Element Having a Porous Wall

This invention relates to an element having a porous wall. More particularly, this invention relates to a filtration element.

As is known, various types of elements have been provided for the filtration of various fluids. For example, British Pat. No. 2,011,796 describes a filter element which is disposed within a vessel so as to filter a fluid flow. In this case, the filter element is formed as a tubular structure with a porous wall through which a filtrate may pass into an internal chamber for subsequent removal from the vessel.

One problem which always arises in the filtration of any media or fluid is to give each individual part of the medium a chance to expose the filtrate to the filter collecting chamber. That is, the filter is more efficient as the filter is better able to filter out all the filterable proportion from a given fluid flow. However, achieving this state becomes difficult in practical filtration. Specifically, boundary layers form inside the vessel on the walls which bound the filtrate collecting chambers and the rate of flow or the passage of the filtrate in the boundary layers decreases so that only a small proportion of the through-flowing fluid contacts the actual porous wall. Further, the removal of the filtrate often causes an increase in the viscosity of the fluid to be filtered. This, in turn, adds to or, at least, preserves the boundary layers.

Heretofore, various attempts have been made to provide an additional exchange of those zones of the through-flowing fluid which are near the porous walls, for example, by positioning a series of wire screens in those zones so as to increase the turbulence of the fluid flowing over the porous wall. In some cases, the filter surface has been moved relative to the fluid flow. Unfortunately, at flow speeds which provide satisfactory take-up of the filterable proportion, actions of these kind either consume substantial energy or are of limited effect and also expensive. These difficulties also occur with various eddy-producing devices on the porous walls as well as with the variously known agitators or scraper vanes which have been operative along the filtration surfaces of a filter or with devices known generically as static mixers.

By way of example, guide or deflecting surfaces have sometimes been provided in the flow to a filtration surface in order to produce a braided or plaited flow after such a surface. In addition, the filter surface can also be moved across the flow direction of the treatment material. In many cases, the flow speeds are in the laminar range. However, it must be possible for the proportion of that flow which is to be removed by filtration to be in contact with the filter surface for a sufficiently long time. Braided flows, on the one hand, decay rapidly and have little effect so far as the subsequent filter surfaces are concerned. Further, moving filter surfaces are effective but are technologically very elaborate.

The range of problems noted above also becomes increasingly difficult as the filter pore size decreases.

Where turbulence generators have been used to produce eddy currents in the flow issuing from them, such eddy currents, in the light of the Reynolds numbers normal in such systems, are sometimes the characteristic dimensions of the turbulence generator. They therefore have only a very limited effect as far as filter surfaces are concerned.

Accordingly, it is an object of the invention to increase the contact time of the filtrate of a fluid flow with a filter surface.

It is another object of the invention to remove residues building up on a porous filter surface during operation in a relatively efficient manner.

It is another object of the invention to prevent the build-up of residues on a porous filter surface for a fluid flow.

It is another object of the invention to even out differences in concentration in a fluid being filtered.

It is another object of the invention to be able to filter a fluid flow at reduced flow losses and technological outlay.

It is another object of the invention to provide a filter structure which can be used in processes requiring small to very small pore sizes in the material to be filtered.

Briefly, the invention provides an element for positioning in a fluid flow which has an inner chamber and a porous wall bounding the chamber, at least in part. In addition, the element is of a shape to define a turbulence generator for generating turbulence particularly in the form of a static mixer in a fluid flow passing thereover.

The element may be constructed with a plate-like cross-section, for example in the form of a lamella, or may have a tubular cross-section.

The shape of the element may be similar to the shape of a static mixer element and may be combined with like elements in a static mixer array.

A filter employing the element may be constructed with a vessel for a fluid flow wherein a wall of the vessel separates the fluid flow from the exterior of the vessel. In this case, at least one of the elements is disposed in the vessel so as to generate turbulence in the fluid flow while at the same time filtering a filtrate from the fluid flow through the porous wall into the inner chamber of the element for subsequent outlet through the wall of the vessel to the exterior. Alternatively, the element may be used to introduce a fluid such as a gas into the fluid flow.

The construction of the filter element is such that the element provides guide or deflecting surfaces in a constructionally unitary manner. Thus, braided flows which issue from the deflecting surfaces are operative for the filter surface even as they arise. Consequently, higher shearing stresses on the filter surfaces are available than in previously known systems which are disposed after or before a filter element. Further, the filter surface remains open and the pores are not restricted by any deposits. Thus, a thorough mixing of the fluid flow is combined with the exposure of the filter surface to the various proportions of the fluid flow.

The filter element may be formed in a corrugated manner so that wave like surfaces are provided to the fluid flow in order to increase turbulence in the fluid flow. Because of the geometry of the element, a continuous reorientation and intensive mixing of a passing fluid flow occurs in such a manner that the boundary layers of the fluid near the surfaces of the element are renewed and replaced by components which tend to move towards the center of the fluid flow. Thus, a so called plug flow arises.

