Spiral-wound membrane element

Abstract

The present invention relates to a spiral-wound membrane element. The membrane element comprises a central collection tube, a separation membrane, a feed water flow path spacer, and a permeate-side flow path spacer. The feed water flow path spacer has a mesh structure formed by filament rows X arranged in one direction and filament rows Y arranged in a different direction, wherein the filament rows X and the filament rows Y three-dimensionally intersect each other to form intersection points. In the present invention, by controlling the ratio of the width of a feed water flow path to the thickness of the intersection points of the feed water flow path spacer in the spiral-wound membrane element, high mechanical strength of the membrane element can be maintained while pressure loss of the membrane element is greatly reduced, anti-fouling capability of the membrane element during operation is improved, energy consumption of the membrane element is reduced, and the membrane element has high resistance to physical damage.

Description

A spiral membrane element TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, and particularly relates to a spiral separation membrane element which can be used for seawater desalination, brackish water desalination, ultra-pure water production and wastewater treatment. BACKGROUND

[0002] In material separation, membrane separation technology is increasingly widely used in the field of water treatment due to its high efficiency, energy saving, simple equipment, convenient operation and other characteristics. Separation membranes are classified into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes and forward osmosis membranes from the perspective of their pore size and separation function. These membranes are widely used in the fields of seawater desalination, brackish water desalination, ultra-pure water production and wastewater treatment, and are used separately according to different purposes of separation components and separation performance.

[0003] Separation membrane elements, their uses and purposes have various shapes such as spiral membrane elements, hollow fiber type, flat plate type and rotating flat membrane type. The spiral membrane element is the main type of reverse osmosis and nanofiltration membranes at present. The spiral membrane element has a water collecting pipe and separation membrane units wound around the periphery of the water collecting pipe. The separation membrane units are separated by raw water flow path spacers.

[0004] In addition to the function of separating the separation membranes to form a raw water flow channel, the raw water flow path spacer is usually used to disturb the flow of raw water and promote fluid mixing, so as to reduce the concentration polarization on the membrane surface and improve the desalination rate of the membrane element. In order to increase the disturbance of raw water flow, the flow rate on the membrane surface is usually increased, but with the increase of flow rate, the void fraction of the opposite flow path will be reduced, thereby causing the system pressure difference to increase, and easily leading to the accumulation of impurities and microorganisms in the raw water, causing the flow path to be blocked and the performance of the membrane element to be reduced. On the other hand, the membrane element with high physical strength has higher strength of the raw water flow path spacer, thicker wire of the raw water flow path spacer and more contact points with the separation membrane, which will cause the pressure loss of the membrane element to increase. Generally, when reducing the pressure loss of the membrane element, a raw water flow path spacer with low void fraction is usually designed, which will cause the support strength of the raw water flow path spacer to be reduced, the physical strength of the membrane element to be reduced, and the physical damage of the membrane element during operation to occur. SUMMARY

[0005] The present application aims to reduce the flow resistance on the raw water side without affecting the desalination rate of the membrane element, and to reduce the physical damage of the membrane element during operation.

[0006] The object can be achieved by the present application described below.

[0007] The application discloses a kind of roll type membrane element, at least including water collecting pipe, separation membrane, raw water flow path spacer, permeation side flow path spacer.The raw water flow path spacer is placed between separation membrane to form raw water flow path, the distance between the separation membrane is the width of raw water flow path, the raw water flow path spacer is formed with intersection by the net shape of the intersection of the filament column X arranged in a direction and the filament column Y arranged in the different direction, the ratio of the width of raw water flow path and the intersection thickness of raw water flow path spacer is 78%~92%.The application embeds raw water flow path spacer in separation membrane by adopting but not limited to controlling the intersection thickness of raw water spacer, membrane element rolling pressure, membrane piece softness and other ways, while maintaining the width of raw water flow path, further increases the support surface of raw water flow path spacer and separation membrane, to reduce raw water side flow resistance, reduce membrane element pressure difference, and reduce the effect of physical damage in the process of membrane element operation.The smaller the ratio of the width of raw water flow path and the intersection thickness of raw water flow path spacer, the higher the degree of embedding of raw water flow path spacer, the greater the degree of deformation of separation membrane, which will increase raw water flow resistance and pressure loss, which is not conducive to energy saving.On the other hand, the greater the ratio of the width of raw water flow path and the intersection thickness of raw water flow path spacer, the smaller the support surface of raw water flow path spacer and separation membrane, which is easy to cause raw water flow path spacer to be washed out during operation, etc., so the ratio of the width of raw water flow path and the intersection thickness of raw water flow path spacer is preferably 82%~88%.

