Nanofiltration membrane element and production process thereof

Abstract

The invention relates to a nanofiltration membrane element and a production process thereof, and relates to the technical field of membrane separation, the nanofiltration membrane element comprises a central pipe, a membrane unit piece and a fiber winding layer, the central pipe is provided with a plurality of water inlet holes, the membrane unit piece is wound on the outer side of the central pipe, the fiber winding layer is wound on the outer side of the membrane unit piece, and the membrane unit piece comprises a membrane, water inlet mesh cloth and runner cloth; the runner cloth is divided into two cloth layers in the thickness direction of the runner cloth, and each cloth layer is provided with a filtering area, a glue line area and a side line area. A plurality of supporting lines are clamped between the two cloth layers, the supporting lines are located in the filtering area, all the supporting lines are arranged in the axial direction of the center pipe, the supporting lines extend in the radial direction of the center pipe when the cloth layers are in the spreading state, and one ends of the supporting lines are bonded to the positions, away from the connecting edges, of the glue line area; and a gap between the two cloth layers is communicated with the water inlet hole. The compressive strength of the runner cloth can be improved, so that the water passing amount is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a nanofiltration membrane element and a production process thereof. BACKGROUND

[0002] In recent years, membrane separation process has been widely used in seawater purification, raw water treatment, pure water production and the like as a new type of high separation, concentration, purification and purification technology.

[0003] Membrane separation technology is a separation method for separating, purifying and concentrating a mixture under the action of external force by using a special membrane with selective permeation performance. The membrane must have the characteristics that some substances can pass through and some substances cannot pass through. Membrane separation technology is generally divided into four categories: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). Nanofiltration is a new type of membrane separation process developed in the mid-to-late 1970s. It has different selectivity to one and two valence ions, high rejection rate to small molecular organic matter, energy saving and other characteristics.

[0004] The nanofiltration membrane element comprises a center tube and a membrane unit element, the membrane unit element is wound outside the center tube, and the membrane unit element comprises a membrane sheet, a water inlet mesh cloth and a flow channel cloth. Raw water contacts the membrane sheet through a water inlet channel formed by the water inlet mesh cloth. Under the action of pressure, the purified water in the raw water is filtered by the membrane sheet, and the purified water enters the flow channel cloth. The purified water in the flow channel cloth enters the center tube through the holes in the outer wall of the center tube, and finally the purified water is discharged from the center tube.

[0005] Under the action of water pressure, the membrane sheets on both sides of the flow channel cloth will squeeze the flow channel cloth. Therefore, the weaving density of the flow channel cloth needs to be high enough to have sufficient pressure resistance, so as to reduce the excessive squeezing of the flow channel cloth and the insufficient water flow of the flow channel cloth. However, when the weaving density of the flow channel cloth is high, the porosity of the flow channel cloth itself is small, and the water flow is limited. That is, too high or too low weaving density will affect the water flow. SUMMARY

[0006] In order to improve the water flow, the present application provides a nanofiltration membrane element and a production process thereof.

[0007] The nanofiltration membrane element provided by the present application adopts the following technical scheme: The application relates to a nanofiltration membrane element, which comprises a central tube, a membrane unit element and a fiber winding layer, the central tube is provided with a plurality of water inlet holes, the membrane unit element is wound on the outer side of the central tube, and the fiber winding layer is wound on the outer side of the membrane unit element; the membrane unit element comprises a membrane sheet, a water inlet mesh cloth and a flow channel cloth, one side of the flow channel cloth is provided with a connecting edge fixedly connected with the central tube, the flow channel cloth is divided into two cloth layers along the thickness direction of the flow channel cloth, the cloth layers are provided with a filtering area, a glue line area and a side line area, the shape of the glue line area is in the form of a 'N' character, the filtering area is located in the region surrounded by the glue line area, the opening of the glue line area is the connecting edge, the weaving density of the glue line area is 60-70% of the weaving density of the filtering area, and the weaving density of the side line area is consistent with that of the filtering area; a plurality of supporting lines are arranged between the two cloth layers, the supporting lines are located in the filtering area, the supporting lines are arranged along the axial direction of the central tube, the supporting lines are arranged in the radial direction of the central tube in the unwound state of the cloth layers, and one end of the supporting lines is bonded to the position of the glue line area away from the connecting edge; and the gap between the two cloth layers is connected with the water inlet holes.

