BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for mixing at least two liquid flows with one another in connection with paper and board making, the method comprising: conveying to a inlet chamber included in a mixer at least one first liquid flow substantially in the tangential direction, whereby the first liquid flow resembles a spiral and comprises in the inlet chamber a tangential speed component and a speed component in the direction of the centre axis of the mixer, the method also comprising mixing the first liquid flow with at least one other liquid flow utilizing at least one guide surface in the mixer.

[0002] The invention also relates to a mixer for mixing flows to be used in connection with paper and board making, the mixer comprising: at least one inlet chamber, which is restricted by at least an outer periphery and end walls, and the inlet chamber is provided with at least one discharge opening in the direction of a centre axis thereof, at least two inlet channels, from which the liquid flows to be mixed can be fed into the mixer, and at least one guide surface for guiding the liquid flow discharged from the inlet chamber, and the mixer further comprising at least one inlet channel arranged on the periphery of the inlet chamber substantially in the tangential direction, whereby a tangential liquid flow can be fed from the inlet channel in order to form a spiral liquid flow in the inlet chamber.

[0003] When processing different fluent masses, mixtures and liquids, a need arises to mix such liquid flows with one another. For example during the paper making process, chemicals used in paper making, such as retention agents or filling agents, are mixed with the pulp flow. In addition, tail water or other liquids can be mixed with the pulp flow. It is also possible to mix mixtures of liquids and solids to the pulp flow. How successfully the components are mixed obviously have a considerable effect on the quality of the end product. Furthermore, if the mixture is efficient, then the amount of expensive chemicals may be reduced.

[0004] US patent 4,861 ,165 discloses a mixer, in which an axial main flow is conveyed through the inlet chamber thereof. A second flow is fed to the main flow from a tangential channel in the inlet chamber that is later mixed with the main flow in the mixing section of the mixer. According to the publication the mixing section is provided with several consecutive conical

spaces, through which the flows must be conveyed in order to mix them with one another. Such a mixer is necessarily relatively long in the axial direction. What also causes a problem to the solution is that it is not suitable to be used in situations where various liquid flows should be mixed with each other.

BRIEF DESCRIPTION OF THE INVENTION

[0005] It is an object of the present invention to provide a new and improved method for mixing several liquid flows with one another, and a mixer.

[0006] The method according to the invention is characterized by using the mixer, which comprises at least two inlet chambers as considered in the axial direction of the mixer; forming spiral liquid flows in at least two consecutive inlet chambers by feeding at least one liquid flow tangentially into each inlet chamber; guiding the liquid flow formed in the previous inlet chamber to a mixing point, and guiding in the mixing point the spiral liquid flow formed in the latter inlet chamber around the liquid flow.

[0007] The mixer according to the invention is characterized in that the mixer comprises consecutively as considered in the axial direction at least a first inlet chamber and a second inlet chamber, the inlet chambers being separated from one another with a partition wall, that the periphery of the first inlet chamber and the second inlet chamber comprises at least one tangential inlet channel, whereby a first spiral liquid flow is arranged to be formed in the first inlet chamber and a second spiral liquid flow is arranged to be formed in the second inlet chamber, and that a guide element included in the mixer is arranged to guide the second spiral liquid flow around the first spiral liquid flow.

[0008] The basic idea of the invention is to form spiral flows in at least two consecutive inlet chambers of the mixer, both flows being provided with a tangential speed component and an axial speed component. The flow formed in the first inlet chamber is conveyed to a mixing point, where the spiral liquid flow formed in the second inlet chamber is conveyed around the flow.

[0009] The invention provides such an advantage that the structure of the mixer allows mixing in consecutive stages several liquid flows with one another. Regardless thereof the mixer may be relatively short in the axial direction. In addition, the liquid flow to be fed into the tangential direction of the inlet chamber is appropriately distributed on the periphery of the inlet chamber and is provided with an adequately sized tangential speed component and axial speed component. Since a relatively significant speed difference can easily be

formed for the liquid flows to be mixed with each other, the mixing takes place at the mixing point efficiently. By impact of the speed difference the liquid flow to be mixed penetrates nicely into the flow, with which it is being mixed. Consequently heavy turbulence is formed between the liquid flows to be mixed at the mixing point that efficiently mixes the flows together.

