Method and reactor for producing PCC

Abstract

The invention discloses a method and a reactor for producing PCC. The invention relates to a method and a reactor for crystallizing calcium carbonate and forming crystals inside or on the surface of a fibrous dispersion containing solid matter in a liquid stream (F) at a concentration of 2.5-5%,-feeding carbon dioxide (CO2) (CO2) and milk of lime (LM) (Ca (OH) 2) into the liquid stream (F) in order to react them with each other,-cross-injecting carbon dioxide (CO2) and / or milk of lime (LM) into the liquid stream (F) with a mixer (3, 31, 32), -injection is carried out in the feed pipe (2) such that the residence time of the crystallization reaction before the nozzle (20) of the reactor (1) is 0.5-10 seconds, after which the liquid flow (F) is mixed with the liquid or fiber suspension in the container (4).

Description

Technical Field

[0001] The present invention relates to a method and a reactor for crystallizing calcium carbonate and forming crystals in a liquid stream. More specifically, the present invention relates to a method for continuously producing calcium carbonate or PCC along the paper / board process of a soft paper / tissue machine, said calcium carbonate or PCC being used as a filler in paper and board production.

[0002] The invention relates in particular to a process as encompassed in the preamble of claim 1. The invention also relates to a reactor as encompassed in the preamble of claim 10. Background Art

[0003] Calcium carbonate is commonly used in paper production and fillers and coating agents, for example, due to the high whiteness and economical price of the carbonate. The use of calcium carbonate can also provide significant additional properties in soft paper / toilet paper applications. Calcium carbonate can be manufactured by grinding chalk, marble or limestone, in which case it is generally referred to as GCC (ground calcium carbonate). Another method for producing calcium carbonate is a chemical method, in which, for example, the minor components of calcium hydroxide, calcium ions and carbon dioxide, are dissolved in water to produce carbonate ions, which are then reacted to precipitate the resulting calcium carbonate from the solution into crystals, the shape of which depends, for example, on the reaction conditions. The final product of this manufacturing method is called PCC, which is the abbreviation for precipitated calcium carbonate. The present invention focuses on the use of PCC, particularly its use as a paper or paperboard filler.

[0004] Traditionally, the production of PCC is carried out separately from the papermaking process. To date, PCC has either been manufactured in facilities near the paper mill, where the PCC sludge is transferred to the papermaking process by pipeline pumping, or in similar facilities, from which the PCC sludge is transported to a more distant paper mill by tank trucks. PCC produced in this way requires the use of retention aids in the papermaking process so that the PCC can adhere to the fibers, regardless of whether the fibers are chemically produced or mechanically produced cellulose fibers. The traditional methods of producing PCC briefly discussed above involve other problems in addition to the problems involving the use of retention aids mentioned above. Transporting PCC from a chemical plant by tank trucks results in transportation costs and requires the use of dispersants and biocides. The use of these additives can impair the performance of the PCC.

[0005] Building a separate PCC facility in connection with a mill is an expensive investment and requires many workers to work 24 hours a day. In addition, PCC facilities also increase water consumption. Therefore, in order to reduce the cost of paper production, many different proposals have been made recently to produce PCC directly in the paper mill, which would remove the transportation costs of PCC from the cost structure of paper. In addition, it has been noted that producing PCC in the presence of a fiber suspension results in better adhesion of the PCC crystals to the fibers, thereby reducing the need for retention aids and sometimes even eliminating them completely. A group of patent publications covering the production of PCC in connection with paper production is discussed below.

[0006] WO A1-0107365 covers a conventional PCC production method. The method is generally based on the following procedure: a suspension containing calcium ions is produced, wherein the calcium is present in the form of dissolved ions and undissolved solid matter. The suspension is then transferred to a high-pressure reactor, into which gaseous carbon dioxide is introduced and its contents are continuously mixed. In this case, the reaction of carbon dioxide with water produces carbonate ions, which further react with calcium ions to produce calcium carbonate. The process is driven by monitoring the pH value of the batch. At the beginning, i.e. before the introduction of carbon dioxide, the pH of the suspension in the reactor is higher than 12. Carbon dioxide is continued to be fed into the reactor until the pH is reduced to 6.5-7.5, after which the PCC suspension can be pumped to a storage container of the papermaking production process by a sorting pump.

