METHOD FOR OPERATING A BLASTING MILL AND BLASTING MILL

Description

[0001] The present invention relates to a method for operating a jet mill according to the preamble of claim 1.

[0002] When producing ultrafine particles by milling, the surface area of ​​the milled solid increases approximately inversely to the square of the particle size. Simultaneously, the particle mass decreases with the cube of the particle size. Due to these physical properties, surface-acting forces, such as the van der Waals force or electrostatic forces, have a disproportionately large effect as the particle size decreases.

[0003] This can be observed particularly in the range of d 50 < 2 µm, with a strong increasing tendency towards even smaller particles. The result is a reagglomeration of the generated fine particles. The air classifier integrated into both fluidized bed and closed-bed jet mills for upper particle size limitation prevents the discharge of these agglomerates consisting of the finest particles (it "recognizes" them as coarse particles) from the mill, so that they are subjected to further processing. Thus, additional grinding energy is expended to deagglomerate the already fine particles, which immediately form new agglomerates. This leads to a significant increase in the energy consumption of the grinding process. An example is known from EP2301667.

[0004] The present invention has and achieves the goal of making the operation of jet mills more efficient.

[0005] This objective is achieved by a method for operating a jet mill according to claim 1.

[0006] Accordingly, the invention provides a method for operating a jet mill with an integrated dynamic air classifier, wherein particles are fed into a grinding chamber of the jet mill as material to be ground and are ground there into fine particles by using superheated steam, which can also be referred to as process or grinding steam, or technical gases (He, H₂), which can also be referred to as process or grinding gases, as operating media. At least one surface-active additive is added to the material to be ground in order to stabilize the fine particles produced.

[0007] Such additives for stabilizing the generated fine particles can be used in preferred embodiments. before grinding, they are mixed with the material being ground, introduced directly into the grinding chamber, and / or fed to the jet mill together with the operating material.

[0008] It is further preferred if the operating equipment contains technical gases (He, H 2 ) and has an inlet temperature of at least 50° C.

[0009] Alternatively, it may be preferable to provide that the operating medium is superheated steam, which has at least such an inlet temperature that it is dry after passing through the jet mill.

[0010] Another preferred embodiment consists in the fact that it contains at least one surface-active additive for stabilizing the generated fine particles: Stearic acid for hydrophobic stabilization, or diols, polyols or other long-chain alcohols for hydrophilic stabilization.

[0011] Furthermore, it may be preferable to include at least one surface-active additive to stabilize the generated fine particles: Silanes, and / or condensates of naphthalenesulfonic acid or phenolsulfonic acid.

[0012] The additive addition amounts to approximately 0.1% to about 4% of the mass throughput of the milled material.

[0013] To carry out the process, the jet mill can be provided with a grinding chamber into which particles as material to be ground are supplied via material feed devices and superheated steam or technical gases (He, H2) as operating materials are supplied via operating material feed devices and in which the material to be ground is ground into fine particles by grinding, and wherein feed devices for at least one surfactant additive for stabilizing the fine particles produced are provided.

[0014] Preferably, the supply devices for the at least one surface-active additive lead into the material feed devices, the grinding chamber and / or the operating material feed devices.

[0015] It is further preferred if the jet mill is a fluidized bed jet mill or a dense bed jet mill.

[0016] Another preferred embodiment consists in the supply devices including at least one nozzle that surrounds a central inlet opening for the at least one additive in a ring-like manner. This can preferably be further designed such that the at least one nozzle is an I-nozzle.

[0017] Further preferred and / or advantageous embodiments of the invention and its individual aspects result from combinations of the dependent claims as well as from the entire application documents presented.

[0018] The invention is explained in more detail below by way of example embodiments with reference to the drawing, in which Fig. 1 illustrates a fluidized bed jet mill as a first embodiment in a schematic sectional view, Fig. 2 illustrates a closed bed jet mill as a second embodiment in a schematic sectional view, and Fig. 3 illustrates a medium nozzle with a central inlet opening for the at least one additive in a partial schematic sectional view.

[0019] The invention is explained in more detail by way of example using the embodiments and applications described below and illustrated in the drawings; that is, it is not limited to these embodiments and applications. Method and device features can also be derived analogously from the device and method descriptions, respectively.

[0020] Individual features that are specified and / or illustrated in connection with a specific embodiment are not limited to that embodiment or the combination with the other features of that embodiment, but can be combined, within the limits of what is technically possible, with any other variants, even if they are not specifically addressed in the present documentation.

[0021] Identical reference numerals in the individual figures and illustrations of the drawing denote identical or similar components, or components with the same or similar effect. The representations in the drawing also clearly indicate features that are not marked with reference numerals, regardless of whether such features are described subsequently or not. Conversely, features included in this description but not visible or depicted in the drawing are readily understandable to a person skilled in the art.

[0022] In the Fig. 1 Figure 1 is a schematic cross-sectional representation of a fluidized bed jet mill. Material M is fed via a feed chute 2 from material feed devices 3 into a mill housing 4, which surrounds a grinding chamber 5. A fluidized bed 6 forms in the grinding chamber 5, which is fluidized by jets of grinding gas or steam 8 exiting from operating nozzles 7. The process gas or steam is referred to as the operating medium.

