COLLOID MILL

Abstract

A colloid mill for reducing a particle size of particles having a rotor and a stator, which are arranged coaxially one inside the other. The colloid mill has a material inlet for introducing a suspension or emulsion on a first axial side and a product outlet for conducting away the suspension or emulsion on a second axial side. The rotor has a rotor grinding surface, and/or the stator has a stator grinding surface. The rotor grinding surface has a grinding tooth with a shearing surface and/or shearing edge, the cross-sectional surface of which grinding tooth tapers, in a plane perpendicular to the axis of rotation, wherein the cross-sectional surface has a first leg, which adjoins a base side and encloses an angle with the base side.

Claims

1. A colloid mill for reducing a particle size of particles suspended in a first liquid, and/or a droplet size of a second liquid emulsified in a first liquid, wherein the first liquid is in particular a fat-based mass, having at least one rotor and at least one stator, which are arranged coaxially one inside the other, wherein the rotor is preferably arranged or can be attached within the stator, wherein the colloid mill preferably has at least one material inlet for introducing particles, a liquid, a suspension and/or emulsion on a first axial side and at least one product outlet for conducting away the suspension or emulsion on a second axial side, wherein the at least one rotor has a rotor grinding surface facing or to be faced toward the stator, and/or the at least one stator has a stator grinding surface facing or to be faced toward the rotor, wherein the rotor grinding surface has at least one grinding tooth with a shearing surface and/or shearing edge, wherein the cross-sectional surface of the grinding tooth tapers, in a plane perpendicular to the axis of rotation, in the radial direction toward the opposite stator grinding surface, wherein the cross-sectional surface has a first leg, preferably a straight first leg, which adjoins a base side, running in the circumferential direction, of the cross-sectional surface, points in the direction of rotation of the rotor, encloses an angle of 80?-100?, preferably 85?-95?, with the base side and is preferably located on a radial line through the axis of rotation, and/or the stator grinding surface has at least one grinding tooth with a shearing surface and/or shearing edge, the cross-sectional surface of which grinding tooth tapers, in a plane perpendicular to the axis of rotation, in the radial direction toward the oppositerotor grinding surface, wherein the cross-sectional surface has a second leg, preferably a straight second leg, which adjoins a base side, running in the circumferential direction, of the cross-sectional surface, wherein the second leg points counter to the direction of rotation of the rotor, and the second leg encloses an angle of 80?-100?, preferably 85?-95?, with the base side and is preferably located on a radial line through the axis of rotation.

2. The colloid mill according to claim 1, wherein the cross-sectional surface of at least one grinding tooth forms a polygon, in particular a quadrilateral, which has a longer base side, which runs in the circumferential direction, and a shorter base side, which is parallel to the first base side and in particular located on a shearing surface of the grinding tooth.

3. The colloid mill according to claim 1, wherein the cross-sectional surface of at least one grinding tooth forms a polygon, in particular a triangle, the tip of which points toward the opposite grinding surface or the grinding surface to be arranged opposite thereto and is in particular located on a shearing edge of the grinding tooth.

4. The colloid mill according to claim 1, wherein the grinding tooth is formed as a rib with a constantly large cross-sectional surface along its longitudinal extension.

5. The colloid mill according to claim 1, wherein the shortest distance between the rotor grinding surface and the stator grinding surface is between 0.05 mm and 1.2 mm.

6. The colloid mill according to claim 2, wherein the value of a shearing surface rate is less than 0.07, wherein the value of the shearing surface rate indicates the product of the proportion of the smaller base sides of the cross-sectional surfaces of grinding teeth of the rotor grinding surface in the circumference of a circle formed by a bottom of the rotor grinding surface around the axis of rotation, and the proportion of the smaller base sides of the cross-sectional surfaces of grinding teeth on the stator in the circumference of a circle formed by a bottom of the stator grinding surface around the axis of rotation.

7. The colloid mill according to claim 1, wherein the colloid mill has a housing, and the stator and the housing are not manufactured of one piece so that the stator is in particular exchangeable.

8. A system for processing food masses, preferably containing fat-based masses, comprising a colloid mill according to claim 1, which is in particular arranged upstream of a ball mill and/or which is in particular arranged downstream of a mixer.

9. A method for reducing a particle size of particles suspended in a first liquid, and/or a droplet size of a second liquid emulsified in a first liquid, wherein the first liquid is in particular a fat mass, in a colloid mill according to claim 1, wherein, in order to form a suspension or emulsion, material is guided along between the stator grinding surface and the rotor grinding surface, from a first axial end of the colloid mill to the second axial end of the colloid mill, wherein the temperature of the material increases by less than 40? C. on the path through the colloid mill.

