Abstract:
The invention relates to a method and device for separating a mixture, made of particles of a first particle type and a second particle type, especially aleurone particles and shell particles made of comminuted bran, said particles being scarcely distinguishable in terms of size and density, into various types of particles. Separation occurs according to particle-type specific triboelectric charging of said particles in a first active area and subsequent separation of the differently charged moving particles in an electric field.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of International Application No. PCT/CH02/00547, filed Oct. 2, 2002 and German Application No. 101 54 462.6, filed Nov. 8, 2001, the complete disclosures of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   a) Field of the Invention 
   The invention relates to a method and a device for separating the various sorts of particles in a mixture comprised of particles produced by comminuting the grains of cereal grains, in particular wheat, and are present as a mixture consisting of at least a first and second sort of particle. In addition, the invention relates to a product which is also obtained via the method and device according to the invention. 
   b) Description of the Related Art 
   WO 85/04349 describes a method for obtaining aleurone cell particles from wheat gain. In this case, the grain particles are comminuted in a hammer mill in a first step, so that aleurone cell particles and shell particles are present as a mixture. This mixture is given an electrical charge through exposure to frictional electricity in a second step, wherein the aleurone cell particles and the shell particles receive different electrostatic charges. In a third step, the mixture with the differently charged particles is moved through an electrical field, so that the differently charged particles are varyingly deflected, wherein the shell particles and aleurone cell particles are caught in separate containers. The frictional electric charge (step 2) takes place in a stream of dry air, into which the mixture is introduced, and which moves in a hollow column. In this case, obviously turbulent air streams arise in the column (“elutriator”), wherein the particles in the mixture rub against both each other and the interior wall of the elutriator, thereby receiving the respective electrostatic charge. 
   In this method of prior art, however, large quantities of air had to be moved. Nonetheless, no intensive frictional electric interaction takes place between the particles and the interior elutriator walls. 
   OBJECT AND SUMMARY OF THE INVENTION 
   Therefore, the primary object of the invention is to separate a mixture comprised of various sorts of particles, in particular aleurone and shell particles from comminuted grain, which hardly differ in terms of size and density, into its various sorts of particles more efficiently than in prior art. 
   This object is achieved by a method in which:
         a) The particles of the first particle sort and second particle sort in the mixture are moved along at least one surface of at least one solid material in a first impact area in such a way as that at least one portion of their particle surface is at least sectionally in contact with the solid material surface as they move along the at least one solid material surface, as a result of which the particles of the first particle sort and the particles of the second particle sort become electrically charged in such a way that the electrical charge of the particles of the first particle sort differs from the electrical charge of the particles of the second particle sort enough to enable an electrostatic separation of particles of the first particle sort from particles of the second particle sort;   b) in a second impact area, the particles of the first particle sort and second particle sort with the sufficiently different electrical charges are subsequently moved into an electrical field between a first electrode area and a second electrode area, between which there is an electrical potential difference, at essentially the same velocity, as a result of which the particles of the first particle sort and second particle sort with the sufficiently different electrical charges move along sufficiently different paths as they travel through the electrical field; and   c) the particles of the first particle sort and the particles of the second particle sort are caught at a first location and at a second location at the end of their journey through the electrical field, characterized in that the at least one surface of the at least one solid material is concave in the first impact area, and that the particles of the first sort and particles of the second sort in the mixture moving along the concave surface are pressed against the concave surface of the solid material as a result of their centrifugal force as they move inside the first impact area.       

   The particles can be gathered at this first and second location, and removed after enough have accumulated. As an alternative, they can also be continuously, e.g., pneumatically, conveyed further in step c) after separation in step b), and then be routed to a packaging system, for example. 
   In particular, the particles of the first particle sort are aleurone particles, and the particles of the second particle sort are residual particles from which aleurone has been removed, in particular shell particles, of the comminuted grain. 
