DE10217966A1 - filter means - Google Patents

Abstract

The filter device for filtering liquids comprises a filter membrane (2), a main body which is arranged upstream from the filter membrane (2),and which has a feed channel (3) perpendicular to the surface of the filter membrane (3), a gap (5) extending between the filter membrane (2) and the main body forming a tangentially directed cross-flow, and a return channel (6) which is used to return the tangential flow to the feed channel. Said flow is primarily returned thereto by means of a contraction (3') in the feed channel (3) at the mouth of the return channel (6). Preferably, a solid separator (20) is disposed in the return channel. At least one chicane element (7, 8, 9) is arranged in the feed channel in order to create a turbulent flow . The tangential flow along the filter membrane is used to clean said membrane.

Description

The invention relates to a filter device for Filtering fluids according to the preamble of the patent claim 1.

Such a filter device is from DE 72 25 662 U1 known. There is a tangential or cross flow fil tration carried out in which predominantly a tangential flow takes place along the membrane.

Another filter device is known from DE 39 24 658 A1 known, for the filtration of solids-containing liquid with at least one filter surface for prevention a filter cake formation and a relocation of the filter pores it is proposed to ver the filter surface in motion  put. Alternatively or additionally, the filter can liquid, a flow is generated which is a speed directed tangentially to the filter surface component of at least 0.1 m / sec. To keep clear the filter surface there preferably becomes a turbulent one Flow generated, for example, by passing gas-liquid mixture. But it can also with pumps, nozzles, stirring units, baffles, guide sheet metal, rotating rollers or vibrating devices the desired turbulence is generated by the filter counteract cake formation. In addition, the filter surface can also be electrically charged to solids repel.

The known device has several dirty water chambers and a corresponding number of pure water chambers that are separated from each other by a membrane. The main flow direction in the dirty water chambers tangential to the membrane. Also the supply of the to be filtered Liquid runs parallel to the membrane. Is essential also that the filtering is largely without pressure. It occurs in front of the filter surfaces in the dirty water chambers to accumulate solids in the liquid, which are then drained off via pipes and pumps, what depending on the turbidity of the liquid in the dirty water chambers should take place. This includes a measuring probe and a control device are provided, which ent speaking pump controls.

The phenomenon of blocking occurs in membrane filtration or "fouling" of filter membranes, in which Filtration course the flow rate per unit of time (dV / dt) through the filter membrane or the filter medium decreases. Different subprocesses carry individually or together for fouling at. For one, the pores of the Membrane partially blocked, which is relatively quick Leads to a decrease in the flow rate; on the other hand forms on the upstream side of the filter medium  a so-called "filter cake" (often also as a "secondary membrane "), which further increases the flow resistance increases and thus the flow rate through the filter medium wider, but slower than when blocking the pores Ringert. There can also be one on the filter cake So-called concentration polarization layer (concentration polarization layer).

The different processes leading to fouling can are divided into reversible and irreversible processes, which by certain measures such. B. Backwash (back flushing) reversed or not reversed (e.g. adsorption) can be.

In addition, the retained substances can not only on the upstream side (inflow side) of the filter form the filter cake, but at least partially penetrate into the filter medium and there the channel or block pore structures. In this case it is Cleaning by common procedures difficult to impossible.

These mechanisms reduce the possible useful life (Service life) of the filter media and thus increase the costs and the effort (maintenance, monitoring, etc.) for the fil tration.

To remove the filter cake, according to the state of the art Technology numerous approaches, processes and facilities known. Procedures to remove the detained Substances or for cleaning the filter include physical ones and chemical processes.

In the physical cleaning processes such. B. Computing or vibrating equipment used. In such The filter cake is made by the rake or a process similar facility from the upstream side of the Filter medium removed. Sometimes the filters too vibrated or turbulent flow is generated.  

To generate turbulent flows z. B. baffles and / or frequency transmitters (such as ultrasonic generators) used. In some versions according to the state of the art is used to remove particles of the filter cake a flow parallel to the filter surface (transverse flow) z. B. with the aid of a suitably introduced gas generated. Such mechanisms, however, require one sufficient flow through the filter medium large Filter surfaces.

