NL2002981C2

NL2002981C2 - Membrane filtration unit.

Info

Publication number: NL2002981C2
Application number: NL2002981A
Authority: NL
Inventors: Adrianus Henricus Cornelis Son
Original assignee: Vanson Innovations
Priority date: 2009-06-08
Filing date: 2009-06-08
Publication date: 2010-12-09

Description

Membrane filtration unit

Field of the invention

The invention relates to a membrane filtration unit and to a method for filtering a 5 liquid into a filtrate and retentate with the membrane filtration unit.

Background of the invention

Filtration of liquids, especially water, is used on a large scale to provide water containing less solids, for instance to provide potable water. In the art, a lot of filtration 10 apparatus are suggested of which many use membranes.

An example is described in US4025425. This document describes an apparatus for purifying waste water or another feed fluid, which includes a stack of membrane packs wherein each pack contains a conduit sheet, a pair of support sheets of filter paper or the like, each lying against a face of the conduit sheet, and a pair of 15 membranes each lying over a filter paper sheet. The pack has exit holes and the filter paper extends up to the exit hole walls and has a region thereabout which is impregnated with an adhesive which seals the filter paper against the inflow of concentrate while also holding the filter paper to the conduit sheet and membranes. The packs are spaced apart by inner and outer gaskets, the radially inner gaskets having 20 central holes forming a feed pipe for carrying the feed fluid to all the packs. The stack of membrane packs is rapidly rotated to provide centrifugal forces that help sweep away membrane-plugging material during radial flow of feed fluid from the feed pipe to the peripheries of the packs, and the exit holes of all of the packs are formed near their peripheries and are aligned to thereby form a concentrate-carrying "pipe" with 25 gaps that receive the concentrate.

Further, US6165365 describes a filtration apparatus of the type that includes a stack of rapidly rotating membrane packs and a stack of stationary separator elements interleaved with the membrane packs to leave thin gaps between them, which obtains the advantages of both series-connected and parallel-connected systems. A feed conduit 30 connects the radially outer ends of the gaps, to carry feed fluid into and out of each gap. The rapidly rotating membrane packs cause radially outward near their surfaces, which causes radially inward flow near the surfaces of the stationary elements, to cause fluid flow radially inwardly and then outwardly through each gap. The system is operated so 2 that particles of the feed fluid can build up on the rotating pack surfaces only to a thickness that is much less than one-half the thickness of the gap, before commencing any procedure to clean the membrane pack surfaces. The stationary elements have apertures to equalize the pressure on opposite sides thereof and to promote fluid shear 5 at the membrane surfaces. Permeate migrating into the membrane packs flows radially inwardly to a hollow shaft, with the permeate flowing in opposite axial directions along the shaft. An accumulator is coupled to the feed inlet to maintain feed fluid pressure during an abnormal loss of feed fluid pressure, for the time required to stop rotation of the stack of membrane packs.

10 US6613231 describes an apparatus, system and process for liquid separation by reverse osmosis, nano-, ultra- and micro-filtration under the joint action of the differential pressure built up on the either side of the membrane located in the apparatus for membrane separation, continuous rotation of the body in the immediate proximity to the selective layer of the said membrane, oscillation of the liquid flow, 15 caused by the means and induced vibration of the said membranes. The superposition of the said continuous rotary movements, liquid oscillations and membrane vibrations on each other result in the reduction of membrane clogging with the substances being retained.

20 Summary of the invention A disadvantage of prior art filtration apparatus are that prior art apparatus may not easily be applied as stand-alone apparatus. Further, efficiency of filtration may not be as high as desired. In addition, in prior art apparatus it is often imperative to circulate liquid in order to concentrate the retentate and/or it is necessary to rotate at 25 high speed, which is energy inefficient.

Hence, it is an aspect of the invention to provide an alternative membrane filtration unit, which preferably further at least partly obviates one or more of above-described drawbacks.

According to a first aspect, the invention provides a membrane filtration unit 30 (herein also indicated as “filtration unit”), arranged to filtrate a liquid and to provide thereby a filtrate and a retentate (also known as “concentrate”), wherein a. the membrane filtration unit comprises a vessel having a vessel chamber wall enclosing a chamber volume, which is divided in a filter volume containing a 3 rotatable cylinder unit and a vessel retentate volume, external from the rotatable cylinder unit (wherein the retentate volume is in liquid contact with the retentate receiver); b. the rotatable cylinder unit (also shortly indicated as “rotatable cylinder” or 5 “cylinder unit” or “cylinder”) is arranged to receive the liquid from an external liquid source, and is arranged to separate the liquid into filtrate and retentate; c. the rotatable cylinder unit comprises a cylinder outer wall, a cylinder inner wall forming a central cavity within the rotatable cylinder unit, and a plurality of radially arranged tubular membranes (herein further also indicated as “membranes”) 10 arranged as at least part of channels between the cylinder inner wall and the cylinder outer wall, wherein the tubular membranes are arranged to allow the liquid flow in a direction from the central cavity to the vessel retentate volume, and wherein the tubular membranes are arranged to selectively pass filtrate through membrane walls of the tubular membranes to a filtrate cavity of the rotatable cylinder unit.