[0008] By adopting the technical scheme, firstly, the plurality of supporting lines are arranged to form the framework of the flow channel cloth, so that the compression resistance of the flow channel cloth is improved, that is, the weaving density of the filtering area can be reduced under the condition that the compression resistance of the flow channel cloth meets the requirements, the pore is large, and thus the water passing capacity is improved; secondly, the supporting lines are arranged in the radial direction of the central tube, the gap between the adjacent supporting lines forms a shaped flow channel, the shaped flow channel facilitates the radial flow of the purified water into the central tube, that is, the water pressure loss of the purified water flow is reduced, and thus the purified water efficiency and the water passing capacity are improved.

[0009] Furthermore, the filtering area with high weaving density can well resist the pressure of the membrane sheet, so that the water passing capacity is ensured, the glue line area with low weaving density enables the glue to easily and uniformly penetrate to the other side of the flow channel cloth, so that the flow channel cloth and the membrane sheet are better bonded together, and thus the condition of low bonding strength caused by uneven or poor permeability of the glue is reduced, the high weaving density of the side line area is arranged, the weaving density of the side line area is consistent with that of the filtering area, the glue in the glue line area is locked by the side line area and the filtering area, so that the flow loss of the glue is reduced, the glue bonding strength is increased, and the excessive glue overflow is reduced.

[0010] In summary, the water passing capacity of the flow channel cloth is improved from two dimensions by arranging the supporting lines, the glue line area and the side line area, the first dimension is the framework support and the shaped flow channel construction, the weaving density of the filtering area can be reduced under the condition that the compression resistance of the flow channel cloth meets the requirements, the pore is large, and thus the water passing capacity is improved, and the rapid flow of the purified water is guided; the second dimension is the weaving density limitation of different subareas, the glue in the glue line area is effectively locked to prevent the glue from overflowing into the filtering area or the side line area with lower weaving density.

[0011] Optionally, the support wire is a hollow tubular structure, and the support wire has micropores; and the end of each support wire is connected to the center tube.

[0012] Optionally, the support wire is a hollow tubular structure, and the support wire has micropores; and the end of each support wire is connected to the center tube.

[0013] Optionally, the support wires are arranged in parallel along the center tube.

[0014] Optionally, the support wires are arranged in parallel along the center tube.

[0015] Optionally, the support wires are arranged in parallel along the center tube.

[0016] Optionally, the support wires are arranged in parallel along the center tube.

[0017] Optionally, the center tube has a plurality of mounting holes corresponding to the support wires, and the mounting holes have a plurality of elastic tabs arranged in a circle and formed integrally on the hole wall; the elastic tabs are arranged in a direction inclined towards the center of the center tube; the support wires pass through the mounting holes coaxially; and the elastic tabs clamp the support wires.

[0018] The application provides a production process of a nanofiltration membrane element. A production process of a nanofiltration membrane element, comprising the following steps: S1, membrane unit element manufacturing: brushing glue on the glue line area of the cloth layer, arranging the support wire on the surface of the cloth layer, bonding one end of the support wire to the glue line area, and then covering the cloth layer to sandwich the support wire to manufacture a flow channel cloth; S2, membrane unit element winding; S3, fiber winding layer winding.

[0019] In summary, the present application includes at least one of the following beneficial technical effects: 1. By setting the support wire, glue line area and edge line area, the water flow of the flow channel cloth is improved from two dimensions, the first dimension is the skeleton support and the formation of the flow channel, under the condition of meeting the pressure resistance of the flow channel cloth, the weaving density of the filter area can be reduced, so that the pore is larger, thereby improving the water flow and guiding the rapid passage of clean water; The second dimension is the weaving density limitation of different partitions, effectively locking the glue in the glue line area to prevent the glue from overflowing into the filter area or the edge line area with lower weaving density than the existing one. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a cross-sectional view of the nanofiltration membrane element of Example 1.

[0021] Figure 2 is a schematic view of the membrane unit element of Example 1 in an unfolded state.

[0022] Figure 3 is an exploded view of the flow channel cloth of Example 1.

[0023] Figure 4 is a schematic view of the cloth layer of Example 1 in an unfolded state.

[0024] Figure 5 is a schematic view of the cloth layer of Example 2 in an unfolded state.