[0007] The source of calcium ions in the above method can be calcium oxide or calcium hydroxide. The open document describes how to transport quicklime (CaO) from a local silo to a PCC facility by train, truck or pneumatic pipeline. The quicklime is digested into calcium hydroxide using water from the factory. Steam can be added as needed to ensure a suitable reaction temperature. The lime milk obtained from the digestion is pumped to the above reactor through a sorting pump, and large particles are removed during the sorting. In addition to the pure CO2 introduced into the process as a liquid, the source of carbon dioxide fed into the reactor can also be some suitable flue gas that has been purified using a process suitable for this application.

[0008] US-A-5,223,090 describes the precipitation of PCC into fibers in a paper mill by utilizing the hydrophilic nature of the raw pulp fiber filaments by first mixing the raw pulp with lime milk and then contacting the resulting suspension (with a water concentration of 40-95%) with a gaseous or liquid agent (carbon dioxide) under vigorous mixing in a pressurized vessel in order to precipitate the filler particles into the fibers, especially into the inner cavities of the fibers. One proposed mixer option is a pressurized paper stock grinder.

[0009] The slow mixing of carbon dioxide and milk of lime results in an uneven size distribution of PCC crystals, since throughout the mixing process the size of existing PCC crystals increases and new crystals are generated until at least one of the chemicals is exhausted. In practice, this problem has been solved by trying to make the mixing time of the chemicals fast enough. This means in practice and in some solutions, for example, that when PCC of as uniform a size as possible is required, carbon dioxide is dissolved into the liquid or suspension stream and the milk of lime is mixed into the stream only after the time required for the carbon dioxide to be almost completely dissolved. At the moment the milk of lime is mixed, the time used or required for the precipitation reaction begins; the faster and more effectively the milk of lime is mixed in the stream, the shorter this time. Faster and more effective mixing at this stage means making the concentration differences in the stream as small as possible, thereby preventing the formation of oversized PCC crystals, agglomerates and sediments. In the experiments conducted, it was observed that the appropriate mixing time to produce PCC with a regular size distribution for conventional paper production is about 1 to 3 seconds.

[0010] EP 2262948 B1 shows a method of mixing carbon dioxide and milk of lime into the process liquid of a fibrous web machine approach system. Summary of the invention

[0011] The aim of the present invention is to advance the current state of the art by proposing a solution that can be easily added to existing process equipment by implementing relatively simple modifications. One aim is to create a system that can be used even in real production lines without interrupting production.

[0012] It is also an object of the present invention to provide a functional and efficient way to establish the connection between PCC and fibers and to minimize the adverse effects caused by the precipitation of PCC into difficult locations.

[0013] The object of the present invention is also to create a method for achieving the above-mentioned objects. In addition, the object of the present invention is also to create a reactor that makes this method possible.

[0014] The objects of the invention are mainly achieved according to the independent claims 1 and 10 and are presented in more detail in the other claims. Further additional features of the invention are revealed in the dependent claims and in the following description of the embodiments of the drawings.

[0015] One embodiment of the present invention is a method for crystallizing calcium carbonate and for forming crystals in a suspension of solid matter fibers and / or on its surface in a liquid stream at a concentration of 2.5 to 5%,

[0016] - feeding carbon dioxide (CO2) and lime milk (Ca(OH)2) into the liquid stream so that they react with each other,

[0017] - injecting carbon dioxide and / or milk of lime crosswise into the liquid stream in the form of sufficiently small particles or bubbles using a mixer so that the carbon dioxide and / or milk of lime are fairly uniformly dispersed in the liquid stream regardless of the flow conditions of the liquid stream, thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC deposits and PCC precipitates, and controlling the reaction between carbon dioxide and milk of lime,

[0018] Injection is carried out in the feed pipe so that the residence time of the crystallization reaction before the nozzle is 0.5 to 10 seconds, after which the liquid stream mixes with the liquid or fiber suspension in the container.