10. The method according to claim 9, wherein the area between the cross-sectional surfaces of two circumferentially adjacent grinding teeth on the stator grinding surface and/or the rotor grinding surface, in a plane perpendicular to the axis of rotation, provides space for the cross-sectional surfaces of 3-10 particles and/or droplets.

11. A rotor for a colloid mill according to claim 1, wherein the rotor has a rotor grinding surface to be faced toward a stator, and wherein the rotor grinding surface has at least one grinding tooth with a shearing surface and/or shearing edge, the cross-sectional surface of which grinding tooth tapers, in a plane perpendicular to the axis of rotation, in the radial direction toward the opposite stator grinding surface, the cross-sectional surface has a first leg, preferably a straight first leg, which adjoins a base side, running in the circumferential direction, of the cross-sectional surface, points in the direction of rotation of the rotor and encloses an angle of 85-95? with the base side.

12. A stator for a colloid mill according to claim 1, wherein the stator has a stator grinding surface to be faced toward a rotor, and wherein the stator grinding surface has at least one grinding tooth with a shearing surface and/or shearing edge, the cross-sectional surface of which grinding tooth tapers, in a plane perpendicular to the axis of rotation, in the radial direction toward the opposite rotor grinding surface, the cross-sectional surface has a second leg, preferably a straight second leg, which adjoins a base side, running in the circumferential direction, of the cross-sectional surface, points counter to the direction of rotation of the rotor and encloses an angle of 85-95? with the base side.

Description

[0088] In the figures:

[0089] FIG. 1 shows a schematic representation of a detail view of a first example of a stator and a rotor in plan view;

[0090] FIG. 2 shows schematic representations of detail views in plan view of a second example of a stator and a rotor in two different positions relative to one another;

[0091] FIG. 3 shows schematic representations in plan view of detail views of various configurations for grinding teeth on a stator and a rotor;

[0092] FIGS. 4a-4e show schematic representations in plan view of further examples of a stator and a rotor;

[0093] FIGS. 5a-4c show schematic representations in plan view of further examples of a stator and a rotor;

[0094] FIG. 6a shows results for flow rates calculated for two exemplary profiles;

[0095] FIG. 6b shows results for shear rates calculated for the exemplary profiles according to FIG. 6;

[0096] FIG. 7a shows an example of a rotor in a perspective view;

[0097] FIG. 7b shows an example of a stator in a perspective view;

[0098] FIG. 8 shows a schematic view of a system.

[0099] FIG. 1 shows a schematic representation of a detail view of a first example of a rotor 1 and a stator 2 in plan view. The rotor 1 and the stator 2 are arranged coaxially one inside the other, wherein the rotor 1 is arranged within the stator 2 and rotates against the stator 2 in a direction of rotation 15.

[0100] The rotor 1 has a rotor grinding surface 3 facing the stator 2, and the stator 2 has a stator grinding surface 4 facing the rotor 1.

[0101] The rotor grinding surface 3 has grinding teeth 5a with a shearing surface 6, the cross-sectional surfaces 8a of which grinding teeth taper, in a plane perpendicular to the axis of rotation D, as shown in the figure, in the radial direction (Ra) toward the opposite stator grinding surface 4. The cross-sectional surface 8a has a straight first leg 14a, which adjoins a base side 11a, running in the circumferential direction 15, of the cross-sectional surface 8a and points in the direction of rotation 15 of the rotor 1. The first leg 14a encloses an angle ? of 90? with the base side 11a.

[0102] The cross-sectional surfaces 8a of the grinding teeth 5a on the rotor 1 each form a quadrilateral. This has a longer base side 11a, which runs in the circumferential direction, and a shorter base side 12a, which is parallel to the first base side and is located on the shearing surface 6 of the respective grinding tooth 5a.

[0103] The stator grinding surface 4 has grinding teeth 5b with a shearing edge 7, the cross-sectional surface 8b of which grinding teeth tapers, in a plane perpendicular to the axis of rotation (D), in the radial direction Rb toward the opposite rotor grinding surface 3.

[0104] The cross-sectional surface 8b has a straight second leg 14b, which adjoins a base side 11b, running in the circumferential direction, of the cross-sectional surface 8b. The second leg 14b points counter to the direction of rotation 15 of the rotor (1). The second leg 14b encloses an angle ? of 90? with the base side 11b.

[0105] The cross-sectional surfaces 8b of the grinding teeth 5b on the stator each form a triangle, the tip of which points in the radial direction Rb and forms a shearing edge 7.

[0106] FIG. 2 shows schematic representations of detail views in plan view of a second example of a stator 2 and a rotor 1 in two different positions relative to one another, wherein the rotor 1 has moved further in the direction of rotation in the second image.

[0107] The material 102 to be processed is located between the rotor 1 and the stator 2.

[0108] The rotor 1 has grinding teeth 5a and the stator has grinding teeth 5b, the cross-sectional surfaces of which are quadrangular in both cases.