[0023] From this product fluid bed 6, grinding material particles (hereinafter simply referred to as particles) enter the grinding gas or steam jets 8, where they are accelerated to high speeds. Along the grinding gas or steam jets 8 and in the center of the grinding chamber 5, the accelerated particles collide and are thereby crushed.

[0024] The relaxed operating fluid, laden with milled material particles or other contaminants, rises in the center of the jet mill 1 to a classifier wheel 9 of an integrated dynamic air classifier 10. The classifier wheel 9 is driven by a speed-controlled motor 12 via a belt drive 11. Excessively coarse particles or contaminants are rejected by the classifier wheel 9 and return directly to the product flow bed 6. Fine and ultrafine particles exit the jet mill 1 along with the operating fluid and are separated from it in a suitable separator or dust filter.

[0025] The operating medium, i.e., process or grinding gas or process or grinding steam, is fed to the operating medium nozzles 7 via operating medium supply devices 13. Superheated steam or technical gases, such as helium or hydrogen, are used as operating media.

[0026] To avoid the reagglomeration that usually occurs with fine particles produced as desired, i.e. d 50 < 2 µm, as explained at the beginning, feed devices 14a, 14b and / or 14c for at least one surface-active additive for stabilizing the fine particles produced are now also provided.

[0027] The feed devices 14a open into a reservoir or material stream of the material to be ground, MDh, before the material to be ground M enters the mill housing 4 or the grinding chamber 5, ensuring that the material to be ground M is already mixed with at least one surfactant additive before entering the grinding chamber 5 and thus the product fluid bed 6. The mixture of material to be ground M and surfactant additive is then captured and treated by the grinding gas or steam jets 8.

[0028] The feed devices 14b open separately into the mill housing 4 and the grinding chamber 5, respectively, so that at least one surface-active additive can be directed into the product fluid bed 6 consisting of the ground material and operating fluid. The feed devices 14b do not necessarily have to open into the grinding chamber 5 and thus the product fluid bed 6 only in the lower region of the mill housing 4. Depending on the operating conditions and the materials / substances involved, the feed devices 14b can alternatively or additionally open above the product fluid bed 6, up to and including the classifier wheel 9.

[0029] The feed devices 14c ultimately open into the operating material feed devices 13 or together with these into the grinding chamber 5, so that in any case the operating material is mixed with the at least one surface-active additive or the latter is transported / carried along. An inlet opening 15 for the at least one additive in the mill housing 4 is accordingly arranged in close proximity to an operating material nozzle 7 for the operating material. In particular, it can be provided that the operating material feed devices 13 contain at least one operating material nozzle 7 which surrounds a central one in an annular manner, as shown in the separate enlarged and partially sectional view in the Fig. 3This is further clarified. The combination of the operating fluid nozzle 7 with an inlet opening 15 for the additive, realized as a so-called I-nozzle, is particularly preferred. Regarding the design and function of I-nozzles, reference is made here to DE 195 13 035 A1 to avoid mere repetition.

[0030] The operation of such a jet mill 1 with an integrated dynamic air classifier 10 with various process variants is described below.

[0031] Particles are fed into the grinding chamber 5 of the jet mill 1 and ground there into fine particles. Superheated steam or technical gases, such as helium or hydrogen, are used as operating media. Furthermore, at least one surfactant additive is added to the grinding material to stabilize the resulting fine particles.

[0032] The feed of the material to be ground can be like this, that at least one additive for stabilizing the fine particles produced is mixed with the material being ground before grinding, that at least one additive for stabilizing the fine particles produced is introduced directly into the grinding chamber, and / or that at least one additive for stabilizing the fine particles produced is supplied to the jet mill together with the operating medium.

[0033] If technical gases, such as He or H2, are used as operating materials, their inlet temperature should preferably be at least 50°C.

[0034] If superheated steam is used as the operating medium, it is preferred if it has an inlet temperature of at least such a degree that it is dry after passing through the jet mill.

[0035] Preferably, at least one surface-active additive is used to stabilize the generated fine particles: Stearic acid for hydrophobic stabilization, or diols, polyols or other long-chain alcohols for hydrophilic stabilization.

[0036] However, at least one surface-active additive can be used to stabilize the generated fine particles and can also be advantageously employed: Silanes, and / or condensates of naphthalenesulfonic acid or phenolsulfonic acid.

[0037] Furthermore, the additive addition amounts to approximately 0.1% to about 4% of the material mass throughput of the jet mill 1. A second embodiment of the jet mill 1 in the form of a dense bed jet mill is described in the Fig. 2shown in a schematic sectional view. Since the additive feed does not depend on design-specific features of the fluidized bed jet mill and the dense bed jet mill, the above information on both the components and functions of the fluidized bed jet mill can be transferred to the dense bed jet mill, particularly with reference to the reference numerals, without the need for a repetition of the above explanations or separate descriptions, with the exception, of course, of the product fluidized bed 6 in the design of the Fig. 1 The dense bed jet mill accordingly contains a product fluid bed. Regarding the design and function of dense bed jet mills, reference is made here to DE 44 31 534 A1 to avoid mere repetition.