15 The membrane filtration unit is especially arranged to filtrate the liquid from an external liquid source. Further, the membrane filtration unit is especially arranged to provide the filtrate to an external filtrate receiver. Further, the membrane filtration unit is especially arranged to allow the retentate flow to an external retentate receiver. Especially, the filtrate cavity is in liquid contact with a the filtrate receiver.

20 The liquid to be separated is in general a liquid comprising solids (such as particles). The pure liquid may pass the membrane wall (or membrane surface), thereby forming filtrate, and the solids, or at least part of the total range of solids, may not pass the membrane wall of the tubular membranes, thereby forming retentate. Liquid that may need to be filtrated may for instance be waste water from industries and/or house 25 holds, from market farming or fruit farming, from car washes, from laundries, etc. Such liquid may comprise solids. In general, the liquid will be water containing solid solids. The part of the liquid that docs not cross the membrane is indicated as retentate, as opposed to the part that crosses the membrane, which is indicated as filtrate or diffusate. Retentate is sometimes also indicated as “sludge” or “concentrate”.

30 In prior art systems, water may be distributed over the surface of the membrane walls with a high speed in order to remove (accumulated) solids; with the present invention this is not necessary. In the invention, by centrifugal forces the solids may be transported to the external of the cylinder, i.e. the retentate volume, from which it may 4 be transported to a retentate receiver external from the membrane filtration unit. The farther solids may penetrate the tubular membrane in a direction from the internal cavity to the retentate volume, the stronger the centrifugal forces become; this may also advantageously help purifying the liquid from solids. Or in other words, this facilitates 5 providing a concentrate to the retentate volume external from the cylinder and keeping the purified water within the cylinder to allow passing the membranes surface to escape to the filtrate volume.

Therefore, the rotation is not necessarily used to let a liquid flow with a high speed over the membrane surface in order to remove membrane fouling, but the 10 rotation is primarily used to transport by centrifugal forces heavier solids in the liquid within the membrane tubes to the retentate volume. In an embodiment, the rotational speed may be in the range of about 0.1-20 s'1, such as about 0.5-10 s'1, especially in the range of about 1-5 s'. Hydrocylcones may have a rotational speed that are an order of magnitude larger.

15 In a specific embodiment, the vessel chamber wall comprises a protrusion protruding into the retentate volume, wherein the protrusion is arranged to provide a back pulse to at least part of the total number of plurality of tubular membranes when this part passes during rotation the protrusion. This back pulse is provided with retentate in the retentate volume. The retentate, which is a liquid, may also rotate, and 20 when passing a protrusion, retentate is “squeezed” between the protrusion and the (rotating) cylinder unit, which may cause such back pulse.

The term “a protrusion” may also relate to a plurality of protrusions. Hence, in a variant, the membrane filtration unit (more precisely the vessel chamber wall) comprises a plurality of protrusions. With such protrusion(s) in a pulsed way liquid 25 (which may thus be retentate) may be pressed into at least part of the membrane tubes. Thereby, accumulated solids may be removed from the membrane surface. The protrusion(s) may thus be used to provide a back pulse. In general, the more protrusions (and thus also deepenings between the protrusions), the more back pulses may be provided while rotating the rotatable cylinder.

30 Further, the retentate may, as a result of the rotation of the rotatable cylinder, and optionally also due to roughness of or due to the optional presence of screw elements at for instance the external of the cylinder outer wall, rotate. The higher the rotational speed of the retentate in the retentate volume, also the more back pulses may be 5 provided. Likewise, the higher the roughness of the cylinder outer wall, the better the retentate in the retentate volume is carried away with the rotation of the rotatable cylinder.

In a specific embodiment, the protrusion has a shape (also) arranged to direct 5 flow of retentate in a predefined direction, preferably in a direction of the bottom of the vessel. Note that preferably the membrane filtration unit is arranged to have the axis of rotation of the rotatable cylinder unit perpendicular to earth’s surface; this may facilitate sedimentation of solids. For instance, a protrusion with a spiral like shape may be provided, arranged to facilitate flow of retentate escaping from the rotatable cylinder 10 in a direction to the bottom of the membrane filtration unit.

