Method for dispersing and grinding particles in a fluid

Abstract

The present invention relates to a method and system for dispersing particles in a fluid. The method includes agitating a fluid 160 containing particles 164 in a stirred vessel 110 using a stirring means 120. During agitation, the fluid is circulated by continuously withdrawing a predetermined amount of fluid from a collection location 131. Furthermore, the particles are crushed, and the particle size of the recovered fluid is reduced each time the fluid passes through the crushing means 140. The recovered fluid that has passed through the crushing means is continuously reintroduced into the stirred vessel at a reintroduction location 151. The reintroduced fluid mixes with the fluid in the stirred vessel in a mixing region 161 defined by the stirring means, and the collection location is determined so that the recovered fluid contains particles having an average particle size different from the average particle size of the particles in the mixing region.

Description

Technical Field

[0001] The present invention relates to a method for dispersing and grinding particles by recirculation in a fluid and an optimized system therefor.

Background Art

[0002] It can be very difficult to uniformly disperse and grind particles in a fluid. In many applications, such as during the production of paints using particles of a liquid binder and a coloring pigment, it is necessary to reduce the size of the particles and aggregates dispersed in the fluid by grinding. One solution for dispersing particles in a fluid while further reducing the particle size of the particles in the fluid (e.g., coloring pigments in a binder) is to provide recirculation through a bead mill. In this case, the fluid containing the particles is continuously stirred in a stirring vessel such as a container, mixing tank, stirring tank, homogenizer, etc., and at the same time is recirculated through the mill, which reduces the particle size of each pass through the mill until the desired particle size and the properties of the target mixture, e.g., a stable product over time with good wetting of the small particles by the binder, are obtained. In the current design of such recirculation systems, the average diameter of the particles in the fluid only very slowly decreases each time the fluid passes through the mill. Therefore, many cycles are required to reach the desired average particle size, where one cycle refers to one stirring vessel volume of the liquid that has passed through the mill.

[0003] Related technologies include, for example, US2007 / 025178A1, US1781435A, EP2657263A1, US2004 / 134930A1.

[0004] Therefore, it is advantageous to provide a method and system that enable reduction of the number of cycles of the fluid passing through the mill so that the time and energy for producing a product containing particles dispersed in a fluid can be reduced.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] US2007 / 025178A1 [Patent Document 2] US1781435A [Patent Document 3] EP2657263A1 [Patent Document 4] US2004 / 134930A1 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a method and system for dispersing particles in a fluid that enables a reduction in the production time and energy of products manufactured in a recirculation process. [Means for solving the problem]

[0007] A first aspect of the present invention provides a method for dispersing and grinding particles in a fluid, the method comprising: a) introducing a fluid containing particles into a stirring vessel, wherein the particles have an initial average particle diameter; and b) stirring the fluid in the stirring vessel using stirring means positioned at a predetermined stirring position in the stirring vessel, wherein during stirring, i) recirculating the fluid containing particles by continuously recovering a predetermined amount of the fluid containing particles from a predetermined recovery position in the stirring vessel using recovery means; ii) grinding the particles in the continuously recovered fluid using grinding means, wherein each time the particles pass through the grinding means, if the particle size exceeds a predetermined particle diameter, the particle diameter in the recovered fluid is reduced; and iii) continuously reintroducing the recovered fluid that has passed through the grinding means into the stirring vessel at a predetermined reintroduction position using reintroduction means, wherein the reintroduced fluid containing the reduced-size particles is mixed with the fluid in the stirring vessel in a mixing region defined by the stirring means, the recovery position being determined by the average particle diameter of the particles in the fluid in the mixing region. Larger thanThe process includes determining to include particles having an average particle size.

[0008] The recovery position for recovering the fluid from the stirring vessel after it has passed through the pulverizer is determined by the average particle size of the particles in the fluid within the mixing region defined by the stirring means. Larger than Since it is determined that the fluid contains particles with an average particle size, it can be assumed that fluid containing particles that have not passed through the grinder a sufficient number of times, i.e., particles that are too large, is sent to the grinder, while the amount of particles in the recovered fluid that have already been ground in the previous pass is reduced. Therefore, the particle size can be reduced more effectively, i.e., in each pass, more larger particles are sent to the grinder than already smaller particles. Thus, the number of passes required to reach a given average particle size can be reduced, which leads to a reduction in manufacturing time and energy for producing a given final product.

[0009] In particular, the inventors have found that in a stirring vessel that uses a stirring means such as an impeller to stir the fluid, mixing between the introduced fluid and the fluid inside the vessel does not occur throughout the entire vessel. Thanks to the vortex phenomenon, that is, the phenomenon in which at least one vortex is formed in the fluid, mixing mainly occurs around the stirring means, for example, in the region around the impeller.

