Patent Publication Number: US-6986733-B2

Title: Solid bowl helical conveyor centrifuge with a pressurized housing

Description:
This application is a Continuation and hereby claims benefit under 35 U.S.C. §120 to the following applications Ser. No. PCT/EP02/09993 filed Sep. 6, 2002. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     This invention relates to a solid bowl or drum helical conveyor centrifuge having a rotating drum, which includes a centrifuge space with a screw that can rotate and having an inlet tube for supplying a material for centrifugation into the centrifuge space. 
     2. Description of Prior Art 
     To ensure pressure-tight and airtight operation of a solid drum helical conveyor centrifuge, it is known that the entire drum (i.e., the entire rotating area of the drum) can be surrounded with a housing that is sealed with respect to the environment. 
     Within this housing, it is possible to maintain the boundary conditions of the process to be carried out and to move the mass flows under the desired pressure conditions. 
     The friction occurring in particular between the gas molecules and the drum surface, especially at high rotational speeds and/or large diameters of the drum, requires considerable driving power and increases the power consumption by the centrifuge in a manner that is a disadvantage. Another problem is that this energy causes heating of the gas and the rotating part. The wall friction increases in proportion to the increase in pressure and thus there is also an increase in required driving power. 
     This will now be explained in greater detail on the basis of an example. 
     If the pressure in a conventional commercial solid bowl helical conveyor centrifuge is increased from 0 bar to 5 bar, for example, it is quite possible for the frictional energy to be increased by a factor of approximately 5 (e.g., from 10 kW to 50 kW or from 100 kW to 500 kW, depending on the diameter and/or the type of machine). 
     SUMMARY OF THE INVENTION 
     The object of this invention is therefore to improve upon a generic solid bowl helical conveyor centrifuge such that the driving power applied during operation under pressure is reduced. 
     This invention achieves this object through a solid bowl helical conveyor centrifuge including a rotating drum having a centrifuge space with a rotatable screw. The centrifuge includes a liquid discharge and a solids discharge wherein only the opening of the solid discharge is covered with a pressure tight housing. 
     According to this claim, the liquid and/or solid discharge is designed in the form of at least one or more openings in a rotating part of the solid bowl helical conveyor centrifuge, in particular through openings in the wall of the drum, and at least one of the openings is covered by a housing that encloses the drum of the solid bowl helical conveyor centrifuge but only in some sections, with at least one or more gaskets being provided between the at least one housing and the drum and/or other rotatable elements of the solid bowl helical conveyor centrifuge (drum heads, hubs). 
     According to this invention, the pressure-tight (and thus essentially airtight) housing is preferably reduced only to the area of the at least one (or more) solids discharge and/or liquid discharge. Since the entire exterior space of the drum need no longer be placed under pressure but instead only a portion thereof is placed under pressure on the outside thereof, this reduces the driving power required to operate the solid bowl helical conveyor centrifuge. 
     The negative effects of an increase in temperature can also be drastically reduced, in particular in a ring-type design of the housing, so that it covers only the openings. 
     Since most of the drum is in an environment without an elevated pressure due to the process, this results in only a very minor increase in frictional energy. The increase in temperature can be reduced significantly. Furthermore, it is conceivable that additional cooling equipment may be eliminated and/or the cooling power may be reduced. 
     The solid bowl helical conveyor centrifuge can also be manufactured inexpensively because the pressure-tight housing, that is to be put under pressure, is smaller. The relevant regulations for operation of machinery under increased pressure can also be satisfied more easily. 
     It is also advantageous that the product area is reduced in size (see  FIGS. 2 and 7 ) because smaller quantities of gas than in the state of the art are used for inertization, for example, and operation with toxic substances is simplified. 
     Since only a mechanical lining of the drum is needed for protection against electric shock, the cost of manufacturing can be reduced significantly by reducing the cost of materials. In addition, the total construction space required is also reduced. 
     In particular at least one scraper disk is recommended as the liquid discharges, so that no pressurized housing is necessary in the area of the liquid discharge. The scraper disk could be supplemented by a special pressurized housing. 
     As an alternative, however, it is also possible to provide one or more housings and gaskets on the side of the liquid discharge to cover the at least one or more liquid discharges. 
     The gaskets are preferably designed as bearing ring gaskets that surround the outside circumference of the drum, for example, and/or may be in contact with an axial wall of the drum. Bearing ring gaskets ensure a tight seal between the rotating drum and the nonrotating housing. 
     It is especially preferable for the at least one housing to extend only over the area of the openings of the drum. To do so, it is suggested that the at least one housing be designed in a simple and inexpensive ring shape. 
     The at least one housing is preferably designed for operation from a pressure of more than 0.5 bar, preferably 3 to 6 bar. 
     The peripheral velocity of the gaskets is preferably greater than 30 m/sec. The temperature in the pressurized area in processing centrifuged material is preferably more than 50° C., especially 100° C. to 160° C. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are described in greater detail below on the basis of the drawings, which show: 
         FIG. 1  is a sectional diagram of a first variant of a solid bowl helical conveyor centrifuge; 
         FIG. 2  is the solid bowl helical conveyor centrifuge from  FIG. 1 , with the high-pressure area shown as a dotted area; 
         FIG. 3  is a sectional diagram of a second variant of a solid bowl helical conveyor centrifuge; 
         FIG. 4  is a schematic diagram of a third variant of a solid bowl helical conveyor centrifuge; 
         FIG. 5  is a schematic diagram of a fourth variant of a solid bowl helical conveyor centrifuge; 
         FIG. 6  is a schematic diagram of a solid bowl helical conveyor centrifuge according to the state of the art; and 
         FIG. 7  is the solid bowl helical conveyor centrifuge from  FIG. 6 , with the high-pressure area indicated as a dotted area. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a solid bowl helical conveyor centrifuge having a bowl or drum  1  and a screw  3  situated in the drum, having a screw body  5  and a screw blade  7  surrounding the screw body  5  in a helix. A channel  11  for conveying/transporting a centrifuged material that is to be processed is provided between the screw threads  9   a ,  9   b , etc. Bearings  4  and gaskets  6  are provided on both ends of the solid bowl helical conveyor centrifuge between the drum  1  and the screw body  5 . 