The vessel may contain an outlet, preferably at the bottom of the unit, providing the liquid contact between the retentate volume and the retentate receiver. Preferably, the bottom has a tapering bottom, thereby facilitating concentration of the solids.

The flow from the retentate volume of retentate to the retentate receiver may not 15 be constant. This may be a pulsed wise or otherwise discontinuous flow.

Hence, the term “in liquid contact” does not exclude the presence of shutters or valves or other means that may temporarily interrupt a flow from one item to another item. A non-constant removal of the retentate from the retentate volume may also be advantageous in view of energy consumption.

20 Advantageously, liquid comprising solids that have to be separated from the liquid does in the invention not need to be circulated (a number of times) in order to concentrate the retentate, whereas in the art this is often necessary. Of course, circulation of the liquid is not excluded and may, if desired, be applied. In the invention, the “dead end” principle may be applied, i.e.: essentially all of the liquid 25 entering the filter is either retained as permeate or as retentate, so the conversion can approach 100%, all in a first pass.

Advantageously, the desired concentration of the retentate can be controlled by controlling the flow of retentate leaving the membrane filtration unit, i.e. leaving the retentate volume. Further, advantageously, concentration of the retentate (with 30 centrifugal forces) and filtration are performed in “one step”.

As mentioned above, the rotational speed may be relatively low, such as in the order of 1-5 s'1, which advantageously also reduced frictional forces and thus energy 6 loss. Depending upon the solids or solids spectrum to be removed, the rotational speed may be adjusted.

The central cavity will in general have a cylindrical shape. Further, the central cavity may extend within the rotatable cylinder along a substantial part of the 5 longitudinal cylinder axis length.

In a specific embodiment, the central cavity comprises a screw element arranged to generate a rotational force to the rotatable cylinder unit due to a flow from the liquid through the central cavity in a direction from an inlet of the rotatable cylinder (arranged to allow the liquid enter the central cavity), such as from the external liquid source, to 10 the vessel retentate volume. In this way, simply by providing liquid to the membrane filtration unit, the rotatable cylinder may start rotating and rotate during use. However, alternatively or additionally, the membrane filtration unit may further comprise a device, such as a motor, arranged to provide a rotational force to the rotatable cylinder unit. Hence, this device, such as a motor, may provide all rotational force to rotate the 15 rotatable cylinder or may assist the rotation. The phrase “generating a rotational force to the rotatable cylinder unit” especially indicates that the rotatable cylinder unit will be rotated along the cylinder axis.

The tubular membranes that may be used may be selected from the group of types reverse osmosis, nano filtration, ultra filtration, micro filtration, and particle filtration, 20 especially ultra or micro filtration. The membrane filtration unit is especially arranged to transport with solids polluted liquid from the central cavity to the retentate volume, whereby at the cavity side or inlet side of the tubular membranes this polluted liquid may be found, whereas at the retentate volume end of the tubular membranes, concentrated polluted liquid (retentate) may be found. The membrane filtration unit 25 may be able to separate liquids for instance up to about 5000 1/h.

The tubular membranes filtrate liquid, thereby providing filtrate at a filtrate side of the tubular membranes. Filtrate is provided to the filtrate cavity of the rotatable cylinder unit.

The volume of the cylinder unit comprises in general essentially two parts: the 30 central cavity, wherein liquid is received, and the rest of the volume. The rest of the volume is at partially occupied by the channels between the cylinder inner wall and the cylinder outer wall. Free space, such as between the channels, at the filtrate sides of the tubular membranes, is herein indicated as filtrate cavity. Hence, the rotatable cylinder 7 unit is arranged to allow liquid pass from the central cavity to the vessel retentate volume and is arranged to allow liquid only as filtrate pass the tubular membranes to the filtrate cavity. Filtrate from the filtrate cavity may be transported to the external filtrate receiver (via an outlet in the central cavity). Thus, substantially only filtrate may 5 flow from the central cavity to the filtrate cavity. The central cavity is thus at least partially surrounded by filtrate cavity.

The cylinder unit in general may comprise a hollow shaft, that partly provides the central cavity, and a part separate from the central cavity, which part is indicated as filtrate cavity, and which is at least partly penetrated by channels from the central 10 cavity to the external of the cylinder unit, and which channels comprise the membranes. Another part of the hollow shaft may form part of the central cavity. Hence, the cylinder unit may be arranged to allow liquid enter the central cavity of the cylinder, via especially the hollow shaft, flow as retentate through the channels to the external (vessel retentate volume) from the cylinder unit and partly pass as filtrate the 15 membranes and enter the central cavity (within the cylinder unit but separate from the central cavity), and escape from the central cavity via another part of the hollow shaft.