[0010] From there, the mixed fluid is slowly sent to the rest of the stirring vessel. Therefore, if the fluid being mixed in the stirring vessel contains particles of different sizes, for example, if the fluid in the vessel contains particles of a first particle size and the fluid introduced into the stirring vessel contains particles of a second particle size, and the first particle size is larger than the second particle size, then the particles of different sizes are also mixed only in the mixing region. Thus, the average particle size is first reduced in the mixing region, while in all other regions of the vessel, the average particle size is reduced very slowly as the mixed fluid is sent to the rest of the stirring vessel. The inventors have recognized that this mixing phenomenon, involving different internal flows, can be utilized as an advantage of a more effective method and system for recirculating fluids containing particles that need to be reduced in size by passing the fluid through a grinder during the recirculation process. By recovering the fluid containing particles from the region of the vessel outside the mixing region, it is ensured that the amount of particles in the recovered fluid that must be ground at least once is maximized. Thus, particle grinding becomes more effective, and the time required to produce a final product containing a given average particle size is reduced.

[0011] In the method according to the present invention, first, a fluid containing a basic product, i.e., particles having an initial average particle size, is introduced into a stirring vessel. The basic product is, for example, a resin containing a color pigment, or an aqueous solution containing an ink pigment. The stirring vessel can be any container suitable for use in the stirring process; for example, the stirring vessel may be cylindrical.

[0012] After the fluid is introduced into the container, the fluid containing particles is stirred using stirring means positioned at a predetermined stirring position within the stirring vessel. The stirring means can be any means suitable for stirring the fluid in the container. The stirring means may include, for example, an impeller that is electrically or hydraulically driven to rotate in the fluid (or a stirring rod that is driven by a magnetic field to rotate within the stirring vessel). The predetermined stirring position is the height at which the stirring means is positioned, and may be, for example, at or near the bottom of the container, in the middle of the container, or at the top of the container. The stirring means defines a mixing region in which mixing between the fluid in the stirring vessel and the reintroduced fluid occurs, for example, through turbulent or quasi-turbulent mixing. This region can be determined for any structure of the stirring vessel and stirring means, for example, by experiment or numerical simulation.

[0013] During stirring, the fluid is recirculated; that is, a predetermined amount of fluid is taken out of the container, sent through a pulverizer, and then reintroduced into the container. Specifically, a predetermined amount of fluid is continuously recovered by a recovery means from a predetermined recovery position within the stirring container. In particular, the recovery position is determined such that the recovered fluid contains particles having an average particle size larger than the average particle size of the particles in the fluid within the mixing region. The recovery means refers to, for example, a pipe or duct through which the recovered fluid can flow. The predetermined amount of fluid continuously recovered from the container can be determined by the size of the recovery means, for example, the diameter of the pipe or duct, and the flow velocity of the fluid through the recovery means. The flow of the recovered fluid through the recovery means can be driven, for example, by a pump connected to the recovery means.

[0014] In another step of the recirculation process, the continuously recovered fluid passes through a grinding means for grinding particles in the recovered fluid. The grinding means is adapted to reduce the particle size with each pass through the grinding means if the particles are larger than a predetermined particle size, i.e., to reduce the particle size until it reaches a predetermined particle size that allows the particles to pass through the grinder without substantially changing. This predetermined particle size may be determined by the structure of the grinding means. Furthermore, the grinding means can refer to any means suitable for reducing the particle size in the fluid.

[0015] After the particles have been pulverized, the recovered fluid containing the particles with reduced particle size is continuously reintroduced into the stirring vessel at a predetermined reintroduction location by a reintroduction means. The reintroduction means may also include, for example, pipes or ducts through which the fluid flows into the stirring vessel. Preferably, a predetermined amount of fluid recovered from the stirring vessel at any given time is substantially the same as a predetermined amount of fluid reintroduced into the stirring vessel at any given time. Furthermore, it is preferable that the recovery means and the reintroduction means are directly connected to the pulverizing means so that the fluid flows continuously through the recovery means to the pulverizing means and from the pulverizing means through the reintroduction means to the stirring vessel. The reintroduction location can be at a different location within the stirring vessel; for example, the reintroduction location can be at the top of the vessel. Furthermore, the reintroduction means may be connected to the stirring means so that the fluid is reintroduced into the vessel at or near the location of the stirring means. Preferably, the fluid is reintroduced at or near the surface of the fluid in the stirring vessel, and more preferably, on the surface of the fluid near or opposite the inner wall of the stirring vessel. Generally, it is preferable to select a reintroduction location such that the reintroduced fluid cannot flow to the recovery location without first mixing with the fluid in the container, that is, it cannot flow to the recovery location without passing through the mixing region.

