Abstract:
A decanter centrifuge that carries out solid-liquid separation by centrifugal force on an object to be processed that is fed into a rotating bowl and designed from a solid and a saturated solution wherein that solid is dissolved, and discharges solid phase components from a solid discharge opening and discharges liquid phase components from a solvent discharge opening thereof by rotationally operating a screw conveyor disposed within the rotating bowl, said decanter centrifuge being provided with a dilution solvent supply unit for supplying, during centrifuging of the object to be processed, dilution solvent that reduces the concentration of the saturated solution to a discharge path, which is a discharge path for saturated solution moving within the rotating bowl, and which is designed closer to the solvent discharge opening side—than a chamber for supplying the object to be processed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a decanter centrifuge that carries out solid-liquid separation by centrifugal force on an object to be processed that is designed from a solid and a saturated solution in which the solid is dissolved, etc. 
       BACKGROUND ART 
       [0002]    In the food field, for example, processing has been performed in which a saturated solution containing dissolved solids such as food residues is cooled to produce an object to be processed in a solid-liquid mixture state, which is designed from a saturated solution and solids, and solid-liquid separation is carried out on the object to be processed with a decanter centrifuge. 
         [0003]    The decanter centrifuge includes: a rotating bowl provided with a solvent discharge opening on one end side in the direction of its rotation axis and a solid discharge opening on the other end side thereof; and a screw conveyor disposed within the rotating bowl. The decanter centrifuge is configured to carry out solid-liquid separation by the centrifugal force of the rotationally operating rotating bowl on the object to be processed and to collect the solids from the solid discharge opening and discharge separated liquid from the solvent discharge opening with the screw conveyor. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: JP47-40556 
         [0005]    Patent Literature 2: JP2013-662 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    The present inventor has found out a problem in which the solids are precipitated from the centrifuged saturated solution and the precipitated solids obstruct the solvent discharge opening. As one method for eliminating such obstruction, a method of temporarily stopping the operation of the decanter and removing the solids adhering to the solvent discharge opening by washing is conceivable In order to carry out this method, however, the washing needs to toe performed after the large decanter rotating at high speed is decelerated and stopped. Additionally, no object to be processed can be fed unless the decanter is accelerated to a predetermined speed (for example, 4000 rpm) after the washing. In other words, the decanter needs to stop the centrifuge processing during the decelerating, washing, and accelerating periods of the decanter, thus impeding the efficient processing. 
         [0007]    From another perspective, a method of heating a centrifuged saturated solution to obtain an unsaturated solution is also conceivable. The saturated solution becomes more soluble by being heated, thus suppressing the precipitation of the solids. According to this method, however, a rapidly rotating large decanter having high heat capacity needs to be heated. Thus, its practicability is low. 
         [0008]    Here, a method for suppressing the precipitation of the solids by adding a dilution solvent that reduces the concentration of the saturated solution to the decanter together with the object to be processed is also conceivable. However, the solids having undergone the solid-liquid separation may be dissolved by the dilution solvent, thus lowering the recovery rate of the solids. 
         [0009]    In view of this, it is an object of the present invention to prevent the obstruction of a solvent discharge opening by solids precipitated from a saturated solution without lowering the recovery rate of solids while continuing operation of a centrifuge. 
       Solution to Problem 
       [0010]    A centrifuge of the present invention is (1) a decanter centrifuge including a rotating bowl and a screw conveyor disposed within the rotating bowl. The decanter centrifuge carries out solid-liquid separation by centrifugal force on an object to be processed that is fed into the rotating bowl from a chamber for supplying the object to be processed, that is designed within the screw conveyor and designed from a solid and a saturated solution in which the solid is dissolved, and discharges a solid phase component from a solid discharge opening designed on one end side in an axial direction of the rotating bowl and discharges a liquid phase component from a solvent discharge opening designed on the other end side thereof by rotationally operating the screw conveyor. The decanter centrifuge includes a dilution solvent supply unit supplying, during centrifuging of the object to be processed, a dilution solvent, which reduces a concentration of the saturated solution, to a discharge path for the saturated solution moving within the rotating bowl toward the solvent discharge opening. The discharge path is designed closer to a side of the solvent discharge opening in the axial direction than the chamber for supplying the object to be processed. 
