Filter device

Abstract

The invention relates to a filter device for a liquid medium, in particular for water, comprising a hollow supporting body (6) having passages (14) for the liquid medium, wherein: a first filter (8) is associated with the hollow supporting body (6); the first filter (8) is designed as a surface filter; the filter device has a backwash device (11) in order to remove impurities from the first filter (8); a second filter (9) is associated with the supporting body (6); the second filter (9) is designed as a depth filter; and the second filter has a porous body (17) made of a sintered plastics material.

Description

[0001] Filter system

[0002] The invention relates to a filter device for a liquid medium, in particular for water, comprising a hollow support body with passages for the liquid medium, wherein a first filter is associated with the hollow support body, and wherein the filter device has a backwashing device to remove impurities from the first filter.

[0003] The filtration of liquid media is carried out to remove impurities from the liquid medium. For example, it is already known to filter water from a household plumbing system, for instance to filter out particulate impurities.

[0004] US 2005 / 0115886 A1 describes a filtration device for liquid media that includes multiple filters.

[0005] Filter elements for drinking water containing activated carbon are known from RU 174 088 U1 and US 2006 / 0049096 A1. Activated carbon can also remove dissolved substances, such as chlorine, from water.

[0006] There is a need for filter systems that achieve good filtration even for small particles. Fine filters can be used for this purpose, but they have the disadvantage of tending to clog relatively quickly. This then requires manual intervention, such as replacing the filter.

[0007] The invention aims to provide a filter device that, while offering good filtration efficiency for small particles, also has a long service life. This objective is achieved by the features of claim 1. Accordingly, a filter device for a liquid medium, in particular water, is provided, comprising a hollow support body with passages for the liquid medium, wherein a first filter is associated with the hollow support body, the first filter being designed as a surface filter, the filter device having a backwashing device to remove contaminants from the first filter, and wherein a second filter is associated with the support body, the second filter being designed as a depth filter, and the second filter having a porous body made of a sintered plastic material.

[0008] These measures enable multiple filtration stages of the liquid medium. The filter system includes a first filter, designed as a surface filter. This surface filter primarily retains contaminants on its surface. A second filter, designed as a depth filter, is also included. This filter consists of a porous body made of sintered plastic material. The depth filter material contains a filter medium with recesses that trap particles. This multi-stage combination allows for the highly effective removal of particulate contaminants, even small ones, from the liquid medium. Specifically, particles larger than the pores of the first and second filters are removed during this process.With this sophisticated combination, the tendency of the filters to become clogged is significantly reduced. Furthermore, contaminants from the first filter can be removed by the backwashing system without replacing the first filter, for example, by temporarily reversing the flow direction. All these measures significantly increase the service life of the filter system. This considerably reduces maintenance effort and costs. In addition, unwanted pressure drops across the filter are avoided. The filter is particularly suitable for filtering water from a public water supply as it enters a building's plumbing system. The porous body can preferably be made of plastic particles bonded together by sintering. The filter system is suitable for various liquid media. Although it is particularly suitable for water, it can also be used for other liquid media, such as...Dispersions are used.

[0009] The following describes preferred features of the filter device that further promote the aforementioned advantages, both individually and collectively.

[0010] A preferred embodiment of the invention provides that one of the first and second filters is arranged on the inside of the hollow support body and the other of the first and second filters is arranged on the outside of the hollow support body. Preferably, the first filter is arranged on the inside and the second filter on the outside of the hollow support body.

[0011] According to the invention, it is preferred that the sintered thermoplastic material has hydrophobic properties. This contributes surprisingly to good filtration. In particular, the thermoplastic material can be nonpolar.

[0012] Preferably, the porous body comprises sintered thermoplastic material, such as polyethylene. This material not only provides good filtration but is also resistant to acids and alkalis. Furthermore, polyethylene (PE) offers advantageous hydrophobic properties.

[0013] Preferably, the porous body is designed to be open-pored.

[0014] Preferably, the porous body has filter channels through which the liquid medium can pass through the porous body.

