Patent Publication Number: US-7712611-B2

Title: Apparatus for controlling the separation of particulate material

Description:
RELATED APPLICATION 
   This application is a continuation of application Ser. No. 09/678,045 filed Oct. 3, 2000, now U.S. Pat. No. 6,889,843 B1, issued May 10, 2005. 

   This invention relates to apparatus, especially useful in the manufacture of cement, for controlling the separation of particulate material into relatively fine and relatively coarse particles. 
   BACKGROUND OF THE INVENTION 
   In the manufacture of granular materials such as cement it is conventional to introduce comminuted particulate material to a sifter or separator having a separating zone in which the particulate material is reduced to relatively fine and relatively coarse particles. A gas stream flows through the separating zone at such velocity as to entrain relatively fine particles and convey them downstream of the separating zone for storage or further processing. The coarse particles which are not entrained in the gas stream are discharged from the separating zone for further comminution or other treatment. The fine particles which are entrained in the gas stream conventionally are separated from the gas downstream of the separating zone. 
   The separation of the gas and fine particles conventionally occurs in a cyclone separator in which the gas and the particles flow out of the separator along different paths. The efficiency of such separators depends in large part upon the volume and rate of flow of the gas. Any reduction in the volume of such gas could affect adversely the separation of the particles from the gas. 
   The treatment to which the relatively fine particles downstream of the separating zone may be subjected depends in large measure on the size or fineness of the relatively fine particles entrained by the gas stream. The fineness of such particles may be regulated by the volume and velocity of the gas stream that passes through the separating zone. However, and as is indicated above, changes in the volume and velocity of the gas stream affect the efficiency of the gas/fine particle separation. Reductions in the efficiency of the gas/fine particle separation can have adverse consequences on the further treatment of the particles downstream of such separation. 
   In some instances the gas stream that is introduced to the separating zone may be heated for the purpose of drying or preheating the particles. In other instances, the gas may be cooled for the purpose of cooling the particles. In either instance a reduction in the volume of air which is used to transport entrained fine particles to the gas/fine particle separator may have adverse consequences on the dryness or temperature of the fine particles. 
   A principal object of the invention is to provide apparatus which overcomes the undesirable effects referred to above. 
   SUMMARY OF THE INVENTION 
   Particulate material of the kind with which the invention is concerned is delivered from a source to a comminution zone at which the material is crushed to form relatively coarse and relatively fine particles. The crushed material is separated into relatively coarse and relatively fine particles. A gas stream is introduced to the separator independently of the material and passes through the separating zone at such velocity as to entrain fine particles and convey them from the separator to a gas/particle separator at which the particles are separated from the gas and conveyed to a collection bin for storage or subsequent treatment. The gas separated from the coarse particles preferably is returned from the gas/particle separator to the separating zone for further separation of relatively coarse and fine particles. 
   In accordance with the invention a gas passageway is provided for enabling a selected portion of the gas stream presented to the separator to bypass the separating zone following which such portion of the gas stream is recombined with the gas and the entrained fine particles. In one embodiment the bypass comprises a passageway within the particle separator housing and is so positioned that material enroute to the separating zone passes through the diverted portion of the gas. In another embodiment the passageway is external of the separator, but is in communication with both the gas inlet and the outlet through which gas and entrained fine particles pass. 
   One or more dampers are provided in the bypass passageway for controlling the admission of gas to the bypass passageway. The position of the dampers can be adjusted in such manner as to control the fineness of particles entrained in the gas stream and such control can be regulated in response to changes in the weight of fine particles contained in the collection bin which is downstream from the gas/particle separator. 

   
     THE DRAWINGS 
     Apparatus constructed in accordance with presently preferred embodiments of the invention are illustrated in the accompanying drawings in which: 
       FIG. 1  is a diagrammatic flow sheet illustrating the apparatus and the method of its operation; 
       FIG. 2  is a diagrammatic, isometric view of one embodiment of the separator; 
       FIG. 3  is a vertical sectional view of the separator shown in  FIG. 2 ; 
       FIG. 4  is a diagrammatic, isometric view of a second embodiment of the separator but rotated 180° from the portion shown in  FIG. 1 ; and 
       FIG. 5  is a vertical sectional view of the separator shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   Apparatus constructed in accordance with the invention is disclosed as forming part of an otherwise conventional cement production facility wherein particulate material from a silo or other source  1  is delivered by a conveyor  2  to a bucket elevator  3  which discharges the particulate material to a conveyor  4  that supplies a hopper  5 . From the hopper the material is delivered to a high pressure, roller comminuting zone  6  at which the material is crushed in known manner and delivered to a conveyor  7  that conveys such material to an elevator  8  from which the material is discharged to a separator  9  constructed in accordance with the invention. 
