SEPARATION SYSTEM FOR SIMULTANEOUS REMOVAL OF BOTH SOLID PARTICLES AND LIQUID DROPLETS SUSPENDED IN ANOTHER LIQUID

Abstract

The invention relates to a separation system for simultaneous removal of a solid phase particles and a dispersed phase droplets from a medium being a continuous phase to be purified by filtration, wherein said separation system comprises: a filtration-coalescing element (1) in a form of a fibrous structure, a separating element (2), which is a barrier layer for droplets of said dispersed phase and a drainage gap (3), disposed there between and separating said elements (1) and (2) from each other. Said filtration-coalescing element (1) is a non-woven fibrous structure in the form of a depth non-woven structure composed of fibers packed in a form of a cartridge and it comprises: a filtration layer (1a) being an initial depth filtration layer comprising polymer fibres of nanometric sizes, wherein said fibres composing the layer (1a) have extensively phobic surface properties and having across its thickness a porosity gradient, a coalescing layer (1b) and adjacently following it a dripping layer (1c), both composed of polymer fibres and jointly forming a coalescing structure (1b, c) packaged in the form of a depth gradient structure of fibres, and wherein a porosity gradient across the entire coalescing structure (1b, c) changes in the opposed direction with respect to said porosity gradient in said filtration layer (1a).

Claims

1.-12. (canceled)

13. Separation system for simultaneous removal of a solid phase particles and a dispersed phase droplets from a medium to be purified by filtration, that is a filtered medium in a form of a suspension or emulsion, that is a liquid continuous phase comprising particles of said solid phase and a liquid dispersed phase which liquid is dispersed in the form of droplets suspended in an immiscible with them liquid continuous phase, which said continuous phase constitutes of said medium to be filtered, wherein the separation system has a form of a multilayer fibrous structure of a self-supported design construction or a construction supported on one or more perforated supporting elements, preferably cylindrical, and it is provided with an inlet and an outlet of said medium to be filtered, wherein said separation system comprises, arranged successively in a flow direction of said medium to be filtered from said inlet to said outlet, following elements in the form of successive layers: a filtration-coalescing element in a form of a fibrous structure, a separating element, which is a barrier layer for droplets of said dispersed phase, said element is formed of fibres with phobic properties relative to droplets of said dispersed phase, and a drainage gap, disposed there between and separating said elements and from each other, which gap being a free space for dripping of droplets of said dispersed phase under influence of gravity and being in fluid communication with the accumulation space in which dripped droplets of said dispersed phase are collected, which accumulation space is located immediately below the separation system or above the system and it is provided with a valve, wherein the filtration-coalescing element is a non-woven fibrous structure composed of at least two layers including at least a filtration structure, the separation system is characterized in that: the filtration-coalescing element is in the form of a depth non-woven structure composed of fibres packed in a form of a cartridge and it comprises, viewing in a flow direction from said inlet of inflowing medium to be filtered towards said outlet and arranged in sequence one following another: a filtration layer being an initial depth filtration layer comprising polymer nanofibres, wherein said fibres composing the layer have extensively phobic surface properties, and preferably superphobic properties of their surface relative to droplets of said dispersed phase, defined by contact angles equal to or greater than 120, and further the filtration layer is a structure having across its thickness a porosity gradient, namely: its porosity decreases from the inlet side to the outlet side across said layer in said direction of a flow of said medium to be filtered, which porosity is within limits of an average porosity ranging from about 90% to about 95%; a coalescing layer composed of polymer fibres, and adjacently following it is arranged, a dripping layer composed of polymer fibres, wherein both latter layers, which jointly form a coalescing structure are packaged in the form of a depth gradient structure of fibres, and wherein a porosity gradient across the entire coalescing structure changes in the opposed direction with respect to said porosity gradient in said filtration layer, namely the porosity increases in said flow direction of said medium to be filtered stream, and wherein polymer fibres from which the above listed layers are composed demonstrate variable surface properties defined by variable contact angles with respect to droplets of said dispersed phase along a path of said flow of said medium across said coalescing structure in said flow direction, in such a way that a porosity in said coalescing layer changes in gradient ranging from about 75% to about 95% along said flow direction, and said fibres in said coalescing layer exhibit poor philic surface properties and/or poor phobic properties relative to droplets of said dispersed phase which properties are defined by contact angles in the range from about 45 to about 95, whereas said dripping layer has an average porosity in the range of about 85% to about 98%, and the contact angles defining surface properties of said fibres composing said dripping layer are in the range from about 75 to about 105.

14. The separation system according to claim 13, characterized in that the filtration layer comprises fibres whose diameters are in the range between about 250 nm and about 800 nm, and having thickness in the range between about 5 mm and about 20 mm, the coalescing layer of said filtration-coalescing element comprises fibres of diameter sizes in the range between about 0.5 m and about 30 m, and a thickness in the range between about 2 mm and about 6 mm, and the dripping layer of the filtration-coalescing element comprises fibres of diameter sizes in the range between about 40 m and about 120 m, and a thickness in the range between about 4 mm and about 8 mm.

