Patent Publication Number: US-2003224920-A1

Title: Rotating-machine bowl assembly with flow guide

Description:
BACKGROUND OF THE INVENTION  
       [0001] This invention relates to rotating machines of the kind used to separate heavier phases from lighter phases such as found in separating solids from a liquid phase of a suspension or slurry, a solid phase from more than one liquid phase each with a different density, a liquid phase from several solid phases each with a different density, or several liquid phases each with a different density. Such rotating machines are typically termed “centrifuges” and operate under the action of centrifugal force.  
       [0002]FIG. 1 shows a tubular centrifuge conventionally used in solid-liquid separation. A vertically oriented bowl  12  has a cylindrical sidewall  14  and disk shaped bowl heads  16 ,  18 . A feed slurry or suspension is introduced into bowl  12  at  13  via a stationary feed pipe  20 . The feed slurry or suspension is provided with an angular velocity through the action of feed accelerating vanes  22  at feed pipe  20 . Rotation of bowl  12  about a vertical axis  24  induces the settling of solids particles in a sediment layer  26  along an inner surface  28  of bowl sidewall  14 . Heavier solids have trajectories indicated by arrows  30 . The liquid in a pool  32  exits bowl  12  as fluid effluent at  34 . The level or height of pool  32  is controlled or determined by overflow weirs  36  disposed along bowl head  18 .  
       [0003] Settled solids are allowed to accumulate in bowl  12  until the sediment builds up to a significant layer  26  in which the effluent liquid  34  starts to turn turbid or dirty, in which the machine is stopped and is taken apart to clean the solids out of the bowl  12  before resuming operation. Typical operating centrifugal force can be as much as 20,000-40,000 times gravity (g). The whole unit is suspended from the top with only one bearing (not shown). This rotating machine works like a spinning “top” at high speed and the axis of the rotor may gyrate to a stable operating position. Applications are polishing and clarification of liquid with low solid. Disadvantages includes the fact that solids handling is small and solids should not be hazardous for operator handling and contact during cleaning of bowl  12 .  
       [0004]FIG. 2 diagrammatically depicts shows a prior-art tubular centrifuge for solids, light liquid and dense liquid separation. A feed slurry or suspension has heavy solids, a lighter liquid phase and an immiscible heavier liquid phase and is introduced at  37  into a bowl  38  via a feed pipe  40  and accelerated to a predetermined tangential velocity by a plurality of accelerator vanes  42 . The slurry or suspension forms a pool  44  in bowl  38 , with solid particles falling out along trajectories  46  to form a sediment or solid-phase layer  48  on an inner surface  50  of a cylindrical sidewall  52  of bowl  38 . The light and heavy separated liquids  53  and  55  are removed at two different radii of the pool  44 . The heavier liquid  55  is channeled by a baffle  54  to a chamber  56  where the heavy liquid overflows a weir  58  and forms a first effluent stream at  60 , while the lighter separated liquid  53  is skimmed by a stationary pairing disc or centripetal pump  62  at the surface (not designated) of pool  44  to form a second effluent stream  64 . Alternatively rotating skimming pipes can be used to skim either the light or heavy phases at their respective discharge radii.  
       [0005] When the solids fill bowl  38  resulting in dirty liquid streams  60  and  64 , the bowl needs to be emptied. It is also to be noted that the tubular bowl shown in FIG. 2 can separate a mixture with two liquid phases without solids in which separation can be continuous without cleaning of the bowl and process interruption.  
       [0006]FIG. 3 schematically illustrates an automatic tubular centrifuge of the prior art, wherein the whole purification or separation process including filling of the bowl, cake removal, and bowl cleaning are fully automatic. Unlike the tubular centrifuge of FIG. 1, the centrifuge of FIG. 3 can handle more solids in the feed as the whole cycle is fully automatic. Typically 20,000 g is used in separation. A feed slurry or suspension  66  enters a bowl  68  through a feed pipe  70  and is accelerated to a predetermined tangential velocity, as indicated by arrows  72 . The feed slurry forms a pool  74  in bowl  68 . Solids accumulate in a layer  76  along an inner surface  78  of a cylindrical sidewall  80  of bowl  68 , while a liquid effluent  82  exits the bowl at overflow weirs  84 . A plurality of longitudinally spaced annular baffles  86  extend inwardly from sidewall surface  76  to stop longitudinal traveling waves in the case of long slender centrifuges operating at high centrifugal gravity, G.  