[0008] Preferably, the intersection angle of the filament column X and the filament column Y along the raw water flow direction is 30° to 60°, within a certain range, the smaller the angle, the smaller the resistance received by raw water flow, and the smaller the pressure loss of membrane element. However, too small angle will increase the filament density of raw water flow path spacer on the other hand, which will reduce the porosity of raw water flow path and increase the pressure loss of membrane element. Therefore, the intersection angle of the filament column X and the filament column Y along the raw water flow direction is preferably 30° to 60°.

[0009] Preferably, the interval between filaments of the filament column X along the direction of the filament column Y and the interval between filaments of the filament column Y along the direction of the filament column X is 4.0~7.5mm, when the filament interval is too small, raw water flow resistance is large, which leads to too large membrane element pressure difference; when the filament interval is too large, it will lead to too sparse filaments, and the strength of raw water flow path spacer will decrease, thereby causing physical damage during operation. Therefore, the interval between filaments of the filament column X along the direction of the filament column Y and the interval between filaments of the filament column Y along the direction of the filament column X is preferably 4.0~7.5mm.

[0010] Preferably, the softness of the raw water flow path spacer is 0.55-0.94. The present application controls the softness of the raw water flow path spacer by, but not limited to, changing the configuration (such as the cross-sectional shape of the wire diameter, thickness, etc.), material (such as PP, PE, additive material enhancer, etc.), wire column thickness (such as different wire diameters between intersections, different wire diameters in the same direction wire column, etc.) of the raw water flow path spacer. The greater the softness of the raw water flow path spacer, the more conducive to controlling the ratio of the width of the raw water flow path to the intersection thickness of the raw water flow path spacer, but at the same time, the strength of the raw water flow path spacer itself is reduced, and the raw water flow path spacer itself is prone to stretch deformation during the operation of the membrane element. Therefore, the softness of the raw water flow path spacer is preferably 0.55-0.94. Since the smaller the softness of the raw water flow path spacer, the thicker the wire diameter, the overall porosity of the raw water flow path spacer will decrease, which will greatly increase the differential pressure of the membrane element, so the softness of the raw water flow path spacer is further preferably 0.62-0.87.

[0011] Preferably, the ratio of the contact arc length of the intersection of the raw water flow path spacer to the wire circumference in the wire direction is 9%-15%. The smaller the ratio, the smaller the support surface of the raw water flow path spacer and the separation membrane, which is prone to cause problems such as the raw water flow path spacer being knocked out during operation. On the other hand, the larger the ratio, the larger the flow dead zone formed between the raw water flow path spacer and the separation membrane, and the higher the pressure loss. Therefore, the ratio of the contact arc length of the intersection of the raw water flow path spacer to the wire circumference in the wire direction is preferably 9%-15%.

[0012] Meanwhile, the present application discloses a liquid filtration method, which adopts the above-mentioned spiral membrane element.

[0013] Meanwhile, the present application also discloses a membrane filtration device, which comprises a membrane element, and the membrane element comprises the above-mentioned spiral membrane element.

[0014] The spiral membrane element disclosed by the present application can greatly reduce the pressure loss of the membrane element while maintaining high physical strength of the membrane element without affecting the desalination rate of the membrane element by controlling the ratio of the width of the raw water flow path to the intersection thickness of the raw water flow path spacer.

[0015] The filtration method disclosed by the present application can reduce the differential pressure of the filtration system without affecting the desalination rate of the membrane element, thereby improving the stability of the filtration and reducing the energy consumption of the system.

[0016] The filtration device disclosed by the present application can effectively reduce the system differential pressure, enhance the anti-pollution ability of the device, and reduce the energy consumption of the device. BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a schematic view of a spiral membrane element.

[0018] Fig. 2 is a schematic view of a raw water flow path in a membrane element.

[0019] Fig. 3 is a schematic view of a vertical cross section along the direction of the wire row.

[0020] Fig. 4 is a schematic view of a cross section of a raw water flow path spacer wire and a separation membrane.

[0021] Reference numeral 1: separation membrane; 2: raw water flow path spacer; 3: water collecting pipe; 4: permeated side flow path spacer; L: raw water flow path spacer contact arc length with separation membrane; D: raw water flow path spacer intersection thickness; W: width of raw water flow path. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with the accompanying drawings and specific examples, but the content of the drawings does not constitute any limitation on the present application. The following examples are merely used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application, and those skilled in the art can modify or equivalently replace the technical solutions of the present application without departing from the essence and scope of the technical solutions of the present application.

