Mixing device

Abstract

A mixing device (1a-1f) for performing mixing of a fluid (2) into a fiber pulp (3) in a fiber pulp arrangement (5a-5f), said mixing device (1a-1f) comprising: - a fluid inlet (7) configured to be connected to a fluid source (9) for providing fluid (2) into the mixing device (1a-1f); and5 - at least one fluid outflow part (11a-11f) which is in fluid connection with said fluid inlet (7) and which comprises a porous metallic material (12) produced by additive manufacturing, wherein said fluid outflow part (11a-11f) is positioned in relation to said fiber pulp arrangement (5a-5f) such that fluid (2) delivered out via the fluid outflow part (11a-11f) will be dispersed through the porous metallic material (12) 10 and enter into the fiber pulp (3), wherein said porous metallic material (12) of said at least one fluid outflow part (11a-11f) has a degree of porosity which is varying over a surface of the fluid outflow part.

Description

[0001] MIXING DEVICE

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a mixing device for performing mixing of a fluid into a fiber pulp in a fiber pulp arrangement and to a method for mixing of a fluid into a fiber pulp.

[0004] BACKGROUND

[0005] In different parts of a fiber pulp processing system fluids, i.e. both gases and liquids, may need to be mixed into the fiber pulp. Mixing of fluids into the fiber pulp can for example be performed in specific mixing vessels used in the processing systems or directly in a fiber pulp treating vessel, a fiber pulp transferring pipe or a screw conveyer of the fiber pulp processing system. Mixing devices in the form of nozzles and inlets of different configurations are often provided in for example dedicated mixing vessels or directly in treatment vessels and in transferring pipes of fiber pulp processing systems. The mixing may not always be efficient enough.

[0006] In AU6467186 an apparatus for dispersing and mixing oxygen into a pulp slurry is disclosed. The oxygen is introduced into the slurry through diffusing means having a porous surface in contact with the moving slurry. The diffusing means is typically a sintered stainless steel element.

[0007] SUMMARY

[0008] An object of the present invention is to provide an improved mixing device and a method for mixing in a fiber pulp arrangement.

[0009] This is achieved in a mixing device and a method according to the independent claims.

[0010] According to one aspect of the invention a mixing device for performing mixing of a fluid into a fiber pulp in a fiber pulp arrangement is provided. Said mixing device comprises: a fluid inlet configured to be connected to a fluid source for providing fluid into the mixing device; and at least one fluid outflow part which is in fluid connection with said fluid inlet and which comprises a porous metallic material produced by additive manufacturing, wherein said fluid outflow part is positioned in relation to said fiber pulp arrangement such that fluid delivered out via the fluid outflow part will be dispersed through the porous metallic material and enter into the fiber pulp, wherein said porous metallic material of said at least one fluid outflow part has a degree of porosity which is varying over a surface of the fluid outflow part.

[0011] According to another aspect of the invention a method for mixing a fluid into a fiber pulp in a fiber pulp arrangement is provided. Said method comprises the step of delivering the fluid into the fiber pulp via at least one fluid outflow part of a mixing device as defined above.

[0012] Hereby the fluid to be mixed into the fiber pulp will be dispersed effectively through the porous metallic material and hereby enter the fiber pulp in a suitable way for being mixed effectively with the fiber pulp. By additive manufacturing a porosity of the porous metallic material can be easily controlled by changing process parameters, such as laser parameters in a laser powder-bed fusion system and material parameters such as type of material. Hereby a porosity of the porous metallic material of the fluid outflow part of the mixing device can be adopted specifically for different uses and for different fluids to be mixed and hereby be designed for providing an efficient mixing. The degree of porosity is also provided to be varying over a surface of the fluid outflow part. This is possible thanks to the use of additive manufacturing in contrast to for example sintering. Any variation of porosity degree can easily be designed and produced by additive manufacturing. Hereby the mixing device can be specifically designed for different applications for efficient mixing. When the mixing is more efficient the amount of fluid to be mixed into the fiber pulp may be decreased and hereby a cost may be reduced. Furthermore, wear of the system may be decreased by avoiding introduction of excess amounts of fluid into the system. Furthermore, dedicated mixing vessels which are often used in a fiber pulp processing system can maybe be omitted when efficient mixing can be provided directly in for example a treating vessel or transporting pipe of the fiber pulp processing system. In some embodiments of the invention the at least one fluid outflow part comprises at least one wall part which is a part of a fiber pulp enclosure wall of the fiber pulp arrangement. Hereby fluid can be efficiently mixed into a fiber pulp directly through the fiber pulp enclosure wall.