       [0007] When effluent  82  gets dirty, indicative that bowl  68  is filled with solids, feed slurry  66  is blocked from flow through feed pipe  70  and the machine rotation about a vertical axis  88  is slowed down. Then, a cake plow or unloader knife  89 , having a comb shape to accommodate annular baffles  86 , is used to scrape accumulated cake or sediment layer  76  to discharge from the machine through a solids compartment  90  which becomes accessible via gate valves  92  upon an opening thereof during a solids-discharge cycle.  
       [0008] The centrifuge of FIG. 3 is used in the field of biotechnology for cell harvesting, inclusion body recovery, and cell debris classification, in the pharmaceutical field for plasma fractionation, precipitate capture, vaccines and serums, and in the specialty chemical field for catalysts recovery, sub-micron classification, pigments, dyes, and toners. To avoid cross contamination in pharmaceuticals and biotech applications, clean-in-place (CIP) and sanitary-in-place (SIP) processes are practiced, using wash nozzles (not shown) to flush out residual solids hanging to walls and trapped in crevices to prevent cross contamination between batches of different products.  
       [0009]FIG. 4 illustrates a tubular centrifuge with a bowl  94  having a cylindrical central sidewall  96 , a conical top section  98  and a conical bottom section  100 . A feed suspension  102  is introduced into bowl  94  via a feed chamber  104  and is accelerated at  105  to a predetermined velocity by accelerating vanes  106  located in conical bowl section  98 . The suspension forms a pool  108  in bowl  94 , with clarified product or effluent  110  being slowed down at  111  by decelerating vanes  112  in conical bowl section  100  and exiting the machine via a product chamber  114 . Decelerating vanes  112  decelerate the product  110  to solid-body rotation to discharge at a small radius reducing power consumption. The separation pool  108  is open with axial vanes (not shown) for stirring up sediment during shut-down. During rotation of bowl  94  about a vertical axis  1   16 , solids accumulate in a sediment layer  118  along an inner surface (not separately designated) of cylindrical bowl sidewall  96 . Bowl  94  is supported by both an upper bearing  120  and a lower bearing  122  and is rotated, as indicated by an arrow  124 , by a drive shaft  126  connected to a center shaft  128 .  
       SUMMARY OF THE INVENTION  
       [0010] The present invention is directed to an improvement in the operation of various rotating machines used particularly in the separation of solids phases from liquid phases in slurry or suspensions. The present invention enhances centrifuge operation by providing for an increased output or enhances the quality of the separated phases for the same output.  
       [0011] A bowl assembly for a rotating machine comprises, in accordance with the present invention, a bowl mounted for rotation about an axis of rotation, a feed inlet connected to the bowl for introducing a feed slurry into the bowl, a liquid-phase outlet provided in the bowl, and a flow guide member disposed inside the bowl about the axis for guiding the suspension in an at least partially circumferential or annular path about the axis, the guide member having an outer edge spaced a predetermined distance from an inner surface of the bowl.  
       [0012] Preferably, the guide member extends along the axis from one end to an opposite end of the bowl.  
       [0013] In several embodiments of the present invention, the bowl has an at least partially conical sidewall. The entire sidewall of the bowl or only a portion thereof may be conical. Particularly where no active conveyor mechanism is provided for moving the cake along the inner surface of the bowl sidewall, it is preferred that a conical portion of the bowl be formed to exhibit a half conical angle greater than the angle of friction for a granular cake or a sufficiently large half angle so that fluid-like cake can flow under the component of the centrifugal gravity along the cone from the small toward the large diameter.  
