CN107021546B

CN107021546B - Membrane element

Info

Publication number: CN107021546B
Application number: CN201610075157.XA
Authority: CN
Inventors: 黄燕; 薛莲; 王晨
Original assignee: AO Smith Nanjing Water Treatment Products Co Ltd
Current assignee: AO Smith Nanjing Water Treatment Products Co Ltd
Priority date: 2016-02-02
Filing date: 2016-02-02
Publication date: 2023-04-11
Anticipated expiration: 2036-02-02
Also published as: WO2017133641A1; CN107021546A

Abstract

The invention discloses a membrane element, comprising: filtration membrane, filtration membrane has the raw water runner and the pure water runner of mutual isolation, the export of raw water runner is located filtration membrane's at least one side, membrane protection device cover is established outside filtration membrane, its have with the opening of at least one of the export intercommunication of raw water runner, membrane protection device passes through the fluid that the opening will flow from the export of raw water runner is derived outside the membrane protection device. The membrane element provided by the invention can reduce the deposition of pollutants at the outlet of the raw water channel of the filtering membrane, and effectively prolong the service life of the membrane element.

Description

Membrane element

Technical Field

The invention relates to the technical field of water treatment, in particular to a membrane element.

Background

The common application form of the filtration membrane technology in water treatment is generally to make spiral wound membrane elements, also called wound membrane elements. The membrane element is wound around the central tube while the opening of the wound membrane element is bonded to the central tube having the opening, so that feed water flows through the outside of the filtration membrane, and fresh water is introduced into the central tube through the membrane element under feed water pressure.

The invention patent with chinese patent publication No. CN102976447A discloses a membrane element, and fig. 1 is a schematic diagram of the appearance of a membrane element in the prior art of the above patent. As shown in fig. 1, the membrane element has a central tube in the casing, and when in use, raw water enters the casing from two ends of the casing, and a part of the raw water forms water with lower concentration under the action of pressure through the action of the filtering membrane, and the water flows out from one end or two ends of the central tube after entering the central tube, and the water can be called pure water or fresh water; the other part flows out from the side of the shell and can be called waste water or concentrated water. However, it has been found that during long-term use, some or more contaminants or deposits may accumulate in the membrane element at the waste water outlet of the membrane, which affects the filtration efficiency of the membrane element and also reduces its service life.

Disclosure of Invention

In the conventional art, the filtration membrane 11 is wound around the central tube 12 and is filled in the membrane housing 5, and wastewater flows out from the outlet of the raw water flow path of the filtration membrane 11 and enters the membrane housing 5, and the wastewater is collected by the membrane housing 5 and discharged from the wastewater outlet 51 provided in the membrane housing 5. Since the filtering membrane 11 wound on the central tube 12 needs to be filled into the inside of the membrane housing 5, the side wall inside the membrane housing 5 has a certain inclination, and the gap between the membrane protecting device 2 and the membrane housing 5 must be large, so that the filtering membrane 11 can be conveniently inserted into the membrane housing 5. However, the large gap causes a sudden drop in the flow velocity of the wastewater to substantially 0 after the wastewater flows out from the outlet of the raw water flow path. At a very low speed, the pollutants in the wastewater are continuously deposited on the filtering membrane 11 at the outlet of the raw water flow channel and further expand to the side wall of the whole filtering membrane 11. Thus, the service life of the membrane element can be greatly reduced in the using process.

In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a membrane element capable of reducing the deposition of contaminants at the outlet of a raw water flow passage of a filtration membrane.

The specific technical scheme of the embodiment of the invention is as follows:

a membrane element, comprising:

a filtering membrane, wherein the filtering membrane is provided with a raw water flow passage and a pure water flow passage which are mutually isolated, the outlet of the raw water flow passage is positioned at least one side edge of the filtering membrane,

the membrane element further comprises:

and the flow rate control device is communicated with the outlet of the raw water flow channel and is used for controlling the speed of the fluid flowing through the flow rate control device.

Preferably, the flow rate control device comprises a membrane protection device, the membrane protection device is sleeved outside the filtering membrane and is provided with at least one opening communicated with the outlet of the raw water flow channel, and the fluid flowing out of the outlet of the raw water flow channel is guided out of the membrane protection device through the opening.

Preferably, the membrane element further comprises a membrane housing for accommodating the filtration membrane and the membrane protection device, and a gap between the membrane protection device and the filtration membrane is smaller than a gap between the membrane protection device and the membrane housing.

Preferably, a gap between the membrane protection device and the filtration membrane ranges from a thickness of the membrane element raw water flow passage to a gap between the membrane element and the membrane housing.

Preferably, the membrane protection device comprises a flexible member which is coated outside the filter membrane.

Preferably, the membrane element comprises a first end cover and a second end cover which are arranged at two ends of the filter membrane, and the flexible piece is respectively sealed with the first end cover and the second end cover through glue.

Preferably, the flexible member is made of polypropylene or polyester material.

Preferably, the membrane protection device comprises a cylinder made of a rigid material.

Preferably, filtration membrane is including setting up the graticule mesh of raw water runner, the inside wall of barrel with interval between the lateral wall of filtration membrane is the thickness of graticule mesh.

Preferably, a ratio of a flow rate of water flowing out of the opening to a flow rate of water flowing in from the inlet of the raw water flow passage conforms to a first preset ratio range.

Preferably, said first predetermined ratio is in the range of 0 to 1.

Preferably, the membrane element comprises a first end cover and a second end cover which are arranged at two ends of the filter membrane, and the first end cover and the second end cover are respectively connected with the cylinder body.

Preferably, the rigid material is one of ABS, PP, PA, POM and stainless steel material.

Preferably, the outlet of the raw water flow path is located at a short side of the membrane when the membrane is developed.

Preferably, the filtering membrane is one of a reverse osmosis membrane and a nanofiltration membrane.

Preferably, the flow rate control means includes a baffle plate provided at an outlet of the raw water flow passage.

Preferably, the flow rate control device comprises an extension part which is arranged at the raw water flow passage outlet of the filtering membrane and extends along the winding direction of the filtering membrane, and the cross-sectional area of a flow passage formed between the extension part and the filtering membrane is smaller than that of a raw water flow passage in the filtering membrane.

The technical scheme of the invention has the following remarkable beneficial effects:

1. the invention is provided with a flow rate control device which has a certain control function on the flow rate of the waste water. When the fluid flows out from the outlet of the raw water channel of the filtering membrane, the flow speed control device enables the flow speed of the wastewater on the surface of the filtering membrane to be in a relatively slow descending trend without sudden attenuation, and the flushing speed of the outer ring of the membrane element can be improved. The above structure can effectively reduce the pollution degree of the outlet of the raw water channel of the filtering membrane. Meanwhile, the polluted flow rate control device can be sleeved outside the membrane element, and impurities remained outside the flow rate control device can not directly influence the filtering membrane, so that the service life of the membrane element can be effectively prolonged.

2. The membrane protection device can be made of rigid materials, the ratio of the flow rate of wastewater flowing out of the raw water channel to the flow rate of pure water flowing out of the pure water channel of the whole membrane element can be effectively controlled by controlling the size of the opening formed on the membrane protection device, or the ratio of the flow rate of wastewater flowing out of the raw water channel to the flow rate of raw water flowing in the raw water channel, so that the function of adjusting the wastewater ratio is achieved. By means of the structure, the waste water ratio device can be saved, and therefore the cost of products can be reduced. Secondly, when being provided with waste water than the device simultaneously, borrow by above-mentioned structure and play certain effect of adjusting waste water ratio, and then can increase the aperture of the waste water ratio device of use to can effectively prevent the jam of waste water ratio device.

3. In one embodiment of the invention, the flexible piece is wound on the outer side of the membrane element to serve as a membrane protection device, the distance between the protection device and the membrane piece in the membrane element is the thickness of a grid in the filtering membrane, the flexible piece is provided with openings, the openings are uniformly distributed at the outlet of the raw water flow channel, and the area of the openings can be the same as the sectional area of the water inlet flow channel. The membrane protection device can ensure that the flow speed of wastewater contacting with the membrane elements is not suddenly attenuated, and the scouring speed of the outer rings of the membrane elements is improved, so that the accumulation of pollutants is reduced.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes, the proportional sizes, and the like of the respective members in the drawings are merely schematic for facilitating the understanding of the present invention, and do not specifically limit the shapes, the proportional sizes, and the like of the respective members of the present invention. Those skilled in the art, having the benefit of the teachings of this invention, may choose from the various possible shapes and proportional sizes to implement the invention as a matter of case.

FIG. 1 is a schematic view of an external shape of a side-flow reverse osmosis membrane element.

Fig. 2 is a front view of a membrane element of the present invention.

Fig. 3 isbase:Sub>A cross-sectional viewbase:Sub>A-base:Sub>A of the membrane element of fig. 2 according to the present invention.

Reference numbers to the above figures: 11. a filtration membrane; 12. a central tube; 121. a through hole; 2. a membrane protection device; 21. an opening; 3. a first end cap; 4. a second end cap; 5. a membrane shell; 51. a waste water outlet; 6. an inlet of the raw water flow passage.

Detailed Description

The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the present invention. However, the specific embodiments of the present invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Any possible variations based on the present invention may be conceived by the skilled person in the light of the teachings of the present invention, and these should be considered to fall within the scope of the present invention.

Fig. 2 is a front view of a membrane element of the present invention, as shown in fig. 2, which discloses a membrane element comprising: the membrane protection device 2 is sleeved outside the filtering membrane 11 and provided with at least one opening 21 communicated with the outlet of the raw water flow passage, and the fluid flowing out of the outlet of the raw water flow passage is led out of the membrane protection device 2 by the membrane protection device 2 through the opening 21.

FIG. 3 isbase:Sub>A sectional view taken along line A-A in FIG. 2 of the membrane element of the present invention, as shown in FIG. 3, in which raw water flows intobase:Sub>A filtration membrane 11 from an inlet 6 ofbase:Sub>A raw water flow passage in the filtration membrane 11, and the raw water is converted into two parts of pure water and wastewater by treatment of the filtration membrane 11, wherein the pure water flows out along the pure water flow passage, and the wastewater flows out along an outlet of the raw water flow passage. The inlet 6 of the raw water flow path may be provided at both the upper and lower ends of the membrane element, or may be provided only at any one of the upper and lower ends of the membrane element. In other words, when the filtration membrane in the membrane element is in the expanded state, the inlet of the raw water flow path is located on the long side of the filtration membrane, and the outlet of the raw water flow path is located on the short side of the filtration membrane.

As shown in fig. 2, the filter membrane 11 is wound around the center tube 12, the center tube 12 is provided with a through hole 121, the outlet of the raw water flow path is positioned outside the filter membrane 11 wound around the center tube 12, the wastewater flows out from the outside of the filter membrane 11 wound around the center tube 12, and the pure water flows into the center tube 12 from the through hole 121 of the center tube 12. The membrane protection device 2 is sleeved on the outer side of the filtering membrane 11, at least one opening 21 is formed in the membrane protection device 2, and after wastewater flows out from the outer side of the filtering membrane 11, the wastewater continuously flows out from the opening 21 of the membrane protection device 2 from the inside of the membrane protection device 2 and finally flows to the outside of the membrane protection device 2.

In particular, in one embodiment, the membrane protection device 2 may be a flexible member that is wrapped around the filtration membrane. In this embodiment, the flexible member may be made of a flexible bendable material such as an adhesive tape or rubber, and the flexible member is directly wound around the filtering membrane 11, so that the flexible member and the filtering membrane 11 can be tightly attached to each other, and the gap between the flexible member and the filtering membrane 11 is small. The flexible member has at least one opening 21 formed therein along the axis of the central tube 12. The opening 21 may be opposite to the position of the raw water passage outlet of the filtering membrane 11, and when the wastewater flows out from the raw water passage outlet, the wastewater directly flows into the opening 21 of the flexible member coated outside the filtering membrane 11. Due to the flexible member, the flexible member has a certain control function on the flow speed of the wastewater in the process from the raw water flow passage outlet of the filtering membrane 11 to the opening 21 of the flexible member. After the wastewater flows out from the raw water channel outlet of the filtering membrane 11, the flow speed of the wastewater on the surface of the filtering membrane 11 is in a relatively slow descending trend due to the opening 21 of the flexible piece. In this way, the pollutants in the wastewater can be less deposited on the raw water flow passage outlet of the filtering membrane 11 and the surface of the filtering membrane 11. When the waste water is led out of the membrane guard 2 through the opening 21 in the flexible member, i.e. the membrane guard 2, the flow rate of the waste water suddenly drops due to the sudden increase of the space outside the membrane guard 2. At this time, since the water flow rate is greatly reduced, the contaminants in the wastewater may remain outside the membrane guard 2. So, can effectively reduce the contaminated degree in the exit of filtration membrane 11 raw water runner, simultaneously, the membrane protection device 2 cover that the surface is contaminated is established outside filtration membrane 11, and the outer impurity of residual membrane protection device can not produce direct influence to filtration membrane 11, can effectively prolong the life of film element like this.

In this embodiment, the membrane element comprises a first end cap 3 and a second end cap 4 arranged at both ends of the filter membrane 11, the flexible members being sealed with the first end cap 3 and the second end cap 4, respectively, by glue. As such, the inlet of the raw water channel may be located at the first and/or second end caps 3 and 4, specifically, at the inner sides of both ends of the wound filtering membrane 11. The outer sides of the two ends of the filtering membrane 11 are sealed through glue until the outer sides of the two ends of the filtering membrane 11 are sealed to the flexible parts coated outside the filtering membrane 11. After this, waste water flows out from the export of filtration membrane 11's raw water runner, only can flow out from the opening 21 department of flexible piece, can not flow out from the upper and lower both ends of flexible piece, can avoid the both ends department of flexible piece to appear the pollutant sediment like this.

In the present embodiment, the membrane element further comprises a membrane housing 5 for accommodating the filtration membrane 11 and the membrane protection device 2. A waste water chamber communicated with the outlet of the raw water flow passage is formed between the membrane shell 5 and the membrane protection device 2. Since the filter membrane 11 is a consumable part, it needs to be replaced periodically or aperiodically. The gap between the membrane housing 5 and the membrane protection device 2 is large in order to facilitate the assembly of the membrane element, so that the installation of the membrane protection device 2 and the filtration membrane 11 into the membrane housing 5 is facilitated.

In the present embodiment, the gap between the membrane protective device 2 and the filtration membrane 11 is smaller than the gap between the membrane protective device 2 and the membrane housing 5. By controlling the size of the membrane protective device 2, the gap between the membrane protective device 2 and the filtration membrane 11 can be controlled such that the gap between the membrane protective device 2 and the filtration membrane 11 is smaller than the gap between the membrane protective device 2 and the membrane housing 5. Waste water is when flowing through the clearance between membrane protection device 2 and the filtration membrane 11, because the clearance between these two is less, its velocity of flow can not take place to descend by a wide margin, and the pollutant in the waste water is difficult for deposiing on filtration membrane 11's lateral wall at this moment, when waste water flows to the clearance between membrane protection device 2 and the membrane shell 5, because the clearance is great, the sudden drop takes place for the waste water velocity of flow, and the pollutant deposit in the waste water is in the 2 lateral walls of membrane protection device, in the waste water chamber between membrane protection device 2 and the membrane shell 5 promptly. Therefore, the outer side wall of the filtering membrane 11 is prevented from being polluted, and the service life of the membrane element is effectively prolonged. The gap between the membrane protective device 2 and the membrane housing 5 can facilitate removal of the membrane element with the membrane protective device 2 from the membrane housing 5. In a preferred embodiment, the gap between the membrane protection device 2 and the filtration membrane 11 ranges from the thickness of the raw water flow channel of the membrane element to the gap between the membrane element and the membrane housing 5. Within this range, on the one hand, the wastewater can be ensured to flow through the gap between the two at a certain large flow rate, and on the other hand, the wastewater is ensured to have a certain flow velocity so as to reduce the occurrence of pollutant precipitation.

In another embodiment, the membrane protective device 2 may comprise a cylinder made of a rigid material. The rigid material is one of rigid materials such as PP (polypropylene), ABS (ABS plastic), PA (polyamide plastic), POM (polyformaldehyde) and stainless steel. In the present embodiment, at least one opening 21 is opened in the cylindrical body, and the cylindrical body guides the fluid flowing out from the outlet of the raw water flow path out of the membrane guard 2 through the opening 21. In some cases, the membrane guard 2 needs to have a certain strength to withstand a high pressure, so the membrane guard 2 needs to be made of a rigid material. After the cylinder is arranged, the cylinder has a certain control function on the flow speed of the wastewater in the process from the raw water flow passage outlet of the filtering membrane 11 to the opening 21 of the cylinder. After the wastewater flows out from the raw water channel outlet of the filtering membrane 11, the flow velocity of the wastewater on the surface of the filtering membrane 11 is in a relatively slow descending trend due to the opening 21 of the cylinder. In this way, the pollutants in the wastewater can be less deposited on the raw water flow passage outlet of the filtering membrane 11 and the surface of the filtering membrane 11. When the waste water is led out of the membrane guard 2 through the opening 21 of the cylinder (i.e. the membrane guard 2), the flow rate of the waste water suddenly decreases due to the sudden increase of the space outside the membrane guard 2. At this time, since the water flow rate is greatly reduced, the contaminants in the wastewater may remain outside the membrane guard 2. Therefore, the degree of pollution at the outlet of the raw water flow passage of the filtering membrane 11 can be effectively reduced, meanwhile, the membrane protection device 2 with the polluted outer surface is sleeved outside the filtering membrane 11, impurities outside the residual membrane protection device cannot directly influence the filtering membrane 11, and therefore the service life of the membrane element can be effectively prolonged.

The membrane element further comprises a first end cover 3 and a second end cover 4 which are arranged at two ends of the filtering membrane 11, and the first end cover 3 and the second end cover 4 are fixedly connected with the cylinder body respectively. First end cover 3 and second end cover 4 are used for sealing the both ends of barrel, and first end cover 3 and second end cover 4 can be sealed through glue with filtration membrane 11's both ends simultaneously, so guarantee that the raw water runner that filtration membrane 11 formed can not reveal at filtration membrane 11's both ends.

In this embodiment, filtering membrane 11 may further include a grid disposed on the raw water flow channel, and the distance between the inner sidewall of the cylinder and the outer sidewall of filtering membrane 11 is the thickness of the grid. The graticule mesh that sets up in raw water runner can make to have certain clearance between membrane and the membrane in filtration membrane 11, so can make things convenient for raw water to flow in filtration membrane 11. When the interval between the inside wall of barrel and filtration membrane 11's the lateral wall is the thickness of graticule mesh, waste water is in between barrel and filtration membrane 11's the lateral wall from the export outflow of raw water runner after, waste water not only can flow between barrel and filtration membrane 11's lateral wall, can keep very fast flow rate simultaneously, the pollutant in the waste water can not take place to deposit on filtration membrane 11's lateral wall and then pollute filtration membrane 11, so reach the purpose of protection filtration membrane 11. Currently meshes are used between 0.254mm and 1.016mm, although it is not excluded that they will be thinner or thicker afterwards.

In the present embodiment, the ratio of the flow rate of water flowing out of the opening 21 to the flow rate of water flowing in from the inlet of the raw water flow passage corresponds to a first predetermined ratio range. Specifically, the cylinder is provided with at least one opening 21, the size of all the openings 21 can be controlled, and the cylinder is made of a rigid material, so that the flow rate of water flowing out of the openings 21 can be further controlled after the size of the openings 21 is controlled. When the opening 21 is small, the pressure born by the opening 21 is large, and because the cylinder is made of rigid material, the size of the opening 21 cannot be increased due to the large pressure, so that the small opening 21 can be always ensured, and the stability of the flow of the wastewater flowing out of the opening 21 of the raw water channel, namely the stability of the flow of the wastewater flowing out of the outlet of the raw water channel, is ensured. In the membrane element, when the flow rate of the wastewater at the inlet of the raw water channel is constant, the flow rate of the pure water flowing out from the pure water channel is increased when the flow rate of the wastewater at the outlet of the raw water channel is decreased, and thus, the ratio of the flow rate of the wastewater flowing out from the raw water channel to the flow rate of the pure water flowing out from the pure water channel, or the ratio of the flow rate of the wastewater flowing out from the raw water channel to the flow rate of the raw water flowing in from the raw water channel can be effectively controlled by controlling the size of the opening 21 formed in the membrane element. That is, adjusting the size of the opening 21 to change the phase can achieve the purpose of adjusting the waste water ratio of the membrane element. Thus, the waste water ratio device can be saved, and the product cost can be reduced. Experiments are carried out on different membrane elements by changing the size of the opening 21, the first preset ratio range can be 0-1, and the purpose of adjusting the wastewater ratio of the membrane elements can be achieved by changing the size of the opening 21 in the range. Secondly, when being provided with waste water than the device simultaneously, borrow by above-mentioned structure and play certain effect of adjusting waste water ratio, and then can increase the aperture of the waste water ratio device of use to can effectively prevent the jam of waste water ratio device.

In one embodiment, the flow rate control means may include a baffle plate disposed at an outlet of the raw water flow passage. The baffle may be provided on the filtration membrane 11 at the raw water flow passage outlet, specifically, may be provided on the inner wall of the outermost layer of the filtration membrane 11 after winding, or may be provided on the outer wall of the second layer of the filtration membrane from the outside to the inside of the filtration membrane 11 after winding. Generally, after the baffle is arranged, the cross-sectional area of the outlet of the raw water channel is reduced, so that when the waste water in the raw water channel flows out from the outlet of the raw water channel, the baffle has a certain control effect on the flow velocity of the waste water, the reduction degree of the flow velocity of the waste water is reduced, the precipitation of pollutants in the waste water at the outlet of the raw water channel can be reduced, and the pollution degree of the outlet of the raw water channel of the filtering membrane 11 is reduced.

In one embodiment, the flow rate control means includes an extension portion provided at the raw water flow passage outlet of the filtering membrane 11 and extending in a winding direction of the filtering membrane 11, and a cross-sectional area of a flow passage formed between the extension portion and the filtering membrane 11 is smaller than a cross-sectional area of a raw water flow passage in the filtering membrane. In the present embodiment, the extension part may be provided at the outermost end of the wound filtering membrane 11 and continuously wound in the winding direction of the filtering membrane 11, as in the winding form of the filtering membrane 11, and the flow passage formed between the wound extension part and the filtering membrane 11 is communicated with the raw water flow passage in the filtering membrane 11 and has a cross-sectional area smaller than that of the raw water flow passage in the filtering membrane 11. When a certain amount of wastewater flows out from the outlet of the raw water channel to the channel formed between the extension and the filtering membrane 11, the flow velocity of the wastewater is increased. When the waste water flows out of the flow channel formed between the extension part and the filtering membrane 11, the extension part has a certain control function on the flow speed of the waste water, so that the reduction degree of the flow speed of the waste water is reduced, the possibility that pollutants are precipitated in the waste water at the opening of the flow channel is reduced, and the degree of pollution at the outlet of the raw water flow channel of the filtering membrane 11 is reduced. Secondly, when the wastewater flows out of the flow channel formed between the extension part and the filtering membrane 11, due to the arrangement of the extension part, pollutants in the wastewater are precipitated on the extension part and are not directly precipitated on the filtering membrane, so that the pollutants do not directly influence the filtering membrane 11, and the service life of the membrane element can be effectively prolonged.

In one embodiment, the filtering membrane 11 may be one of a reverse osmosis membrane and a nanofiltration membrane, and of course, the type of the filtering membrane 11 is not limited to the above description, and any other filtering membrane 11 that can filter water may be used in the present embodiment. Other modifications are possible in light of the above teachings, but are intended to be covered by the present disclosure as long as the functions and effects of the present disclosure are the same or similar.

The embodiments in the present specification are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A membrane element, comprising:

characterized in that, filtration membrane is including setting up the graticule mesh of raw water runner, the membrane element still includes:

a flow rate control device communicated with the outlet of the raw water flow passage for controlling the speed of the fluid flowing through the flow rate control device; the flow rate control device comprises a membrane protection device, the membrane protection device is sleeved outside the filtering membrane and is provided with at least one opening communicated with the outlet of the raw water flow channel, the membrane protection device leads the fluid flowing out of the outlet of the raw water flow channel out of the membrane protection device through the opening, and the membrane protection device comprises a cylinder body made of rigid materials;

the membrane element also comprises a membrane shell for accommodating the filtering membrane and the membrane protection device, and the clearance between the membrane protection device and the filtering membrane is smaller than the clearance between the membrane protection device and the membrane shell; the ratio of the flow rate of the water flowing out of the opening to the flow rate of the water flowing in from the inlet of the raw water flow channel accords with a first preset ratio range; the first preset ratio ranges from 0 to 1.

2. The membrane element according to claim 1, wherein a gap between the membrane protection device and the filtration membrane ranges from a thickness of the raw water flow passage of the membrane element to a gap between the membrane element and the membrane housing.

3. A membrane element as claimed in claim 1, characterized in that the membrane protection means comprise a flexible part which is coated outside the filter membrane.

4. A membrane element as claimed in claim 3, wherein the membrane element includes first and second end caps provided at both ends of the filter membrane, and the flexible member is sealed from the first and second end caps by glue, respectively.

5. A membrane element as claimed in claim 3, wherein the flexible member is of polypropylene or polyester material.

6. A membrane element as claimed in claim 1, wherein the spacing between the inner side wall of the cartridge and the outer side wall of the filter membrane is the thickness of the grid.

7. A membrane element as claimed in claim 1, wherein the membrane element comprises a first end cap and a second end cap disposed at both ends of the filter membrane, the first end cap and the second end cap being respectively connected to the cartridge.

8. A membrane element as claimed in claim 1, wherein the rigid material is one of polypropylene, ABS plastic, polyamide plastic, polyoxymethylene and stainless steel material.

9. A membrane element according to claim 1, wherein the outlet of the raw water flow path is located on a short side when the filtration membrane is expanded.

10. A membrane element as claimed in claim 1, wherein the filtration membrane is one of a reverse osmosis membrane and a nanofiltration membrane.

11. A membrane element as claimed in claim 1, wherein the flow rate control means comprises a baffle plate provided at an outlet of the raw water flow channel.

12. A membrane element according to claim 1, wherein the flow rate control means includes an extension portion provided at a raw water flow passage outlet of the filtration membrane and extending in a winding direction of the filtration membrane, and a cross-sectional area of a flow passage formed between the extension portion and the filtration membrane is smaller than a cross-sectional area of a raw water flow passage in the filtration membrane.