Patent Application
20220314171
The present invention relates to a separation membrane element to be used for separating impurities from various kinds of liquid containing impurities, in particular, to be used for desalination of seawater and brackish water, manufacture of ultrapure water, wastewater treatment, etc.
Among techniques for removing ionic substances contained in seawater, brackish water, etc., a separation method using a separation membrane element has come to be used widely in recent years as a process for energy saving and resource saving. Separation membranes used for the separation method using a separation membrane element are classified, according to the hole diameter and separation function, into a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, and a forward osmosis membrane. These kinds of membranes are used for, for example, manufacture of drinking water from seawater, brackish water, water containing harmful substances, etc., manufacture of industrial ultrapure water, and wastewater treatment and collection of valuables, and are used suitably for respective target components to be separated on the basis of respective kinds of separation performance.
Whereas there are various forms of separation membrane elements, they have a common feature that raw water is supplied to one surface of a separation membrane and permeated fluid is obtained from the other surface. Equipped with many bundled separation membranes, a separation membrane element is formed so that the membrane area per separation membrane element becomes large, that is, the amount of permeated fluid obtained per separation membrane element becomes large. Various kinds of shapes such as a spiral type, a hollow fiber type, a plate-and-frame type, a rotating flat-sheet membrane type, and a flat membranes accumulation type are proposed for separation membrane elements so as to meet uses and purposes.
For example, spiral-type separation membrane elements are used widely for reverse osmosis filtration. Spiral-type separation membrane element includes a water collecting pipe and a separation membrane unit that is wound around the water collecting pipe. The separation membrane unit is formed by stacking supply-side channel members for supplying raw water (i.e., water to be treated) as supply water to the surfaces of separation membranes, the separation membranes for separating components contained in the raw water, and permeation-side channel members for guiding permeate that has permeated through the separation membranes and has thereby been separated from the supply water to the water collecting pipe. Enabling application of pressure to raw water, spiral-type separation membrane elements are used preferably because they make it possible to take out a large amount of permeated fluid.
In treating supply water using a separation membrane element, concentration polarization may occur in which substances dissolved in supply water, such as salts, form a concentration gradient in the direction perpendicular to the separation membrane. A reduction in element performance due to such concentration polarization can be suppressed by, for example, decreasing the thickness of a concentration polarization layer formed on the membrane surface by decreasing the thickness of the supply-side channel member and increasing the membrane surface linear velocity of supply water. However, the thickness reduction of the supply-side channel member causes problems. For example, fouling substances produced by microbes and impurities in supply water clog the supply-side channel, resulting in reduction in element performance. For another example, a resulting pressure loss in the element becomes large to require a pump for supplying supply water to produce more power, resulting in an increased electricity cost and damage of the element. In view of this, measures for increasing the performance of a separation membrane element by improving the supply-side channel member have been proposed.
More specifically, Patent documents 1 and 2 each propose a net whose flow resistance is decreased by controlling the arrangement of fibrous objects in a supply-side channel member. As disclosed in Patent document 3, a fabric channel member has been conceived in which warps and wefts are non-circular in cross section.
However, the above-mentioned separation membrane elements are insufficient in the balance between the reduction of the flow resistance of the supply-side channel and the suppression of concentration polarization. Furthermore, there may occur an event that, when a separation membrane element is constructed, a supply water inflow end surface portion and the supply-side channel inside the element are partially clogged due to membrane deformation. In view of these problems, an object of the present invention is to provide a separation membrane element capable of suppressing concentration polarization while decreasing the flow resistance of the supply-side channel by suppressing clogging of a supply water inflow end surface portion and the supply-side channel inside the element.
To attain the above object, the invention provides a separation membrane element including at least a water collecting pipe, separation membranes, a supply-side channel member, and a permeation-side channel member, in which:
the supply-side channel member is interposed between two surfaces of the separation membranes to form a supply-side channel;
the supply-side channel member has a net shape in which plural fibrous rows X including fibrous objects A and arranged in one direction and plural fibrous rows Y including fibrous objects B and arranged in a different direction than the fibrous rows X cross each other sterically to form intersections;
at least one of the fibrous objects A and the fibrous objects B have a large diameter portion and a small diameter portion along a longitudinal direction;
in a longitudinal cross section including an arbitrary fibrous row and taken along a longitudinal direction of the arbitrary fibrous row, at least one of the fibrous objects A and the fibrous objects B includes a thread that is thinner at a central portion located between intersection portions of the fibrous rows X and the fibrous rows Y than at the large diameter portion;
a supply-side channel area ratio is in a range of 45% to 65%; and
when a surface of the supply-side channel member is observed from a thickness direction, a fiber between an arbitrary intersection and an adjacent intersection is a tapered fiber whose diameter increases like a taper in a direction from one intersection to the other intersection.
A preferable mode of the invention provides a separation membrane element in which the tapered fiber has a taper ratio in a range of 1/20 to 1/3.
A preferable mode of the invention provides a separation membrane element in which the tapered fiber has a tapered shape from a raw water side toward a concentrate side.
A preferable mode of the invention provides a separation membrane element in which the supply-side channel member has a bending resistance (m) larger than or equal to 0.07 m and smaller than or equal to 0.14 m.
A preferable mode of the invention provides a separation membrane element in which the supply-side channel member has a ratio of a void volume v to a total volume V which is represented by a product of a thickness and an area of the supply-side channel member in a range of 90% to 97%.
A preferable mode of the invention provides a separation membrane element in which a ratio of a supply-side channel volume F of the separation membrane element to the void volume v of the supply-side channel member is larger than or equal to 90%.
A preferable mode of the invention provides a separation membrane element in which an interval between intersection portions in a direction perpendicular to a raw water flow direction of the supply-side channel member is in a range of 3 to 5 mm.
A preferable mode of the invention provides a separation membrane element in which an interval between intersection portions in a direction parallel with a raw water flow direction of the supply-side channel member is in a range of 4 to 8 mm.
A preferable mode of the invention provides a separation membrane element in which in a transverse cross section Z taken perpendicularly to a longitudinal direction of an arbitrary fibrous object of the supply-side channel member, the supply-side channel member satisfies a relationship of 1.2<W1/W2<3.0, where W1 is a maximum diameter of the arbitrary fibrous object and W2 is a maximum diameter in a direction perpendicular to the direction of the maximum diameter W1.
Furthermore, a preferable mode of the invention provides a separation membrane element in which the permeation-side channel member is made of a circular-knit tricot.