15. The separation system according to claim 13, characterized in that between said fibrous structure of the coalescing layer and said fibrous structure of the dripping layer during fibres manufacturing process, a transition region of a fibrous structure is formed, in which region a continuous, smooth change of a porosity between boundary values occurs, respectively from said porosity on a border of the coalescing layer to said porosity on a border of the dripping layer, wherein a thickness of said transition region is in the range between about 1 mm and about 3 mm.

16. The separation system according to claim 13, characterized in that the filtration layer, that is the first one viewing from the inflow side of said medium to be filtered to the system, has a thickness between about 20% and about 70% of the thickness of the whole depth structure of the filtration-coalescing element and wherein fibres of which said filtration layer is composed are covered with a substance having phobic properties with respect to the dispersed phase forming droplets suspended in said continuous phase and/or on said fibres of said filtration layer a roughness is formed.

17. The separation system according to claim 13, characterized in that the coalescing layer and the dripping layer jointly have a thickness which is between about 30% and about 80% of the thickness of the whole depth structure of the filtration-coalescing element.

18. The separation system according to claim 13, characterized in that the separating element is made of a porous material having a pore size between about 0.5 m and about 50 m, a surface of which is coated with a material of phobic properties with respect to the dispersed phase forming droplets suspended in said continuous phase and it has a thickness between about 0.5 mm to about 2 mm.

19. The separation system according to claim 13, characterized in that a geometric surface of the filtration-coalescing element on its inlet side, that is, on the side of an inflow of said medium to be filtered is between about 5 to about 50 times smaller than a geometric surface of the separating element at its inlet side, that is at the side facing towards the drainage gap, wherein the sizes of those geometric surfaces are selected so that at a given volumetric flow rate of said medium to be filtered through the separation system, the linear velocity at said inflow side of the filtration-coalescing element is between about 1 mm/s to about 20 mm/s.

20. The separation system according to claim 13, characterized in that both the filtration-coalescing element and the separating element are in a form of hollow cylinders, the walls of which form filtration structures and said cylinders are arranged coaxially with respect to each other, one inside the other, and are separated by the drainage gap forming an annular space between them, that drainage gap is in direct fluid communication with said accumulation zone for collecting large droplets flowing out from the filtration-coalescing element and being removed from the system upstream to the separating element, wherein the separation element is formed as a pleated element.

21. The separation system according to claim 13 or according to any one preceding claims, characterized in that in said annular space constituting said drainage gap a number of swirling guiding vanes are further arranged, which guiding vanes are spaced apart one from each other along a circumferential surface of the filtration-coalescing element facing towards the drainage gap, that is an outlet side surface of the dripping layer, on which guiding vanes are spaced, wherein said guiding vanes are positioned and oriented on said side of outflow of droplets of said dispersed phase from said dripping layer at an angle, set in a range between about 15 to about 45 relative to a tangent to a cylindrical surface defined by said surface of the dripping layer facing towards the drainage gap.

22. The separation system according to claim 21, characterized in that it comprises a supporting element, forming an inner core of the filtration-coalescing element.

23. The separation system according to claim 21, characterized in that the filtration-coalescing element has a self-supporting construction which does not require any additional support and wherein no separate supporting element forming an inner core of said filtrationcoalescing element is provided, while said swirling guiding vanes are mounted to their own supporting structure and form with this supporting structure a separate constructional element, configured to be inserted in the drainage gap and to form an additional constructional support of the filtration-coalescing element.

24. The separation system according to claim 21, characterized in that said swirling guiding vanes have a length between about 10 mm and about 45 mm and a number of said swirling guiding vanes disposed in the annular space in the drainage gap between about 8 and about 32.

25. The separation system according to claim 22, wherein the supporting element is a separate constructional element to which the swirling guiding vanes are mounted.

Description

DESCRIPTION OF FIGURES OF DRAWINGS

[0046] The separation system according to the invention in its preferred embodiments is shown in the drawings, in which:

[0047] FIG. 1 presents schematic longitudinal section of the separation system according to a first embodiment of the invention,

[0048] FIG. 2schematic cross section of the separation system according to a second embodiment of the invention with spaced swirling guide vanes,

