Abstract:
The invention relates to an air separator for sifting material suspended in a flow of gas having course material and fine material by using a sifting wheel which rotates in a sifting chamber and which has blades fixed on the external periphery thereof. The blade channels are cross-flown radially from the outside by gas containing the suspended fine particles. The oversized particles are rejected before reaching he internal end of the blade canal. The flow of fine particles is guided through the blade channels in a forced manner in a plurality of consecutive layers in the direction of the axis of rotation. The arrangement in layers of the flow of fine particles after it leaves the blade channels remains in place until it leaves the sifting chamber.

Description:
BACKGROUND OF THE INVENTION 
   The present invention pertains to the separation of material to be separated, which is suspended in a gas flow, in such a form that a crude gas flow is forced to enter the blade channels between the blades of a separator wheel rotating in a separation space against the action of the centrifugal force, in which channels coarser separated material is deflected radially toward the outside under the effect of the centrifugal force, while finer separated material is carried by the gas flow radially inwardly, and this gas flow containing the fines is removed from the separator wheel in the center of the separator wheel for further processing. This air separation is known state of the art and is, e.g., already state of the art according to EP 0 641 609 B1. 
   It is also a general state of the art that the cross section of a fluid flow is divided into a plurality of partial flows in order to affect the partial flows independently from one another in order to make uniform an overall flow that is nonuniform over its cross section due to unintended but unavoidable effects, i.e., to compensate the effects, or, in the contrary case, to make different an overall flow that is uniform over its entire cross section from the very beginning in a specific manner in different cross-sectional areas. 
   This principle described last was applied in DE-OS 36 22 413 in air separation in such a form that to favorably affect the separation effect of the separator and to save energy, the separating air to be fed to the separator wheel is divided by partitions into individual partial flows and each partial flow can be affected independently from the other partial flows in terms of volume and/or flow velocity. Corresponding to the number of the partial flows separated from each other, the blades of the separator wheel are divided in terms of their length. It is considered to be essential in this prior-art solution concerning the present invention that even though the separating air flowing to the separator wheel is divided by partitions in the incoming flow channel and the fluid mixture consisting of separating air and crude gas flow (air with particles suspended in it) by dividing the separating blades in terms of their height into partial flows, this forced division into partial flows is eliminated on the way from the outlet from the separator wheel to the fines outlet of the separator, and the composition of the flow of fines is more or less random over its entire cross section, and a forced effect is not provided, which in turn means that the separation limit is affected favorably only insufficiently. 
   SUMMARY OF THE INVENTION 
   This is where the present invention begins, by showing how the separation limit can be favorably affected from the beginning of the entry of the material to be separated into the separator until the material leaves the separator, how a flow of fines that is uniform over its entire cross section is subjected to further processing or how a flow of fines that is intentionally stratified over its entire cross section is sent for further processing, and how, in particular, coarse product is separated in a plurality of steps, so that a maximum of fines-gas flow freed from coarse material to the maximum extent possible is removed from the air separator. 
   The present invention consequently proposes the maintenance of the flow stratification achieved by the division of the blade channels even after the blade channels have been left in order to avoid that energy is lost due to the merging of the partial flows into the overall flow after leaving the flow channels, as this energy would have to be compensated because of the design of the plant by providing a larger amount of initial energy, which would lead to an uncontrolled and consequently random particle distribution over the entire cross section of the flow of fines from the viewpoint of the desired optimal separation. In particular, the present invention creates the possibility of separating coarse material in a plurality of consecutive steps, which are strictly separated from one another until the transition from one step to the next step, so that coarse material is separated at the end in the best possible manner and the product leaving the separator is freed from coarse material in the best possible manner. 
   The present invention makes possible an air separation in which less energy needs to be used than in the state of the art, but this is only one of the advantages of the present invention, because a general goal that is desirable for the person skilled in the art in flow mechanics for many different reasons is to avoid superfluous vortex formation. A particle distribution that is more uniform on the whole over the entire cross section is achieved with the present invention, which results in a favorable effect on the separation effect. Finally, optimal separation is achieved between coarse material and fines. 
   Consequently, the present invention proposes an air separator according to the patent claims, in which optimal separation of the coarse material is guaranteed and the other problems mentioned above are also solved optimally. 