[0109] The shortest distance 17 between the rotor grinding surface 3 and the stator grinding surface 4 is the distance 17 of the grinding teeth 5a and 5b when they are exactly opposite, as shown in the second image. Since the cross-sectional surfaces 8a, 8b taper radially, the shear gap, which is defined by the region in which the material 102 must pass through the shortest distance 17, occupies only a comparatively short length proportion of the entire circumferential line.

[0110] The value of the shearing surface rate (SSR) indicates the product of the proportion of the smaller base sides 12a of the cross-sectional surfaces 8a of grinding teeth 5a of the rotor grinding surface 3 in the circumference of a circle formed by a bottom line 16a of the rotor grinding surface 3 around the axis of rotation, and the proportion of the smaller base sides 12b of the cross-sectional surfaces 8b of grinding teeth 5b on the stator 2 on the circumference of a circle formed by the bottom line 16b of the stator grinding surface 4 around the axis of rotation.

[0111] If the grinding teeth 5a, 5b are distributed evenly over the circumference, it is sufficient to in each case consider only one grinding tooth 5a, 5b and the lengths s1+b1 and s2+b2, which each describe the distance of the steep flanks, wherein s1 and s2 are the lengths of the short base sides 12a and 12b. In this case, the shearing surface rate is s1/(s1+b1)*s2/(s2+b2).

[0112] Based on the shearing surface rate SSR, the dissipation and the temperature rise can be calculated.

[0113] The dissipation is

{dot over (Q)}.sub.diss=?({dot over (?)}).Math.{dot over (?)}.sup.2.Math.V.sub.G

wherein the shear rate is calculated from

[00001]$\stackrel{?}{?}=\frac{4.Math.?.Math.n}{60.Math.\left(1-{\left(\frac{R_2}{R_1}\right)}^2\right)}$

and the volume in the grinding gap is assumed to be

V.sub.G=?.Math.(R.sub.1.sup.2?R.sub.2.sup.2).Math.h.Math.SSR.

[0114] Substituted, this results in

{dot over (Q)}.sub.diss=?({dot over (?)}).Math.{dot over (?)}.sup.2.Math.?.Math.(R.sub.1.sup.2?R.sub.2.sup.2).Math.h.Math.SSR

[0115] The temperature rise can be determined therefrom as

[00002]$?T=\frac{{\stackrel{.}{Q}}_{diss}}{\stackrel{.}{m}.Math.c_p}.$

[0116] In this case, n is the rotational speed in rpm, R.sub.1 is the inner radius of the stator in m (see FIG. 5c), R.sub.2 is the outer radius of the rotor in m (see FIG. 5c), h is the shortest distance 17,

is the flow rate in kg/h, ? is the viscosity of the mass and c.sub.p is the specific heat capacity in J/kg/K.

[0117] The temperature increase thus depends linearly on the shearing surface rate.

[0118] FIG. 3 shows schematic representations in plan view of detail views of various configurations for a stator and a rotor, wherein for each configuration, the stator 2 is shown in the upper half and the rotor 1 is shown in the lower half.

[0119] Configurations 1 and 2 show conventional cross-sectional surfaces of grinding teeth that do not taper radially. The corresponding values for the shearing surface rate SSR are large.

[0120] The more the cross-sectional surfaces 8a, 8b taper radially, the smaller the value for the shearing surface rate SSR becomes.

[0121] FIGS. 4a-4e show schematic representations in plan view of further examples of a stator 2 and a rotor 1 arranged coaxially within the stator 2.

[0122] The examples have, in each case, different distances 18 between the bottom lines 16a, 16b, different shortest distances 17 between opposite grinding teeth 5a, 5b, a different number of grinding teeth 5a, 5b.

[0123] In the example according to FIG. 4b, the grinding teeth 5a, 5b in each case adjoin one another without a distance.

[0124] According to FIG. 4c, the grinding teeth 5a, 5b each have a relatively large distance 19a, 19b from one another in the circumferential direction.

[0125] According to FIG. 4d, only the legs 14a of the grinding teeth 5a of the rotor 1 form a steep flank.

[0126] According to FIG. 4e, the grinding teeth 5a, 5b of the stator 2 and of the rotor 1 each have triangular cross-sectional surfaces 8a, 8b, the tips 9 of which point toward the respectively opposite grinding surface 3, 4.

[0127] FIGS. 5a-4c schematic representations in plan view of further

[0128] examples of a stator 2 and a rotor 1.

[0129] The distance 18 between the bottom lines 16a and 16b (see FIG. 5a), the number of grinding teeth 5a on the rotor 1 and the radial extension 20 of the rotor grinding teeth 5a are selected such that the area 21 between the cross-sectional surfaces 8a of two circumferentially adjacent grinding teeth 5a, in a plane perpendicular to the axis of rotation, as shown in the figures, provides space for the cross-sectional surfaces 100 of 3-10 particles 101.