[0023] In conjunction with Fig. 1, a kind of roll type membrane element of the present application, at least including water collecting pipe, separation membrane, raw water flow path spacer, permeated side flow path spacer.

[0024] Test conditions and test methods of each parameter and significance in the examples are shown as follows:

[0025] In order to observe the width of the raw water flow path of the membrane element, the membrane element is cut along the vertical direction of the raw water flow. Since the width of the raw water flow path of the membrane element usually refers to the width of the central part of the membrane element, the above cutting process is carried out at the central part of the membrane element. The distance between the separation membranes is measured, and 100 data are taken to calculate the average width of the raw water flow path of the membrane element. Specifically, the cutting surface is scanned by X-ray CT, and 100 data are taken from 10 cross-sectional photos taken by X-ray CT. The tube voltage-tube current during observation is 150 kV-100 μA, and the resolution is 19.8 μm / voxel. In order to observe the intersection thickness of the raw water flow path spacer, the raw water flow path spacer in the membrane element is taken, and the thickness of the intersection of the raw water flow path spacer is measured using a thickness gauge. Ten data are tested, and the average value calculated from ten parallel samples is taken as the thickness of the intersection of the raw water flow path spacer. The ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer is taken as the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer. For the roll type membrane element of the present application, the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer is 78% to 92%. Considering the actual level of production test, the value can have an error of ±1%. That is, the value within the error range of ±1% is also considered to fall within the scope of the present application.

[0026] Crossing angle of wire column X and wire column Y in raw water flow direction: The crossing angle of wire column X and wire column Y in the raw water flow direction when viewed from top to bottom of the raw water side flow path spacer. The specific test method is to test with a protractor, and the average value of 10 data is taken as the crossing angle.

[0027] Interval of intersection along the wire column direction: The interval distance of the intersection of wire column X and wire column Y along the wire direction when viewed from top to bottom of the raw water side flow path spacer. The specific test method is to observe the front shape of the raw water side flow path spacer by electron microscope (20 times), measure the interval distance of the intersection along the wire column direction, test 10 data, and at the same time, calculate the average value of 100 data of 10 parallel samples.

[0028] Softness of raw water flow path spacer: Cut the raw water flow path spacer, the size is 80mm*30mm, of which 30mm is along the raw water flow direction. Fix the cut sample along the 80mm long direction to the water platform surface, the fixed length is 30mm, and the other 50mm is exposed to the platform. Hang a 0.1g weight on the edge of the raw water flow path spacer exposed to the platform, measure the vertical distance of the edge of the raw water flow path spacer to the water platform, and take the average value of 10 parallel samples divided by 50mm as the softness of the raw water flow path spacer.

[0029] The ratio of the contact arc length of the intersection of the raw water flow path spacer along the wire direction to the wire circumference: Use X-ray CT to scan the membrane element to take a photo of the cross section of the intersection of the raw water flow path spacer along the wire direction. The tube voltage-tube current for observation is 150kV-100μA, and the resolution is 19.8μm / voxel. Based on the 10 cross section photos taken by X-ray CT, take 10 "contact arc length of the intersection of the raw water flow path spacer along the wire direction" data and "wire circumference" data from the cross section photos, each 100, and calculate the average value of the ratio of the contact arc length of the intersection of the raw water flow path spacer along the wire direction to the wire circumference. For the roll type membrane element of the present application, the ratio of the contact arc length to the wire circumference is preferably 9% to 15%. Considering the actual level of production test, the value can have an error of ±0.5%, that is, the value within the error range of ±0.5% is also considered to fall within the above range.

[0030] The test conditions of the membrane element in the examples are as follows:

[0031] Sodium chloride removal rate: The adjusted water having a temperature of 25±1°C, pH of 6.5-7.5, and a sodium chloride concentration of 2000 mg / L was supplied to the membrane element at an operating pressure of 1.55 MPa, and membrane filtration treatment was performed for 1 hour under a recovery rate of 15%. The conductivity of the raw water and the permeated water was measured using a conductivity meter manufactured by HACH Co., USA, to obtain the respective actual salinity, i.e., the sodium chloride concentration. Based on the sodium chloride concentration thus obtained and the following equation, the sodium chloride removal rate was calculated. Sodium chloride removal rate (%) = [1- (sodium chloride concentration in permeated water) / (sodium chloride concentration in supplied water)] x 100.

