Device for sifting granular material

Abstract

An apparatus for separating granular material into at least three fractions a static cross-flow sifter and a dynamic sifter. The static has several impact and flow-conducting elements stepped one below the other in a housing having a first material inlet, at least one sifting-gas inlet and at least one coarse-particle outlet. The dynamic sifter has a rod basket rotatable about a vertical axis, a housing containing the basket, and at least one medium-particle outlet and one fine-particle outlet. The housing of the static sifter merges directly horizontally and laterally into the housing of the dynamic sifter.

Claims

1. An apparatus for separating granular material into at least three fractions and comprising: at least one static cross-flow sifter having several impact and flow-conducting elements stepped one below the other in a housing having a first material inlet, at least one sifting-gas inlet and at least one coarse-particle outlet, and a dynamic sifter having a rotary rod basket and a housing containing the basket and having at iz least one medium-particle outlet and one fine-particle outlet, the housing of the static sifter merging directly horizontally and laterally into the housing of the dynamic sifter, the rod basket of the dynamic sifter being rotatable about a vertical axis.

2. The apparatus according to claim 1, wherein the housing of the static sifter merges with a tangential, spiral, or radial orientation, or an orientation between a radial or tangential orientation into the housing of the dynamic sifter.

3. The apparatus according to claim 1, wherein the housing of the dynamic sifter has an upper housing section holding the rotary rod basket and a lower housing section into which merges the housing of the static sifter.

4. The apparatus according to claim 1, wherein the impact or flow-conducting elements that are angled relative to each other.

5. The apparatus according to claim 4, wherein the angle of impact or flow-conducting elements is adjustable.

6. The apparatus according to claim 1, wherein the impact or flow-conducting elements are formed by roof-shaped structures.

7. The apparatus according to claim 6, wherein the roof-shaped structures can be displaced horizontally.

8. The apparatus according to claim 1, wherein at least one chute wall of the housing of the static sifter is oriented at an acute angle between 10 and 70 relative to the vertical.

9. The apparatus according to claim 1, wherein a sifting zone of the static sifter formed between the impact or flow-conducting elements stepped one above the other is oriented at a preset angle of 10 to 70 relative to the vertical.

10. The apparatus according to claim 1, wherein the sifting-gas inlet is formed by at least one inlet opening that extends at an angle above the elements.

11. The apparatus according to claim 1, wherein the sifting-gas inlet is formed alternately or additionally by a plurality of openings formed in a chute wall of the housing of the static sifter.

12. The apparatus according to claim 1, further comprising: air distributors upstream in the direction of flow of the impact or flow-conducting elements inside the housing of the static sifter.

13. The apparatus according to claim 1, wherein the housing of the dynamic sifter has at least one second material inlet.

14. The apparatus according to claim 1, wherein the housing of the dynamic sifter is cylindrical at least in sections.

15. The apparatus according to claim 1, wherein two or more of the static sifters are laterally connected to the dynamic sifter by one housing.

16. The apparatus according to claim 15, wherein the static sifters are angularly equispaced at 360/n, where n is the number of the static sifters.

17. A grinding mill for the comminution of granular material having at least one first comminuter and the apparatus according to claim 1, wherein material discharged from the first comminuter enters the static sifter through the first material inlet, coarse material discharged via the coarse-particle outlet of the static sifter is fed to the first comminuter, and medium material discharged from the dynamic sifter is fed to the first comminuter or an additional second comminuter.

18. The mill according to claim 17 having a second comminuter, wherein medium material discharged from the dynamic sifter is fed at least partially to the second comminuter, and material discharged from the second comminuter is fed via the second material inlet to the dynamic sifter or to a separate, second air classifier.

19. The mill according to claim 18, wherein the first comminuter is a roll crusher or the second comminuter is a ball mill.

