Method and device for adding additional raw material components to the approach flow system of a fiber web machine

Abstract

The present invention relates to a method and an apparatus for adding at least one additional stock component to a flow system (30) of a fiber web machine. More specifically, the present invention relates to mixing at least one additional stock component with a fiber stock such that the stock flow is equalized (50) and the at least one additional stock component is introduced into the stock flow by injection mixing (80).

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for adding at least one additional stock component to an approach flow system of a fiber web machine headbox. More specifically, the present invention relates to mixing at least one additional stock component with fiber stock flowing in the approach flow system of a fiber web machine headbox. Background Art

[0002] A paper machine, or more generally a fiber web machine, is preceded by an approach flow system, in which a fiber suspension (usually referred to as stock) for manufacturing a fiber web at the fiber web machine is prepared. At the approach flow system, the various stock components (i.e. virgin and / or recycled pulp and / or waste) are mixed together with white water recovered from the fiber web machine, fillers and other desired additives are mixed with the stock, and if deemed necessary, the stock or one or more of the stock components are degassed. Furthermore, at the approach flow system, the stock is introduced by a headbox feed pump (usually a specially designed centrifugal pump) into the headbox screen, where the stock is finished for web manufacturing at the headbox. The approach flow system is also provided with one or more mixers for adding flow-aiding chemicals and possibly other chemicals or additives to the stock. Depending on the type of chemicals, these can be added to the stock as early as possible (e.g. into the mixing pool) or as late as possible (e.g. only upstream of the headbox, i.e. between the headbox screen or the machine screen and the headbox).

[0003] Wet-end chemicals have been used in papermaking for a long time, for example to retain fine solids such as fillers and other additives used in papermaking in the fiber web, while water (so-called white water) is discharged from the fiber web at the forming and drying section of a fiber web machine. Soon after the wet-end chemicals (such as flow-aid chemicals) are introduced into the mixture of fibers and solids, the wet-end chemicals bind the solids to each other and to the fibers of the raw material. The introduction of wet-end or flow-aid chemicals can take place before or after the headbox screen. However, carrying out the introduction at such a stage usually results in that the agglomerates formed by the wet-end or flow-aid chemicals are formed only after the headbox screen, because, on the one hand, the screen may easily separate the agglomerates from the raw material used later for the production of the web, or, on the other hand, the screen may destroy the agglomerates due to the turbulence generated, thus reducing the retention of the solids in the web. Therefore, wet-end or flow-aid chemicals are often added to the outlet duct of the headbox screen, where only a weak turbulence remains, which cannot destroy the agglomerates to be formed, but can still help the mixing of the wet-end or flow-aid chemicals.

[0004] As long as paper has been made on paper machines, there has been a constant drive towards higher quality end products. A factor that plays an important role in paper quality is the use of various chemicals and / or additives. However, there has always been a goal to reduce the use of chemicals and additives for a number of reasons. Firstly, chemicals are more expensive compared to cellulose fibers, so cost considerations drive a reduction in the amount of chemicals used. Secondly, naturally, when chemicals are mixed with the papermaking raw material, a portion of the chemicals ends up in the circulating water, and no matter how efficient the water recycling is, there is always a small portion of the chemicals that enters the wastewater treatment and may end up in a lake, river or sea. Therefore, for economic and environmental reasons, chemicals and additives should be used as efficiently as possible. In other words, the minimum amount of chemicals should be used and the chemicals should be mixed with the raw material stream as evenly as possible.

[0005] The starting point of the present invention is a chemical mixer from Valmet Corporation, which is called OptiMixer TM , and discussed in US-A1-2002 / 0121350. The US document discloses a static mixer comprising a mixer flow tube having a diameter equal to the diameter of a stock flow tube that feeds papermaking stock toward the headbox of a paper machine. The mixer flow tube is fixed to the stock flow tube by a flange, and a plurality of circumferentially arranged forming parts are provided on the inner circumference of the mixer flow tube. The function of the forming parts is to generate turbulence to mix chemicals into the stock. The US document teaches several methods of adding chemicals to the stock. In a first embodiment, the chemicals are introduced into the stock via the forming parts, in a second embodiment, the chemicals are introduced into the stock just upstream of the forming parts, and in a third embodiment, the chemicals are introduced just behind the forming parts. And, in a fourth embodiment, the chemicals are introduced into the stock between the forming parts in the circumferential direction.