This category of cleaning processes can, for example the so-called "backwashing" of the filter can also be included. In this process, the filtration process is interrupted the filter medium in the original current direction flushed in the opposite direction with a cleaning fluid and the filtration process (with a certain "lead time") then continued.

In chemical processes, for example, the filter medium rinsed with one or more cleaning solutions. This Cleaning solutions can be found in the filter medium after Filter cleaning may remain and may have to be washed out (e.g. by continuing of the filtration process, which is immediately after the Resumption of the filtration process filtered fluid cannot be used, but must be disposed of).

The known methods for removing the filter cake (e.g. DE 39 24 658 A1) have the following disadvantages. On the one hand, they require considerable technical effort (Calculators or agitators, gas inlet, vibration device services etc.) and make the process prone to failure and complicated. In addition, the maintenance and cost elevated.

Conventional cleaning procedures are not always perfect effective, d. H. they clean the upstream side of the Filter membrane not complete.  

Another disadvantage is that in some cases State-of-the-art systems, large systems, filters areas, etc. are required to ensure adequate To achieve filtrate throughput.

Another disadvantage of these cleaning methods is that for the cleaning process the filtration process is interrupted must become. This reduces the filter throughput and increases the costs.

In addition, it is disadvantageous with these common methods the energy requirement and the associated costs.

DE 38 18 437 A1 also becomes the further prior art called which is a filter battery with baffle elements shows that cause turbulence. The battery will alternately operated in the filtering and flushing mode. DE 43 29 587 C1 shows a device for filtering of liquid with a self-cleaning device, where the filter is integrated into the wall of a pipe and the liquid to be filtered is fed to the pipe that passes the filter in part to as a filtrate to be forwarded and the other part, enriched with solids, from the outward opening end of the tube comes out.

WO 97/32652 shows a filter in which the filter to be filtered Medium is also exposed to strong turbulence for example by a rotor, sound waves, electrical Fields and the like are generated.

DE 35 20 489 C1 shows a filter with a tangential inlet, where the fluid is under controlled swirling is fed to the interior of a container and a stirrer plant over the filter membrane a constantly changing Alternating pressure field generated to the membrane of residues kept clear.  

DE 14 36 287 A1 finally also shows a Tangen tial filter with a rinse of the filter wall to loosen Impurities.

The object of the invention is the known filter device to improve that on the upstream Side (upstream side) of the filter membrane the formation of a Cover layer (filter cake) from through the filter membrane retained substances at least slowed down, if not is completely prevented.

This should essentially be done in that the inflow side of the filter membrane is cleaned automatically. in particular in particular, the filter membrane should preferably have no external input attacked by staff, if possible without interrupting the Filtration, without additional media (e.g. introduced gases) and be cleaned as continuously as possible. Preferably an exchange of the filter arrangement or one of their Components simplified and maintenance work reduced become. Finally, the service life of the filter membrane be extended with reduced costs at the same time.

This object is achieved by the specified in claim 1 Features solved. Advantageous refinements and further Formations of the invention are to be found in the dependent claims to take.

The basic principle of the invention is a circle run, d. H. a cross flow to clean the filter membrane and to form a reflux while the main filter direction is perpendicular to the membrane. So that can go back substances kept constantly and with continuous filtration removed and disposed of. In contrast to the beginning DE 72 25 662 U1 mentioned is primarily a so-called. "Dead-end filtration" is carried out at the main flow runs vertically through the filter membrane and the fluid Imprinted cross-flow component primarily for removal retained substances on the upstream side of the filter  membrane serves. That the retained substances trans porting fluid from the cross flow component is over Tapping points directed to a return channel and over this is fed back into the feed channel. In the area of The return channel is preferably a solids separator arranged, in which a further depletion of Solids from the fluid is carried out.

The driving force for filtration is one of the Causes main flow in the feed duct device, such as B. a main pump.