20. An apparatus for separating granular material into at least three fractions and comprising: at least one static cross-flow sifter having a housing having a first material inlet and a sifting-gas inlet, several impact and flow-conducting elements stepped one below the other in the housing below the inlets, and a downwardly opening coarse-particle outlet below the elements; and a dynamic sifter having an upper housing part having a fine-particle outlet, a rotary rod basket rotatable about a vertical axis and contained in the upper housing part, and a lower housing part underneath the upper housing part and having a downwardly opening medium-particle outlet, the housing of the static sifter being level with and merging in a spiral or tangential manner and directly laterally into the lower housing part.

21. The apparatus according to claim 20, wherein the housing of the dynamic sifter is provided with one or several additional air supplies in the upper housing part thereof.

22. The apparatus defined in claim 20, wherein the fine-particle outlet opens upwardly out of the upper housing part flow through the apparatus is from the inlets down through the static filter where coarse particles are separated and fed out through the coarse-particle outlet and medium and fine particles are fed up to the upper housing part whence fine particles are separated and fed upward out of the fine-particle outlet and medium particles are fed downward through the lower housing part to the medium-particle outlet.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be illustrated in further detail based on drawings describing embodiments. Therein:

(2) FIG. 1 is a partial vertical section through an air classifier according to the invention in a simplified view;

(3) FIG. 2 is a top view of a first embodiment of the lower part of the classifier of FIG. 1;

(4) FIG. 3 is a top view of a second embodiment of the lower part of the classifier of FIG. 1;

(5) FIG. 4 is a modified embodiment of the apparatus of FIG. 1 with the lower part in section;

(6) FIG. 5 is a top view of the lower part of the apparatus of FIG. 4; and

(7) FIG. 6 is a schematic view of a dual-stage grinding mill with an air classifier according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(8) The air classifier 1 shown in FIGS. 1 to 5 serves for separating granular material such as, for example, cement into at least three fractions. The apparatus 1 is composed of a static sifter 2 and a dynamic sifter 3 combined in a particularly compact fashion. The static sifter 2 constitutes a first sifting stage; the dynamic sifter 3 is downstream of the static sifter 2 in the direction of sifter medium flow and constitutes a second sifting stage.

(9) The static sifter 2 has a housing 4 having a first material inlet 5, a sifting-gas inlet 6 and a coarse-particle outlet 7. A plurality of impact and conducting elements 8 and 9 are stepped one below the other inside the housing 4. In this embodiment, these elements are impact plates 8 and 9 also acting as flow conductors for the static sifter. FIG. 1 shows that two groups of impact plates 8 and 9 are angled relative to each other, and these impact plates 8 and 9 are adjustable about pivot axes 10 such that the angles of the impact plates 8 and 9 can be adjusted.

(10) The second sifting stage is formed by the dynamic sifter 3 that has a housing 11. This cylindrical housing 11 has a cylindrical upper section 11a and a cylindrical lower section 11b. A rotating rod basket 12 in the upper section 11a of this housing 11 is surrounded by a set of guide vanes 13. These are stationary guide vanes lying at a fixed or adjustable angle of incidence relative to the axis of rotation of the rod basket. The rod basket 12 rotates about a vertical axis 14. A drive mechanism 15 is connected to the upper end of the rod basket 12. A discharge cone 16 connected below the rod basket 12 inside the second housing 11 in turn is connected to a medium-particle outlet 17. A fine-particle outlet 18 is connected to the upper section 11a of the housing 11 and serves to discharge the suspension comprised of gas and fine material. Further material inlets 19 are connected, moreover, to the upper housing part 11a.

(11) The starting material that is to be sifted is fed into the air classifier 1 via the first material inlet 5. The material to be sifted thus reaches the first sifting stage and the static sifter 2 through this material inlet 5. The gas inlet 3 supplies sifting gas such as, for example, air. This can also be, for example, hot drying gas. The material to be sifted now drops onto the array of impact and guide plates 8 and 9 for, in particular, breaking up the scale agglomerate that formed earlier during the grinding step in a roll crusher. The sifter medium flows through the material possibly providing simultaneous drying action. The static sifter operates as a cross-flow air classifier in that the coarse material drops through the housing 2 into the lower discharge cone 20 and is discharged from there via the coarse-particle outlet 7. This discharge cone 20 is structurally connected to the lower section 11b of the housing 11 of the dynamic sifter 3.