[0032] Physical damage evaluation parameter: The length of the raw water-side flow path spacer that flew out when the pressure difference exceeded 500 kPa was used to judge the degree of physical damage of the membrane element at a high flow rate.

[0033] Membrane element pressure difference: The pressure difference, i.e., the pressure loss, of a single 8-inch membrane element was directly measured using a pressure difference gauge under the conditions that the permeated water was closed and the flow rate was 10 m 3 / h.

[0034] Membrane element pressure difference increase amount after a pollution experiment: The pressure difference increase amount of a single 8-inch membrane element after 1500 hours of operation under actual industrial wastewater conditions.

[0035] Comparative Example 1

[0036] The spiral membrane element contained a separation membrane, a water collecting pipe, a raw water-side flow path spacer, and a permeated water-side flow path spacer. The average thickness of the intersection of the raw water-side flow path spacer was 34 mil, the intersection angle of the raw water-side flow path spacer was 75°, the distance of the intersection of the raw water-side flow path spacer in the direction of the wire was 3.5 mm, the flexibility of the raw water-side flow path spacer was 0.17, the ratio of the raw water flow path width to the intersection thickness of the raw water-side flow path spacer was 98.5%, and the ratio of the contact arc length with the membrane surface to the wire circumference of the intersection of the raw water-side flow path spacer in the direction of the wire was 3.9%. Under the test conditions of a 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5, and a recovery rate of 15%, the sodium chloride removal rate of the spiral membrane element was 99.70%, the length of the raw water-side flow path spacer that flew out when the pressure difference exceeded 500 kPa was 1.4 mm, the membrane element pressure difference under the conditions that the permeated water was closed and the flow rate was 10 m 3 / h was 17.9 kPa, and the pressure difference increase amount of the single membrane element after 1500 hours of operation under the condition that the raw water was industrial wastewater was 155.2 kPa.

[0037] Comparative Example 2

[0038] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the wire intersection angle of the raw water side flow path spacer is 40°, the intersection distance of the raw water side flow path spacer along the wire direction is 4.5 mm, the softness of the raw water side flow path spacer is 0.87, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 94.6%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 7.4%, the sodium chloride removal rate of the spiral membrane element is 99.34% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 8.5 mm when the pressure difference exceeds 500 kPa, the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 7.4 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 24.6 kPa.

[0039] Comparative Example 3

[0040] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 39 mil, the wire intersection angle of the raw water side flow path spacer is 40°, the intersection distance of the raw water side flow path spacer along the wire direction is 7.5 mm, the softness of the raw water side flow path spacer is 0.74, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 76.9%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 18.5%, the sodium chloride removal rate of the spiral membrane element is 99.61% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 1.2 mm when the pressure difference exceeds 500 kPa, the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 20.1 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 243.1 kPa.

[0041] Example 1

[0042] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the intersection angle of the raw water side flow path spacer is 75°, the intersection distance of the raw water side flow path spacer along the wire direction is 9 mm, the softness of the raw water side flow path spacer is 0.90, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 79.5%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 15.5%, the sodium chloride removal rate of the spiral membrane element is 99.60% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 1.8 mm when the pressure difference exceeds 500 kPa, the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 14.8 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 97.8 kPa.

[0043] Example 2

[0044] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the intersection angle of the raw water side flow path spacer is 75°, the intersection distance of the raw water side flow path spacer along the wire direction is 9 mm, the softness of the raw water side flow path spacer is 0.90, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 79.5%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 15.5%, the sodium chloride removal rate of the spiral membrane element is 99.60% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 1.8 mm when the pressure difference exceeds 500 kPa, the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 14.8 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 97.8 kPa.

[0045] Example 3

[0046] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the wire intersection angle of the raw water side flow path spacer is 30°, the intersection distance of the raw water side flow path spacer along the wire direction is 9 mm, the softness of the raw water side flow path spacer is 0.96, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 78.4%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 14.8%, the sodium chloride removal rate of the spiral membrane element is 99.51% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 4.6 mm when the pressure difference exceeds 500 kPa, and the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 13.8 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 79.3 kPa.