[0025] Figure 6 is a partial enlarged view of the cross section of the center tube of Example 3.

[0026] Figure 7 is a schematic view of the pressing strip of Example 3.

[0027] Figure 8 is Figure 7 a partial enlarged view of A in FIG. 6.

[0028] Figure 9 is a schematic view of the cloth layer of Example 4 in an unfolded state.

[0029] Figure 10 is a schematic view of Example 5 for showing the state change of the support wire before and after rolling.

[0030] Figure 11 is Figure 10A local enlarged view at B.

[0031] Reference numerals: 1, flow channel cloth; 2, membrane sheet; 3, water inlet mesh cloth; 5, support wire; 6, pressing strip; 7, winding pipe; 10, center pipe; 101, mounting groove; 102, perforation; 103, mounting hole; 1031, elastic sheet; 11, cloth layer; 110, connecting edge; 111, filtration zone; 112, glue line zone; 113, edge line zone; 20, membrane unit element; 30, fiber winding layer; 61, protruding tooth. DETAILED DESCRIPTION

[0032] The following will be described in detail in combination with the accompanying drawings. Figure 1 - the accompanying drawings Figure 11 The present application is further described in detail. Example 1

[0033] Example 1 discloses a nanofiltration membrane element, as shown in Figure 1 、 Figure 2 (Wherein the solid arrow in the figure indicates the flow direction of raw water, and the dotted arrow in the figure indicates the flow direction of clean water), the nanofiltration membrane element comprises a center pipe 10, a membrane unit element 20 and a fiber winding layer 30, the center pipe 10 has a plurality of water inlet holes (not shown in the figure), the membrane unit element 20 is wound on the outside of the center pipe 10, and the fiber winding layer 30 is wound on the outside of the membrane unit element 20, the membrane unit element 20 comprises a membrane sheet 2, a water inlet mesh cloth 3 and a flow channel cloth 1, one side of the flow channel cloth 1 is provided as a connecting edge 110 fixedly connected with the center pipe 10, and the connecting edge 110 is connected with the water inlet hole of the center pipe 10, the membrane sheet 2 is in a folded state, the water inlet mesh cloth 3 is clamped in the folded membrane sheet 2, and the opposite sides of the two membrane sheets 2 are respectively adhered and covered on both sides of the flow channel cloth 1.

[0034] As shown in Figure 3 、 Figure 4As shown, the flow channel cloth 1 is divided into two cloth layers 11 along the thickness direction of the flow channel cloth 1, the cloth layer 11 is a woven cloth, the cloth layer 11 has a filter area 111, a glue line area 112 and a edge line area 113, the shape of the glue line area 112 is a "N" shape, the filter area 111 is located in the area enclosed by the glue line area 112, the opening of the glue line area 112 is a connecting edge 110, the weaving density of the glue line area 112 is 60%-70% of the weaving density of the filter area 111, the weaving density of the edge line area 113 is consistent with that of the filter area 111, that is, by setting the glue line area 112 and the edge line area 113, the filter area 111 with high weaving density can well resist the pressure of the membrane 2, thereby ensuring the water flow, and the glue line area 112 with low weaving density allows the glue to easily and uniformly penetrate to the other side of the flow channel cloth 1, so that the flow channel cloth 1 and the membrane 2 are better bonded together, thereby reducing the occurrence of low bonding strength due to uneven or poor permeability of the glue, and because the weaving density of the edge line area 113 is consistent with that of the filter area 111, the glue in the glue line area 112 can be locked together to reduce the flow loss of the glue, thereby increasing the bonding strength of the glue, and also reducing the excess overflow of the glue.

[0035] The gap between the two cloth layers 11 is communicated with the water inlet hole, and a plurality of support lines 5 are clamped between the two cloth layers 11, the support lines 5 can be fish line or other lines or tubes with certain toughness and elasticity, the support lines 5 are located in the filter area 111, each support line 5 is arranged axially along the center pipe 10, and in the laid state of the cloth layer 11, the support lines 5 are arranged radially along the center pipe 10, in this embodiment, the support lines 5 are linear, one end of the support line 5 is bonded to a position of the glue line area 112 away from the connecting edge 110, and the other end of the support line 5 is not connected between the center pipes 10.

