Rotary Kiln and Method for Burning Carbonate-Containing Material, in Particular Limestone or Dolomite

Abstract

The present invention relates to a rotary kiln for burning carbonate-containing material, in particular limestone or dolomite, including a rotary tube having an inlet end for feeding in the material to be burned and an outlet end for discharging the burned material; and a calciner unit which is arranged in the region of the outlet end, the rotary tube having an inlet zone at its inlet end and having an outlet zone at its outlet end, with a preheating zone and a burning zone being arranged between the inlet zone and the outlet zone in the transport direction of the material. The rotary kiln is characterized according to the invention in that a plurality of projections are arranged in the preheating zone of the rotary tube, the projections being arranged in groups one behind the other and substantially in parallel with the longitudinal axis of the rotary tube, with projections of adjacent groups of projections that are adjacent in the circumferential direction of the rotary tube being offset relative to one another in the longitudinal direction of the rotary tube such that spiral transport paths for the material to be burned are formed in the preheating zone. The present invention further relates to a method for burning carbonate-containing material, in particular limestone or dolomite.

Claims

1. A rotary kiln for burning carbonate-containing material, in particular limestone or dolomite, comprising a rotary tube having an inlet end for feeding in the material to be burned and an outlet end for discharging the burned material, and a calciner unit which is arranged in the region of the outlet end, the rotary tube having an inlet zone at its inlet end and having an outlet zone at its outlet end, with a preheating zone and a burning zone being arranged between the inlet zone and the outlet zone in the transport direction of the material, wherein a plurality of projections are arranged in the preheating zone of the rotary tube, the projections being arranged as groups one behind the other and substantially in parallel with the longitudinal axis of the rotary tube, with projections of adjacent groups of projections that are adjacent in the circumferential direction of the rotary tube being offset relative to one another in the longitudinal direction of the rotary tube such that spiral transport paths for the material to be burned are formed in the preheating zone.

2. The rotary kiln according to claim 1, wherein the projections each contain a refractory material, optionally the refractory material being concrete, in particular refractory concrete.

3. The rotary kiln according to claim 1, wherein at least some of the projections have a prismatic geometry, in particular the geometry of a trapezoidal prism, preferably an isosceles trapezoidal prism.

4. The rotary kiln according to claim 1, wherein at least some projections have a height in the radial direction in relation to the rotary tube of between 50 mm and 500 mm, preferably of between 100 mm and 300 mm, and particularly preferably of approx. 200 mm, and/or at least some projections have a length in the longitudinal direction of the rotary tube of between 50 mm and 2000 mm, specifically of between 100 mm and 1000 mm, preferably of between 200 mm and 750 mm, and particularly preferably of between 350 mm and 450 mm, and/or in that at least some projections have a width perpendicular to the longitudinal direction of the rotary tube of between 50 mm and 1000 mm, preferably of between 100 mm and 500 mm, and particularly preferably of between 150 mm and 300 mm.

5. The rotary kiln according to claim 3, wherein at least some projections have the geometry of a trapezoidal prism, the width of the lower trapezoidal base being between 100 mm and 400 mm, preferably between 150 mm and 300 mm, and the width of the upper base being between 30 mm and 200 mm, preferably between 50 mm and 200 mm, and particularly preferably between 70 mm and 130 mm.

6. The rotary kiln according to claim 1, wherein the ratio between the length of a projection in the longitudinal direction of the rotary tube and the distance between two projections adjacent in the longitudinal direction of the rotary tube between approx. 2:1 and 1:2, preferably between approx. 1.5:1 and 1:1.5, and particularly preferably is approx. 1:1.

7. The rotary kiln according to claim 1, wherein at least some of the projections are fixed to the inner wall of the rotary tube by means of a metallic anchorage, in particular a welded metallic anchorage.

8. The rotary kiln according to claim 1, wherein distributed across the circumference of the rotary tube, 3 to 9, especially 4 to 8, particularly preferably 5 to 7, and most preferably 6 groups of projections arranged one behind the other in the longitudinal direction are provided.