[0047] Example 4

[0048] The spiral membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeated water side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the wire intersection angle of the raw water side flow path spacer is 30°, the intersection distance of the raw water side flow path spacer along the wire direction is 9 mm, the softness of the raw water side flow path spacer is 0.96, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 78.4%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 14.8%, the sodium chloride removal rate of the spiral membrane element is 99.51% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer fly-out length of a single membrane element is 4.6 mm when the pressure difference exceeds 500 kPa, and the membrane element pressure difference under the condition of closing the permeated water and the flow rate of 10 m 3 / h is 13.8 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition that the raw water is industrial wastewater is 79.3 kPa.

[0049] Example 5

[0050] The spiral-wound membrane element comprises a separation membrane, a water collecting pipe, a raw water side flow path spacer and a permeate side flow path spacer. The intersection average thickness of the raw water side flow path spacer is 37 mil, the wire intersection angle of the raw water side flow path spacer is 60°, the intersection distance of the raw water side flow path spacer along the wire direction is 9 mm, the softness of the raw water side flow path spacer is 0.94, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 79.5%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 15.4%, the sodium chloride removal rate of the spiral-wound membrane element is 99.53% under the test conditions of using 2000 mg / L sodium chloride solution, 1.55 MPa, pH 6.5-7.5 and 15% recovery rate, the raw water side flow path spacer flying length of a single membrane element is 4.2 mm when the pressure difference exceeds 500 kPa, and the membrane element pressure difference under the conditions of closing the permeate water and a flow rate of 10 m 3 / h is 14.2 kPa. The pressure difference increment of a single membrane element after running for 1500 hours under the condition of using industrial wastewater as raw water is 85.8 kPa.

[0051] Example 6

[0052] Compared with Example 2 and Example 4, the wire intersection angle of the raw water side flow path spacer in Example 6 is 40°, the softness of the raw water side flow path spacer is 0.36, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 90.8%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 8.9%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0053] Example 7

[0054] Compared with Example 3 and Example 5, the wire intersection angle of the raw water side flow path spacer in Example 7 is 40°, the softness of the raw water side flow path spacer is 0.95, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 78.9%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 15.0%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0055] Example 8

[0056] Compared with Example 6 and Example 7, the intersection distance of the raw water side flow path spacer along the wire direction in Example 8 is 4 mm, the softness of the raw water side flow path spacer is 0.48, the ratio of the raw water side flow path width to the intersection thickness of the raw water side flow path spacer is 91.9%, the ratio of the contact arc length of the intersection of the raw water side flow path spacer along the wire direction to the wire circumference is 8.7%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0057] Example 9

[0058] Compared with Example 8, the intersection of the raw water flow path spacer in Example 9 is 4.5 mm in the direction of the wire, the softness of the raw water flow path spacer is 0.55, the ratio of the raw water flow path width to the intersection thickness of the raw water flow path spacer is 91.4%, and other original parameters are the same, and the specific values are shown in Table 1.

[0059] Example 10

[0060] Compared with Example 9, the average thickness of the intersection of the raw water flow path spacer in Example 10 is 39 mil, the intersection of the raw water flow path spacer is 6 mm in the direction of the wire, the softness of the raw water flow path spacer is 0.87, the ratio of the raw water flow path width to the intersection thickness of the raw water flow path spacer is 88.5%, the ratio of the contact arc length to the wire circumference of the cross section of the intersection of the raw water flow path spacer along the wire direction is 10.1%, and other original parameters are the same, and the specific values are shown in Table 1.

[0061] Example 11

[0062] Compared with Example 10, the intersection of the raw water flow path spacer in Example 11 is 7.5 mm in the direction of the wire, the softness of the raw water flow path spacer is 0.94, the ratio of the raw water flow path width to the intersection thickness of the raw water flow path spacer is 88.2%, and other original parameters are the same, and the specific values are shown in Table 1.

[0063] Example 12

[0064] Compared with Example 9, the softness of the raw water flow path spacer in Example 12 is 0.87, the ratio of the contact arc length to the wire circumference of the cross section of the intersection of the raw water flow path spacer along the wire direction is 8.5%, and other original parameters are the same, and the specific values are shown in Table 1.

[0065] Example 13

[0066] Compared with Example 11, the softness of the raw water flow path spacer in Example 13 is 0.74, the ratio of the raw water flow path width to the intersection thickness of the raw water flow path spacer is 87.9%, the ratio of the contact arc length to the wire circumference of the cross section of the intersection of the raw water flow path spacer along the wire direction is 10.5%, and other original parameters are the same, and the specific values are shown in Table 1.

