SPIRAL JET MILL AND METHOD FOR GRINDING MATERIALS TO BE GROUND IN A SPIRAL JET MILL

Abstract

The invention relates to a spiral jet mill (1) having a grinding chamber (10), which is delimited by a bottom (11), a cover (12), and a wall (13) that connects the bottom (11) and the cover (12), and having a plurality of grinding gas nozzles (14) that pass through the wall (13) and are connected to a grinding gas source, wherein each of at least part of the grinding gas nozzles (14) is provided with an associated switchable shut-off mechanism (15), which is able to independently open and close the connection to the grinding gas source. In addition, a method for grinding milling materials in a spiral jet mill is also disclosed.

Claims

1. A spiral jet mill having a grinding chamber, which is delimited by a bottom, a cover, and a wall that connects the bottom and the cover, and having a plurality of grinding gas nozzles that pass through the wall and are connected to a grinding gas source, characterized in that comprising each of at least part of the grinding gas nozzles is provided with an associated switchable shut-off mechanism, which is able to independently open and close the connection to the grinding gas source.

2. The spiral jet mill according to claim 1, wherein each grinding gas nozzle is provided with an associated switchable shut-off mechanism.

3. The spiral jet mill according to claim 1, wherein the grinding gas source communicates with the grinding gas nozzles by supply lines that each lead to a respective grinding gas nozzle, wherein the switchable shut-off mechanism is provided in the supply lines.

4. The spiral jet mill according to claim 3, wherein 3 to 40 grinding gas nozzles are provided.

5. The spiral jet mill according to claim 1, wherein the grinding gas nozzles are embodied as de Laval nozzles.

6. The spiral jet mill according to claim 5, wherein a control unit is provided for independently triggering the shut-off mechanisms.

7. The spiral jet mill according to claim 6, wherein the wall is embodied as cylindrical.

8. The spiral jet mill according to claim 7, wherein an inlet opening for supplying the milling material into the grinding chamber and a discharge opening for discharging the milling material that has been is ground in the grinding chamber are embodied in the cover.

9. A method for grinding milling materials in a spiral jet mill, wherein the spiral jet mill has a grinding chamber, which is delimited by a bottom, a cover, and a wall and into which the milling material is introduced and acted on by a grinding gas flow from a plurality of grinding gas nozzles that pass through the wall, wherein the grinding gas flow is regulated by varying the number of grinding gas nozzles that are acted on with the grinding gas flow.

10. The method according to claim 9, wherein grinding gas nozzles are opened and acted on by the grinding gas flow or closed and disconnected from the grinding gas flow separately and independently from the other grinding gas nozzles.

11. The method according to claim 10, wherein in order to regulate the grinding gas flow, the flow of grinding gas into the grinding chamber per unit time is varied by changing the number of grinding gas nozzles that are acted on with the grinding gas flow.

12. The method according to claim 11, wherein viewed in the direction around the circumference of the wall, a regular sequence of grinding gas nozzles are opened or closed in alternating fashion.

13. The method according to claim 11, wherein viewed in the direction around the circumference of the wall, a number of grinding gas nozzles adjacent to one another in sequence are closed or opened.

14. The method according to claim 13, wherein the grinding gas nozzles are opened or closed during the time that the grinding chamber is being acted on with the grinding gas flow.

15. The method according to claim 14, wherein the grinding gas flow from the grinding gas nozzles is introduced into the grinding chamber at supersonic speed.

16. The method according to claim 15, wherein the opening or closing of the grinding gas nozzles is varied as a function of the desired grain size of the milling material, the hardness of the milling material, and/or the pressure in the grinding chamber.

17. The spiral jet mill according to claim 1, wherein the grinding gas source communicates with the grinding gas nozzles by supply lines that each lead to a respective grinding gas nozzle, wherein the switchable shut-off mechanism is provided in the supply lines.

18. The spiral jet mill according to claim 1, wherein 3 to 40 grinding gas nozzles are provided.

19. The spiral jet mill according to claim 1, wherein the grinding gas nozzles are embodied as de Laval nozzles.

20. The spiral jet mill according to claim 1, wherein a control unit is provided for independently triggering the shut-off mechanisms.

21. The spiral jet mill according to claim 1, wherein the wall is embodied as cylindrical.

22. The spiral jet mill according to claim 1, wherein an inlet opening for supplying the milling material into the grinding chamber and a discharge opening for discharging the milling material that is ground in the grinding chamber are embodied in the cover.

23. The method according to claim 9, wherein in order to regulate the grinding gas flow, the flow of grinding gas into the grinding chamber per unit time is varied by changing the number of grinding gas nozzles that are acted on with the grinding gas flow.

24. The method according to claim 9, wherein viewed in the direction around the circumference of the wall, a regular sequence of grinding gas nozzles are opened or closed in alternating fashion.