[0006] In all the above-mentioned embodiments, the principle of mixing chemicals is the same. However, in experiments recently carried out, it has been learned that the use of chemicals can be made more efficient if some facts are taken into account. First, the stock flow from the headbox screen or machine screen or any other device along the stock flow tube to the static mixer has an irregular consistency distribution, just like in any flow tube. In other words, the stock portion flowing closest to the flow tube surface has the lowest concentration, while the portion flowing in the center of the flow tube has the highest concentration. Secondly, since the chemicals are introduced into the stock either directly through the mixer flow tube wall or via a shaped part, the chemicals come into contact with the stock portion with the lowest concentration. The American document also discusses an embodiment in which the chemicals are introduced into the stock flow at a distance from the wall, where the stock concentration is slightly higher than the stock concentration at the tube surface, but still different from the concentration in the middle of the flow. And this embodiment has the obvious disadvantage that the nozzle extending from the tube wall inside the tube will collect impurities, which make the feeding of the chemicals more difficult and reduce the quality of the final product.

[0007] The above-mentioned concentration-related problems mean in practice that the concentration of active chemical (which has not yet reacted with or fixed to the solid material) is highest where the solid concentration of the raw material is lowest. Therefore, the chemical reacts effectively with the solids in the low-concentration raw material, and as a result, the concentration of the chemical is reduced and less chemical is left for the solids in the higher-concentration raw material. Therefore, the solids in the higher-concentration raw material have less chemical to react with or fix with. Therefore, the net result of this mixing is uneven treatment of the solids by the chemical, and in order to ensure that there is a sufficient amount of chemical in all parts of the raw material, the dosage of the chemical must be increased beyond the optimal range. In addition, there is a risk that, for example, the filler retention is uneven throughout the raw material, so that the machine-lateral distribution of the filler in the final product is uneven, and the quality of the final product is also unsatisfactory. Summary of the invention

[0008] It is therefore an object of the present invention to address at least one of the problems discussed above.

[0009] Another object of the present invention is to use optimal amounts of chemicals and / or additives, thereby reducing the chemical / additive costs involved in producing the web-like article.

[0010] Yet another object of the present invention is to reduce the amount of chemicals / additives required in the treatment of paper mill wastewater.

[0011] Yet another object of the invention is to improve the construction of the headbox feed pipe so that a minimum amount of consistency differences eventually occur in the headbox.

[0012] Another object of the present invention is to improve the construction of the headbox feed pipe so that the positions of various devices connected to the headbox feed pipe are carefully determined.

[0013] Another object of the present invention is to provide a method of chemical / additive dosing for new functional fiber based products which have higher requirements for chemical / additive dosing than conventional paper and paperboard manufacturing.

[0014] At least part of the objectives are achieved by one aspect of the present application.

[0015] In addition, at least part of the objects are achieved by another aspect of the present application.

[0016] At least one of the above objects is achieved by arranging a stock flow equalizer in the headbox feed pipe, which effectively mixes the stock flow upstream of the introduction of chemicals so that any concentration differences are minimized or completely eliminated. The stock flow equalizer forms a high turbulence zone of chaotic turbulence, which lasts until the introduction of chemicals. The chemicals are introduced into the equalized, but still turbulent stock flow by an injection mixing station, which is known to be able to evenly spread the chemicals over the entire cross-section of the stock flow pipe. A good example of such an injection chemical mixer or injection mixing station is the TrumpJet from Wetend Technologies Ltd. TM mixer, which has gained wide recognition in the art of mixing flow aid chemicals and other chemicals into fiber suspensions. The TrumpJet described above is discussed in, for example, EP-B1-1219344 TM Mixers and their use. TrumpJet TM The mixer serves as a mixing station which consists of a single injection mixing unit or a plurality of injection mixers or injection mixing units arranged on the circumference of a raw material flow pipe in which the medium with which the chemical is to be mixed flows.

[0017] At least part of the objects of the present invention are achieved by a method for adding at least one additional stock component to a stock flow in the flow system of a headbox of a fiber web machine, wherein fiber stock is introduced into the headbox of the fiber web machine by a headbox feed pump via a headbox screen, a headbox feed pipe and a chemical mixer, and in the method the stock flow is treated by equalizing the concentration differences prevailing in the stock flow downstream of the headbox screen and mixing the at least one additional stock component with the stock.

