Roller grinding mill
Patent Information
- Application Number
- EP2023767828
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-01
- Publication Date
- 2025-11-12
Smart Images
Figure EP2023074025_06032025_PF_FP_ABST
Abstract
Description
[0001] roller mill
[0002] The invention relates to a roller mill with a rotating grinding bowl, wherein the grinding bowl has a grinding bowl rim. Grinding rollers or grinding bodies roll on the grinding bowl. These are preferably arranged stationary to the grinding bowl but rotatable. Furthermore, a grinding chamber wall is provided which surrounds the grinding bowl at least at the level of the grinding bowl rim. It can also enclose the entire roller mill. Between the grinding chamber wall and the grinding bowl rim there is a free space which is fluidically connected to a process air supply so that during operation of the roller mill a process air stream flows upwards through the free space. The free space can be considered not only the area between the grinding bowl rim and the grinding chamber wall but also the area between the grinding bowl, in particular its side, and the grinding chamber wall.
[0003] Roller mills are used to crush various materials. One main area of application is the crushing of fuels such as coal or coke, and the crushing of cement clinker. They are also used for processing rock for ore extraction. The material to be ground is fed onto the rotating grinding bowl. The rotation conveys the material to be ground, which is fed centrally onto the grinding bowl, outwards towards the edge of the grinding bowl. On its way there, it is transported under the stationary grinding rollers, which rotate on their own axis, where it is crushed. The at least partially crushed material to be ground is then thrown over the edge of the grinding bowl into the free space and, during operation, is carried upwards by the process air stream, which is provided from below the mill and flows against gravity.Above the grinding bowl, also called the grinding table, a sifter is often provided, in which the at least partially ground material is separated into coarse and fine particles. The combination of the process air flow, which carries the particles that have fallen over the edge of the grinding bowl upwards, with these particles can also be referred to as a dust / air mixture. On their way up to the sifter, the coarsest particles of the dust / air mixture rain down over the grinding bowl, while the finer part of the coarse fraction and the finished product are pneumatically transported to the dynamic sifter.
[0004] The fine material is removed from the grinding process, whereas the coarse material is usually returned to the grinding bowl for further grinding.
[0005] The blade ring plays a key role in determining the required process air flow, product throughput, and energy efficiency of the mill. Located below the free space, it directs, guides, and influences the process gas flow.
[0006] The gas flow entering the mill interior through the blade ring should be suitable in terms of its momentum and orientation to lift and mix a large mass flow of ground material and prevent too much material from falling in countercurrent into the annular channel which serves to supply the process air flow.
[0007] The development of the appropriate blade ring geometry took place over a long period of iterative testing with incremental improvements. Nevertheless, the blade ring geometry used in the current state of the art is still subject to intensive optimization during commissioning when setting up a roller mill. For example, if the reject rate is too high, the commissioning engineer must either adversely increase the mill's gas flow or completely or partially cover individual blade ring segments with sheets aligned orthogonally to the flow direction. Both measures significantly increase the energy requirements of the mill blower and can weaken performance guarantees and competitiveness.
[0008] The invention is therefore based on the object of providing a roller mill which can be operated efficiently.
[0009] This object is achieved according to the invention by a roller mill having the features of claim 1.
[0010] Preferred embodiments of the invention are specified in the subclaims, the description and in the figures and their explanation.
[0011] The roller mill according to the invention is further developed in that mixing bodies are arranged in the free space for generating, in particular, stationary, air vortices of the process air flowing through the free space. The mixing bodies have a substantially flat main body. They are arranged at an angle of inclination of at least 15° and at most 60° to the flow direction of the process air flow during operation, with more than 90% of the mixing bodies' bodies being located below the grinding bowl edge. Furthermore, the mixing bodies are arranged and designed in the free space such that at least 66% of the circumference of the mixing bodies can be freely flowed around by the process air flow during operation. In other words, this means that the mixing bodies are attached to the grinding bowl, for example, with a maximum of 34% of their circumference.
[0012] The invention is based on the finding that it is advantageous to deviate from the known blade ring design and geometry. As described, it has previously been assumed that it is advantageous for the process air flow to flow as evenly and as directed as possible from below the grinding bowl upwards toward the optionally provided separator.