These and other objects and advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a cross-sectional view through an element constructed in accordance with the invention;

FIG. 2 illustrates a cross-sectional view of an element having a plate or a tubular cross-section in accordance with the invention;

FIG. 3 illustrates a cross-sectional view of a filter structure employing a vessel and an element in accordance with the invention;

FIG. 4 illustrates a part perspective view of a further embodiment of an element in accordance with the invention;

FIG. 5 illustrates a plan view of a vessel having a corrugated filter element in accordance with the invention;

FIG. 6 illustrates a view taken on line A--A of FIG. 5;

FIG. 7 illustrates a corrugated element constructed in accordance with the invention;

FIG. 8 illustrates a cross-sectional view of a vessel containing a plurality of elements constructed in accordance with the invention;

FIG. 9 illustrates a cross-sectional view of a different cross-section of the vessel in FIG. 8;

FIG. 10 illustrates a diagrammatic perspective view of an element shaped to form a helical static mixer fitted within a vessel in accordance with the invention;

FIG. 11 illustrates a diagrammatic view of two-shaped elements combined to form a static mixer in accordance with the invention;

FIG. 12 illustrates a diagrammatic view of plate-like elements combined to form a static mixer in accordance with the invention;

FIG. 13 illustrates a diagrammatic view of corrugated elements combined to form a static mixer in accordance with the invention;

FIG. 13a illustrates a view taken on line C--C of FIG. 13; and

FIG. 14 illustrates a view taken on line B--B of FIG. 6.

Referring to FIG. 1, the element is formed of a pair of porous walls 1 each of which is carried by a support mesh or lattice 19 which defines a closed inner chamber 4. As indicated, the porous walls 1 form the boundary of the inner chamber 4 and are in parallel relation to each other. This element has a plate-like cross-section and is shaped, for example as indicated in FIG. 7, to define a corrugated or wavy shape which functions as a turbulence generator 8 for generating turbulence in a fluid flow passing thereover.

Each porous wall 1 of the element is of a porosity to permit a proportion, i.e. a filtrate of the fluid flow to pass through into the inner chamber 4.

Referring to FIG. 2, the element may be constructed with a pair of porous walls 1, each of which is mounted on a separate support mesh 19 with the inner chamber 4 disposed between the two meshes. As indicated, each support mesh 19 has a structure which is inherently pervious. In this regard, the meshes 19 have average apertures which are at least three times as large as those of the pores of the walls 1 in order to enable fluid to flow through the walls 1 and into the inner chamber 4.

Of note, the element may be of tubular cross-section wherein the porous wall 1 is tubular and is mounted on a mesh 19 of tubular shape.

Referring to FIG. 3, an element constructed with a cross-section as indicated in FIG. 1 and corrugated in a manner similar to that shown in FIG. 7, is placed in a vessel 3 having an internal wall 10 to define a path for a fluid flow, as indicated by the arrows 2. As indicated in FIG. 3, the element is disposed on a diametric plane of the vessel 3 while being shaped to conform to the cylindrical interior surface of the vessel 3 along the length of a vessel 3 as indicated in FIG. 5. The element itself forms a turbulence generator for the fluid flow 2 so as to generate turbulence within the flow.

As indicated FIG. 3, the vessel 3 may be disposed in a second tube 22 in spaced concentric relation so that a chamber 5 is disposed between the vessel 3 and tube 22. Further, a plurality of tubes 11 are connected between an opening in the filter element and an opening in the wall 10 of the vessel 3 in order to communicate the inner chamber 4 of the filter element with the chamber 5 exterior to the vessel 3. In this way, filtrate which passes through the porous walls 1 of the filter element is able to pass through the tubes 11 into the chamber 5 for subsequent processing or recycling, as is known.

Referring to FIG. 6, in an alternative construction, the filter element may extend through the vessel 3 may have a solid wall with an inside diameter D1 and an outside diameter D2 and the wall 10 of the tubular vessel 3 so as to communicate the inner chamber 4 of the element directly with the chamber 5 exterior to the vessel wall 10.

If the element is to be used as a filter element, the walls 1 are porous only with respect to the component fluid flow 2 in the vessel 3 which is to flow through the wall 1 as a filtrate into the inner chamber 4 for a subsequent flow into the exterior chamber 5.

If the element is used to carry some other fluid, for example, a gas or a nutrient solution, the wall 1 may have a porosity relative to the fluid so as to mix this second fluid into the fluid flow 2. In this case, the element is a mixing element and the gas or nutrient solution would flow from the exterior chamber 5 into the inner chamber 4 and thereafter through the porous walls 1 in order to be mixed into the fluid flow 2 in the vessel 3. In the case of the embodiment illustrated in FIG. 3, the gas or nutrient solution would flow from the exterior chamber 5 through the tubes 11 and into the inner chamber 4 or as in the embodiment of FIG. 6, the gas or nutrient solution would flow directly from the exterior chamber 5 into the inner chamber of the element.

Each porous wall 1 may consist of at least one layer of a material of a porosity or of a pore size to impart a porosity for use in a microfiltration to ultrafiltration range i.e. in a micron, sub-micron or molecular range. In such a case, the layer may be a semi-permeable layer in the form of a diaphragm. Further, the layer of material may be a layer of polysulphone applied to or impregnated into a laminated sintered support mesh or lattice 19.