   The object according to the invention is also achieved with a device according to the invention, with:
         a) a first impact area with at least one surface of at least one solid material, along which the particles of the first particle sort and the second particle sort of the mixture can move in such a way that at least one portion of their particle surface is at least sectionally in contact with the solid material surface as they move along the at least one solid material surface; and   b) a second impact area subsequent to the first impact area, with a first electrode area and a second electrode area, between which an electrical voltage can be applied; and with a first accumulation area for particles of the first sort and an accumulation area for particles of the second sort separate from the first accumulation area, characterized in that the at least one surface of the at least one solid material is concave in the first impact area, so that the particles of the first sort and second sort that can move along the concave surface are pressed against the concave surface of the solid material as a result of their centrifugal force as they move inside the first impact area.       

   In particular, the at least one surface of the at least one solid material is concave in the first impact area, so that the particles of the first sort and second sort that can move along the concave surface are pressed against the concave surface of the solid material as a result of their centrifugal force as they move inside the first impact area. 
   The product according to the invention, in particular aleurone particles, which was obtained by separating the various particle sorts of the mixture through the use of steps a), b) and c) of the aforementioned method, has a high level of purity. 
   It is preferably obtained through the repeated application of steps a), b) and c). 
   Additional advantages, features and possible applications of the invention will be presented in the following description of two exemplary embodiments of the invention based on the drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  shows a first exemplary embodiment of the invention; and 
       FIG. 2  shows a second exemplary embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The first device according to the invention shown on  FIG. 1  comprises a supply vessel  22  in which the mixture  1  to be separated, which contains at least a first particle sort  2  and a second particle sort  3 , is routed to the first impact area  13 ,  14 , in which particles  2 ,  3  of mixture  1  are given an electrical charge varying by particle sort before the particles  2 ,  3  carrying different electric charges are supplied to the second treatment area  31 ,  32 ,  35 , where they accumulate at different locations  33 ,  34  in a separation vessel  35 , sorted according to type of particle based on their electric charge. 
   Through the force of gravity, the mixture  1  goes out of the feed vessel  22 , which tapers toward the bottom, into a conveyor device  18 ,  19  consisting of a conveyor screw  18  and into a conveyor channel  19 . The conveyor screw  18 , which is driven by a drive motor  23 , conveys the mixture  1  through a product inlet  15  into a housing  14 , where a rotor element  13  is rotatably mounted. 
   There is a gap area  21  between the rotor element  13 , which is driven by a drive motor  24 , and the housing  14 , such that the mixture  1 , which is supplied through the product inlet  15  and strikes the rotor element  13 , is accelerated both radially and tangentially through this gap area due to friction at the surface of the rotor element. The mixture  1  accelerated in this way passes through the gap area  21  and obliquely strikes the surface  11  of the inside wall of the housing, which has a concave curvature. Due to its own inertia (centrifugal force) and due to constantly resupplied mixture, the mixture  1  is pressed against the surface  11  having a concave curvature and is conveyed along this surface until it comes out of the housing  14  through the product outlet  16  and enters a separation vessel  35 . 
   The disk-shaped rotor element  13  has elevations  20 , which are situated on its disk surface facing the product inlet  15 . In addition to the above-mentioned friction on the surface of the rotor element  13  (“baffle disk”), these elevations  20  also contribute toward the acceleration of the mixture  1  and the ever-present air through the gap area  21 , and on the other hand, they also exert an impact effect (baffle effect) on the particles  2 ,  3  of the mixture, so that any agglomerates of multiple particles which might be present are broken up. This impact separation (baffle separation) of agglomerates before or during the buildup of electric charge on the particles due to friction on the solid body surfaces is important, because such agglomerates may of course also consist of particles of different types, which would then reach the collecting site  33  or at the collecting site  34 , depending on their total charge. Then, however, in any case one would have “foreign particles” at the respective collecting sites  33  and  34 . 