[0015] According to the invention, it is preferred that the porous body has pores with a pore size between 5 pm and 100 pm. A mean pore size of the porous body between 10 pm and 30 pm is particularly preferred. The mean pore size can be determined using the bubble pressure test described below. Filter particles larger than the pore size are retained. This allows the second filter to filter even very small particles. A further improvement provides that the porosity of the porous body is between 40% and 60%. This contributes to good filtration efficiency and long filter service life. The porosity represents the ratio of the void volume to the total volume of the porous body.

[0016] Preferably, the porous body has a density between 1.6 g / cm³. 3 and 1.7 g / cm³ 3This contributes to good filtration efficiency and long filter lifespans. These densities can be achieved through sintering under pressure and / or the use of fillers.

[0017] An advantageous embodiment of the invention provides that the porous body exhibits a bubble point during the bubble pressure test at a pressure difference across the porous body between 0.003 bar and 0.005 bar. It has been shown that this results in good filtration with a particularly long service life.

[0018] The pressure difference at the bubble point can be determined using the bubble point test according to DIN EN 13443-2:2007-10. In this test, a filter material loaded with a liquid is pressurized from one side with a gas, and the pressure is increased until the gas displaces the liquid from the pores and passes through the filter material. This can be observed by the formation of bubbles. The pressure at which the first bubbles form is called the bubble point. The size of the largest pores can be derived from the pressure at the bubble point. By further increasing the pressure, the open bubble point can be determined, which can be considered a measure of the average pore size. Preferably, the open bubble point is reached at a pressure difference across the porous material between 0.005 bar and 0.02 bar (preferably more than 0.0075 bar and / or less than 0.015 bar).

[0019] A preferred embodiment of the invention provides that the porous body has a surface with a mean roughness (Ra) of more than 15 pm in at least a portion of the surface. Preferably, the aforementioned mean roughness (Ra) is greater than 17 pm. Preferably, the portion of the surface with the aforementioned mean roughness (Ra) comprises at least 25% (particularly preferably at least 40%) of the surface of the porous body. Preferably, the mean roughness (Ra) is less than 30 pm. The mean roughness (Ra) can be determined according to the standard DIN EN ISO 21920-2:2021-12. The invention has demonstrated that a particularly good filtering effect with a long service life can be achieved with a porous body exhibiting the aforementioned mean roughness values.

[0020] According to the invention, it is preferred that the second filter is cylindrical and has a cylindrical surface. Preferably, the filter unit is configured such that the liquid medium flows through the second filter in a direction perpendicular to the cylindrical surface. Preferably, the second filter is tubular and open at both ends.

[0021] The advantages of the invention are further enhanced if the cylindrical surface of the second filter has a material thickness between 1 mm and 5 mm. Preferably, the material thickness is more than 1.5 mm and / or less than 3 mm, and particularly preferably less than 2.5 mm.

[0022] Another preferred improvement provides that the filter unit is set up so that, during operation, the first filter is filtered before the second filter.

[0023] According to the invention, it is preferred that the first filter has filter openings with an opening width greater than 20 pm. In particular, the opening width of the filter openings of the first filter can be greater than 25 pm. Preferably, the opening width is less than 50 pm, and particularly preferably less than 35 pm. This contributes to good separation and a long service life.

[0024] Preferably, the first filter comprises a sheet-like structure with fibers, wherein passages are formed between the fibers. These passages form the filter openings. The fibers can be made of plastic and / or metal. Stainless steel is particularly preferred as the metal material. The plastic material preferably comprises a polysulfone compound, such as polyethersulfone (PES), which, in the described combination, results in particularly good filter properties with a long service life.

[0025] Preferably, the fibers are arranged in a fiber mat or fiber fabric.

[0026] A preferred embodiment provides that the woven fabric has warp and weft threads arranged with a mesh size of more than 20 pm and less than 50 pm. Preferably, the mesh size is more than 25 pm and / or less than 35 pm. In this way, the passages that form the filter openings can be created.

[0027] Preferably, the first and second filters are designed as particle filters. In particular, it can be provided that the first filter is designed for coarse filtration and the second filter for fine filtration.