9. The rotary kiln according to claim 1, wherein the groups of projections arranged one behind the other and substantially in parallel with the longitudinal axis of the rotary tube extend across one fifth to one third of the total length of the rotary tube.

10. The rotary kiln according to claim 1, wherein at least one further projection, preferably a plurality of further projections, is provided in the inlet zone of the rotary tube, the at least one further projection having at least one sliding surface inclined to the longitudinal axis of the rotary tube for conveying the material to be burned from the inlet zone into the preheating zone.

11. The rotary kiln according to claim 10, wherein a plurality of further projections is provided in the inlet zone of the rotary tube, the further projections being arranged in a row as a group such that the respective sliding surfaces of the further projections form a common sliding surface for the material to be burned.

12. The rotary kiln according to claim 11, wherein the common sliding surface formed by the plurality of further projections extends substantially across the entire length of the inlet zone.

13. The rotary kiln according to claim 10, wherein the at least one sliding surface of the at least one further projection has an inclination to the longitudinal axis of the rotary tube of 15 to 70, in particular of 25 to 65, especially of 35 to 55, and particularly preferably of 40 to 50.

14. The rotary kiln according to claim 1, wherein a plurality of additional projections is provided in the region of the outlet zone, the additional projections being arranged as groups in the circumferential direction of the rotary tube, preferably offset from one another in the longitudinal direction of the rotary tube, wherein, optionally, a plurality of groups of additional projections is provided in the longitudinal direction of the rotary tube.

15. A method for burning carbonate-containing material, in particular limestone or dolomite characterized by the following steps: introducing the carbonate-containing material into the rotary tube of a rotary kiln according to claim 1, burning the carbonate-containing material, the carbonate-containing material moving through the rotary tube from the inlet zone through the preheating zone and the burning zone to the outlet zone, the rotary tube rotating in a direction of rotation, conveying the carbonate-containing material through the burning zone, the groups of projections that are arranged one behind the other and substantially in parallel with the longitudinal axis of the rotary tube being arranged offset in relation to one another in the longitudinal direction of the rotary tube, and the rotational speed and inclination of the rotary tube being adjusted such that the material is conveyed through the preheating zone on spiral transport paths.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention is explained in more detail below in reference to a drawing depicting an exemplary embodiment. Shown are:

[0042] FIG. 1 the rotary tube of a rotary kiln in a perspective view,

[0043] FIG. 2 the rotary tube of FIG. 1 in truncated perspective longitudinal sectional view,

[0044] FIG. 3 an enlarged section of the preheating zone of the rotary tube of FIG. 1 in a perspective longitudinal sectional view,

[0045] FIG. 4 a projection of the preheating zone of the rotary tube of FIG. 1 in a perspective view,

[0046] FIG. 5 the two-dimensional truncated representation of the unwound inner kiln wall of the rotary tube of FIG. 2 in a highly schematic form,

[0047] FIG. 6 a sectional enlargement of the rotary tube of FIG. 1 with partially cut out kiln wall in a perspective view,

[0048] FIG. 7 an enlarged section of the inlet zone of the rotary tube of FIG. 1 in a perspective longitudinal sectional view,

[0049] FIG. 8 a further projection in the inlet zone of the rotary tube of FIG. 1 in a perspective view,

[0050] FIG. 9 an enlarged section of the outlet zone of the rotary tube of FIG. 1 in a perspective longitudinal sectional view, and

[0051] FIG. 10 an additional projection in the outlet zone of the rotary tube of FIG. 1 in a perspective view.