[0038] The effect of using at least one surfactant additive is explained in more detail below. During milling, surfactants adhere to the fresh fracture surfaces of particle fragments in an ideally monomolecular layer, creating a boundary layer on their surfaces. This boundary layer, due to similar polarity on these surfaces, effectively prevents reagglomeration. Depending on the intended use of the milled materials, hydrophobic or hydrophilic systems can be employed. The type of "ideal" additive can also be determined based on the material being milled and its composition. For example, long-chain alcohols have proven effective in tests with metal oxides, carbonates, hydroxides, and nitrides, whereas condensates of naphthalenic or phenolsulfonic acid have shown greater efficacy with carbon compounds.

[0039] The additive can be introduced in a variety of ways; however, addition via the milled material or with the milling steam / gas has proven particularly effective. These two methods of additive introduction result in the most even distribution of the additive within the milled material. Experimental results:

[0040] I. For example, when grinding a yellow pigment on a Netzsch-Condux s-Jet 500 steam jet mill, a reduction in specific energy consumption by a factor of 2.6 was achieved with otherwise identical parameters (milling steam pressure, temperature, classifier speed, steam mass flow) while simultaneously producing a finer end product: without additive with additive (approx. 0.5%) specific adiabatic energy demand [kWh / kg] 11,40 4,40 d 99 [µm] 0,36 0,29 d 50 [µm] 0,13 0,13 II. The effect was even more pronounced when grinding a blue pigment. The reduction in specific energy consumption reached a factor of 3.3, resulting in a significantly finer final product. without additive with additive (approx. 0.5%) specific adiabatic energy demand [kWh / kg] 6,14 1,87 d 99 [µm] 1,10 0,61 d 50 [µm] 0,42 0,20 III. Finally, the third example illustrates a somewhat coarser grinding of a magnesium compound. This still resulted in a reduction of energy consumption by a factor of 1.9 while maintaining virtually the same fineness. without additive with additive (approx. 0.5%) specific adiabatic energy demand [kWh / kg] 0,53 0,28 d 99 [µm] 6,70 6,50 d 50 [µm] 1,80 1,90

[0041] The invention is illustrated by way of example in the description and in the drawing and is not limited to these embodiments, but includes all variations, modifications, substitutions and combinations that the person skilled in the art can derive from the present documents within the scope of the claims. Reference symbol list

[0042] 1 Jet mill 2 Feed gate 3 Material feed devices 4 Mill housing 5 Grinding chamber 6 Product fluid bed 7 Operating fluid nozzles 8 Grinding gas or steam jets 9 Classifier wheel 10 Dynamic air classifier 11 Belt drive 12 Variable speed motor 13 Operating fluid feed devices 14a Additive feed devices before material entry 14b Additive feed devices separately in mill housing 14c Additive feed devices in operating fluid 15 Material inlet

Claims

1. A method for operating a jet mill (1) with an integrated dynamic air classifier (10), wherein particles are fed into a grinding chamber (5) of the jet mill (1) as material to be ground (M) and are ground there into fine particles by using superheated steam or technical gases (He, H2) as operating medium, wherein at least one surface-active additive to stabilize the fine particles produced is added to the material to be ground (M), characterized in that the additive addition is approximately 0.1 % to approximately 4 % of the material mass throughput of the jet mill (1).

2. The method according to claim 1, characterized in that the at least one additive for stabilizing the fine particles produced is mixed with the material to be ground (M) before grinding.

3. The method according to claim 1 or 2, characterized in that the at least one additive for stabilizing the fine particles produced is introduced directly into the grinding chamber (5).

4. The method according to any one of the preceding claims, characterized in that the at least one additive for stabilizing the fine particles produced is supplied to the jet mill (1) together with the operating medium.

5. The method according to any one of the preceding claims, characterized in that the operating medium contains technical gases (He, H2) and has an entry temperature of at least 50°C.

6. The method according to any one of claims 1 to 4, characterized in that the operating medium is superheated steam having at least such an entry temperature, such that it is dry after the jet mill (1).

7. The method according to any one of the preceding claims, characterized in that the at least one surface-active additive for stabilizing the fine particles produced contains: - stearic acid for hydrophobic stabilization, or - diols, polyols, or other long-chain alcohols for hydrophilic stabilization.

8. The method according to any one of the preceding claims, characterized in that the at least one surface-active additive for stabilizing the fine particles produced contains: - silanes, and / or - condensates of naphthalenesulfonic acid or phenolsulfonic acid.

9. The method according to any one of the preceding claims, characterized in that the operating medium is supplied via operating medium supply means (13) with at least one operating medium nozzle (7) that annularly surrounds a central inlet opening (15) for the at least one additive.

10. The method of claim 9, characterized in that the at least one operating medium nozzle (7) is an I-nozzle.

11. The method of any one of the preceding claims, characterized in that the jet mill is a fluidized bed jet mill.

12. The method of any one of claims 1 to 10, characterized in that the jet mill is a high-density bed jet mill.