[0049] FIG. 3schematic cross section of the separation system according to the third embodiment of the invention without swirling guide vanes.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0050] The proposed separation system according to the invention for simultaneous removal of both solid phase particles and dispersed phase in the form of fine droplets of a liquid from a continuous phase being a filtered medium is characteristic by that it comprises in series connected sequence of two filtration elements: first element 1 and a second element 2 (see FIG. 1), both having a multilayer structure, wherein the first element 1 as seen from the side of an inflowing medium to be filtered, further referred to also as filtered medium, is a filtration-coalescing member or element 1, which comprises non-woven fibrous layers 1a, 1b and 1c, which layers together form a deep filtration structure comprising fibres with different surface properties and structural characteristics, such as fibres morphology and their packing densities, which structure serving as a filtration-coalescing member 1. The second element 2 is a separation element 2 responsible for separation of droplets of a dispersed phase and a continuous phase, in particular liquid droplets which sizes increase during flow through the filtration-coalescing member 1, particularly in its part forming a coalescer 1b, 1c from filtered medium. Both said elements 1 and 2 are separated by a drainage gap 3, and both are preferably cylindrically shaped and coaxially disposed with respect to each other i.e. one inside the other. In one embodiment of the invention they are arranged on a supporting core which forms a support element EN1, EN2 having a circular cross-section, and they are separated by an annular space 3, allowing a free falling of droplets of the dispersed phase, and forming a drainage gap 3, wherein in the embodiment shown in FIG. 1 the filtration-coalescing element 1 in the form of a deep layer is arranged outside with respect to the separation element 2, on the inlet side of the inflowing medium to be filtered, preferably liquid medium. In contrast, the separation element 2 is made of fibres having hydrophobic properties and it has the form of a pleated layer. The separation element 2 can be supported on a second supporting element EN2 forming a support perforated core, preferably having cylindrical shape and located preferably coaxially on an inner side of the separation element 2 as shown in FIGS. 2 and 3.

It is possible a reverse configuration, that means coaxial location of the filtration-coalescing element 1 inside the outer separation element 2, wherein a flow direction is then also reversed from the inside to the outside. In such of configuration, the order of the layers 1a, 1b and 1c in the filtration-coalescing element 1 according to the flow direction would be also reversed from the inside to the outside, and thus the hydrophobic surface of the separation element 2 would be located on the side of the out flowing liquid (i.e. from outer side of the system). This arrangement seems to be less favourable from point of view of reducing filtration surface of the element 1 and thus undesirable reduction of throughput of the entire system.
According to the FIG. 1, directly below the separation system, in flow communication with the drainage gap 3, an accumulation space 4 with a draining valve 5 is disposed, however, it is possible to arrange the accumulation space 4 above the separation system and the drainage gap 3, in particular for the case where a liquid of a continuous phase has a higher density and a mass density than the liquid of a dispersed phase. In the embodiment shown in FIG. 1 the separation system adapted especially for filtration of such a filtered medium is presented, wherein the liquid of the continuous phase has a lower density than the liquid of the dispersed phase, for example in case of purification of fuel (continuous phase) from the water droplets suspended therein (dispersed phase).

[0051] The element 1 in the form of the filtration-coalescing member 1 is a deep non-woven structure made of fibres packed in a form of a cartridge in which local porosity values and fibre diameters alter across the structure in the direction of a flow of a filtered medium, having in particular a slurry form.

[0052] Within the filtration-coalescing element 1 or member the following layers can be distinguished, namely: the filtration layer 1a and following it the layers forming components of the filtration-coalescing structure as a whole, namely: the coalescing layer 1b, which the coalescing layer is responsible for capturing of all droplets of a dispersed phase, and the dripping layer 1c in the form of a dripping structure that allows increasing of droplet sizes to large droplets and disconnection of such large droplets of a dispersed phase from fibre surfaces, which droplets having similar sizes or closely to similar or equal sizes i.e. which have a narrow size distribution. The contribution of the individual layers in a total thickness of the structure of the filtration-coalescing element 1 is as follows: [0053] 20-70%, and preferably 30-50%, of the thickness of the entire structure of the filtration-coalescing element 1 occupies the filtration layer 1a, also referred to as pre-filtration layer or a depth filtration layer; [0054] 30-80%, preferably 50-70%, of the thickness of the entire structure of the filtration-coalescing element 1 is a structure designed for separation of a dispersed liquid phase, which form the coalescing layer 1b and the dripping layer 1c together; [0055] wherein the thickness of the coalescing layer 1b may comprise 15-50%, preferably 20-45%, of the thickness of the entire coalescing structure 1b and 1c jointly.

[0056] The filtration-coalescing element 1 has a multilayer gradient structure, wherein the first layer at its inlet side i.e. the side facing the inlet, that is the upstream filtration layer 1a of the element 1, viewing from the side of inflowing medium to be filtered in the direction towards the outlet, is a non-woven fabric having a medium porosity, preferably in the range 90-95%, more preferably 92-93% comprising nanometric sized fibres, i.e. nanofibres, namely having fibre diameters in the range of 250 nm-800 nm, and in particular of 400-600 nm and a thickness preferably in the range 5-20 mm and in particular 10-15 mm, wherein surfaces of said fibres are modified in such a way that they have highly phobic surface properties in relation to the liquid which is the dispersed phase, i.e. forming droplets, and in particular super-phobic surface properties, for example super-hydrophobic properties when the dispersed phase is composed of water droplets. In that first filtration layer 1a the submicron solid particles are retained with a great effectiveness while the particles of the dispersed phase, particularly liquid droplets, and for example water droplets, pass through.

