Method for controlling the particle size distribution of a material being ground in a hammer mill, hammer mill for grinding a material being ground

Abstract

Method for controlling the particle size distribution of a material ground in a hammer mill (1), wherein a grinding chamber (11) of the hammer mill (1) is laterally bounded by at least one grinding wall (12) and a hammer-equipped rotor (14) is rotatorably mounted within the grinding chamber (11), comprising the process steps: - Driving the hammer-equipped rotor (14) of the hammer mill (1), - Supplying liquid to wet the at least one grinding wall (12) to form a liquid film (2) with a predetermined film thickness (d) on at least one section of the at least one grinding wall (12), - Feeding the material to be ground into the grinding chamber (11) of the hammer mill (1) for grinding the material to be ground, - Discharge of the crushed material from the grinding chamber (11) of the hammer mill (1), and adjustment of the film thickness (d) of the liquid film (2) on the at least one grinding wall (12) by controlling the amount of liquid supplied per defined period of time to influence the particle size of the material ground, the method is characterized by the fact that the amount of liquid supplied is changed per defined period of time depending on the rotational speed of the rotor (14) of the hammer mill (1).

Description

[0001] The present invention relates to a method for controlling the particle size distribution of a material being ground in a hammer mill and to a hammer mill for crushing a material being ground.

[0002] Hammer mills for grinding materials are already known in the art. These mills comprise a housing with an upper material feed opening and a lower material outlet. Within the housing, a grinding chamber is laterally bounded by at least one grinding wall, and a hammer-equipped rotor is rotatably arranged within the grinding chamber. During operation, the hammer-equipped rotor of the hammer mill is driven, with material to be ground being fed into the upper part of the grinding chamber via the material feed opening. The material fed into the hammer mill, which may be, for example, salts, ores, or minerals, is gripped and ground by the hammers rotating within the grinding chamber.The comminution process is achieved by accelerating the material particles with the rotating hammers and hurling them against at least one grinding wall of the hammer mill. Upon impact with the grinding wall, the material's kinetic energy is dissipated, the particles are crushed, and then reflected back from the grinding wall. Due to this reflection, the material re-enters the impact zone of the rotor's hammers and is accelerated again. This process repeats several times until, finally, the pulverized material, after multiple collisions with the grinding wall, is discharged from the mill's grinding chamber through a lower material outlet.

[0003] Prior art, such as US Patent 3,929,293 A, already discloses methods for binding dust generated during hammer mill operation by adding a liquid to the material being ground. In particular, prior art also discloses methods for pre-mixing the material to be ground with a liquid before it enters the hammer mill. This has the advantage of reducing clogging or blockage of the hammer mill when dealing with moist material. In some processes, the nature of the material being ground makes it essential to mix the material with a liquid, especially a salt solution.

[0004] The previously known methods, in which a liquid is mixed with the material to be ground before being introduced into the hammer mill, have the significant disadvantage that the liquid, along with the material to be ground, enters the rotor and must be accelerated by the rotating hammers or the rotor of the hammer mill. A further disadvantage of this approach is that the grinding process requires considerably more energy when liquid is added to the material, as the necessary quantities of liquid are significantly higher.

[0005] The advantage of well-known hammer mills is their high throughput of the material being ground. However, a significant disadvantage is that the grinding process in a hammer mill produces an undesirably high proportion of small particles, particularly if the material is ground too finely.

[0006] Based on the aforementioned prior art, the object of the present invention is to control the particle size distribution of the material being ground in a hammer mill and at the same time to reduce the amount of energy required for the operation of a hammer mill.

[0007] The problem is solved according to the invention by a method according to claim 1 and with a hammer mill having the features according to claim 8.