[0010] An essential idea of an embodiment of the invention is that tangential liquid flows are fed into inlet chambers which are substantially circular in cross section and the flows formed in the inlet chambers are guided to a mixing point as flows which are circular in cross section. The highest tangential speed is achieved on the outer periphery of the circular inlet chamber, a fact that is utilized for increasing the speed difference between the liquid flows to be mixed.

[0011] Another essential idea of an embodiment of the invention is that the substantially tangential inlet channels are located at different points on the outer periphery of the inlet chamber in two consecutive inlet chambers, in which case the inlet channels of the consecutive inlet chambers are placed at a predetermined angle in relation to one another in the axial direction of the mixer. When inlet channels are placed on different sides of the mixer, then more space will be available for leading pipe ducts to the mixer.

[0012] A further essential idea of an embodiment of the invention is that in two consecutive inlet chambers the flow directions of the tangential inlet channels are placed in relation to one another such that the direction of rotation of the spiral liquid flows in the consecutive inlet chambers is the opposite in respect of one another about the centre axis of the mixer. When such opposite flows are conveyed together at the mixing point, the flows within each other touch one another in the tangential direction. Touching of the opposite flows causes heavy turbulence and mixing of the flows.

[0013] Another essential idea of an embodiment of the invention is that at least one of the inlet chambers of the mixer comprises several substantially tangential inlet channels, the flow directions of which are arranged such that a spiral liquid flow is arranged to be formed in the inlet chamber provided with a determined direction of rotation about the centre axis of the mixer. It is thus possible to feed liquid flows to one inlet chamber from various inlet channels.

[0014] Still another essential idea of an embodiment of the invention is that the mixer comprises several consecutively arranged mixing modules.

The module structure allows constructing a mixer specifically for each mixing purpose. In addition the mixer may later be changed by adding one or more mixing modules thereto or by removing modules. The module structure also simplifies the structure and production of the mixer.

[0015] A further essential idea of an embodiment of the invention is that the mixer is structured in modules and comprises at least two chamber modules. A chamber module comprises an outer periphery and at least one inlet channel arranged substantially tangentially on the outer periphery. An intermediate flange is placed between the two consecutive chamber modules and said flange is arranged to form a partition wall for the consecutive inlet chambers. The intermediate flange comprises a discharge opening substantially on the centre axis of the mixer. In addition, a guide element is placed on the side of one side surface of the intermediate flange, the guide element substantially resembling a truncated circular cone in cross section. The length of the guide element is dimensioned in the axial direction so that it is arranged to separate the spiral flow formed in the previous inlet chamber from the spiral flow formed in the following inlet chamber on the portion of one inlet chamber. The structure formed of separate chamber modules and partition walls allows forming mixers with structures differing from one another. The chamber modules may mutually be substantially alike but they may be arranged in the mixer in different positions in relation to the centre axis or the vertical axis rotated in such a manner that mixers provided with different properties are formed. Furthermore, intermediate flanges including different discharge openings and guide elements may case-specifically be arranged between the chamber modules.

[0016] An essential idea of an embodiment of the invention is that no axial flow is conveyed to the mixer, instead all liquid flows to be mixed are fed into the inlet chambers substantially in the tangential direction.

[0017] A further essential idea of an embodiment of the invention is that the mixer is connected to a mixing channel, which conveys the liquid flows mixed with one another by means of the mixer inside a flow channel that is larger in cross section. The area of the outermost end of the mixing channel comprises a mixing part provided with a wavelike shape in cross section that dispenses the liquid flow from the mixing channel to the liquid flow flowing in the flow channel.