[0019] One of the embodiments of the method is that, in the method, the injection is carried out in the feed pipe before the container, so that the residence time of the crystallization reaction before the nozzle at the end of the feed pipe is 0.5 to 10 seconds, at which the pressure of the liquid flow is reduced, after which the liquid flow is mixed into the fiber suspension already in the container with the help of the nozzle.

[0020] Similarly, one embodiment of the present invention is a reactor for producing calcium carbonate and for forming crystals in a suspension of solid matter fibers and / or on its surface in a liquid stream at a concentration of 2.5 to 5%, the reactor comprising:

[0021] - a feed pipe for a liquid stream into which carbon dioxide and milk of lime can be fed in order to react them with one another,

[0022] - a mixer for injecting carbon dioxide and / or milk of lime and cross-mixing them into the liquid stream in the form of sufficiently small particles or bubbles so that the carbon dioxide and / or milk of lime are fairly uniformly dispersed in the liquid stream regardless of the flow conditions of the liquid stream, thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC deposits and PCC precipitates, and controlling the reaction between carbon dioxide and milk of lime,

[0023] The mixer is located in the feed pipe so that the residence time of the crystallization reaction before the nozzle can be set to 0.5 to 10 seconds.

[0024] In one embodiment of the reactor, the nozzle is arranged at the end of the feed pipe away from the mixer, and the nozzle comprises at least one flow restrictor to reduce the pressure of the liquid flow. Injection can be carried out in the feed pipe so that the residence time of the crystallization reaction before the nozzle can be set to 0.5 to 10 seconds, after which the nozzle can be used to mix the liquid flow with the fiber dispersion in the container.

[0025] Using the above method and reactor, a fiber dispersion containing PCC is already produced in the production process at an earlier stage in the online process than, for example, presented in the publication EP2262948B1, at such a location in the production facility, making the modification of the reactor easier and simpler than before, and without the need to change the shape or characteristics of particularly critical process parts. In one embodiment of the invention, the liquid streams are mixed in a mixing container or a pulping tank (machinechest) or other container. In addition, potential harmful PCC deposits will not form and their control is easier than before. The possibility of deposits forming on the container walls is not great, and they will not affect the process itself as quickly as deposits formed near the headbox (headbox) or similar locations. When scaling up the reactor, the planned flow rate in the pipeline and the resulting residence time must be taken into account. Therefore, in practice, when the flow rate is a certain parameter defined by the rest of the process, the residence time of the reaction determines the required feed pipe length.

[0026] Advantageously, the carbon dioxide and / or milk of lime are injected using a TrumpJet mixer, which can be used to mix the carbon dioxide and milk of lime with the liquid stream in the desired manner.

[0027] In one embodiment of the invention, the liquid stream is mixed in a mixing container or machine container or other container so that the liquid stream reaches the suction flow area (suction flow) of a container mixer operating in the above-mentioned container, wherein the shear force / mixing effect caused by the container mixer acts on the liquid stream, which further mixes the liquid stream with the fiber dispersion in the above-mentioned container. Therefore, in practice, the reactor can be installed in connection with the container so that the liquid stream discharged from the reactor can be mixed in the mixing container or machine container or other container, whereby the liquid stream can be guided to the suction flow area (suction area) of the container mixer of the above-mentioned container, so that the shear force caused by the container mixer affects the existing liquid stream, which further mixes the liquid stream with the fiber dispersion in the above-mentioned container. Advantageously, the liquid stream is divided into a dispersed branch flow or a plurality of smaller branch flows in the nozzle, and the branch flows are guided so that the residence time of the branch flows in the container is short before they reach the direct action range of the container mixer rotor. This can be achieved, for example, in such a way that the nozzle includes one or more flow ports to disperse or divide the liquid stream into smaller branch flows, which can be guided so that the branch flows reach the immediate vicinity of the container mixer rotor. A short residence time in the container means that the distance is less than 1 / 3, 1 / 4 or 1 / 6 of the circumference of an imaginary flow circle or ellipse that can be drawn on the liquid surface in the container in parallel planes defined by the bottom and two opposing walls of the container and the axis of rotation of the container mixer rotor. In this case, it can be considered that the flow or partial flow of the nozzle can be directed to the vicinity of the container mixer rotor in the container.