   
     DESCRIPTION OF THE DRAWINGS 
     Air separators and processes to be carried out with same will be described below in preferred embodiments on the basis of the drawings; in the drawings, 
       FIG. 1  shows a view of a separator housing used in the present invention at right angles to its longitudinal axis, which is at the same time the axis of rotation of the separator wheel arranged in the separator housing (direction of view A in FIG.  2 ), 
       FIG. 2  shows an air separator of the design according to the present invention as a section along line II—II in  FIG. 1 , 
       FIG. 3  shows a separator wheel according to the present invention as a cross section, and 
       FIG. 4  shows an air separator according to the present invention as a section along line IV—IV in FIG.  2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3  shows a central longitudinal section of a rotor or separator wheel  1  for an air separator, into the hub  2  of which rotating forces are to be introduced such that the entire rotor  1  is rotatable around its central longitudinal axis  3 . In the outer area, blades  4  are associated with the hub, the said blades being distributed uniformly on the outer circumference of the hub such that a blade channel, which is intended to be flown through radially from the outside to the inside (direction of arrow  6 ), is formed between two blades each following each other in the circumferential direction. The fluid flowing through the blade channels from the outside to the inside is a gas, preferably air, in which solid particles of various weights are suspended, the different weights being preferably manifested by different particle sizes. During the air separation, particles down to a defined, preferably very small grain size are entrained by the flowing gas against the action of the centrifugal force and they leave the blade channels together with the flowing gas at the inner ends of the blade channels. Particles of a higher weight or larger particle size are, by contrast, either already prevented by the centrifugal force from entering the blade channels, or they are delivered again to the outside after entering the blade channels. The particles entrained by the separating gas are below the “separation limit,” which is set as accurately as possible and shall be maintained obligatorily, and the deflected particles are above the “separation limit.” The rejected coarse material is sent first once again into a mill before it is fed again to the separator wheel. This process is optionally repeated several times until the separated material comes below the separation limit and is entrained by the separating gas against the action of the centrifugal force. The fines suspended in the separating gas are deflected with, the separating gas from the radial direction of flow into the axial direction of flow after leaving the blade channels, and they leave the separator through an outlet opening (not shown in  FIG. 3 ) located opposite the hub in order to be subjected to further treatment, which consists, in general, first of the separation of the separating air and the fines, e.g., in a filter. 
   The design and the mode of operation of the separator wheel are conventional up to this point. 
   In a manner that is likewise known but generally not usual, the blades  4  are divided in their overall height  7  by two ring disks  8   a,    8   b,  which divide the total suspension flow (fluid with solid particles suspended in it) into a plurality of partial suspension flows—into three partial suspension flows in the embodiment being shown—together with the hub  2  and a discharge-side blade end  8   c,  in order to affect, e.g., each partial flow independently from the other partial flows flowing through the separator wheel, but possibly even under the consideration that a total flow that is more uniform over the total cross section can already be obtained due to the division alone. However, the effect achieved is abolished especially in the latter case when the partial flows leave the blade channels in the same manner and the partial flows mix immediately after leaving the flow channels. Even the swirling associated herewith is undesirable, because it means losses of energy, which must be compensated by using a larger amount of energy. However, there also is, above all, an uncontrolled distribution of the fines over the entire cross section of the fluid flow, which means an impairment of the unambiguous definition and maintenance of the separation limit. The stratification of the fines suspended in the separating air is therefore maintained according to the present invention in the separator wheel space  9  adjoining the blade channels and ending in the fines outlet by the division of the separator wheel blades according to their height. 
   The separator wheel according to the present invention, which is shown in  FIG. 3 , is characterized for this purpose in that the diameters D 1 , D 2 , D 3  at the inner edges of the blade decrease in a stepwise manner from the fines outlet opening (which is not shown, but is to be assumed to be located to the right of the view) toward the hub  2 , i.e., the diameter D 1  is greater than the diameters D 2 , D 3 , and the diameter D 2  is in turn greater than the diameter D 3 . As a result, the fluid flow flowing out of the blade channels between the blade sections  4   b  in a cylindrical form comes to lie over the fluid flow flowing out of the blade channels between the blade sections  4   a  in a cylindrical form, and the fluid flow flowing out of the blade channels between the blade sections  4   c  in a cylindrical form comes to lie over the fluid flow flowing out of the blade channels between the blade sections  4   b  in a cylindrical form, without mixing taking place to an essential extent between the individual fluid flows. 
   To improve the effect, suction diaphragms  10 ,  11 ,  12 , whose diameters likewise decrease from the suction opening toward the hub  2  like those of the inner edges of the partial blades  4   a,    4   b,    4   c,  are attached to the inner edges of the ring disks  8   a ,  8   b  as well as of the blade end  8   c . The diaphragms  10 ,  11 ,  12  form rounded end areas, which facilitate the deflection of the flow from the radial direction into the axial direction in a trouble-free manner and facilitate the maintenance of the stratifications, which was mentioned several times. 
   The principle of this air separator, in which a separator wheel  1  according to  FIG. 3  is used, is first explained by FIG.  1 . The inlet  13  for the material to be separated and the inlet  14  for the separating air are associated with the separator housing  15  one after another in a radial plane, while the outlet  18  for the coarse material is arranged in another radial plane offset in the direction of the axis  3 , directed radially opposite the inlet  14  for the separating air and the inlet  13  for the material to be separated. 
   The separation chamber  17  is enclosed by a stationary vane ring  19  within the separator housing  15 , which is helical in the view in the direction of the longitudinal axis  3  (FIG.  2 ). 
   A separator wheel  1 , which is designed according to  FIG. 3 , is arranged in the separation chamber  17  enclosed by the vane ring  19 , again concentrically to the separator axis  3 . The annular space between the outer circle of the separator wheel  1  and the inner circle of the vane ring  19  is relatively narrow, because no separation is to take place in it. The width of the annular space between the separator wheel and the vane ring is selected to be only as great as is necessary with respect to the ordered transfer of the coarse material consisting of material to be separated and separating air—the transfer of the latter from the vane ring—into the separator wheel  1 . 
   The inlet  13  for the material to be separated opens tangentially into the separation chamber in the area of the annular space between the vane ring  19  and the separator wheel  1 . The inlet  14  for the separating air opens tangentially into the annular space between the vane ring  19  and the housing  15 , which is helical in the view in FIG.  2 . The inlet  13  for the material to be separated and the inlet  14  for the separating air are pipes arranged in parallel to one another. The outlet  18  for the coarse material is a pipe, which is located opposite the inlet  14  for the separating air and the inlet  13  for the material to be separated in the view in  FIG. 2 , i.e., it is directed downwardly, and the two inlets  13 ,  14 , on the one hand, and the outlet  16  for the coarse material, on the other hand, are offset in relation to one another in the direction of the longitudinal axis  3  of the separator or the axis of rotation of the separator wheel  1  by at least one turn of the helix, i.e., the housing  15  is a helical housing, which appears especially from the view in FIG.  1 . 
   The separating air flows through the flow channels between the guide vanes of the vane ring  19  from the outside to the inside. 
   The guide vanes lie on a helical contour predetermined by the housing and are mounted rotatably in the housing  15  such that both the angle at which the separating gas flows in and the gap width through which the flow takes place between the blades can be varied. 
   The vane ring  19  is used at most for a comparatively slight preseparation, but above all for the intense dispersion and disagglomeration of the material to be separated. The separation proper takes place with good efficiency in the separator wheel. 
   The fines finally leave the separator via the fines outlet  21 . Scattered material, which circulates close to the vane ring  19 , is preferably removed from the separation space via the discharge  18  for coarse material. As a consequence of the offset of the inlet  13  for the material to be separated and the inlet  14  for the separating air, on the one hand, and the outlet  18  for coarse and scattered material, on the other hand, in the axial direction of the housing  15 , the coarse material and possibly scattered material reach the area of the coarse material outlet  18  along the inner side of the housing wall, without special additional built-in elements, such as a baffle plate or a discharge screw being necessary. 
   Circular arc-shaped diaphragms  25 ,  26 , which divide the separation space into a plurality of sections, by which the charge is separated from the fines in helical movements, not continuously but stepwise, and leaves the separation space as coarse material, are arranged according to the present invention in the annular space between the separator wheel  1  and the vane ring  19 . 