[0018] Still another essential idea of an embodiment of the invention is that the mixer is connected to the mixing channel that conveys the liquid flows mixed with one another by means of the mixer to a mixing container,

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The embodiments of the invention will be explained in greater detail in the accompanying drawings, in which

Figure 1 schematically shows a mixer according to the invention in connection with the short circulation of a paper or board machine,

Figures 2a to 2c schematically show alternatives for locating inlet channels in inlet chambers,

Figure 3 schematically shows a side view in cross-cut of the mixer according to the invention,

Figure 4 schematically shows the mixer shown in Figure 3 cut open along line A - A, and

Figure 5 schematically shows a side view a module-structured mixer.

[0020] For clarity, the Figures illustrate the invention in simplified form. Same reference numerals are used in the Figures to describe similar parts.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0021] In Figure 1 , three separate liquid flows V1 , V2 and V3 are conveyed to a mixer 1 , which are mixed together in the mixer 1 and thereafter conveyed along a mixing channel 2 connected to the mixer 1 forward to the next stage of the process. In the case shown in Figure 1 the outermost end of the mixing channel 2 is arranged within a flow channel 3, in which case liquid flow VA mixed in the mixer 1 can be conveyed to liquid flow VB of the flow channel 3. The portion of the outermost end of the mixing channel 2 may be provided with a mixing part 4 which may be provided with a wavelike shape in cross section that intensifies the mixing of flow VA with flow VB. Alternatively the mixing channel 2 may direct the mixed liquid flow VA to a mixing container, where it may be subjected to further processing and from where it may be dispensed as desired to the production process.

[0022] The arrangement shown in Figure 1 is particularly well applicable for mixing solids used in paper and board making. Thus, liquid flows V1 , V2 and V3 may be fibre suspensions or filling agents provided with different

compositions, which are connected to form liquid flow VA that is further connected with tail water flow VB. Combined flow VC can be forwarded to a short circulation purifying apparatus and further towards a headbox.

[0023] As shown in Figure 1 , the mixer 1 comprises several consecutive inlet chambers 5 as considered in axial direction B of the mixer 1. In this case the number of inlet chambers 5 is three, but the number may be two, four, five or more depending on the number of liquid flows to be mixed. A liquid flow V1 to V3 is conveyed to each inlet chamber 5a to 5c along a specific inlet channel 6a to 6c. The inlet channels 6a to 6c are located on an outer periphery 7 of the inlet chambers 5a to 5c substantially in the tangential direction of the periphery 7. When liquid flows V1 to V3 are fed into the inlet chambers 5a to 5c substantially in the tangential direction, the flows start to rotate about a centre axis 8 of the mixer 1. A substantially large tangential speed component is then formed for liquid flows V1 to V3. In addition, liquid flows V1 to V3 fed into the inlet chambers 5a to 5c tend to shift by impact of feed pressure and guided by guide surfaces 18 to 20 included in the inlet chambers 5a to 5c in axial direction B of the mixer 1 towards the mixing channel 2. Thus, an axial speed component is in addition to the tangential speed component also formed for liquid flows V1 to V3 in the inlet chambers 5a to 5c.

[0024] The mixer 1 may be provided with one or more centre elements 10, which is arranged substantially on the centre axis 8 of the mixer 1. The centre element 10 may for instance be an elongated bar or tube, the outer surface of which may be substantially circular in cross section. The centre element 10 may be arranged to restrict one or more inlet chambers 5a to 5c. In the case shown in Figure 1 , the centre element 10 extends substantially through the entire mixer 1. Thus, each inlet chamber 5a to 5c is shaped substantially as a circular ring in cross section. Feeding the liquid flow substantially in the tangential direction to such a circular space allows providing the liquid flow with a high tangential speed in the inlet chamber 5 that improves the mixture considerably. It is generally preferable to provide the liquid flows to be mixed with a speed difference that is as large as possible in respect of one another before the flows meet at mixing points 21 , 22. The aim is to double the relative speed difference, preferably to provide a twofold to sevenfold speed difference.

[0025] In the embodiment shown in Figure 1 a tube 40 may be used to separate discharge flow Va from liquid flow V1 that can be conveyed to be used for instance as auxiliary stock for a disc filter.

[0026] For clarity, Figures 2a to 2c show a significantly simplified schematic view of a couple of alternatives for feeding substantially tangential liquid flows from inlet channels 6a to 6d into consecutive inlet chambers 5a to 5d of the mixer 1. Arrow C illustrates the axial direction of the main flow in the Figures.