The tangentially directed cross flow is achieved by the geometry of the filter membrane and the main body assigned to it. The return flow in the return channel, which has an essential component against the main direction in the supply channel, is preferably achieved by a flow restriction, which causes local pressure differences at the return point of the return channel in the supply channel. Because of the relatively short distances and a low pressure drop along these distances, only a relatively small pressure difference is required for the return of the fluid. According to the Bernoulli equation:

(with p = pressure; ρ = density and v = velocity) and the continuity equation:
A ₁ v ₁ = A ₂ v ₂
(A = cross-sectional area perpendicular to the flow velocity)
the relationship between pressure and flow speed or channel cross-section and flow speed is described. According to these two equations, the speed increases and the pressure decreases as the cross section decreases. Due to the flow restriction in the feed channel at the point at which the return channel opens into the feed channel, a pressure difference can be created between this point and the surface of the filter membrane, which causes or at least supports the return.

Alternatively, or alternatively, a pump can also be used be provided, which are effective in the return duct is arranged.

The end of the return duct is preferably a tube trained, which protrudes into the feed channel and in Is bent towards the filter membrane. In the neighborhood the cross-section of the feed channel is narrowed at the end of the pipe, what about a smaller diameter or in that area used "baffle elements" is reached. in this connection it is, for example, a rotationally symmetrical Insert piece whose job is to do it immediately a pressure locally after the pipe end due to a narrowing train the difference that initiates the return Fluids in the supply channel causes. It is by the in the narrowing faster flowing fluid a suction effect achieved.

With conventional tangential or cross flow filtration is the throughput per unit area of the filter and Time unit very small. This enforces for higher and thus more economical throughputs the use of very large Filter surfaces. The separation takes place via the filter predominantly by means of diffusion through the filter.

The device according to the invention is very compact and manages with relatively small filter areas. Also works the filter device according to the invention with a high Throughput. It is not in the so-called cross-flow process but in the so-called dead-end process (inflow to the membrane  parallel to the normal of the membrane) even at high pressures worked what a compact design of the filter system allowed at high throughput. The expenditure on equipment the invention is small since no moving parts are required be what costs, susceptibility to failure, energy and labor expenses (maintenance, operation) greatly reduced.

The in a preferred embodiment of the invention The baffle elements used primarily serve to over the necessary cross-flow across the entire membrane area to generate so that there are essentially no membrane areas that may not be cleared. The Turbulence is primarily a combination of Speed and small gap dimensions created, the baffle elements only further contributing to the turbulence wear. Furthermore, this geometry allows, at high Work pressures and thus high throughputs. With this configuration, without additional resources, such as B. pumps, nozzles, agitators etc. and thus without additional very high transverse speeds is sufficient, which has an excellent transport effect as well Ensure turbulence generation. It is also after the Invention proposed structure with interchangeable Schika elements to different process requirements easily adapt.

By including electrical fields, the intended cleaning effects are intensified.

The design of the filter arrangement according to the invention creates in addition to cleaning the filter membrane and Disposal of the separated substances also a certain Securing the membrane against pressure surges.

In the following the invention is based on exemplary embodiments play in more detail in connection with the drawing explained. It shows:  

. Figure 1 shows a filter device according to the invention in two embodiments, which are shown in the left and the right half of Fig. 1;

Figures 2a to 2d show various sub-variants of the recirculation and discharge of solids.

FIGS. 3a and 3b is a modification of the baffle element or the main body;

4 shows an embodiment illustrating the assembly of baffle elements in the filter device according to the invention. and

Fig. 5 shows an alternative embodiment of the assembly of a baffle element in the filter device according to the invention.

Fig. 1 shows some variants of filter devices according to the invention. The filter device 1 has a filter membrane 2 , which is supplied with a fluid to be filtered via a feed channel 3 , which is perpendicular to the surface of the filter membrane 2 . The fluid is usually a liquid contaminated with solids. But it can also be a gas contaminated with solids. In the flow direction (see arrow F _in ) in front of the filter membrane 2 , a main body 4 is arranged, which on the one hand continues and thus also forms the feed channel 3 and has a contour which extends laterally beyond the feed channel 3 and essentially parallel to the filter membrane 2 runs a small distance B to the filter membrane and thus forms a gap 5 . This gap has a constant width B in the left part of FIG. 1. In the variant shown in the right part of FIG. 1, the gap is reduced from the center, ie the feed channel 3 , to the outside, which creates a nozzle effect.