       [0014] In one specific embodiment of the present invention, the bowl has two conical portions provided at opposite ends of the bowl. The bowl is provided with accelerating vanes in one of the conical portions at the input feed for accelerating feed liquid to a tangential speed of a pool and is further provided with liquid-decelerating vanes in the other of the conical portions to reduce power as the product liquid is channel to a small radius for discharge to reduce power consumption.  
       [0015] In accordance with another feature of the present invention, the flow guide may be fixed relative to the bowl and rotate at a common angular velocity therewith. In that case, the guide member may be rigidly connected to a central shaft, to the inner (circumferential) surface of the bowl, or to headers at opposite ends of the bowl.  
       [0016] Pursuant to a specific design, the guide member is a helical fin. The helical fin advantageously has a pitch optimized to enhance separation.  
       [0017] The bowl may be used in virtually any orientation. Typical orientations are horizontal and vertical. Where the bowl has a vertical orientation, the bowl may be provided with a bottom having a discharge port closure or cap temporarily openable at intervals to discharge granular non-flowable solids. In this kind of machine, the guide member may define an annular space proximate to the bottom for temporary accumulation of cake before the discharge port opens to discharge cake.  
       [0018] Pursuant to another feature of the present invention, a conveyor is disposed in the bowl for moving the deposited solids along the inner surface of the bowl. During operation of the rotating machine, the conveyor rotates at a different speed than the bowl to transport deposited cake solids down an annular path formed between the guide member and the inner surface of the bowl. The conveyor may take the form of a ribbon conveyor, which is disposed at a radial distance (from the rotation axis) greater than the distance of the guide member from the axis.  
       [0019] The guide member and the conveyor may be integrally formed for directing flow to enhance centrifugal separation and for conveying cake along the bowl toward a discharge outlet port.  
       [0020] In alternative embodiments of the present invention, the guide member is either rotatably mounted to the bowl for rotation relative to the bowl or fixed relative to the bowl. In the latter case, the guide member may be mounted directly (a) to bowl heads respectively located at opposite ends of the bowl, (b) to a shaft disposed in the bowl coaxially with the axis, or (c) to the inner surface of the bowl, for instance, by studs.  
       [0021] The path defined by the flow guide member typically has a circumferential or annular component and an axial or longitudinal component, as where the guide member takes the form of a spiral. Preferably, the circumferential or annular component is larger than the axial or longitudinal component.  
       [0022] Where the rotating machine incorporating the bowl assembly of the present invention operates in a continuous rather than a batch mode, the bowl may be provided with a plurality of solid-phase discharge ports disposed at axially spaced locations in the bowl. Typically, a first plurality of circumferentially spaced cake discharge ports or nozzles are located at one axial position, for instance, at a downstream end of the bowl, while a second plurality of circumferentially spaced cake discharge ports or nozzles are located at an intermediate axial location, spaced from the opposite ends of the bowl.  
       [0023] In another embodiment of the present invention, baffles are disposed in the bowl along the guide member to force the liquid phase to flow substantially circumferentially in a predetermined direction.  
       [0024] Pursuant to another feature of the present invention, the bowl assembly further comprises a plurality of rakes disposed in the bowl for rotating at a differential speed relative to the bowl to propel and agitate deposited solids to induce same to flow down an annular path formed between the guide member and the inner surface of the bowl. Another important function of the flow guide is that it blocks longitudinal (along axis) traveling waves from propagating that can be damaging especially under high-speed rotation.  
       [0025] A decanter centrifuge with a flow guide in accordance with the present invention is simpler and less expensive to manufacture and operate than conventional machines, having a cake conveyor that moves at a differential speed relative to the centrifuge bowl. This omission of a conveyor results in a reduction in manufacturing expense in part because no gearbox or backdrive is necessary. Moreover, bearing design is simplified. The omission of a conveyor also results in a reduction in operating expense since the power requirement is reduced: no conveyance power, thus there are fewer moving parts and a reduced requirement for repair and maintenance procedures.  
