Patent Publication Number: US-8529425-B2

Title: Horizontal centrifugal separator in which the hermeticity of a casing is improved by using a sealing element having a simple structure

Description:
BACKGROUND OF THE INVENTION 
     I. Technical Field 
     The present invention relates to a horizontal centrifugal separator including a rotary bowl and a screw conveyor inserted into the rotary bowl. In particular, the invention relates to a horizontal centrifugal separator including sealing means that, while having a simple structure, can improve the hermeticity of a casing containing the rotary bowl and the screw conveyor. 
     II. Description of the Related Art 
     A horizontal centrifugal separator referred to as a decanter is one type of known solid-liquid separator that uses centrifugal force. For example, as shown in  FIG. 1 , a decanter  1  has a basic structure in which a rotary bowl  11  rotatable about its horizontal axis and a screw conveyor  12  inserted into the rotary bowl  11  are contained in a casing  2  serving as an exterior casing. The casing  2  is separated into a lower casing  21  having a solids outlet  21   a  and a separated-liquids outlet  21   b  formed in the lower part thereof and an upper casing  22  detachable from the lower casing  21 . The lower casing  21  and the upper casing  22  have flanges  23  formed along the respective opening edges thereof. The casing  2  having a substantially cylindrical shape is formed by securing the flanges  23  to each other with securing means  24  such as bolts. 
     Openings  25  having, for example, a circular shape are formed in the opposite end faces of the casing  2 , and the rotary shafts of the rotary bowl  11  and the screw conveyor  12  extend through the openings  25  and are rotatably supported by bearing means  13 . Mechanical seal housings  14  for sealing the rotary shafts are disposed in the openings  25 , and O-rings  15  provided on the outer circumferences of the mechanical seal housings  14  hermetically seal the gaps between the mechanical seal housings  14  and the openings  25 . 
     The barrel portion of the rotary bowl  11  is composed of three portions, i.e., a cylindrical portion on a first end side thereof, an intermediate conical portion, and a circular portion on a second end side. The portion formed into a conical shape forms a beach portion in which solids conveyed by the screw conveyor  12  are separated from liquids and are thereby dewatered. The cylindrical portion on the first end side forms a screen portion for washing the dewatered solids with washing water, and the washed solids are discharged through solids outlets  16 . The cylindrical portion on the second end side forms a pool (fluid pool) portion for reserving a feed fluid supplied to the inside of the rotary bowl  11  and has separated-liquids outlets  17  formed in the end face thereof. A screw vane  18  and feed fluid supply ports  19  are formed in the barrel portion of the screw conveyor  12  inserted into the rotary bowl  11 , the feed fluid supply port  19  being provided for supplying the feed fluid fed from a feed fluid supply nozzle  3  to the rotary bowl  11  through the action of centrifugal force. 
     In the structure described above, by transmitting the power of a motor  32  serving as a driving mechanism to a pulley  33  through a rotary belt  31 , the rotary bowl  11  is rotated at a predetermined rotation speed. When the feed fluid is supplied to the pool portion while the rotary bowl  11  is rotated, the solids are settled out through the action of the centrifugal force. The solids are conveyed to the beach portion by the screw conveyor  12  rotated through a gearbox  34  used as a differential speed generating mechanism and are then dewatered. The dewatered solids are then washed with washing water from washing water injection ports  35  when they pass through the screen portion. The washing drainage used for washing the solids is discharged through discharge holes  36  formed in the screen portion. The solids having been washed in the screen portion are discharged from the solids outlets  16  and are then discharged to the outside of the separator through the solids outlet  21   a . The liquids separated from the solids (separated liquids) are discharged from the separated-liquids discharge outlets  17  and are then discharged to the outside of the separator through the separated liquids outlet  21   b .  FIG. 1  shows the decanter of the screen bowl type. However, decanters of the solid bowl type that do not have the screen portion are also widely known. 