[0016] Preferably, recirculation and mixing are stopped when the particles, on average, reach a predetermined final size corresponding to the particle diameter desired for the final product. The predetermined final size can be considered a first threshold for controlling the recirculation and mixing process and can correspond to a predetermined size defined by the grinding means, for example, a size attainable by the grinding means, or a size larger than the size defined by the grinding means, for example, a size larger than the size attainable by the grinding means. Preferably, when the particles in the product have the final size on average, the final product has desired properties such as desired color, viscosity, and rheology.

[0017] In one embodiment, the mixing region is determined as the region of the internal volume of the stirring vessel where the rate of change of the average particle size of the particles in the fluid is highest compared to the rate of change of the particles in the fluid in other regions of the internal volume of the vessel. Since the particles that have most recently passed through the grinder, and therefore have become smaller in size, are first mixed in the mixing region of the stirring vessel, i.e., the region where the fluid in the stirring vessel and the reintroduced fluid are mixed, with particles that have not yet passed through the grinder or have not passed through the grinder a sufficient number of times, the average particle size changes significantly faster in this region than in any other part of the stirring vessel. Preferably, the average particle size decreases much faster in the mixing region than in other parts of the stirring vessel. Thus, the mixing region can be easily determined by measuring the rate of change of the average particle size in the stirring vessel, where the mixing region is the region showing the highest rate of change of the average particle size. Alternatively, the expected average particle size and the mixing region can also be determined in advance by computer simulation or by experimentation using glass apparatus with similar dimensions, shapes, and conditions to those of the later industrial equipment.

[0018] In one embodiment, the method includes determining the recovery location by defining a recovery region as a region within the internal volume of a stirring vessel, where the recovery region is determined to contain the highest average particle size in the stirring vessel compared to other regions of the stirring vessel, and the recovery location is located within the determined recovery region. This embodiment corresponds to determining the recovery region as the region with the highest proportion of particles that have not yet passed through the grinder or have not passed through the grinder a sufficient number of times compared to all other regions of the fluid in the stirring vessel.

[0019] The recovery region refers to a three-dimensional region within the stirring vessel having any shape and any volume much smaller than the volume of the stirring vessel. Preferably, the volume of the recovery region is less than 10% of the volume of the stirring vessel. Furthermore, it is preferable that any shape of the recovery region has a height much smaller than the height of the stirring vessel; for example, the height of the recovery region can be less than 10% of the height of the stirring vessel. The recovery region can be determined particularly accurately if the average particle diameter within the recovery region can be determined with sufficient precision, i.e., if a statistically relevant amount of particles is always found within the recovery region, for example, if at least 10% of the particles are always found within the recovery region. In other embodiments, the recovery region can be determined using theoretical considerations regarding the average particle diameter, independently of the actual amount of particles within the recovery region.

[0020] The recovery region can be determined, for example, during computational simulations, or experimentally by placing candidate regions with selected volumes and shapes at multiple locations within the volume of a stirring vessel simulating a stirring vessel to be used in a later industrial application. The candidate regions can be arranged such that the entire volume of the stirring vessel is part of a candidate region at least once. This can be achieved by subdividing the volume of the stirring vessel so that there is no overlap of candidate regions, or by arbitrarily placing candidate regions within the volume of the stirring vessel so that overlap occurs. The average particle size is then determined for each of these candidate regions during the recirculation process and can be compared with the average particle size of all other candidate regions. The candidate region with substantially the highest average particle size throughout the entire recirculation process compared to the other candidate regions is selected as the recovery region for the industrial application. The recovery location can be anywhere within this recovery region, for example, in the center of the recovery region. Alternatively, the recovery region can be determined in a computer simulation or experiment by dividing the simulated stirring vessel into several smaller volumes of the same size, each volume being much smaller than the volume of the stirring vessel and only large enough to allow for proper statistics of the average particle size in the experiment or simulation, i.e., large enough to contain, on average, at least 10% of the particles over the simulated recirculation process. The average particle size over the time of the recirculation process can then be calculated for each volume. The recovery region can then be defined as the region in which the small volume exhibits the highest average particle size among all volumes over the time of the recirculation process.

[0021] The determination of the recovery area can be carried out using experiments, numerical simulations, or theoretical calculations of the reintroduction process. When using experiments, the recovery area can be determined, for example, by using a small test facility having the same fluid flow as the subsequent industrial application and by using a suction pipe as a recovery means with adjustable position. Then, the average particle size can be determined for different regions or volumes from the fluid extracted by the suction pipe at different positions during the experiment, i.e., during the processes of recirculation and grinding.

[0022] In a preferred embodiment, the mixing area and the recovery area do not overlap. Further, in one embodiment, the mixing area can also be determined according to the above principles.