Method

According to a further aspect, the invention provides a method for filtrating a 20 liquid (from an external liquid source) and to provide thereby a filtrate (to an external filtrate receiver) and a retentate (to an external retentate receiver), the method comprising providing a membrane filtration unit as described above, and wherein the method further comprises flowing the liquid from the liquid source to the central cavity and rotating the rotatable cylinder unit by a rotational force.

25 As mentioned above, at least part of the rotational force may be derived from a flow from the liquid through the central cavity in a direction from the external liquid source to the vessel retentate volume.

In a preferred embodiment, the flow of the liquid in the central cavity, the flow of the filtrate to the filtrate receiver, and the flow of the retentate to the retentate receiver 30 are controlled to maintain a pressure difference over the tubular membranes in the range of about 0.05-10 bar. Hence, there may be a pressure difference over the tubular membranes (i.e. a pressure difference of between inlet and outlet of the channel) in the order of about 0.05-10 bar, such as about 0.1-5 bar.

8 Τη an embodiment, the rotational speed of the rotatable cylinder unit is especially maintained in the range of 1-5 s'1 (see also above).

Hence, the invention also provides the use of rotation of a rotatable cylinder unit comprising a plurality of radially arranged tubular membranes for filtrating a liquid to 5 provide thereby a filtrate and a retentate. Herein, especially the retentate flows through the membranes to a volume external from the rotatable cylinder, and filtrate, such as potable water, flows to a volume, such as a collection volume (herein indicated as filtrate cavity), within the cylinder. This volume may be the volume between the channels, such as in an embodiment, the tubular membranes within the rotatable 10 cylinder.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding 15 reference symbols indicate corresponding parts, and in which:

Figures la-lb schematically depict embodiments of the membrane filtration unit; and

Figures 2a-2f schematically depict specific variants, for instance on the embodiments of figures la and lb.

20 The schematically depicted embodiments may not be on scale.

Description of preferred embodiments

Figure la schematically depicts a membrane filtration unit 100 according to an embodiment of the invention. The membrane filtration unit 100 is arranged to filter a 25 liquid 1 from an external liquid source 10, such as an industry, and to provide thereby a filtrate 2, such as potable water, to an external filtrate receiver 20, such as households or public potable water distributors, and a retentate 3, such as sludge (or concentrate). Retentate 3 may permanently, but preferably intermittently be released from the retentate volume (see below) to an external retentate receiver 30, such as a sludge 30 depot, a disposal, a sewerage, etc. At least part of the retentate may also be circulated. Further, retentate may comprise reusable components, and may thus at least partly be reused.

9

The membrane filtration unit 100 comprises a vessel 40 having a vessel chamber 41, with vessel wall 42, enclosing a chamber volume 46. The chamber volume 46 comprises a rotatable cylinder unit 50. Hence, the chamber volume 46 is divided in a filter volume containing the rotatable cylinder unit 50 and a vessel retentate volume 43, 5 the latter being external from the rotatable cylinder unit 50. The retentate volume 43 is in liquid contact with the retentate receiver 30. As mentioned above, the term “in liquid contact” indicates that there is a connection such that retentate 3 from the retentate volume 43 may flow to the retentate receiver 30, but does not exclude that a shutter or valve, during operation of the membrane filtration unit 100, temporarily interrupts this 10 liquid contact. The vessel 40 has a vessel chamber wall 42, which encloses the chamber volume 46. Retentate 3 may leave the membrane filtration unit 100, i.e. especially the retentate volume 43 via outlet 49 (to a retentate receiver 30).

The rotatable cylinder unit 50 is arranged to receive the liquid 1 from the liquid source 10, and is arranged to separate the liquid 1 into filtrate 2 and retentate 3. Liquid 15 1 may enter the rotatable cylinder unit 50 at inlet 58, which allows liquid 1 flow in or in or to the central cavity (see below). The liquid 1 in general contains solids, and the filtrate 2 contains no solids, or less solids relative to the liquid 1, whereas the retentate 3 may comprise solids in a content higher than the liquid 1.