In the area of the cross section of the feed channel 3 , the fluid reaches the filter membrane 2 essentially with a velocity component running perpendicular to the surface of the filter membrane 2 . A substantial part of the flow is then passed through the gap 5 , which serves as a transverse channel, parallel to the surface of the filter membrane 2 , as shown by the arrows v _q (for transverse speed). The cross channel 5 then merges into a return channel 6 , which conducts the fluid emerging from the gap 5 back into the supply channel 3 . The opening into the supply passage 3 end of the return channel 6 is designed as a pipe end 6 ', which is bent towards the filter membrane 2 out so that the recirculated fluid parallel to the main flow again passes (see FIG. Arrow F _in) in the supply channel. In the embodiment example of FIG. 1, the feed channel 3 has a constriction 3 ', the narrowest point preferably being in the region of the outlet of the pipe ends 6 ' of the return channel 6 . As a result of this constriction - as described at the beginning - a higher flow velocity occurs in this area and thus a pressure drop, so that the pressure at the outlet end of the return channel is lower than at the surface of the filter membrane or the inlet of the return channel 6 . In addition, the pipe ends 6 ′ projecting into the feed channel 3 also cause a cross-sectional constriction, which supports the effect described.

Alternatively or cumulatively to the cross-sectional constriction 3 ', insert pieces can also be arranged in the region of the outlet opening of the return duct 6 , which for example have the shape of a spherical body 9 ', which also serves as a flow constriction.

Alternatively or cumulatively, a pump 6 ″ can also be arranged in the return duct 6 , which effects the return conveyance.

A plurality of tubular, rotationally symmetrical baffle elements 7 and 8 and a spherical baffle element 9 are arranged in the feed channel 3 . The entire device 1 including the main body, baffle elements, etc. is here rotationally symmetrical to the axis A. In the exemplary embodiment in FIG. 1, the baffle element 7 is purely cylindrical and the baffle element 8 is approximately funnel-shaped with perforations 10 , which ensure greater swirling. These perforations can also be rotationally symmetrical to the axis A.

X relative to a bottom in the right corner of FIG. 1 represented Cartesian coordinate system with the two axles and y, the fluid of the y-axis negative flows in the direction of the arrow F _in in the direction parallel to the symmetry axis A along the baffle elements 7, 9 and through the perforated baffle element 8 in the direction of the inflow side of the filter membrane 2nd In this case, a turbulent flow is generated on the upstream side of the membrane 2 , in particular but not exclusively in the middle thereof, which at least slows down the accumulation of substances retained by the membrane 2 on the upstream side. In addition, a flow with a high cross-flow velocity (v _q ) is generated parallel to the membrane 2 in the gap 5 and transports the retained substances along the upstream side of the membrane (parallel to the x-direction). The cross flow in the gap 5 is preferably turbulent, as a result of which substances located on the membrane 2 are "whirled up" by it and transported away with the cross flow.

The retained substances are removed from the cross flow or separated therefrom and the cross flow substantially freed from the retained substances is returned through the return duct 6 to the inflow side into the main stream, ie the feed duct 3 . In this way, the membrane 2 is cleaned without interrupting the filtration process.

In the right and left halves of FIG. 1, different variants for the formation of the return channel are shown. In the left part it runs straight upwards, in the right part first vertically upwards and then over a kinked, a horizontal and a kinked section back into the feed channel 3 . Other shapes are of course also possible.

If the distance from the center of the membrane 2 to its edge is not too long, the pressure drop along the distance is relatively small and a sufficient transport effect is guaranteed, as is approximated by the law of Hagen-Poiseuille (G-HP):

where L = length of a tube, r = radius of the tube and ent speaks roughly B.

The flow state of a fluid is described using the Reynolds number Re, which is given in the following equation (1):

Re = 2 r ρ v / η (1)

Here, r (m) is the radius of the cross-sectional area through which the fluid flows, ρ the (fluid temperature-dependent) density of the fluid, v (m / s) the flow rate, and η (Pa.s) the viscosity of the fluid. The corresponding values for water are, for example: η = 1.8 × 10 ^-3 Pa.s (at 0 ° C) or 1.0 × 10 ^-3 Pa.s at 20 ° C; ρ = 1000 kg / m ³ . The flow is laminar for values of Re <approx. 2000, while it is turbulent for values of Re <approx. 3000 (in the range 2000 <Re <3000 the flow state is unstable and changes from one type to the other).