[0036] Each support line 5 is arranged axially along the center pipe 10 with a spacing interval, and the spacing interval of adjacent support lines 5 is 0.5-5 times the diameter of the support line 5, and a shaped flow channel is arranged between the adjacent two support lines 5.

[0037] In this way, by arranging a plurality of support lines 5, the skeleton of the flow channel cloth 1 is formed to improve the pressure resistance of the flow channel cloth 1, that is, in the case that the pressure resistance of the flow channel cloth 1 meets the requirements, the weaving density of the filter area 111 can be reduced to make the pore larger, thereby improving the water flow, and secondly, the support lines 5 are arranged radially along the center pipe 10, and the shaped flow channel between the adjacent support lines 5 facilitates the radial flow of the purified water into the center pipe 10, thereby reducing the water pressure loss of the purified water flow, and improving the purified water efficiency and the water flow.

[0038] In summary, by setting the support line 5, the glue line area 112 and the edge line area 113, the water flow of the flow channel cloth 1 is improved in two dimensions. The first dimension is the skeleton support and the construction of the forming flow channel. In the case of meeting the compression resistance of the flow channel cloth 1, the weaving density of the filter area 111 can be reduced, so that the pore is larger, thereby improving the water flow and guiding the rapid passage of clean water. The second dimension is the weaving density limitation of different partitions, which effectively locks the glue in the glue line area 112 to prevent the glue from overflowing into the filter area 111 or the edge line area 113 with lower weaving density than the existing one.

[0039] It should be noted that the support line 5 can be a solid line, and the support line 5 can also be a hollow tubular structure, and at the same time, the surface of the hollow tubular support line 5 is provided with micropores, so that the support line 5 can also become a pipeline for absorbing and guiding the flow of clean water, thereby improving the flow efficiency of clean water. On this basis, in other embodiments, each support line 5 can be arranged in parallel along the axis of the center pipe 10, that is, the outer circumferential surface of each support line 5 is tangent to each other. Although the cross-sectional area of the forming flow channel is small, the hollow support line 5 can still play a role in guiding clean water. At the same time, due to the more dense support line 5, the overall supportability is greatly improved, which can resist the winding pressure and water pressure, and the overall water flow is taken into account.

[0040] The embodiment also discloses a production process of the nanofiltration membrane element. The production process of the nanofiltration membrane element comprises the following steps: S1, membrane unit element 20 manufacturing: fold the membrane sheet 2, the folding position of the membrane sheet 2 is close to the center pipe 10, the inlet water mesh cloth 3 is clamped in the folded membrane sheet 2, two cloth layers 11 are respectively laid on the two sides of the membrane sheet 2, then glue is brushed on the glue line area 112 of the two cloth layers 11 respectively, the glue on both sides of the cloth layer 11 is adhered to the membrane sheet 2, then the support line 5 is arranged on the surface of the cloth layer 11, one end of the support line 5 is adhered to the glue line area 112, then the cloth layer 11 is covered to clamp the support line 5, so as to manufacture the membrane unit element 20.

[0041] S2, winding of the membrane unit element 20: winding the membrane unit element 20 on the center pipe 10 by using a winding machine.

[0042] S3, winding of the fiber winding layer 30. Embodiment 2

[0043] The difference between embodiment 2 and embodiment 1 is that, as shown in Figure 5 Each support line 5 is arranged in parallel along the center pipe 10, and the arrangement gap between adjacent support lines 5 gradually increases along the flow direction of the raw water into the nanofiltration membrane element (see the arrow direction in Figure 5 .

[0044] Since the water pressure of the raw water gradually decreases from the water inlet end to the water outlet end, and the arrangement gap of the support wire 5 is sequentially defined, the support wire 5 arranged more densely can effectively resist the high water pressure of the raw water to cause the extrusion deformation of the cloth layer 11, and the support wire 5 arranged less densely can take into account the water flow of the cloth layer 11, so that the arrangement of the support wire 5 is rationalized and the increase of the water flow is maximized. Example 3

[0045] Example 3 is different from example 1 or example 2, as shown in Figure 6 , Figure 7 , Figure 8 shown, one end of each support wire 5 close to the center pipe 10 is provided with two pressing strips 6, specifically, an installation slot 101 is formed in the inside of the center pipe 10, the installation slot 101 is a strip-shaped slot and extends axially along the center pipe 10, a through hole 102 communicating to the outer wall of the center pipe 10 is radially formed in the bottom of the installation slot 101, the through hole 102 is located on one side of the water inlet hole, the water inlet hole and the through hole 102 are both communicated with the installation slot 101, the pressing strip 6 extends axially along the center pipe 10, one side of the pressing strip 6 has a plurality of protrusions 61, the tips of the protrusions 61 of the two pressing strips 6 abut, the support wire 5 is clamped in the gap between the two adjacent protrusions 61, and the gap between the protrusions 61 can be used for the flow of clean water.