[0013] In some embodiments of the invention the at least one fluid outflow part comprises at least one internal part which is protruding into or is provided inside the fiber pulp arrangement.

[0014] In some embodiments of the invention at least a part of said at least one fluid outflow part is configured such that it can be rotated and / or translated. Hereby a contact surface between the fluid outflow part of the mixing device and the fiber pulp can be increased and mixing can be improved. Furthermore, a turbulence can be provided to the fiber pulp by the mixing device whereby mixing may be improved.

[0015] In some embodiments of the invention said at least one fluid outflow part further comprises fluid distribution channels produced by additive manufacturing. Hereby a mixing device can be produced by additive manufacturing to comprise both channels and a porous metallic material in combination for efficient distribution of the fluid. Any combination of channels and variation in porosity degree can easily be designed and produced by additive manufacturing according to the invention and an efficient mixing device is achieved.

[0016] In some embodiments of the invention at least a part of a surface of said porous metallic material has been polished by vibration polishing. A surface of the porous metallic material, which may be somewhat rough due to the additive manufacturing production process, is polished by a method which is both gentle and effective. With vibration polishing there is less risk than with other polishing methods, that the porous structure at the surface is destroyed and clogged which could impair the porosity of the material. The vibration polishing of the porous metallic material may even improve the porosity of the porous metallic material thanks to a cleaning effect from the vibration polishing. In addition to a polished and smooth surface achieved by the vibration polishing the porous metallic material will also be cleaned during the polishing. Any loose material will be removed in the polishing process and there is no risk that material will clog pores in the material. Even further the vibration polishing will give rise to a shining surface of the porous metallic material which may be advantageous for some applications. In some embodiments of the invention the mixing device further comprises a turbulence producing organ which is provided in said fiber pulp arrangement in vicinity of or integrated with said at least one fluid outflow part. Hereby turbulence is provided to the fiber pulp in vicinity to where the mixing is performed and mixing will be further improved.

[0017] Further embodiments of the invention are disclosed in the dependent claims and in the detailed description.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure la shows schematically a mixing device positioned in a fiber pulp arrangement according to one embodiment of the invention.

[0020] Figure lb shows the same mixing device as shown in Figure la with fiber pulp provided in the fiber pulp arrangement and the mixing device connected to a fluid source.

[0021] Figure 2 shows schematically a mixing device positioned in a fiber pulp arrangement according to another embodiment of the invention.

[0022] Figure 3 shows schematically a mixing device positioned in a fiber pulp arrangement according to another embodiment of the invention.

[0023] Figure 4 shows schematically a mixing device positioned in a fiber pulp arrangement according to another embodiment of the invention.

[0024] Figure 5 shows schematically a mixing device positioned in a fiber pulp arrangement according to another embodiment of the invention.

[0025] Figure 6 shows schematically a mixing device positioned in a fiber pulp arrangement according to another embodiment of the invention.

[0026] DETAILED DESCRIPTION OF EMBODIMENTS

[0027] As used in this patent text there is a difference between a perforated material and a porous material. In a perforated material there are perforations which have been designed and which have defined sizes and positions in the material. A porous material on the other hand, as the term porous is used in this text, does not have perforations which are designed and predetermined in size and location. A material can be porous without having any designed perforations, i.e. a porous material has open spaces randomly distributed in its volume. A degree of porosity can be measured as an amount of such open spaces. A degree of porosity and also other porosity characteristics such as how course or fine meshed the porous material is may depend on certain production parameters as will be further described below.