According to equation (1), the parameters can be selected appropriately r, v (and possibly also the temperature T and thus the viscosity of the fluid) the flow of the fluid optionally into a turbu  lente and / or laminar flow are transferred. This Circumstances are used for the present invention. To change the corresponding parameters over a channel section, the flow state also changes accordingly.

As an example, the filter device of FIG. 1 is considered, the z. B. has the following parameter values (in SI units): ρ = 1000 kg / m ³ , η = 1.8 × 10 ^-3 Pa.s, r = 0.5 × 10 ^-3 m (0.5 mm) = B / 2; v = 10 m / s (pressure difference 1 bar): With these values, a Re ≈ 5500 results for the gap area 5 between the underside 12 , 16 and the membrane 2 ; so turbulent flow with very high flow speed v.

If the parameters (in particular r or B) are varied via the fluid path, zones with turbulent and laminar flow can be created and the pressure drop along the upstream side of the membrane 2 can be set. Of course, this also applies to any other area in the fluid flow, in particular also in the area of the baffle elements 7 , 8 and 9 . Through the appropriate parameterization and shaping of the baffle elements, a turbulent flow with a strong transverse component is created in the area z of the surface of the membrane 2 .

In the right part of FIG. 1, a second embodiment of the filter device according to the present invention is shown. This embodiment is similar to that shown on the left part of FIG. 1, but the underside 12 of the main body 4 no longer runs parallel to the membrane 2 as the underside 11 in the left part of FIG. 1, but rather in the direction of the edge of the Membrane 2 narrowing gap 5 forms. In particular, the contour can be determined in accordance with the Hagen-Poiseuille equation so that the ratio dV / dt × L / r ⁴ or dV / dt × L / B ^{4 has} a constant value. According to the Hagen-Poiseuille equation, this leads to a constant pressure drop (Δp) over the length L on the upstream side of the membrane 2 . Depending on the choice of parameters (e.g. dV / dt, L, r or B as well as η), the pressure drop required for the removal of substances retained can thus be determined as desired. This feature increases the transport efficiency and allows a reduction in the pressure on the upstream side of the membrane 2 (reduction in energy consumption, smaller pumps and lower pump output necessary). In this embodiment of the filter device 1 , no additional energy expenditure and no additional medium (e.g. gases or the like) are necessary to clean the membrane 2 . Rather, it is cleaned automatically.

According to a development of the invention, at least one electrode 14 can additionally be provided. In the left part of FIG. 1, a main electrode 14 in the spherical chicane and two secondary electrodes 15 in the main body 4 are shown as an example. The number of electrodes can of course be different, as can their arrangement. It is also possible, for example, to attach electrodes 11 , 17 to the main body 4 , for example directly on the underside 16 or 12 thereof . The electrodes can also be arranged so that they perform the function of baffles in the gap 5 . In this case, they should be sheathed to protect them from exposure to the fluid. With the help of the electrodes, 2 electric fields can be generated in the fluid and in particular in the vicinity of the filter membrane, and preferably pulsed electric fields, which has a supportive effect when detaching retained substances on the membrane 2 . Finally, a further electrode 19 can also be provided on the downstream or the upstream side of the membrane 2 , which of course is coarser-meshed than the membrane and has a repulsive effect on the solid particles.

The electrodes partially protrude into the fluid flow, ie in particular in the gap 5 , and from the spherical Schika element 9 in the direction of the membrane 2 and are z. B. switched as an anode. On the upstream side of the membrane, electrical conductors are applied, which are switched as a cathode. If a current pulse is sent through the fluid via the cathode and anode, e.g. B. generated by electrolytic decomposition of water, gas bubbles that break up or disassemble an eventual deposit layer on the upstream side of the membrane and at least facilitate their detachment from the membrane. Extremely reactive free radicals are also generated, which at least complicate, if not prevent, the formation of biofilms.

The values of the current pulses are, for example, in the range from a few 10 mA / cm ² to a few 100 mA / cm ² . The number of current pulses per hour can be between 2 and 12 or more per hour, depending on the course of the possible fouling, the composition of the unfiltrate, and the membrane values. The duration of the current pulses is in the range from a few seconds (1-5 s) to around a few 10 seconds.