[0046] The two pressing strips 6 can be fixed by adhesive or buckled.

[0047] During installation, one end of the support wire 5 is inserted through the through hole 102 and located in the inner cavity of the center pipe 10, the outside of the pressing strip 6 is brushed with glue, the pressing strip 6 is placed in the center pipe 10 and clamps the support wire 5, and then the two pressing strips 6 are placed in the installation slot 101, and the outside of the pressing strip 6 is adhered to the slot wall of the installation slot 101.

[0048] In this way, by setting the pressing strip 6, one end of the support wire 5 is fixedly connected with the center pipe 10, and the other end of the support wire 5 is adhered with the glue line area 112, that is, the two ends of the support wire 5 are fixed and the gap between the adjacent support wires 5 is limited, thereby improving the position stability of the support wire 5, making it not easy to run out of position, and the shape of the formed flow channel is relatively stable, so that the flow of clean water is stable. Example 4

[0049] Example 4 is different from example 1, as shown in Figure 9 The support wire 5 is in a wavy shape, the two end portions of the support wire 5 are still straight line segments, the rising and falling direction of the support wire 5 is the axial direction of the center pipe 10, that is, the rising and falling surface of the support wire 5 is parallel to the surface of the cloth layer 11 in the laid state of the cloth layer 11, at the same time, the wave crests of the adjacent support wires 5 correspond to each other, the wave troughs of the adjacent support wires 5 correspond to each other, and the gap between the adjacent support wires 5 is still the above-mentioned formed flow channel.

[0050] In this way, by arranging multiple wave-shaped support lines 5, the cloth layer 11 is uniformly supported to uniformly resist subsequent rolling pressure, so that the cloth layer 11 is extruded and deformed more uniformly, thereby reducing the occurrence of the situation that the forming runner is compressed. Embodiment 5

[0051] Embodiment 5 differs from embodiment 4 in that, as shown in Figure 10 , Figure 11 the first state diagram of Figure 10 is the state of the support line 5 before rolling, and the second state diagram is the state of the support line 5 after the film unit element 20 is rolled. In order to intuitively display, the cloth layer 11 in the second state diagram of Figure 10 is extended to a planar shape by rolling adjustment, so as to display the state of the support line 5), the pipe wall of the center pipe 10 is radially penetrated by a mounting hole 103 corresponding to the support line 5, and the hole wall of the mounting hole 103 is integrally formed with multiple elastic pieces 1031 uniformly arranged around the axis of the mounting hole 103. The elastic pieces 1031 are arranged in a direction inclined toward the axis of the center pipe 10, the support line 5 passes through the mounting hole 103 coaxially, and each elastic piece 1031 clamps the support line 5.

[0052] The inner cavity of the center pipe 10 is coaxially provided with a winding pipe 7, and the outer wall of the winding pipe 7 and the inner wall of the center pipe 10 have a radial gap therebetween, which is used for the subsequent hot pipe to enter. One end of the support line 5 is fixed to the winding pipe 7, and the fixing form can be adhesive bonding, such as that a groove is arranged on the outer wall of the winding pipe 7, glue is arranged in the groove, and the end of the support line 5 is in contact with the glue in the groove to be solidly bonded and connected.

[0053] Before the film unit element 20 is wound, the cloth layer 11 is in an unfolded state, the support line 5 is in a wave shape, and the two ends of the support line 5 are fixed to the glue line area 112 and the winding pipe 7, respectively. Meanwhile, each elastic piece 1031 clamps the support line 5. Since the support line 5 is in a wave shape when the film unit element 20 is rolled and the fiber winding layer 30 is wound, the cloth layer 11 is uniformly supported to uniformly resist subsequent rolling pressure, so that the cloth layer 11 is extruded and deformed more uniformly, thereby reducing the occurrence of the situation that the forming runner is compressed. Meanwhile, the winding pressure forces the two cloth layers 11 to press the wave-shaped support line 5, that is, the support line 5 and the cloth layer 11 have static friction therebetween. In order to increase the subsequent dynamic friction, the surface of the support line 5 can be roughened, or the support line 5 can be arranged in a hollow tubular microporous structure, and the densely distributed micropores on the surface can also increase the friction coefficient.

