Method for cleaning a filter

Abstract

The invention relates to a method for cleaning filters (10) having a filter housing (11), wherein the filter (10) has two opposite inlet connections (12a, 12b), at least one outlet connection (14a) and at least one membrane (24), wherein the outlet connection (14a) is separated from the inlet connections (12a, 12b) by the at least one membrane (24) and wherein the membrane (24) has a lumen (25) connecting the two inlet connections (12a, 12b) to one another, which has an inner diameter of 180-600µm and a length of 50 to 200 cm, said method comprising the following steps: - blocking the outlet connection (14a); - introducing fluid, in particular raw fluid, into a first inlet connection (12a); - opening the second inlet connection (12b) to discharge the fluid.

Description

[0001] Procedure for cleaning a filter

[0002] Field of the invention

[0003] The invention relates to a method for backwashing and cleaning filters, in particular industrial filters.

[0004] State of the art

[0005] Ultrafilters for water filtration must be washed regularly to restore their filtration capacity. Typically, this involves backwashing the filter, in which water is introduced from the clean side of the filter and passed through the filter to the raw water side, washing the filtered particles from the filter. The water used for this backwash process must therefore be free of contaminants to avoid contaminating the clean side of the filter. This contaminant-free backwash water typically comes from a separate tank or a second ultrafilter running in parallel with the first ultrafilter. In backwash mode, the raw water is filtered by the second ultrafilter and then directed to the outlet of the ultrafilter to be cleaned.From there, this clean water flows through the membrane of the ultrafilter being cleaned to the feed side, flushing particles out of the membrane and out through the feed side inlet into a drain. After this ultrafilter has been cleaned, the process can be reversed, and the second ultrafilter can be cleaned with the first ultrafilter. Such a two-filter system provides a continuous source of clean water for backwashing. Furthermore, the fluid flow through the membrane structure flushes particles out of the membrane pores.

[0006] However, this approach always requires at least two interconnected ultrafilters, or a container filled with filtered water that can be connected to the ultrafilter. A two-filter system is therefore considerably more costly, and there is high resistance for the backwash water to reach the core of the membrane bundle. This can lead to unbalanced fiber cleaning. Furthermore, parts of the membrane bundle may be more easily damaged due to the high pressure required.

[0007] Description of the invention

[0008] The object of the invention is therefore to provide a method by which an ultrafilter can be cleaned in a simple manner without the aid of another filter or a container filled with filtered water and by which, in particular, a high degree of uniformity of cleaning down to the core of the membrane bundle is achieved.

[0009] This object is achieved by a method according to claim 1. Further features embodying the invention are contained in the subclaims.

[0010] The method according to the invention for backwashing and cleaning filters with a filter housing, wherein the filter has two opposite inlet connections, at least one outlet connection and at least one membrane, wherein the outlet connection is separated from the inlet connections by the at least one membrane and wherein the membrane has a lumen, in particular a cylinder-shaped lumen, which connects the two inlet connections to one another and has an inner diameter of 180-600 pm, in particular at least 200 pm, in particular 230, to at most 400 pm or 300 pm, and a length of at least 50 cm, preferably 70 cm or 100 cm, and at most 200 cm, in particular 150 cm or 120 cm, comprising the steps of blocking the outlet connection, introducing fluid, in particular raw fluid, into a first inlet connection and opening the second inlet connection to discharge the fluid.By blocking the outlet connections and the design of the membrane, the membrane is able to first filter the water it is being cleaned with in the area of ​​the flow inlet. This filtrate is then returned to the lumen of the membrane in the area of ​​the flow outlet by backwashing, which constitutes the cleaning process. This provides a simple way to clean a single ultrafilter without the need for additional filters or auxiliary equipment to provide purified water. Ultrafilter backwashing for a single filter enables the construction of systems with minimal hydraulic complexity. This process is very cost-effective and capable of producing clean water between two backwash cycles. Furthermore, a two-filter system can achieve continuous flow around the clock and can even operate intermittently if one ultrafilter is defective.In addition, a defective filter has no effect on the intact filter and does not contaminate the clean side with biomaterial or other dirt.

[0011] After the fluid has been discharged, in one embodiment, the second inlet port is used to introduce the fluid, and the fluid is discharged through the first inlet port. This ensures that both end regions of the membrane and also the entire length are flushed and cleaned particularly evenly. Furthermore, the inlet ports are preferably arranged one above the other, in particular aligned with one another and preferably arranged coaxially, and backwashing preferably occurs first from bottom to top and then vice versa. As a result, gravity can increase the pressure difference of the cleaning fluid during the second backwash, making cleaning more effective.