(12) The static and the dynamic sifter are connected to each other by a very compact assembly, with the static sifter 2 merging into the dynamic sifter 3. In fact, the static sifter is laterally connected by the housing 4 thereof to the housing 11 of the dynamic sifter. In this embodiment the housing 4 of the static sifter 2 merges into the lower housing section 11b of the housing 11, so that the housing section 11b of the housing 11 can be functionally assigned in some sections, on the one hand, to the static sifter and in some sections, on the other hand, to the dynamic sifter. It also forms the connection between the static sifter and the dynamic sifter, and the cylindrical lower housing section 11b can also act as a cyclone.

(13) At any rate, the fraction that is sifted out in the static sifter 2 enters together with the sifting gas into the dynamic sifter 3, namely the upper section 11a of the housing 11 and therein into the area of the rod basket 12. The desired fine sifting action occurs between this rotating rod basket 12 and the guide vanes 13. The coarser or medium fractions reach via the inner discharge funnel or discharge cone 16 and therefore the medium-particle outlet 17 (granule discharge pipe). This medium fraction is also referred to as granules. The fine material is discharged together with the gases from the sifter through the fine-particle and gas outlet 18. Further material can be directly added to the second sifter stage via the additional material inlets 19. This can be, for example, material that is supplied from an additional comminuter such as, for example, a ball mill. This aspect will be addressed in further detail in the context of the description of FIG. 6.

(14) FIGS. 2 and 3 show that, according to the invention, the static sifter 2 is directly connected to the second housing 11 of the dynamic sifter 3 by a chute-like first housing 4 that extends at an angle relative to the vertical; in this particular embodiment this is achieved by a tangential or spiral-like orientation. FIG. 2 shows an embodiment with a spiral-like connection, while FIG. 3 shows an embodiment with a tangential connection.

(15) In both embodiments two static sifters 2 are connected by respective housings 4 to the housing 11 of the dynamic sifter 3. The dynamic sifter 3 thus receives material in parallel from two static sifters 2. To this end, the two sifters 2 in the embodiment are positioned offset by 180. The direction of rotation of the rod basket can correspond to the orientation of the connection of the tangential or spiral-like input connection or can be opposite thereto.

(16) The embodiment shown in FIGS. 4 and 5 substantially corresponds to the embodiment according to FIGS. 1 and 3. This embodiment differs geometrically by the arrangement and design of the discharge funnel 16 of the dynamic sifter 3 that extends, in the embodiment according to FIGS. 4 and 5, over the entire height of the lower section 11b of the housing 11 and also over the entire height of the housing 4 of the static sifter 2. Aside from this, the embodiments according to FIGS. 1 to 3, on the one hand, and according to FIGS. 4 and 5, on the other hand, differ in terms of the geometric design thereof, particularly in the area of the static sifter and the conducting elements thereof. The basic structural assembly and functionality are identical, though.

(17) The chute-like first housing, which is connected in a tangential or spiral-like orientation to the second housing, is of special significance. The figures demonstrate that this first chute-like first housing 4 or the lower chute wall 21 thereof is oriented angled at a preset angle relative to the vertical. In the embodiment, this angle is approximately 40 to 60, for example approximately 50. Furthermore, the sifter zone of the static sifter, which is created between the conducting plates 8 and 9 arrayed in steps one on above the other, is oriented at a certain angle relative to the vertical. In the embodiment, this angle is approximately 20 to 40, for example 25. According to the invention, this housing 4 that is overall oriented at an angle is connected to the housing of the dynamic sifter in a spiral-like or tangential manner.

(18) The figures show an embodiment where the static sifter, although it is laterally connected to the dynamic sifter, is spatially positioned, however, below the rotating rod basket. Nonetheless, it is also optionally possible to use embodiments where the static sifter is provided (at least in sections) at the same height as the rotating rod basket. This applies with regard to embodiments having a plurality of static sifters.