Capable of lowering concentration polarization while suppressing differential pressure increase due to clogging of the supply-side channel, the invention can provide a separation membrane element that is superior in operation stability. Furthermore, in the separation membrane element according to the invention, since the supply-side channel member can be made thinner, the area of membranes packed per element, that is, the element water production rate, can be increased. Still further, in the separation membrane element according to the invention, since each fibrous object has tapered portions when a surface of the supply-side channel member is observed from its thickness direction, the frequency of occurrences of rapid expansion and contraction of the channel is decreased and the flow resistance can thereby be lowered. In addition, since the three-dimensional shape of each fiber intersection portion is gentle, damaging of the membrane surfaces of each separation membrane can be suppressed.
An embodiment of the present invention will be hereinafter described in detail.
In this specification, the terms “mass” and “weight” are the same in meaning. Furthermore, in the specification, the mark “−” means that numerical values written before and after it are included as a lower limit value and an upper limit value.
A separation membrane element according to the invention includes at least a water collecting pipe, a separation membrane, a supply-side channel member, and a permeation-side channel member.
In a spiral-type separation membrane element 1 shown in
In the spiral-type separation membrane element 1, supply water 7 is usually supplied from one side surface and is gradually separated into permeate 8 and concentrate 9 while flowing parallel with the water collecting pipe 6. The permeate 8 goes out of the spiral-type separation membrane element 1 from a side surface that is opposite to the side surface to which the supply water 7 is supplied.
This type has a feature that since supply water 7 flows from the one side surface to the other side surface of the spiral-type separation membrane element 1, it is necessarily brought into contact with the membranes over a long distance and hence is separated into permeate 8 and concentrate 9 sufficiently. Whereas there are various types of separation membrane elements, they have a common feature that supply water is supplied to one surface of separation membranes and permeate is obtained from the other surface. Separation membrane elements other than a spiral-type one having various shapes and using flat membranes, such as a plate-and-frame type and a flat membranes accumulation type, can be employed as a separation membrane element of the invention according to respective uses and purposes.
As shown in
To suppress concentration polarization occurring on the separation membrane surfaces in the separation membrane element, it is important to decrease the number of positions where supply water stays, that is, clogged positions in supply-side channel and increase the degree of turbulence around the fibrous objects. This is because turbulence enables supply, to the surface of a separation membrane, of supply water that is not in contact with the membrane yet.
Since supply water flows while expanding between the fibrous objects of each supply-side channel member, fibrous objects that are not parallel with the flow direction of the supply water become obstacles to the flow of the supply water and play a role of increasing the degree of turbulence. On the other hand, the fibrous objects that are not parallel with the flow direction of the supply water tend to increase the flow resistance because they clog the channel and obstructs the flow of the supply water. In view of the above, in a longitudinal cross section including an arbitrary fibrous row and taken along the longitudinal direction of the arbitrary fibrous row, at least one of the fibrous object A and the fibrous object B is formed by a thread that is thinner at a central portion between intersection portions of a fibrous row X and a fibrous row Y than the intersection portions. As a result, the balance between the turbulence intensity and the flow resistance can be improved.
In the separation membrane element, since the permeation drive power is a transmembrane pressure difference, to increase the water production rate it is effective to increase the transmembrane pressure difference. The transmembrane pressure difference is obtained by subtracting the flow resistance and the osmotic pressure from the pressure applied to the separation membrane element. Thus, to increase the transmembrane pressure difference, it is necessary to increase the applied pressure, decrease the flow resistance, or decrease the membrane osmotic pressure. Where the applied pressure is kept the same, the water production rate can be increased by decreasing the flow resistance or the membrane osmotic pressure.
The porosity of the supply-side channel members has a great influence on the flow resistance. If the porosity is increased, the number of positions of obstacles to fluid decreases and hence the flow resistance lowers. If the porosity is decreased, the number of positions of obstacles to fluid increases and hence the flow resistance increases. However, if the porosity is increased to lower the flow resistance, the amount of resin or the like that is part of the supply-side channel members decreases and hence the stiffness of the supply-side channel members decreases. For example, a net in which threads are narrow between the intersections and has positions of necking (i.e., a phenomenon that when a polymer material is stretched it is not stretched uniformly and a constriction occurs locally after yielding) is advantageous in terms of the flow resistance because of a high porosity. However, such a net suffers stiffness reduction and is prone to expand and contract, possibly causing trouble, such as difficulty in cutting a net into prescribed dimensions and reduction in the ease of passage of the net through the device at the time of winding. Furthermore, reduction in the stiffness of the net may cause trouble such as slipping of the net during operation of the element.
In the embodiment, at least one of each of the fibrous objects A and each of the fibrous objects B has large diameter portions and small diameter portions that are arranged in its longitudinal direction and is composed of a fiber having tapered portions. The tapering will be described in a section “(fiber shape)” to be described later.
Since at least one of each of the fibrous objects A and each of the fibrous objects B is made of a tapered fiber, a suddenly contracted flow and a suddenly enlarged flow of fluid that are causes of increase in flow resistance can be suppressed and hence the flow resistance can be lowered while necessary stiffness of the supply-side channel members is maintained. Either one or both of each of the fibrous objects A and each of the fibrous objects B may be a tapered fiber.
The osmotic pressure increases as the concentration polarization occurring on the surface of a separation membrane becomes larger. In the separation membrane element, the concentration polarization becomes larger if the flow rate of supply water is low, fluid is separated from membrane surfaces, or fluid is less apt to flow in front of and behind fibers. That is, increasing the membrane surface velocity or decreasing the number of fibers that are in contact with the membrane surface is effective in suppressing the concentration polarization. Thus, if in a longitudinal cross section including an arbitrary fibrous row the fibrous object A or B is formed by a thread that is thinner at central portions between intersection portions of the fibrous row X and the fibrous row Y than at large diameter portions, or is tapered from one intersection to the adjacent one, the number of fibers that are in contact with the membrane surface of the separation membrane becomes smaller and increase of the concentration polarization can be suppressed. Furthermore, such a structure increases the porosity of the supply-side channel member and hence is effective in decreasing the flow resistance.
In the embodiment, in
The term “tapering” used in the embodiment means that a fiber between an intersection formed by a fibrous object A and a fibrous object B and an adjoining intersection increases in diameter from one intersection to the other, more specifically, the fiber increases or decreases in diameter as the position goes toward its tip. Here, for the sake of convenience, the shape of a tapered fiber will be called a “tapered shape”, the shape of a fiber that is not tapered and has a uniform diameter will be called a “cylindrical shape,” and the shape of a fiber that is thin between intersections and has a necking will be called a “necked shape.” For example, the shape of a fiber between intersections of a fibrous row of each of supply-side channel members 2a-2c shown in
As shown in
It is also preferable that when a surface of the supply-side channel member is observed it is found that each fiber overlap portion may be formed with a web portion w as shown in
Where fibers have a tapered shape, the amount of resin at each intersection point is made larger than in fibers having a cylindrical shape or a necked shape and intersection portions are wider and gentler in outline shape than central portions, as a result of which the membrane is less prone to be hurt and the removal rate is less prone to decrease.