[0018] At least part of the objects of the present invention are achieved by an apparatus for adding at least one additional stock component to a stock flow in a flow system of a headbox of a fiber web machine, the flow system comprising a headbox feed pump, a headbox screen, a chemical mixer and a headbox feed pipe; a stock flow equalizer is arranged in the headbox feed pipe at a distance from the chemical mixer arranged between the headbox screen and the headbox.

[0019] Other features of the invention are discussed throughout the application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, the prior art and the present invention are discussed in more detail with reference to the accompanying drawings, in which:

[0021] Figure 1 A partial view showing a prior art approach flow system of a fiber web machine,

[0022] Figure 2A A partial view showing a novel approach flow system of a fiber web machine according to a preferred embodiment of the invention,

[0023] Figure 2B A partial view showing a novel approach flow system of a fiber web machine according to another preferred embodiment of the invention,

[0024] Figure 3 A partial cutaway view showing a feed stream equalizing mixer or a feed stream equalizer according to a preferred embodiment of the present invention,

[0025] Figure 4a showing the operation of the forming part of the material flow equalizer as seen from the forming part side,

[0026] Figure 4b The operation of the shaping components of the stock flow equalizer is shown as seen from the direction of the headbox. DETAILED DESCRIPTION

[0027] Figure 1A partial view of a prior art approach flow system of a fiber web machine is shown. According to the figure, in addition to components not shown, the approach flow system 10 of the fiber web machine comprises a headbox feed pump 12, a stock flow pipe 14, a headbox screen 16, a chemical mixer 18 and a headbox 20, via which the fiber stock is conveyed to the forming section of the fiber web machine, typically to its wire section or forming section. The chemical mixer 18 is the OptiMixer of Valmet, discussed in more detail in the prior art US-A1-2002 / 0121350. The chemical mixer 18 has a plurality of feed openings arranged on the circumference of the mixer, which are arranged to cooperate with the forming components of the mixer. Each feed port may have only one chemical feed channel, or may have two feed channels 22' and 22", as shown in the figure. According to the US document, feed channel 22' may be used to feed filler or fiber slurry, while feed channel 22" is used to feed some other chemical so that the two components are mixed with each other before being introduced into the raw material in the raw material flow pipe 14 via the feed port.

[0028] As already discussed above, feeding one or more chemicals into a feedstream that has not been fully mixed so that concentration variations in the feedstream will be equalized can lead to problems that can be seen in both the quality of the final product and unnecessary high dosages of chemicals, leading to increased chemical costs.

[0029] Figure 2A A partial view of a flow system of a fiber web machine according to the invention is shown. In addition to components not shown, the novel flow system 30 of the fiber web machine comprises a headbox feed pump 32, a stock flow pipe 34, a headbox screen 36, a headbox feed pipe 38 and a headbox 40, via which the fiber stock is conveyed to the forming section of the fiber web machine, typically to its wire section or forming section. The headbox feed pipe 38, which extends from the headbox screen 36 or machine screen to the headbox 40, is provided with a stock flow equalizer 50 (at Figure 3 and Figure 4a to Figure 4b ) and injection mixing station 80. Figure 2AAs shown, the injection mixing station 80 has at least one inlet channel or a group of inlet channels 82 for one or more chemicals to be introduced into the stock flow in the headbox feed pipe 38. The injection mixing station 80 also has at least one inlet channel 84 for receiving injection liquid. The injection liquid is preferably extracted from the headbox feed pipe 38 and pumped to the injection mixing station 80 by a pump 86. According to the most preferred embodiment of the present invention, the injection liquid is taken from the headbox feed pipe 38 between the stock flow equalizer 50 and the injection mixing station 80, where the concentration variations in the stock flow have been equalized. According to another embodiment (shown by the dotted line), the injection liquid is taken from the headbox feed pipe upstream of the stock flow equalizer 50. According to yet another embodiment, the injection liquid is taken from the headbox feed pipe downstream of the injection mixing station 80. The injection mixing station is preferably, but not necessarily, composed of one or more TrumpJet TM The TrumpJet is discussed in, for example, EP-B-1219344. TM Injection mixer and its use.

