Patent Publication Number: US-6217502-B1

Title: Centrifugal separator having a liquid filled transmission chamber

Description:
FIELD OF THE INVENTION 
     The present invention relates to a centrifugal separator for freeing a liquid from solids particles suspended therein and having a density larger than that of the liquid. The centrifugal separator comprises a rotor having a centre axis, around which it is rotatable, and comprising two axially separated end walls and a surrounding wall situated therebetween, said walls surrounding a separation chamber, at least one conveyor screw device which is arranged in the separation chamber and is rotatable relative to the rotor for axial transportation of separated solid particles along the surrounding wall, two or more transmission shafts for the operation of the conveyor screw device, which extend from the separation chamber through respective openings in one of said end walls and are rotatable around rotational axes substantially parallel with the centre axis of the rotor, and bearings for radial journalling of the transmission shafts in the rotor. 
     BACKGROUND OF THE INVENTION 
     A centrifugal separator of this kind is shown and described in U.S. Pat. No. 3,685,721. Within the rotor of this known centrifugal separator four conveyor screws are arranged. Each one of these has or is connected with a transmission shaft of the above mentioned kind, which extends out through one of the rotor end walls. 
     If the rotor in a centrifugal separator of this kind is to be caused to rotate at a very high rotational speed for accomplishing high separation efficiency, rotation of the conveyor screws relative to the rotor will encounter a large resistance, and the bearings through which the transmission shafts are journalled in the rotor will be strongly loaded, especially because the conveyor screws as well as their transmission shafts have to rotate at a high speed in a path at a large distance from the rotational axis of the rotor. A problem in this connection is to maintain in said bearings, which in their entirety rotate around the rotational axis of the rotor, the necessary amount of lubricant during a long time of operation for the rotor. 
     The object of the present invention is to provide an arrangement which is as advantageous as possible as to the operation conditions for the said bearings, as a consequence of the fact that these together with the transmission shafts rotate during operation of the rotor around the rotational axis of the rotor. 
     According to the invention this object may be achieved in a centrifugal separator of the initially defined kind in a way such that the rotor delimits a transmission chamber that is liquid tightly separated from the separation chamber and that the rotor is formed to maintain in the transmission chamber during rotation of the rotor an auxiliary liquid in contact with at least part of each one of said bearings. 
     In this way the said bearings, which are preferably constituted by slide bearings, may be constantly lubricated by said auxiliary liquid. This may preferably be constituted by water. The transmission chamber, which preferably is annular and is delimited between said one end wall and a further wall extending around the rotational axis of the rotor, may have an overflow outlet for said auxiliary liquid. 
     In an advantageous embodiment of the invention each transmission shaft supports a bearing member in the transmission chamber, which has a bearing surface extending around the transmission shaft along a circle having a substantially larger diameter than that of said openings in the rotor end wall, through which the transmission shaft extends. Hereby, the pressure per unit of surface in each bearing will become somewhat reduced. Furthermore, a relatively large part of each bearing member will be immersed in auxiliary liquid in the transmission chamber and, thereby, be acutated during rotation of the rotor by a hydraulic force directed towards the rotational axis of the rotor. This force results in a certain unloading of the bearing. 
     Preferably, said bearing members are used also for transmission of rotational movement from a central transmission member in the rotor to said transmission shafts. Then, it is desirable that the transmission forces being transferred are acting as close to the bearings of the transmission shafts as possible. According to the invention each bearing member, therefore, has a surrounding part, which has an inside with a bearing surface facing the transmission shaft and also an outside through which it engages with the central transmission member. This engagement may be direct, e.g. through cogs, or indirect, e.g. through a tooth belt. In both cases the said surrounding part should be in a driving engagement with the central transmission member in an axial plane that substantially coincides with an axial plane through said bearing surface of the surrounding part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in the following with reference to the accompanying drawing, in which 
     FIG. 1 shows in a longitudinal section a centrifugal separator according to a preferred embodiment of the invention. 
     FIG. 2 shows a section along the line II—II in FIG.  1 . 
     FIG. 3 shows an enlarged part of FIG.  1 . 
     FIG. 4 shows a cross-section through the centrifugal rotor shown in FIG. 1 taken between two adjacent separation discs. 
     FIG. 5 shows a separation disc of the kind shown in FIG.  4 . 
     FIG. 6 shows a cross-section, similar to that in FIG. 4, of a somewhat modified embodiment of the invention. 