The rotatable cylinder unit 50 comprises a cylinder outer wall 53, a cylinder inner 20 wall 57 forming a central cavity 51 within the rotatable cylinder unit 50, and a plurality of radially arranged tubular membranes 52 arranged as at least part of channels between the cylinder inner wall 57 and the cylinder outer wall 53. In embodiments, the channels between the cylinder inner wall 57 and the cylinder outer wall 53 essentially are the tubular membranes 52. The tubular membranes 52 are arranged to allow the liquid 1 25 flow in a direction from the central cavity 51 to the vessel retentate volume 43. Further, the tubular membranes 52 are arranged to selectively pass filtrate 2 through membrane walls 55 of the tubular membranes 52 to the filtrate cavity 54 of the rotatable cylinder unit 50. The filtrate cavity 54 is in liquid contact with a the filtrate receiver 20. Filtrate 2 may escape from the rotatable cylinder 50 (to the external filtrate receiver) via outlet 30 59. This outlet is arranged to allow filtrate 2 from the filtrate cavity 54 escape and leave the membrane filtration unit 100. In this embodiment, the central cavity 51 extends within the rotatable cylinder along a substantial part, here about > 85% of the longitudinal cylinder axis length.

10

The rotatable cylinder unit 50 thus encloses a rotatable cylinder unit volume. This volume is essentially composed of the volume of the central cavity 51, the volume occupied by the tubular membranes 52 and the remaining volume. The latter may essentially consist of the volume occupied by the filtrate cavity 54. Liquid 1 may in 5 principle only enter this filtrate cavity 54 by passing the membrane walls 55 of the tubular membranes 52 (i.e. filtration). The cylinder inner wall 57 substantially encloses the central cavity 51.

As is clear from the schematic drawing, the liquid 1 is directed to the central cavity 51. The liquid source 10 may thus be in liquid contact with the central cavity 51. 10 The membrane filtration unit 100 is arranged to allow liquid 1 flow from liquid source 10 only to central cavity 51 (thus not directly into the retentate volume 43 or into other parts of the filtration cylinder 50 than the central cavity 51). Downstream from the central cavity 51, liquid 1 flows through the tubular membranes 52 an by filtration by the membranes 52 and by centrifugal forces when the filtration cylinder 50 rotates, 15 solids are removed concentrated and accumulated in the retentate volume 43, from which the solids permanently or intermittently may be removed (from instance as sludge). Further, the tubular membranes 52 may separate at least part from the liquid 1 as filtrate 2, which leaves the membranes 52 through the membrane surface, thereby diverging from a flow of liquid 1 from the central cavity 51 to the retentate volume 43, 20 and arriving in the filtrate cavity 54. The filtrate cavity 54 may be a volume between the tubular membranes 52, and may optionally also further include an additional volume of the filtration cylinder 50, as schematically depicted in figure la. As mentioned above, liquid 1 may not directly flow into filtrate cavity 54. Cavity closure 65 is depicted (see also below), which may prevent such unhindered flow of liquid 1. 25 The filtration cylinder 50 is arranged to allow liquid 1 arrive into filtrate cavity 54 only after filtration through the tubular membranes 52.

Thus, the central cavity 51 is in liquid contact, through tubular membranes 52 with the retentate volume 43 and may be arranged to be in liquid contact with the filtrate cavity 54 for filtrate 2, i.e. for filtered liquid 1. Retentate volume 43 and filtrate 30 cavity 54 are both arranged downstream of the filtrate cavity. The retentate volume 43 is downstream of the central cavity 51 and upstream of the retentate receiver 30. The filtrate cavity 54 is downstream of the central cavity 51 and upstream of the receiver 20.

11

Herein, the terms “upstream” and “downstream” relate to an arrangement or presence of items or features relative to the propagation of the liquid, wherein relative to a first position within a flow of liquid, a second position in the flow of liquid closer to the liquid source is “upstream”, and a third position within the flow of liquid further 5 away from the source is “downstream”.

In the schematic drawing of figure la, the central cavity 51 comprises a screw element 56 (which is optional) arranged to generate a rotational force to the rotatable cylinder unit 50. Due to a flow from the liquid 1 through the central cavity 51 in a direction from the external liquid source 10 to the vessel retentate volume 43, rotational 10 forces are applied to the rotatable cylinder unit 50. In this way, the cylinder unit 50 may rotate, either by the liquid flow alone, or also with help of an motor (not depicted). Therefore, in an embodiment, the membrane filtration unit may further comprise a motor arranged to provide a rotational force to the rotatable cylinder unit 50. This motor, or other device, may be arranged external from the vessel 40.