         [0011]    (2) In the configuration of (1) described above, the dilution solvent supply unit may spray the dilution solvent to the solvent discharge opening. According to the configuration of (2), the dilution solvent is directly sprayed to the solvent discharge opening where the solid is precipitated. Consequently, the obstruction of the solvent discharge opening can be more effectively prevented from occurring. 
         [0012]    (3) In the configuration of (2) described above, the dilution solvent supply unit may be provided with a solvent spraying opening at a position closer to a rotation axis of the rotating bowl than the solvent discharge opening. According to the configuration of (3), there is no need to spray the solvent while resisting the centrifugal force of the rotating bowl. Thus, the injection pressure of the dilution solvent can be reduced. 
         [0013]    (4) In any one of the configurations (1) to (3) described above, the dilution solvent supply unit may include a pipeline extending along the screw conveyor, and the pipeline may be connected to a dilution solvent supply chamber designed within the screw conveyor. 
         [0014]    A method for operating a centrifuge according to the present invention is (5) a method for operating a decanter centrifuge, the decanter centrifuge including a rotating bowl and a screw conveyor disposed within the rotating bowl, wherein the decanter centrifuge is configured to carry out solid-liquid separation by centrifugal force on an object to foe processed that is fed into the rotating bowl from a chamber for supplying the object to be processed that is designed within the screw conveyor and designed from a solid and a saturated solution in which the solid is dissolved, and to discharge a solid phase component from a solid discharge opening designed on one end side in an axial direction of the rotating bowl and discharge a liquid phase component from a solvent discharge opening designed on the other end side thereof by rotationally operating the screw conveyor. The method for operating the decanter centrifuge includes supplying, during centrifuging of the object to be processed, a dilution solvent, which reduces a concentration of the saturated solution, to a discharge path for the saturated solution moving within the rotating bowl toward the solvent discharge opening. The discharge path is designed closer to a side of the solvent discharge opening in the axial direction than the chamber for supplying the object to be processed. 
       Advantageous Effects of Invention 
       [0015]    According to the present invention, supplying the dilution solvent to the discharge path for the saturated solution moving toward the solvent discharge opening can prevent the obstruction of the solvent discharge opening by the solids precipitated from the saturated solution. Moreover, since the process of supplying the dilution solvent is performed during the operation of the centrifuge, the processing efficiency of the centrifuge is prevented from degrading. Furthermore, since the dilution solvent is supplied only to the discharge path for the saturated solution, the centrifuged solids can be prevented from being dissolved in the dilution solvent to lower the recovery rate of the solids. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a diagram illustrating an overall configuration of a decanter according to an embodiment of the present invention. 
           [0017]      FIG. 2  is an enlarged view illustrating part of the decanter. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    Hereinafter, a centrifuge according to a preferred embodiment of the present invention will be described taking a horizontal decanter as an example. Note however that embodiments, which will be described below, are not to be construed as limiting the technical scope of the present invention.  FIG. 1  is a front view of the decanter and a cross-sectional view illustrating part thereof.  FIG. 2  is an enlarged view illustrating elements shown in the cross-sectional view. 
         [0019]    With reference to these figures, the decanter  1  includes a rotating bowl  10  and a screw conveyor  20  disposed within the rotating bowl  10 . The rotating bowl  10  rotates about a rotation axis L indicated by a chain doable-dashed line. One end of the rotating bowl  10  in the direction of the rotation axis L is rotatably supported by a bearing  11 , whereas the other end thereof is rotatably supported by a bearing  12 . A plurality of solvent discharge openings  13  are designed on the one end side of the rotating bowl  10  in the direction of the rotation axis. These solvent discharge openings  13  are arranged around the rotation axis L of the rotating bowl  10 . Intervals between adjacent ones of the solvent discharge openings  13  are set at approximately equal distances. The opening shape of the solvent discharge opening  13  may be circular, for example. 