[0028] In the process of one embodiment, the liquid stream is fed below the surface of the fiber dispersion in the container. This can be achieved by installing the reactor in such a way that the nozzle is arranged in a position in the container so that in normal operation the liquid stream can be discharged below the surface of the fiber dispersion in the container. The pressure in the reactor is generally 100 to 400 kPa, and when discharging in the container, the pressure is the standard air pressure (atm) plus the hydrostatic pressure generated by the surface liquid level. If the discharge is carried out above the surface, the miscibility of the liquid stream in the container with the existing fiber dispersion will be negligible, and in addition, a large amount of air may be present in the fiber dispersion, which may lead to undesirable foaming of the fiber dispersion. The container can also be closed and pressurized, but in this case, the liquid stream is still similarly fed below the surface.

[0029] In one embodiment, the injection in the reactor is carried out so that the average particle size of the lime milk is less than 3 micrometers (μm), advantageously less than 1.5 micrometers, more advantageously less than 0.5 micrometers, the bubble size of the carbon dioxide is less than 100 micrometers, more advantageously the carbon dioxide is completely dissolved in the injection liquid before being fed into the liquid stream. Advantageously, the flow rate used in the injection is at least three times the flow rate of the liquid stream, at most fifteen times, advantageously 5 to 10 times. This effectively mixes the injected liquid or gas.

[0030] In one embodiment, the feed pipe of the reactor is equipped with an anti-precipitation protection device, which can prevent calcium carbonate from crystallizing or precipitating into the wall of the feed pipe. Most advantageously, this protection device is implemented electrically, such as has been proposed in the patent EP2544808B1 of the applicant. In this case, most advantageously, the last section of the reactor between the mixer and the nozzle is straight, but before that it can be an elbow, most preferably 90 degrees, wherein an electric protection rod can be introduced into the middle of the reactor feed pipe, so that the feed pipe and the protection rod produce a coaxial structure that is conducive to flow. In some cases, a coating can also be used to prevent precipitation.

[0031] Advantages of the present invention are, for example, its effectiveness and simplicity as well as economical cost compared to other techniques. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention and its operation are explained below with reference to the accompanying drawings, in which

[0033] Figure 1 One embodiment of the reactor of the present invention is presented in diagrammatic form,

[0034] Figure 2 An embodiment of a reactor installed in connection with a container according to the present invention is presented in a graphical form.

[0035] Figure 3 One embodiment of a reactor according to the present invention mounted in connection with a vessel is presented in diagrammatic form. DETAILED DESCRIPTION

[0036] Figure 1 An embodiment of a reactor 1 according to the invention is presented in diagrammatic form. This is a reactor 1 for crystallizing calcium carbonate and for forming crystals in a liquid stream F in a concentration of 2.5 to 5% in a fiber dispersion containing solid matter or on its surface, the reactor 1 comprising:

[0037] a feed pipe 2 for a liquid stream F into which carbon dioxide CO2 and milk of lime LM can be fed in order to react with each other,

[0038] -Mixer 3, in Figure 1In an embodiment of the present invention, a separate mixer 31 for injecting carbon dioxide CO2 and / or a mixer 32 for injecting milk of lime LM is included and cross-mixed into the liquid flow F in the form of sufficiently small particles or bubbles, so that the carbon dioxide CO2 and / or milk of lime LM are fairly uniformly dispersed in the liquid flow F regardless of the flow conditions of the liquid flow F, thereby producing homogeneous calcium carbonate crystals of a suitable size distribution, preventing the formation of oversized PCC crystals, PCC deposits and PCC precipitates, and controlling the reaction between the carbon dioxide CO2 and the milk of lime LM,