The number of electrodes assigned to the membrane area (number of electrodes / membrane area) can of course be selected as required. In one embodiment, eight electrodes are provided in the main body and one electrode in the spherical baffle element. The electrodes can also be protected against the fluid by a sheath that does not influence the electrical field. This additional feature can further complicate or completely prevent the formation of a fouling layer. As a result, the throughput through the membrane 2 can be increased significantly. This in turn allows a reduction in the filter area with the same throughput or requires a lower pressure (pump power, energy consumption) or lower fluid speeds with the same throughput. The effects on filtration costs are therefore obvious.

Fig. 1 can also be seen that at the radial end of the gap 5 and in the transition region to the return channel 2, a removal device 20 is attached, through which substances transported to the edge of the membrane are separated and no longer get into the return channel. In the simplest case, this removal device 20 is a ring-shaped container. This container can be rotationally symmetrical to the axis A, into which the transverse flow of the fluid enters. If the contaminants filtered out are heavier than the liquid, they can settle and are "collected" in the removal device 20 . From there they can be removed intermittently without having to interrupt the filtration operation.

Fig. 2A shows an embodiment of a sampling device 20, which is attached to the main body 4. It is a collecting container, which on a side connected to the main body 4 has a conventional inexpensive filter element 22 (e.g. made of cellulose, metal or the like) with preferably larger nominal pore diameters than the membrane 2 . The removal device 20 is, for. B. tightly attached to a shoulder or flange 24 of the main body 4 via a simple locking mechanism 23 . Between the locking mechanism 23 and the edge of the membrane 2 , a valve 24 is provided, which can be, for example, a simple rotary valve of known type. When assembling or replacing the extraction device 20 , the valve 24 is briefly closed while the filtration operation is running, so that the conversion can be carried out without interrupting the filtration operation.

The function of the removal device 20 is explained below. During the filtration process, the substances retained by the membrane 2 are transported along the upstream side of the membrane 2 to the edge thereof in the direction of the removal device 20 . Due to the larger pore size of the conventional filter element 22 , the retained substances can pass through the filter element 22 into the collecting container 20 . Because of the "dead zone effect" of the collecting container 20 , the probability of a return of the substances accumulated in the collecting container through the filter element 22 is relatively low. The entire space (collecting container 20 , gap 5 and return channel 6 ") is filled with fluid. In this way, a sort of filtration takes place in the removal device 20 , in which the substances to be retained are removed by a suitable combination of current supply (including dead zone = Collection container 20 and return duct 6 ), cross flow and filtration with the membrane 2 is achieved.

In order to support the return line of the fluid into the main flow F _in , the return line channel 6 can e.g. B. with a non-constant, ie changing, diameter. In particular, the diameter of the return channel 6, for example, up to the initiation point of the valve 24 to decrease in the main current, the flow speed thereby increases and the pressure decreases along the Rücklei underflow channel. This creates a certain pressure drop, which in addition to the flow restriction 3 '(or 9' in FIG. 1) also "drives" the return line.

Via the return duct 6 formed in the main body 4 , the fluid freed from the retained substances at least partially, but preferably largely, returns to the main stream F _in and with it back to the membrane 2 . This closes the cleaning cycle. If you consider a volume element in the fluid flow, z. B. in a first pass of the cleaning circuit substances retained on the membrane 2 , transported to the removal device 20 with the aid of the cross flow and deposited there to a certain extent, and the fluid is finally returned to the main stream with a substantially reduced proportion of substances to be retained. If the remaining proportion of substances to be retained in the volume element under consideration is still too high, the filtration process is repeated on the membrane 2 . There is a kind of dynamic equilibrium in which the membrane 2 simultaneously and continuously performs the desired filtration, the membrane 2 is cleaned automatically and the substances to be retained are withdrawn from the fluid stream.

The removal device 20 can be made of stainless steel, plastic or other materials which are customary in the branch or application.