[0023] In one embodiment, the formation of the mixing area is determined based on the stirring position of the stirring means. Since the stirring means stirs the fluid in the stirring container, a turbulent or quasi-turbulent flow is introduced into the flow of the fluid in the container in the area around the stirring means, particularly in the area extending outward from the stirring means to the wall of the container. Therefore, the mixing of the fluid in the container and the reintroduced fluid is mainly carried out at the position of the stirring means. Thus, the formation and position of the mixing area can be determined based on the stirring position of the stirring means.

[0024] In one embodiment, the reintroduction position is provided above the stirring position. Preferably, the reintroduction position is provided in the upper half of the container, preferably on or above the surface of the fluid in the stirring container. Preferably, the reintroduction position is provided above the surface of the fluid in the stirring container such that the fluid is reintroduced in the direction of the inner wall of the stirring container. This configuration can reduce the risk of electrostatic charge accumulation.

[0025] In one embodiment, the stirring position is located in the upper half of the stirring vessel, and the recovery position is located in the lower half of the stirring vessel. Experiments and simulations have shown that when the stirring position is in the upper half of the stirring vessel, mixing of the reintroduced fluid with the fluid in the vessel occurs mainly in the upper half. Therefore, particles that have not passed through the grinder, or have not passed through as repeatedly as others, are mainly found in the lower half of the stirring vessel. Thus, the average particle size in the lower half of the stirring vessel remains higher than that in the upper half of the stirring vessel during the recirculation process. Therefore, in this configuration, it is advantageous to have the recovery position in the lower half of the stirring vessel. Preferably, this embodiment is used in applications involving high-viscosity fluids that may cause difficulties when pumping. In such cases, the recovery position at the bottom can facilitate the pumping of the fluid.

[0026] Alternatively, in one embodiment, the stirring position is located in the lower half of the stirring vessel, and the recovery position is located in the upper half of the stirring vessel. Experiments and simulations have shown that when the stirring position is located in the lower half of the stirring vessel, mixing between the reintroduced fluid and the fluid in the vessel occurs mainly in the lower half of the stirring vessel, even though the fluid is reintroduced into the upper half of the vessel. Therefore, it is advantageous to have the recovery position located in the upper half of the stirring vessel. In a preferred modification of this embodiment, an additional recovery means is provided at the bottom of the stirring vessel, and the recovery means is connected to the additional recovery means, which includes a fluid regulating means, such as a valve or a positive displacement pump with a variable speed device, for regulating the recovery of fluid by the additional recovery means. Preferably, the fluid regulating means is adapted to regulate the flow through the additional recovery means so that the flow increases when it is determined that the load for pumping has increased, for example, when cavitation noise is detected from the pump pumping fluid through the recovery means. This embodiment is particularly advantageous for saving energy to operate the pump.

[0027] In one embodiment, the fluid contains a binder and the particles contain a coloring pigment. For example, the binder may include a resin, a wetting additive and / or a solvent.

[0028] In one embodiment, the stirring means includes an impeller, and the step of stirring the fluid contents of the stirring vessel includes rotating the impeller. Preferably, the impeller is rotated via a rotating means such as an electric motor connected to the impeller via a rotating rod. Alternatively, the impeller may be rotated using a rotating magnetic field. Preferably, the impeller is rotated using a speed change provider that can change the rotational speed of the impeller. The speed change provider is preferably adapted to adjust the rotational speed of the impeller so as to avoid the settling of particles at the bottom of the stirring vessel. Furthermore, the speed change provider is preferably adapted to adjust the rotational speed of the impeller so as to drive a vortex around the central part of the stirring vessel, for example, around the rotating rod, by the rotation of the impeller. A preferred rotational speed of the impeller corresponds to 1 / 2 to 1 / 3 of the speed used to disperse the particles in the fluid before initiating recirculation and grinding, and for example, in a particular embodiment, the speed may be 200 to 300 revolutions per minute (RPM). The impeller could be, for example, a cowl disc, or it could correspond to an axial propeller.

[0029] In one embodiment, the method is a control method that includes the step of controlling the recirculation rate based on the average particle size in the recovered fluid. The average particle size in the recovered fluid can be determined directly, for example, by an optical particle size measurement method that can measure the particle size in the flowing fluid. Alternatively, the average particle size can be determined indirectly, for example, by measuring specific properties of the fluid containing particles that vary with the average particle size. These properties may include, for example, the light diffusion properties of the fluid, the color of the fluid, the transparency of the fluid, and fluid flow properties such as viscosity. The recirculation rate can then be controlled based on the determined average particle size of the fluid recovered from the agitated vessel.