[0039] - The mixers 3, 31, 32 are located in the feed pipe 2 so that the residence time of the crystallization reaction before the nozzle 20 can be set to 0.5 to 10 seconds. In practice, the required residence time defines the length L of the feed pipe 2 between the mixers 3, 31, 32 and the nozzle 20. The velocity of the liquid flow F in the feed pipe is determined by the required volume flow and the diameter of the feed pipe, where the length L=flow velocity×residence time. Of course, it should be taken into account that part of the reaction, i.e. part of the crystallization, can also take place in the container, so that it is not necessary to use a very long length L of the feed pipe 2. The liquid flow F can be the entire feed flow or a part of the feed flow of the fiber dispersion used in the production of the fiber web.

[0040] exist Figure 1 An embodiment is also presented in which the feed pipe 2 is equipped with an anti-precipitation protection device 21, which can prevent calcium carbonate from crystallizing or precipitating into the wall of the feed pipe 2. Most advantageously, the last section of the reactor between the mixers 3, 31, 32 and the nozzle 20 is straight, but before that it can be a bend, most preferably 90 degrees, in which an electric protection rod 21 can be introduced into the middle of the feed pipe 2 of the reactor 1, so that the feed pipe 2 and the protection rod 21 form a coaxial structure that is conducive to flow.

[0041] exist Figure 2 In the embodiment of the present invention, the reactor 1 has been installed in its application, connected to the container 4. The reactor 1 implements a method for crystallizing calcium carbonate and for forming crystals in a solid matter fiber suspension and / or on its surface in a liquid flow F at a concentration of 2.5-5%,

[0042] - feeding carbon dioxide CO2 (CO2) and milk of lime LM (Ca(OH)2) into the liquid stream F so that they react with each other,

[0043] - cross-injection of carbon dioxide CO2 and / or milk of lime LM into the liquid flow F in the form of sufficiently small particles or bubbles by means of mixers 3, 31, 32, so that the carbon dioxide CO2 and / or milk of lime LM are fairly uniformly dispersed in the liquid flow F regardless of the flow conditions of the liquid flow F, thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC deposits and PCC precipitates, and controlling the reaction between carbon dioxide CO2 and milk of lime LM,

[0044] - injection is carried out in the feed pipe 2 so that the residence time of the crystallization reaction before the nozzle 20 of the reactor 1 is 0.5 to 10 seconds, after which the liquid stream F is mixed with the liquid or fiber suspension in the container 4. Figure 2 In the embodiment, the liquid flow F is divided into the fractions F' in the nozzle 20. Most advantageously, the nozzle 20 is arranged at the end of the feed pipe 2, and the nozzle 20 comprises at least one flow restrictor to reduce the pressure of the liquid flow F. The pressure loss in the nozzle 20 / flow restrictor can be, for example, about 200-300 kPa.

[0045] Figure 2 A container 4 is shown, the interior of which shows the liquid volume in the space bounded by the container bottom 40, the container wall 41 and the container surface (liquid surface in the container) 4s. The reactor 1 is mounted with the container 4 in such a way as to ensure mixing and prevent foaming, i.e. the nozzle 20 is arranged in a position in the container 4 so that in normal use the liquid flow F can be discharged below the surface 4s of the fiber suspension in the container 4 (opposite arrows, arrow 4s and another arrow below the surface indicate the liquid level above the nozzle 20). If the liquid level 4s in the container 4 varies significantly under different driving conditions, the reactor can be equipped with an adjustable feed pipe 2, which can ensure that the position of the nozzle 20 is below the surface 4s. Furthermore, the installation of the reactor 1 and the position of the nozzle 20 have been selected so that the liquid flow F can be mixed in the container 4, which can be a mixing container 4 or a machine container 4 or other container 4, so that the liquid flow F can be directed to the rotor 420 flow field / suction zone (in practice, behind the rotor 420) of the container mixer 42 of the above-mentioned container 4, so that when the container mixer 42 is used, the shear force / mixing effect generated by the container mixer 42 is directed to the liquid flow F, thereby further mixing the liquid flow F with the fiber suspension in the above-mentioned container 4. Figure 1 (and Figure 2 ) shows the hypothetical flow conditions (flow rate) of the liquid in the container inside the container 4, presented in different dark tones and gradient curves.