     As described in, for example, patent documents such as Japanese Patent Application Laid-Open No. 2007-44671, a number of studies have previously been conducted to improve the sealing properties of mechanical seals. However, only a few studies have been made to ensure the hermeticity between the mechanical seal housing  14  and the casing  2 , which are non-rotating mechanisms. If the set pressure is increased, leakage can occur between the mechanical seal housing  14  and the casing  2 . Therefore, in horizontal decanters having a casing structure composed of two separated (upper and lower) casings, the internal pressure thereof during use is limited to several tens kPa or less. At present, when the internal pressure reaches a higher level, the treatment is performed using decanters having an integral cylindrical structure or vertical decanters. However, in decanters having an integral cylindrical structure, the rotary members must be pulled out in the axial direction thereof when disassembled. Therefore, such decanters have drawbacks in that the assembling-disassembling process is complicated and that a sufficiently large space must be provided for maintenance. In particular, decanters of the screen bowl type in which the ratio between the diameter and length of the bowl is large have an influence on the size of buildings. Accordingly, the integral cylindrical structure has not practically been used in such decanters. 
     SUMMARY OF THE INVENTION 
     With reference to  FIG. 2 , the structure of the portion from which leakage occurs is described, in order to elucidate the cause of the leakage. Specifically, as shown in  FIG. 2 , a groove  27  is formed in an end surface  26  of the lower casing  21 , and an O-ring  28  used as a sealing member is disposed in the groove  27 , whereby the joint surface between the lower casing  21  and the upper casing  22  is sealed. However, since the opening  25  for allowing the rotary shafts to pass therethrough is formed in the lower casing  21 , the O-ring  28  cannot be provided over the entire circumference of the lower casing  21 , and the O-ring  28  is discontinuous at the opening  25 . In this sealing structure, the end of the O-ring  28  is in point contact with the O-ring  15  of the mechanical seal housing  14 , and therefore the hermeticity is low. Moreover, the O-ring  28  is contracted when the separator is operated under, for example, a reduced pressure condition. In such a case, a gap is formed between the O-ring  28  and the O-ring  15 , and this results in a further increase in the amount of leakage. 
     Moreover, in the structure shown in  FIG. 2 , the O-ring  15  of the mechanical seal housing  14  can be caught between the upper casing  22  and the lower casing  21  when the upper casing  22  is placed on the lower casing  21 , for example, at the time of assembly of the separator or after the maintenance. In such a case, the O-ring  15  is deformed, and this causes a problem in that the hermeticity is reduced. In addition, in this structure, the assembling and maintenance operations are “blind” operations in which whether or not the O-ring  15  is caught cannot be visually determined. Therefore, disadvantageously, the point of leakage is not easily determined, and the workability is low. 
     As described above, the horizontal decanter  1  has a drawback in that the hermeticity is low but has advantages in that its structure is simpler and the cost is lower than those of vertical decanters. Therefore, there is a demand for a horizontal decanter to overcome the problem of hermeticity. However, as the sealing structure becomes complicated, the above advantages of the horizontal decanter  1  are reduced. Therefore, the sealing structure must be as simple as possible. The advantages of the structure of the inventive decanter against the integral cylindrical structure will be described later. 
     The present invention has been made in view of the above circumstances, and it is an object of the invention to provide a horizontal centrifugal separator in which the hermeticity of a casing is improved by using sealing means having a simple structure. 
     It is another object of the invention to provide a horizontal centrifugal separator including sealing means configured such that an O-ring of a mechanical seal housing is prevented from being caught between an upper casing and a lower casing when the upper casing is placed on the lower casing. 
     A horizontal centrifugal separator of the present invention includes: a rotary bowl; a screw conveyor that is inserted into the rotary bowl; a casing that contains the rotary bowl and the screw conveyor; and bearing means for supporting a rotary shaft of the rotary bowl that extends through an opening of the casing. The horizontal centrifugal separator further includes sealing means for hermetically sealing the casing by providing a groove formed along a joint surface between an upper casing and a lower casing constituting the casing so as to be outwardly bent near the opening thereof, and disposing an elastic sealing member in the groove such that an end of the elastic sealing member abuts against a sealing surface provided on a ring member, the ring member being provided so as to surround an outer circumference of the opening and being pressed against the casing. 
