Within the scope of the present invention, double-cone mixers are to be understood as apparatus in which a mixing vessel comprising a drum with a cylindrical middle portion and in each case with an attached cone rotates about a horizontal axis. The arrangement of the vessel walls and the rotation of the drum then usually provide satisfactory uniform, three-dimensional mixing of the product. The product is driven upwards by centrifugal forces and frictional forces, and then slides down, according to its gradient. At higher rotary speeds, the product is lifted farther, and then drops back following a parabolic trajectory. The intensity of mixing increases, at the same time with greatly increasing power consumption. With the simultaneous use of baffles, an improvement of mixing is achieved in the direction of the axis of rotation (=axial direction).
The baffle improves mixing efficiency, for example by increasing turbulence within the product, supplementing the centrifugal and frictional forces arising during rotation and in particular, with a suitable arrangement, forcing an axial direction of flow of the product.
Preferably the double-cone mixer according to the invention comprises 1 to 16 baffles, especially preferably 2 to 8, quite especially preferably 4 baffles.
In an especially preferred embodiment the number of baffles used is selected so that both cones each have the same number of baffles and within one cone the flow-spoiling internals are arranged so that in the equal-sized half-spaces, into which a cone is divided by a middle plane M that is perpendicular to the axis of rotation D, there is in each case the same number of baffles.
Preferably, to achieve the desired axial mixing, baffles of types S1 or S2 described below are used, which can be used either individually or in combination with one another in the double-cone mixers according to the invention.
Baffles of type S1 are characterized in that, as in
For example, as shown in
Theoretically, angles β and β′ can assume absolute values from 0° to 90° depending on the properties of the product being mixed and depending on the purpose of mixing, with 5° to 85°, especially 10° to 70° and quite especially 15° to 50° being preferred.
Basically, angles β or β′ of the baffles used can vary in each case within a double-cone mixer according to the invention, preferably with all baffles rotated through the same angle (absolute value) relative to the middle line ML of the mixer.
The baffle of type S2 is characterized in that it is positioned on a plane of projection AE that is rotated through angle α or in the case of S2′ through angle α′ relative to the axis of rotation D (cf.
Theoretically, angles α and α′ can assume values from 0° to 90°, and for the boundary case of angles α and α′ of 90°, baffles S2 or S2′ no longer have an axial mixing action. Absolute values for angles α and α from 5° to 85°, especially 10° to 70°, quite especially 20° to 60° are preferred, depending on the properties of the product being mixed and depending on the purpose of mixing.
The baffles S1, S1′, S2 and S2′ shown in
The double-cone mixer described in this invention can be equipped, as described above, with the most varied combinations of baffles of various types, a symmetrical arrangement of baffles with respect to the direction of feed, in which both types S1 and S2 are used, in each case symmetrically, is preferred; especially preferably, a symmetrical arrangement of baffles with respect to direction of feed and intensity of the axial conveying action, in which both types S1 and S2 are used, in each case symmetrically, and in which angles β and β′ and α and α′ in each case are of equal magnitude (absolute value) in pairs and in which all baffles give rise to an axial direction of feed outwards for a given sense of rotation of the double-cone mixer, is especially preferred.
The axial conveying action according to the invention can not only be achieved with the baffles of type S1 and S2, but in some circumstances also with combinations of these types of baffles.
The size of the baffles is determined by their length (c), by their height (d), by their thickness (f) and by their distance from the wall of the mixing vessel (e) (cf.
The baffles within the scope of this invention have, as a ratio to the length of the wall of the mixing vessel (a), a length (c) that is typically 1.0*(a) to 0.15*(a), preferably 0.2*(a) to 0.8*(a), and especially preferably 0.3*(a) to 0.75*(a).
The height (d) of the baffles as a ratio to segment (L) of the mixing vessel is typically 0.01*(L) to 0.2*(L), preferably 0.02*(L) to 0.15*(L), and especially preferably 0.03*(L) to 0.1*(L).
A minimum thickness (f) of the baffles is predetermined by the mechanical strength of the material used (as a rule steel). In the case of enamelled baffles, additional manufacturing characteristics must be taken into account, for example relating to the permissible thermal expansion and specified minimum radii. A further increase in the thickness (f) of the baffles does not give any operational advantages. The thickness (f) is typically from 0.2*(d) to 0.5*(d).
The distance (e) of the baffles from the wall of the mixing vessel has an effect on the one hand on the mixing action and on the other hand on aspects of cleanability and residual emptying. In the case of enamelled baffles and double-cone mixers, special manufacturing characteristics must again be taken into account, which possibly require minimum dimensions. The distance (e) of the baffles from the wall of the mixing vessel is typically 10 mm to 250 mm, preferably 40 mm to 200 mm, and especially preferably 60 mm to 150 mm.
The ratio of segment (b) to segment (a) characterizes the arrangement of the baffles on the wall of the mixing vessel. Typical values for (b)/(a) are 0.1 to 0.9, preferably 0.2 to 0.8 and especially preferably 0.3 to 0.7.
Basically, the baffle proper is mounted on one or more feet (
The double-cone mixers according to the invention equipped in this way have volumes of typically 10 dm3 to 25 000 dm3, preferably 100 dm3 to 8000 dm3, and especially preferably 1000 dm3 to 6500 dm3.
Basically, embodiments of the double-cone mixers according to the invention both with and without internal lining are conceivable. In particular, with an enamel internal lining it is even possible to carry out process steps in which reactive and aggressive reactants and media are used, by means of such a mixer according to the invention.
The mixers according to the invention are especially suitable for the area of treatment and processing of solids. The double-cone mixers described above are particularly important in the production and processing of low-molecular polysaccharide derivatives, preferably based on starch or cellulose.
Another object of the present invention is therefore a method for the production or processing of low-molecular polysaccharide derivatives, in which a double-cone mixer of the kind according to the invention is used.
Suitable process steps in which such a mixer finds application are for example reduction of molecular weight by the action of if necessary gaseous acids such as hydrogen chloride.
Preferred polysaccharides are those based on starch and cellulose.
All the references described above are incorporated by reference in its entirety for all useful purposes.
While there is shown and described certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.
Number | Date | Country | Kind |
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06013181.0 | Jun 2006 | EP | regional |