[0013] According to the invention, this concept is fundamentally deviated from.
[0014] According to the invention, mixing bodies are arranged in the free space between the grinding chamber wall and the grinding bowl edge, as well as in the free space below. The mixing bodies are designed and arranged in such a way that they actively generate air vortices in the process air flow. In other words, this represents a fundamental departure from the previous concept of guided and uniform air flow. The invention recognized that this can be achieved particularly with essentially flat mixing bodies, which are arranged at an angle of inclination between 15° and a maximum of 60° to the flow direction of the process air flow. In principle, the mixing bodies can be placed anywhere. The angle of inclination is preferably between 25° and 45°, ideally around 35° to the local flow direction of the process gas.
[0015] The purpose of the air vortexes generated by the mixing elements is to transport the material to be ground, which flows or falls from the edge of the grinding bowl into the free space, upwards toward the outlet of the roller mill and / or the designated classifier, while simultaneously separating, i.e., dispersing, the particles of the material to be ground. In contrast to traditional directed, low-turbulence air flows, the air vortexes offer the advantage of separating the material that has fallen over the grinding bowl into particles, enabling efficient static or dynamic classifying above the grinding bowl.
[0016] A further advantage is that since roller mills are also used for grinding and drying, the warm or hot process air can reach the particles particularly well due to the separation of the particles, thus ensuring efficient drying.
[0017] According to the invention, it was recognized that it is advantageous if the mixing bodies for generating the, in particular stationary, air vortices are inclined against the flow direction of the process air stream and are located below or largely below the grinding bowl rim. This results in air vortices that arise at the edges of the mixing bodies continuing and increasing in the flow direction. Since the mixing bodies are inclined downwards against the flow direction, the largest air vortices tend to be present where the ground material runs over the grinding bowl rim. This means that the air vortices absorb the ground material particularly well and disperse it significantly more efficiently. The air vortices also detach themselves from the mixing bodies and continue to propagate into free space.
[0018] A key aspect of the invention was recognized that air vortices arise particularly at the edges of the mixing bodies. Therefore, these are preferably arranged in the free space so that at least 66% of the circumference of the mixing bodies is freely accessible to the process air flow. It has been shown that, while an arrangement with only 50% or less is in principle possible, this creates significantly smaller and less stable air vortices compared to the preferred 66%.
[0019] In principle, the mixing bodies can be arranged anywhere in the space between the grinding bowl and the grinding chamber. However, it is preferred if the mixing bodies are arranged at an angle toward the grinding chamber wall. It has been found that this preferentially creates air vortices that become larger the further they are removed from the grinding chamber wall. Since the largest and most intense air vortices are desirably located at the point where the material to be ground leaves the grinding bowl, namely at the edge of the grinding bowl, such an arrangement is advantageous for achieving the advantages of the invention.
[0020] In principle, the mixing bodies can be designed and shaped as desired. However, it has been shown that the air vortices generated by the mixing bodies are larger and more stable if the mixing bodies are arranged and designed in such a way that the surface area of the mixing bodies widens, at least in sections, in the direction of flow of the process air stream. In other words, the mixing bodies can be dimensioned and arranged in the space between the grinding bowl and the grinding chamber wall in such a way that they have a smaller cross-section at their lowest point than at a higher point. This means, for example, that they are arranged diagonally downwards in this space and widen upwards towards the classifier or the grinding chamber.According to the invention, the term "deep" in this sense can be understood to mean that this region is located closer to the source of the process air flow than a region referred to as higher. This also takes into account the fact that, as already explained, the process air flow essentially runs against gravity.
[0021] Possible shapes for the mixing elements include a triangular shape, an oval shape, a round shape, or even a polygonal shape. In principle, the mixing elements don't all have to have the same shape; they can also have different shapes. However, it's also possible to use only the same shape for each element to simplify tuning.