Where fibers have a necked shape, the proportion of portions that are small in thread diameter is large, the supply-side channel area ratio can be increased easily, the porosity of the supply-side channel member is made large, and the flow resistance can be lowered. However, when comparison is made with a tapered shape having the same channel area ratio, in the case of a necked shape the channel expands or contracts rapidly at the necking portion and an energy loss occurs and the differential pressure tends to become large. Furthermore, in the case of a necked shape, in many cases the thread diameter is small and hence the stiffness tends to be low.
In a longitudinal cross section of one fibrous row taken along its longitudinal direction, in
In the embodiment, it is preferable that the thread diameter (average thickness L5) of the central portion R2 may be larger than or equal to 0.10 mm and smaller than or equal to 0.75 mm, even preferably larger than or equal to 0.15 mm and smaller than or equal to 0.50 mm and further preferably larger than or equal to 0.20 mm and smaller than or equal to 0.40 mm. If the thread diameter of the central portion R2 is in this range, even in decreasing the thickness of the supply-side channel member the concentration polarization can be suppressed while the flow resistance of the supply-side channel is lowered, whereby the salt rejection rate and the water productivity of the separation membrane element can be increased.
Thread diameters (thicknesses) of intersection portions and central portions can be determined by observing a longitudinal cross section that is parallel with a fibrous row using a microscope or an X-ray CT measuring instrument on the market and measuring distances. This may be done by measuring diameters of 30 arbitrary intersection portions or central portions using a measurement mode and calculating their average.
The thickness of the supply-side channel member substantially corresponds to the thickness L4 of intersection portion of the fibrous object A (21) and the fibrous object B (22), that is, the sum of the thickness of a fibrous object A (21) there and the thickness of a fibrous object B (22) there. As shown in
In the embodiment, it is preferable that the average thickness of the supply-side channel member may be larger than or equal to 0.20 mm and smaller than or equal to 1.5 mm, even preferably larger than or equal to 0.30 mm and smaller than or equal to 0.85 mm and further preferably larger than or equal to 0.50 mm and smaller than or equal to 0.80 mm. If the average thickness of the supply-side channel member is in this range, the membrane surface linear velocity of supply water becomes high and a flow adjacent to the membrane surface is disordered, whereby a concentration polarization layer occurring on the membrane surface becomes thinner and hence the separation performance of the element can be increased. Furthermore, the clogging of the supply-side channel by foulants such as impurities in supply water and microbes can be suppressed and stable operation of the separation membrane element is enabled for a long time without need for increasing the necessary motive power of a pump.
Furthermore, in the invention, it is preferable that the ratio, L5/L4, of the average thickness L5 of central portions to the thickness L4 of intersection portions may be larger than or equal to 0.2 and smaller than or equal to 0.55, even preferably larger than or equal to 0.25 and smaller than or equal to 0.50. If the ratio of the thread diameter of central portions to that of intersection portions is in this range, the supply-side channel area ratio can be increased and a sufficiently wide supply-side channel can be secured inside the separation membrane element.
An average thickness of the supply-side channel member is an average of thickness values of randomly selected 10 or more intersection portions of fibrous objects A and fibrous objects B, namely sum of thickness values of a fibrous object A and a fibrous object B, as measured by a microscope, an X-ray CT measuring instrument, a precise thickness gauge, or the like and calculated according to (sum of measurement values)/(the number of measurement positions).
Still further, it is preferable that the thickness variation of the supply-side channel member may be 0.9 times or more and 1.1 times or less of an average thickness of the supply-side channel member. If the thickness variation of the supply-side channel member is in this range, supply water can be supplied to the separation membrane element uniformly and hence the performance of the separation membrane is allowed to manifest uniformly.
In the embodiment, the supply-side channel area ratio in a longitudinal cross section, taken along longitudinal direction of one fibrous row is in a range of 45% to 65%. As shown in
An average of supply-side channel area ratios measured at arbitrary 30 positions can be employed as a supply-side channel area ratio.
The void volume of the supply-side channel member employed in the embodiment is the volume of portions, capable of constituting the supply-side channel, of the supply-side channel member. A void volume v of the supply-side channel member can be determined by calculating a volume of a supply-side channel member main body by dividing a weight of the supply-side channel member per a cut-out area (e.g., 30 cm×30 cm) by a specific gravity of the material of the supply-side channel member material and subtracting the calculated volume of the supply-side channel member main body from a total volume V that is represented by the product of the thickness of the supply-side channel member and the cut-out area of the supply-side channel member.
In the embodiment, it is preferable that the proportion of the void volume v of the supply-side channel member may be in a range of 90% to 97%. If the void volume v of the supply-side channel member is in this range, the separation membrane element is improved in the balance between the turbulence intensity and the flow resistance of supply water without lowering the handling performance of the supply-side channel member.
The supply-side channel volume of the separation membrane element according to the embodiment is a volume of a portion that can be a supply-side channel formed by the supply-side channel member that is set between two planar portions of separation membranes in a separation membrane element manufactured by using the supply-side channel member. It is preferable that the ratio of the supply-side channel volume F of the separation membrane element to the void volume v of the supply-side channel member may be larger than or equal to 90%. If the ratio of the supply-side channel volume F of the separation membrane element to the void volume v of the supply-side channel member is larger than or equal to 90%, a sufficiently large supply-side channel can be secured in the separation membrane element and the pressure loss due to a flow of supply water can be reduced.
It is preferable to measure a void volume v of the supply-side channel member in such a manner that an X-ray CT measuring instrument shoots in a state that the separation membrane element is not broken, that is, influence of membrane deformation that occurred at the time of manufacture of the separation membrane element is reflected. However, where the size of the separation membrane element is so large that non-destructive shooting is difficult, a method can be employed that the separation membrane element is cut into plural parts having measurable sizes as appropriate and portions that are free of influence of the cutting are shot in the same manner. A sectional image is obtained by an X-ray CT measurement in a state that the supply-side channel member is set between two surfaces of separation membranes and a volume F of the supply-side channel that is actually formed inside the separation membrane element is calculated by performing image analysis on the thus-obtained cross-section image. A cut-out area at the time of image analysis is the same as at the time of measurement of a void volume v of the supply-side channel member.
In the embodiment, it is preferable that the interval c shown in
It is preferable that the interval d between intersection portions in the direction that is parallel with the supply water flow direction of the supply-side channel member may be in a range of 4 to 8 mm, even preferably in a range of 4.5 to 6.0 mm. If the interval d between intersection portions in the direction that is parallel with the supply water flow direction of the supply-side channel member is in this range, the turbulence intensity and the flow resistance of supply water can be balanced and hence the salt rejection rate and the water productivity of the separation membrane element can be increased.