[0027] As shown in Figure 2a the inlet channels 6a to 6d can be placed in the consecutive inlet chambers 5a to 5d alternatively on different sides. Thus, more space is provided around the mixer 1 for bringing the pipe ducts to the inlet channels 6a to 6d. In the consecutive inlet chambers the spiral flows to be formed may have the same direction of rotation about the centre axis 8 as shown in Figure 2a, or alternatively the direction of rotation in the consecutive inlet chambers may be reversed as shown in Figure 2b. It is also possible to form the mixer 1 as shown in Figure 2c, where in relation to one another parallel flows or flows in different directions can be formed in the consecutive inlet chambers. In accordance with need, different inlet chambers can be combined in order to form the mixer.

[0028] Figure 3 shows a mixer 1 in cross section. The mixer 1 comprises three consecutive inlet chambers 5, i.e. a first inlet chamber 5a, a second inlet chamber 5b and a third inlet chamber 5c. Naturally the number of inlet chambers 5 may be only two, or then again the number of inlet chambers may be four or more. Since the mixer 1 according to the figure is module- structured, the number and structure of the inlet chambers 5 can be affected fairly easily. The mixer 1 comprises three consecutively arranged chamber modules 11a to 11c, each one of which comprising at least an outer periphery 7 and at least one inlet chamber 6, which is located substantially tangentially on the periphery 7, A first intermediate flange 12a is provided between the first chamber module 11a and the second chamber module 11 b, and a second intermediate flange 12b is provided between the second chamber module 11b and the third chamber module 11c. The chamber modules 11a to 11c may be arranged between a base element 13 and a cover element 14 and the entity may be assembled as a single unit by means of binding bolts 15 or similar joints. In axial direction B the first inlet chamber 5a is thus restricted by the base element 13 and the first intermediate flange 12a. Furthermore, the sec-

ond inlet chamber 5b is restricted by the first intermediate flange 12a and the second intermediate flange 12b in axial direction B, and also the third inlet chamber 5c is restricted in axial direction B by the second intermediate flange 12b and the cover element 14. The intermediate flanges 12a and 12b and a flange 16 in the cover element 14 are provided with discharge openings 17a to 17c, through which the liquid flows are forwarded in axial direction B.

[0029] The base element 13 may comprise an elongated centre element 10 substantially on the centre axis 8, the centre element 10 being arranged to extend in axial direction B through all inlet chambers 5 and may if need be extend further to the portion of the cover element 14. Furthermore, the portion at the end of the centre element 10 and the base element 13 may be provided with a first guide element 18, which is arranged to restrict the first inlet chamber 5a in the radial direction and to guide the flow fed to the first inlet chamber 5a. The first guide element 18 may resemble a truncated circular cone in cross section and it may be fastened from the first end thereof to the side surface of the base element 13 and from the second end thereof to the outer surface 10a of the centre element 10. Alternatively the guide element 18 forms an integrated part of the centre element 10. The first guide element 18 extends in axial direction B at least from the side surface of the base element 13 past the partition wall at the side of the second inlet chamber 5b of the first intermediate flange 12a. Preferably the first guide element 18 extends in axial direction B above the middle of the second inlet chamber 5b, most preferably on the portion between the middle of the second inlet chamber 5b and the second intermediate flange 12b. In addition, at the discharge opening 17a of the first intermediate flange 12a a second guide element 19 is provided, which extends in axial direction B at least until the partition wall on the side of the second inlet chamber 5b of the second intermediate flange 12b. Also, a third guide element 20 is provided at the discharge opening of the intermediate flange 12b, the guide element extending in axial direction B at least until the end wall on the side of third inlet chamber 5c of the flange 16 of the cover element 14. The second guide element 19 and the third guide element 20 may resemble truncated circular cones in cross section and they are arranged to taper towards the cover element 14. As shown in Figure 3 the first guide element 18 may be placed partly within the second guide element 19. Then the guide elements 18 and 19 are dimensioned such that a gap 21 is provided between the outer surface of the guide element 18 and the inner surface of the