     FIG. 7 shows a cross-section, similar to that in FIG. 4, of a further modified embodiment of the invention. 
     FIG. 8 shows a separation disc of the kind included in the modified embodiment of the invention according to FIG.  7 . 
     FIG. 9 shows in a longitudinal section part of a centrifugal separator having separation discs of the kind shown in the FIGS. 7 and 8. 
     FIG. 10 shows in a longitudinal section a centrifugal separator according to a further embodiment of the invention. 
     FIG. 11 shows a cross-section through the centrifugal rotor shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a centrifugal separator for freeing a liquid from solid particles suspended therein and having a density larger than that of the liquid. The centrifugal separator comprises a frame  1 , a rotor  2  that is rotatably supported by and within the frame  1  and a motor  3  that is also supported by the frame but on its outside and that is adapted for rotation of the rotor  2  about a vertical rotational axis  4  coinciding with the centre axis of the rotor. For this purpose the motor  3  supports on its drive shaft a belt pulley  5  and the rotor supports at its lower part a belt pulley  6 . A drive belt  7  surrounds both the belt pulleys  5  and  6 . 
     The motor  3  supports on its drive shaft a further belt pulley  8 , which together with an annular transmission member  9  arranged coaxially with the rotor  2  and rotatable relative thereto is surrounded by a further drive belt  10 . 
     The rotor  2 , which is rotatably suspended in the frame by means of a lower bearing  11  and an upper bearing  12 , comprises a lower end wall  13  and an upper end wall  14 . The lower end wall  13  is formed in one piece with a shaft  15  that extends all the way from the area of the lower bearing  11  past the lower end wall  13  up to the upper end wall  14  and through a central opening therein. By means of a locking member  16  the upper end wall  14  is fixed relative to the shaft  15  at least in a way such that it cannot move in a direction away from the lower end wall  13 . By means not shown the end wall  14  is also fixed relative to the shaft  15  in its circumferential direction. The rotor further comprises a circular-cylindrical surrounding wall  17 , which extends axially between the end walls  13  and  14 , coaxially surrounding the shaft  15  spaced therefrom. The surrounding wall  17  shall not transfer any substantial axial force and, therefore, is not firmly connected with the end walls  13  and  14 . Instead, the surrounding wall  17  abuts at its ends through annular gaskets  18  and  19  radially against the respective end walls  13  and  14 . However, the surrounding wall  17  is formed such that it can take up very large forces in its circumferential direction and, therefore, is reinforced by carbon or glass fibres extending substantially in said circumferential direction. 
     The end walls  13 ,  14  and the surrounding wall  17  surrounds a separation chamber  20  within the rotor. The separation chamber  20  surrounds the shaft  15  and has an axial extension substantially larger than its radial extension. 
     Within the separation chamber  20  coaxially with the rotor a stack of frustoconical separation discs  21  is arranged between the end walls  13 ,  14 . By means of spacing members the separation discs are maintained at some axial distance from each other. 
     The upper end wall  14  on its outside is connected with an inlet member  22  forming a central, vertical inlet channel  23 . This inlet channel  23  communicates at its upper end with an inlet  24  for liquid to be treated within the rotor, and it branches off at its lower end in several branch channels  25 . The branch channels  25  which are formed partly in the inlet member  22  and partly in the upper end wall  14  open into the upper part of the separation chamber  20  radially about half-way between the central rotor shaft  15  and the surrounding wall  17 . 
     The lower end wall  13  has a number of branch channels  26  intended for liquid having been treated in the rotor. The branch channels  26  start from the lower part of the separation chamber  20  and extend to a common outlet channel  27  which in its turn extends further centrally in the rotor shaft  15  to and out through the lower end thereof. 
     For solid particles having been separated from said liquid in the separation chamber  20  the rotor has several outlet channels  28  extending from the uppermost part of the separation chamber axially through the upper end wall  14  at the radially outermost portion thereof. For transportation of particles separated in the separation chamber  20  to the outlet channels  28  the rotor comprises a conveyor screw device including several conveyor screws  29 . These extend axially through the separation chamber  20  close to the surrounding wall  17  and are evenly distributed around the rotor shaft  15 . Each conveyor screw  29  is journalled at its ends in the respective end walls  13 ,  14  and is rotatable around its centre axis relative to the rotor walls during the rotation of the rotor around its rotational axis  4 . 