15 In the schematic drawing of figure la, the vessel chamber wall 42 of the membrane filtration unit 100 further comprises a protrusion 44 (which is optional), here (and also preferably), a plurality of protrusions 44, protruding into the retentate volume 43. The protrusion(s) 44 is (are) arranged to provide a back pulse to at least part of the total number of plurality of tubular membranes 52 when this part passes during rotation 20 the protrusion 44. Due to the rotation of the cylinder, also liquid in the retentate volume 43 will flow (i.e. rotate), when passing the protrusion 44, the liquid may be pressed into the tubular membrane(s) 52. In this way, a back pulse may be provided and the tubular membrane(s) 52 may (partly) be cleaned from solids, such as solids accumulating at the surface of the tubular membranes 52. Hence, in an embodiment, the vessel chamber 25 wall 42 comprises a protrusion 44 (including optional a plurality of protrusions 44) protruding into the retentate volume 43, wherein the protrusion 44 is arranged to provide (during use of the membrane filtration unit) with retentate 3 (within the retentate volume 43) a back pulse to at least part of the total number of plurality of tubular membranes 52 when this part passes during rotation the protrusion 44. 30 Preferably, the protrusion(s) 44 has (have) a shape (also) arranged to direct flow of retentate 3 in a predefined direction, preferably in a direction of the bottom of the vessel 40.

12

Figure lb schematically depicts another embodiment of the membrane filtration unit 100. This drawing in some more detail shows channels 60, connecting the central cavity 51 and the retentate volume 43, and which at least partly comprise the tubular membranes 52. The channels 60, have inlets 61, at the central cavity side, and outlets 5 62 to the retentate volume. In this drawing, also an embodiment of the closure 65 of the central cavity 51 is depicted.

Figure 2a schematically depicts a cross section of an embodiment of the membrane filtration unit 100. Further, embodiments of protrusions 44 are shown. The protrusions 44 may have a part of increasing thickness, in a direction along part of the 10 perimeter of the vessel chamber wall 42. Assuming an arrangement of the membrane filtration unit 100 with the axis of rotation perpendicular to the earth’s surface, the protrusion(s) 44 may also have a part of increasing thickness, in along part of the vessel chamber wall 42 a direction parallel to the axis of rotation and in a direction away from the earth’s surface (see also figure la).

15 Figure 2b schematically depicts another embodiment of the membrane filtration unit 100 according to the invention, wherein the vessel chamber wall 42 has an oval shape; i.e. the vessel 40 has an oval cross section. Also such shape, with or without protrusions 44, may facilitate the generation of back pulses when the filtration cylinder 50 rotates in the (retentate) liquid contained in the retentate volume 43. The rotatable 20 cylinder unit 50 will in general have a cylindrical shape, or optionally a conical shape.

Figure 2c schematically depicts an embodiment, wherein the vessel 40 has a cross section that may vary in perimeter. Here, again assuming an arrangement of the membrane filtration unit 100 with the axis of rotation perpendicular to earth’s surface, the membrane filtration unit 100 may have a perimeter that decreases along at least part 25 of the vessel chamber wall in a direction to the earth surface. Hence, in an embodiment, the membrane filtration unit 100 has a tapered bottom part, or is substantially entirely tapered (i.c. the vessel chamber wall 42 has a tapered part or is substantially entirely tapered (as schematically depicted in figure 2c)). Such shape may further enable collection of solids at the bottom of the retentate volume 43, thereby facilitation 30 removal of the solids, either permanently or with intervals from the retentate volume to the retentate receiver 30. Note that the oval vessel of figure 2b may also have a tapered part of the vessel chamber wall 42.

13

Figure 2d schematically depicts an embodiment wherein the filtration cylinder 50 may be arranged as removable part. The filtration cylinder 50 may be arranged at end position in ball bearing connection(s) 70, which are arranged to allow rotation of the filtration cylinder 50 along its rotation axis and which are arranged to hold the filtration 5 cylinder in this rotational arrangement. For instance, the bottom or top part of the vessel 40 may be removable, or at least partly removable, which may allow removing or replacing the filtration cylinder 50. This may advantageously allow easy maintenance or replacement of the filtration cylinder 50. The ball bearing connection 70 comprises a ball bearing 71. By way of example, such ball bearing connection 70 is 10 only depicted at one side of the filtration cylinder 50, but as will be clear to the person skilled in the art, also at the other side thereof, such ball bearing connection 70 may be arranged. Such ball bearing connection 70 may be waterproof.

Figure 2e schematically depicts an embodiment of the filtration cylinder 50, wherein the channels 60 are substantially formed by tubular membranes 52, which are 15 end parts integrated in the cylinder inner wall 57 and cylinder outer wall 53, respectively. One or both walls may be double walls, with for instance a resin in between. Such resin may allow a good connection with the tubular membranes 52, providing a waterproof enclosure of the tubular membranes at the respective walls. The presence of the openings 62 at the cylinder outer wall 53 may provide a certain 20 roughness to the surface of the outer wall 53. This may advantageously facilitate drawing the retentate 3 with the rotation of the rotatable cylinder 50. Further, optionally screw elements (not drawn) may be provided to the exterior of the rotatable cylinder unit 50, whereby also the rotation of the retentate 3 within the retentate volume 43 may be facilitated. This rotation, together with the optional protrusion(s) 44 and the optional 25 oval shape of the vessel 40 may provide the back pulses directed into the tubular membranes 52.