[0030] Figure 2B A partial view of an approach flow system of a fiber web machine according to the invention is shown. Figure 2A Similar, but Figure 2B Another option is given for carrying out the method of mixing at least one additional stock component with the stock phase before and / or after equalizing the concentration differences prevailing in the stock flow downstream of the headbox screen. Figure 2B The apparatus shown in FIG. 1 shows that the chemical mixer 80 is arranged upstream of the feed stream equalizer 50. For some types of additional feed components (perhaps fiber components), this is a preferred option, while for some additional feed components, Figure 2A The embodiment is preferred. Figure 2A and Figure 2B Combinations of embodiments are also possible (not shown in the figures), whereby chemical mixers 80 are arranged upstream and downstream of the stock flow equalizer 50. At least one but possibly more additional stock components are then mixed with the stock before and after equalizing the concentration differences prevailing in the stock flow downstream of the headbox screen 36. This device may be preferred, for example, for mixing cationic and anionic additional stock components in a selected sequence. If it is necessary to mix even more additional stock components, it is also possible to double or triple one of the chemical mixers.

[0031] Figure 3A partial cutaway view of a stock flow equalizer 50 of the present invention is shown. In the embodiment shown in this figure, the stock flow equalizer 50 is fastened to the headbox feed pipe 38 by means of flanges 52' and 52". The stock flow equalizer 50 has a tubular wall 54, the diameter of which corresponds to the diameter of the headbox feed pipe 38. The inner surface 56 of the tubular wall 54 is provided with shaped parts 58, which in this embodiment are arranged on the same periphery of the inner surface 56. In another embodiment, the shaped parts are directly attached to the inner surface of the headbox feed pipe, so that no additional pipe flanges are required, but only The headbox feed pipe is fastened at its first end to the machine screen and at its second end to the headbox. Each forming part 58 has a leading surface 60, which is fastened to the inner surface 56 of the tubular wall 54 along its leading edge 62. Arrow F indicates the direction of stock flow through the stock flow equalizer 50. Downstream of the leading edge 62, the leading surface 60 rises from the inner surface 56 so that the triangular side surfaces 64' and 64" can be arranged between the side edges of the leading surface 60 and the side edges of the inner surface 56. The leading surface 60 tapers towards its trailing tip 66 so that the side surfaces 64' and 64" can be fastened to each other at the trailing edge 68 of the forming part 58.

[0032] The forming member 58 acts (see Figure 3 , Figure 4a and Figure 4b ), so that the leading surface 60 of the forming part raises the low-concentration stock flow closer to the center of the tubular flow tube from the vicinity of the inner surface 56 to mix the low-concentration stock with the higher-concentration stock closer to the axis of the flow tube. At the same time, a portion of the stock flowing along the leading surface 60 meets the side edge 70 between each leading surface 60 and the side surfaces 64' and 64", so that this portion of the stock flow generates two counter-rotating vortices at both sides of each forming part 58. First, the vortices are mixed with the low-concentration stock flow still flowing through the forming part along the inner surface 56. Thereafter, when the vortices of two adjacent forming parts meet each other, the vortices mix with each other and form a chaotic turbulent zone extending downstream of the forming part. Such a turbulent zone extends over the entire diameter of the stock flow equalizer and equalizes the concentration differences that already exist. In the experiments conducted, it has been understood that the distance required to completely equalize the stock flow is at least 1*D, preferably 3*D, where D is the diameter of the headbox feed pipe.

[0033] With regard to the stock flow equalizer 50, it should be understood that the number of its forming parts 58 can vary between 3 and 15, the forming parts can be arranged on the same circumference of the inner surface 56 of the stock flow equalizer 50, or they can be divided into several groups on several circumferences, or they can be freely arranged at any position on the inner surface. Naturally, their axial distance from each other should not be too long, which will reduce the efficiency of the stock flow equalization function. The preferred length of the stock flow equalizer, that is, the preferred length from the leading edge of the upstream forming part to the trailing tip of the downstream forming part is 0.5*D to 3*D, where D is the diameter of the headbox feed pipe. The radial height of the forming part 58 is preferably between 0.1*D and 0.5*D, where D is the diameter of the headbox feed pipe. The width of the forming part is preferably 0.1 to 1 times the length of the forming part. In addition, the leading surface 60 of the forming part does not have to be planar in its radial or axial cross section or in both its radial and axial cross sections, but can be curved, that is, convex or concave.