   Depending on their geometric shapes, these elevations  20  may have primarily an accelerating and/or pumping effect on the mixture and/or the air, or they may have primarily a dispersing effect on the particles of the mixture. A blocky, angular shape of these elevations  20  promotes a dispersing effect, while a paddle shape increases the acceleration or pumping effect. Elevations of different shapes may also be provided on the rotor element  13  to achieve a controlled effect. 
   To prevent the mixture  1 , which is supplied through the product inlet  15 , from traveling even a very short distance through the gap area  21  between the product inlet  15  and the product outlet  16  and thereby escaping the necessarily intense action in the first treatment area  13 ,  14 , the product inlet  15  is situated eccentrically with respect to the rotor element  13 . In addition (and not for reasons of better illustration as in  FIG. 1 ), the product inlet  15  is situated directly behind the product outlet  16  in the direction of rotation of the rotor element  13  peripherally, so that the mixture travels at least approximately 360° on a spiral pathway in the gap area  21  between the product inlet  15  and the product outlet  16 . This prevents “short-circuiting” of the pathway of the mixture between the product inlet and the product outlet. 
   During its path through the gap area  21 , the particles  2 ,  3  of the mixture  1  come in intense contact with the inside surfaces  11 ,  12  of the housing  14  and with the surface of the rotor element  13 , in particular its elevations  20  and the concave curvature of the inside surface  11  of housing  14 . This leads to a specific electric charge buildup on the particles of the different types of particles  2 ,  3 . 
   Because of their high velocity, the dispersed particles coming out through the product outlet  6  go approximately horizontally into the separation vessel  35 , whereby the cylindrical neck area  35   a  of the separation vessel serves as a calming zone for the particles carrying different electric charges as they come out of the housing  14 . They then settle out in the interior of the separation vessel under the influence of gravity. In the interior of the separation vessel  35 , there is a first electrode  31  and a second electrode  32  opposite it. The first electrode  31  is grounded by a line  38 , which contains a voltage source  37 , while the second electrode  32  is grounded directly via a line  39 . The differently charged particles settling out in the electric field between the two electrodes  31  and  32  travel downward on different paths, depending on their electric charge. A partition  36 , which projects from the bottom area  35   b  of the collecting vessel  35  into the electric field between the electrodes  31 ,  32  subdivides the lower interior space of the separation vessel  35  into a first collecting area  33  and a second collecting area  34  in which the particles of the first type and/or the particles of the second type are collected. 
   In an advantageous modification of this first exemplary embodiment from  FIG. 1 , an air classification is also performed in the first treatment area  13 ,  14 . To this end, air or another gas mixture is pumped through an air inlet (not shown) into the first treatment area  13 ,  14  and is guided within the first treatment area  13 ,  14  so that the fines (“flour” from endosperm residues, optionally still adhering to the aleurone particles) are separated from the coarse fraction (pure aleurone particles and pure husk particles), the fines being removed with the air stream through an air outlet (not shown) and only the coarse fraction passing through the product outlet  16  into the second treatment area  31 ,  32 ,  35 . 
   The second device according to this invention as shown in  FIG. 2  differs from that shown in  FIG. 1  in its first treatment area. Otherwise all the elements are identical and carry the same reference notation as those in  FIG. 1 . Instead of the housing  14  with the rotor element  13  which is rotatably mounted on it and can be driven by the drive motor  24 , the device in  FIG. 2  has a curved channel with a first end  27   a  and a second end  27   b.  The mixture  1  coming from a feed vessel  22 , in particular aleurone particles and husk particles of the bran, is supplied through a product inlet  15 , and a moving fluid, in particular air, is supplied through a fluid inlet  29  to a fluidization area  17  at the end of which there is a dispersion angle  26 , which is connected to the first end  27   a  of the curved channel  27  and through which the fluidization area  17  opens into the curved channel  27 . The second end  27   b  of the curved channel  27  opens into a product separator  28  with a fluid outlet  30  and a product outlet  16 , which opens into the separation vessel  35 . 
