Abstract:
Disclosed is a grinding mill including a roller press configured to comminute grinding stock, a first conveying mechanism in communication with the roller press and configured to transport downstream at least one of fresh grinding stock or grinding stock comminuted by the roller press, and a static sifter disposed downstream of the first conveying mechanism and configured to sift at least one of the fresh grinding stock or grinding stock comminuted by said roller press. The static sifter includes a sifting stock inlet disposed in an upper sifting space, and sifting gas inlet disposed in a lower sifting space, and an aeration plate separating the upper sifting space from the lower sifting space. The aeration plate also permits sifting gas to pass there through from the lower to the upper sifting space. The static sifter also includes oversized material outlets disposed in each of the respective upper and lower sifting spaces.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Entry of International Patent Application Serial Number PCT/EP2013/071031, filed Oct. 9, 2013, which claims priority to German patent application no. DE 102012109644.9 filed Oct. 10, 2012, the entire contents of both of which are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a grinding installation for comminuting brittle grinding stock. 
     BACKGROUND 
     A recirculating grinding installation with a static sifter arranged above the roller press is known from EP 0 650 763 A1, wherein the oversized material from the sifter arrives in the feed shaft of the roller press by means of gravity. The fresh material, together with the slugs from the roller press output, is fed via a conveying mechanism to the static sifter. Furthermore, DE 10 221 739 A1 shows an arrangement in which the roller press is arranged above the static sifter. In this context, the width of the sifter is essentially matched to the width of the grinding rollers, such that the comminuted grinding stock reaches the static sifter with an optimum distribution across the width. However, both variants require a high expenditure in terms of construction and lead to a very great overall height. In particular, arranging the roller press above the static sifter is associated with enormous costs on account of the high weight. 
     In the interim, it has further been found that the efficiency of the static sifter can be increased if it is made wider and accordingly not as high. According to EP 1 786 573 B1, in that context, a ratio of width to vertical height of the aeration plate of at least 0.45 has been found to be particularly advantageous. However, roller presses are usually only 1.5 to maximum 2 m wide and a significant width increase cannot currently be envisaged. For that reason, very high and narrow static sifters are presently used. If one wished to position a wider and accordingly lower sifter beneath a roller press, it would be necessary to provide means for distributing the roller press output material over the breadth of the sifter. However, such measures require additional overall height. 
     Moreover, U.S. Pat. No. 1,002,504 A discloses a grinding installation which contains a roller press for comminuting brittle grinding stock with two counter-rotating grinding rollers, and also a static sifter with a sifting stock inlet for grinding stock comminuted in the roller press, with an outlet for oversized material and an outlet for fine material, wherein the outlet for oversized material is connected to the roller press. This grinding installation further contains a conveying mechanism which lifts the output of the roller press to the sifting stock inlet of the static sifter. 
     Finally, DE 694 21 994 T2 shows a grinding installation with a roller mill and a classifying device of the fluidized bed type. The box-shaped housing of this classifying device is divided, by a porous, inclined separating plate, into an upper fluidized bed chamber and a lower air inlet chamber. The grinding stock to be classified is introduced on one side from above into the fluidized bed chamber, while on the other side the fluidized fine material is removed upward and the oversized material which does not float is withdrawn downward. 
     SUMMARY 
     It is an object of the present disclosure to simplify, in terms of construction, a grinding installation and at the same time making a high sifting efficiency possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a schematic front view diagram of an embodiment of a grinding installation of the present disclosure. 
         FIG. 2  is a schematic plan view of the grinding installation of  FIG. 1 . 
         FIG. 3  is a schematic side view of an embodiment of a sifter of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With the roller press, the conveying mechanism and the sifter being arranged one next to the other in terms of construction, the overall height and thus the construction expenditure can be markedly reduced. Also, with the installation parts being arranged in a straight line one behind the other in terms of the material flow direction, the construction can be simplified since it is not necessary for material to be redirected laterally between the roller press and the sifter. The material to be sifted is thus transported in one direction and, in that context, raised up only by the conveying mechanism. 
     For the purpose of efficient sifting in the static sifter, it is important that the material be fed onto the sifter as evenly as possible. It is therefore of particular importance that, on the conveying mechanism, the width distribution of the material to be sifted is not disrupted by any redirections which deviate from the actual transport direction. 