[0034] As already combined above Figure 2A As discussed, after the stock flow equalizer 50 on the headbox feed pipe 38 is the injection mixing station 80. The distance between the stock flow equalizer and the injection mixing station should be arranged so that the chaotic turbulence has equalized the concentration, but has not decayed to the extent that concentration differences have begun to form. In practice, the distance from the tail tip of the last forming part (in the stock flow direction) to the injection mixing station should be 0.5 to 10 times, preferably 2 to 5 times, the diameter D of the headbox feed pipe 38, i.e., 2*D to 5*D. In addition, it is important for the optimization of the headbox feed pipe and additional stock component mixing that the stock flow equalizer 50 is arranged at a distance from the headbox 40. The distance from the injection mixing station 80 to the headbox 40 needs to be carefully considered. Naturally, if the stock flow equalizer 50 together with the injection mixing station 80 is too close to the headbox, the turbulence caused by the equalizer will have an impact on the stock flow in the headbox, and it will be more difficult to obtain a uniform basis weight distribution for the web to be formed. If the stock flow equalizer 50 together with the injection mixing station is too far from the headbox, the stock flow in the headbox feed pipe 38 will have time to start to develop concentration differences in the stock flow. Therefore, the preferred distance from the stock flow equalizer 50 to the headbox 40 is between 5*D and 15*D, where D is the diameter of the headbox feed pipe 38.

[0035] Preferably, the chemical mixer 80 is an injection mixing station, which can be formed by a single injection mixer or a group of injection mixers. In narrow pipes a single injection mixer may be sufficient, but for larger pipes an injection mixing station with several injection mixers is required around the headbox feed pipe. In operation, at least one additional stock component and an injection liquid are brought into the injection mixer, each along its own feed channel. The additional stock component and the injection liquid are introduced into the equalized stock flow via a common nozzle, so that the additional stock component mixes with the injection liquid, and the injection liquid, due to its high speed and injection pressure, ensures that the relatively small amount of the mixture of the additional stock component and the injection liquid penetrates deep enough into the equalized stock flow in the headbox feed pipe. The injection liquid is preferably, but not necessarily, the same stock as the stock to be mixed with the additional stock component. Preferably, but not necessarily, the injection liquid is brought upstream of the mixer to be injected into the stock flow in the headbox feed pipe through the mixer together with the additional stock component. As mentioned above, the injection liquid can be taken from the headbox feed pipe upstream of the stock flow equalizer, between the equalizer and the injection mixing station, or downstream of the injection mixing station. Other options for injection liquid are fresh pulp, recycled pulp, white water, fresh water, etc., just to name a few options, and it is not intended to limit the applicable liquids to only the listed options.

[0036] It will also be appreciated that the invention encompasses mixing a single additional feed component or two or more additional feed components into the feed upstream and / or downstream of the feed flow equalizer. In other words, it is feasible that, where more than one additional feed component is used (in addition to the one mixed downstream of the feed flow equalizer), one additional feed component is mixed into the feed between the headbox screen and the feed flow equalizer, and / or one additional feed component is mixed into the feed upstream of the headbox screen. Naturally, it is preferred that in the latter two alternatives, the additional feed component is a slow-reacting additional feed component, which thus only acts or forms agglomerates after the feed flow equalizer.

[0037] Finally, it is also understood that the at least one additional raw material component is at least one of the following: a flow-aiding chemical, a sizing agent such as alkenyl succinic anhydride (ASA) or alkyl ketene dimer (AKD), starch, filler, paper dye or pigment, microcellulose or nanofibrillated cellulose (MFC, NFC) or other natural / bio-based or synthetic fibers, to name a few. These additional raw material components can be mixed with the raw material together with other additional raw material components or independently. If introduced with some other additional raw material components, it can either be pre-mixed with the additional raw material components before being injected into the raw material, or it can be injected into the raw material only together with the additional raw material components.

[0038] It is also understood that in different embodiments, the above dimensions related to the headbox feed pipe diameter D may vary significantly depending on the actual application. In a small flow system of a fiber web machine headbox, the diameter D may be 50 mm to 100 mm. In a large fiber web machine, the diameter D may be approximately 1200 mm.

[0039] Although the present invention has been described with reference to the particular illustrated embodiments, it should be emphasized that the scope of the present invention is limited only by the appended claims.

Claims

1. A method for adding at least one additional stock component to a stock flow in an approach flow system (30) of a fiber web machine headbox (40), wherein: The fiber raw material is introduced into the headbox (40) of the fiber web machine by means of a headbox feed pump (32) via a headbox screen (36), a headbox feed pipe (38) and a chemical mixer (80), characterized in that the raw material flow is treated by equalizing the concentration differences prevailing in the raw material flow downstream of the headbox screen but not attenuating them to the extent that concentration differences have begun to form, and mixing the at least one additional raw material component with the equalized raw material.