[0008] The inventive method for controlling the particle size distribution of a material ground in a hammer mill, wherein a grinding chamber of the hammer mill is laterally limited by at least one grinding wall and a hammer-equipped rotor is rotatorably mounted within the grinding chamber, comprises the following process steps: - Driving the hammer-equipped rotor of the hammer mill, - Supplying liquid to wet the at least one grinding wall of the hammer mill to form a liquid film with a predetermined film thickness on at least one section of the at least one grinding wall, - Feeding the material to be ground into the grinding chamber of the hammer mill for grinding the material, and - Removal of the crushed material from the grinding chamber of the hammer mill.

[0009] The formation of a water film on at least one section of the grinding wall offers the advantage that heavy or large particles of the material being ground can easily penetrate the liquid film and be reflected off the grinding wall. The resulting fine dust particles or small particles of the material being ground are immediately slowed down by the liquid film during the grinding process and bound within it. These bound small particles are not returned to the impact zone of the rotating hammers, but rather are carried away from the grinding chamber by the continuously flowing liquid film. The liquid can be discharged from the grinding chamber at the bottom via a material outlet. This outlet can also be equipped with a grid arrangement for classifying the material being ground, such that only particles below a defined size are discharged.The liquid film is ejected from the cavity. Applying a liquid film to at least one section of the grinding wall has the advantage that the liquid essentially does not penetrate the impact zone of the rotor or the hammers of the hammer mill. Due to gravity, the liquid generally flows along the grinding wall of the hammer mill, which extends essentially vertically. The liquid film also adheres to the surface of the grinding wall, which is concave relative to the rotor. This is because the rotating rotor and the rotating hammers exert pressure on the liquid film, forcing it against the surface of the grinding wall.

[0010] According to the inventive method, the thickness of the liquid film on the at least one grinding wall is adjusted by controlling the amount of liquid supplied over a defined period of time. The targeted adjustment or selection of the liquid film thickness has the advantage that the size of the particles of the material being ground, which can be flushed out via the liquid film during the impact process, can be directly influenced. Furthermore, by adjusting the thickness of the liquid film, it is possible to control which particle sizes, based on the kinetic energy carried, can still reach the grinding wall through the passage of the water film and be broken down at the grinding wall.

[0011] It can further be provided that the liquid is applied to the upper section of at least one grinding wall of the hammer mill in order to wet the grinding wall with a liquid film. By applying the liquid to an upper region of the grinding wall, gravity, in conjunction with the centrifugal force of the hammer-equipped rotor, can be used to form a liquid film extending along the grinding wall.

[0012] The liquid can be applied to the at least one grinding wall via at least one nozzle assembly. The nozzle assembly can, in particular, be a jet-forming nozzle. Using the at least one nozzle assembly, the supplied liquid can be applied precisely to a defined area of ​​the grinding wall. Furthermore, by providing different nozzle geometries, the liquid can be applied to the grinding wall surface in the desired shape.

[0013] Preferably, several nozzle assemblies can be provided, with the nozzle assemblies being distributed across the grinding wall width. By providing multiple nozzle assemblies distributed along the grinding wall width, it can be ensured that the thickness of the liquid film is uniform across the entire grinding wall width. Any potentially thinner liquid film in the edge regions of the nozzle assembly's application area can be compensated for by overlapping the nozzle assembly's application areas.

[0014] A saturated salt solution is particularly advantageous when used as the liquid for wetting the grinding wall. The saturated salt solution offers the advantage that no substances, especially salts, can be leached from the material being ground or dissolved in the liquid during the grinding process. Furthermore, the salt solution has a higher viscosity compared to the same liquid without dissolved salts. Due to this higher viscosity, the liquid film exhibits greater stability. The energy required for penetration of the liquid film by, for example, particles of the material being ground increases accordingly. By precisely adjusting the salt concentration of the liquid, even the smallest particle sizes can be controlled and specifically influenced.

[0015] According to another advantageous aspect, it can be provided that the volume ratio between the material being ground and the liquid being supplied for wetting the at least one grinding wall is in the range of 10:1 to 1:2.