As for a method for measuring an interval between intersection portions, it can be measured by observing the supply-side channel member from above in the thickness direction (i.e., from above a surface of the supply-side channel member) and measuring a distance with a microscope, for example.
When a surface of the supply-side channel member is observed, the flow resistance tends to increase as the angle between the supply water flow direction (i.e., the longitudinal direction of the water collecting pipe) and the fibrous objects increases though the turbulence intensity becomes higher. Therefore, this angle is preferably larger than or equal to 15° and smaller than or equal to 50°, and more preferably larger than or equal to 30° and smaller than or equal to 45°.
In the embodiment, it is preferable that the proportion of the area of contact of the supply-side channel member to a separation membrane may be in a range of 0.05 to 0.2, even preferably in a range of 0.1 to 0.15. If the proportion of the area of contact of the supply-side channel member to a separation membrane is in this range, supply water stagnation portions on the surface of the separation membrane can be made smaller and supply water can be supplied to the surface of the separation membrane efficiently. Thus, the turbidity removability during operation can be increased. In particular, trouble such as formation of scale can be suppressed even in the case of a high recovery rate operation.
Example methods that can be employed to set the proportion of the area of contact of the supply-side channel member to the separation membrane in the range of 0.05 to 0.2 are a method of using a net that is small in the proportion of the area of contact, to each separation membrane, of a supply-side channel member that is formed by stretch forming which will be described later so that it has regions having different thread diameters in each fibrous object between intersection portions while the thickness is kept the same in the intersection portions, and a method of manufacturing a separation membrane element by adjusting the pressure employed at the time of winding separation membrane leaves in each of which a supply-side channel member is sandwiched on a water collecting pipe together with permeation-side channel members so that the proportion of the area of contact of the supply-side channel member falls within the above range.
Example methods for measuring a proportion of the area of contact of the supply-side channel member to the separation membrane are a method of calculating it by disassembling the separation membrane element and cutting out a portion measuring 5 cm×5 cm from a separation membrane, observing that portion of the separation membrane with a microscope from above in its thickness direction, and dividing the area of marks formed by pressing the supply-side channel member against the separation membrane at the time of manufacture of the separation membrane element by the cut-out area, and a method of manufacturing a separation membrane element in such a manner that pressure-sensitive paper is sandwiched between a supply-side channel member and a separation membrane, recovering the pressure-sensitive paper after disassembling the separation membrane, and calculating a proportion of the area of contact of the supply-side channel member to each separation membrane by an image analysis in which colored portions of the pressure-sensitive paper are regarded as portions of contact of the supply-side channel member to the separation membrane.
As shown in
As shown in
(Taper ratio T)=|(D1−D2)/L3| [Formula 1]
It is preferable that the taper ratio may be in a range of 1/20 to 1/3, even preferably 1/15 to 1/4. If the taper ratio is in this range, fluid separation from the threads can be suppressed, a suddenly contracted flow and a suddenly enlarged flow of fluid can be prevented, and the flow resistance can be lowered. If the taper ratio is larger than 1/3, since the taper ratio is too large, the intersection portions are so large as to increase the flow resistance. Furthermore, the area of contact to a membrane surface becomes so large to produce a tendency that the amount of sticking of scale increases.
When the supply-side channel member 2 is observed from a direction that is parallel with its plane and perpendicular to an arbitrary fibrous object A or B, the fibrous object A or B may be tapered in the direction from one intersection portion P to the other intersection portion P as shown in
As shown in
It is preferable that the flat shape may be such that in a transverse cross section Z taken perpendicularly to the longitudinal direction of an arbitrary fibrous object of the supply-side channel member, a maximum diameter W1 of the fibrous object and a maximum diameter W2 in the direction perpendicular to the direction of the maximum diameter W1 satisfy a relationship 1.2<W1/W2<3.0. It is even preferable that the ratio W1/W2 may be in a range of 1.5 to 2.5. If the ratio W1/W2 is in the above range, since the intersection portions are gentle in shape, damaging of the membrane surfaces by a long-term operation can be suppressed. Furthermore, if the ratio W1/W2 is in the above range, since the channels formed between the supply-side channel member and the membranes expand or contract gently, the separation of fluid from the membrane surfaces and increase of the concentration polarization of dissolved salts can be suppressed
Each of the maximum fiber diameter W1 and the maximum fiber diameter W2 in the direction perpendicular to the direction of the maximum fiber diameter W1 is an average of measured values obtained by observing 10 or more randomly selected transverse cross sections taken perpendicularly to the longitudinal direction of an arbitrary fibrous object with a microscope, an X-ray CT measuring instrument, or the like and can be calculated according to (sum of measurement values)/(number of measurement positions).
The inclination angle of a cross section of a fiber of the supply-side channel member is defined as follows. As shown in
An inclination angle is obtained as an average of measured values obtained by observing 10 or more randomly selected transverse cross sections taken perpendicularly to the longitudinal direction of an arbitrary fibrous object with a microscope, an X-ray CT measuring instrument, or the like and can be calculated according to (sum of measurement values)/(number of measurement positions).
It is preferable that the unit weight of the supply-side channel member may be in a range of 15 to 120 g/m2. If the unit weight is in this range, the balance between the flow resistance and the sticking-out and slipping of the net during a long-term operation of the element is excellent and the element performance can thus be increased.
A unit weight of the supply-side channel member can be calculated according to (sum of measurement values)/(number of measured pieces) by measuring weights of at least five 1 m×1 m pieces that are cut out of the supply-side channel member.
It is preferable that the variation of unit weights of supply-side channel members may be 0.9 times or more and 1.1 times or less of an average unit weight of the supply-side channel members. If the variation of unit weights of supply-side channel members is in this range, supply water can be supplied uniformly to the separation membrane element and hence the performance of the separation membrane can be exhibited uniformly.
It is preferable that the bending resistance of the supply-side channel member may be in a range of 0.07 m to 0.14 m. If the bending resistance of the supply-side channel member is 0.07 m or larger, the handling performance of the supply-side channel member such as insertion into the device and cutting into prescribed dimensions tend to increase. If the bending resistance of the supply-side channel member exceeds 0.14 m, in the spiral-type separation membrane element, when the separation membrane unit is wound, the separation membranes are prone to be scratched by being rubbed by end portions of the supply-side channel members in a region close to the water collecting pipe where the radius of curvature is large. The bending resistance varies depending on the thickness or pitch of the supply-side channel member and the material of the supply-side channel member. A supply-side channel member that is high in handling performance can be manufactured by combining these factors properly. The bending resistance becomes smaller than 0.07 m if the thickness of the supply-side channel member is too small or its pitch is too large. The bending resistance becomes larger than 0.14 m if the thickness of the supply-side channel member is too large or its pitch is too small.