[0057] Such respective modification of the filtration layer 1a located at the inlet-facing side of the element 1, which allows to achieve an effect of selective retention of particles of the solid phase while minimizing or totally eliminating deposition of droplets of the dispersed phase on the fibres is novel. This is achieved through giving super-phobic, for example superhydrophobic, properties to the fibres of which the filtration layer 1a of the element 1 is composed, which superphobic surface properties can be obtained in known manner by changing chemical composition of a substance of which fibres are composed and produced by melt-blowing fibre formation technique, i.e. of composition which the fibres are produced of. This change can be achieved by adding e.g. among others compounds containing in their structure chlorine and fluorine, such as, for example, perfluoroethers, chloro- and fluorocarbons copolymers, polydimethylsiloxane, to the polymer from which the fibres are formed. The above-mentioned compounds are most often added to the main polymer granulate as an admixture, then they are melted, mixed to form a mixture, and then of such a mixture said fibres are produced (by melt-blowing technique). However, in the case of polydimethylsiloxane it is also possible to coat surface of polymer fibres by dip-coating technique, for example, from a solution of a suitable concentration of PDMS in hexane.

[0058] The superphobic properties of the fibres can also or additionally be obtained by simultaneously forming the greater roughness (i.e. the coarseness of fibre surfaces) on the surfaces of fibres composing the structure of the filtration layer 1a. In the case of polypropylene and polyester fibres, which are commonly used for production of filtration layers and filters of this kind and may be used alternatively, it was developed in the above mentioned purpose an effective method of coating a surface of fibres with silica nanoparticles and/or production of microroughness on a surface of said fibres in a fibre formation process in the high intensity electric field causing micro-cracks on the fibre surfaces. These methods are well known in the art and therefore they will not be discussed in more detail here.

[0059] Therefore, novelty of the solution according to the invention lies in using of the first filtration layer 1a of the filtration-coalescing element 1, which is the pre-filtering layer of depth filtration and whose function is not only an initial retention of the solid phase particles, including those of nanometric sizes, that means prefiltration, that means not only protection of the coalescing layer 1b located deeper in the direction of a flow of the continuous filtered phase and simultaneously initial coalescence i.e. pre-coalescence, but especially its selective action in relation to dispersed elements, suspended in the flowing continuous phase, i.e. the dispersed phase, consisting of solid phase particles and liquid droplets of the dispersed second liquid phase, and more specifically its function of capturing and retention of solid particles by simultaneous absence of accumulation of droplets of the dispersed phase in a volume area of the said filtration layer 1a.

[0060] In the filtration layer 1a, which is the first layer an initial coalescence can occur with the participation and involvement of fibres, but dominant mechanism of influencing an initial coalescence in this layer is different than in known coalescing layers, as well as in the duly coalescing layer 1b according to the invention, namely the initial coalescence in the first layer 1a, i.e. in the filtration layer 1a of the filtration-coalescing member 1 is due to collisions and joining together of fine droplets, which collisions occur in the high shear stress area in this layer 1a, composed of nanometric size fibres, in particular composed of nanofibres.

[0061] Thus, the fibres in this filtration layer 1a fulfil, apart from the initial filtration, a role of components for ordering the medium flow in a porous structure and affecting on the local hydrodynamic conditions, however, deposition of droplets and, the resulting from this, saturation of the layer 1a structure with a liquid of the dispersed phase retained on the fibres, which is generally considered as a beneficial effect to the coalescence of droplets in the layer 1a is a negligible effect here. An initial coalescence of droplets of the dispersed phase of the filtered medium in the form of an emulsion is going on during the flow through the filtration layer 1a, however, it occurs without influencing participation of the fibres and occurs in small pores between the fibres, in which the local shear stress values are significantly high, which promotes collisions between droplets and their joining (known in the art literature as the shear-induced coalescence or gradient coagulation).

[0062] In the filtration layer 1a a gradient of porosity occursnamely, the porosity changes across the structure, and particularly the structure porosity decreases in the direction of a flow of the filtered medium, which is mainly due to an increase in local surface mass of the filtration non-woven fabric of the downstream deeper layers. In addition, it can be accompanied by decrease of fibre diameters in the range of 250-800 nm (shown previously) across the structure along the filtered fluid path in the direction of flow, whereas the porosity can simultaneously vary in the range of 90% to 95%i.e. said porosity descending in the flow direction from higher to lower values.

[0063] Downstream the first filtration layer 1a of the filtration-coalescing element 1 the layers 1b and 1c are arranged in sequence, which are respectively the coalescing layer 1b and the dripping layer 1c, and which are jointly referred to as a coalescing structure 1b, c, in which coalescence of the droplets of the dispersed phase, for example water or other liquid droplets, is proceeded. The coalescing layer 1b is made of fibres with a diameters preferably in the range 0.5 m-30 m, and especially 0.8 m-15 m, having a thickness preferably in the range 2 mm-6 mm, and more preferably 2 mm-4 mm. The dripping layer 1c is made of fibres with diameters preferably in the range 40 m-120 m, and especially 60 m-90 m, having a thickness preferably in the range 4 mm-8 mm, and more preferably 4 mm-6 mm.

[0064] In contrast to existing known filtration systems described in the above cited patents, the coalescing 1b and dripping 1c layers which jointly form so called coalescing structure 1b,c are the fibrous layers containing meltblown fibres and they both have a multilayer structure, wherein, as seen in the direction of the flow i.e. downstream direction, the initial fibres of the coalescing layer 1b are characterized in that they have poor philic surface properties and/or poor phobicity in relation to the dispersed phase liquid (i.e. droplets), which characteristic surface properties are determined by wetting angles i.e. angles of contact in the range from 45 to 105 wherein those values are related to the so-called static wetting angles values, measured on a surface of flat materials (not on a non-woven fabric).