[0030] Preferably, the method includes a step of reducing the recirculation rate when the average particle size of a predetermined amount of recovered fluid is lower than a predetermined first threshold, and / or when the difference between the average particle size of a predetermined amount of recovered fluid and the average particle size in the mixing region is lower than a predetermined second threshold. More preferably, the reduction in the recirculation rate includes stopping recirculation when the above conditions are met. Thus, the process can be controlled to stop when a predetermined criterion is met, such as when the average particle size of a predetermined amount of recovered fluid, or the difference between the average particle size of a predetermined amount of recovered fluid and the average particle size in the mixing region, falls below a predetermined threshold. The threshold can be defined based on a quality criterion for the desired final product. Furthermore, recirculation may be controlled based on the recirculation time, based on the pressure measured in the grinder, based on the temperature of the fluid in the stirring vessel, based on the total energy, etc.

[0031] In a further aspect of the present invention, a system for dispersing and grinding particles in a fluid is provided, the system comprising: a) a stirring vessel adapted to hold a fluid containing particles; b) stirring means for stirring the fluid in the stirring vessel, wherein the stirring means is positioned at a predetermined stirring position within the stirring vessel; c) a recirculation means, i) a recovery means adapted to continuously recover a predetermined amount of fluid containing particles from a predetermined recovery position within the stirring vessel; ii) a grinding means adapted to grind particles in the continuously recovered fluid, wherein if the particles have a size exceeding a predetermined particle diameter, the grinding means reduces the particle diameter in the recovered fluid each time it passes through the grinding means; and iii) a reintroduction means for continuously reintroducing the recovered fluid that has passed through the grinding means into the stirring vessel at a predetermined reintroduction position, wherein the stirring means defines a mixing region within the stirring vessel where the reintroduced fluid containing particles of the reduced size is mixed with the fluid in the stirring vessel, and the recovery position is defined by the average particle diameter of the particles in the fluid within the mixing region. Larger than The system includes a recirculation means provided to contain particles having an average particle diameter.

[0032] In a further aspect of the present invention, a recirculation means including a recovery means, a grinding means and a reintroduction means is used together with a stirring vessel having a stirring means such that the number of times the fluid in the stirring vessel passes through the grinding means required to reach a predetermined average particle size is reduced. Preferably, such a reintroduction means is used together with the stirring means, as described above.

[0033] It should be understood that the method of claim 1, the system of claim 14, and the use of claim 15 have similar and / or identical preferred embodiments, particularly as defined in the dependent claims.

[0034] It should be understood that preferred embodiments of the present invention may be dependent claims or any combination of the above embodiments and their respective independent claims.

[0035] These and other aspects of the present invention will become apparent from and by reference to the embodiments described below. [Brief explanation of the drawing]

[0036] [Figure 1] This figure schematically and illustratively illustrates one embodiment of a system for dispersing and pulverizing particles in a fluid by recirculation. [Figure 2] This flowchart illustrates one embodiment of a method for dispersing and pulverizing particles in a fluid by recirculation. [Figure 3] This figure schematically and illustratively illustrates the process that takes place during the execution of one embodiment of a method for pulverizing particles in a fluid by recirculation. [Figure 4] Figure 4, including Figures 4A to 4E, schematically and illustratively shows the internal fluid flow of one embodiment of a system for pulverizing particles in a fluid by recirculation. [Modes for carrying out the invention]

[0037] Figure 1 schematically and illustratively shows one embodiment of a system for dispersing and grinding particles in a fluid by recirculation. In this embodiment, the system 100 comprises a stirring vessel 110 into which a fluid 160 containing particles 164 can be introduced. A stirring means 120 is provided at a stirring position 121 within the stirring vessel 110. In this exemplary embodiment, the stirring position 121 is located in the lower half of the stirring vessel 110. In this embodiment, the stirring means 120 includes an impeller, which is rotated to generate turbulent fluid flow near the impeller. In this embodiment, the impeller is a cowl disc. In a preferred embodiment, the impeller is rotated at a rotational speed 2 to 3 times the rotational speed used to disperse the particles in the fluid before initiating recirculation and grinding. Preferably, the speed of the impeller is adjusted to generate vortices within the stirring vessel 110. The turbulent fluid flow near the impeller defines a mixing region 161 in which the fluid 160 can be mixed with the fluid to be reintroduced into the stirring vessel 120. The system 100 further comprises a recirculation means including a recovery means 130, a crushing means 140, and a reintroduction means 150.

[0038] In this embodiment, the recovery means 130 refers to a pipe connected to a pump 170 for pumping the fluid that is recovered from the stirring vessel 110 by the recovery means 130, through the recovery means 130 to the grinding means 140, and further returned to the stirring vessel 110 through the reintroduction means 150. The recovery means 130 preferably includes an opening configured to facilitate the operation of the pump 170 using the rotational energy of the fluid flowing through the pipe. For example, the opening in the pipe can be adapted so that the recovery means 130 opens in the direction of the surrounding fluid flow, for example, by cutting the end of the pipe obliquely to form an elliptical opening in the direction of the fluid flow.