         [0020]    A plurality of solid discharge openings  14  are designed in the other end of the rotating bowl  10  in the direction of the rotation axis L. These solid discharge openings  14  are arranged around the rotation axis L of the rotating bowl  10 . Intervals between adjacent ones of the solid discharge openings  14  are set at approximately equal distances. The opening shape of the solid discharge opening  14  may be circular, for example. 
         [0021]    A beach part  15  inclined toward the solid discharge openings  14  in the direction of the rotation axis L is designed on an inner wall surface on the other end side of the rotating bowl  10  in the direction of the rotation axis L. Note, however, that the present invention can be applied also to a rotating bowl  10  having no beach part  15  and thus having a fixed inner diameter. 
         [0022]    The screw conveyor  20  has the function of conveying solids to which centrifugal force is applied in the rotating bowl  10 . The screw conveyor  20  rotates with a differential speed rate relative to the rotating bowl  10 . In other words, the screw conveyor  20  rotates at a rotational speed slower than that of the rotating bowl  10  by the transmission of power from a gearbox  30 . A planet gear, for example, may be employed in the gearbox  30 . 
         [0023]    A screw blade  22  is spirally designed on the outer peripheral surface of a barrel  21  of the screw conveyor  20 . A hollow (buffer part) is designed with in the barrel  21 . The hollow includes a chamber  21   a  for supplying an object to be processed and a solvent supply chamber  21   b  for supplying a dilution solvent to a centrifuged saturated solution. A plurality of passages  210   a  for the object to be processed are designed on the outer peripheral surface of the chamber  21   a  for supplying the object to be processed. 
         [0024]    A supply pipe  40  extends in the direction of the rotation axis L of the rotating bowl  10  through a pulley  31  for driving the rotating bowl  10 . The supply pipe  40  is configured to have a double pipe structure including a main supply pipe  41  and a secondary supply pipe  42  designed on the outer periphery of the main supply pipe  41 . One end of the main supply pipe  41  forms an opening  41   a  for introducing the object to be processed at the outer side of the rotating bowl  10 . The other end of the main supply pipe  41  forms an opening  41   b  for supplying the object to be processed inside the chamber  21   a  for supplying the object to be processed. 
         [0025]    The object to be processed, which has been introduced from the opening  41   a  for introducing the object to be processed, is introduced into the chamber  21   a  for supplying the object to be processed via the main supply pipe  41 . A saturated solution containing solids is used as the object to be processed. Such solids are obtained, for example, as a result of precipitation by the cooling of the saturated solution or as those remaining undissolved in the saturated solution. In other words, the object to be processed by the decanter  1  of the present embodiment is a solution in a solid-liquid mixture state in which solids are precipitated by the cooling of a saturated solution. Examples of the saturated solution may include a saturated solution in which monosodium glutamate is dissolved, a saturated solution in which food residues are dissolved, and a saturated solution used in the field of chemicals. Examples of the saturated solution used in the field of chemicals may include solutions containing ammonium sulfate, salts such as sodium chloride, and amino acids. 
         [0026]    One end of the secondary supply pipe  42  forms a dilution solvent introduction opening  42   a  at the outer side of the rotating bowl  10 , whereas the other end of the secondary supply pipe  42  is closed. The provision of the secondary supply pipe  42  results in the formation of an annular dilution solvent passage along the outer periphery of the main supply pipe  41 . A plurality of dilution solvent supply openings  42   b  are designed in a region of the secondary supply pipe  42  extending along the rotation axis L. These dilution solvent supply openings  42   b  are in communication with the solvent supply chamber  21   b.    