25. The method according to claim 9, wherein viewed in the direction around the circumference of the wall, a number of grinding gas nozzles adjacent to one another in sequence are closed or opened.

26. The method according to claim 9, wherein the grinding gas nozzles are opened or closed during the time that the grinding chamber is being acted on with the grinding gas flow.

27. The method according to claim 9, wherein the grinding gas flow from the grinding gas nozzles is introduced into the grinding chamber at supersonic speed.

28. The method according to claim 9, wherein the opening or closing of the grinding gas nozzles is varied as a function of the desired grain size of the milling material, the hardness of the milling material, and/or the pressure in the grinding chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other embodiments and details of this invention will be explained below based on the drawings, which show an exemplary embodiment, wherein:

[0035] FIG. 1 shows a schematic depiction of a view of a spiral jet mill according to this invention;

[0036] FIG. 2 is an enlarged depiction showing a section taken through the spiral jet mill according to FIG. 1; and

[0037] FIG. 3 is another enlarged depiction showing a milling material supply of the spiral jet mill according to this invention shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The figures show a simplified schematic depiction of a spiral jet mill 1 for grinding milling materials of the kind that is used, for example, in the pharmaceutical, special chemical, and fine chemical industry, for example, for grinding particulate solids.

[0039] In this context, particulate solids are understood to include, for example, iron oxides, in particular ?-, ?-, ?- and/or ?-FeOOH phases and/or Fe(OH)2 phases, ferrihydrite phases as well as mixed and intermediate phases thereof, particularly preferably hematite, the modification ? Fe2O3, ?-Fe2O3 maghemite, magnetite, manganese- or zinc ferrites, titanium dioxides such as in the rutile or anatase modification or as rutile mixed-phase pigments, chromium oxides, zinc oxides, zinc sulfides, ultramarine, nickel or chromium antimony titanium dioxides, cobalt blue, cobalt green, chromium oxides, or carbon forms such as carbon black, graphite, or graphene. Inorganic pigments from the above-mentioned group are mentioned as being particularly preferable.

[0040] The spiral jet mill 1 comprises a circular cylindrical, closed grinding chamber 10, which is delimited by a bottom 11, a cover 12 that is spaced apart from the bottom 11, and a wall 13 that connects the bottom 11 and the cover 12. The wall 13 thus likewise has a circular cylindrical embodiment. Through a corresponding arching of the bottom 11 and/or cover 12, the grinding chamber 10 can also have a lenticular shape.

[0041] The wall 13 is penetrated by a number of grinding gas nozzles 14, a total of four in the example shown here, which feed into the grinding chamber 10 at a predetermined entry angle that is roughly tangential.

[0042] Via or by supply lines 16 that are merely indicated, the grinding gas nozzles 14 communicate with a grinding gas source that is not shown, for example, a compressor, and are acted on with a corresponding grinding gas flow from it, for example compressed air. Via or by the grinding gas nozzles, the grinding gas travels roughly tangentially into the grinding chamber 10 and in the exemplary embodiment shown, produces a spiral-shaped counter-clockwise grinding gas flow inside the grinding chamber 10.

[0043] Via or by an inlet opening 120, which is positioned off-center in the region of or near the cover 12 and is shown in greater detail in FIG. 3, the milling material is supplied via or by a funnel 121 from a corresponding storage receptacle and by a gas flow emitted by an injector nozzle 122, is accelerated in an injector tube 123 and introduced into the grinding chamber 10. In this chamber, the milling material is captured and entrained by the grinding gas flow that rotates in a spiral shape, wherein the acceleration forces and collisions of the individual pieces of the milling material bring about the desired comminution and grinding of the milling material. Once the milling material falls below a desired grain size, it collects in the central region of the grinding chamber 10 due to the decreasing centrifugal forces in the spiral flow and from there, is discharged from the spiral jet mill 1 together with the calmed grinding gas via a central discharge opening 125 likewise provided in the cover 12, possibly with the use of filters or cyclones that are not shown here.

[0044] An essential feature for the spiral jet mill shown is that in order to regulate the grinding procedure inside the grinding chamber 10, each individual grinding gas nozzle 14, in the region of or near its supply line 16 for the grinding gas, is provided with a separately and independently controllable shut-off mechanism 15, and these make it possible to act on any one of the individual grinding gas nozzles 14 with the grinding gas flow and correspondingly activate it or to disconnect it from the grinding gas flow and correspondingly deactivate it. As soon as a shut-off mechanism 15 is opened, the corresponding grinding gas nozzle 14 is acted on with the grinding gas of the grinding gas source and conversely, is disconnected from the grinding gas as soon as the associated shut-off mechanism 15 is closed. The shut-off mechanisms 15 can, for example, be embodied by shut-off valves that can be switched between an open and closed position.