   One embodiment of the separator  9  is shown in  FIGS. 2 and 3  and comprises a housing  10  having opposed side walls  11 , opposed end walls  12 , a top wall or cover  13  and an inclined bottom wall  14 . The cover  13  has three openings therein. One opening  15  is near the center of the cover and has an upwardly extending chute  15   a  connected thereto. The other openings  16  and  17  are adjacent opposite ends of the cover for reasons to be explained in more detail hereinafter. The opening  15  is an inlet for particulate material delivered from the comminuting zone  6 , the opening  16  is a gas inlet, and the opening  17  is an outlet for fine particles and gas. At the bottom of the housing  9  is an opening  18  to which is fitted a conical chute  19  through which coarse particles may be discharged. 
   The walls of the housing  9  form a chamber within which are two vertical ranks of inclined vanes  20  and  21  which are supported by the side walls  11  and are in chevron form so that particulate material introduced to the housing  10  will cascade downwardly and be reduced to relatively fine and relatively coarse particles. The area in which the vanes  20  and  21  are positioned forms a separating zone  22  in which downwardly cascading particulate material is separated into the relatively coarse and the relatively fine particles. 
   At a level above that of the separating zone  22  is a passageway  23  formed by a partition or wall  24  which spans the width of the side walls  11  and parallels the cover  13 . It is appreciated from  FIGS. 1-3  that the passageway  23  can be generally horizontal. Within the passageway  23  are two spaced apart dampers  25  and  26 . Each damper is rotatable about a horizontal axis and each damper is of such dimensions as selectively to close and open the passageway. Connected to the damper  25  is a rotary control or actuator  27 . A similar control  28  is coupled to the damper  26 . The controls  27  and  28  may be coupled to one another in known manner for conjoint operation. 
   As is best shown in  FIG. 3 , the partition  24  has an opening  29  aligned with the material inlet  15 . Such opening enables material which enters the material inlet  15  to pass through the passageway  23  upstream of the separating zone  22  so that, in the event gas is flowing through the passageway, the incoming material may be preheated, precooled, or predried enroute to the separating zone  22 . 
   The separator  9  disclosed in  FIGS. 4 and 5  corresponds to that shown in  FIGS. 2 and 3 , but differs from the latter in that the passageway  23   a  is formed by a duct  24   a  which is external of the housing  10   a  and communicates by suitable connections at its opposite ends with the gas inlet  16  and the outlet  17 , respectively. It is appreciated that the passageway  23   a  can be generally horizontal. A single damper  25   a  is pivotally mounted in the passageway  23   a  adjacent the gas inlet end thereof. The damper  25   a  is movable to any selected one of a number of positions between its open and closed positions by a control  27   a.    
   The method of operation of the apparatus described thus far is that raw material is conveyed from the silo  1  or other source via the conveyors  2 ,  3 , and  4  to the hopper  5  and thence to the comminuting zone  6 . The comminuted, particulate material is conveyed from the comminuting zone  6  via the conveyors  7  and  8  to the material inlet  15  of the separator  9 . 
   At the same time a stream of gas from a source thereof is delivered independently of the material via a blower  30  to the gas inlet  16  of the separator  9 . If the dampers  25  or  25   a  are closed, the gas stream will flow toward and through the separating zone  22  to and through the outlet  17  and into the conduit  31 . 
   Material entering the separator  9  through the material inlet  15  independently of the gas stream flows downwardly by gravity through the separating zone  22  along a path leading to the coarse particle outlet  18 . As the material flows downwardly it will be cascaded by the vanes  20  and  21  and reduced to relatively coarse and relatively fine particles. 
   The velocity of the gas flowing through the separating zone  22  should be such as to entrain fine particles of various sizes and convey them to and through the fine particle and gas outlet  17 . Particles which are too coarse to be entrained in the gas stream will continue their downward movement and be discharged from the separator via the coarse particle outlet and chute  19 . Such particles may be returned to the comminuting zone  6  by the elevator  3  and the conveyor  4  for further comminution. 
   The gas and entrained particles discharged through the outlet  17  are conveyed by the conduit  31  to a gas/particle separator  32  which, in the form shown, comprises a pair of cyclones  33  and  34  arranged in series. The gas from which the particles have been separated flows out of the cyclones via a line  35  for discharge to atmosphere or other apparatus or, if desired, partially may be recirculated to the gas inlet  16  by a line  36 . A secondary fan (not shown) may communicate with the line  35  or  36  for supplying additional gas. If desired, either or both of such fans may be coupled to a source of gas, such as air, which may be cooled, heated, or at ambient temperature. 
   Particulate material from the gas/particle separator  32  flows to a collector or bin  37  which is supported by one or more load cells  38  of conventional construction and which are capable of sensing changes in weight of material in the bin. Material from the bin  37  may pass therefrom to a grinding mill  39  such as a ball mill, wherein the fine particulate material is subjected to grinding operations to reduce the particles to the desired fineness. Ground material passes from the mill  39  to a storage area or other suitable destination. 