     For the rotation of the conveyor screws  29  relative to the rotor the rotor shaft  15  supports immediately below the lower end wall  13  the above said annular member  9 . This member  9  surrounds the rotor shaft  15  and is adapted by means of the motor  3  through the driving belt  10  to be rotated around the rotational axis  4  of the rotor at a speed different than that of the rotor. The annular member  9  has on its outside axially above the driving belt  10  a gear ring  30  engaging several bearing members  31  evenly distributed around the rotor shaft  15 . Each bearing member  31  is connected with a conveyor screw  29  and forms part of a slide bearing through which the conveyor screw  29  is journalled in the lower end wall  13 . The bearing member  31  and its co-operation with the gear ring  30 , the end wall  13  and the conveyor screw  29  is described more in detail below with reference to FIG.  3 . 
     At its upper end each conveyor screw  29  is journalled in the upper end wall  14  by means of a pin  32 . Radially outside the uppermost end portion of each conveyor screw  29  and axially in the area of the uppermost separation disc  21  there is delimited in the separation chamber  20  by the upper end wall  14  a space or a pocket  33  which extends radially outwardly from said end portion of the conveyor screw to a level radially outside the inside of the surrounding wall  17 . At the radially outermost part of each such pocket one of the afore-mentioned outlet channels  28  is situated. FIG. 2 shows a section through the upper end wall  14 , taken along the line II—II in FIG.  1 . Between adjacent pockets  33  parts of the end wall  14  form filler pieces which prevent communication between the sludge pockets in the circumferential direction of the rotor. 
     For closing and intermittent uncovering of the outlet channels  28  the rotor is provided with an axially movable slide  34 . By means of springs  35  arranged between the inlet member  22  and the slide  34  the slide  34  is kept pressed against the outside of the upper end wall  14 , axial protuberances of the slide  34  abutting sealingly against the end wall around the openings of the respective outlet channels  28 . 
     Between the slide  34  and the end wall  14  there is delimited radially inside the outlet channels  28  a so called opening chamber  36 , which via channels through the inlet member  22  and the rotor shaft  15  communicates with the interior of a narrow tube  37  extending axially upwardly through and out of the inlet member  22  to an upper pressure source of air (not shown). Through supply of pressurised air to said opening chamber  36  the slide  34  during rotation of the rotor may be caused to move axially upwardly against the action of springs  35 , so that the outlet channels  28  are uncovered. 
     FIG. 3 shows in an enlarged scale part of FIG.  1 . It can thus be seen from FIG. 3 that the bearing member  31  is supported by a transmission shaft in the form of a short tap  38  extending within a bore  39  in the end wall  13  and connected with the conveyor screw  29 . The bearing member  31  with its tap  38  as well as the conveyor screw  29  may be made of plastic. A sealing device  40  is arranged in the bore  39  and is adapted to seal, between the tap  38  and the end wall  13 . 
     The bearing member  31  has a tubular surrounding part  41 , which on its outside is provided with cogs  42  and on its inside has a slide bearing surface  43 . The cogs  42  engage the gear ring  30  of the annular member  9 . and the slide bearing surface  43  co-operates with a corresponding slide bearing surface  44  formed on an annular protuberance  45  on the outside of the end wall  13 . The protuberance  45  which may have a surface layer of a ceramic material provided with said slide bearing surface  44  surrounds the opening of the bore  39  in the end wall  13 , and the two co-operating slide bearing surfaces  43 ,  44  thus have a substantially larger circumference than the bore  39 . 
     On the outside of the rotor end wall  13  there is mounted an annular further wall  46 . This confines between itself and the outside of the end wall  13  an annular transmission chamber  47 , which is closed radially outwardly but open radially inwardly towards the rotor shaft  15 . The chamber  47  during operation of the rotor may be filled with liquid, e.g. water, trough a supply pipe  48  and is intended always to be filled during operation of the rotor. A radially inner edge  49  of the further wall  46  may serve as an overflow outlet for liquid being supplied to the chamber  47 . 
     As can be seen from FIG. 3, a substantial part of the bearing member  31  will be present during operation of the rotor in liquid present in the chamber  47 . This liquid has two purposes; firstly, it shall operate as a lubricator between the slide bearing surfaces  43  and  44 , when the conveyor screw  29  rotates relative to the rotor, and secondly it shall create an hydraulic force to which the bearing member is subjected during its rotation around the rotational axis  4  of the rotor and, thereby, acts unloading on the slide bearing formed by the bearing member  31  and the protuberance  45  on the rotor end wall  13 . 