Bending resistance of the supply-side channel member is measured according to the JIS standard L1096 (2010) 8.21 (45° cantilever method). More specifically, five test pieces measuring 20 mm×150 mm in the direction perpendicular to the longitudinal direction of the supply-side channel member and the direction parallel to it are prepared by cutting them out from flat parts without a curl of a supply-side channel member. The bending resistance is an average of values obtained by measuring, with a scale or the like, movement distances of test pieces when they are slid from a flat stage until their tips come into contact with a slope of 45°; the value can be calculated by (sum of the measurement values)/(the number of measured portions). If a test piece is curled, it is preferable to remove the curl by pushing the test piece for three hours or more by a force that is so weak that the test piece itself is not deformed.
Although there are no particular limitations on the material of the supply-side channel member, from the viewpoint of forming property it is preferable that the supply-side channel member may be made of a thermoplastic resin; in particular, polyethylene and polypropylene are preferable because they are less prone to damage the surface of the separation membrane and inexpensive. In the supply-side channel member, the fibrous objects A and the fibrous objects B may be made of either the same material or different materials.
As for the forming of a net-shaped supply-side channel member, in general, molten resin is supplied from an extruder while two inside and outside spinnerets in each of which many holes are arranged on two inside and outside circumferences are rotated in opposite directions and molten threads that are ejected from the inside and outside spinnerets are crossed when or immediately after they are output from the spinnerets, whereby a net-shaped structure is formed. At this stage, the net has a cylindrical shape. Then the cylindrical net is cooled and solidified, whereby a thickness, thread diameters, an interval between intersection portions are determined. Then the net is cut open and taken as a sheet-shaped net.
To manufacture, as in the embodiment, a supply-side channel member in which the intersection thickness is maintained and each fibrous object between intersection portions have a region where the fiber diameter varies and the fiber is tapered when a surface of the supply-side channel member is viewed, a method can be employed that resin is supplied from small spinnerets at a high resin discharge pressure, a jig whose diameter is larger than the inner diameter of a cylindrical net is caused to pass through the inside of the cylindrical net before the resin constituting the cylindrical net is cooled and solidified completely, and the cylindrical net is caused to be cooled and solidified while it is pulled in the width direction and the longitudinal direction simultaneously. A net that has been manufactured by causing the jig whose diameter is larger than the inner diameter of the cylindrical net to pass through inside of a cylindrical net before the resin constituting the cylindrical net is cooled and solidified completely has a feature that the thread diameter of each fibrous object decreases gently from an intersection portion to a central portion. To manufacture a supply-side channel member having a cylindrical shape in which each fibrous object between intersection portions is uniform in thread diameter, resin is supplied from spinnerets at a low resin discharge pressure, a jig whose diameter is larger than the inner diameter of a cylindrical net is caused to pass through inside of the cylindrical net before the resin constituting the cylindrical net is cooled and solidified completely, and the cylindrical net is caused to be cooled and solidified while it is pulled in the width direction and the longitudinal direction simultaneously at a ratio that is smaller than in the case of a supply-side channel member having a tapered fiber shape.
On the other hand, by employing a method that after a cylindrical net is caused to be cooled and solidified it is subjected to longitudinal stretching and lateral stretching in a heating furnace, a net can be manufactured in which a thread diameter of a fibrous object has a necked shape at a central portion with respect to an intersection portion. The difference between the two kinds of manufacturing methods can be recognized by observing a thread shape of a net.
Methods for manufacturing a net that is made up of threads in which the diameter is smaller at central portions between intersection portions of fibrous rows than at the intersection portions are not limited to the above methods. Such a net may be manufactured by a method in which fibrous objects between intersection portions are compression-deformed by embossing, imprinting, pressing etc., a method of casting molten resin into a die and taken out a resulting mold, a method using a 3D printer.
In the envelope-like membrane 5, the separation membranes 3 are laid on each other in such a manner than their permeation-side surfaces are opposed to each other, the permeation-side channel member 4 is set between these separation membranes 3, and the permeation-side channel member 4 constitutes the permeation-side channel. There are no limitations on the material of the permeation-side channel member; tricot, nonwoven fabric, a porous sheet to which projections are adhered, a film produced by concavo-convex forming and punching, and concavo-convex nonwoven fabric can be used. Projections that function as permeation-side channel members can be adhered to the permeation-side surface of each separation membrane.
Among the above materials, use of circular-knit tricot manufactured by a circular knitting machine is preferable in terms of improving the water production rate of the element because when a needle loop width and a sinker loop width are made approximately the same both kinds of loops can be used to form a channel; an optimum channel width determined by taking into consideration membrane falling during operation of the separation membrane element can be obtained uniformly; and a permeation-side channel member that is sufficient in pressure resistance and flow properties even if it is thin can be manufactured.
Each separation membrane leaf may be formed either by folding a separation membrane so that its permeation-side surface is located inside or laying two separate separation membranes so that their permeation-side surfaces are opposed to each other and sealing the separation membranes at their circumferences.
Example “sealing” methods are bonding by an adhesive, a hot-melt adhesive, or the like, fusion by heating, laser light, or the like, and insertion of a rubber sheet. Sealing by bonding is particularly preferable because it is simplest and highly effective.
Separation membrane elements may be used as a separation membrane module by connecting them in series or parallel and housing a resulting assembly in a pressure container.
A fluid separation device can be constructed by combining the above separation membrane element or separation membrane module with a pump for supplying fluid to it, a device for preprocessing the fluid, etc. Use of such a separation device makes it possible to obtain water that is suitable for a purpose by, for example separating supply water into permeate such as drinking water and concentrate that has not permeated the membranes.
Taking into consideration the fact that as the manipulation pressure of the fluid separation device increases the removal rate increases but the energy necessary for operation also increases as well as the ease of maintenance of the supply-side channel and the permeation-side channel of the separation membrane element(s), it is preferable that the manipulation pressure in causing supply water to permeate the separation membrane module may be higher than or equal to 0.2 MPa and lower than or equal to 5 MPa.
Whereas the salt removal rate decreases as the temperature of supply water becomes higher, the membrane-permeation flux decreases as the temperature of supply water becomes lower. Thus, it is preferable that the temperature of supply water may be higher than or equal to 5° C. and lower than or equal to 45° C.
If the pH of raw water is in a neutral range, generation of scale such as magnesium is suppressed even if the raw water is a high salt-concentration liquid such as seawater and deterioration of the membranes can be suppressed.