(19) Otherwise, in the shown embodiments, air is supplied, in particular, via the illustrate sifting-gas inlet 6. Alternately or additionally, it is possible to provide further sifting-gas inlets that are constituted in particular as openings in the chute wall 21. This situation is shown in the figures. It is possible to provide suitable means such as, for example, doors, slides, or the like for opening and blocking such openings, and it is possible to variably adjust such means, thereby varying the volume of air supplied.

(20) The arrangement of the impact plates 8 and 9 is shown only by way of example in the figures. The pivots of the impact plates 8 and 9 do not necessarily have to lie on a common straight line; instead, they can be spaced relative to each other. This can be seen in particular in FIG. 4. However, alternately, it is also within the scope of the present invention that the pivots for the impact or conducting plates are approximately in a straight line, or that they overlay and are thus configured as engaging in each other. However, they can also be configured with intervening spaces as shown in the figures, the spacing being greater in FIG. 4 than in FIG. 1. The vertical spacings between the individual plates do not have to identical; instead, they can vary from plate to plate. Further, the plates can also be connected at different angles.

(21) The multistage sifter 1 according to the invention can be integrated in a single-stage or multistage grinding mill, as shown by way of example in FIG. 6, a modality that is particularly preferred. An exemplary cement grinding mill is shown there. In the center of the figure, the multistage sifter 1 is visible; it is composed of a static sifter 2 and dynamic sifter 3. Shown below the sifter 1 is a first comminuter 22 that is a roll crusher, representing a material bed roll mill 22. Furthermore, also visible is a comminuter 23 that is a ball mill 23.

(22) The shown two-stage grinding mill operates as follows:

(23) The starting material that is to be comminuted is supplied from one or several bunkers 24 such as; for example, via the conveyors 25 and 26, which end in the air classifier 1 at the material inlet 5. The material is here sifted into three fractions as described above. The coarse material that is sifted and discharged via the coarse-particle outlet 7 is returned to the roll crusher 22. From there, the conveyors 27, 25, and 26 transport it to the air classifier 1 once more. The material that is sifted and discharged in the second sifting stage, meaning the middle fraction, is then fed to the ball mill 23 via the conveyors 28.

(24) The grinding mill thus has the roll crusher 22 for pregrinding the material and the ball mill 23 for postgrinding the material. The ball mill 23 is provided, for example, with a material exhaust 29, a dust removal filter 30 and a mill fan 31. The material discharged from the ball mill 23 is therefore fed via the conveyors 29, 32, 33 to the dynamic sifter 3. It there undergoes the second sifter stage once more via the material inlets 19.

(25) The finest fraction is drawn off from the air classifier, specifically the dynamic sifter 3 together with the gases through the fine gas outlet 18 and into the separating cyclones 34 that are downstream. The finished product is separated here from the gases that were drawn off by the fan 35 and in part recirculated into the air classifier 1 and in part or completely to a dust removal modality.

(26) The shown two-stage grinding mill can be modified by an alternate design. Thus, it is possible to place for example the roll crusher 22 above the air classifier 1, unlike in the illustrated design. In this case, the fresh material that is to be ground is first fed to the roll crusher, and from there the preground material is fed into the air classifier according to the invention. Here, the material is separated once more into three fractions in the manner as described above. This embodiment is not shown.

(27) Alternately, it is possible to integrate a second, separate air classifier in the dual-stage grinding mill, so that the discharged material from the ball mill is not fed to the first air classifier as shown in the figures but instead to a separate second air classifier, not shown here. As an alternate option, it is also possible to operate only with a single comminuter such as, for example, the shown roll crusher, which is why the additional ball mill can be omitted. Finally, the finishing milling step occurs in the roll crusher, and the air classifier according to the invention and the roll crusher constitute a simple, single-stage recirculating grinding mill. This aspect is not shown in the drawing. Nevertheless, the multistage sifter according to the invention can be used with equal effectiveness in different types of grinding mills.