located on the upstream side) 7. The fresh water producing method according to claim 6, wherein the raw water is treated so as to satisfy the following relationship: