A flat ceramic membrane stack

Abstract

The present invention relates to a flat ceramic membrane stack, comprising a frame (1) and a membrane stack (2), wherein the frame (1) is closed on all sides to form a cylindrical shape, and the upper and lower surfaces are open, and the membrane stack (2) is installed in the frame (1), and the frame (1) is also provided with an aeration pipe (3), and the aeration pipe (3) aerates from the bottom of the frame (1) into the cylindrical frame, so that a density difference is formed inside and outside the cylindrical frame, and external liquid and aerated bubbles enter the membrane stack (2) from the bottom of the frame (1) and flow upward, and after leaving the frame (1), the bubbles continue to rise and the liquid flows downward along the outer cylinder wall of the frame (1), forming a circulating flow. Compared with the prior art, the present invention overcomes the influence of the accumulation of dead-end filtration cake on the membrane surface on the filtration flux while retaining the advantage of high dead-end filtration recovery rate.

Description

Technical Field

[0001] The invention relates to a filtering device, in particular to a flat ceramic membrane stack. Background Art

[0002] The separation pore size of the flat ceramic membrane is 50-200nm. It is a kind of ultrafiltration membrane. It is a proprietary inorganic membrane with a flat structure and a clean water flow channel. The membrane support is made of high-purity alumina powder sintered at a high temperature of >1000℃, and the surface is coated with a functional membrane layer with a certain separation accuracy and uniform distribution. In order to ensure the separation function of the membrane, the two ends of the single diaphragm of the finished product are sealed with glue, and the sealing water collection end is made of industrial durable engineering plastics with long service life and stable physical and chemical properties to make a single flat ceramic membrane component.

[0003] If the flat ceramic membrane uses internal pressure filtration, the insoluble matter will block the water production channel. Therefore, external pressure filtration is used in engineering applications, that is, the pollutants are retained on the outer surface of the membrane, and the permeate passes through the membrane layer and collects in the water production channel. The membrane element is placed in the material or water to be filtered. The material larger than the pore size of the membrane layer is retained on the outside of the separation layer. The clean filtered water passes through the separation layer and the support body under pressure and enters the water collection channel inside the membrane element, and then enters the water production pipeline of the membrane component from the packaged water collection end.

[0004] Different numbers of membrane modules are connected together to form a membrane stack. Depending on the actual situation, the flat ceramic membrane modules can be installed in vertical or horizontal frames and installed naked on the frames. Each ceramic membrane is connected by a pipe and collected to the water production main pipe. The water production main pipe is connected to the suction pump. The pressure difference between the inside and outside of the membrane formed by the negative pressure generated by the suction pump and the atmospheric pressure of the liquid surface is used as the driving force for filtration.

[0005] Since the membrane stack is immersed in liquid, when the suction pump is started, a certain negative pressure is formed between the membrane water collection channel and the outer surface of the membrane, and the liquid passes through the separation layer into the water collection channel. The insoluble matter is retained on the outer surface of the membrane to form a filter cake. Due to the formation of the filter cake, the filtration resistance increases and the filtration flow gradually decays. Therefore, the current flat ceramic membrane stack can only be a typical dead-end filtration method. The schematic diagram is shown in the figure. Figure 1 Although this filtration method has a high recovery rate, due to the attenuation of the flow rate, in order to meet the production capacity requirements, a higher average filtration flow rate can only be obtained by increasing the filtration area. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a flat ceramic membrane stack with high filtration recovery rate and capable of overcoming the influence of filter cake accumulation on filtration flux.

[0007] The object of the present invention can be achieved through the following technical scheme: a flat ceramic membrane stack, including a frame and a membrane stack, the frame is closed on all sides to form a cylindrical shape, and the upper and lower surfaces are open, the membrane stack is installed in the frame, and the frame is also provided with an aeration pipe, the aeration pipe aerates from the bottom of the frame into the cylindrical frame, so that a density difference is formed inside and outside the cylindrical frame, and the external liquid and the aeration bubbles enter the membrane stack from the bottom of the frame and flow upward. After leaving the frame, the bubbles continue to rise and the liquid flows downward along the outer cylindrical wall of the frame to form a circulating flow.

[0008] The membrane stack is provided with at least one layer, and each layer of the membrane stack includes a plurality of flat ceramic membranes, and each flat ceramic membrane includes a separation layer on the side and a water collection channel in the middle.

[0009] One end of the water collection channel is blocked, and the other end is connected to the clear liquid main pipe, which is connected to a suction pump. The suction pump creates a pressure difference inside and outside each flat ceramic membrane. Driven by the pressure difference, the water to be treated passes through the separation layer and enters its internal water collection channel. Materials larger than the micropore diameter of the flat ceramic membrane are retained on the outside of the separation layer.

[0010] An aeration pipe is provided under each membrane stack, and aeration pipe delivers a large amount of air bubbles between each flat ceramic membrane to scrub the insoluble matter trapped on the surface of each flat ceramic membrane.

[0011] Aeration is another key factor in forming the pressure difference between the inside and outside of the membrane stack to make the filtered liquid circulate. The amount of air, the rising speed of the bubbles and the flow of the liquid are particularly important. The amount of aeration used for each membrane stack is not less than 2m 3 / min.

[0012] The membrane stack is in the shape of a hexahedron, and the installation methods include horizontal installation or vertical installation. No matter whether it is vertical installation or fixed installation, as long as the outer surface of the membrane is perpendicular to the horizontal plane, the four surfaces of the membrane stack hexahedron perpendicular to the horizontal plane are sealed with flat plates, and the flat plates are fixed on the frame to form a cylindrical shape closed on all sides.

[0013] The material of the plate used for sealing depends on the material properties of the filtered liquid. The mold frame can be the same. It can be made of metal materials such as SS304, SS316L, Ti, Al, or organic polymer materials with a certain hardness such as PVC, CPVC, PP, ABS, etc.

[0014] Since the sealed flat plate is subjected to relatively little pressure, the thickness of the flat plate should be no less than 2 mm, preferably 2 mm to 5 mm.

[0015] The height of the membrane stack is also one of the factors that affect the liquid flow rate. Considering the installation density, the height of each membrane stack should not be less than 1 meter to ensure that the bubbles rise and drive the liquid to reach a certain flow rate, while bringing out the insoluble matter trapped on the membrane surface; the height of each membrane stack is preferably 1 to 2.5 meters.

[0016] The flat ceramic membrane stack is placed in the filter tank. In order to ensure the smooth circulation of the liquid, the lowest layer of the membrane stack cannot be placed directly on the bottom of the membrane tank. A liquid circulation channel needs to be left with a height of not less than 20 cm. Preferably, the distance between the bottom of the lowest layer of the membrane stack and the bottom of the filter tank is 20 cm to 40 cm.

[0017] A mud hopper is provided at the bottom of the filter tank. The insoluble matter carried away from the membrane surface by the liquid circulation flow formed by air scrubbing is deposited in the mud hopper at the bottom of the membrane tank and discharged regularly. The sludge is pumped to the sludge dewatering device in the form of slurry through a slurry pump. The sludge is pumped into the sludge dewatering equipment by the slurry pump for dehydration to obtain filtered liquid and mud cake. The dehydrated filtered liquid returns to the flat ceramic membrane tank;

[0018] The sludge slurry is pumped into the sludge dewatering equipment by a sludge pump. The sludge dewatering equipment is a plate and frame filter press, a screw press, a vacuum filter, a belt filter, etc., preferably a plate and frame filter press. The filtrate of the filter press is returned to the membrane pool.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) In order to transform the dead-end filtration of the flat ceramic membrane into cross-flow filtration, the present invention overcomes the influence of the accumulation of the dead-end filtration cake on the membrane surface on the filtration flux while retaining the advantage of high recovery rate of dead-end filtration. The four side walls of the hexahedral structure of the membrane stack are sealed, leaving only the top and bottom to maintain the flow of liquid; aeration is performed at the bottom. During aeration, the bubbles rise to drive the liquid flow and the particles to rise at the same time. When the bubbles reach the top of the membrane stack, they continue to rise, and the liquid outside the membrane stack flows downward and enters the membrane stack from the bottom. While the insoluble matter flows downward with the liquid, some particles participate in the circulation, and some particles are deposited at the bottom of the membrane pool. As the liquid in the membrane stack flows upward and the liquid outside the membrane stack flows downward, a circulation flow of the liquid in the membrane pool inside and outside the membrane stack is formed, so that the filtration direction is perpendicular to the liquid flow direction. The flowing liquid takes the insoluble matter trapped on the membrane surface out of the membrane stack, and is accelerated by the liquid flowing downward from the outside, and the large particles of insoluble matter are deposited at the bottom of the membrane pool. The slurry at the bottom can be sent to the sludge dewatering device by a slurry pump, the dry slag is discharged, and the filtrate returns to the membrane pool for continued membrane filtration.

[0021] (2) Conventional flat ceramic membrane stacks are generally equipped with air scrubbing devices, which remove particles on the membrane surface through aeration bubbles. However, since only bubbles rise, liquid circulation cannot be formed; in addition, the rising bubbles also affect the sedimentation of insoluble matter, making subsequent sludge dehydration more difficult. The flat ceramic membrane stack with a new structure of the present invention can make the liquid inside and outside the membrane stack circulate without affecting the sedimentation of insoluble matter.

[0022] (3) While retaining the high recovery rate of the original flat ceramic membrane dead-end filtration, the present invention changes the dead-end filtration mode to a cross-flow filtration mode by changing the structure and function of the flat ceramic membrane stack, resulting in a large and stable filtration flow rate.

[0023] (5) Since the average flux of the new structure flat ceramic membrane filtration is higher, the system investment and land occupation can be greatly reduced.

[0024] (6) Compared with the typical cross-flow filtration method of tubular ceramic membranes, the new structure of flat ceramic membranes has lower filtration (transmembrane pressure difference ΔP < 0.1MPa), thus continuing to maintain the advantage of low energy consumption of flat ceramic membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The existing flat filter membrane filtration principle diagram

[0026] Figure 2 It is a schematic diagram of the structure of the flat ceramic membrane stack of the present invention;

[0027] Figure 3 A top view of a flat ceramic membrane stack of the present invention;

[0028] Figure 4 This is a schematic structural diagram of the flat ceramic membrane stack of the present invention after removing the sealing flat plate;

[0029] Figure 5 It is a schematic diagram of the structure of the flat ceramic membrane stack of the present invention placed in the filter tank;

[0030] Figure 6 It is a framework diagram of the flat ceramic membrane stack of the present invention placed in the filter tank;

[0031] Figure 7 Schematic diagram of the structure of a flat filter membrane;

[0032] Figure 8 for Figure 7 AA section view;

[0033] Fig. 9 for Figure 8 A partial enlarged view of

[0034] Fig.10 It is a schematic diagram of fluid flow between adjacent flat ceramic membrane sheets;

[0035] Fig.11 This is the schematic diagram of cross-flow filtration. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] like Figure 2-4 As shown, a flat ceramic membrane stack includes a frame 1, a membrane stack 2, an aeration pipe 3, and a clear liquid main pipe 4.

[0039] Among them, the frame 1 includes a support frame for installing the membrane stack 2, and a flat plate 11 arranged around the support frame. The membrane stack 2 is in a hexahedral shape, and the installation method includes horizontal installation or vertical installation. Whether it is vertical installation or permanent installation, as long as the outer surface of the membrane is perpendicular to the horizontal plane, the four surfaces of the hexahedron of the membrane stack 2 perpendicular to the horizontal plane are sealed with a flat plate 11, leaving only the top and bottom surfaces open, so that the frame 1 is in a cylindrical shape with four sides closed.

[0040] The aeration pipe 3 and the clear liquid main pipe 4 are installed on the frame 1. The aeration pipe 3 includes an aeration main pipe and an aeration branch pipe. The aeration main pipe is provided with an aeration pipe opening flange 31 for connecting an air pump. A plurality of aeration branch pipes are led out according to the number of membrane stacks 2. Each aeration branch pipe is located under a different membrane stack 2, and a plurality of aeration openings are opened on the aeration branch pipe. The compressed air SO2 delivered by the air pump is delivered to the aeration branch pipe through the aeration main pipe and enters the membrane stack through the aeration opening.

[0041] The membrane stack 2 is installed in the frame 1. The membrane stack 2 has at least one layer. Each layer of the membrane stack 2 includes a plurality of flat ceramic membranes. Each flat ceramic membrane includes a separation layer 21 on the side and a water collection channel 22 in the middle. Figure 7-9 As shown, one end of the water collection channel 22 is blocked, and the other end is connected to the clear liquid main pipe 4 through the water production branch pipe 42. The clear liquid main pipe 4 is provided with a flange 41 for connecting a suction pump. The suction pump forms a pressure difference inside and outside each flat ceramic membrane. Driven by the pressure difference, the liquid S01 to be treated passes through the separation layer 21 and enters the internal water collection channel 22. The clear liquid S03 enters the clear liquid main pipe 4 through the water production branch pipe 42 and is extracted. The material larger than the micropore diameter of the flat ceramic membrane is retained on the outside of the separation layer 21. Fig.10 As shown, an aeration pipe 3 is provided under each membrane stack 2, and the aeration pipe 3 transports a large number of bubbles between each flat ceramic membrane to perform air scrubbing on the insoluble matter trapped on the surface of each flat ceramic membrane.

[0042] like Figure 5-6 As shown, the flat ceramic membrane is stacked in the filter tank 5, the frame 1 is cylindrical, and the aeration pipe 3 aerates from the bottom of the frame 1 into the cylindrical frame. During aeration, the density of the liquid in the cylinder is reduced due to a large number of bubbles, and the liquid outside the cylinder still maintains the original density, thus forming an inside-outside density difference. The external treated liquid S01 and the aerated bubbles enter the membrane stack 2 from the bottom of the frame 1 and flow upward. After leaving the frame 1, the bubbles continue to rise and the liquid flows downward along the outer cylinder wall of the frame 1, forming a circulating flow.

[0043] Aeration is another key factor in forming the pressure difference between the inside and outside of the membrane stack to make the filtered liquid circulate. The amount of air, the rising speed of the bubbles and the flow of the liquid are particularly important. The aeration volume used for each membrane stack is not less than 2m 3 / min, preferably 2-30m 3 / min. In this embodiment, the aeration rate is 22m / min for each membrane stack. 3 / min.

[0044] The material of the plate 11 used for sealing can be determined according to the material properties of the filtered liquid, and can be the same as the frame 1, and can be made of metal materials such as SS304, SS316L, Ti, Al, or organic polymer materials such as PVC, CPVC, PP, ABS, etc. with a certain hardness. In this embodiment, PVC material is used.

[0045] Since the sealed flat plate is subjected to less pressure, the thickness of the flat plate is not less than 2 mm, preferably 2 mm to 5 mm. The thickness of the flat plate 11 used in this embodiment is 2 mm. On the one hand, it has a sealing effect, and on the other hand, it can be used as a guide plate. That is, in the process of circulating flow, a large number of bubbles are rubbed on the membrane surface to take away large particles trapped on the membrane surface to prevent them from being deposited on the membrane surface. The large particles move from bottom to top in the sealed cylinder with the bubbles and the fluid. After leaving the cylinder, they can sink to the bottom of the filter tank 5 along the flat plate 11. At this time, the flat plate 11 can be used as a guide plate to guide the mud.

[0046] The height of the membrane stack is also one of the factors that affect the flow rate of the liquid. Taking the installation density into consideration, the height of each membrane stack should be no less than 1 meter to ensure that the bubbles rise and drive the liquid to reach a certain flow rate, while bringing out the insoluble matter trapped on the membrane surface; the height of each membrane stack is preferably 1 to 2.5 meters, and the membrane stack height used in this embodiment is 1 meter.

[0047] like Figure 5-6 As shown, the flat ceramic membrane stack is placed in the filter tank 5. In order to ensure the smooth circulation of the liquid, the lowest layer of the membrane stack cannot be placed directly on the bottom of the membrane tank. A liquid circulation channel is required, and its height is not less than 20 cm. Preferably, the distance between the bottom of the lowest layer of the membrane stack and the bottom of the filter tank is 20 cm to 40 cm. In this embodiment, the distance is 20 cm.

[0048] A mud hopper 6 is provided at the bottom of the filter tank 5. The insoluble matter carried away from the membrane surface by the liquid circulation flow formed by air scrubbing is deposited in the mud hopper at the bottom of the membrane tank and discharged regularly. The sludge is pumped to the sludge dewatering device in the form of slurry through a slurry pump. The sludge is pumped into the sludge dewatering equipment by the slurry pump for dehydration to obtain filtrate and mud cake, and the dehydrated filtrate is returned to the flat ceramic membrane tank; the sludge slurry is pumped into the sludge dewatering equipment by the slurry pump. The sludge dewatering equipment is a plate and frame filter press, a screw press, a vacuum filter, a belt filter, etc., preferably a plate and frame filter press. The filtrate of the filter press returns to the membrane tank.

[0049] With the above structure of the present invention, the water inlet direction is perpendicular to the water production direction. Fig.11 As shown, part of the influent water carries insoluble matter and is discharged as concentrated water. Filter cake accumulation and concentration polarization are not easy to occur on the membrane surface. The filtration flow is relatively stable, the effective operation cycle is long, the filtration flux can be increased, and the filtration recovery rate is high.

[0050] Comparative Example 1

[0051] Commercially available flat ceramic membrane stack.

[0052] The two flat ceramic membrane stacks of Example 1 and Comparative Example 1 are placed in a filter tank filled with crude brine. Negative pressure suction is performed by a suction pump, and the trans-membrane pressure difference ΔP<0.1MPa. Insoluble substances such as calcium carbonate, magnesium hydroxide, and silt in the crude brine are retained on the surface of the flat ceramic membrane and are carried away from the surface of the flat ceramic membrane by circulating brine formed by air scrubbing. The brine passes through the flat ceramic membrane to obtain refined brine.

[0053] The results are shown in Table 1 below:

[0054]

[0055]

[0056] Note: Each backwash needs to remove the negative pressure in the membrane assembly (about 10 seconds), use the backwash pump to pump the filtered liquid from the clean liquid pipe into the membrane assembly in the reverse direction (about 30 seconds), and the insoluble matter removed from the surface of the membrane assembly settles for about 40 seconds. The total time is about 80 seconds, which is the invalid filtration time. The more frequent the backwashing, the longer the invalid filtration time, and the lower the filtration efficiency.

[0057] It can be seen that: under the same material conditions, the new structure flat ceramic membrane stack retains the high recovery rate of the old structure flat ceramic membrane stack, the filtration flux is larger and more stable, the backwash cycle can be greatly extended, the filtration efficiency is higher, the insoluble matter sedimentation effect is better, and the solid content in the sludge is higher.

[0058] In the above embodiment, the transmembrane pressure difference ΔP is 0.08 MPa. Under this condition, the filtration recovery rates of Example 1 and Comparative Example 1 are both 100%. However, if the suction pressure P is reduced, the filtration fluxes of Example 1 and Comparative Example 1 will be very different, as shown in Table 2 below:

[0059] Transmembrane pressure difference ΔP (MPa) Example 1 Comparative Example 1 ～0.08 <![CDATA[0.22~0.16m 3 / m 2 .h]]> <![CDATA[0.2~0.05m 3 / m 2 .h]]> 0.06 <![CDATA[0.22~0.15m 3 / m 2 .h]]> <![CDATA[0.18~0.04m 3 / m 2 .h]]> 0.05 <![CDATA[0.18~0.14m 3 / m 2 .h]]> <![CDATA[0.1~0.01m 3 / m 2 .h]]> 0.01 <![CDATA[0.05~0.02m 3 / m 2 .h]]> 0 0.001 <![CDATA[0.02~0.01m 3 / m 2 .h]]> 0

[0060] It can be seen that the filtration flux of the flat ceramic membrane stack of the present invention can still be maintained at 0.18-0.14 m / s when the transmembrane pressure difference ΔP is reduced to 0.05 MPa. 3 / m 2 .h, when reduced to 0.01MPa, it can still reach 0.05~0.02m 3 / m 2 .h, but the filtration flux of the membrane stack of comparative example 1 has been reduced by 50% to 20% when the transmembrane pressure difference ΔP is 0.05MPa. When the transmembrane pressure difference ΔP is reduced to 0.01MPa, comparative example 1 can hardly complete the filtration task, indicating that the flat ceramic membrane stack of the present invention has lower filtration energy consumption (transmembrane pressure difference ΔP<0.1MPa).