2. The method according to claim 1, characterized in that A stock flow equalizer (50) is disposed between the headbox screen (36) and the chemical mixer (80) and at a distance from the chemical mixer (80) to equalize concentration differences prevalent in the stock flow.

3. The method according to claim 1 or 2, characterized in that: The at least one additional stock component is mixed with the stock before and / or after equalizing concentration differences prevailing in the stock flow downstream of the headbox screen (36).

4. The method according to claim 2, characterized in that: An injection mixing station is used to add the at least one additional feedstock component to the equalized feedstock stream by using at least one of fresh pulp, regenerated pulp, white water and fresh water as injection liquid.

5. The method according to claim 3, characterized in that: An injection liquid is used to cause the at least one additional feed component to penetrate into the equalized feed stream.

6. The method according to claim 4, characterized in that Stock is taken from the headbox feed pipe located upstream or downstream of the stock flow equalizer (50) and upstream of the injection mixing station to serve as injection liquid for feeding the at least one additional stock component into the stock flow.

7. The method according to claim 1, characterized in that The at least one additional raw material component is at least one of: a flow-aiding chemical, a sizing agent, a starch, a filler, a paper dye or pigment, micro- or nanofibrillated cellulose or other natural / bio-based or synthetic fibers.

8. The method according to claim 7, characterized in that The sizing agent is alkenyl succinic anhydride or alkyl ketene dimer.

9. A flow system for a headbox (20, 40) of a fiber web machine, comprising: An apparatus for adding at least one additional stock component to a stock flow in a flow system (10, 30), the flow system comprising a headbox feed pump (12, 32), a headbox screen (16, 36), a chemical mixer (18, 80) and a headbox feed pipe (38), characterized in that a stock flow equalizer (50) is arranged in the headbox feed pipe (38) at a distance upstream of the chemical mixer (80) arranged between the headbox screen (36) and the headbox (40) so as to equalize the concentration differences prevailing in the stock flow but not to the extent that concentration differences have begun to form.

10. The streaming system according to claim 9, characterized in that: The chemical mixer (80) is arranged upstream and / or downstream of the feed flow equalizer (50).

11. The flow system according to claim 9 or 10, characterized in that: The chemical mixer (80) is an injection mixing station including one or more injection mixers, which feeds the at least one additional feedstock component into the feedstock stream by using an injection liquid.

12. The streaming system according to claim 11, characterized in that Between the stock flow equalizer (50) and the injection mixing station, upstream of the stock flow equalizer (50), or downstream of the injection mixing station, an inlet channel (84) is connected to the headbox feed pipe (38).

13. The streaming system according to claim 11, characterized in that: The distance from the stock flow balancer (50) to the chemical mixer (80) is 0.5 to 10 times the diameter of the headbox feed pipe (38), and the distance from the stock flow balancer (50) to the headbox (40) is 5 to 15 times the diameter of the headbox feed pipe (38).

14. The streaming system according to claim 11, characterized in that: The distance from the stock flow equalizer (50) to the chemical mixer (80) is 2 to 5 times the diameter of the headbox feed pipe (38), and the distance from the stock flow equalizer (50) to the headbox (40) is 5 to 15 times the diameter of the headbox feed pipe (38).

15. The streaming system according to claim 11, characterized in that: The material flow equalizer (50) has a tubular wall (54), an inner surface (56) of the tubular wall having a circumference, and the inner surface (56) is provided with a plurality of shaped parts (58) arranged on the circumference thereof.

16. The streaming system according to claim 15, characterized in that The radial height of each forming member (58) is 0.1 to 0.5 times the diameter of the headbox feed pipe (38).

17. A headbox feed pipe for the flow system according to claim 10, the headbox feed pipe being used for connection between a headbox screen and a headbox of a fiber web manufacturing machine, the headbox feed pipe comprising a chemical mixer, characterized in that: A stock flow equalizer (50) is arranged in the headbox feed pipe (38), between the headbox screen (36) and the chemical mixer (80), upstream of the chemical mixer (80) and at a distance from the chemical mixer, so as to equalize the concentration differences prevailing in the stock flow but not to the extent that concentration differences have begun to form.

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