   The conveyor device  18 ,  19  transports the mixture  1  out of the feed vessel  22 , through the product inlet  15  and into the fluidization area  17 . A sufficient amount of fluid at a sufficient velocity is used to achieve airborne conveyance without any accumulation of particles in the interior of the curved channel  27 . Due to the abrupt deflection when the particles impact on the dispersing angle  26 , the above-mentioned dispersion/de-agglomeration of the particles of the mixture is accomplished. During their subsequent movement in the fluid stream and due to the friction between the particles moving along the inside surface of the curved channel  27 , there is a particle type-specific buildup of electric charge on the particle types  2 ,  3  of mixture  1 . The fluid is separated through the fluid outlet  30  in the downstream product separator  28 , and the mixture of the differently charged particles according to type of particle then enters the separation vessel with its electric field. 
   In principle, two cases of electric charging of the particles can be differentiated: 
   The particles of the first type of particle are negatively (positively) charged and the particles of the second type of particle are negatively (positively) charged, but to a different extent. These particles thus differ only in the absolute value of their charge, but not in the polarity of the charge. 
   The particles of the first type of particle are negatively (positively) charged and the particles of the second type of particle are positively (negatively) charged. The particles thus differ in polarity and possibly also in the absolute value of their charge. 
   In the first case, the electrically charged particles of the first type and those of the second type repel one another, and there is practically no re-agglomeration of different particles. Separation takes place in the electric field due to different amounts of deflection in the same direction. 
   In the second case, the electrically charged particles of the first type and those of the second type attract one another and re-agglomeration of different particles is possible. Separation takes place in the electric field due to different amounts of deflection in opposite directions. 
   To prevent re-agglomeration of particles in any case before they are separated into the different types of particles in the electric field, the “particle densities” must be kept low and the “particle dwell times” must be kept short during the buildup of electric charge in the first treatment area accordingly. 
   In the first exemplary embodiment in  FIG. 1 , this is accomplished because of the selected geometry due to the cross section of the gap area, which becomes wider in the radial direction, and due to a sufficiently high rotational speed of the rotor element  13 . 
   In the second exemplary embodiment in  FIG. 2 , this is accomplished by adjusting a sufficiently low product throughput/fluid throughput ratio in the fluidization area  17  and a sufficiently high fluid velocity. 
   In all the exemplary embodiments of the device according to this invention, the type of particle and the type of solid material on which the particles develop a triboelectric charge play a significant role whether the first case or the second case is obtained. 
   Thus, for example, very good charge buildup and separation results would be achieved for an aleurone particle/husk particle mixture if the solid surfaces  11  and  12 , which play a crucial role in the charge buildup, are made of stainless steel. 
   While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention. 
   List of Reference Notation 
   
       
         1  mixture of particles 
         2  first type of particle 
         3  second type of particle 
         11  first surface (concave) 
         12  additional surface 
         13 ,  14  first treatment area (first exemplary embodiment) 
         13  rotor element 
         14  housing 
         15  product inlet 
         16  product outlet 
         17  fluidization area 
         18 ,  19  conveyor device 
         18  conveyor screw 
         19  conveyor channel 
         20  elevation (baffle element, paddle element, . . . ) 
         21  gap area 
         22  feed vessel 
         23  drive motor (for conveyor screw) 
         24  drive motor (for rotor element) 
         26  dispersing angle 
         27 ,  28  first treatment area (second exemplary embodiment) 
         27  curved channel 
         27   a  first end of  27   
         27   b  second end of  27   
         28  product separator 
         29  fluid inlet 
         30  fluid outlet 
         31 ,  32 ,  35  second treatment area (first or second exemplary embodiment) 
         31  first electrode area 
         32  second electrode area 
         33  first location/collecting area 
         34  second location/collecting area 
         35  separation vessel 
         35   a  neck area 
         35   b  bottom area 
         36  partition 
         37  voltage source 
         38 ,  39  electric lines