[0039] The recovery means 130 is positioned so that the fluid 160, along with the particles 164 in the fluid 160, is recovered from the stirring vessel 110 at the stirring position 131. In this particular embodiment, the recovery position 131 is selected to be located within a region 162 of the stirring vessel 110, which has a cylindrical ring shape. The recovery region 162 is defined as the region having the highest average particle diameter relative to other regions within the vessel 110. The recovery region 162 is determined for this particular structure of the stirring vessel 110, for example, by experiment and / or numerical simulation. For example, in a numerical simulation, the simulated stirring vessel 110 may be divided into several small volumes of equal size, and for each volume, the average particle diameter over time of the recirculation process can be calculated. The recovery region 162 is then defined as the region where the volume exhibits the highest average particle diameter among all volumes over time of the recirculation process. The recovery means 130 can then be configured so that the recovery position 131 is located within the recovery region 162.

[0040] After the fluid containing particles is recovered by the recovery means 130, the fluid flows through the recovery means 130 to the grinding means 140. The grinding means may include any type of grinder that can reduce the size of the particles 164 in the recovered fluid 160.

[0041] Next, the recovered fluid 160 containing the reduced-size particles 165 is reintroduced into the stirring vessel 110 at a reintroduction position 151 by a reintroduction means 150. In this embodiment, the reintroduction position 151 is located near the surface 163 of the fluid 160 in the stirring vessel 110. In an alternative embodiment, the reintroduction position 151 may be located above the surface of the fluid 160 so that the reintroduced fluid faces the inner wall of the stirring vessel 110 and flows down along the inner wall of the stirring vessel 110 to the surface of the fluid 160.

[0042] Figure 1 further illustrates an exemplary flow of the reintroduced fluid, represented by crushed and thus smaller particles 165. After the reintroduction of the fluid containing the crushed particles 165, the fluid circulates spirally over the upper surface of the fluid in the stirring vessel, and then the fluid in each spiral is drawn into the formed vortex, along and around the shaft holding the stirring means 120 in this embodiment, until the fluid with smaller particles 165 reaches the stirring means 120. Such a fluid flow is also called a helicoidal flow. In the region of the stirring means 120, the fluid is then discharged radially to form a substantially disk volume, which grows over time like a "stack of plates". This general fluid flow in the stirring vessel can be subject to specific modifications based on the particular structure and design of the stirring means. For example, if the stirring means 121 includes blades connected to the shaft by a simple rod, the helicoidal flow takes the form of a cylinder having a larger diameter than the shaft and not in contact with the shaft. If the blades are welded directly to the shaft, the helicoidal flow will be in direct contact with the shaft, like a coating. However, the general principle of the reintroduced fluid flow described above remains independent of the specific embodiment of the agitation means 120.

[0043] Furthermore, Figure 1 shows a modified example of the embodiment described above. In this modified example, indicated by the dotted line, an additional recovery means 132 including a valve 133 is provided. In this embodiment, a predetermined small amount of fluid, for example, 20 to 30 percent of a predetermined amount of fluid recovered by the recovery means 130, is also recovered at the bottom of the stirring vessel 110 by the additional recovery means 132. The valve 133 is provided to adjust the predetermined amount of fluid recovered by the additional recovery means 132. Preferably, the valve is controlled based on the current pumping performance of the pump 170. For example, if the viscosity of the fluid is not optimal for the pumping performance, the valve is opened so that additional recovered fluid, subject to gravity, can support the pumping of the fluid. Furthermore, if cavitation occurs in the pump 170, for example, if cavitation noise is detected, it is preferable to use the valve 133 to supply more recovered fluid from the additional recovery means 132 to avoid damage to the pump. This embodiment is particularly advantageous in applications involving high-viscosity fluids.

[0044] Figure 2 schematically and illustratively shows another embodiment of a system for pulverizing particles in a fluid by recirculation, and components similar to those in the above-described embodiment of the system shown in Figure 1 have the same reference numerals. In system 200, the agitator 220 is located at the agitator position 221, which in this embodiment is located in the upper half of the agitator 110. Thus, the mixing area 261 can also be found in the upper half of the agitator 110 in this embodiment. The recovery area 262 in this embodiment is determined to be located in the lower half of the agitator 110. Thus, in this embodiment, the recovery 230 is arranged such that the recovery position 231 is located within the recovery area 262. In particular, in this embodiment, the recovery position 231 is located at the bottom of the agitator 110.

[0045] Referring to Figures 3 and 4, a method for dispersing and grinding particles in a fluid by recirculation according to the present invention is described schematically and illustratively below. In the first step 310 of Method 300, a fluid 160 containing particles 164 having an initial mean particle size is introduced into a stirring vessel 110, for example, as shown in Figure 1. In the next step 320, the fluid 160 in the stirring vessel is stirred using a stirring means 120, for example, as also shown in Figure 1. During stirring, the fluid 160 is recirculated in step 330.