[0012] Preferably, after backflushing, the introduction of the fluid is stopped and air or gas is introduced through an inlet port and / or the outlet port for gas purging. This reliably removes the cleaning fluid and any residual contaminants that were not removed from the pores during backflushing, for example, which is particularly ensured when the gas is introduced through the outlet port. Introducing the gas through the inlet port is advantageous if contaminants trapped on the inner surface of the membrane lumen are to be removed by shearing. This air purge also takes advantage of the pressure difference of the ultrafilters used and ensures thorough cleaning of the membrane. Furthermore, the gas can be introduced into the outlet port, with one inlet port blocked and one open.This allows specific parts of the membrane to be additionally cleaned with gas. In another embodiment, air can be introduced simultaneously to the outlet port through the upper or lower inlet port, while the other inlet port serves as the drain. This ensures that the central region along the length of the membrane bundle is subjected to particularly thorough cleaning.

[0013] As a further step, one inlet port can be opened to the atmosphere, while the other inlet port, especially the lower inlet port, serves as a drain. This removes all fluid from the filter and terminates the cleaning process, allowing the filtration process to begin again. Additionally, air can be reintroduced into the outlet port during emptying to assist the emptying process and remove any remaining contaminants.

[0014] During the process, an integrity test may preferably be performed, particularly after the first air purge, to test the function of the filter and ensure that the filter is operating at its optimal level.

[0015] Brief description of the figures Figure 1 shows a schematic representation of a filter for the method according to the invention;

[0016] Figure 2 shows an enlarged, not to scale, view of a fiber with a membrane;

[0017] Figures 3a-f show different stages of the process according to the invention.

[0018] Description of the preferred embodiments

[0019] Figure 1 shows a schematic representation of a filter 10 with which the method according to the invention can be carried out. This filter 10 has a filter housing 11 and at least two inlet connections 12a, 12b into which raw water is introduced during normal operation. This raw water then flows through the filter device 20 to at least one outlet connection 14a. However, two or more outlet connections 14a, 14b are preferably provided. The inlet connections 12a, 12b are arranged one above the other and, in particular, on opposite sides or concentrically.

[0020] The filter device 20 comprises a plurality of fibers 22, each enclosing a membrane 24. The fibers 22 extend along the filter's longitudinal axis and are clamped at the upper and lower ends in a holding device 21 that secures the fibers in the filter 10. The holding device is porous, allowing the raw water to flow unhindered into the membrane 24. The membrane 24 is preferably cylindrical and encloses a lumen 25 (cavity) that extends between the inlet ports 12a, 12b and connects the inlet ports 12a, 12b to one another.

[0021] Figure 2 shows a not-to-scale enlargement of the membrane 24 and the lumen 25. The lumen 25 has an inner diameter of 180 to 600 μm, or the minimum and maximum dimensions previously mentioned. The very narrow diameter of the lumen, compared to conventional fibers, ensures that the raw water flowing into the filter through the inlet connections is slowed down in this lumen. This is important for the process explained below and leads to an unexpected effect that enables backwashing as a single filter. Diameter The length of the lumen, i.e. the longitudinal extent, is between 50 and 200 cm, in particular between 70 and 150 cm, and further in particular between 70 and 120 cm.

[0022] During normal operation, raw water flows into the inlet connections 12a, 12b. From there, it enters the lumen of the fibers via the pores in the holding device 21 and is filtered to the filtrate side as it passes through the membrane 24 and then pumped out of the outlet connections 14a, 14b. Figures 3a to 3f show various steps of the process, although the filter is only shown schematically. Figure 3a shows the first step, in which the outlet connections 14a, 14b are blocked so that no more filtered water can escape. Raw water is then poured into the filter 10 through an inlet connection, here the lower connection 12b. This fills the filtrate side with filtered water, which cannot flow out. The flow resistance in the longitudinal direction in the lumen 25 creates a pressure drop.In Figure 3a, the pressure at the top of the lumen 25 (i.e., on the side of the inlet connection 12a) is lower than at the bottom, where the raw water is pumped into the filter 10. Additionally, the water pushes toward the filtrate side of the membrane 24, so that the filtered water on the top side must flow through the membrane back to the raw water side, thus removing the contaminants in the pores of the membrane and cleaning them. The fiber bundle is therefore cleaned only by longitudinal shear forces and reduced flow. In principle, the filter device 20 can be at least partially cleaned using this procedure.

[0023] Figure 3b shows the preferred step, in which the flow direction is then reversed. By reversing the flow direction, the opposite part (here the lower part) of the fiber bundle is cleaned in the same way by backfiltration. Because the water penetrates all fibers in parallel, the flow conditions at the inner fibers of the fiber bundle are similar to those at the outer fibers, so that essentially all fibers are cleaned evenly. Although the upper and lower ends of the fibers are cleaned better than the middle, reversing the backwash ensures that this effect is reduced, i.e., that the fibers experience a certain amount of backwash along the entire fiber.