[0045] In this way, a constantly high operating pressure of the grinding gas from the grinding gas source can be applied in all of the supply lines 16 and, by opening individual shut-off mechanisms 15 or all of them, a corresponding number of associated grinding gas nozzles 14 can be activated from which the grinding gas flow then travels into the grinding chamber 10 at a constant pressure and a correspondingly constant maximum speed.

[0046] Such a switching on and off of individual grinding gas nozzles 14 can be used to adjust the comminution action and intensity of the spiral jet mill 1 by changing the total grinding gas flow into the grinding chamber 10 without reducing the discharge speed of the grinding gas into the grinding chamber 10. This results in one most efficient possible utilization of the grinding gas and a significantly more energy-efficient operation of the spiral jet mill 1.

[0047] The number of open and closed shut-off mechanisms 15 and associated grinding gas nozzles 14 can be selectively changed before and during the operation of the spiral jet mill. In the exemplary embodiment shown, for example, every other grinding gas nozzle 14 can be acted on with the grinding gas flow by opening the associated shut-off mechanisms 15. It is also possible, however, for only one individual grinding gas nozzle 14 to be opened or for three adjacent grinding gas nozzles 14 or all of the grinding gas nozzles 14 to be opened. The same is true for spiral jet mills 1 with a larger or smaller number of grinding gas nozzles, with numbers ranging from 3 to 40 such grinding gas nozzles 10 being considered as suitable in the context of this invention. The respective currently desired actuation of the individual shut-off mechanisms 15 can advantageously be carried out by a corresponding control unit, for example, in accordance with an electronic system control.

[0048] In comparison to embodiments of spiral jet mills that were used previously, the depicted embodiment of a spiral jet mill 1 has modifications only in the region of or near the supply of the grinding gas to the individual grinding gas nozzles 14 in that each individual grinding gas nozzle 14 is equipped with a separate supply line 16 in which an independently switchable shut-off mechanism 15 is provided. Previously customary pre-distributors and pressure regulating devices for the supplied grinding gas, however, can be eliminated.

[0049] In comparison to the previously used pressure regulation of the grinding gas in order to control the flow of the grinding gas into the grinding chamber 10, the embodiment explained above achieves an ideally constant high pressure at the inlet of the grinding gas nozzles. This makes it possible to embody the grinding gas nozzles not only as cylindrical or conical, but also in the form of de Laval nozzles. Through the above-explained switching on and off of individual grinding gas nozzles, possibly with an adaptation of the milling material discharge flow, it is possible to adapt the pressure in the grinding chamber 10, but a constantly high pressure is always present at the open grinding gas nozzles. The individual open grinding gas nozzles can thus always be operated in the vicinity of or near the optimal operating point, which particularly when embodied as de Laval nozzles, ensures an energy-efficient operation since extremely high exit speeds of the grinding gas of up to several times the speed of sound with a low jet divergence can be achieved. This is reflected in a much more energy-efficient grinding action.

[0050] Energy losses that do not contribute to the comminution and are due to compression impacts or large jet divergences due to the operation of grinding gas nozzles 14 embodied as de Laval nozzles above or below the optimal operating point can be reliably avoided by keeping the grinding gas pressure and the pressure inside the grinding chamber 10 constant.

[0051] Even when, for example, cylindrical grinding gas nozzles 14 are used, the exit speed of the grinding gas into the grinding chamber 10 can be increased up to the speed of sound by limiting the number of active and open grinding gas nozzles 14 with a predetermined flow of milling material, which likewise enables an energy-efficient grinding.

[0052] A conventional flow limiting by regulating the pressure of the grinding gas also inevitably reduces the pressure of the grinding gas that is present at the grinding gas nozzles, which is accompanied by a corresponding reduction in the speed of the grinding gas flow discharged from the grinding gas nozzles and negatively affects the energy balance. With the above-explained regulation of the flow by reducing the number of available grinding gas nozzles 14 that are acted on with the grinding gas flow, the flow of the grinding gas is likewise reduced to the desired degree, but the maximum pressure is still present at the open grinding gas nozzles 14, which means that the maximum flow speed of the discharged grinding gas is also still achieved without any change. This achieves a powerful improvement of the previously inevitable energy-inefficient operation of the spiral jet mill.

[0053] The spiral jet mill explained above and the method can be achieved not only in newly constructed spiral jet mills, but also as part of a comparatively simple retrofit of already existing spiral jet mills according to the prior art.

[0054] While in the foregoing specification this invention has been described in relation to certain preferred embodiments, and many details are set forth for purpose of illustration, it will be apparent to those skilled in the art that this invention is susceptible to additional embodiments and that certain of the details described in this specification and in the claims can be varied considerably without departing from the basic principles of this invention.