[0016] According to the invention, the quantity of liquid supplied is further provided that it is varied per defined period of time depending on the rotational speed of the rotor of the hammer mill. As the rotational speed of the rotor and the hammers increases, so does the energy transferred to the material being ground. With an increasing rotational speed of the hammer mill, the kinetic energy of the particles of the material being ground also increases simultaneously. By increasing the quantity of liquid supplied per defined period of time when the rotational speed of the hammer mill increases, it can be ensured that the desired smallest particle sizes of the material being ground can still be slowed down in the liquid film and removed from the grinding chamber. The thickness of the liquid film can preferably be increased proportionally to the rotational speed by increasing the quantity of liquid supplied per period of time.

[0017] In particular, it can be provided that the liquid forms a continuous liquid film on the surface of the at least one grinding wall.

[0018] The continuous liquid film ensures that the entire surface of the grinding wall is available for the impact of the material being ground, with the resulting particle sizes being influenced by the liquid film as described above.

[0019] Furthermore, according to the invention, a hammer mill for comminuting a material to be ground can be provided comprising a housing with an upper material filling opening and a lower material outlet, wherein a grinding chamber in the housing is laterally limited by at least one grinding wall, wherein a hammer-equipped rotor is rotatably arranged in the grinding chamber, and wherein at least one liquid supply device is arranged in the housing and is designed to form a liquid film on the at least one grinding wall, wherein the film thickness of the liquid film on the at least one grinding wall can be controlled by controlling the amount of liquid supplied per unit of time, and wherein, according to the invention, the amount of liquid supplied per defined unit of time is changed as a function of the rotational speed of the rotor of the hammer mill.According to the invention, the liquid essentially forms a liquid film on the grinding wall surface. The introduction of liquid into the area of ​​the rotating rotor or into the area of ​​the hammer impact circuit is prevented by the design of the at least one liquid supply device. The at least one grinding wall extends essentially vertically from the area of ​​the upper material feed opening to the lower area of ​​the lower material outlet. The surface of the at least one grinding wall is concavely curved in the vertical direction to form the grinding chamber.

[0020] According to the invention, the liquid supply device can be formed via at least one liquid line comprising at least one liquid outlet opening, wherein the at least one liquid line is arranged in the region of an upper section of the at least one grinding wall. The design of the liquid supply device via at least one liquid line comprising at least one liquid outlet opening has the advantage that a compact liquid injection system can be achieved with simultaneously high liquid flow rates, which can be realized in the confined installation space of the hammer mill and, in particular, in the region of the upper material feed opening. Commercially available nozzle systems cannot be used due to their larger dimensions compared to the arrangement according to the invention, as these would not fit in the housing and, in particular, in the grinding chamber of the hammer mill.The geometry of the housing and grinding chamber of the hammer mill would have to be extensively adapted to integrate commercially available nozzle systems. Due to its compact design, the inventive design of the liquid supply device also makes it possible to retrofit commercially available hammer mills with the inventive liquid supply device and thus implement the inventive method.

[0021] According to the invention, the liquid line can be, for example, a pipe or a hose.

[0022] Furthermore, it may be provided that a longitudinal axis of the at least one liquid line is arranged at a defined distance from the surface of the grinding wall.

[0023] Preferably, the longitudinal axis of the liquid line can be arranged substantially parallel to the grinding wall surface. According to a further preferred embodiment, the liquid line can have a substantially circular cross-section, with the liquid outlet openings arranged at a constant distance from one another along the longitudinal axis of the liquid line and with the liquid outlet openings being located at substantially the same circumferential position of the liquid line. By designing a plurality of liquid outlet openings along the longitudinal axis of the liquid line, a compact design of the liquid supply device can be achieved, which simultaneously enables a high liquid throughput by varying the number, size, and spacing of the liquid outlet openings.

[0024] According to the invention, it can be provided that a quantity of liquid in the range of approximately 100 l / minute is discharged into the area of ​​the grinding chamber via each liquid outlet opening.