       [0026] In a decanter-type centrifuge in accordance with the present invention, used for classification or fractionating a suspension into a product stream containing valuable fine particles and a reject stream containing oversize, coarse particles, the feed suspension continuously drops out coarse solids, flows around the helical fin to the overflow weir whereas the coarse reject flows down an annular path along a cone angle driven by a component of the G-force to nozzle discharge locations. More pool volume is provided for separation, since the shaft (if any) supporting the flow guide may be thinner than the shaft necessary for supporting a conveyor screw. The deep pool design, with longer retention time, further enhances classification.  
       [0027] There are other advantages of a decanter design in accordance with the present invention.  
       [0028] With the new invention of a conical bowl, the cake can be discharged continuously, and the “opened” flow guide can stop traveling waves and enhances sedimentation. This is especially favorable at high rotation speed and high G. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0029]FIG. 1 is a schematic longitudinal cross-sectional view through a bowl assembly of a prior-art centrifuge.  
     [0030]FIG. 2 is a schematic longitudinal cross-sectional view through a bowl assembly of another prior-art centrifuge.  
     [0031]FIG. 3 is a schematic longitudinal cross-sectional view through a bowl assembly of a further prior-art centrifuge.  
     [0032]FIG. 4 is a schematic longitudinal cross-sectional view through a bowl assembly of yet another prior-art centrifuge.  
     [0033]FIG. 5 is a schematic longitudinal cross-sectional view through a bowl assembly of a centrifuge in accordance with the present invention.  
     [0034]FIG. 6 is a schematic longitudinal cross-sectional view through a bowl assembly of another centrifuge in accordance with the present invention.  
     [0035]FIG. 7 is a schematic longitudinal cross-sectional view through a bowl assembly of a further centrifuge in accordance with the present invention.  
     [0036]FIG. 8A is a schematic longitudinal cross-sectional view through a bowl assembly of an additional centrifuge in accordance with the present invention, showing the centrifuge in one mode of operation.  
     [0037]FIG. 8B is a schematic longitudinal cross-sectional view similar to FIG. 8A, showing the centrifuge of that figure in another mode of operation.  
     [0038]FIG. 9 is a schematic longitudinal cross-sectional view through a bowl assembly of yet another centrifuge in accordance with the present invention.  
     [0039]FIG. 10 is a schematic longitudinal cross-sectional view through a bowl assembly of yet a further centrifuge in accordance with the present invention.  
     [0040]FIG. 11 is a schematic longitudinal cross-sectional view through a bowl assembly of a modification of the centrifuge of FIG. 10, in accordance with the present invention.  
     [0041]FIG. 12 is a diagram showing a bowl and rakes of FIG. 11 in a developed or rolled out configuration, represented by arrows A-A in FIG. 11.  
     [0042]FIG. 13 is a schematic longitudinal cross-sectional view through a bowl assembly of another modification of the centrifuge of FIG. 10, in accordance with the present invention.  
     [0043]FIG. 14 is a graph of solids-capture performance, comparing a centrifuge with a flow guide in accordance with the present invention and a conventional centrifuge without such a flow guide.  
     [0044]FIG. 15A is a schematic partial longitudinal cross-sectional view of a bowl assembly with a profiled flow guide in accordance with the present invention.  
     [0045]FIG. 15B is a schematic partial longitudinal cross-sectional view of a bowl assembly with another profiled flow guide in accordance with the present invention.  
     [0046]FIG. 16 is a cross section along the streamwise direction of a flow guide in accordance with the present invention, showing a gate arrangement to alter the flow path of the feed suspension in the course of flowing toward the effluent liquid discharge. 
    
    
     [0047] In the drawings, like parts are designated with the same reference numbers.  
     DEFINITIONS  
     [0048] The phrase “an at least partially circumferential or annular path” is used herein to denote a path that has at least one path segment with a circumferential or annular component. Thus, a quantity of fluid traveling along that path segment has a velocity vector with a circumferential or annular component. A spiral path is an example of an at least partially circumferential or annular path.  
     [0049] The phrase “an at least partially helical path” is used herein to denote a path that has at least one path segment with a circumferential or annular component and an axial or longitudinal component. Thus, a quantity of fluid traveling along that path segment has a velocity vector with a circumferential or annular component and an axial or longitudinal component.  