[0028] Additive manufacturing, such as laser powder-bed fusion, is suitable for production of porous materials. By changing certain process parameters and / or material parameters porosity characteristics and degree of porosity can be adjusted as required. The process parameters to be changed could be for example laser parameters such as one or more of a laser power, a laser pulse duration, a laser pulse frequency, laser beam interspacing, laser scan speed and laser beam radius. Another process parameter which can be changed in order to adjust porosity of the material is thickness of each powder layer provided during the additive manufacturing. Material parameters which can be changed for adjusting a porosity are for example type of material and size of granulation of the material powder used for building the porous metallic material by the additive manufacturing. For example, a porous material may be achieved if a laser power is decreased and laser beam interspacing is increased compared to production parameters when producing a compact material.

[0029] Figures 1-6 show schematically different embodiments of mixing devices la-lf according to the invention. Some common features are first described with reference to all the Figures 1-6 and then the different embodiments are described in order below. Same or similar features of the embodiments are given the same or similar reference numbers. According to the invention a mixing device la-lf for performing mixing of a fluid 2 into a fiber pulp 3 in a fiber pulp arrangement 5a-5f is provided. The mixing device la-lf comprises a fluid inlet 7 configured to be connected to a fluid source 9 for providing fluid 2 into the mixing device la- lf and at least one fluid outflow part lla-llf which is in fluid connection with said fluid inlet 7 and which comprises a porous metallic material 12 produced by additive manufacturing. The fluid outflow part lla-llf is positioned in relation to said fiber pulp arrangement 5a-5f such that fluid 2 delivered out via the fluid outflow part lla-llf will be dispersed through the porous metallic material 12 and enter into the fiber pulp 3. Hereby the fluid can be finely dispersed and an effective mixing can be provided. The porous metallic material 12 of the fluid outflow part lla-llf can be designed to have a suitable porosity by changing production parameters for the additive manufacturing as described above.

[0030] The fiber pulp arrangement 5a-5f is shown as a cross section of a pipe in all the embodiments as shown in Figures 1-6. However, the fiber pulp arrangement 5a-5f in all these embodiments can as well be in another form, such as for example a vessel. The present invention is applicable to any part in a fiber pulp processing system where a fluid needs to be mixed into the fiber pulp. For example the mixing device la-lf according to all the embodiments of the invention can be positioned in a side wall of a vessel instead of a side wall (also called fiber pulp enclosure wall) of a pipe as shown in Figures 1-6.

[0031] Furthermore, in some embodiments of the invention the porous metallic material 12 of the fluid outflow part lla-llf may be built by additive manufacturing to comprise a controlled variation of porosity degree over one or more directions of extension of the porous metallic material 12. Hereby a dispersion degree for the fluid to be transferred out via the fluid outflow part lla-llf of the mixing device la-lf can in some embodiments be varied at different parts of the mixing device la-lf and a mixing device can be tailored with a varying porosity as required by different applications. A porosity degree of the porous metallic material 12 can be designed to be different at different parts of the fluid outflow part lla-llf. In some examples one end or one side of the fluid outflow part lla-llf can be designed to have a different porosity degree than other parts of the fluid outflow part lla-llf. Furthermore, in some embodiments, a designed perforation of the material, i.e. specifically sized and positioned fluid distribution channels 41 (can be seen in Figure 6), can be combined with the porosity and be built together by additive manufacturing to make up the mixing device having a suitable distribution configuration for the fluid. Hereby a porosity and a perforation can be combined in the mixing device la-lf and be produced together by additive manufacturing. Hereby an effective distribution of a fluid can be provided and a mixing can be effective. Different combinations of fluid distributions channels 41 and different parts of the fluid outflow part lla-llf having different porosity degrees can be combined in any suitable way hereby providing a fluid dispersion which can be designed for being optimal for all different applications.