[0046] The recirculation and its effects will be explained in more detail with reference to Figure 4. Figure 4 schematically and illustratively illustrates the effects of a method for dispersing particles in a fluid. Figure 4A shows the state of the fluid containing particles at the start of the recirculation process. In this state, the particles are mainly of the same size, i.e., a first particle diameter. In step 331, according to the embodiment of the system shown in Figure 1, a predetermined amount of fluid is continuously recovered from the stirring vessel from the recovery position shown in Figure 4A, i.e., recovered from the left side of the upper half of the vessel. In this state, since the fluid in the vessel contains only particles of the first particle diameter, the recovered fluid also contains only particles of the first particle diameter. In step 332, the recovered fluid is supplied to a grinding means that reduces the particle diameter in the fluid. Therefore, after grinding, the recovered fluid contains particles with a reduced particle diameter, i.e., particles with a second particle diameter. For ease of understanding in the schematic process shown in Figure 4, the second particle size also refers to a predetermined final particle size to be provided in the final product of the process, and for explanatory reasons, the particles of the second particle size pass through the grinder unchanged. As shown in Figure 4B, the recovered fluid containing the particles with reduced particle size (in this case, particles with the second particle size) is reintroduced into the stirring vessel near the surface of the fluid in the fluid container in step 333. Also shown in Figure 4B, due to the vortex, the fluid containing the particles with the second particle size flows along the surface of the fluid in the stirring vessel and then flows downward to the impeller along the vortex around the rod holding the impeller, without substantially mixing with the fluid in the container containing the particles with the first particle size. Only in the region where the impeller causes turbulence do the fluid containing the particles with the second particle size and the fluid in the container containing the particles with the first particle size mix. Therefore, as can also be seen in Figure 4B, in this region the average particle size decreases very rapidly because particles with the second particle size are continuously supplied to this region. Conversely, the average particle size in the recovery region still substantially corresponds to the first particle size and changes very slowly due to the slow transport process from the mixing region to the upper region of the stirring vessel. This slow transport process is schematically shown in Figures 4C and 4D.Furthermore, Figures 4C and 4D show that the overall average particle size decreases with the continuous supply of smaller particles to the mixing region and the recovery of larger particles from the recovery region, and the average particle size decreases faster in the mixing region than in the recovery region until the average particle size in the mixing region almost corresponds to the second particle size. Figure 4E shows the state where the reintroduction process is stopped because the average particle size of the particles in the recovered fluid is slightly above the second particle size and below the threshold, and therefore the final product meets the predetermined quality criteria.

[0047] In the embodiments described above, a specific configuration exhibiting a particular flow pattern has been described, but in other embodiments, the flow pattern may be different. For example, other flow patterns of the fluid and, accordingly, other specific configurations of the stirring vessel and stirring means that can determine regions having a higher average particle size are also conceivable. In general, the present invention refers to recovering the fluid for grinding from a region of the stirring vessel that contains particles that are still larger on average, i.e., recovering the fluid that has particles with a higher average particle size than other regions of the stirring vessel, and by this principle, the efficiency of the grinding process can be increased and high-quality grinding products can be achieved in a shorter time.

[0048] Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art and by practitioners of the planned invention, based on an examination of the drawings, disclosures, and dependent claims.

[0049] In a claim, the term “including” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude plurals.

[0050] The reference numerals in the claims should not be construed as limiting the scope.

[0051] The present invention relates to a method and system for dispersing and grinding particles in a fluid. The method includes stirring a fluid containing particles in a stirring vessel using a stirring means. During stirring, the fluid is recirculated by continuously recovering a predetermined amount of the fluid from a recovery point. Furthermore, the particles are ground, and the particle size in the recovered fluid decreases each time it passes through the grinding means. Furthermore, the fluid recovered after passing through the grinding means is continuously reintroduced into the stirring vessel at a reintroduction point. The reintroduced fluid is mixed with the fluid in the stirring vessel in a mixing region defined by the stirring means, and the recovery point is determined by the average particle size of the particles in the mixing region of the recovered fluid. Larger than It is determined that the particles include a particle having an average particle diameter.