     [0050] The term “bowl” is used herein to denote a rotatable outer casing of a rotating machine. A bowl, as that term is used herein, may include both bowl heads and a sidewall. Solid phase outlets are typically provided in the sidewall, whereas liquid phase outlets are generally located in a bowl head. However, the arrangement of outlets may be different, as where a liquid phase is siphoned off via a pipe or tube extending through the sidewall. The sidewall of a bowl may be completely imperforate or partially perforated, as in the case of a screen bowl.  
     [0051] A “guide member” or “flow guide” as that term is used herein refers to any physical structure capable of deflecting and directing flow. A guide member may take the form of a baffle, a fin, or a vane, or any other form suitable for controlling the direction of fluid flow. A guide member or flow guide as disclosed herein directs a suspension in a pool of a centrifuge or rotating machine at least partially and preferably substantially in a circumferential or annular direction. A guide member or flow guide in accordance with the present disclosure may be a continuous structure or may be a segmented or interrupted structure. For instance, a guide member or flow guide may be a plurality of helical fins spaced from one another along an axis of a rotating machine. In addition, a guide member or flow guide as disclosed herein may extend throughout the length of a bowl or alternatively may extend only along part of the bowl length.  
     [0052] The term “suspension” or “slurry is used herein to describe a flowable composition that contains components (phases) of different densities. For example, a suspension may be a liquid that contains solid particulate material. Alternatively, a suspension may be a mixture of two or more liquids of different densities, with or without particulate material. The term “suspension” thus encompasses both a feed slurry or liquid-solids suspension after introduction thereof into a rotating bowl and the liquid portion of the slurry after separation or settling of at least some of the solids contained in the slurry. The amount of solids in the suspension varies from a highest concentration at a feed input to a lowest concentration at a liquid phase discharge port. More generally, the word “suspension” encompasses a flowable mixture of components of different densities where the concentration or amount of a heavy phase varies from a highest concentration at a feed input to a lowest concentration at a light phase discharge port. Where solids of a suspension are deposited under the action of centrifugal force on the inner cylindrical and/or conical surface of the bowl, the solid-phase material mixed with a residual amount of liquid is frequently termed “cake” and may be removed automatically in a continuous process through one or more solids-phase discharge ports. Cakes vary in consistency from granular to pasty.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0053]FIG. 5 illustrates a modification in the bowl assembly of FIG. 1. Bowl  12  is provided with a flow guide member  130  in the form of a helical fin extending the entire length of the bowl, from bowl head  16  to bowl head  18 . Guide fin  130  ensures that the solids-carrying liquid phase, with a solids concentration varying from a high at the input end to a low at the output end, travels along a substantially circumferential or annular path inside bowl  12 . Guide fin  130  is preferably fixed relative to bowl  12  and rotates at the same angular velocity as the bowl. Fin  130  may be fixed to inner surface  28  of bowl  12  via spaced studs (not shown). Alternatively or additionally, fin  130  may be fixed to a central shaft (not shown) and/or to bowl heads  16  and  18 . Preferably, fin  130  has a spiraling outer edge (not separately designated) that is spaced a predetermined distance from inner surface  28  of bowl  12 . This spacing facilitates the removal of sediment layer  26  from bowl sidewall  14 . Fin  130  advantageously has a pitch optimized to enhance separation.  
