METHOD FOR THE THERMAL TREATMENT OF BULK MATERIALS IN A ROTARY TUBE WITH AT LEAST ONE INFRARED LIGHT UNIT

Abstract

A method for the thermal treatment of bulk materials in a rotary tube with at least one infrared light unit. Bulk material is introduced into the rotary tube, which is provided on its inner wall with at least one mixing element and in the interior space of which the pressure of the ambient atmosphere prevails. A heat treatment of the bulk material is performed by at least one electrical infrared light unit, which is arranged at the center of the rotary tube and the light cone of which is directed onto the bed of bulk material that lies on the inner wall of the rotary tube. The bulk material is discharged from the rotary tube. Water vapor is directed onto the surface of the bulk material. The vapor is introduced into the interior space of the rotary tube through a nozzle tube.

Claims

1. A method for thermal treatment of bulk materials in a rotary tube with at least one infrared light unit, the method comprising: introducing bulk material into the rotary tube, which is provided on its inner wall with at least one mixing element and in an interior space of which a pressure of the ambient atmosphere prevails; carrying out a heat treatment of the bulk material by at least one electrical infrared light unit, which is arranged in a center of the rotary tube and the cone of light of which is directed onto the bed of bulk material, which rests on the inner wall of the rotary tube; discharging the bulk material from the rotary tube; directing steam for the heat treatment onto the surface of the bulk material; introducing the steam into the interior space of the rotary tube through at least one nozzle tube provided with multiple steam nozzles; arranging the nozzle tube with its steam nozzles in the cone of light of the infrared light unit and outside a cross section of the interior space of the rotary tube covered by the bulk material; and after-heating the steam by the infrared light unit within the part of the flowed-through nozzle tube that is located in the cone of light beyond its exit temperature at the steam nozzles.

2. The method as claimed in claim 1, wherein the radial distance of the steam nozzles from the bulk material is 0.1 times to 2.0 times the screw flight height of a screw flight mounted on the inner wall of the rotary tube.

3. The method as claimed in claim 1, wherein the temperature of the steam at the surface of the bed of bulk material is more than 140° C.

4. The method as claimed in claim 2, wherein steam superheated by way of the steam nozzles is introduced.

5. The method as claimed in claim 1, wherein, in addition to the steam, water is directed onto the bed of bulk material, and wherein the outlet nozzles of a water line are arranged above or below the cone of light of the infrared light unit.

6. The method as claimed in claim 1, wherein an airshield, the air flow of which is directed onto the bed of bulk material is provided at the infrared light unit, and wherein the cone of light and the air flow of the airshield are directed substantially perpendicularly onto the surface of the bulk material.

7. The method as claimed in claim 1, wherein food in the form of bulk material is used as the bulk material.

8. The method as claimed in claim 1, wherein particles of plastic tainted with organic-aromatic and/or other chemical compounds are treated as the bulk material.

9. The method as claimed in claim 8, wherein particles of thermoplastic vulcanizates are used as the bulk material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0036] FIG. 1 shows an infrared rotary tube unit in a schematic sectional view;

[0037] FIG. 2 shows a diagram with a temperature profile over time according to an exemplary method, given by way of example, and

[0038] FIG. 3 shows a diagram with a temperature profile over time according to an exemplary method, given by way of example.

DETAILED DESCRIPTION

[0039] FIG. 1 shows an infrared rotary tube unit 10 in a schematic sectional view. It substantially comprises a rotatable rotary tube 1, which has a closed casing at its circumference, and, arranged in the clear cross section therein, an infrared light unit 2, which radiates infrared light in a cone of light 3. The cone of light 3 is directed onto a bed of bulk material 20, which rests on the inner wall in the lower region of the rotary tube 1. Mixing elements and conveying elements, such as a screw flight, provide constant recirculation and conveyance, but are not shown here. The direction of rotation is indicated by the block arrow. The rotation has the effect that the bed of bulk material 20 assumes a sloping alignment due to friction with the wall. Both the cone of light 3 and an air flow of an air shield 5 indicated by the arrows 6 are directed perpendicularly onto the surface of the bulk material. Steam 7 leaves from a steam lance 4, which lies in the cone of light and has multiple steam nozzles over its length. The arrangement of the steam lance 4 with respect to the direction of rotation is important because the steam lance 4 should be arranged such that it is positioned at the lower edge of the bed of bulk material 20 resting on the inner wall of the rotary tube 1. Consequently, after leaving the steam lance 4, the steam automatically passes over the bed of bulk material 20. Preferably, the air flow 6 of the air shield 5 additionally forces the emerging steam 7 onto the surface of the bed of bulk material 20 and prevents the steam 7 from rising vertically upward on account of its significantly higher temperature, and consequently lower density, in comparison with the air temperature inside the rotary tube 1.

[0040] In the diagram that is shown in FIG. 2, the temperature is plotted over time according to a first way of conducting the method, given by way of example.

[0041] Beginning at the time to, the product is heated in a time phase Δt.sub.1 up to a base temperature. In a subsequent time phase Δt.sub.2, a further rise in the temperature is achieved by the spraying in of steam. After the time phases Δt.sub.1, Δt.sub.2, the heating-up phase is ended and this is followed by the actual treatment phase over a time phase Δt.sub.3, in which the high temperature is maintained. The comparison shows that the treatment temperature T.sub.max (steam) achievable by spraying in steam is higher than the holding temperature achieved by the known method, which lies at the level T.sub.max (water). The cooling-down time Δt.sub.4 from the high temperature level T.sub.max (steam), measured from the ending of the supply of steam and switching off of the infrared light, is not much greater in comparison with the cooling down from the lower temperature level T.sub.max (water), because the process according to the invention especially has the effect that the surface is heated up much more, but the core of the product is heated up much less.

[0042] In FIG. 3, the temperature is plotted over time according to another way of conducting the method, given by way of example. Here, the product is subjected to steam from the time to, and a much higher peak temperature in comparison with the prior art is already achieved within a short time span Δt.sub.1′.

[0043] In the case of both variants of the method of the invention, the product is not damaged in spite of the much higher final temperature in the layers near the surface as a result of the additional spraying in of steam.

[0044] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.