[0032] In Figures la and lb one embodiment of a mixing device la according to the invention is schematically shown. In this embodiment the at least one fluid outflow part 11a of the mixing device la comprises at least one wall part 21 which is a part of a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5a. Figure la shows only the mixing device la as integrated with the fiber pulp arrangement 5a. Figure lb shows the same mixing device la and fiber pulp arrangement 5a as shown in Figure la where a fluid inlet 7 of the mixing device la is connected to a fluid source 9. Furthermore, in Figure lb both a fluid 2 and a fiber pulp 3 are illustrated. The fluid 2 is entering into the fiber pulp arrangement 5a via the fluid inlet 7 and the fluid outflow part 11a of the mixing device la and the fiber pulp 3 is provided in the fiber pulp arrangement 5a. The fluid 2 is being mixed into the fiber pulp 3 when the fluid 2 is dispersed out through the fluid outflow part 11a via the porous metallic material 12. In the rest of the Figures, Figures 2-6, no fluid 2, fluid source 9 or fiber pulp 3 are illustrated. The principle is however the same as shown in Figure lb.

[0033] In Figure 2 another embodiment of a mixing device lb according to the invention is schematically shown. In this embodiment the at least one fluid outflow part lib can be the same or similar to the one shown in Figures la and lb, i.e. the fluid outflow part lib is integrated in a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5b. However, in this embodiment the mixing device la further comprises a turbulence producing organ 45 which is provided in said fiber pulp arrangement 5b in vicinity of said at least one fluid outflow part lib. The turbulence producing organ 45 is in this embodiment shown to be an obstruction 45 for a flow of fiber pulp 3, which obstruction 45 is provided inside the fiber pulp arrangement 5b. The turbulence producing organ 45 in the form of an obstruction 45 is provided close to the position of the fluid outflow part lib. The turbulence producing organ 45 is suitably positioned such that the flow of fiber pulp 3 first enters the turbulence producing organ 45 and then the fluid outflow part lib of the mixing device lb (i.e. flow of fiber pulp 3 is entering from the left in Figure 2 in the same way as shown in Figure lb). The turbulence producing organ 45 can be any type of obstruction or restriction which will produce a turbulence to the flow, such as for example illustrated in Figure 2, a short passage of the fiber pulp arrangement 5b having a smaller diameter. This is in the example where the fiber pulp arrangement is a pipe for transportation of fiber pulp. Another example could as discussed above instead be a vessel.

[0034] In Figure 3 another embodiment of a mixing device lc according to the invention is schematically shown. The fiber pulp arrangement 5c is also in this embodiment illustrated as a pipe. However, a vessel or another type of fiber pulp arrangement is also possible. In this embodiment the mixing device lc comprises at least one internal part 31c which is protruding into the fiber pulp arrangement 5c. The internal part 31c comprises the fluid outflow part 11c and at least a part of the internal part 31c comprises a porous metallic material 12. More than one internal parts 31c can be provided spaced apart along a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5c. The internal part 31c is in this embodiment shown to be integrated into a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5c. However, in another embodiment the internal part 31e, 31f can instead be a separate part which is protruding through an opening in the fiber pulp enclosure wall 23 as will be further described in relation to Figures 5 and 6.

[0035] In Figure 4 another embodiment of a mixing device Id according to the invention is schematically shown. The fiber pulp arrangement 5d is also in this embodiment illustrated as a pipe. The mixing device Id comprises an internal part 31d which is integrated into a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5d. The internal part 31d is in this embodiment provided over the whole circumference of the pipe and is protruding towards a center of the pipe and will hereby in itself be a turbulence producing organ 45 for the fiber pulp flow coming from the left in Figure 4. The fluid outflow part lid of the mixing device Id is in this embodiment positioned such that a fiber pulp flow which is passing through the fiber pulp arrangement 5d first is passing the turbulence producing organ 45 of the internal part 31d and then comes to the fluid outflow part lid. At least a part of the internal part 31d comprises hereby a porous metallic material 12 which porous metallic material 12 will be a part of the fluid outflow part lid. The fluid outflow part lid can furthermore, as shown in Figure 4, be angled in order to direct a flow of fluid in a suitable direction for efficient mixing of fluid into the fiber pulp.