[0046] also, Figure 2It is shown how a liquid flow F introduced vertically from top to bottom is divided in the nozzle 20 into a dispersed sub-flow or a plurality of smaller sub-flows F', which are directed so that the sub-flows have a short residence time in the container 4 before reaching the direct action range of the container mixer rotor 420. Therefore, in practice, the nozzle 20 includes one or more flow ports to disperse or divide the liquid flow F into smaller sub-flows F', which can be directed so that the sub-flows F' arrive in the immediate vicinity of the container mixer rotor 420. This short residence time or close proximity in the container 4 can mean that the liquid flow F or sub-flow F' of the nozzle 20 can be directed to the vicinity of the rotor 420 of the container mixer 42, which means that the distance is less than the imaginary flow circle or ellipse 4v (in Figure 2 The imaginary flow circle or ellipse can be drawn on the liquid surface 4s in the container in a parallel plane defined by the bottom and two opposing walls 41 of the container 40 and the axis of rotation 421 of the container mixer rotor. The purpose of the imaginary flow circle 4v is to show how large a rotating vortex can be generated in the container 4 by the liquid in the container 4. The entire flow circle 4v has a definable circumference, of which 1 / 3, 1 / 4 or 1 / 6 can be considered to be close or at a short residence time. Therefore, the nozzle 20 has been arranged at such a position in the container 4 that, during normal use, the liquid flow F can be discharged below the surface 4s of the fiber suspension in the container 4, and the liquid flow F or the partial flow F' of the nozzle 20 can be directed to a position inside the container close to the rotor 420 of the container mixer 42, so that the distance between the nozzle 20 and the rotor 420 is less than 1 / 3, 1 / 4 or 1 / 6 of the circumference of an imaginary flow circle or ellipse 4v, which can be drawn on the liquid surface 4s in the container in parallel planes defined by the container bottom 40 and the two opposite walls 41 and the rotation axis 421 of the container agitator rotor.

[0047] Figure 3 Shows the corresponding Figure 1 and 2 Reactor 1, but in Figure 3 In the embodiment of the present invention, the feed pipe 2 is introduced into the container 4 in the horizontal direction. The reactor 1 has Figure 2 The reactor 1 is configured to crystallize calcium carbonate and form crystals in a fiber dispersion containing solid matter in a concentration of 2.5 to 5% in a liquid flow F, or on its surface, and the reactor 1 comprises:

[0048] a feed pipe 2 for a liquid stream F into which carbon dioxide CO2 and milk of lime LM can be fed in order to react with each other,

[0049] - mixers 3, 31, 32 for injecting carbon dioxide CO2 and / or milk of lime LM and cross-mixing them in the form of sufficiently small particles or bubbles into the liquid flow F so that the carbon dioxide CO2 and / or milk of lime LM are fairly uniformly dispersed in the liquid flow F regardless of the flow conditions of the liquid flow F, thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC sediments and PCC precipitates, and controlling the reaction between carbon dioxide CO2 and milk of lime LM,

[0050] - injection can be carried out in the feed pipe 2 before the container 4, so that the residence time of the crystallization reaction before the nozzle 20 at the end of the feed pipe 2 can be set to 0.5 to 10 seconds; the nozzle 20 includes at least one flow regulator, which reduces the pressure of the liquid flow F, and after which the liquid flow F can be mixed with the fiber suspension in the container 4 with the help of the nozzle 20.