[0065] In both cases, the appropriately designed coalescing structure according to the invention provides significantly lower values of a flow resistance than the highly hydrophilic structures recommended in the known developments of coalescing structures. High effectiveness of the system according to the invention is obtained due to an internal geometry of the porous structure with a high value of the specific surface area.

[0066] The entire coalescing structureincluding the coalescing layer 1b and the dripping layer 1cis characterized in that the gradient of porosity changes in it, seen in the direction of flow of the filtered medium from the inlet to the outlet, in opposition to the gradient of porosity in the filtration layer 1a, that is in the depth filtration layer. Namely, the porosity in the coalescing layer 1b is in the range 70-95% and changes gradually with a gradient within the limit boundary values from 70% to 95% downstream in the flow direction across the layer thickness, while in the dripping layer 1c the value of an average porosity is in the range of 85-98%.

[0067] Wherein the meltblown technology in the apparatus configuration used for the production of this kind filtration layers, that is filters, in particular in the case of the embodiment of the structure of the separation system according to the invention enables a smooth and continuous change of the porosity between the boundary values for the coalescing layer 1b and for the dripping layer 1c on a distance of 1-3 mm forming a transition area TR having a thickness in the range of 1-3 mm, arranged in a contact area of layers 1b and 1c. In addition, during forming the fibrous structure of the present invention, a twin-screw extrusion technology with the side screw is used, which allows admixture of a polymer with suitable modifying additives during the manufacturing process of extrusion of fibres.

[0068] The suitable modifying additives, which contain, for example chloro- and fluoropolymers, the metering of which to the extruded polymer forming fibres during extrusion cycle, which polymers are blown in the form of fibres, can be switched on or off during the manufacturing cycle, with suitably controlled metering rate, allowing changing the surface properties of such manufactured fibres.

[0069] It is also possible metering of nano-particles containing re-granulates that during blowing of a polymer are exposed on the fibre surface, which also results in a change of droplet-fibre interactions, and thus it changes phobicity/philicity of the surface of fibres.

[0070] From the point of view of effectiveness of coalescence process it is recommended to choose such type of polymers or such additives used, so that contact angles of fibres forming the coalescing layer 1b are in the range of 45-95, while contact angles of fibres forming the dripping layer 1c are in the range of 75-105. The dripping layer 1c located at the outlet side of the filtration-coalescing element 1 i.e. downstream, guarantees dropping down of the majority of droplets of the dispersed phase to a volume 4 accumulating the dispersed phase, located directly below or above the annular drainage gap 3, separating the elements 1 and the element 2 one another.

[0071] Small size of the drainage gap 3, being in the range 2-10 mm, preferably 3-6 mm, and particularly preferably 4-5 mm, allows, however, large droplets, separated as a result of a coalescence, having an initial velocity at an outlet side of the dripping layer 1c large enough to make their trajectory resulting from superposition of the speed of falling of dropping down (caused by gravity in the drainage gap) and the above mentioned speed of the movement of the medium in the flow direction, i.e. towards the hydrophobic surface of the separation element 2 to allow them to impact on the surface of the separation element 2, on which surface fine, poorly dropping down droplets are collected.

[0072] Novelty of the solution according to the invention lies therefore in supporting cleaning of the surface of the hydrophobic separation element 2 facing the drainage gap 3 from droplets of the removed dispersed phase retained on it by means of providing favourable hydrodynamic conditions in the drainage gap 3. Hydrodynamic conditions of the flow in the drainage gap 3 have therefore essential significance for a long time of effective working of the second stage of the filter, that is the separation element 2, in particular under conditions where the filtered medium are stable emulsion systems, for example, such as, aqueous emulsions in low sulphur diesel oil or containing biocomponent additives, particularly when fine droplets which don't undergo coalescing are gathered on the surface of the element 2 side facing the gap 3, so that in such a case their excessive over-accumulation leads to increase in the flow resistance and to so called filter breakthrough, previously discussed.

[0073] In the above case the most important is a design of the coalescing structure, and in particular of the dripping layer 1c, which is made by means of melt-blown technique and which is a depth structure that is not pleated, i.e. does not have any pleats, similarly to the filtration layer 1a and coalescing layer 1b, which are also not pleated but they are produced as depth structures. In such system the droplets separated from the internal layer of the filtration-coalescing element, that is from outlet surface of the dripping layer 1c i.e. its surface facing the gap 3, are more efficiently accelerated in the direction toward the inlet surface of the separation element 2 i.e. its surface facing the gap 3, due to much higher values of a local linear flow velocity within the pores of the dripping layer 1c, that layer discharges and disposes a liquid of the continuous phase and large droplets of the dispersed phase on the outside of the filtration-coalescing element 1 into the drainage gap 3. Thus the separation element 2 is purified by droplets hitting under miscellaneous angles its separation surface that is its inlet side surface, i.e. by droplets hitting under different angles depending on their sizes which droplets are separated from the flowing filtered continuous phase. As a result of collisions of said droplets of the dispersed phase with a hydrophobic surface of the separation element 2 on which small, poorly falling droplets, are deposited it can come to a coalescence of such small droplets and formation of larger, easily falling and dripping down droplets or to tearing off the droplets retained on the separation element 2. After such separation said droplets may be again deposited on the separation element 2 surface, but in a place located closer to the accumulation volume zone 4 for collecting the dispersed phase. Multiple repetitions of the above described collisions process during filtration process will result in bringing about the droplets into the accumulation volume 4, from which it is possible to drain such liquid from the bottom part of the filter housing through the draining valve 5.