[0025] In a preferred embodiment, the outlet openings can each be arranged at a defined distance and in a defined angular position, and a liquid deflection device is arranged, wherein the liquid ejected through the outlet opening is directed by means of the liquid deflection device towards the at least one grinding wall surface.

[0026] The fluid diverting devices can be attached to the outer surface of the fluid line.

[0027] They show: Fig. 1 a side sectional view of an exemplary embodiment of a hammer mill, Fig. 2. Detailed view of a grinding wall of the hammer mill with a liquid supply device, Fig. 3a the side view of a liquid supply device, as well as Fig. 3b the sectional view of a liquid supply device.

[0028] The Fig. Figure 1 shows a side sectional view of a hammer mill 1 according to the invention, which comprises a housing 15 with an upper material feed opening 17 and a lower material outlet 19. The lower material outlet 19 is, by way of example, equipped with a grid for further classifying the ground material. The spacing of the grid bars determines the maximum particle size for the ground material.

[0029] The housing 15 contains a grinding chamber 11, which, in the exemplary embodiment shown, is laterally bounded by two opposing grinding walls 12. A hammer-equipped rotor 14 is rotatably mounted in the grinding chamber 11. As is also shown in the Fig. Two liquid supply devices 3 are arranged in the housing 15 to form a liquid film 2 on the grinding walls 12. In the illustrated embodiment, the two liquid supply devices 3 are each arranged in the housing 15 in the upper region of the respective grinding wall 12, so that the respective opposing grinding walls 12 can each be supplied with a liquid film 2 by a liquid supply device 3. Also via Fig. As can be seen from Figure 1, the design of the liquid supply device 3 according to the invention allows for a very compact design which is optimally adapted to the available installation space in the housing 15 or the grinding chamber 11.

[0030] In Fig. 2 has been removed for better clarity. Fig. Figure 1 shows a section of a grinding wall 12 with parts of the housing 15 as well as a liquid supply device 3. The liquid supply device 3 is formed via a liquid line 31 with a circular cross-section, wherein the liquid supply device 3 further comprises several liquid outlet openings 33, as shown in the section view of the Fig. 2 only shows one of the liquid outlet openings 33. Furthermore, the liquid supply device 3 in the illustrated embodiment has a liquid diverting device 35. In the Fig. Figure 2 also illustrates the process of applying a liquid film 2 to the surface 121 of the grinding wall 2. The liquid for wetting the grinding wall surface 121 is supplied to the liquid supply device 3 via the liquid line 31 and introduced into the grinding chamber 11 of the hammer mill via the liquid outlet openings 33. The liquid exits the liquid outlet opening 33 as a jet and is directed onto the surface 121 of the grinding wall 12 by means of the liquid deflection device 35. As this is shown, Fig. When liquid is removed from the grinding wall, it forms a liquid film 2 with a liquid film thickness d on the grinding wall surface 121. In the Fig. Figure 2 represents a continuous liquid film 2, which essentially covers the entire grinding wall surface 121. The liquid of the liquid film 2 is discharged from the grinding chamber 11 via the material outlet 19.

[0031] In the Fig. Figure 3a shows a schematic side view of a liquid supply device 3 in isolation. The liquid supply device 3 comprises a liquid line 31, which in the illustrated example is formed by a pipe, the liquid line in turn comprising several liquid outlet openings 33. The several liquid outlet openings 33 are arranged along the longitudinal axis 311 of the liquid line 31 at a constant distance a from each other. The liquid outlet openings 33 are essentially located at the same circumferential position of the liquid line 31. Fig.Figure 3b shows a further detailed sectional view of the liquid supply device 3. The liquid supply device 3 is formed by a liquid line 31 with a circular cross-section, which has several liquid outlet openings 33 and includes a liquid deflection device 35. The liquid deflection device 35 has a defined angular position α relative to the wall of the liquid line 31.