[0022] Advantageously, in the case of a square mixing body, for example, a triangular, pentagonal, or square shape, the mixing body's deepest corner has an interior angle between 10° and 90°, preferably around 30°. It has been shown that the formation of vortices, which serve to transport and disperse the particles falling over the grinding bowl, is particularly pronounced at such interior angles of the corners or edges.
[0023] As explained, the mixing elements can, in principle, be arranged anywhere in the space between the grinding bowl and the grinding chamber wall, including in the free space. However, good results have been achieved by arranging the mixing elements so that they extend from the edge of the grinding table toward the grinding chamber wall, extending downwards from the edge of the grinding table against the flow direction of the process air flow. In other words, the mixing elements can be arranged so that they extend downwards against the process air flow, viewed from the edge of the grinding table. In this case, their cross-section or diameter should be smaller further down than in the area of the edge of the grinding table.
[0024] It is preferred if the highest point of the mixing bodies in the flow direction of the process air stream is arranged substantially at the level of the retention edge. Such an arrangement allows the largest and most stable air vortices to form where the mixing bodies are present at the grinding table edge and the particles leave the grinding table. This, in turn, supports the advantageous properties of the arrangement according to the invention, such as the good dispersion and cloud-like transport of the individual particles toward the classifier and / or mill outlet.
[0025] In principle, however, it is also possible that at least one area of the mixing bodies is located above the edge of the grinding table.
[0026] The grinding table edge is often a retention edge, which ensures that a certain grinding bed height is maintained on the grinding bowl. In this case, the invention equates the grinding table edge with the retention edge. It is important to note that reference is made to the edge from which the material to be ground, after partial comminution by the grinding rollers, falls due to centrifugal forces, or from which the material to be ground is thrown horizontally.
[0027] There are basically no restrictions on the exact arrangement of the mixing elements. They can be designed to rotate with the grinding table, meaning they can be attached directly to the grinding table, for example.
[0028] It is also possible for them to be fixed relative to the rotating grinding table. For example, they can be attached to the grinding chamber wall, the mill housing, or a corresponding support structure.
[0029] In a preferred embodiment, the clear width between the point of a mixing body that is closest to the grinding chamber wall and the grinding chamber wall is between 0%, preferably 5%, and 30% of the clear width between the grinding table and the grinding chamber wall at this point. In other words, it is preferred if the mixing bodies do not extend as far as the grinding chamber wall. How far they can extend in the direction of the grinding chamber wall depends on the clear width between the grinding table and the grinding chamber wall. It has been shown that, in order to generate the flow vortices, it is advantageous if the process air flow in the region of the grinding chamber wall is not yet influenced by the mixing bodies. For example, with a grinding table diameter of approximately 6 m and a grinding chamber diameter of approximately 8 m, a distance of approximately 0.1 m between the grinding chamber wall and the beginning of a mixing body is preferred.
[0030] Preferably, the mixing bodies are arranged such that a projected area of the mixing bodies, which lies on a virtual plane perpendicular to the flow direction of the process air flow during operation of the free space, occupies between 25% and 55% of this plane. The plane is arranged such that it touches the lowest point of the lowest mixing body. In other words, the mixing bodies arranged obliquely in the free space only occupy 25% to 55% of the flow cross-section of this free space when projected onto a corresponding plane. This means that a large part of the free space or plane is not occupied by the mixing bodies. This is necessary to allow sufficient air flow so that the desired process air flow vortices can arise at the edges of the flow or mixing bodies. In general, the mixing bodies can be subjected to any desired flow of process air flow.A particularly good formation of the airflow vortex is achieved when a flow straightener is arranged at the same height as or below the mixing elements to generate a guided and essentially directed airflow. This results in the mixing elements being approached by a correspondingly guided, low-turbulence flow, allowing the desired vortex to be formed particularly well.
[0031] As already explained, the mixing bodies can be designed and shaped as desired. They can be either different or uniform. A uniform design of the mixing bodies offers the advantage of making it easier to optimize the air vortices.
[0032] It is also advantageous if the mixing elements are spaced apart from each other so that the air vortices created by two adjacent mixing elements do not influence each other. This means, for example, that, depending on the grinding bowl diameter, a distance of at least 5 cm to 15 cm is provided between the closest point of two adjacent mixing elements. In other words, the distance can be 2% to 10% of the side or width of the mixing element located at the dam edge.