[0074] Although satisfactory results were achieved for the above described design of the separation system of the invention in the form of a 2-stage filter, further improvement of the 2-stage filter operation was directed toward the effective prevention of settling of droplets, particularly fine droplets, and ensuring efficient removal of droplets of the dispersed phase deposited on a separation element 2 by supporting the system operation with appropriate filtered medium flow hydrodynamics.

[0075] To achieve this purpose, it is proposed to use in further one of embodiment of the invention additional constructional components in the form of plurality of guiding vanes 6 arranged in the predetermined volume of the drainage gap 3, located between the filtration-coalescing element 1 and the separating element 2 (see FIG. 2), which additional elements would be responsible for division of the dispersion stream flow from the determined outlet surface of the dripping layer 1c of the filtration-coalescing element 1 i.e. its surface facing the gap 3, and for directing such stream into a properly constructed drainage gap 3. The said guiding vanes 6, each having a length L, are arranged in spaces one from another around a circumference of the outlet side surface of the dripping layer 1c, facing the drainage gap 3 and extend from said surface under an angle into the drainage gap 3, wherein preferably said guiding vanes 6 extend along a whole height of said filtration-coalescing element 1, that means a height extension of said guiding vanes 6 is preferably equal or smaller than the height of said filtration-coalescing element 1. Between adjacently located guiding vanes 6 gaps 7 are formed, that can be particularly defined between free end of one guiding vane 6 and a surface of the adjacent vane 6 (as shown in FIG. 2). Small cross sectional area of the vanes gaps 7 formed between adjacent guiding vanes 6 with respect to the outer surface of the dripping layer 1c, i.e. the outlet layer of the element 1, from which a liquid is supplied to the drainage gap 3, ensures a significant increase in an average linear flow velocity in this location to a value in the range of 5-25 mm/s in their i.e. the vanes gaps 7 narrowest places or areas.

[0076] Proper orientation of the filtered medium flow in the drainage gap 3, namely tangentially to a surface of an imaginable cylinder defined by outer ridges 8 of pleats of the pleated separation element 2, causes creation of a centrifugal force, an influence of which on water droplets, being the dispersed phase, which droplets having a higher density than a diesel oil constituting the continuous phase, limits possibility of penetration of such droplets into gaps formed between the pleat ridges 8 of the separation element 2 and also limits possibility of reaching by such droplets the hydrophobic surface of the separation element 2 at that locations.

[0077] In addition, the flow velocity component directed tangentially to a periphery of the separation element 2, that is designed as a pleated layer provided with circumferentially spaced pleats with pleat ridges 8 and gaps 8 formed by recesses between adjacent ridges 8 of the pleats, which periphery is defined by external ridges 8 of the pleats of pleated structure of the separation element 2 supports removing of droplets of the dispersed phase that are deposited in a short distance from the ridges 8 of the pleats, as a result of shear stress acting on the droplets. The number of swirling guiding elements i.e. guiding vanes 6 on the periphery circumference can vary in the range 8-32 and a width of a gap 7 formed between the adjacent guiding vanes 6 is in the range 1-4 mm.

[0078] Especially important for the operational effectiveness of the guiding vanes 6, supporting the dripping of droplets of the dispersed phase into the accumulation volume 4 is a geometry of these guiding vanes 6 swirling the medium flow, because said geometry determines generation of additional effect allowing to effectively reduce of a number of droplets reaching the surface of the separation element 2 and thanks to appropriate hydrodynamics to support cleansing of the surface of the hydrophobic separation element 2. A number of swirling guiding vanes 6, their dimensions and an angle of their inclination with respect to the outer surface of the dripping layer 1c of the filtration-coalescing element 1 i.e. its surface facing the gap 3 depend not only on the hydrodynamic effect which can be obtained, but they also depend on the geometry of the drainage gap 3. It is preferred that a length of the guiding vanes 6 is in the range of 10-45 mm, and the angle of their inclination (FIG. 2) with respect to a tangent to a circle defined by the inner supporting core EN1 of the filtration-coalescing element 1, or alternatively defined by cylinder surface of outlet side of dripping layer 1c is in the range of 10-45 preferably 15-45, particularly preferably 25-40, especially about 30+13.