         [0027]    A plurality of openings  210   b  are provided in the circumference of the solvent supply chamber  21   b.  One ends of dilution solvent passage pipes  23  are connected to these opening  210   b.  Consequently, the dilution solvent passage pipes  23  rotate together with the screw conveyor  20 . Note that the number of the dilution solvent passage pipes  23  equals the number of the openings  210   b.    
         [0028]    The dilution solvent passage pipe  23  extends along the direction of the rotation axis of the screw conveyor  20 . A solvent spraying opening  23   a  is designed at a termination of the dilution solvent passage pipe  23 . The solvent spraying opening  23   a  is provided at a position closer to the solvent discharge opening  13  than at least the chamber  21   a  for supplying the object to be processed. In other words, the solvent spraying opening  23   a  is designed at an appropriate position capable of spraying the dilution solvent to a solution discharge path of the saturated solution having undergone the solid-liquid separation by centrifugation. The solution discharge path refers to a region within the rotating bowl and outside the screw conveyor  20  and closer to the solvent discharge openings  13  than the chamber  21   a  for supplying the object to be processed in the direction of tine rotation axis L of the rotating bowl  10  (note, however, that a region at which the solvent discharge openings  13  are positioned is also included). The solvent supply chamber  21   b,  the dilution solvent passage pipes  23 , and the secondary supply pipe  42  work together to constitute a dilution solvent supply unit. 
         [0029]    The saturated solution is diluted by supplying the dilution solvent to the aforementioned solution discharge path, thereby suppressing the precipitation of the solids. This can prevent the solvent discharge opening  13  from being obstructed by the precipitated solids. If the precipitated solids obstruct the solvent discharge opening  13 , the precipitated solids can be dissolved by bringing them into contact with the unsaturated solution diluted by the dilution solvent. This can eliminate the obstruction of the solvent discharge opening  13 . As just described, the obstruction of the solvent discharge opening  13  can be prevented from occurring by making the precipitation of the solids less likely to occur or by dissolving the precipitated solids according to the present embodiment. 
         [0030]    Moreover, the dilution solvent is supplied only to a solvent discharge path of the solvent discharge path and a solid discharge path adjacent to each other in the direction of the rotation axis L of the rotating bowl  10 . Thus, the centrifuged solids can be recovered without being in contact with the dilution solvent. In other words, the centrifuged solids can be prevented from being dissolved in the dilution solvent and thus being unrecoverable as solids. 
         [0031]    More specifically, the solvent spraying opening  23   a  is designed at a position for spraying the solvent toward the solvent discharge opening  13  in the case of the present embodiment. This allows for the direct spraying of the dilution solvent toward the solvent discharge opening  13  at which the solids are more likely to precipitate. Consequently, the obstruction in the solvent discharge opening  13  can be more reliably prevented from occurring. 
         [0032]    Preferably, the solvent spraying opening  23   a  is disposed in a region closer to the rotation axis L of the rotating bowl  10  than the solvent discharge opening  13 , i.e., on a radially more central side of the rotating bowl  10 . If the solvent spraying opening  23   a  is disposed closer to the radially outer side of the rotating bowl than the solvent discharge opening  13 , such a configuration needs to spray the dilution solvent to the solvent discharge opening  13  while resisting the centrifugal force of the dilution solvent passage pipe  23  rotating together with the screw conveyor  20 . Thus, when the injection pressure of the dilution solvent is small, the dilution solvent cannot be allowed to reach the solvent discharge opening  13 . 
         [0033]    Disposing the solvent spraying opening  23   a  at a position closer to the rotation axis L of the rotating bowl  10  than the solvent discharge opening  13  eliminates the need to spray the dilution solvent while resisting the centrifugal force. Thus, the dilution solvent can be sprayed to the solvent discharge opening  13  with a smaller injection pressure. An appropriate solvent capable of diluting a saturated solution to obtain an unsaturated solution can be used as the dilution solvent. Water or acetone, for example, may be employed as the dilution solvent. 