There are no particular limitations on the supply water to be supplied to the separation membrane element according to the embodiment; the supply water may be preprocessed tap water or water containing a large amount of impurities such as seawater or brackish water. Where the separation membrane element according to the embodiment is used for, for example, water treatment, raw water (supply water) is, for example, a liquid mixture containing TDS (total dissolved solids) at 500 mg/L or higher and 100 g/L or lower, such as seawater, brackish water or drainage water. In general, the term “TDS” means a total amount of dissolved solids and is represented by “mass divided by volume” and may also be represented by “weight ratio” by regarding 1 L as weighing 1 kg. According to a definition, TDS can be calculated from a weight of residues obtained by evaporating a solution filtered by a 0.45-μm filter at 39.5° C. to 40.5° C. More simply, TDS is calculated through conversion from a practical salinity (S).
When separation membrane elements operate in a low range that the flow speed of a separation membrane surface crossing flow is lower than or equal to 10 cm/sec, in general, stagnant portions occur in front of and behind fibrous objects and cause reduction of the water production rate and the desalination rate due to increased membrane surface concentration polarization and scaling/fouling. Separation membrane elements including supply-side channel members whose supply-side channel area ratio is in a range of 45% to 65% are small in the number of stagnant portions formed in front of and behind fibrous objects and hence have features that the water production rate and the desalination rate are not prone to decrease and scaling and fouling are less likely to occur. Since permeate is pulled out in a front stage of a vessel including plural elements, the flow speed of a separation membrane surface crossing flow in the rear stage may become low. Thus, it is preferable to use the separation membrane element according to the invention in the rear stage of such a vessel.
As the supply-side channel member employed in the invention is made thinner, the flow speed of a crossing flow can be increased and hence the risk of occurrence of scaling and fouling can be lowered.
Although the invention will be described below in more detail using Examples, the invention is not restricted at all by these Examples.
A longitudinal cross section taken parallel with a fibrous row of a net-shaped sample was observed at a magnification ×20 using a high-precision shape measuring system KS-1100 produced by Keyence Corporation and thread diameters of intersection portions and central portions were checked. More specifically, thread diameters of centers of 30 arbitrary intersection portions and thread diameters of 30 arbitrary central portions each of which exists in a region of 20% from the center of two adjacent intersection portions toward those intersection portions were measured and their averages were calculated.
A longitudinal cross section taken parallel with a fibrous row of a net-shaped sample was observed at a magnification ×20 using the high-precision shape measuring system KS-1100 produced by Keyence Corporation, and thicknesses of 30 arbitrary intersection portions and their average was calculated.
A longitudinal cross section taken parallel with a fibrous row of the supply-side channel member was observed at a magnification ×20 using the high-precision shape measuring system KS-1100 produced by Keyence Corporation, and a distance between two adjacent intersection portions and a thickness of an intersection portion (a thickness of the supply-side channel member) were measured at 30 positions and their averages were calculated. An area between two adjacent intersection portions in the longitudinal cross section was calculated by multiplying the distance between two adjacent intersection portions by the thickness of an intersection portion.
Then an area of a space that is formed between two adjacent intersection portions was calculated by performing an image analysis on a longitudinal cross section image. The image analysis was performed for 30 arbitrary positions and an average thereof was calculated. An area ratio of the supply-side channel was calculated according to (average area of space in longitudinal cross section)/(average area between two adjacent intersection portions in longitudinal cross section)×100.
A 30 cm×30 cm piece was cut out of a net-shaped sample and its weight was measured. A total volume was calculated by multiplying a thickness of the supply-side channel member by a cut-out area. Then a volume of a net-shaped sample main body was calculated by dividing the weight of the cut-out piece of the net-shaped sample by a specific weight of the material of the supply-side channel member and a void volume of the supply-side channel member was calculated by subtracting the volume of a net-shaped sample main body from the total volume.
The spiral-type separation membrane element was cut into a cylinder of 30 cm in length and it was shot with X-ray intensity of 100 kV using a 3D measurement X-ray CT instrument (TDM3000H-FP) produced by Yamato Scientific Co., Ltd. A volume (internal volume), per a cut-out area 30 cm×30 cm of a piece, which can become a supply-side channel, of a net-shaped sample interposed between two surfaces of separation membranes was calculated by an image analysis.
A net-shaped sample was observed from above in the thickness direction at a magnification ×20 using high-precision shape measuring system KS-1100 produced by Keyence Corporation, and an interval between arbitrary intersection portions of the supply-side channel member in the direction perpendicular to the flow direction of supply water and an interval between arbitrary intersection portions of the supply-side channel member in the direction parallel with the flow direction of supply water were measured at 30 positions and their averages were calculated.
A net-shaped sample was shot from a plane direction using high-precision shape measuring system KS-1100 produced by Keyence Corporation and drawing work was done on the image using PowerPoint. The corners of an arbitrary polygon S were connected using straight lines and an intersection P1 was determined. Four intersections that were located on extensions of straight lines that determine the intersection P1 and were closest to the intersection P1 were denoted by B1-B4, respectively. Among points where line segments P1B1 to P1B4 intersected the outlines of the fibers, a point Q1 having the longest distance to P1 was selected and the length of a line segment P1Q1 was represented by L1. A point Q2 was determined by performing, for an arbitrary intersection P2 adjacent to the point P1, the same manipulations as performed above for the intersection P1 and the length of a line segment P2Q2 was represented by L2. Circles C1 and C2 having L1 and L2 as radii, respectively, were drawn and a length obtained by subtracting L1 and L2 from the length of the line segment connecting the intersections P1 and P2 was represented by L3. Tangential lines, perpendicular to the line segment P1 P2 and intersecting the line segment P1 P2, to the respective circles C1 and C2 were drawn and thread diameters that are obtained by these tangential lines were denoted by D1 and D2, respectively. Lengths L1-L3, D1, and D2 were measured on the basis of the scale bars of an image obtained by the high-precision shape measuring system KS-1100 produced by Keyence Corporation and a taper ratio T was calculated according to the following equation. These manipulations and measurements were performed for 15 positions on each of the front and back surfaces of the supply-side channel member, for 30 positions in total, and an average of calculated taper ratios T was calculated.
(Taper ratio T)=|(D1−D2)/L3| [Formula 2]
(Measurement about Large Diameter Portions)
One, made of a fiber having a smaller diameter, of fibrous object A and fibrous object B is selected. If the fibrous object A, for example, was selected, a net-shaped sample was frozen by liquid nitrogen and a fibrous object B was cut in a direction parallel with a fibrous object A in vicinity of the fibrous object A. Cross sections were observed from a direction that is parallel with the plane of the net-shaped sample and perpendicular to an arbitrary fibrous object A or B at a magnification ×20 using the high-precision shape measuring system KS-1100 produced by Keyence Corporation, whereby thread diameters of large diameter portions D3 and D4 were checked. More specifically, thread diameters of arbitrary large diameter portions D3 and D4 were measured and the thread diameter of one, having a larger thread diameter, of them was employed as a thread diameter of a large diameter portion. This manipulation was performed at a total of 30 positions and an average of resulting thread diameters was calculated.