     FIG. 4 shows a cross section through the rotor  2  in FIG.  1 . The section is taken between two adjacent conical separation discs  21 . FIG. 5 shows a single separation disc  21  of the kind also shown in FIG.  4 . 
     From FIG. 4 it can be seen further that the centre shaft  15  of the rotor has axial grooves  50  forming axial flow paths radially inside the separation discs  21  for liquid which has been freed from solid particles in the separation chamber  20 . The separation discs  21  are supported radially in all directions by the shaft  15 . FIG. 4 also shows that the separation discs  21  are provided with several conventional spacing members  51  which are evenly distributed around the shaft  15  and keeps the separation discs at a desired distance from each other. 
     The separation discs  21  have several through-holes  52 , each being placed between two adjacent spacing members  51 , the holes being axially aligned with corresponding holes in the other separation discs  21 . The holes  52  form axial so called distribution channels  53  (FIG. 1) through the stack of separation discs axially aligned with the openings of the previously mentioned branch channels  25  in the upper rotor end wall  14 . 
     A filler piece  54  extends inside the surrounding wall  17  around the stack of separation discs  21  and the conveyor screws  29 . This filler piece has recesses for the conveyor screws  29  and extends in the areas between the conveyor screws radially inwardly forming axially extending ridges which have contact with the separation discs  21 . The separation discs which are relatively thin and may be made of plastic receive during operation of the rotor, therefore, radial support from the said ridges of the filler piece  54 . Between the conveyor screws the filler piece is so formed that solid particles which during operation of the rotor are separated from the liquid and move radially outwardly between the separation discs will slide on the hills  55  of said ridges in a direction towards the conveyor screws and in between their threads. 
     FIG. 5 shows that each separation disc has both recesses  56  for the conveyor screws  29  and recesses  57  for the filler piece  54 . 
     The filler piece  54  may be formed in one piece, suitably from plastic or some other relatively light material. Alternatively, it may be composed of several annular elements having the cross-sectional form shown by the filler piece  54  in FIG. 4, or from several straight axially extending elements, which are evenly distributed around the rotational axis of the rotor. For covering of the interspaces which may remain between annular or straight elements of this kind a lining  58  of plastic or other material, as shown in FIG. 6, may be arranged on the inside of the filler piece  54 . 
     A further alternative for the forming of the filler piece  54  is that the conical separation discs are formed so that they form together said filler piece. This alternative is illustrated in the FIGS. 7-9. 
     As can be seen from the FIGS. 7 and 8 a separation disc  21  in this case has an entirely circular circumference and extends into contact with the surrounding wall  17  of the rotor around the whole of its circumference. The separation disc has through-holes  59  intended for the conveyor screws  29 . 
     Like the separation disc shown in FIG. 5 the separation disc in FIG. 8 has spacing members  51  formed on its underside. In case these spacing members  51  are formed in one piece with the separation disc  21 , this has a certain thickness in the areas of the spacing members  51  and a smaller thickness in the areas  60  situated between the spacing members  51 . In the areas  60  there is thus created, when two separation discs abut against each other in a stack, a space in which liquid may flow between the separation discs. 
     The thickness that the separation disc in FIG. 8 has at the spacing members  51  it also has in a continuous area  61  extending along the whole of the circumference of the separation disc radially outside the holes  59  and between adjacent such holes  59  a distance radially inwardly towards the rotor shaft  15 . 
     In a stack of separation discs formed as shown in FIG. 8 the separation discs will abut against each other in the areas  61  (see FIG. 9) and they will thus form in these areas a filler piece similar to the filler piece  54  in FIG.  4 . 
     Common to the different embodiments of the filler piece  54  is that this is created around the whole of the rotor radially inside the circular-cylindrical surrounding wall  17 , which is formed to take up large forces in the circumferential direction of the rotor. It is thus important that the surrounding wall of the rotor has a circular-cylindrical strong portion that surrounds the separation chamber  20  and the sludge conveyor screws  29 . 
     The centrifugal separator described above with reference to the FIGS. 1-9 operates briefly in the following manner. 
     After the rotor  2  has been caused to rotate around its rotational axis  4  and the conveyor screws  29  simultaneously have been caused to rotate around their respective rotational axes relative to the rotor  2 , a suspension of liquid and particles dispersed therein and having a density larger than that of the liquid is supplied through the inlet  24 . The suspension is conducted through the channels  23  and  25  to the distribution channels  53  in the stack of separation discs  21 . From respective holes  52  in the separation discs  21  the suspension flows out into the spaces between the separation discs  21  and is conducted between adjacent spacing members  51  to the axial channels  50  at the rotor shaft  15  (see FIG.  4 ). 