[0130] The cross-sectional surfaces 8a of the grinding teeth 5a of the rotor preferably comprise a proportion of less than 50% in a circular ring with inner radius R.sub.3 and outer radius R.sub.2, wherein the inner radius R.sub.3 is the distance of the bottom line 16a from the axis of rotation and the outer radius R.sub.2 is the distance of the shorter base side 12a from the axis of rotation, i.e., corresponds to the outer radius of the rotor 1 (see FIG. 5c).

[0131] The cross-sectional surfaces 8b preferably comprise a proportion of less than 50% in a circular ring with inner radius R.sub.1 and outer radius R.sub.4, wherein the inner radius R.sub.1 is the distance of the shorter base side 12b from the axis of rotation, thus corresponds to the inner radius of the stator 2, and the outer radius R.sub.4 is the distance of the bottom line 16b from the axis of rotation (see FIG. 5a).

[0132] FIG. 6a shows results calculated for two exemplary profiles for flow rates of material 102 between grinding teeth 5a, 5b. The left image corresponds to the configuration 3 of FIG. 3; the right image corresponds to the configuration 2 of FIG. 3.

[0133] The flow rates indicated by different coloring were obtained by a computer simulation of the fluid dynamics according to the Herschel-Bulkley model.

[0134] It is found that larger areas with higher speeds are achieved with the profile according to the invention (left image) and a small SSR value than for a conventional profile (right image). This indicates higher mass transfer and better comminution effect.

[0135] FIG. 6b shows results calculated for the exemplary profiles according to FIG. 6a for shear rates of material 102 between grinding teeth 5a, 5b.

[0136] The shear rates indicated by different coloring were obtained by a computer simulation of the fluid dynamics according to the Herschel-Bulkley model.

[0137] It is found that smaller areas with higher shear rates are achieved with the profile according to the invention (left image) and a small SSR value than for a conventional profile (right image). This indicates less heating of the material 102.

[0138] FIG. 7a shows an example of a rotor 1 in a perspective view.

[0139] The rotor 1 has a conical basic shape.

[0140] The grinding teeth 5a on the rotor grinding surface 3 are formed as ribs 13, which enclose an angle ?1 of less than 90? with the direction of rotation 15 and are thus inclined.

[0141] FIG. 7b shows an example of a stator 2 in a perspective view.

[0142] The stator grinding surface 4 has a conical basic shape.

[0143] The grinding teeth 5b are formed as ribs 13, which enclose an angle ?2 of less than 90? with the direction of rotation 15.

[0144] Table 1 below shows results for the comminution of peanuts with a conventional colloid mill, which has grinding teeth according to the configuration 3 of FIG. 3. Peanuts have a high fat content, approximately 49%, so that fat does not need to be added.

TABLE-US-00001 TABLE 1 Colloid mill Flow Temp. Mass T. reduction Energy Gap rate Power [? C.] ?T new vs Old consumption Prodct [mm] rpm [kg/h] [kW] Inlet Outlet [? C.] [? C.] [%] [kW/t] Peanut 0.45 2950 624 14 27 67 40 22 Peanut 0.25 2950 684 19 27 70 43 28 Peanut 0.05 2950 657 19 27 77 50 29

[0145] The shortest distance 17 or grinding gap (referred to here as gap), the flow rate in kg/h, the power in kW, the temperature of the material at the material inlet (inlet) and the temperature of the material at the product outlet (outlet) in ? C., the difference between them, and also the energy consumption in kW/t are listed.

[0146] Depending on the grinding gap, the material is heated by more than 40? C.

[0147] Table 2 below shows results for the comminution of peanuts with a colloid mill according to the invention.

TABLE-US-00002 TABLE 2 Colloid mill Flow Temp. Mass T. reduction Energy Gap rate Power [? C.] ?T new vs Old consumption Prodct [mm] rpm [kg/h] [kW] Inlet Outlet [? C.] [? C.] [%] [kW/t] Peanut 0.45 2950 893 19 27 54 27 ?13 ?33% 21 Peanut 0.25 2950 1100 20 27 59 32 ?11 ?26% 18 Peanut 0.25 2950 1062 20 27 56 29 ?14 ?33% 19 Peanut 0.05 2950 850 20 27 61 34 ?16 ?32% 24 Peanut 0.05 2950 780 20 27 62 25 ?15 ?30% 26

[0148] The same values as in Table 1 are listed, and additionally also the reduction of the temperature difference compared to the conventional colloid mill with the same grinding gap.

[0149] It can be clearly seen that not only does less heating occur, a higher flow rate is also a lower energy consumption.

[0150] FIG. 8 shows a schematic view of a system 70 comprising a mixer 60, a colloid mill 40 and a ball mill 50.