Claims

1. A method for dispersing and grinding particles in a fluid, The above method involves the following steps: - A step of introducing a fluid (160) containing the particles (164) into a stirring vessel (110), wherein the particles (164) have an initial average particle size, - A step of stirring the fluid (160) in the stirring container (110) using stirring means (120, 220) positioned at predetermined stirring positions (121, 221) within the stirring container (110), wherein during stirring, By using the recovery means (130, 230), a predetermined amount of fluid containing particles is continuously recovered from predetermined recovery positions (131, 231) within the stirring container (110), thereby recirculating the fluid (160) containing the particles (164). The particles in the fluid are continuously pulverized using the pulverizing means (140), and in this pulverization, each time the particles pass through the pulverizing means (140), if the particles have a size exceeding a predetermined particle diameter, the particle diameter in the recovered fluid is reduced. The process involves using a reintroduction means (150) to continuously reintroduce the recovered fluid that has passed through the crushing means (140) into the stirring container (110) at a predetermined reintroduction position (151), wherein the reintroduced fluid, which contains reduced-size particles, is mixed with the fluid in the stirring container (110) in a mixing region (161, 261) defined by the stirring means (120, 220), and the recovery position (131, 231) is determined such that the recovered fluid contains particles having an average particle diameter larger than the average particle diameter of the particles in the fluid in the mixing region (161, 261). Includes, The method includes determining the recovery location (131, 231) by determining the recovery area (162, 262) as a region within the internal volume of the stirring container (110), The recovery region (162, 262) is determined to contain the highest average particle size within the stirring vessel (110) compared to other regions of the stirring vessel, and The aforementioned recovery locations (131, 231) are located within the determined recovery area (162, 262). The mixing region (161, 261) and the recovery region (162, 262) do not overlap. method.

2. The method according to claim 1, wherein the mixing region (161, 261) is determined as a region of the internal volume of the stirring vessel (110) having the highest rate of change in the average particle size of the particles in the fluid compared to the particles in the fluid in other regions of the internal volume of the stirring vessel (110).

3. The method according to claim 1, wherein the formation of the mixing region (161, 261) is determined based on the stirring position (121, 221) of the stirring means (120, 220).

4. The method according to claim 1, wherein the reintroduction position (151) is provided above the stirring positions (121, 221).

5. The method according to claim 4, wherein the reintroduction position (151) is provided in the upper half of the stirring container (110).

6. The stirring positions (121, 221) are located in the upper half of the stirring container (110), and, The method according to claim 5, wherein the recovery positions (131, 231) are provided in the lower half of the stirring container (110).

7. The stirring positions (121, 221) are located in the lower half of the stirring container, and The method according to claim 5, wherein the recovery positions (131, 231) are provided in the upper half of the stirring container (110).

8. The method according to claim 1, wherein the fluid comprises a binder and the particles comprise a coloring pigment.

9. The stirring means (120, 220) includes an impeller, and The method according to claim 1, wherein the step of stirring the fluid contents of the stirring container (110) includes rotating the impeller.

10. The above method is a control method, and The method according to claim 1, further comprising controlling the recirculation rate based on the average particle size in the recovered fluid.

11. The method according to claim 10, further comprising reducing the recirculation rate when the average particle diameter of a predetermined amount of the recovered fluid is lower than a predetermined first threshold, and / or when the difference between the average particle diameter of a predetermined amount of the recovered fluid and the average particle diameter in the mixing region (161, 261) is lower than a predetermined second threshold.

12. A system for recirculating and grinding particles in a fluid, The aforementioned system, - A stirring vessel (110) adapted to hold the fluid (160) containing the particles (164), - A stirring means (120, 220) for stirring the fluid (160) in the stirring container (110), wherein the stirring means (120, 220) is positioned at predetermined stirring positions (121, 221) within the stirring container (110), - A means of recycling, and that means of recycling is A recovery means (130, 230) adapted to continuously recover a predetermined amount of fluid containing particles from predetermined recovery positions (131, 231) within the stirring container (110), A grinding means (140) adapted to grind particles in the continuously recovered fluid, wherein if the particles have a size exceeding a predetermined particle diameter, the grinding means (140) reduces the particle diameter in the recovered fluid each time it passes through the grinding means (140), A recirculation means including a reintroduction means (150) adapted to continuously reintroduce the recovered fluid that has passed through the grinding means into the stirring container (110) at a predetermined reintroduction position (151). and The stirring means (120, 220) define a mixing region (161, 261) within the stirring vessel (110) where the reintroduced fluid containing particles having a reduced size is mixed with the fluid (160) within the stirring vessel (110). The recovery positions (131, 231) are provided such that the fluid to be recovered contains particles having an average particle diameter larger than the average particle diameter of the particles in the fluid within the mixing region (161, 261). The system includes determining the recovery location (131, 231) by determining the recovery area (162, 262) as a region within the internal volume of the stirring container (110), The recovery region (162, 262) is determined to contain the highest average particle size within the stirring vessel (110) compared to other regions of the stirring vessel, and The aforementioned recovery locations (131, 231) are located within the determined recovery area (162, 262). A system in which the mixing region (161, 261) and the recovery region (162, 262) do not overlap.

13. A method characterized by using the system described in claim 12 in order to carry out the method described in claim 1.

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