In other embodiments, the channels and / or the current routing can be varied as required. The filter element 22 can thus be arranged at an angle different from 90 ° against the transverse flow (v _q ) from the gap 5 (cf. FIG. 2B). In addition, the inlet opening in the collecting container 20 can be located at its upper end, so that a substance that has entered it can settle even better on its bottom and can hardly or preferably not return to the return duct 6 . In addition, further inflow geometries are conceivable, as are sketched in FIG. 2C. The flow can be guided into the collecting container 20 by a corresponding deflection 26 of the gap 5 to the return duct 6 .

If the inflow opening in the collecting container 20 is designed to be comparatively small, a filter element 22 can possibly be completely dispensed with. The filter element 22 mainly has the task of preventing or at least complicating a backflow of the substances previously retained by the membrane 2 and into the collecting container 20 into the return flow stream and the return duct 6 . The likelihood that particles get back into the return flow and thus back into the return duct 6 can also be reduced by structural measures. An example of this is sketched in Fig. 2D. This can be achieved with appropriate guide bodies 27 and a concavely curved leading edge 28 inclined towards the gap 5 and a further guide plate 29 which only leaves a small gap 30 towards the leading edge 28 . This opening geometry can be integrated into the removal device 20 so that 20 standard elements can be used at the connections and the piping of the removal device. The baffle elements 27 and 29 contained in the removal device 20 narrow the inlet channel into the collecting container 20 from the connection 23 to a significantly smaller opening 30 . The probability of a backflow of the substances once into the collecting container 20 through the opening 30 is approximately proportional to the ratio of the area of the opening 30 to the area of the entire inner wall of the collecting container 20 . It should be noted that in the "retracted state" the entire space ( 20 , 5 , 6 ) is filled with fluid and the removal is based on an "enrichment or concentration" of the substances to be retained in the collecting container 20 . The inertia of these substances is used during their transport into the removal device 20 .

The fastening mechanisms of the collecting container 20 can also be modified. Threaded and / or clamp connections can be used as long as the tightness of the connection is guaranteed.

A filter device according to the present invention preferably uses more than one extraction device 20 , namely at least two or more extraction devices. In the case of four removal devices, these are arranged symmetrically on four sides. The use of more than one extraction device also ensures that the maintenance process (such as exchange, etc.) of the extraction process and thus the filtration on the membrane 2 and its cleaning continue.

The principle of operation of those described in this application Withdrawal device provides a kind of additional filtration represents, if necessary, as an independent and / or allei Filtration principle can be used. For example with a suitable design (scaling, ducting etc.) inertia in a circuit of the fluid flow of substances in the fluid that are to be extracted from the fluid,  be used to collect these substances in "dead zones". At the point where the cycle begins, an increased flow resistance in the outflow channel for the depleted fluid can be set up (e.g. by means of Membranes, baffle elements, a non-constant channel diameter etc.) and if necessary the removal device also be designed as a centrifuge filter.

Fig. 3 shows that the individual elements also have corrugated, ie non-planar surfaces. In Fig. 3A, the baffle element 7 is corrugated or ribbed, while the main body 4 still has a smooth wall. Of course, the main body 4 can also be corrugated. In Fig. 3B, the bottom 12 of the main body is corrugated. Zones with turbulent flow can be specifically formed in areas with greater distances from the adjacent element. Of course, the membrane 2 can also be corrugated.

FIG. 4 shows how a baffle element is built into the main body 4 like a shell. The main body 4 has at least two, here three parts 31 of an internal thread projecting into the feed channel 3 , the surfaces 32 pointing radially inwards forming the internal thread. A rotationally symmetrical baffle element 33 has a corresponding external thread and is screwed to the internal thread 32 . Other baffle elements, such as. B. the baffle element 30 are also provided with corresponding bonding threads. This shell-like structure can be expanded as required depending on the application.

Instead of screwing the baffle elements alternately, they can of course also be used with other fastening devices. For example, they can be easily inserted and locked into place in the corresponding parts (main body and baffle element) using pins and appropriately designed grooves. The two mechanisms mentioned for installing the baffle elements create a high degree of flexibility in maintenance and replacement. In particular, the baffle elements and of course - if required - the main body can be exchanged for other components depending on the process conditions, the fluid used, etc. The spherical baffle element 30 is locked with the help of jumps before, for example on the baffle element 33 .