[0028] Preferably, the openings connect the interior of the support body with the exterior of the support body. Preferably, the openings comprise elongated slots formed in the support body. Preferably, the greatest length of one of the slots is more than twice the shortest width of the slot.

[0029] According to the invention, the support body can comprise a cylindrical section, with the elongated slots arranged in the cylindrical section. Preferably, the cylindrical section of the support body and the second filter are arranged coaxially.

[0030] Preferably, the first filter is arranged on the inside of the cylindrical section and the second filter on the outside of the cylindrical section.

[0031] Preferably, an inner surface of the support body forms a contact surface for the first filter.

[0032] Preferably, the elongated slots have a longitudinal direction, with the longitudinal direction extending circumferentially around the cylindrical section. Preferably, the elongated slots are arranged in rows. Preferably, each row comprises more than 10 elongated slots. Preferably, between 4 and 15 rows of elongated slots are provided in the cylindrical section.

[0033] Preferably, continuous longitudinal ribs are formed between the rows, each separating two rows of elongated slots.

[0034] Preferably, the filter unit has an inlet for the liquid medium to be filtered and an outlet for the filtered liquid medium. Preferably, the filter unit further includes a drain for the liquid medium produced during rinsing. Preferably, the inlet and outlet are arranged coaxially in a single connection element.

[0035] A preferred embodiment provides that the filter unit includes a pressure reducer. Preferably, the pressure reducer is integrated into the filter unit. It is further preferred that the pressure reducer includes an actuator by which the pressure reduction can be adjusted.

[0036] According to the invention, it is preferred that the filter unit has a housing that encloses the support body. Preferably, a viewing window is arranged in the housing through which the second filter is visible.

[0037] According to the invention, it is preferred that the filter device has a control unit that automatically activates the backwashing device. For this purpose, the backwashing device can include a solenoid valve that opens a flow channel to carry out the backwashing.

[0038] Furthermore, the backwashing device may include a spring designed to close a flushing valve of the backwashing device.

[0039] The backwashing device can be activated by the controller at regular intervals after a time period stored in the controller has elapsed. Advantageously, the controller may include a sensor device that detects a differential pressure at the first filter and / or at the second filter and activates the backwashing device when the measured differential pressure exceeds a setpoint for the differential pressure stored in the controller.

[0040] Preferably, the second filter is designed as a tubular cartridge that is interchangeably arranged in the filter device.

[0041] Preferably, the second filter is arranged on the support body in a replaceable manner.

[0042] Further objectives, features, advantages, and possible applications of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. All features described and / or illustrated, individually or in any meaningful combination, constitute the subject matter of the invention, even independently of their inclusion in individual claims or their cross-references.

[0043] They show:

[0044] Fig. 1: a side view of a filter device;

[0045] Fig. 2: a perspective view of the filter device from Fig. 1 shown without the second filter;

[0046] Fig. 3: a schematic representation of the support body of the filter device from Fig. 1, with the second filter partially shown;

[0047] Fig. 4a: a perspective view of the second filter of the filter assembly from Fig. 1;

[0048] Fig. 4b: a side view of the second filter from Fig. 4a;

[0049] Fig. 4c: a cross-section along line AA through the second filter from Fig. 4b;

[0050] Fig. 4d: an enlarged detail X of the second filter from Fig. 4c;

[0051] Fig. 5: Measurements to determine the bubble point on various porous bodies for the second filter; Fig. 6: Measurements to determine the roughness on various porous bodies for the second filter;

[0052] Fig. 6a: A comparison of the amount of treated water and the pore size resulting from the measurements;

[0053] Fig. 7: a schematic representation of a section of the first filter;

[0054] Fig. 8: a section through the support body with the first and second filters.