[0079] The swirling guiding vanes 6 can be disposed at an angle () relative to the dripping layer 1c on its outflow side, that means its side facing the drainage gap 3, of which droplets of the dispersed phase flow out of said dripping layer 1c, the angle () preferably is set in a range of 15-45 relative to a tangent to the side surface of a cylinder defined by the outer surface of the dripping layer 1c on its outlet side, i.e. its surface facing the drainage gap 3. The supporting core element EN1 that forms the inner core of the filtration-coalescing element 1 can be a separate constructional element of the system to which element EN1 the swirling guiding vanes 6 are mounted. Alternatively, in another embodiment of the system the supporting element EN1 may be omitted, and the structure of the filtration-coalescing element 1 is then self-supporting and no separate constructional support is required. The use of swirling guiding vanes 6 is still possible in such embodiment but they are mounted on an additional constructional element, that is provided and forming the guiding vanes 6 own supporting structure (not shown), with which they form jointly a separate complete constructional element. This constructional element is designed to be arranged in the drainage gap 3, and can provide additional support for the structure of filtration-coalescing element 1 after insertion of such complete element into the drainage gap 3.

[0080] The second element of the separation system, as mentioned above, that is a separation element 2 has a form of a partition 2 made of a material having phobic surface properties relative to droplets of the dispersed phase, which layer constituting a separating element 2 in the form of a partition is made of a surface-modified cellulose fibres or of glass fibres having average pore diameter preferably in the range 0.5-25 m, preferably 0.5-10 m, wherein a thickness of the layer of said separation element 2 is preferably in the range of 0.5-2 mm, especially 0.5-1.5 mm. The separation element 2 is formed as a pleated one, while the medium flow guiding elements arranged in the drainage gap 3 in the form of the swirling guiding vanes 6 guide the flow of the main stream of a purified liquid i.e. the continuous phase in the gap 3 tangentially to a surface of an imaginable cylinder determined by the ridges 8 of the pleats of the pleated separation element 2 structure.

[0081] The separation system according to the invention that is two-stage system in the form of a serial sequence of the following elements: filtration-coalescing element 1drainage gap 3separating element 2 is characterized especially in that a linear velocity of a slurry to be purified (i.e. the filtered medium) flowing through the structure of the separation element 2 is preferably in the range 5-50 times and in particular 10-40 times smaller than a linear velocity of the slurry exiting the filtration-coalescing element 1. This is achieved by means of developing of the geometric outer surface of the separation element 2, that is preferably in the range 5-50 times and in particular 10-40 times greater in relation to the outer surface of the filtration-coalescing element 1 facing the gap 3. Such developing is achieved usually by shaping it in the form of a pleated member. The distance between the elements 1 and 2 being the width of the drainage gap 3 is preferably in the range of 2-10 mm, particularly 3-6 mm and that space, i.e. the space of the drainage gap 3 is used to free falling i.e. dripping down of large droplets of the dispersed phase that are formed of small dispersed droplets in the filtration-coalescing element 1 in the manner described above.

[0082] According one of preferred embodiments of the invention the filtration layer 1a of the filtration-coalescing element 1 comprises fibres having superphobic surface properties, for example superhydrophobicity in the case when the liquid of said dispersed phase is a water. High phobicity of surfaces of the fibres, that is super-phobicity defined by contact angles exceeding 120, i.e. larger or equal to 120 preferably greater than 150 of fibres contained in the fibrous structure of the filtration layer 1a, of the filtration-coalescing element 1 ensure free filtered medium flow and particularly free flow of said continuous phase through the filtration layer 1a, whereas fine droplets of the dispersed phase dispersed in said continuous phase during the flow inside fibrous structure of the filtration layer 1a bounce off from the fibres and are joined to form large droplets only in the following coalescing layer 1b and the dripping layer 1c of the filtration-coalescing element 1. Large droplets leaving the filtration-coalescing element 1 effectively detach from dripping layer 1c in a form of large uniformly sized droplets and sediment in a space of the drainage gap 3, where from they are directed by gravity to the accumulation tank 4 disposed below the separation system.

[0083] The above indicated aims of the invention are achieved by providing a solution in which a multi-stage separation system is used, comprising an outer multi-layered non-woven structure forming the filtration-coalescing element 1, which element comprises in its individual layers 1a,1b and 1c fibres having appropriate affinity of their surface properties with respect to the particles of the solid phase and to droplets of the liquid of the dispersed phase, as well as the liquid of the continuous phase and also forming the separation element 2, separating droplets of the dispersed phase from the fluid to be purified, between which elements 1 and 2 there is a space 3 allowing droplets to fall, wherein a schematic diagram of such system is shown in FIG. 1 and FIG. 2. In the ideal situation, following the filtration-coalescing element 1 a perfectly purified liquid of the continuous phase, which is free of particles of the solid phase and tiny, fine droplets of the dispersed phase, as well as rapidly sedimenting large droplets separated from a dripping layer 1c flows towards the separating element 2.