     Within the scope of the invention, however, it is also possible for multiple roller presses and/or multiple conveying mechanisms and/or multiple static sifters to be used. 
     Since, according to the invention, the sifting stock inlet is arranged on that side of the sifter which is oriented toward the conveying mechanism, while the sifting gas inlet is connected on the sifter in a region which is oriented away from the conveying mechanism, it is possible for the installation parts which are arranged in a line one after the other, in particular the conveying mechanism and the sifter, to be arranged in a very compact manner 
     According to the invention, the static sifter has two has two sifting spaces which are arranged one above the other and are separated from one another by the aeration plate, wherein the sifting stock inlet for the fresh grinding stock and/or the grinding stock comminuted in the roller press opens into the upper sifting space and the sifting gas inlet is connected to the lower sifting space. Furthermore, according to the invention, the first outlet for oversized material is connected to the upper sifting space and the lower sifting space is provided with a second outlet for oversized material. 
     The present disclosure is explained in further detail below with reference to the attached drawing figures. 
     The grinding installation shown in  FIGS. 1 and 2  has, in essence, a roller press  1 , a conveying mechanism  2  and a sifter  3 . The roller press is equipped, for the purpose of comminuting brittle grinding stock such as limestone, with two counter-rotating grinding rollers which form between them a grinding gap and which are pressed against one another at high pressure. The roller press is in particular well suited to comminuting a bed of material, as is described in more detail in EP 0 084 383. The static sifter  3  has a sifting stock inlet  4  for fresh grinding stock  5  and/or grinding stock  5  comminuted in the roller press  1 , an aeration plate  7  which is arranged at an angle to the horizontal and through which sifting gas  6  flows, an outlet  8  for oversized material and an outlet  9  for fine material. The conveying mechanism  2  is preferably formed as a bucket elevator, wherein its upper end  2   a  is connected to the sifting stock inlet  4  of the sifter  3  via a chute  10 . 
     Furthermore, there is provided a conveying device  11 , for example a conveyer belt or a belt conveyer, which is connected to a fresh material feed  12  and to the roller press  1  in order to transport fresh grinding stock  13  and/or grinding stock  14  comminuted in the roller press to the lower end  2   b  of the conveying mechanism  2 . 
     As shown in  FIGS. 1 and 2 , the roller press  1 , the conveying mechanism  2  and the sifter  3  are arranged one next to the other in terms of construction and in a straight line one behind the other in terms of the material flow direction  15 . In order to achieve an optimal width distribution of the sifting stock when the latter is fed into the sifter  3 , the width of the conveying mechanism  2  essentially corresponds to the width of the sifting stock inlet  4  of the sifter  3 . In that context, the width of the conveying mechanism and of the sifter are for example at least 2.5 m, 3 m, 3.5 m or 4 m. The conveying mechanism can of course also be formed by two or more conveying mechanisms which are correspondingly narrower and are arranged immediately next to one another perpendicular to the conveying direction  15 . 
     The sifter  3  will be described in more detail below with reference to  FIG. 3 . It consists, in essence, of an upper sifting space  16 , a lower sifting space  17  and the aeration plate  7  which is arranged at an angle to the horizontal and separates the two sifting spaces from one another. The aeration plate  7  is formed as an inclined plane with aeration openings, or as an inclined perforated plate. The openings of the aeration plate can have different opening geometries distributed over the entire surface. That has the advantage that, by means of both the arrangement and also the respective opening geometry, it is possible to influence the distribution, the speed and the direction of the sifting gas in order to ensure that the sifting stock is flowed through optimally at every point of the aeration plate. It is thus possible to further raise the sifting efficiency. 