[0033] Particularly good results were achieved when the mixing elements were arranged completely below the grinding bowl rim or, if present, the retaining rim. It has been shown that the vortices are relatively stable, so it is sufficient if the mixing elements end slightly below the grinding bowl rim or retaining rim, and only the corresponding air vortices extend upward in the direction of flow away from the mixing elements to the grinding bowl rim or retaining rim.
[0034] The invention is explained in more detail below using schematic embodiments with reference to the figures. The drawings show:
[0035] Fig. 1 is a schematic view of a roller mill according to the invention with an integrated classifier; Fig. 2 is a perspective partial view of a grinding bowl with mixing bodies;
[0036] Fig. 3 shows a partial cross-section through a roller mill according to the invention at the level of the grinding bowl;
[0037] Fig. 3a is a simplified sectional view along line AA of Fig. 3;
[0038] Fig. 3b is a simplified view along line BB of Fig. 3;
[0039] Fig. 4 is a highly schematic drawing of a mixing body according to the invention; and
[0040] Fig. 5 various possible shapes of mixing bodies according to the invention.
[0041] Fig. 1 shows a highly simplified sectional view of a roller mill 1 according to the invention. This mill has a grinding bowl 4, which rotates as indicated. It has a grinding bowl rim 5, which in this embodiment is formed with a retaining rim 6. However, this is not absolutely necessary.
[0042] Stationary grinding rollers 8 are provided on the grinding bowl 4. These rollers can rotate about their axes and can be hydraulically pressed onto the grinding bowl. In the form shown here, only two grinding rollers 8 are shown, but roller mills 1 with three, four, five, or six, and up to eight grinding rollers 8 are now also known.
[0043] Above the grinding bowl 4 there is a dynamic classifier 7, which can also rotate around its indicated axis.
[0044] The roller mill 1 is surrounded by a mill housing 12, with the area at the level of the grinding bowl also being referred to as the grinding chamber wall 13 of the mill housing 12. The grinding chamber wall 13 also extends from below the grinding bowl 4 to the classifier ?. A free space 15 is formed between the mill housing 12 and the grinding chamber wall 13. The mixing bodies 20 according to the invention, which are explained in more detail below, extend from the grinding bowl edge 5 into the free space 15 in the direction of the grinding chamber wall 13. In principle, however, they do not have to be provided extending away from the grinding bowl edge 15 or the retention edge 6. The basic functional principle of a roller mill 1 according to the invention is explained in detail below. Below the grinding bowl 4 is an annular channel 18. During operation, this is supplied with a process air stream 17. This can be hot drying gases or just conveying air.To operate the roller mill 1, the grinding bowl 4 rotates. The material to be ground is fed onto the grinding bowl 4, although the feed is not illustrated here. The rotation of the grinding bowl 4 conveys the material to be ground 31 to the edge of the grinding bowl 5. In doing so, it passes under the grinding rollers 8. For the purposes of the invention, grinding rollers can also be understood as other grinding media geometries, such as spheres.
[0045] A so-called grinding bed of ground material 31 forms. The grinding bed and the rotation of the grinding bowl 4 also cause the grinding rollers 8 to rotate. Essentially, the grinding material 31 is crushed by pressure and shear. Partially crushed ground material 31 and also uncomminuted ground material 31 are thrown over the grinding bowl 4 into the free space 15 by the rotation of the grinding bowl 4. The height of the grinding bed can be influenced based on the height of the retaining edge 6.
[0046] As previously described, a process air stream 17 is blown into the annular channel 18, which flows within the roller mill 1 toward the classifier 7. This air stream carries at least a portion of the material 31 to be ground, which falls over the edge of the grinding bowl 5 and is referred to below as particles, upwards toward the classifier 7.
[0047] Depending on the mass of the particles 32, these either fall back onto the grinding bowl 4 shortly above the grinding rollers 8 or are carried to the classifier 7. A portion of the particles 32 enters the classifier 7, carried by the process air stream 17. Another portion is rejected in advance and falls back onto the grinding bowl 4. In the classifier 7, classification takes place according to particle mass or size, with the particles 32 rejected as coarse material falling back onto the mill bowl 4.