[0061] Aeration is another key factor in forming the pressure difference between the inside and outside of the membrane stack to make the filtered liquid circulate, and the amount of gas, the rising speed of the bubbles and the driving of the liquid flow are particularly important; the following is the filtration results of the membrane stack with the same structure in Example 1 under different aeration rates as shown in Table 3

[0062] The results are shown in Table 1 below:

[0063]

[0064]

[0065] Comparative Example 2

[0066] The height of the membrane stack is also one of the factors that affect the liquid flow rate. When the height of the membrane stack is reduced to 0.5 meters and the rest is the same as in Example 1, under the same testing conditions as in Example 1, the results are shown in Table 4 below:

[0067]

[0068] From the above, it can be seen that even if the structure is the same as that of the present invention, if the aeration volume and the membrane stack height are not controlled, the filtering effect will be greatly affected.

Claims

1. A flat ceramic membrane stack, characterized in that: The invention comprises a frame (1) and a membrane stack (2), wherein the frame (1) is closed on all sides to form a cylindrical shape, and the upper and lower surfaces are open. The membrane stack (2) is installed in the frame (1), and the frame (1) is also provided with an aeration pipe (3). The aeration pipe (3) aerates from the bottom of the frame (1) into the cylindrical frame, so that a density difference is formed inside and outside the cylindrical frame. External liquid and aeration bubbles enter the membrane stack (2) from the bottom of the frame (1) and flow upward. After leaving the frame (1), the bubbles continue to rise and the liquid flows downward along the outer cylindrical wall of the frame (1), forming a circulating flow. The membrane stack (2) is provided with at least one layer, and each layer of the membrane stack (2) includes a plurality of flat ceramic membranes, each flat ceramic membrane including a side separation layer (21) and a middle water collection channel (22); One end of the water collection channel (22) is blocked, and the other end is connected to the clear liquid main pipe (4). The clear liquid main pipe (4) is connected to a suction pump. The suction pump forms a pressure difference inside and outside each flat ceramic membrane. Driven by the pressure difference, the water to be treated passes through the separation layer (21) and enters the water collection channel (22) inside the separation layer. Materials larger than the micropore diameter of the flat ceramic membrane are retained outside the separation layer (21). An aeration pipe (3) is provided under each membrane stack (2), and the aeration pipe (3) transports a large number of bubbles between each flat ceramic membrane to scrub the insoluble matter trapped on the surface of each flat ceramic membrane; The liquid in the membrane stack flows upward, and the liquid outside the membrane stack flows downward, forming a circulation flow of the liquid in the membrane pool inside and outside the membrane stack, so that the filtration direction is perpendicular to the liquid flow direction. The flowing liquid brings the insoluble matter trapped on the membrane surface out of the membrane stack, and the liquid flowing downward from the outside is accelerated, and the large particles of insoluble matter are deposited at the bottom of the membrane pool.

2. A flat ceramic membrane stack according to claim 1, characterized in that: The aeration volume used for each membrane stack (2) is not less than 2m 3 / min.

3. A flat ceramic membrane stack according to claim 1, characterized in that: The membrane stack (2) is in the shape of a hexahedron, and can be installed horizontally or vertically to ensure that the outer surface of each membrane in the membrane stack is perpendicular to the horizontal plane.

4. A flat ceramic membrane stack according to claim 1 or 3, characterized in that: The four faces of the hexahedron of the membrane stack (2) perpendicular to the horizontal plane are sealed with flat plates, which are fixed on the frame to form a cylindrical shape with four sides closed.

5. A flat ceramic membrane stack according to claim 4, characterized in that: The height of each membrane stack is 1~2.5 meters, and the thickness of the flat plate is 2mm~5mm.

6. A flat ceramic membrane stack according to claim 1, characterized in that: The flat ceramic membrane stack is placed in the filter tank (5), and the distance between the bottom of the lowest layer of the membrane stack and the bottom of the filter tank is 20 cm to 40 cm.

7. A flat ceramic membrane stack according to claim 6, characterized in that: A mud hopper (6) is provided at the bottom of the filter tank (5).

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