A net-shaped sample was frozen by liquid nitrogen and was cut in a direction that was perpendicular to the longitudinal direction of an arbitrary fibrous object. Its transverse cross section was observed from the perpendicular direction, whereby a maximum diameter W1 of the transverse cross section and a maximum diameter W2 in the direction perpendicular to the transverse cross section were measured using the high-precision shape measuring system KS-1100 manufactured by Keyence Corporation. The same manipulation was performed repeatedly at 15 positions of arbitrary fibrous objects A and B and averages of resulting sets of diameters were calculated, respectively.
A net-shaped sample was frozen by liquid nitrogen and was cut in a direction that was perpendicular to the longitudinal direction of an arbitrary fibrous object. A transverse cross section was observed from a direction perpendicular to it using the high-precision shape measuring system KS-1100 produced by Keyence Corporation, whereby an angle formed, in the clockwise direction, by the vertical line and the direction of a maximum diameter W1 of the transverse cross section was measured. The same manipulation was performed repeatedly at 15 positions of arbitrary fibrous objects A and B and an average of resulting angles was calculated.
A net-shaped sample was cut into a 1.0 m×1.0 m piece. Weights of 10 such pieces were measured using an electronic scale and their average was calculated.
Bending resistance of the supply-side channel member was measured according to the JIS standard L1096 (2010) 8.21 (45° cantilever method). A net-shaped sample was cut into a piece measuring 20 mm×150 mm in each of a direction perpendicular to the longitudinal direction and a direction parallel with the longitudinal direction to prepare a test piece. If a test piece was curled, a plastic piece having the same size as the test piece was prepared and put on the test piece, a weight of 200 g was put on the plastic piece, and they were held as they were for 3 hours. Then an average of values obtained by measuring, with a scale, movement distances of five test pieces taken along each direction was calculated when they were slid from a horizontal stage at a constant speed until their tips come into contact with a slope of 45°.
A separation membrane element was produced in such a manner that pressure-sensitive paper (produced by FUJIFILM Corporation, two-sheet type, type name: PSC-LLLW, Prescale for ultra super low pressure) was sandwiched between a polypropylene net as a supply-side channel member and a separation membrane and the pressure-sensitive paper was collected later by disassembling the separation membrane. Colored portions of the pressure-sensitive paper were judged as portions of contact of the supply-side channel member to the separation membrane and a proportion of an area of contact of the supply-side channel member, per a cut-out portion having an area 5 cm×5 cm, to the separation membrane was calculated by an image analysis.
A cylindrical net having a net-shaped structure was formed using polypropylene as a material by supplying molten resin at a high discharge pressure from an extruder while two inside and outside spinnerets in each of which many holes were arranged were rotated in opposite directions. Furthermore, a method in which a jig whose diameter was larger than the inner diameter of the cylindrical net was caused to pass through inside of the cylindrical net before the resin constituting the cylindrical net was cooled and solidified completely and the cylindrical net was caused to be cooled and solidified while it was pulled in the width direction and the longitudinal direction simultaneously was employed, whereby each of supply-side channel members shown in Tables 1-5 was manufactured in which the thread diameter of each fibrous object gently decreased from intersection portions to a central portion. Structure controls were performed to finally obtain shapes of supply-side channel members shown in Tables 1-5 by changing the molten resin discharge pressure of the extruder, the dimensions of the jig to be caused to pass through the cylindrical net, and the taking speed.
A porous support layer (thickness: 130 μm) roll formed by a fiber-reinforced polysulfone support membrane was manufactured by casting a DMF solution of 16.0 mass % polysulfone onto nonwoven fabric (fineness: 1 decitex, thickness: about 90 μm, aeration: 1 cc/cm2/sec, density: 0.80 g/cm3) formed by polyethyleneterephthalate fibers at room temperature (25° C.) to obtain a thickness 180 μm, immediately immersing it into pure water and leaving it as it was for 5 minutes, and then immersing it in hot water of 80° C. for 1 minute.
Then the surface of a layer, made of polysulfone, of the porous support membrane was immersed in an aqueous solution containing m-PDA at 5 mass % and ε-caprolactam at 1.0 mass % for 2 minutes and lifted up slowly in the vertical direction. Furthermore, an excessive aqueous solution was removed from the surface of the support membrane by blowing nitrogen over it from an air nozzle.
Subsequently, an n-decane solution containing trimesoyl chloride at 0.08 mass % was applied to the membrane to wet the membrane surface completely and this state was held still for 1 minute. Then an excessive solution was removed from the membrane by air blowing and the membrane was cleaned by hot water of 80° C. for 1 minute, whereby a composite separation membrane roll was obtained.
The thus-obtained separation membrane was subjected to folding cutting so as to have an effective area of 2.6 m2 in a separation membrane element, and separation membrane leaves were produced by sandwiching a polypropylene net (thickness: 0.6 mm) shown in Table 1 to serve as a supply-side channel member.
Tricot (thickness: 0.26 mm) shown in Table 1 to serve as a permeation-side channel member was laid on a permeation-side surface of each of the thus-obtained separation membrane leaves, leaf adhesive was applied to the separation membrane leaves, and the separation membrane leaves were wound spirally on a water collecting pipe made of PVC (polyvinyl chloride) (width: 1,016 mm, diameter: 19 mm, number of holes: 23 on one straight line). After the outer circumferential surface of the wound body was fixed by a tape, the edges at the two respective ends were cut and end plates were attached. Thus, a separation membrane element of 2.5 inches in diameter was manufactured which was to be supplied with supply water from one side surface and discharge concentrate.
The separation membrane element was put into a pressure container and caused to operate for 30 minutes under conditions that the operation pressure was 0.5 MPa and the temperature was 25° C. using, as supply water, saline water of 200 ppm in concentration and an NaCl aqueous solution of pH 6.5. After that, sampling was performed for 1 minute and a permeation amount (in gallon) per day was employed as a water production rate (GPD (gallons/day). The collection rate was set at 8%.
A TDS concentration in each of the supply water that was used in the operation of one minute in the measurement of a water production rate and the sampled permeate was determined by a conductance measurement and a TDS removal rate was calculated according to the following equation:
(TDS removal rate (%))=100×[1−{(TDS concentration in permeate)/(TDS concentration in supply water)}].
An element differential pressure during operation was measured by connecting the upstream side (supply water side) and the downstream side (concentrate side) of a cylindrical pressure container in which the separation membrane element was installed by a pipe in which a differential pressure meter (type name: DG16) produced by Nagano Keiki Co., Ltd. is provided. As for the operation conditions, the supply water flow rate was 9 L/min and the operation pressure was 1.0 MPa. Water processed by a reverse osmosis membrane was used as the supply water. A cock of a permeate pipe was closed after removal of air bubbles from inside the element, and an element differential pressure (in kPa) was measured by an operation that was performed in a state no substantial membrane filtration could be performed, that is, all supply water was discharged as concentrate.