     The elastic sealing member may include: a block member having an end that abuts against the sealing surface; and a linear member having an end that engages with a recess formed in the other end of the block member. 
     The ring member may be a flange portion of a bushing that is fitted, from an axially outward side of the opening, in a gap between the opening of the casing and a mechanical seal housing for sealing the rotary shaft disposed in the opening of the casing. The sealing surface may be configured to be a surface of a gasket sandwiched between the flange portion and a surface of the casing. 
     The present invention employs the structure in which surface sealing is formed as follows. Specifically, the groove formed along the joint surface between the upper casing and the lower casing constituting the casing is provided so as to be outwardly bent near the opening. Then, the elastic sealing member is disposed in the groove such that the end of the elastic sealing member abuts against the sealing surface provided on the ring member, the ring member being provided so as to surround the outer circumference of the opening and being pressed against the casing. In this manner, the hermeticity can be improved without using sealing means having a complicated structure. 
     In addition, the present invention employs the structure further including the bushing that is fitted, from the axially outward side of the opening, in the gap between the opening of the casing and the mechanical seal housing disposed in the opening of the casing. In this manner, the O-ring of the mechanical seal housing can be prevented from being caught between the upper casing and the lower casing when the upper casing is placed on the lower casing. Therefore, a reduction in hermeticity caused by the deformation of the O-ring can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view illustrating the whole structure of a horizontal decanter. 
         FIG. 2  shows a conventional sealing structure. 
         FIG. 3  shows a sealing structure according to an embodiment of the present invention. 
         FIG. 4  shows the sealing structure according to the embodiment of the present invention. 
         FIG. 5  shows a modified example of the sealing structure according to the embodiment of the present invention. 
         FIG. 6  shows another modified example of the sealing structure according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A horizontal centrifugal separator according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The basic structure of the horizontal centrifugal separator of the present embodiment is the same as the structure shown in  FIG. 1 , and a detailed description thereof will be omitted. 
     As shown in  FIGS. 3 and 4 , in the horizontal centrifugal separator of the present embodiment, a groove  27  in which an O-ring (linear member)  28  serving as an elastic sealing member is disposed is bent outwardly near the opening  25  such that an end portion of the O-ring  28  is exposed outward. The end portion of the O-ring  28  may be flush with the surface of the casing or may protrude slightly from the surface of the casing. 
     The horizontal centrifugal separator further includes a bushing  4  fitted in the gap between the opening  25  and the mechanical seal housing  14 . The bushing  4  includes: a tubular portion  41  that is fitted in the gap; and a flange portion  42  serving as a ring member formed in the outer circumference of the tubular portion  41 , and is pressed against the casing  2  using securing means  43  such as a bolt. In this case, it is configured such that the end portion of the O-ring  28  abuts against a surface of a gasket  44  interposed between the flange portion  42  and the casing  2 . 
     When the separator having the above structure is assembled, first the O-ring  28  is disposed in the groove  27 . After the position of the mechanical seal housing  14  is adjusted, the upper casing  22  is placed. Then, the bushing  4  is caused to slide in the axial direction to fit the tubular portion  41  in the gap, and the flange portion  42  is pressed against the casing  2  using the securing means  43 . In this manner, the end portion of the O-ring  28  abuts against the gasket  44 , whereby sealing is formed. 
     Specifically, the sealing means of the present embodiment provides sealing which is constituted by the outwardly bent O-ring  28  and the gasket  44  provided in the bushing  4  in place of the conventional structure in which the sealing is constituted by the O-ring  28  on the casing side and the O-ring  15  of the mechanical seal housing  14 . Therefore, according to the present embodiment, surface sealing using the surface of the gasket  44  is provided. Hence, the hermeticity can be further improved as compared to the conventional point contact sealing. Moreover, no significant modification is made to the conventional sealing structure, and therefore the hermeticity can be improved using a simple structure. In other words, the problem of hermeticity is overcome without sacrificing the advantages of low-cost horizontal decanters having a simple structure. 