DESCRIPTION OF THE INVENTION

[0052] In FIG. 1, the rotary tube 1 of a rotary kiln is shown with conventional mounting and drive components, which will not be discussed in more detail below. The rotary tube 1 comprises an inlet end 2ashown here on the frontand a rear outlet end 4a. Along the longitudinal extension of the rotary tube 1, the rotary tube 1 comprises, with respect to the material feed, burning and material discharge process, an inlet zone 2, a preheating zone 3a (also called transition zone), a burning zone 3b and an outlet zone 4 (see also FIGS. 2 and 5). Arranged in the region of the outlet end 4a is a calciner lance 5, by means of which a flame projecting into the rotary tube 1 is generated during operation of the rotary kiln. If, for example, the rotary tube 1 has a total length of approx. 90 m, the length of the inlet zone 2 is typically approx. 2 m, that of the preheating zone 3a approx. 32 m, the length of the burning zone 3b approx. 53 m, and that of the outlet zone 4 approx. 3 m. The highest temperatures generated by the calciner flame during operation of the rotary kiln are achieved in the burning zone 3b and amount to approx. 1500-1600 C., so that the very predominant part of the calcination reaction takes place in this zone.

[0053] As shown in the perspective longitudinal sectional view of the rotary tube 1 of FIG. 2, the rotary tube 1 comprises a plurality of projections 7 (also called drivers) in the preheating zone 3a. As can be seen, these are arranged one behind the other as groups 71 in parallel with the longitudinal axis of the rotary tube 1. A total of six groups 71 of projections 7 are provided distributed across the inner circumference of the rotary tube 1, as can be seen in particular from the representation of the unwound inner kiln wall of FIG. 5. The projections 7 are arranged in such a way that projections 7 of adjacent groups 71 of projections 7 arranged adjacent to one another in the circumferential direction of the rotary tube 1 are offset from one another in the longitudinal direction of the rotary tube 1 (see FIG. 5). Since, as can be seen in FIGS. 2 and 5, the projections 7 arranged in groups in rows form identical rowsi.e., the length of the projections 7 and the spaces between the projections 7 is identical for each group 71adjacent whole groups 71 are accordingly also offset from one another in the longitudinal direction of the rotary tube 1. The groups 71 of projections 7 preferably occupy one third to one fifth of the total length of the rotary tube 1.

[0054] A more detailed representation of the projections 7 is shown in FIG. 3. Here and in FIG. 4 it can be seen that the projections 7 are each formed as a trapezoidal prism with a length of approx. 400 mm and a height of approx. 200 mm. Furthermore, the width of the lower trapezoidal base is approx. 300 mm, while the upper trapezoidal base has a width of approx. 100 mm. This defines inclined leg surfaces 7a along the longitudinal extension of the projections 7, in the present case at an angle of approx. 76 to the lower trapezoidal base. The trapezoidal design of the projections 7 ensures that the material intermixed by the projections 7 in the preheating zone 3a during kiln operation does not fall off the projections 7 with increased dust formation, but rather slides down along the leg surfaces 7a.

[0055] As can be seen from the kiln lining shown in FIG. 4, the length of the spaces between the projections 7 of a group 71 arranged in a row corresponds approximately to the length of the projections 7 themselves, and the projections 7 of respective adjacent groups 71 are thus offset from each other with a gap. This forms spiral or helical transport paths through the preheating zone 3a of the rotary tube 1 (shown in FIG. 5 as oblique dashed lines S), along which the material to be burned can be transported rapidly through the preheating zone 3a.

[0056] In the longitudinal sectional view of FIG. 2, it can further be seen that a plurality of further projections 6 are arranged in the inlet zone 2 of the rotary tube 1, which projections have a specific shape and are arranged in rows as groups 61 in a stepped form, as described below. The projections 6 are also referred to in technical terms as displacers.

[0057] As shown in FIGS. 1, 2 and 5-8, the further projections 6, which are arranged as group 61 of, in the present case, six further projections arranged in a row, are substantially formed identical to one another and, according to FIG. 8, have substantially the shape of a straight prism with the base of a right isosceles triangle, the non-rectangular angles of the triangle being truncated. Each further projection 6 has a sliding surface 6a, which is arranged inclined to the longitudinal axis of the rotary tube 1. Preferably, an angle of inclination of approx. 45 is selected. As mentioned, the further projections 6 are arranged in rows in a stepped manner, in such a way that a common sliding surface 6a* is formed by the individual sliding surfaces 6a of the further projections 6, which in the present case is likewise inclined at an angle of approx. 45 with respect to the longitudinal axis of the rotary tube 1.