[0055] Figure 1 shows a filter device 1 for a liquid medium, in particular water. The filter device 1 has an inlet 2 and an outlet 3 for the liquid medium. The liquid medium enters the filter device 1 through the inlet 2, while the filtered liquid medium leaves the filter device through the outlet 3. In the illustrated embodiment, the inlet 2 and the outlet 3 are arranged coaxially in a combined connection element, with the outlet 3 arranged annularly around the inlet 2. However, the inlet 2 and outlet 3 can also be provided in separate connections, unlike the one shown.

[0056] The filter device 1 has a head 4. A housing 5 is arranged on its underside, in which a support body 6 is arranged. The liquid-tight housing 5 has an inspection window 7 that allows the interior of the housing 5 to be viewed.

[0057] The first filter 8 and the second filter 9 are arranged on the support body 6 in the manner described in more detail below. To better illustrate the support body 6, the second filter 9 is not shown in Fig. 1.

[0058] The filter assembly 1 has a backwash device 11 located in the head 4. The backwash device 11 reverses the flow direction within the filter to remove impurities retained by the first and / or second filters 8, 9. The liquid containing the impurities can then exit the filter assembly 1 through the drain 10. In the illustrated embodiment, the backwash device 11 includes a solenoid valve 20 that opens a flow channel to perform the backwashing. The solenoid valve 20 has electrical connections 21 through which it can be activated by the controller.

[0059] The support body 6 has passages 14 for the liquid medium, connecting the interior of the support body 6 with its exterior. In the illustrated embodiment, these passages are designed as elongated slots. The maximum length of each of the slotted passages 14 is more than twice the shortest width of the respective slot. Each elongated slot has a longitudinal direction extending along the circumference of the cylindrical section 13.

[0060] The support body 6 has a cylindrical section 13 in which the passages

[0061] 14 are arranged.

[0062] The first filter 8, described in more detail below, is arranged on the inside of the cylindrical section 13. The second filter 9 is arranged on the outside of the cylindrical section 13. The first filter 8 rests against the inside of the cylindrical section. During operation, the liquid medium first passes through the first filter 8, then through the openings 14 in the support body 6, and then through the second filter 9.

[0063] The openings 14 are arranged in rows extending axially along the cylindrical section 13. As shown, each of the rows 15 comprises more than ten elongated slots.

[0064] Between your rows 15 are longitudinal webs 16 formed, each spanning two rows

[0065] Separate 15 of the passages into 14.

[0066] The filter unit 1 can include a control unit that automatically operates the backwashing device. For this purpose, the control unit can include a sensor device (not shown) that detects the differential pressure at the first filter 8 and / or at the second filter 9 and triggers a backwashing process when the measured differential pressure exceeds a setpoint.

[0067] Figure 2 shows the filter assembly 1 from the side. While the filter assembly 1 in Figure 1 is shown without the second filter 9, in Figure 2 the filter assembly 1 is shown with the second filter 9. The second filter 9 is arranged on the outside of the support body 6.

[0068] Figure 3 shows the support body 6 with the first filter 8 and the second filter 9. The second filter 9 encloses the cylindrical section 13 and is shown in the lower half of Figure 3. In the upper half of Figure 3, the second filter 9 is only partially shown to reveal the cylindrical section 13 with the openings 14. The first filter 8 is located on the inside of the cylindrical section 13. During operation, the flow through the first filter 8 and the second filter 9 is from the inside out. This allows the first filter 8, located on the inside of the cylindrical section 13, to be supported by the support body 6.

[0069] In the illustrated embodiment, the first filter 8 is operated upstream of the second filter. In the illustrated filter assembly, the support body 6 is subjected to flow from the inside to the outside. The first filter 8 is located on the inside of the support body 6.

[0070] The first filter 8 has filter openings with a larger opening width than the filter openings of the second filter. In this way, the first filter 8 is designed for coarse filtration and the second filter 9 for fine filtration of particles.

[0071] In particular, the first filter can have filter openings with an opening width between 20 and 50 pm, preferably 30 pm. In particular, the first filter 8 can comprise a planar structure with fibers, wherein passages are formed between the fibers. A preferred embodiment provides that the fibers of the planar structure are arranged in a fiber fabric. In this way, the first filter 8 can be designed as a surface filter, in which the particles are separated as contaminants on the surface of the filter material of the first filter 8.