[0036] In Figure 5 another embodiment of a mixing device le according to the invention is schematically shown. The fiber pulp arrangement 5e is also in this embodiment illustrated as a pipe. However, a vessel or another type of fiber pulp arrangement is also possible. In this embodiment the mixing device le comprises an internal part 31e which is protruding into the fiber pulp arrangement 5e via an opening 32 in a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5e. The internal part 31e comprises a fluid outflow part lie which comprises a porous metallic material 12. The internal part 31e is in this embodiment configured such that it can be rotated. Hereby a mixing of a fluid into the fiber pulp can be improved. Furthermore, the rotation of the internal part 31e can provide a turbulence to the fiber pulp in the fiber pulp arrangement 5e whereby more of the fiber pulp will come in contact with the mixing device le and hereby the mixing will be more effective. In another embodiment of the invention an internal part of the mixing device may also be configured such that it can be translated within the fiber pulp arrangement. Furthermore, a mixing device la as disclosed in relation not Figures 1 and 2 which is a part of a fiber pulp enclosure wall 23 can also be configured such that it can rotate. By rotating a wall part comprising a fluid outflow part the mixing may be improved.

[0037] In Figure 6 another embodiment of a mixing device If according to the invention is schematically shown. The fiber pulp arrangement 5f is in this embodiment illustrated as a bent pipe. The mixing device If comprises an internal part 31f which is protruding into the fiber pulp arrangement 5f via an opening 32 in a fiber pulp enclosure wall 23 of the fiber pulp arrangement 5f. The internal part 31f comprises a fluid outflow part Ilf which comprises a porous metallic material 12. The internal part 31f is in this embodiment configured such that it can be rotated. Furthermore, the internal part 31f comprises in this embodiment an impeller 42 or another rotating oragn. A diameter of the impeller 42 can be designed to be almost as large as an inner diameter of the pipe. Hereby an efficient mixing of the fiber pulp is provided when the fiber pulp passes the impeller 42 of the internal part 31f. In this embodiment it is also shown that the internal part 31f can comprise fluid distribution channels 41 which are combined with the porous metallic material 12 to provide a suitable distribution of the fluid. The fluid outflow part Ilf of the internal part 31f can be positioned in relation to the impeller 42 of the internal part 31f such that mixing of fluid into the fiber pulp is efficiently provided when the fiber pulp has been mixed by the impeller 42.

[0038] The rotating internal parts 31e, 31f of the mixing devices le, If as illustrated in Figures 5 and 6 can also be called turbulence producing organs as they produce a turbulence to the fiber pulp.

[0039] In some embodiments of the invention at least one surface of said porous metallic material 12 of the fluid outflow part lla-llf has been polished by vibration polishing. Vibration polishing is performed by vibrating the object to be polished together with a processing media in the form of a number of processing bodies of a suitable material. For example, ceramic or steel processing bodies can be used as processing media. The use of vibration polishing as polishing method allows the surface of the porous metallic material to maintain its porosity, i.e. the surface will not be clogged and pores will not be obstructed as could be the case when using other polishing methods. The vibration polishing will have a cleaning effect which may improve porosity features of the material. This can be especially useful in some technical areas where the porosity needs to be reliable and controllable.

[0040] Vibration polishing is often performed by the addition of a grinding compound comprising abrasive particles. However, according to some embodiments of the invention the polishing is provided without an addition of a grinding compound. A grinding compound could clog the pores of the material and according to some embodiments of the invention only water and possibly some detergent and / or flocculating agent and no grinding compound comprising abrasive particles is added during the vibration polishing. Hereby there is less risk that the porous material is clogged and the porosity of the material will be more reliable. However, if a grinding compound is used during the vibration polishing another alternative may be to clean the material afterwards, for example by ultrasonic washing.