Figure 2f schematically depicts a tubular membrane 52, with membrane wall (s) 55, and membrane surface 55a. Retentate may flow through the tubular membrane and filtrate may pass the membrane surface 55a (to the filtrate cavity).

30 With the membrane filtration unit 100, a method for filtrating the liquid 1 from the external liquid source 10 may be performed, thereby providing filtrate 2 to the external filtrate receiver 20 and retentate 3 to the retentate volume 43, which may be drained off to the external retentate receiver 30. The method comprises flowing the 14 liquid 1 from the liquid source 10 to the central cavity 51 and rotating the rotatable cylinder unit 50 by a rotational force.

The rotation of the rotatable cylinder unit 50, for instance as schematically depicted in the above discussed drawings, comprising a plurality of radially arranged 5 tubular membranes 52, may be used for filtrating liquid 1 to provide thereby filtrate 2 and retentate 3.

The invention further provides the following aspects: 1. A membrane filtration unit (100), arranged to filtrate a liquid (1) (from an 10 external liquid source (10)) and to provide thereby a filtrate (2) (to an external filtrate receiver (20)) and a retentate (3), wherein a. the membrane filtration unit (100) comprises a vessel (40) having a vessel chamber wall (42) enclosing a chamber volume (46), which is divided in a filter volume containing a rotatable cylinder unit (50) and a vessel retentate volume (43), 15 external from the rotatable cylinder unit (50)); b. the rotatable cylinder unit (50) is arranged to receive the liquid (1) from an external liquid source (10), and is arranged to separate the liquid (1) into filtrate (2) and retentate (3); c. the rotatable cylinder unit (50) comprises a cylinder outer wall (53), a 20 cylinder inner wall (57) forming a central cavity (51) within the rotatable cylinder unit (50), and a plurality of radially arranged tubular membranes (52) arranged as at least part of channels between the cylinder inner wall (57) and the cylinder outer wall (53), wherein the tubular membranes (52) are arranged to allow the liquid (1) flow in a direction from the central cavity (51) to the vessel retentate volume (43), and wherein 25 the tubular membranes (52) are arranged to selectively pass filtrate (2) through membrane walls (55) of the tubular membranes (52) to the filtrate cavity (54) of the rotatable cylinder unit (50) (and wherein the filtrate cavity (54) is in liquid contact with a the filtrate receiver (20)).

2. The membrane filtration unit (100) according to aspect 1, wherein the 30 central cavity (51) comprises a screw element (56) arranged to generate a rotational force to the rotatable cylinder unit (50) due to a flow from the liquid (1) through the central cavity (51) in a direction from the an inlet (58) of the rotatable cylinder 15 (arranged to allow the liquid (1) enter the central cavity (51), such as from external liquid source (10), to the vessel retentate volume (43).

3. The membrane filtration unit (100) according to any one of the preceding aspects, wherein the vessel chamber wall (42) comprises a protrusion (44) protruding 5 into the retentate volume (43), wherein the protrusion (44) is arranged to provide (during use of the membrane filtration unit) with retentate (3) (within the retentate volume (43)) a back pulse to at least part of the total number of plurality of tubular membranes (52) when this part passes during rotation the protrusion (44).

4. The membrane filtration unit (100) according to aspect 3, wherein the 10 protrusion (44) has a shape arranged to direct flow of retentate (3) in a predefined direction, preferably in a direction of the bottom of the vessel (40).

5. The membrane filtration unit (100) according to any one of aspects 3-4, comprising a plurality of protrusions (44).

6. The membrane filtration unit (100) according to any one of the preceding 15 aspects, further comprising a motor arranged to provide a rotational force to the rotatable cylinder unit (50).

7. The membrane filtration unit (100) according to any one of the preceding aspects, wherein the filtrate cavity (54) is in liquid contact with an external filtrate receiver (20) 20 8. A method for filtrating a liquid (1) from an external liquid source (10) and to provide thereby a filtrate (2) to an external filtrate receiver (20) and a retentate (3), the method comprising providing a membrane filtration unit (100) according to any one of the preceding aspects, and wherein the method further comprises flowing the liquid (1) from the liquid source (10) to the central cavity (51) and rotating the rotatable cylinder 25 unit (50) by a rotational force.