[0058] Furthermore, the sliding surfaces 6a of the further projections 6 or the common sliding surface 6a* of the projections 6 arranged in groups relative to the direction of rotation D of the rotary tube 1 are aligned in such a way that during operation of the kiln the material to be burned (not shown) comes to rest on the sliding surfaces 6a of the further projections 6, and, due to the selected inclination of the sliding surfaces 6a relative to the longitudinal axis of the rotary tube 1, slides rapidly towards the preheating zone 3 due to gravity, without any undesired rearward movement of the material to be burned in the direction of the inlet end 2a.

[0059] As shown in FIGS. 1 and 5, a plurality of groups 61 of further projections 6 arranged in a row in a stepped form are provided across the circumference distributed on the inner wall of the rotary tube 1. In the present case, a number of six groups 61 is selected.

[0060] Furthermore, it is shown in FIG. 2 that a plurality of additional projections 8 are provided in the outlet zone 4 of the rotary tube 1, the additional projections 8 being arranged as groups 81 in the circumferential direction of the rotary tube 1 and offset from one another in the longitudinal direction of the rotary tube 1. These additional projections 8 (in technical terms, swords) serve to prevent the formation of clusters in the burned material. As shown in FIG. 10, these additional projections 8 have the shape of a truncated pyramid with the base of an isosceles acute triangle, the acute angle leading in the direction of rotation D of the rotary tube 1 and being slightly truncated for stability reasons. For the sake of clarity, the outlet zone 4 with the additional projections 8 is shown again in detail in FIG. 9. The relative arrangement of the individual groups 81 of the additional projections 8 (swords) to one another and to the groups 71 of the projections 7 (drivers) in the inlet zone is shown in FIG. 5.

[0061] FIG. 5 now shows in highly schematic form a representation of the unwound inner kiln wall of the rotary tube 1. This means that the distribution of all projections 7 (drivers) provided in the preheating zone 3a, further projections 6 (displacers) in the inlet zone 2 as well as additional projections 8 (swords) in the outlet zone 4 of the rotary tube 1 is shown in two-dimensional representation, whereby the burning zone 3b, in which no projections are provided in the present case, is not shown in full for reasons of space. Accordingly, six groups 61 each of five further projections 6 (displacers) arranged in a row in a stepped form are provided in the inlet zone 2 distributed across the circumference. In the preheating zone 3 adjoining the inlet zone 2, there are also six groups 71 of projections 7 (drivers) according to the invention arranged one behind the other in the longitudinal direction of the rotary tube 1. Projections 7 arranged adjacent to one another in the circumferential direction are positioned offset from one another, as shown by the auxiliary line V in FIG. 5. This offset arrangement results in spiral transport paths in the rotary tube 1, along which the material to be burned can move through the preheating zone 3a without obstruction. The spiral transport paths are shown by way of example in the two-dimensional representation of FIG. 5 as parallel lines S running diagonally.

[0062] Furthermore, FIG. 5 shows the additional projections 8 (swords) provided in the outlet zone 4 of the rotary tube 1. As mentioned, these are arranged in groups 81 in the circumferential direction of the rotary tube 1, with the additional projections 8 of a group 81 being longitudinally offset from one another, in order to process a maximum amount of burned material. The offset in the longitudinal direction of the rotary tube 1 is shown in FIG. 5 by the auxiliary line V. In the present case, two groups 81 of five additional projections 8 are provided. The group 81 arranged at the outlet end 4 of the rotary tube comprises only three additional projections 8. In contrast to the projections 6 of the inlet zone 2, the additional projections 8 do not extend to the outlet end 4a of the rotary tube 1. Rather, a certain distance of preferably approx. 1 m may be selected.