guide element 19, along which gap the liquid flow can be conveyed from the first inlet chamber 5a to a first mixing point 22. Furthermore, from the circular space restricted by the outer surface of the second guide element 19 and the periphery 7 of the second mixing module 11b the liquid flow of the second inlet chamber 5b is conveyed to a mixing point 22. The liquid flow of the first inlet chamber 5a and the liquid flows of the second inlet chamber 5b are allowed to mix with one another in the circular space restricted by the inner surface of the third guide element 20 and the outer surface 10a of the centre element 10. The mixed flow is conveyed in the axial direction to a second mixing point 23. Furthermore, the liquid flow of the third inlet chamber 5c is conveyed from the circular space restricted by the outer surface of the third guide element 20 and the periphery 7 of the third chamber module 11 c to the mixing point 23 and is allowed to mix with the liquid flow conveyed in the axial direction inside the third guide surface 20. A fourth guide element 24 may be provided at the discharge opening 17c of the cover element 14 that may also resemble a truncated circular cone in cross section, the inner surface of which forming a space, in which the flows may be mixed at the same time as they move towards the mixing channel 2 to be fastened to a flange 25. Unlike the guide elements 18, 19 and 20 the guide element 24 may be arranged such that it tapers towards the base element 13. The centre element 10 may extend at least partly within the fourth guide element 24, in which case the second mixing point 23 is provided with a circular cross section.

[0030] Figure 4 shows the mixer 1 according to Figure 3 at line A - A in cross section. As shown in Figure 4 the inlet channels 6a and 6b of the consecutive first inlet chamber 5a and the second inlet chamber 5b are placed at different locations on the periphery 7 of the inlet chamber. When the inlet channels 6 are located in such a manner, pipe fittings 28a to 28c are more easily conveyed to the mixer 1. In addition, the inlet channels 6a and 6b are arranged such that the consecutive inlet chambers 5a and 5b are provided with a flow that is opposite in direction in respect to one another about the centre axis 8. Figure 4 also shows that a guide 27 is provided at a feed opening 26 of the inlet channel 6a that allows guiding the liquid flow to be fed on the outer periphery 7 of the inlet chamber 5. Also, the guide 27 may be used if need be to reduce the feed opening 26 in order to achieve a more significant feed pressure. In addition to the feed direction of the liquid flow and the feed pressure the dimensions of the inlet chamber affect the tangential speed to be achieved.

[0031] Figure 5 illustrates still another modular mixer 1 comprising a base module 29 and several mixing modules 30. The base module 29 may comprise an end element 31 and a centre element 10. The mixing modules 30 may refer to components that can be arranged partly within each other that comprise axial and radial surfaces restricting the inlet chamber, at least one inlet channel and also the required guide surfaces in order to guide and manage the liquid flow.

[0032] In some cases the mixer 1 does not comprise a centre element 10 at all, instead the conical first guide surface 18 is fastened merely to the base element 13. At the same time it is possible that the centre element 10 is shorter than that illustrated in Figure 3 and extends only for instance to the mixing point 22, It is also possible to feed an axial flow to the mixer through an axial opening in the base element and to guide the spiral liquid flow in the first mixing point and the second spiral liquid flow in the second mixing point around this flow.

[0033] In this application the liquid flow refers to a fluent flow that mainly comprises liquid, but may include one or more components dissolved in the liquid or mixed with the liquid. Therefore the liquid flow may be a mixture of for instance water and a paper-making chemical, or it may be a stock suspension formed of liquid and fibrous material. The solution according to the invention is used in particular in connection with paper and board making. Thus the flows to be mixed may include in addition to the different stock suspensions and chemicals different fillers and also tail water that can be used when diluting the fibre suspension.

[0034] It should also be noted that in some cases the features presented in this application may be used as such regardless of the other features. Then again the features shown in this application may when necessary be combined in order to form different combinations.

[0035] The drawings and the description associated therewith are merely intended to illustrate the idea of the invention. As regards the details, the invention may vary within the scope of the claims.