     On the way between the holes  52  and the channels  50  said particles are separated from the liquid and they slide along the underside of the separation discs back radially outwardly towards the conveyor screws  29 . The inclined surfaces  55  on the filler piece  54  (see FIG. 4) makes the particles collecting exactly in the areas of the conveyor screws  29 . 
     In the areas of the conveyor screws  29  the particles form a sludge which by the conveyor screws is transported axially within the separation chamber  20  towards the upper rotor end wall  14 . 
     In the end wall  14  each conveyor screw  29  extends through a short cylindrical bore which opens into a pocket  33  (see FIGS.  1  and  2 ). The sludge formed in the separation chamber  20  is thus transported through these bores and out into the pockets  33 . From here the sludge is discharged intermittently through the outlet channels  28  in that these are uncovered by means of the slide  34  at desired time intervals. The slide can be actuated by supply of pressurised air to the opening chamber  36 . When sludge is supplied through said bore to a pocket  33 , displaced liquid is conducted away from the pocket  33  to the separation chamber  20  in the part of the bore that is situated closest to the centre axis  4  of the rotor, where a narrow slot is formed between the threads of the conveyor screw  29  and the wall of the bore. The liquid having been freed from particles is conducted out of the rotor below the lower end wall  13  through the channels  26  and  27 . 
     The slide  34  alternatively may be adapted automatically to uncover the outlet channels  28 , when a predetermined resistance against turning of the conveyor screws  29  is obtained, indicating that a certain amount of sludge has been collected in the separation chamber. 
     Since the inlet for suspension is arranged at one end and the outlet for liquid at the opposite end of the separation chamber  20 , and the outlet for sludge is arranged at the inlet end of the separation chamber, good prerequisites are obtained for liquid leaving the separation chamber to be substantially free from particles. 
     In the embodiments of the invention having been described above and shown in the drawings the conical separation discs are arranged in a way such that they face with their apex ends upwardly. If desired, they may instead be arranged with their apex ends facing downwardly towards the outlet for cleaned liquid. Then, the end walls  13  and  14  are suitably formed in a corresponding way, the lower end wall  13  then forming an upwardly open funnel which with its apex portion forms the central outlet for cleaned liquid. If the lower end wall  13  is formed in this way a complete emptying of the separation chamber  20  is facilitated after a finished separating operation. 
     During the separating operation axially directed pressures against both the end walls  13  and  14  of the rotor come up as a consequence of the centrifugal force to which the liquid and the particles in the separation chamber are subjected. The whole of this force is taken up by the rotor shaft  15  which is fixed relative to both of the end walls  13  and  14 . 
     The FIGS. 10 and 11 illustrate an alternative embodiment of a centrifugal separator according to the invention. In the following only the most important differences between this embodiment and the previously described embodiments will be mentioned. The same reference numerals have been used in the FIGS. 10 and 11 as in the other figures for details which substantially correspond to each other. 
     The centrifugal separator in the FIGS. 10 and 11 has only one single conveyor screw  62  and this extends helically around the rotor shaft  15  through the separation chamber  20 . 
     At its ends the conveyor screw  62  is journalled by means of bearing members  63  and  64  directly on the rotor shaft  15 . The bearing members  63  and  64  are firmly connected with each other by means of axial rib-formed elements  65  extending axially through the separation chamber  20  at the outer edges of the separation discs  21 . The elements  65  during the rotation of the rotor may give radial support to the separation discs  21  if these are formed for instance of plastic and have a tendency of expanding radially. It is also simultaneously the elements  65  which are supporting the very conveyor screw  62 . 
     The lower bearing member  64  has a tubular surrounding part carrying a gear ring  66  on its inside. This gear ring  66  is in engagement with a number of gear wheels evenly distributed around the rotor shaft  15  and supported by short taps  67  each of which corresponds to the tap  38  in FIG.  3 . The taps  67  thus extend through the rotor end wall  13  and are journalled on its outside by means of bearing members like the bearing members  31  in FIGS. 1 and 3. By rotation of the taps  67  in the same way as has earlier been described with reference to the taps  38  the bearing member  64  and, thereby, the conveyor screw  62  may be rotated relative to the rotor shaft  15 . 
     The centrifugal separator according to the FIGS. 10 and 11 operates for the rest principally in the same manner as the centrifugal separator according to FIG.  1 .