[0041] The polishing comprises according to some embodiments of the invention the use of a processing media in the form of a number of processing bodies, each having a volume smaller than 2 cm3or smaller than 1 cm3, i.e. in some embodiments of the invention the processing bodies each has a volume between 0-2 cm3or between 0-1 cm3. By using comparatively small sized processing bodies as processing media in the vibration polishing there is less risk to destroy the porous material during polishing.

[0042] The porous metallic material 12 of the fluid outflow part lla-llf may further in some embodiments of the invention comprise a reinforcement structure. A reinforcement structure, also called a lattice structure, may be melted into the porous metallic material during the building of the porous metallic material by additive manufacturing. Hereby a suitable mechanical strength of the mixing device la-lf can be provided.

[0043] According to the invention a method for mixing a fluid 2 into a fiber pulp 3 in a fiber pulp arrangement 5a-5f is also provide. The method comprises the step of delivering the fluid 2 into the fiber pulp 3 via at least one fluid outflow part lla-llf of a mixing device la-lf as defined above according to the invention. The method may further comprise the step of rotating and / or translating at least a part of said at least one fluid outflow part lla-llf in order to improve mixing and in order to produce a turbulence to a fiber pulp provided in the fiber pulp arrangement 5a-5f.

Claims

CLAIMS1. A mixing device (la-lf) for performing mixing of a fluid (2) into a fiber pulp (3) in a fiber pulp arrangement (5a-5f), said mixing device (la-lf) comprising: a fluid inlet (7) configured to be connected to a fluid source (9) for providing fluid (2) into the mixing device (la-lf); and at least one fluid outflow part (lla-llf) which is in fluid connection with said fluid inlet (7) and which comprises a porous metallic material (12) produced by additive manufacturing, wherein said fluid outflow part (lla-llf) is positioned in relation to said fiber pulp arrangement (5a-5f) such that fluid (2) delivered out via the fluid outflow part (lla-llf) will be dispersed through the porous metallic material (12) and enter into the fiber pulp (3), wherein said porous metallic material (12) of said at least one fluid outflow part (lla-llf) has a degree of porosity which is varying over a surface of the fluid outflow part.

2. Mixing device according to claim 1, wherein the at least one fluid outflow part (lla- llf) comprises at least one wall part (21) which is a part of a fiber pulp enclosure wall (23) of the fiber pulp arrangement (5a-5d).

3. Mixing device according to claim 1 or 2, wherein the at least one fluid outflow part (lla-llf) comprises at least one internal part (31c-31f) which is protruding into or is provided inside the fiber pulp arrangement (5a-5f).

4. Mixing device according to any one of the preceding claims, wherein at least a part of said at least one fluid outflow part (lla-llf) is configured such that it can be rotated and / or translated.

5. Mixing device according to any one of the preceding claims, wherein said at least one fluid outflow part (Ilf) further comprises fluid distribution channels (41) produced by additive manufacturing.Mixing device according to any one of the preceding claims, wherein at least a part of a surface of said porous metallic material (12) has been polished by vibration polishing. Mixing device according to any one of the preceding claims, further comprising a turbulence producing organ (45) which is provided in said fiber pulp arrangement (5a-5f) in vicinity of or integrated with said at least one fluid outflow part (lla-llf). Method for mixing a fluid (2) into a fiber pulp (3) in a fiber pulp arrangement (5a-5f), said method comprising the step of: - delivering the fluid (2) into the fiber pulp (3) via at least one fluid outflow part (lla- llf) of a mixing device (la-lf) according to any one of the preceding claims. Method according to claim 8, further comprising a step of rotating and / or translating at least a part of said at least one fluid outflow part (lla-llf).

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