The separation membrane element was put into a pressure container and caused to operate for 24 hours under conditions that the operation pressure was 0.5 MPa and the temperature was 25° C. using, as supply water, an aqueous solution of pH 7 containing CaCl2.H2O at 1,150 ppm and NaHCO3 at 660 ppm. The collection rate was set at 50%. After that, the separation membrane element was disassembled and an effective membrane portion measuring 5 cm×5 cm located on the downstream side (concentrate side) in the longitudinal direction of the separation membrane element was cut out. The cut-out separation membrane was dried and observed from above in the thickness direction of the separation membrane with a microscope, whereby a sticking area ratio of scale that precipitated on and stuck to the separation membrane surface was calculated.
Supply water was caused to pass through the manufactured separation membrane element repetitively 100 times with the duration of 1 minute under conditions that the operation pressure was 0.5 MPa and the temperature was 25° C., supply water being saline water of 200 ppm in concentration and an NaCl aqueous solution of pH 6.5. After that, sampling was performed for 1 minute and a TDS concentration in each of supply water used in the operation of 1 minute and sampled permeate was determined by a conductance measurement and a TDS removal rate was calculated according to the following equation:
(TDS removal rate (%))=100×[1−{(TDS concentration in permeate)/(TDS concentration in supply water)}].
This removal rate was employed as a removal rate after repetitive start/stop operations.
Evaluations were made under the above conditions using an evaluation cell for a manufactured supply-side channel member and putting a separation membrane element in the pressure container. Results were as shown in Table 1.
Separation membrane elements were manufactured in the same manner as in Example 1 except that supply-side channel members were as shown in Tables 1-4.
Each separation membrane element was put into the pressure container and each kind of performance was evaluated under the same conditions as in Example 1. Results were as shown in Tables 1-4.
A separation membrane element was manufactured in the same manner as in Example 1 except that a permeation-side channel member was as shown in Table 1.
The separation membrane element was put into the pressure container and each kind of performance was evaluated under the same conditions as in Example 1. Results were as shown in Table 1.
A cylindrical net having a net-shaped structure was formed using polypropylene as a material by supplying molten resin from an extruder while two inside and outside spinnerets in each of which many holes were arranged were rotated in opposite directions, whereby a net having a cylindrical fiber structure was manufactured. Structure controls were performed to finally obtain shapes of supply-side channel members shown in Tables 4 and 5 by changing the molten resin discharge pressure of the extruder and the taking speed.
A cylindrical net was manufactured using polypropylene as a material according to the same procedure as the supply-side channel member Q and then cooled and solidified. The cylindrical net was thereafter stretched in the longitudinal direction and then in the lateral direction in a heating furnace, whereby a net was manufactured that has a necked shape in which the thread diameter of a central portion of a fibrous object is smaller than that of intersection portions. Structure controls were performed to finally obtain shapes of supply-side channel members shown in Table 5 by changing the molten resin discharge pressure of the extruder, the longitudinal and lateral stretching ratios, and the taking speed.
Separation membrane elements were manufactured in the same manner as in Example 1 except that supply-side channel members were as shown in Tables 4 and 5.
Each separation membrane element was put into the pressure container and each kind of performance was evaluated under the above-mentioned conditions. Results were as shown in Tables 4 and 5.
As is apparent from the results shown in Tables 1-4, it can be said that the separation membrane elements of Examples 1-27 do not impair flow of supply water and exhibits superior separation performance stably.
On the other hand, in Comparative Examples 1 and 2, although the interval between intersection portions, in each of the directions perpendicular to and parallel with the supply water flow direction, of the supply-side channel member was the same as in Examples 1 and 2, the thread diameter of the central portions was large. As a result, the supply-side channel area ratio was small, the element differential pressure became high, and the element water production rate and the removal rate were decreased.
In Comparative Example 3, the fiber diameter of the central portion was large and the interval between intersection portions, in each of the directions perpendicular to and parallel with the supply water flow direction, of the supply-side channel member was large.
As a result, the separation membrane main body fell into net void portions during manufacturing the element and stability of a channel in a portion adjacent to the supply water inflow end surface was not established sufficiently, resulting in a large element differential pressure and decrease of the element water production rate and the removal rate.
Furthermore, in Comparative Examples 1-3, since the fiber shape and the side-view shape were cylindrical, the area of contact between the membrane surface and the fibers was large and the supply-side channel area ratio was small. As a result, the flow resistance was high, the element differential pressure was large, resulting in decrease of the element water production rate and the removal rate.
In addition, in Comparative Examples 1-3, since the proportion of the area of contact of the supply-side channel member to a separation membrane was large and there occurred many supply water stagnation portions on the surface of each separation membrane, the turbidity removability during operation was low and much scale stuck to the separation membrane surfaces.
In Comparative Examples 4 and 5, since the fiber shape was a necked shape and the bending resistance was small, the net was prone to slip when repetitive start/stop operations are performed and the removal rate after repetitive start/stop operations was small.
Furthermore, in Comparative Examples 4 and 5, since the supply-side channel area ratio was too large, membrane falling occurred between the intersections of the supply-side channel member, the element differential pressure was high, and the element water production rate and the removal rate were decreased.
In Comparative Example 6, whereas the taper and the supply-side channel area ratio were equivalent, a necking shape was employed. Thus, energy loss occurred due to rapid expansion and contraction of the channels, the element differential pressure was high, and the element water production rate and the removal rate were decreased.
In Comparative Examples 7 and 8, whereas the fiber shape was a tapered shape, the supply-side channel area ratio was too small. As a result, the element differential pressure was high and the element water production rate and the removal rate were decreased.
In particular, the membrane element according to the invention can be used suitably as an RO water purifier and for desalination of brackish water and seawater.
Although the invention has been described above using the particular embodiment, it is apparent that those skilled in the art that various changes and modifications are possible without departing from the spirit and scope of the invention. The present application is based on Japanese Patent Application No. 2019-157773 filed on Aug. 30, 2019, No. 2019-231577 filed on Dec. 23, 2019, and No. 2020-094335 filed on May 29, 2020, the entire disclosures of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-157773 | Aug 2019 | JP | national |
| 2019-231577 | Dec 2019 | JP | national |
| 2020-094335 | May 2020 | JP | national |
This is the U.S. National Phase application of PCT/JP2020/032195, filed Aug. 26, 2020, which claims priority to Japanese Patent Application No. 2019-157773, filed Aug. 30, 2019, Japanese Patent Application No. 2019-231577, filed Dec. 23, 2019 and Japanese Patent Application No. 2020-094335, filed May 29, 2020, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/032195 | 8/26/2020 | WO |