[0067] Example 14

[0068] Compared with Example 9, the softness of the raw water flow path spacer in Example 14 is 0.62, the ratio of the contact arc length to the wire circumference of the cross section of the intersection of the raw water flow path spacer along the wire direction is 8.6%, and other original parameters are the same, and the specific values are shown in Table 1.

[0069] Example 15

[0070] Compared with Example 13, the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer in Example 15 is 82.3%, the ratio of the arc length of the intersection of the raw water flow path spacer in contact with the membrane surface to the circumference of the wire along the wire direction is 15.1%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0071] Example 16

[0072] Compared with Example 12, the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer in Example 16 is 87.8%, the ratio of the arc length of the intersection of the raw water flow path spacer in contact with the membrane surface to the circumference of the wire along the wire direction is 11.9%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0073] Example 17

[0074] Compared with Example 15, the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer in Example 17 is 85.9%, the ratio of the arc length of the intersection of the raw water flow path spacer in contact with the membrane surface to the circumference of the wire along the wire direction is 12.7%, and the other original parameters are the same, and the specific values are shown in Table 1.

[0075] Compared with Comparative Examples 1-3, Example 1 can enhance the anti-pollution ability of the membrane element (the pressure difference increase after the membrane element pollution test) while maintaining the separation performance (sodium chloride removal rate) of the membrane element by controlling the ratio of the width of the raw water flow path to the thickness of the intersection of the raw water flow path spacer, and the decline in the physical strength of the membrane element (the length of the raw water flow path spacer flying out when the pressure difference exceeds 500 kPa). Examples 2-7 further enhance the anti-pollution ability of the membrane element by changing the wire intersection angle of the raw water flow path spacer. Examples 8-11 further enhance the anti-pollution ability of the membrane element while maintaining the physical strength of the membrane element by changing the distance of the intersection of the raw water flow path spacer along the wire direction. Examples 12-14 further enhance the anti-pollution ability of the membrane element while controlling the decline in the physical strength of the membrane element by changing the softness of the raw water flow path spacer. Examples 15-17 make the membrane element have excellent anti-pollution ability while maintaining high physical strength by controlling the ratio of the arc length of the intersection of the raw water flow path spacer in contact with the membrane surface to the circumference of the wire along the wire direction.

[0076] From the results, a membrane element with high physical strength, which has a high strength of the raw water flow path spacer, a thicker wire of the raw water flow path spacer, and more contact points with the separation membrane, can result in an increase in pressure loss of the membrane element. Generally, when reducing the pressure loss of a membrane element, a raw water flow path spacer with a low void ratio is often used, which can result in a decrease in the support strength of the raw water flow path spacer itself, a decrease in the physical strength of the membrane element, and physical damage to the membrane element during operation.

[0077] Compared to the comparative example of the spiral membrane element, the spiral membrane element in the present application controls the ratio of the raw water flow path width to the intersection thickness of the raw water flow path spacer, which can maintain a high physical strength of the membrane element while reducing the pressure loss of the membrane element, so that the membrane element has both high physical damage resistance and high anti-pollution ability.

[0078] [Table 1]

Claims

1. A spiral membrane element comprising at least raw water flow path spacers, water collecting tubes, separation membranes, and permeate side flow path spacers, characterized in that: the raw water flow path spacers are arranged between the separation membranes to form raw water flow paths, the distance between the separation membranes is the width of the raw water flow paths, the raw water flow path spacers have a mesh shape formed by intersecting a row of wires X arranged in one direction and a row of wires Y arranged in a different direction, the ratio of the width of the raw water flow paths to the thickness of the intersections of the raw water flow path spacers is 78% to 92%, the intersection angle of the row of wires X and the row of wires Y is 30° to 60°, the interval of the intersections in the direction of the row of wires is 4.0 mm to 7.5 mm, the flexibility of the raw water flow path spacers is 0.55 to 0.94, and the ratio of the arc length of the cross section of the intersection of the raw water flow path spacers in the direction of the wires to the wire circumference is 9% to 15%. The spiral membrane element according to any one of claims 1 to 5. The spiral membrane element according to any one of claims 1 to 5. ​ ​ 2. The spiral-wound membrane element of claim 1, wherein: ​ 3. The spiral-wound membrane element of claim 1, wherein: ​ 4. The spiral-wound membrane element of claim 1, wherein: ​ 5. The spiral-wound membrane element of claim 1, wherein: ​ 6. A method of filtering a liquid, characterized by: ​ 7. A membrane filtration device characterized by: ​

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