[0072] The second filter 9 is designed as a depth filter and has a porous body made of a sintered plastic material. This porous body comprises filter channels through which the liquid medium can pass. Simultaneously, particles larger than the filter channels are retained by the second filter 9. The second filter is designed as a depth filter, allowing the particles to be retained within the cross-section of the filter material of the second filter 9. Due to the three-dimensional structure of the porous body 17, good filtration efficiency and long service life are achieved.

[0073] The porous body 17 is made of sintered thermoplastic material and can, in particular, comprise polyethylene.

[0074] The mean pore size of the porous body 17 is preferably smaller than the mean opening size of the first filter 8. In particular, the mean pore size of the porous body 17 can be between 15 pm and 35 pm, preferably between 20 pm and 30 pm.

[0075] Figures 4a to d show an embodiment of the second filter 9 of the filter assembly 1. Figures 4a and 4c show that the second filter 9, with its porous body 17, is cylindrical and has a cylindrical surface 18. The second filter 9 is designed to allow the liquid medium to flow through it in a direction perpendicular to the cylindrical surface. As shown, the second filter 9 can be tubular. The cylindrical surface 18 of the second filter 9 has a material thickness S, which can be between 1 mm and 3 mm.

[0076] The porosity of the porous body 17 can be between 40% and 60%. This means that between 40% and 60% of the porous body consists of cavities, while the remaining volume is occupied by the polymer material.

[0077] It was found that a particularly good filtering effect is achieved during long service periods when the porous body 17 of the second filter has 9 pores that are designed in such a way that certain values ​​are achieved in the so-called bubble point test.

[0078] Figure 5 shows measurements taken after the blister point test on different porous bodies 17. These are each cylindrical and have a material thickness S of 2 mm. The measurements were carried out in accordance with DIN EN 13443-2:2007-10.

[0079] The measurement results for three different filter materials are shown. Filter material L1 is on the left, filter material L2 in the middle, and filter material L3 on the right. The respective bubble point is marked B1, B2, and B3.

[0080] The corresponding measurement results are shown in Table 1 below.

[0081] Table 1

[0082] The corresponding pore size D (in micrometers) can be determined from the identified bubble point or open bubble point using the following formula:

[0083] The aforementioned formula is also known as Poiseuille's law, where "o" is the surface tension of the liquid and is 7.3 x 10⁻⁶ for water at 15° Celsius. 2 N / m. “0” denotes the contact angle formed by the surface of a liquid droplet with the surface of the filter material. “P” is the pressure (in Pascals).

[0084] Good filter properties with a long service life are achieved particularly when the mean pore size is between 20 and 30 µm. The mean pore size can be determined from the pressure at the open bubble point.

[0085] Furthermore, it has been shown that the roughness of the porous body 17 reliably indicates whether good filtration efficiency can be achieved over a long service life. Figure 6 shows the measurement of the pressure drop across different filter materials, each subjected to a flow rate of 2000 liters / hour containing 5 mg / l of a contaminant. The measurements show that after a short break-in period, the filter materials initially exhibit a fairly constant pressure drop. This increases sharply when the filter material of the second filter 9 is fully loaded. This is the point at which a filter material replacement becomes necessary. For filter material L1, this point is reached after just over half an hour. For filter materials V1, L2, and V2, the pressure drop only increases after just over an hour.With filter material V3, the increase only occurs after almost two hours, while filter material L3 has a particularly long service life, with the pressure loss only increasing after well over two hours.

[0086] The roughness values ​​of the various filter materials are compiled in Table 2 below:

[0087] Table 2

[0088] The aforementioned measurements demonstrate that particularly good filtration efficiency is achieved over long service lives when the mean roughness Ra of the surface of the porous body 17 is greater than 15 pm, and especially greater than 17 pm. It has thus been shown that somewhat higher values ​​for the mean roughness Ra are more advantageous than mean roughness Ra values ​​below the stated values. Figure 6a shows the quantity of treated water (Y-axis) and the pore size of the bubble point (X-axis) resulting from the measurements. The quantity of treated water is the total quantity of water filtered through the respective filters L1, L2, and L3 until the pressure drop limit was reached. The diagram clearly shows that pore size contributes to improving the service life of the filter material. On the other hand, the pore size cannot be increased arbitrarily without impairing the filtration efficiency.