[0084] In the real situation the hydrophobic separation element 2 provides protection at the outlet of the purified liquid of the continuous phase, stopping a few tiny, fine droplets of the dispersed phase that could get out through the coalescing layer and the dripping layer in its initial form. The filtration-coalescing element 1 of the invention design, which is the melt-blown depth structure, provides a much better protection of the separation element 2 against deposition of solid particles on its surfacesince their penetration especially through the structures of layers 1a and 1b is reduced to a level lower than in the currently offered filtration systems. Thanks to that the hydrophobic properties of the surface of the separation element 2 are not exposed to uncontrolled changes caused by deposition thereon of solid particles. In addition, the hydrodynamic conditions in the drainage gap 3 ensured by an appropriately designed swirling guiding vanes 6 minimize phenomenon of deposition of liquid droplets and solid particles on the surface of the separation element 2 and support self-cleaning of said element 2.

Exemplary Embodiment of the Invention

[0085] In an example illustrating an idea of the separation system according to the invention, that is the two-phase separator which is the aim of the invention, there were performed measurements of the water removal efficiency, which water forms the dispersed phase and the efficiency of removing of solid particles of Fe.sub.3O.sub.4, constituting the solid phase, from a diesel fuel forming the continuous phase (medium to be purified) according to the invention. In the raw material to be filtered that is the filtered medium the continuous phase was a commercially available low sulphur diesel oil, in which water droplets were dispersed and suspended at a concentration of 1500 mg/l (the free water) having sizes in the range 0.4-32 m and particles of the Fe.sub.3O.sub.4 haematite of a size in the range 50-500 nm and the mass concentration of 20 mg/l.

The separation system was constructed in accordance with the embodiment shown in FIG. 1, wherein the filtration-coalescing element 1 was a layered polyester non-woven fabric. The first layer (seen in the direction of the flow of the slurry to be filtered), that is the filtration layer 1a having a thickness of 15 mm was composed of polyester fibres having a diameter between 300-600 nm and an average porosity of 92%, on the surface of which layer 1a grains of colloidal silica having the particles diameter of 5 nm were immobilized. The coalescing layer 1b constituted by a structure which was made of polymeric fibres (such as polypropylene or polyester) having sizes in the range of 0.5-20 m, while the dripping layer 1c constituted the structure made of polymeric fibres (such as polypropylene or polyester) having sizes in the range of 70-120 m. The coalescing structure 1b,c respectively had the following thickness: thickness of the coalescing layer 1b4 mm, thickness of the transition region TR in which the fluent continuous change of the porosity and sizes of the fibres occurs2 mm, and the thickness of the dripping layer 1c5 mm.

[0086] The separating element 2 arranged at a distance of 4-8 mm from the filtration-coalescing element 1 that is the distance calculated between the outlet surface i.e. the surface facing the separating element 2 of the dripping layer 1c and the surface of the imaginable cylinder surface defined by the outer ridges 8 of the pleats of the separating element 2. Said separating element 2 was of the cellulosic material having a developed surface in the form of pleated surface, on which surface the commercially available suspension EC-1206 offered by the company NanoX GmbH was applied for hydrophobization. Development of the surface of the separating element 2 was achieved by shaping the element 2 in the pleated form with pleats of the height of 10 mm and the number of pleats40. The linear flow rate of the filtered suspension at the inlet to the filtration-coalescing element 1 was 2.5 mm/s, and the superficial velocity through the porous structure of the separating element 2 (or the inflow velocity on the surface) was 0.15 mm/s.

[0087] On the basis of measurements of concentrations of separated haematite particles and water droplets it was determined the mass effectiveness of separation of the filtration-coalescing element 1 for haematite particles as equal to 99.95%, and the separation efficiency of insoluble water (i.e. droplets) on the basis of the measurements of its concentration downstream the separating element 2 in the purified diesel oil equal to 99.3%. Both the above efficiency were related to a given concentration of a haematite and water in the inlet stream of the initial diesel oil to be purified to the separation system according to the invention having the above-described structure.

[0088] In the above presented description and embodiments the case is presented in which in the filtration-coalescing element 1 between the coalescing layer 1b and the dripping layer 1c in the region of their interface, there is a transition region TR in which the smooth and continuous change of the porosity from the boundary value of the porosity for the coalescing layer 1b (i.e. the local porosity value on the border of the coalescing layer) to the boundary value of the porosity for the dripping layer 1c (i.e. the local porosity value on the border of the dripping layer 1c) is carried out (i.e. on the common border of the coalescing layer and the dripping layer). However, it is also possible to make the filtration-coalescing element 1 without such transition region between those two layers 1b and 1c, and the change of the porosity can be smoothly carried out in the above mentioned ranges of porosity throughout and across entire coalescing-dripping structure 1 b, c.

[0089] In addition, it should be noted that although in the above description the separation system was presented for use for filtration of the continuous phase in the form of a liquid from impurities in the form of solid particles and droplets of the dispersed phase being also a liquid but another one, and the scope of protection of the invention as claimed also covers such application of the separation system for this kind medium to be filtered, this embodiment of the invention can be easily adapted by one skilled in the art for other uses, for example for using to purify of other liquid or fluid media constituting the continuous phase and/or the dispersed phase, for example also where one or both phases is/are constituted by gaseous medium or liquid/gas mixture.