9. The method according to aspect 8, wherein at least part of the rotational force is derived from a flow from the liquid (1) through the central cavity (51) in a direction from the external liquid source (10) to the vessel retentate volume (43).

10. The method according to any one of aspects 8-9, wherein the flow of the 30 liquid (1) in the central cavity (51), the flow of the filtrate (2) to the filtrate receiver (20), and the flow of the retentate (3) to a retentate receiver (30), which is in liquid contact with the retentate volume (43), are controlled to maintain a pressure difference over the tubular membranes (52) in the range of 0.5-10 bar.

16 11. The method according to any one of aspects 8-10, wherein the rotational speed of the rotatable cylinder unit is maintained in the range of 1-5 s'1.

12. Use of rotation of a rotatable cylinder unit (50) comprising a plurality of radially arranged tubular membranes (52) for filtrating a liquid (1) to provide thereby a 5 filtrate (2) and a retentate (3).

The term “substantially” herein, such as in “substantially consists”, will be understood by the person skilled in the art. The terms “substantially” or “about” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in 10 embodiments the adjective substantially may also be removed. Where applicable, the terms “substantially” or “about” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of’.

15 Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than 20 described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than 25 limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or 30 "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by 17 one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

A membrane filtration unit, arranged to filter a liquid, thereby providing a filtrate and a retentate, the membrane filtration unit comprising a vessel comprising a vessel chamber wall enclosing a chamber volume, which chamber volume is divided into a filter volume containing a rotatable cylinder unit, and a vessel volume for the retentate external to the rotatable cylinder unit; b. the rotatable cylinder unit is arranged to receive the fluid from an external fluid source, and is arranged to separate the fluid into filtrate and retentate; c. the rotatable cylinder unit, which comprises a cylinder outer wall, a cylinder inner wall that forms a central cavity within the rotatable cylinder unit, and a plurality of radially arranged tubular membranes arranged as at least portions of channels between the cylinder inner wall and the cylinder outer wall, the tubular membranes arranged to allow the fluid to flow in a direction from the central cavity to the vessel volume for the retentate, and wherein the tubular membranes are arranged to allow filtrate to pass selectively through the membrane wall of the tubular membranes to a filtrate cavity of the rotatable cylinder unit.

2. The membrane filtration unit according to claim 1, wherein the central cavity comprises a screw element arranged to generate a rotational force on the rotatable cylinder unit as a result of the flow of the liquid through the central cavity in a direction of an entrance to the cylinder unit arranged to admit the liquid to the central cavity of the cylinder unit, to the vessel volume for the retentate.

3. The membrane filtration unit according to one or more of the preceding claims, wherein the vessel chamber wall comprises a protrusion protruding into the vessel volume for the retentate, the protrusion being arranged to provide a back pulse with retentate in operation at least a portion of the total amount of plural of tubular membranes when this portion passes the bulge during rotation.

The membrane filtration unit according to claim 3, wherein the protrusion has a shape arranged to direct a flow of retentate in a predetermined direction, preferably in the direction of the bottom of the vessel.

The membrane filtration unit according to one or more of claims 3-4, comprising a plurality of protrusions.

The membrane filtration unit according to one or more of the preceding claims, further comprising a motor arranged to provide a rotational force on the rotatable cylinder unit.

The membrane filtration unit according to one or more of the preceding claims, wherein the filtrate cavity is in fluid contact with an external filtrate receiver.

The membrane filtration unit according to one or more of the preceding claims, wherein the vessel chamber wall in any case partially has a tapered shape.

9. Method for filtering liquid from an external liquid source to provide a filtrate and a retentate, comprising providing a membrane filtration unit according to one or more of the preceding claims, wherein the method further flows a liquid from an external fluid source to the central cavity and rotating the rotatable cylinder unit by a rotational force.

10. The method of claim 9, wherein the rotational force is derived at least in part from a flow of the fluid through the central cavity in a direction of an entrance of the cylinder unit arranged to allow the liquid to enter the cylinder unit to the vessel volume for the retentate.

11. The method according to any of claims 9-10, wherein the flow of the fluid in the central cavity, the flow from the filtrate to a filtrate receiver, and the flow from the retentate to a retentate receiver, which is in fluid contact with the retentate volume, are controlled to maintain a pressure difference across the tubular membranes tc in the order of 0.5-10 bar.

The method of any one of claims 9-11, wherein the rotational speed of the rotatable cylinder unit is kept in the range of 1-5 s'1.

Use of the rotation of a rotatable cylinder unit comprising a plurality or radially arranged tubular membranes for filtering a liquid to provide a filtrate and a retentate.