[0054] After rolling is completed, the winding pipe 7 is rotated relative to the center pipe 10, the winding pipe 7 winds the support line 5, the support line 5 is continuously threaded through the mounting hole 103 and wound on the winding pipe 7, and the elastic piece 1031 elastically avoids the support line 5 to allow the support line 5 to pass through, so that the support line 5 changes from a wave shape to a straight line, and the forming runner is in a straight line.

[0055] After the support line 5 is taut, stop winding the support line 5. Then, use a heated hot-cutting tube to insert into the radial gap between the outer wall of the winding tube 7 and the inner wall of the central tube 10 (see the direction of movement of the hot-cutting tube). Figure 11 (in the direction of the dashed arrow), the excess support line 5 is thermally sheared off, and under the elastic force of the support line 5 (see the direction of the elastic force), Figure 11 (In the direction of the solid arrow), the retraction of the support line 5 will cause the spring pieces 1031 to close together, further clamping the support line 5 (the clamped part of the support line 5 is compressed and deformed), that is, ensuring that the support line 5 is in a taut state and does not retract. At the same time, in order to further improve the clamping effect, a protruding structure can be provided on the surface of the support line 5, so that the end of the spring piece 1031 is deeply embedded in the gap between adjacent protruding structures, making it difficult for the support line 5 to retract. Figure 11 The solid arrow in the middle moves relative to the spring piece 1031, effectively locking the support line 5. Finally, remove the take-up tube 7.

[0056] In this way, the support line 5 changes from a wavy shape to a straight shape, and the forming flow channel becomes straight, thereby reducing the resistance to the flow of purified water. Secondly, the positional changes of the crests and troughs of the support line 5 will reorganize the gap space between the two fabric layers 11 through dynamic friction, thereby reducing the occurrence of excessive compression of the gap space after rolling, that is, ensuring the stability and flow of the purified water channel.

[0057] Furthermore, the positional changes at the crests and troughs of the support lines 5 will exert a tangential force on the inner surface of the fabric layer 11 through dynamic friction. The tangential forces of multiple support lines 5 combine and are applied together to the fabric layer 11, thus affecting most parts of the fabric layer 11. The direction of the tangential force is shown in [details omitted]. Figure 10 The direction of the dashed arrows in the diagram indicates that the frictional forces at the crests and troughs of the support lines 5 are opposite. Since the perimeter of the fabric layer 11 (the perimeter formed by the U-shaped adhesive line area 112 and the connecting edge 110) is locked, the fabric layer 11 will not undergo overall displacement under the action of the tangential force. The tangential force is evenly applied to the inner surface of the fabric layer 11 through multiple support lines 5 to increase the internal stress of the fabric layer 11. In particular, the fabric layer 11 is located at the intersection of the two tangential forces, where the local internal stress is larger, which acts like a force to stretch the fabric layer 11, thereby improving the compressive strength. That is, if the compressive strength of the flow channel fabric 1 meets the requirements, the weaving density of the filter area 111 can be reduced, resulting in larger pores and thus increasing the water flow rate.

[0058] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A nanofiltration membrane element, characterized in that: It includes a central tube (10), a membrane unit (20) and a fiber winding layer (30). The central tube (10) has a plurality of water inlet holes. The membrane unit (20) is wound around the outer side of the central tube (10), and the fiber winding layer (30) is wound around the outer side of the membrane unit (20). The membrane unit (20) includes a membrane sheet (2), a water inlet mesh cloth (3) and a flow channel cloth (1). One side of the flow channel cloth (1) is set as a connection edge (110) fixedly connected to the central tube (10). The flow channel cloth (1) is divided into two cloth layers (11) along its own thickness direction. The cloth layer (11) has a filtering area (111), a glue line area (112) and a side line area (113). The shape of the glue line area (112) is "U"-shaped. The filtering area (111) is located within the area surrounded by the glue line area (112). The opening of the glue line area (112) is the connection edge (110). The weaving density of the glue line area (112) is 60%-70% of the weaving density of the filtering area (111). The weaving density of the side line area (113) is the same as that of the filtering area (111). A plurality of support lines (5) are sandwiched between the two cloth layers (11). The support lines (5) are located within the filtering area (111). Each support line (5) is arranged along the axial direction of the central tube (10). When the cloth layer (11) is in a laid-open state, the support line (5) extends along the radial direction of the central tube (10). One end of the support line (5) is bonded to a position of the glue line area (112) far from the connection edge (110). The gap between the two cloth layers (11) communicates with the water inlet holes.