     The sifting stock inlet  4  opens into the upper sifting space  16  in the region of the upper end of the aeration plate  7  while, at the lower sifting space  17 , there is provided a sifting gas inlet  18  for the supply of the sifting gas  6 . The sifting gas flows from the sifting gas inlet  18  upward and through the aeration plate  7 . The sifting gas thus flows in an essentially perpendicular manner through the sifting stock  5  in the upper sifting space  16 , wherein the oversized material is ejected via the first outlet  8  for oversized material, arranged at the lower end of the aeration plate  7 . The fine material is fed, together with the sifting gas, via the outlet  9  for fine material, to a downstream dynamic sifter  19 . Thus, in the upper sifting space, there forms a transverse-flow sifting zone while in the lower sifting space there is provided a counter-flow sifting zone for the sifting stock falling through the aeration plate. The configuration of the dynamic sifter  19  and the interplay with the static sifter is for example known from EP 1 786 573 B1. 
     The oversized material of the counter-flow sifting zone falls down onto an inclined plate  20  of the lower sifting space  17 , at the lower end of which there is provided a second outlet  21  for oversized material, for the oversized material of the counter-flow sifting zone. The angle of inclination of the inclined plate  20  is expediently greater than the wall friction angle of the oversized material to be ejected, so as to ensure that the oversized material slides out of the sifter on its own. 
     The fine material of the counter-flow sifting zone is either pressed with the sifting gas  6  through the aeration plate  7  or can in part be drawn off via a second outlet  22  for fine material, provided at the upper end of the lower sifting space  17 , and fed via a line  23  to the dynamic sifter  19 . The partial flow which is to be diverted from the lower sifting space  17  is established via a flap  24  arranged in the line  23 , in order to thereby also be able to influence, in a targeted manner, the sifting conditions in the transverse sifting zone in the upper sifting space  16 . A quantity of sifting gas drawn off via the line  23  accordingly reduces the quantity of sifting gas flowing through the aeration plate  7 . It is thus possible to optimize the sifting gas speed distribution of the static sifter  3  for the dynamic sifter  19 , without the associated aeration plate fall-through, i.e. the material which falls through the aeration plate, being able to negatively influence the entire process. 
     As is evident from  FIGS. 1 and 2 , the sifting stock inlet  4  is arranged on that side of the sifter oriented toward the conveying mechanism ( 2 ), while the sifting gas inlet  18  for the sifting gas  6  is connected to the sifter  3  in a region oriented away from the conveying mechanism, in this case on the opposite side. It is of course also possible, within the scope of the invention, that the sifting gas is supplied via two or more sifting gas inlets. In that context, a lateral supply can also in particular be considered. The angle between the orientation of the sifting stock inlet  4  and that of the sifting gas inlet  18  should be at least 15° and at most 345° in order that the conveying mechanism  2  can be arranged as close as possible to the sifter  3 . The sifting gas inlet  18  with the connected sifting gas line  25  should thus not come into conflict with the conveying mechanism ( 2 ). It must in particular be ensured that the transport direction of the conveyed material runs in a straight line (as seen from above) as far as the sifter and thus also the connection between the conveying mechanism ( 2 ) and the sifting stock inlet  4  is arranged in a straight line in order to avoid any redirections of material, which necessarily result in a worsened width distribution on the aeration plate. 
     The two outlets  8  and  21  for oversized material permit an unrestricted return of the oversized material into the grinding and sifting process. By virtue of the second oversized material outlet  21  in the lower sifting space, the aeration plate fall-through no longer presents a problem. To that end, the oversized material carried off via the oversized material outlets  8  and  21  of the static sifter  3  is conveyed upward by a second conveying mechanism  26 , wherein the upper end is connected via a further conveying device  27  to the feed shaft  1  a of the roller press  1 . In turn, the second conveying mechanism  26  is expediently formed as a bucket elevator, wherein a belt conveyer can be considered for the further conveying device  27 . In the region of the further conveying device  27 , there is moreover provided a metal ejection device  28  by means of which any metal parts falling from the sifter can be removed before the roller press  1 , in order to thus avoid damage to or destruction of the roller surfaces. The fine material  29  from the dynamic sifter  19  is supplied, together with the sifting gas, to a separator  30 . 
     The arrangement according to the invention of roller press, conveying mechanism and sifter permits a substantial reduction in the overall height. Moreover, all heavy loads are arranged close to the ground, which also permits easier access to the individual machines in the case of maintenance work. Moreover, the throughput can be increased by means of the use of wide sifters. Also, the low heights of the conveying mechanisms increase the mechanical reliability and thus permit higher turnover.