[0024] Figure 3c illustrates the preferred air purification process. Another medium, such as gas or air, is connected to the upper inlet port 12a and introduced there. Using ambient pressure, gravity, and / or pressurized gas or air, the liquid is emptied from the lumen and conveyed to the other inlet port 12b. There, the purification liquid is then disposed of into a drain. The phase boundary between liquid and gas increases the shear stress on the inner surface of the membrane and helps transport the contaminants to the drain. Gas purification also occurs equally on the inner and outer fibers. This process can be reversed for the inlet ports 12a, 12b.

[0025] Figures 3d-f show further gas purification options. In Figure 3d, the lower inlet port 12b is closed, and air is introduced via one or more outlet ports 14a, 14b. In addition to the outlet ports, the lower inlet port 12b can also be reconnected to a gas port (Figure 3e). This process can also be reversed for the inlet ports 12a, 12b.

[0026] For the outlet connections, it makes no difference for cleaning purposes which outlet connections 14a, 14b are supplied with gas. However, if multiple outlet connections 14a, 14b are used simultaneously, the gas supply can be increased. In contrast, for the inlet connections 12a, 12b, it makes a difference when and how the upper or lower inlet connection 12a, 12b is filled with gas or raw water, or whether it is opened to the environment or to a drain.

[0027] When cleaning is performed from the top, the backwashed volume generates shear forces along the entire fiber length, transporting the dirt particles out of the filter. The addition of air into the lumen from below creates turbulent phase boundaries between liquid and air, which enhances the cleaning effect of this upward flush.

[0028] If the drain is open at the bottom and the inlet connection is closed at the top, the water stagnates on the upper inlet side and remains there in the filter. In this case, the filtrate side may be completely drained while the inlet side is still full. If the inlet side is also to be drained, the corresponding inlet connection 12a, 12b must be opened to the atmosphere.

[0029] Furthermore, an integrity test can be performed during the backwash process or gas cleaning to detect damage to the fibers and membranes.

[0030] The effective and efficient recovery of filter capacity depends heavily on the type of contaminants in the raw water. In principle, the process steps can be performed individually, but it is preferable to use the various process steps, including the initial filling process, in combination and / or repeatedly, so that all requirements regarding filter life, time, and water consumption are met.

[0031] A possible cleaning process can be structured as follows:

[0032] Step 1: Flush from bottom to top; Step 2: Flush from top to bottom; Step 3: Air purge; Step 4: Integrity test; Step 5: Empty the filtrate upwards with air from below; Step 6: Air purge; Step 7: Filter filling.

[0033] List of reference symbols: Filter

[0034] Filter housing a, 12b Input connections a, 14b Output connections Filter device Holding device Fiber

[0035] membrane

[0036] lumens

Claims

Patent claims 1. A method for cleaning filters (10) with a filter housing (11), wherein the filter (10) has two opposite inlet ports (12a, 12b), at least one outlet port (14a) and at least one membrane (24), wherein the outlet port (14a) is separated from the inlet ports (12a, 12b) by the at least one membrane (24) and wherein the membrane (24) has a lumen (25) connecting the two inlet ports (12a, 12b) to one another, which lumen has an inner diameter of 180-600 μm and a length of 50 to 200 cm, comprising the steps: - blocking the output terminal (14a); - introducing fluid, in particular raw fluid, into a first inlet connection (12a); - Opening the second inlet port (12b) to discharge the fluid.

2. Method according to claim 1, wherein after the discharge of the fluid, the second inlet port (12b) is used to introduce the fluid and the fluid is discharged through the first inlet port (12a).

3. Method according to claim 2, wherein the inlet connections (12a, 12b) are arranged one above the other and preferably the backwashing is carried out first from bottom to top and then vice versa.

4. Method according to one of the preceding claims, in which the introduction of the fluid is stopped and gas is introduced through an inlet connection (12a, 12b) and / or outlet connection (14a, 14b) for gas purging.

5. Method according to one of the preceding claims, in which gas is introduced into the outlet connection (14a, 14b) and one inlet connection (12a, 12b) is closed and one is open.

6. Method according to claim 3 and 4, wherein gas is introduced simultaneously to the outlet connection through the upper or lower inlet connection (12a, 12b) and the other serves as an outlet.

7. Method according to one of the preceding claims, in which as a last step one inlet connection (12a, 12b) is opened to the environment and the other inlet connection (12a, 12b) serves as an outlet.

8. Method according to any preceding claim, wherein an integrity test is performed during the method.

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