         [0034]    Operations of the decanter  1  will be described next. First, the rotating bowl  10  and the screw conveyor  20  are caused to rotate at predetermined speeds. When the rotational speeds of the rotating bowl  10  and the screw conveyor  20  reach predetermined speeds, respectively, the object to be processed is fed into the main supply pipe  41  via the opening  41   a  for introducing the object to be processed. The fed object to be processed is supplied to the chamber  21   a  for supplying the object to be processed from the opening  41   b  for supplying the object to be processed in the main supply pipe  41 . The object to be processed is then supplied into the rotating bowl  10  from the passages  210   a  for the object to be processed in the chamber  21   a  for supplying the object to be processed. 
         [0035]    The centrifugal force by the rotating bowl  10  is applied to the object to be processed, which has been supplied into the rotating bowl  10 . Consequently, the object to be processed accumulates over the whole circumference of a pool part of the rotating bowl  10 , and the solids settle out by difference in specific gravity on the inner peripheral surface side of the rotating bowl  10 . The settled solids on the inner peripheral surface side of the rotating bowl  10  are transferred toward the beach part  15  by the screw blade  22  of the rotationally operating screw conveyor  20 . The solids are separated from the saturated solution by reaching the beach part  15 . The solids separated from the saturated solution ascend the beach part  15  to be discharged to the outside of the rotating bowl  10  through the solid discharge openings  14 . 
         [0036]    The saturated solution, on the other hand, overflows from the solvent discharge openings  13  when the object to be processed is continuously supplied. At this time, if processing for the object to be processed further continues, the solids precipitated from the saturated solution adhere to the solvent discharge openings  13 . Hence, according to the present embodiment, a process of spraying the dilution solvent to the solvent discharge openings  13  is performed at appropriate timing after the feeding of the object to be processed is started. More specifically, the process of spraying the dilution solvent toward the solvent discharge openings  13  via the secondary supply pipe  42 , the solvent supply chamber  21   b,  and the dilution solvent passage pipes  23  is performed after the elapse of a predetermined period of time since the start of the feeding of the object to be processed. The sprayed dilution solvent dissolves the solids, thus preventing the obstruction of the solvent discharge opening  13 . 
         [0037]    While the dilution solvent is sprayed after the elapse of the predetermined period of time since the start of the feeding of the object to be processed in the present embodiment, the present invention is not limited thereto. For example, a method of spraying the dilution solvent at the same time as the start of the feeding of the object to be processed may be employed. The spraying method may be carried out continuously or intermittently. 
         [0038]    The invention has been described in detail according to a specific embodiment, but it will be apparent to those having ordinary skill in the art that various substitutions, modifications, and changes in its form and details are possible without departing from the spirit and scope of the invention as defined by the scope of claims. Thus, the scope of the invention should be determined on the basis of the scope of claims and their equivalents, rather than being limited to the above-described embodiment and the accompanying drawings. 
       REFERENCE SIGNS LIST 
       [0039]      1  decanter 
         [0040]      10  rotating bowl 
         [0041]      11 ,  12  bearing 
         [0042]      13  solvent discharge opening 
         [0043]      14  solid discharge opening 
         [0044]      15  beach part 
         [0045]      20  screw conveyor 
         [0046]      21  barrel 
         [0047]      21   a  chamber for supplying object to be processed 
         [0048]      21   b  solvent supply chamber 
         [0049]      22  screw blade 
         [0050]      23  dilution solvent passage pipe 
         [0051]      23   a  solvent spraying opening 
         [0052]      30  gearbox 
         [0053]      31  pulley 
         [0054]      40  supply pipe 
         [0055]      41  main supply pipe 
         [0056]      41   a  opening for introducing object to be processed 
         [0057]      41   b  opening for supplying object to be processed 
         [0058]      42  secondary supply pipe 
         [0059]      42   a  dilution solvent introduction opening 
         [0060]      42   b  dilution solvent supply opening