[0051] Also in Figure 3 In the embodiment of the present invention, the nozzle 20 is arranged in such a position in the container 4 that, in normal use, the liquid flow F can be discharged below the surface 4p of the fiber dispersion in the container 4. In addition, Figure 3 The feed pipe 2 is shown to be equipped with an anti-precipitation protection device 21, which can prevent calcium carbonate from crystallizing or precipitating into the wall of the feed pipe 2. A similar anti-precipitation protection device 21 can also be installed without any problems in Figure 2 In the implementation scheme of Figure 2 and Figure 3 As shown, the feed pipe 2 comprises a curved pipe, which makes it easy to introduce an anti-precipitation protection device 21 in the middle of the feed pipe of the reactor 1, preferably in a coaxial arrangement.

[0052] It should be noted that the above only covers a few of the most advantageous embodiments of the invention. It is therefore clear that the invention is not limited to the preceding embodiments, but can be applied in a variety of ways as defined in the appended claims. If necessary and with the corresponding technical preparation, it is also possible to combine the features presented in conjunction with the various embodiments with other embodiments and / or combine the various features into different arrangements according to the basic idea of ​​the invention.

[0053] List of reference symbols used:

[0054] 1 Reactor

[0055] 2 Feed pipe

[0056] 20 Nozzles

[0057] 21 Anti-sedimentation protection device

[0058] 3. Mixer

[0059] 31 Mixer (for carbon dioxide)

[0060] 32 mixer (for lime milk)

[0061] 4 Containers

[0062] 40 container bottom

[0063] 41 container wall

[0064] Surface of 4s container

[0065] 4v flow circle or ellipse

[0066] 42 container mixer

[0067] 420 container mixer rotor

[0068] 421 Rotating axis of the container mixer rotor

[0069] F Liquid Flow

[0070] F' split flow

[0071] CO2 Carbon dioxide (CO2)

[0072] LM lime milk (Ca(OH)2)

[0073] L Feed pipe length

Claims

1. A method for crystallizing calcium carbonate and for forming crystals in a solid matter fiber suspension and / or on its surface in a liquid stream (F) at a concentration of 2.5 to 5%, wherein - feeding carbon dioxide (CO2) and milk of lime (LM) (Ca(OH)2) into the liquid stream (F) so that they react with each other, - cross-injecting carbon dioxide (CO2) and / or milk of lime (LM) into the liquid flow (F) in the form of sufficiently small particles or bubbles using mixers (3, 31, 32) so that the carbon dioxide (CO2) and / or milk of lime (LM) are fairly uniformly dispersed in the liquid flow (F) regardless of the flow conditions of the liquid flow (F), thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC sediments and PCC precipitates, and controlling the reaction between carbon dioxide (CO2) and milk of lime (LM), The method is characterized in that Injection is carried out in the feed pipe (2) so that the residence time of the crystallization reaction before the nozzle (20) of the reactor (1) is 0.5 to 10 seconds, after which the liquid stream (F) is mixed with the liquid or fiber suspension in the container (4).

2. The method according to claim 1, characterized in that Injection is carried out in the feed pipe (2) before the container (4) so ​​that the residence time of the crystallization reaction before the nozzle (20) at the end of the feed pipe (2) is 0.5 to 10 seconds, at which the pressure of the liquid flow (F) is reduced and after which the liquid flow (F) is mixed into the fiber suspension already in the container (4) by means of the nozzle (20).

3. The method according to claim 1 or 2, characterized in that: The liquid flow (F) is mixed in a mixing container (4) or a machine container (4) or another container (4) so ​​that the liquid flow (F) reaches the suction zone of a container mixer (42) operating in the above-mentioned container (4), wherein the shear force / mixing effect caused by the container mixer (42) acts on the liquid flow (F), which further mixes the liquid flow (F) with the fiber dispersion in the above-mentioned container (4).

4. The method according to claim 3, characterized in that The liquid flow (F) is divided into a dispersed sub-flow or a plurality of smaller sub-flows (F') in the nozzle (20), and the sub-flow (F') is guided so that the liquid flow (F) or the sub-flow (F') has a short residence time in the container (4) before reaching the direct action range of the container mixer rotor (420).