Claims

[1] Method for controlling the particle size distribution of a material ground in a hammer mill (1), wherein a grinding chamber (11) of the hammer mill (1) is laterally bounded by at least one grinding wall (12) and a hammer-equipped rotor (14) is rotatorably mounted within the grinding chamber (11), comprising the process steps: - Driving the hammer-equipped rotor (14) of the hammer mill (1), - Supplying liquid to wet the at least one grinding wall (12) to form a liquid film (2) with a predetermined film thickness (d) on at least one section of the at least one grinding wall (12), - Feeding the material to be ground into the grinding chamber (11) of the hammer mill (1) for grinding the material to be ground, - Discharge of the crushed material from the grinding chamber (11) of the hammer mill (1), and adjustment of the film thickness (d) of the liquid film (2) on the at least one grinding wall (12) by controlling the amount of liquid supplied per defined period of time to influence the particle size of the material ground, the procedure characterized by , that the amount of liquid supplied is changed per defined period of time depending on the rotational speed of the rotor (14) of the hammer mill (1). [2] Method according to claim 1, characterized by the application of the liquid in the area of ​​an upper section of the at least one grinding wall (12) of the hammer mill (1) to wet the grinding wall (12) with the liquid film (2). [3] Method according to any one of the preceding claims, characterized by the application of the liquid to at least one grinding wall (12) via at least one nozzle device (3). [4] Method according to claim 3, characterized by the formation of several nozzle devices (3), wherein the nozzle devices (3) are arranged distributed over the grinding wall width. [5] Method according to any one of the preceding claims, characterized by the use of a saturated salt solution as the liquid for wetting the grinding wall (12). [6] Method according to one of the preceding claims, wherein the volume ratio between the material to be ground and the liquid supplied for wetting the at least one grinding wall (12) is selected in the range of 10:1 to 1:

2. [7] Method according to any of the preceding claims, wherein the liquid forms a continuous liquid film (2) on the surface (121) of the at least one grinding wall (12). [8] Hammer mill (1) for grinding a material to be ground, comprising: - a housing (15) with an upper material filling opening (17) and a lower material outlet (19); - wherein in the housing (15) a grinding chamber (11) is laterally bounded by at least one grinding wall (12); - wherein a hammer-equipped rotor (14) is arranged to be driven rotationally in the grinding chamber (11); and - wherein at least one liquid supply device (3) is arranged in the housing (15) and is designed to form a liquid film (2) on the at least one grinding wall (12) and the film thickness (d) of the liquid film (2) on the at least one grinding wall (12) can be controlled by controlling the amount of liquid supplied per unit of time in order to influence the particle size of the material ground, characterized by , that the amount of liquid supplied is changed per defined period of time depending on the rotational speed of the rotor (14) of the hammer mill (1). [9] Hammer mill according to claim 8, wherein the liquid supply device (3) is formed via at least one liquid line (31) comprising at least one liquid outlet opening (33), wherein the at least one liquid line (31) is arranged in the region of an upper section of the at least one grinding wall (12). [10] Hammer mill according to claim 9, wherein a longitudinal axis (311) of the at least one liquid line (31) is arranged at a defined distance to the surface (121) of the grinding wall (12). [11] Hammer mill according to claim 9 or 10, wherein the liquid line (31) has a substantially circular cross-section, wherein the liquid outlet openings (33) are arranged at a constant distance (a) from each other along the longitudinal axis (311) of the liquid line (31), and wherein the liquid outlet openings (33) are configured at substantially the same circumferential position of the liquid line (31). [12] Hammer mill according to one of claims 9 to 11, wherein a liquid deflection device (35) is arranged in front of the outlet openings (33) at a defined distance and in a defined angular position (α), wherein the liquid ejected through the outlet openings (33) is directed by means of the liquid deflection device (35) in the direction of the at least one grinding wall surface (121). [13] Hammer mill according to claim 12, wherein the liquid diverting devices (35) are attached to the outer surface of the liquid line (31).

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