     In the rear area in  FIG. 1 , the centrifuge has a cylindrical section  13  and, in its front area adjacent thereto in  FIG. 1 , section  15  tapers conically (or in stages). The drum has another cylindrical section  17  adjacent to and in axial connection to the tapering section  15 . A drum head  18  (and/or a hub) being connectable to this section  17 . 
     A centrifuged material I is passed through the centrally positioned inlet tube  19  into a distributor  21  and from there through radial openings in the distributor  21  into the centrifuge space  23  with the screw  3  and the drum  1  surrounding the screw  3 . 
     The centrifuged material I is accelerated in its passage through the distributor  21  and in entering the centrifuge space  23 . Due to the influence of centrifugal force, solid particles are separated on the wall of the drum. 
     The screw  3  rotates at a somewhat faster or slower speed than the drum  1  and conveys the solids S that have been separated to the solids discharge and out of the drum  1  via the tapering section  15 . The liquid L, however, flows toward the larger drum diameter at the rear end of the drum  1 , where it is drained out. 
     The drum  1  and/or hubs adjacent to it are mounted at their axial ends by means of bearings  25  in a machine frame (not shown here) and are usually provided with a hood or cover (not shown here) to protect the operating person from the rotating parts. 
     The drum  1  is provided with an opening  27  that points at least radially outward in its peripheral wall for the purpose of discharging the solids. 
     To be able to operate the drum  1  so that it is pressure-tight and/or under a high pressure, the areas of the solids discharge and the liquid discharge are sealed with respect to the environment according to the idea of this invention. 
     Unlike the technology depicted in  FIG. 6 , this is not accomplished by the fact that the entire drum is surrounded by a pressure-tight housing G, but instead by a controlled local sealing of the drum in the area of the solids discharge and/or liquid discharge. 
     Thus, the drum  1  of the exemplary embodiment in  FIG. 1  is provided with a ring-like housing  29  in the area of the radial openings  27 , said ring-like housing covering the openings axially so that gaskets  31 , e.g., bearing ring gaskets, can be arranged between the housing  29  (and/or between the inside circumference of the axial walls of the housing) and the drum  1 . This yields a seal between the rotating drum  1  and the stationary housing  29 . 
     On the axial end of the drum opposite the solids discharge, the liquid is removed by means of a scraper disk  32 , which ensures a seal of the interior of the drum, in this area during operation, with respect to the outside. The scraper disk  32  is situated in a chamber  34  of the drum  1 , which is adjacent to the centrifuge space  23  and is connected to it. The chamber being connected to the drum through at least one opening  35 . Another gasket  31  between drum head  41  and the stationary scraper disk  32  (and/or a tubular attachment on the scraper disk) may also be designed as a bearing ring gasket and may thus also ensure the pressure tightness of the drum in this area, even when the drum is at a standstill. 
     The dotted area in  FIG. 2  shows the area that can be operated under pressure. The inlet and outlet lines that are not shown outside of the solid bowl helical conveyor centrifuge are designed for pressurized operation. 
       FIG. 3  differs from the exemplary embodiment in  FIG. 1  in that the openings  27  are arranged in the axial drum wall pointing toward the solids discharge side, with the housing  29  in turn covering these axial openings  27 . The housing  29  has a ring shape and is sealed with respect to the wall of the drum by means of gaskets  31 . The housing  29  also extends over a step  33  in the drum wall housing. 
     The exemplary embodiments in  FIGS. 4 and 5  differ from one another in that the solids discharge in  FIG. 4  corresponds to that in  FIG. 1 , and the solids discharge in  FIG. 5  corresponds to that in  FIG. 3 . 
     The difference in comparison with  FIGS. 1 and 3  is also that the liquid discharge in  FIGS. 4 and 5  is not implemented by one or more scraper disks but instead is implemented by at least one or more overflow openings  35  in the axial wall of the drum  1  facing away from the solids discharge. 
     In order to ensure operation under a high pressure, according to  FIGS. 4 and 5  the overflows  35  are also covered by a housing  37 , with gaskets  39  (e.g., bearing ring gaskets) being situated between the housing  37  and the outside wall of the drum—and/or other corresponding parts of the machine. One of the gaskets ( 39   a ) is in contact with the axial end face of the drum wall and the other ( 39   b ) surrounds a cylindrical drumhead  41  (e.g., a hub) connected to the outside wall of the drum. The drumheads  18 ,  41  and the drum  1  are schematically depicted as being in one piece. In practice, an implementation involving multiple parts is preferred and is essentially known. 
       FIG. 6  illustrates a centrifuge according to the state of the art. Unlike the centrifuge according to the present invention, the entire drum is enclosed by a pressure-tight housing G, so that the entire interior and exterior space of the drum is under pressure during operation ( FIG. 7 ).