   The circular arc-shaped segments  25 ,  26  are aligned with the suction diaphragms  10  through  12  of the separator wheel  1  arranged in a stepped pattern. They form an angle of at least 180□ such that they overlap each other at the ends associated with one another (areas  27 ,  28 ). 
   The essence of the present invention shall finally be summarized once again as follows on the basis of the state of the art according to DE 43 29 706 A1, DE 38 00 843 A1 and DE 196 43 023 A1. 
   In DE 38 00 843,  FIG. 1 , separating air enters the area of ring disks  12 ,  13  and  14  of the separator wheel  11  via an inlet  3  from the outside, entraining with it a mixture of fines and coarse material, which is charged in at  6 , and a stratification of the originally homogeneous mixture of separating air and fines takes place in that area over a relatively short section. After leaving the area of the ring disks, the parts of the mixture of fines and separating air, which were stratified before, are united again in order to be removed from the separator as a mixture that is again homogeneous. Arriving from the charge hopper  6  and crossing the separating air, coarse material is removed in the downward direction still before the separator wheel  11 . Consequently, stratification of the mixture of fines and separating air takes place over the short section of the ring disks  12 ,  13 ,  14  alone. A special multistep stratification of the coarse material does not take place in the separation space. 
   No stratification of separating air and material to be separated takes place in DE 196 43 023. The residence time of the material to be separated, which is charged in above the scattering disk  7  of the separator wheel  3  through an opening surrounding the drive shaft  1 , is rather prolonged in the separation space  6 , which is crossed by the separating air charged in at  4  in the direction of the diameter of the separator wheel  3 , in order to better separate from each other coarse material, on the one hand, and fines and separating air, on the other hand, before the entry of the mixture of separating air and fines into the separator wheel. The residence time of the mixture of material to be separated and separating air in the separation space  6  is prolonged by guiding the material to be separated on a circular arc-shaped path in the separation space by means of a turn of a helix. A special stratification does not take place in the separator wheel. 
   A comparable helical guiding of material to be separated in the separation space is already achieved in DE 43 29 706 A1, and this guiding is forced to take place by the inlet  3  for the material to be separated and the inlet  5  for the separating air, on the one hand, and the outlet  8  for coarse material as well as the outlet  7  for fines, on the other hand, being arranged offset in relation to one another in the longitudinal direction and the circumferential direction of the cylindrical separator housing  1 . 
   Contrary to this, stratification of the material to be separated takes place in the air separator according to the present invention in such a way that (especially in FIG.  4 ), the material to be separated is charged in at  13  and is guided up to the end of a first circular arc-shaped separation chamber part, which is formed by the circular arc-shaped diaphragm  26 , in order to pass over at the end of this separation chamber part into a second circular arc-shaped separation chamber part, which adjoins the first separation chamber part and whose beginning is characterized by the beginning of the second circular arc-shaped diaphragm  26   a,  which follows the first diaphragm  26  offset in the circumferential and longitudinal directions. Finally, the material to be separated enters a third circular arc-shaped separation chamber part, which follows the second circular arc-shaped separation chamber part and whose beginning is characterized by the beginning of the third circular arc-shaped diaphragm  25 . Each circular arc-shaped separation chamber part is exactly separated from the respective other separation chamber part except from the respective transition from one separation chamber part into the other, and separation between fines and coarse material takes place in each separation chamber part, and coarse material enters the next separation chamber part from each separation chamber part, and it finally reaches the coarse material outlet  18 , while fines will finally correspondingly enter the fines outlet  21 ; consequently, optimal separation takes place, on the whole, between fines and coarse material. Important is here the avoidance of “short-circuit flows” and the forcing of the mixture of material to be separated and separating air to flow through the separation chamber parts over their entire length, which is due to the specific cooperation of ring disks  8   a ,  8   b ,  8   c  of the separator wheel and of diaphragms  25 ,  26 ,  26   a,  which can be recognized especially in  FIG. 4 ; without this cooperation, a “short-circuit flow” would take place, e.g., in the area in which it is prevented in the present invention by the cooperation of the diaphragm  24  and the separator wheel.