   In the embodiment of the material separator  9  shown in  FIGS. 2 and 3  the volume of gas admitted to the housing  10  via the gas inlet  16  should be sufficient to enable efficient operation of the gas/particle separator  32 . The quantity and fineness of relatively fine particles that are entrained in the gas stream which flows through the separating zone  22  and through the outlet  17  to the bin  36  may be adjusted by diverting some portion of the gas stream entering the housing  10  from the separating zone  22 . Bypassing the separating zone may be accomplished by moving the dampers  25  and  26  from their passageway-closing positions to selected adjusted positions in which the passageway  23  is at least partially open, thereby enabling a portion of the gas stream entering the housing  10  via the gas inlet  16  to be diverted into the passageway  23  for discharge through the outlet  17 . In this embodiment two dampers  25  and  26  are desirable to ensure that gas which has passed through the separating zone  22  when the inlet end of the passageway  23  is closed does not enter the passageway  23  adjacent the outlet  17 . 
   The volume of gas that is diverted from the separating zone  22  to the passageway  23  affects the fineness of the particles which may be entrained in the gas stream. For example, whenever a portion of the gas stream is diverted from the separating zone  22  the particles which may be entrained in that part of the gas stream which flows through the separating zone will be finer than in the case in which all of the gas stream flows through the separating zone. Consequently, the quantity and weight of particles delivered to the bin  37  following a diversion of a portion of the gas stream from the separating zone  22  will be less than that when all of the gas stream passes through the separating zone. Accordingly, the weight of the material in the bin  37  will be reduced, and the reduction in weight will be sensed by the sensor  38 . The sensor thereupon will generate a signal which may be used to alert the system operator to adjust the positions of the dampers  25 , 26  so as to increase, decrease, or eliminate the diversion of the gas stream from the separating zone. 
   In most instances the sensor  38  will be set to be inactive as long as the weight of material in the bin  37  is at a fairly constant level. Once the sensor has been set, the rate of consumption of such material by the mill  39  may be used to control the fineness of the particles delivered to the bin. For example, if the particles delivered from the bin  37  to the mill  39  are of such fineness as to require minimum grinding by the mill, the throughput of the mill may be sufficiently great as to cause the weight of material in the bin to decrease. In this event the signals from the sensor  38  indicate that the diversion of gas from the separating zone  22  should be reduced, thus enabling more of the gas stream to pass through the separating zone so that a greater quantity of particles is delivered to the bin, thereby increasing the weight of material in the bin. 
   Conversely, if the weight of material in the bin  37  increases, this indicates that the quantity of materials supplied to the bin is greater than that which is being consumed by the mill. In this event the signal from the sensor may be used to signal the need to divert a selected portion of the gas stream from the separating zone  22 , thereby resulting in a reduction in the fineness of particles delivered to the bin. 
   In the embodiment of the separator  9  shown in  FIGS. 4 and 5 , the operation is similar to that previously described. In this embodiment, however, the bypass passageway  23   a  is wholly external of the housing  10   a . A selected portion of air entering the inlet  16  may be diverted into the bypass passageway  23   a  by adjustment of the damper  25   a  which is located adjacent the inlet  16 . In this embodiment only one damper  25   a  is required since there are no openings in the passageway other than those which communicate with the inlet  16  and the outlet  17 . The position of the damper  25   a  is controlled by an operator  27   a.    
   The operation of the embodiment shown in  FIGS. 4 and 5  is quite similar to that of the earlier described embodiment. In this embodiment, however, none of the particulate material introduced to the housing  10   a  via the material inlet  15  passes through the passageway  23   a.    
   In either of the disclosed embodiments the signals from the sensor  38  may be coupled electrically directly to the damper controls  27 , 27   a  in known manner. The coupling is indicated by the reference character  40 . 
   In the operation of the invention utilizing either of the disclosed embodiments the volume and velocity of the gas stream introduced to the separator housing  10  or  10   a  will be sufficient to effect entrainment of relatively fine particles from the separating zone  22  and ensure efficient operation of the gas/particle separating apparatus  32 . Even though a selected portion of the gas stream introduced to the separator housing may be diverted from the separating zone to the bypass passageway, such diverted gas is recombined with the gas in which the relatively fine particles are entrained conveyed to the gas/particle separator  32  via the conduit  31 . As a consequence, the volume of gas that is delivered to the particle/gas separator  32  is sufficient to ensure efficient operation of the latter. 
   The disclosed embodiments are illustrative of presently preferred apparatus according to the invention, but are intended to be illustrative rather than definitive thereof. The invention is defined in the claims.