[0089] Fig. 7 schematically shows a section of the first filter 8. This comprises a planar structure 80 made of fibers 81, 82, between which filter openings 83 are formed. The fibers 81, 82 are arranged crosswise in a fiber weave. The first filter forms a surface filter, in which particles are separated as contaminants on the surface of the first filter 8.

[0090] The filter openings 83 can have an opening width between 20 and 50 pm, preferably 30 pm.

[0091] Fig. 8 shows a cross-section through the support body 6. The longitudinal webs 16 of the support body and the openings 14 arranged between them are clearly visible. The first filter 8 is arranged on the inside of the support body 6. The second support body 9 is arranged on the outside of the support body 6.

Claims

Patent claims 1. Filter device for a liquid medium, in particular for water, comprising a hollow support body (6) with passages (14) for the liquid medium, wherein a first filter (8) is associated with the hollow support body (6), wherein the first filter (8) is designed as a surface filter, wherein the filter device has a backwashing device (11) to remove impurities from the first filter (8), characterized in that a second filter (9) is associated with the support body (6), wherein the second filter (9) is designed as a depth filter and wherein the second filter has a porous body (17) made of a sintered plastic material.

2. Filter device according to claim 1, characterized in that one of the first and second filters (8, 9) is arranged on the inside of the hollow support body (6) and the other of the first and second filters (9, 8) is arranged on the outside of the hollow support body (6).

3. Filter device according to claim 1 or 2, characterized in that a mean pore size of the porous body (17) is between 10 pm and 30 pm.

4. Filter device according to one of claims 1 to 3, characterized in that the porosity of the porous body (17) is between 40% and 60%.

5. Filter device according to one of claims 1 to 4, characterized in that the bubble point is reached in the bubble pressure test at a pressure difference on the porous body between 0.003 bar and 0.005 bar.

6. Filter device according to one of claims 1 to 5, characterized in that the porous body (17) has a surface which has a mean roughness Ra of more than 15 pm in at least a part of the surface.

7. Filter device according to one of claims 1 to 6, characterized in that the second filter (9) is cylindrical and has a cylindrical shell surface.

8. Filter device according to claim 7, characterized in that the cylindrical surface of the second filter has a material thickness of between 1 mm and 5 mm.

9. Filter device according to one of claims 1 to 8, characterized in that the filter unit is configured so that, during operation, the first filter (8) is passed through before the second filter (9).

10. Filter device according to one of claims 1 to 9, characterized in that the first filter (8) has filter openings (83) whose opening width is greater than 20 pm.

11. Filter device according to one of claims 1 to 10, characterized in that the first filter (8) comprises a planar structure with fibers (81 , 82), wherein passages are formed between the fibers which form the filter openings (83).

12. Filter device according to one of claims 1 to 11, characterized in that the first filter (8) is designed for coarse filtration and the second filter (9) is designed for fine filtration.

13. Filter device according to one of claims 1 to 12, characterized in that the support body (6) comprises a cylindrical section, wherein the passages (14) are arranged in rows in the cylindrical section.

14. Filter device according to claim 13, characterized in that the first filter (8) is arranged on the inside of the cylindrical section and that the second filter (9) is arranged on the outside of the cylindrical section.

15. Filter device according to any one of claims 1 to 14, characterized in that the filter unit comprises a pressure reducer.

16. Filter device according to any one of claims 1 to 15, characterized in that the filter device comprises a control unit that automatically actuates the backwashing device.

17. Filter device according to claim 16, characterized in that the control unit comprises a sensor device which detects the differential pressure at the first filter and / or at the second filter and triggers a backwashing process when the measured differential pressure is above a setpoint value for differential pressure stored in the control unit.

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