     Moreover, the present embodiment employs the structure that further includes the bushing  4  fitted, from the axially outward side, in the gap between the opening  25  of the casing  2  and the mechanical seal housing  14 . In this manner, the O-ring  15  of the mechanical seal housing  14  is prevented from being caught between the upper casing  22  and the lower casing  21  when the upper casing  22  is placed on the lower casing  21 . Therefore, a reduction in hermeticity caused by the deformation of the O-ring  15  can be prevented. 
     Furthermore, in the present embodiment, the sealing area between the O-ring  28  and the gasket  44  is easily observed and inspected. Therefore, even when a change in pressure is found in a hermetic test, it is easily determined whether or not the leakage occurs in the sealing area. In other words, advantageously, the point of leakage is easily determined and fixed. 
     Moreover, in a modified example of the elastic sealing member, a block member  5  shown in, for example,  FIG. 5  may be provided. Specifically, in this structure, the block member  5  is fitted in the groove  27  from the bent portion to the end portion thereof. As in the O-ring, one end portion of the block member  5  may be flush with the surface of the casing or may protrude slightly from the surface of the casing. The block member  5  has a recess  51  formed in the other end portion thereof, and the end portion of the O-ring  28  is engaged with the inside of the recess  51 . The O-ring  28  may be bonded or not be bonded to the recess  51  to form the engagement between the O-ring  28  and the recess  51 . Preferably, the O-ring  28  and the recess  51  are not bonded to each other when an appropriate bonding agent is not found for the engagement shape, or since the O-ring  28  and the recess  51  are difficult to reuse when bonded to each other. Even in such a structure, the same effects as those in the above embodiment can be obtained, and the hermeticity can be reliably improved by providing the block member  5  serving as an elastic sealing member. The shape of the block member  5  is not limited to the shape shown in  FIG. 5 , and the shape may be changed appropriately. For example, the shape shown in  FIG. 6  may be used as a modified example. 
     In the above embodiment, the sealing member disposed in the groove  27  is not limited to the O-ring  28  having a circular cross-section. Any linear member may be used so long as it can be disposed in the groove  27 . For example, a sealing member having a rectangular cross-section or other cross-section may be used. 
     The sealing surface against which the end of the elastic sealing member abuts is not limited to the surface of the gasket  44  of the bushing  4  and may be a surface of a sealing member other than the gasket  44 . Alternatively, the sealing surface may be formed by applying RTV (Room Temperature Valcanizing) rubber. The ring member on which the sealing surface is provided is not limited to the flange portion  42  of the bushing  4  and may be other ring members. 
     It is needless to say that the application of the decanter is not limited. The decanter can be used for separation of various materials into solids and liquids and for selection of, for example, waste plastic. 
     While the present invention has been described with reference to the specific embodiments, it is apparent to those having ordinary knowledge in the art that various modifications can be made so long as they do not depart from the scope of the present invention. Accordingly, the technical scope of the present invention is not limited to the above-described embodiments but must be defined by the claims or the equivalence thereof. 
     Example 
     A hermeticity test was actually performed using the sealing means having the structure shown in  FIG. 5 . An example of the results is described below. 
     (Test Conditions) 
     O-ring Cross Section Dia.: 11 mm, Durometer: 50 
     Groove Depth: 8 mm 
     Rubber Ring Gasket Durometer: 60 
     Block Durometer: 70 
     Pressure (kg/cm 2 ): 0.35, 1.0, 1.25, 1.5 
     Retention time: 10 to 20 min 
     (Test Results) 
     Leakage was not found at all the pressures listed above. In other word, sufficient hermeticity was confirmed in the present invention.