In another embodiment, the element may be made with a single porous wall 1 and a non-porous wall with the inner chamber 4 bounded by the two walls.

Referring to FIG. 4, the filter element may be held in a frame 13 which extends in seal-tight relation about the inner chamber 4 while a connecting pipe 14 extends through the frame 13 to communicate the inner chamber 4 with an external chamber.

Referring to FIGS. 8 and 9, a plurality of corrugated elements may be stacked together in parallel relation so as to define a plurality of filter chambers for a fluid flow within a vessel 3. In this case, one group of corrugated elements may be disposed in parallel while a second group of like elements is coaxially and angularly disposed, for example at 90.degree., to the first group as indicated in FIG. 9.

A plurality of a filter elements may be combined to form a module to provide a turbulence generator which functions as a static mixer 8. For example, as indicated in FIG. 10, a series of elements, each of which is of helical shape, may be disposed within a tubular vessel 3 in a coaxial manner. Alternatively, as shown in FIG. 11, each filter element may be formed as a tube with a plurality of tubes contiguous to each other to form a layer 16 as illustrated. In this case, the tubes in the adjacent layers 16 are disposed to cross one another. Further, the individual tubes may be provided with openings 12 in the form of slots which pass through the tubes in sealed relation to the inner chambers so that the fluid flow may pass directly through the filter elements. As indicated in FIG. 12, each filter element is in the form of a plate with the walls of each plate having turbulence producing vanes 21 thereon which act as guide surfaces for guiding the fluid flow therebetween. Further, the vanes 21 of adjacent layers cross each other in a transverse manner. As indicated in FIG. 13, each filter element layer 15 is corrugated with the corrugations 9 of each layer disposed in criss-crossing relation to the corrugations 9 of an adjacent layer 15. Further, openings 20 in the form of circular openings are provided as FIG. 11. In this case, the corrugations 9 of the respective layers 15 define turbulence producing surfaces.

The arrangements of the filter elements in the static mixer arrangements in FIGS. 11, 12 and 13 cause repeated deflections of the fluid flow passing over and through the filter elements. This, in turn, produces eddy currents which continuously bring more layers near the porous walls, so that each portion of the fluid flow has the chance of contacting the porous wall for a sufficiently long period of time to permit filtrate to pass through.

One interesting use of the filter elements is in fluidized reactor technology. In reactors of this kind, particularly in difficult technical areas such as technologies for the culture of living cells, turbulence generators are used to maintain a culture bed in a continuous state of thorough mixing and to make sure that there is no uncontrollable eddying in the bed and that there is no repeated mixing together of elements previously separated from one another. The above described filter elements which inherently form turbulence generators may be used to carry a fluid from an exterior chamber in order to gas the fluidized bed. If the porous wall is appropriately structured, i.e., is provided with an appropriate porous diaphragm, in situ gassing without bubbling can be provided in a reactor of this kind.

Referring to FIG. 14, one method of making a filter element such as illustrated in FIG. 6 may be as follows:

First, the plate-like element is corrugated and then introduced into a rotatable sleeve of a greater diameter D3 than the diameter of a subsequently finished vessel D2; the introduction of the corrugated element being such that the inner chamber is radially disposed. Next, the sleeve is rotated while a hardenable plastic is poured into the sleeve in order to form a hardened peripheral tube having an inside diameter D1 with the element secured therein at opposite radial ends. After curing or hardening is complete, the resulting sleeve with the embedded element is then withdrawn from the sleeve. An outer layer of the fabricated tube is then removed by grinding or turning so that the inner chamber of the filter element is exposed at opposite radial ends. In this respect, the tube is ground or turned down to a diameter D2 as indicated in FIG. 14. This diameter also corresponds to the diameter illustrated in FIG. 6. Once machined to this state, a unit arises in which the inner chamber of the element is open to the outside of the tube (vessel 3 in FIG. 6). This unit can then be inserted into a second tube having an inner diameter which can be as large as the diameter D3 indicated in FIG. 14.

The above method may be used with minor modification in order to produce a filter element as indicated in FIG. 3. However, in this case, the inner chamber 4 must be sealed off against the fluid flow 2 at the places 17 of the wall 10 of the vessel 3.

The invention thus provides a filter element which has a dual characteristic of being capable of filtering a fluid flow while also creating turbulence in the fluid flow. The construction of the filter element is such that a continuous stimulation or turbulence is imparted to a fluid flow flowing over the element. In this way, boundary layers are disturbed during fluid flow in a relatively simple economical manner without the need for additional components.

Further, the shape of the filter element creates turbulence throughout the length of the element without decay of turbulence.

The element may be used within a vessel to filter a filtrate from a fluid flow passing through the vessel or to admix fluid or gas from outside the vessel into the fluid flow. Further, a plurality of elements may be combined into a module, particularly in the form of a static mixer for use in the flow path of the fluid of the vessel.