[0048] According to the invention, mixing bodies 20 are provided in the free space 15 above the annular channel 18. These ensure that the process air 17, which is blown into the mill 1 through the annular channel 18, is swirled or creates air vortices. This reduces the formation of swirls, and also allows the particles 32 entrained by the process air to be dispersed and dried particularly effectively. At the same time, gravity screening is also performed. The precise design of the mixing bodies 20 is crucial here.
[0049] Fig. 2 shows a perspective view of an embodiment of mixing bodies 20 with a section of a grinding bowl 4, also referred to as a grinding table. In this embodiment, the mixing bodies 20 have a triangular shape, with the base of the triangle located at the grinding bowl edge 5. They can be rigidly attached to the grinding bowl 4 or to the grinding bowl edge 5, but can also be stationary by means of another device and not rotate with the rotating grinding bowl 4.
[0050] Fig. 3 shows a section through the representation of Fig. 2. It can be seen that the mixing bodies 20, of which only one is visible, extend downwards toward the annular channel 18. They are spaced a distance l from the grinding chamber wall 13. This is advantageous for the invention in order to form the stationary vortexes according to the invention.
[0051] Approximately at the level of the grinding bowl 4, a beaded cladding 19 is provided on the mill housing 13. This cladding serves to deflect the process air flow 17 toward the interior of the mill. This is not absolutely necessary, however. In this embodiment, the beaded cladding 19 ensures that the process air flow 17 does not flow exactly vertically upwards, but is deflected toward the interior of the mill. This means that the angle of inclination a shown here does not correspond to the angle at which the mixing bodies 20 are inclined against the process air flow 17 or extend into it.
[0052] Fig. 3a shows a simplified schematic view along line AA in Fig. 3. It is clear that a distance s exists between the individual mixing bodies 20. This distance is preferred because, should the mixing bodies 20 directly abut one another, the formation of the flow vortices according to the invention can be minimized or disrupted. In the embodiment shown here, the mixing bodies 20, as already described, have a triangular shape with an angle ß at their tip. This angle ß is preferably around 30°.
[0053] For further clarification, Fig. 3b also shows a simple plan view along line BB from Fig. 3, which once again shows the exact geometric arrangement of the mixing bodies 20. This figure particularly shows that the mixing bodies are dimensioned such that they occupy well under 55% of a projection plane, which is designated E in Fig. 3. This is a virtual plane that runs through the lowest tip of a mixing body 20 and is perpendicular to the flow direction 17. It is important here that the projected area of the mixing bodies 20 is dimensioned such that it occupies a maximum of 55% of this area, ideally around 35%. Plane E can also only extend as far as the perpendicular at the outer diameter of the bowl. Thus, the 55% can refer to the projection of the annular gap between the mill housing and the outer diameter of the grinding bowl, as seen from above.
[0054] The following shows in more detail the formation of the flow vortices according to the invention on a mixing body 20 with reference to Fig. 4. For the sake of clarity, a correct perspective was not taken. On the mixing body 20, which extends against the flow direction of the process air stream 17, small air vortices 28 initially form at the tip 22 and propagate along the edge 21, becoming larger. In the area of the grinding bowl rim 5, where the mixing body 20 ends, the air vortices 28 detach from the mixing body 20 and yet, due to their shape, continue to propagate into the interior. They entrain and disperse grinding material particles falling over the grinding bowl rim 5. This occurs particularly through the air vortices 28 in comparison to a purely directed flow, as occurs in conventional roller mills.
[0055] In general, the mixing bodies 20 can have any shape. Fig. 5 shows various shapes of possible mixing bodies 20. The variants of the mixing bodies a) to m) are each planar or completely flat, whereas the mixing bodies n), o), and p) have a spatial structure.
[0056] It is advantageous that they have a predominantly flat shape, which can be formed, for example, by a base body 24 and a bend 25. However, designs with other bends, as shown in Figures n) or p), are also possible. It is essential that the air vortices 28 according to the invention form at the edges and continue along them. These can also be considered essentially flat within the meaning of the invention.