2. The nanofiltration membrane element according to claim 1, characterized in that: The support line (5) is a hollow tubular structure. The support line (5) has micropores. There is no connection between the end of the support line (5) and the central tube (10).

3. The nanofiltration membrane element according to claim 1, characterized in that: The support line (5) is a hollow tubular structure. The support line (5) has micropores. Two pressure strips (6) are jointly provided at one end of each support line (5). The pressure strips (6) extend along the axial direction of the central tube (10). One side surface of the pressure strip (6) has a plurality of convex teeth (61). The tips of the convex teeth (61) of the two pressure strips (6) are abutted against each other. The support line (5) is clamped in the gap between adjacent convex teeth (61). The pressure strip (6) is fixedly connected to the central tube (10).

4. The nanofiltration membrane element according to claim 2 or 3, characterized in that: Each support line (5) is arranged side by side and abutted along the axial direction of the central tube (10).

5. The nanofiltration membrane element according to any one of claims 1-3, characterized in that: Each support line (5) is arranged at intervals along the axial direction of the central tube (10), and the arrangement interval between adjacent support lines (5) is 0.5-5 times the diameter of the support line (5).

6. The nanofiltration membrane element according to any one of claims 1-3, characterized in that: Each support line (5) is arranged at intervals along the axial direction of the central tube (10), and along the flow direction of the raw water flowing into the nanofiltration membrane element, the arrangement gap between adjacent support lines (5) gradually increases.

7. The nanofiltration membrane element according to claim 1, characterized in that: Each of the support lines (5) is arranged at intervals along the axial direction of the central tube (10), and the arrangement interval of adjacent support lines (5) is 0.5-5 times the diameter of the support line (5). A forming flow channel is provided between two adjacent support lines (5). The support lines (5) are wavy, and the undulation direction of the support lines (5) is the axial direction of the central tube (10). The peaks of adjacent support lines (5) correspond to each other, and the troughs of adjacent support lines (5) correspond to each other.

8. The nanofiltration membrane element according to claim 7, characterized in that: The central tube (10) has a radially penetrating mounting hole (103) corresponding to the support line (5). The mounting hole (103) has a plurality of circumferentially evenly arranged elastic tabs (1031) integrally formed on its wall. The elastic tabs (1031) are inclined towards the axis of the central tube (10). The support line (5) coaxially passes through the mounting hole (103), and each elastic tab (1031) clamps the support line (5). A winding tube (7) is coaxially provided inside the central tube (10), and one end of the support line (5) is fixed to the winding tube (7). Before the membrane unit (20) is wound up, the fabric layer (11) is in an unfolded state. The support line (5) is wavy. After the membrane unit (20) is wound and the fiber winding layer (30) is wound, the winding pressure forces the two fabric layers (11) to press the wavy support line (5) together. Then the winding tube (7) rotates relative to the central tube (10) and the winding tube (7) winds up the support line (5). The support line (5) changes from wavy to straight, and the forming flow channel becomes straight. At the same time, the support line (5) applies a frictional force parallel to the axial direction of the central tube (10) to the fabric layer (11). The frictional forces at the crest and trough of the support line (5) are in opposite directions. Finally, the part of the support line (5) located in the inner cavity of the central tube (10) is cut and the winding tube (7) is removed.

9. A manufacturing process for the nanofiltration membrane element according to claim 1, characterized in that: Includes the following steps: S1. Fabrication of membrane unit (20): Apply glue to the adhesive line area (112) of the fabric layer (11), arrange the support line (5) on the surface of the fabric layer (11), and attach one end of the support line (5) to the adhesive line area (112). Then cover the fabric layer (11) to enclose the support line (5) to form the flow channel fabric (1); S2. Winding of membrane unit (20); S3. Winding of fiber winding layer (30).

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