5. The method according to claim 4, characterized in that A short residence time in the container (4) means a distance less than 1 / 3, 1 / 4 or 1 / 6 of the circumference of an imaginary flow circle or ellipse (4v) which can be drawn on the liquid surface (4s) in the container in a parallel plane defined by the bottom and two opposing walls (41) of the container (40) and the axis of rotation (421) of the container mixer rotor.

6. The method according to any one of the preceding claims, characterized in that The liquid flow (F) is fed below the surface (4s) of the fiber dispersion in the container (4).

7. The method according to any one of the preceding claims, characterized in that The average particle size of the lime milk (LM) is less than 3 microns (μm), advantageously less than 1.5 microns, more advantageously less than 0.5 microns, the bubble size of the carbon dioxide (CO2) is less than 100 microns, more advantageously the carbon dioxide (CO2) has been completely dissolved in the injection liquid before being supplied to the liquid flow (F).

8. The method according to any one of the preceding claims, characterized in that The feed rate used in the injection is at least three times the flow rate of the liquid stream (F) and at most fifteen times, advantageously 5 to 10 times.

9. The method according to any one of the preceding claims, characterized in that The liquid flow (F) is the entire feed flow or a part of the feed flow of the fiber dispersion used in the production of the fiber web.

10. A reactor (1) for crystallizing calcium carbonate and forming crystals in a liquid stream (F) in a concentration of 2.5 to 5% in a fiber dispersion containing solid matter or on its surface, the reactor (1) comprising: a feed pipe (2) for a liquid stream (F) into which carbon dioxide (CO2) and milk of lime (LM) can be fed in order to react with each other, - a mixer (3, 31, 32) for injecting carbon dioxide (CO2) and / or milk of lime (LM) and cross-mixing them in the form of sufficiently small particles or bubbles into the liquid flow (F) so that the carbon dioxide (CO2) and / or milk of lime (LM) are fairly uniformly dispersed in the liquid flow (F) regardless of the flow conditions of the liquid flow (F), thereby producing homogeneous calcium carbonate crystals with a suitable size distribution, preventing the formation of oversized PCC crystals, PCC sediments and PCC precipitates, and controlling the reaction between carbon dioxide (CO2) and milk of lime (LM), characterized in that The mixer (3, 31, 32) is located in the feed pipe (2), so that the residence time of the crystallization reaction before the nozzle (20) can be set to 0.5 to 10 seconds.

11. The reactor (1) according to claim 10, characterized in that The nozzle (20) is arranged at the end of the feed pipe (2) at a distance (L) from the mixer (3, 31, 32), and the nozzle (20) comprises at least one flow restrictor in order to reduce the pressure of the liquid flow (F).

12. The reactor (1) according to claim 10 or 11, characterized in that The reactor is adapted to be installed in connection with a container (4), such as a mixing container (4) or a machine container (4) or another container (4), wherein the liquid flow (F) can be mixed into the fiber dispersion in the container by means of a nozzle (20).

13. The reactor (1) according to claim 12, characterized in that The liquid flow (F) can be guided to the flow field of the rotor (420) of the container mixer (42) of the above-mentioned container (4), so that the shear force / mixing effect caused by the container mixer (42) during use acts on the liquid flow (F), which further mixes the liquid flow (F) with the fiber dispersion liquid in the above-mentioned container (4).

14. The reactor (1) according to claim 10 or 11, characterized in that The nozzle (20) includes one or more flow ports to disperse or divide the liquid flow (F) into smaller fractional flows (F') which can be directed so that the fractional flows (F') arrive in close proximity to the container mixer rotor (420).

15. Reactor (1) according to any one of the preceding claims 10 to 14, characterized in that The feed pipe (2) is equipped with an anti-precipitation protection device (21), which can prevent calcium carbonate from crystallizing or precipitating into the wall of the feed pipe (2).

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