In a further embodiment of the invention, which is shown in Fig. 5, the spherical baffle element 9 is mounted on a spring 35 which in turn is attached to the baffle element 8 . Flow regulation can also be achieved by the spring constant of the spring 35 . If a pressure surge occurs in the inflowing fluid, the spherical baffle element 9 is displaced against the force of the spring 35 in the direction of the membrane 2 , as a result of which the flow channel between the spherical baffle element 9 and the baffle element 8 is narrowed. In this way, an essentially uniform fluid supply to the membrane 2 is realized. In addition, the membrane is protected against pressure surges that damage it and could therefore also lead to an interruption of the filtration.

The filter device described above can in their individual components can be dimensioned as desired, to adapt them to the respective application purposes. The The principle of the invention is also based on an industrial scale Applications such as B. Wastewater treatment applicable.

The filter device with the main body and the baffles elements can also be in a stainless steel housing or other Materials are installed. This housing can over standard connections used in standard pipelines become.

Claims (17)

1. Filter device for filtering fluids with a filter membrane and a device for generating a transverse flow directed tangentially to the surface of the filter membrane, with a main body arranged upstream of the filter membrane, which has a feed channel running perpendicular to the surface of the filter membrane, a gap running between it and the filter membrane to form the tangentially directed transverse flow and has a return channel, characterized in that the return channel ( 6 ) is in flow connection with the supply channel ( 3 ) and in that a device ( 3 ', 6 ', 6 ") for returning the fluid through the return channel ( 6 ) is provided. 2. Filter device according to claim 1, characterized in that the device for returning the fluid is an upstream of the filter membrane ( 2 ) arranged flow restriction ( 3 '). 3. Filter device according to claim 1 or 2, characterized in that the device for returning has at least one in the feed channel ( 3 ) projecting pipe socket ( 6 '), the outlet of the returned fluid parallel to the longitudinal axis of the feed channel ( 3 ) in the feed channel ( 3 ) leads. 4. Filter device according to one of claims 1 to 3, characterized in that the device for returning the fluid has an effectively in the return channel ( 6 ) interposed pump ( 6 "). 5. Filter device according to one of claims 1 to 4, characterized in that a solids separator ( 20 ) is arranged in the return duct ( 6 ). 6. Filter device according to one of claims 1 to 5, characterized in that upstream of the filter membrane ( 2 ) at least one baffle element ( 7 , 8 , 9 ) is arranged, which swirls the flow. 7. Filter device according to claim 6, characterized in that at least one of the baffle elements ( 8 ) has one or more holes ( 10 ). 8. Filter device according to claim 4 or 7, characterized in that the baffle elements ( 7 , 8 , 9 ) are inserted into one another and connected to one another, preferably via threaded parts or pins. 9. Filter device according to one of claims 1 to 8, characterized in that at least in the main body ( 4 ) an electrode ( 15 ) is arranged, through which an electric field is generated in the fluid. 10. Filter device according to claim 9, characterized in that at least one of the baffle elements has an electric de ( 14 ). 11. Filter device according to claim 9 or 10, characterized in that the electrodes produce an alternating electric field gene.   12. Filter device according to one of claims 1 to 11, characterized in that the gap ( 5 ) between the underside ( 12 ) of the main body ( 4 ) and the filter membrane ( 2 ) has a radially increasing width (B). 13. Filter device according to one of claims 3 to 12, characterized in that at least one baffle element ( 9 ) is movably gela gert, preferably by means of a spring ( 35 ). 14. Filter device according to one of claims 2 to 13, characterized in that a further filter element ( 22 ) is arranged between the gap ( 5 ) and the solids separator ( 20 ) and a valve device for shutting off the feed to the solids separator. 15. Filter device according to claim 14, characterized in that the additional filter element ( 22 ) is arranged at an angle different from 90 ° against the incoming fluid. 16. Filter device according to one of claims 5 to 15, characterized in that the area of the opening ( 30 ) to the solids separator ( 20 ) is substantially smaller than the area of the inner wall of the solids separator. 17. Removal device according to one of claims 1 to 16, characterized in that the return channel ( 6 ) has a changing diameter, which preferably decreases in the return direction.