[0057] With the inventive design of the roller mill, it is thus possible to enable more efficient transport to the classifier of particles flowing over the grinding bowl.
Claims
PATENT CLAIMS 1 roller mill (1) with a rotating grinding bowl (4) having a grinding bowl rim (5), with grinding rollers (8) rolling on the grinding bowl (4), with a grinding chamber wall (13) surrounding the grinding bowl (4) at least at the level of the grinding bowl rim, wherein a free space (15) is formed between the grinding chamber wall (13) and the grinding bowl rim (5), which free space is fluidically connected to a process air supply, so that during operation a process air flow (17) flows upwards through the free space (15), characterized in that mixing bodies (20) for generating, in particular stationary, air vortices of the process air are arranged in the free space (15), that the mixing bodies (20) have a substantially flat main body (21), that the mixing bodies (20) are arranged at an angle of inclination of at least 15° and at most 60° to the flow direction of the process air flow (17) during operation are,wherein the mixing bodies (20) are located with more than 90% of their body below the grinding bowl edge (5), and that the mixing bodies (20) are arranged and designed in the free space (15) such that at least 66% of the circumference of the mixing bodies (20) can be freely flowed around by the process air flow (17) during operation.
2. Roller mill (1) according to claim 1, characterized in that the mixing bodies (20) are arranged inclined in the direction of the grinding chamber wall (13).
3. Roller mill (1) according to claim 1 or 2, characterized in that the mixing bodies (20) are arranged and designed such that the surface of the mixing bodies (20) widens at least in sections in the flow direction of the process air flow (17) during operation.
4. Roller mill (1) according to one of claims 1 to 3, characterized in that the mixing bodies (20) have a triangular shape, an oval shape, a round shape or a polygonal shape.
5. Roller mill (1) according to one of claims 1 to 4, characterized in that, in the case of an angular shape of the mixing body (20), the deepest corner of the mixing body (20) has an internal angle (ß) between 10° and 90°, preferably around 30°.
6. Roller mill (1) according to one of claims 1 to 5, characterized in that the mixing bodies (20) are arranged such that they extend from the grinding bowl edge in the direction of the grinding chamber wall (13), whereby they extend from the grinding bowl edge downwards against the flow direction of the process air flow (17) during operation.
7. Roller mill (1) according to one of claims 1 to 6, characterized in that the highest point in the flow direction of the process air flow (17) during operation of the mixing bodies (20) is arranged substantially at the level of the grinding bowl edge.
8. Roller mill (1) according to one of claims 1 to 7, characterized in that the mixing bodies are arranged to rotate with the grinding bowl.
9. Roller mill (1) according to one of claims 1 to 7, characterized in that the mixing bodies (20) are arranged in a fixed manner.
10. Roller mill (1) according to one of claims 1 to 9, characterized in that the clear width between the point of a mixing body (20) which is arranged closest to the grinding chamber wall (13) and the grinding chamber wall is between 0%, preferably 5%, and 30% of the clear width between the grinding bowl edge (5) and the grinding chamber wall (13) at this point.
11. Roller mill (1) according to one of claims 1 to 10, characterized in that a surface of the mixing bodies (20) projected onto a virtual plane (E) which lies at right angles to the flow direction of the process air flow (17) in operation in the free space (15) occupies between 25% and 55% of this plane (E), wherein the plane (E) is arranged such that it touches the lowest point of the lowest mixing body (20).
12. Roller mill (1) according to one of claims 1 to 11, characterized in that a flow straightener for generating a guided, substantially low-turbulence flow is arranged at the same height or below the mixing bodies (20).
13. Roller mill (1) according to one of claims 1 to 12, characterized in that the mixing bodies (20) are of uniform design.
14. Roller mill (1) according to one of claims 1 to 13, characterized in that the mixing bodies (20) are arranged at a distance from one another.
15. Roller mill (1) according to one of claims 1 to 14, characterized in that the mixing bodies (20) are arranged below the dam edge (6) of the grinding bowl edge (5).