     [0054]FIG. 6 depicts an improvement in the bowl assembly of FIG. 2. Bowl  38  is provided with a flow guide member  132  in the form of a helical fin extending the entire length of the bowl, from accelerator vanes  142  at an input end to baffle  54  and pairing disc or centripetal pump  62  at an output end. Guide fin  132  constrains the solids carrying liquid phase to move along a substantially circumferential or annular path inside bowl  38 . The ratio of a circumferential or annular component of the path to an axial or longitudinal component may be increased by decreasing the pitch of the fin flights. This is generally desirable as the degree of solids separation is augmented where the travel path of the liquid phase is more annular than longitudinal. Under some conditions, the pitch of the guide fin may increase to achieve other objectives such as to reduce side-wall friction to flow. Also the adjacent side wall of the guide fins may not need to be parallel as in conventional decanter centrifuge, the side walls can be angled with increasing width either radially inward or radially outward as shown, respectively, by FIG. 15A and FIG. 15B to change the effective channel width opened to flow in the fin. Guide fin  132  is preferably fixed relative to bowl  38  and rotates at the same angular velocity as the bowl. Fin  132  may be fixed directly to inner surface  50  of bowl  38  via spaced studs (not shown). Alternatively or additionally, fin  132  may be fixed to a central shaft (not shown) and/or to bowl heads (not separately designated). Preferably, fin  132  has a spiraling outer edge (not separately designated) that is spaced a predetermined distance from inner surface  50  of bowl  38 . This spacing facilitates the removal of sediment layer  48  from bowl sidewall  52 .  
     [0055] As shown in FIG. 7, a centrifuge bowl assembly  134  comprises a conical bowl  136  having an entirely conical sidewall  138 . Bowl  136  is supported at only an upper end by a bearing  140  and is rotated about an axis  142  by a motor  144 . A feed slurry or suspension  146  enters bowl  136  through a feed pipe  148  at the upper end of the bowl. A flow guide member  150  in the form of a helical fin extends the entire length of bowl  136 . Guide fin  150  constrains the suspension to move along a substantially circumferential or annular path inside bowl  136 . Guide fin  150  has a spiraling outer edge  152  which is spaced a predetermined distance from an inner surface  154  of sidewall  138  to define therewith a cake flow path  156 . Solids that are deposited in a cake layer (not shown) on inner surface  154  during rotation of bowl  136  about axis  142  flow on inner surface  154  along path  156 , from a narrow-diameter end of bowl  136  towards a large-diameter end thereof. Path  156  is oriented at a substantial angle to the flights of guide fin  150 , rather than parallel to the major surfaces (not designated) of the guide fin. In contrast to the suspension path, which is defined by guide fin  150  to have a substantial circumferential or annular component, the cake path  156  is mostly, if not entirely, longitudinal. The cake exits the bowl in continuous streams  157  and  159  at an intermediate axial location through a first series of circumferentially spaced outlet nozzles  158  and at a terminal axial location through a second series of circumferentially spaced outlet nozzles  160 .  
     [0056] Guide fin  150  may be rotatably mounted to bowl  136  for rotation relative thereto. Preferably, however, guide fin  150  is fixed relative to the bowl. In that case, guide fin may be mounted directly (a) to bowl heads  162  and  164  respectively located at opposite ends of bowl  136 , (b) to a shaft (not shown) disposed in the bowl coaxially with rotation axis  142 , or (c) to inner surface  154  of bowl sidewall  138 , for instance, by studs (not shown).  
     [0057] Bowl sidewall  138  exhibits a half angle  166  such as to ensure fluid-like cake flows down the path  154  toward the large bowl diameter. Guide fin  150  is profiled at the large diameter end of bowl  136  to form a temporary storage space  168  for cake a discharge thereof through lower outlet nozzles  160 .  
     [0058] Effluent liquid of a low solids concentration overflows weirs  170  at large-diameter head  162  and enters a stationary effluent catcher  172  for subsequent discharge, as indicated by an arrow  174 .  
     [0059]FIGS. 8A and 8B illustrate another conical bowl assembly  176  for a rotating solid-liquid separation machine. Bowl assembly  176  comprises a conical bowl  178  having an entirely conical sidewall  180 . Bowl  178  is supported at an upper end by a bearing  182  and at a lower end by another bearing  183  and is rotated about an axis  184  by a motor  186 , as indicated by an arrow  188 . A feed slurry or suspension  190  enters bowl  178  through a feed pipe  192  that extends along axis  184  through bowl  178  to a deflector or distributor  194 . (Feed pipe  192  can be rotating in high-speed centrifuges. However, feed pipe  192  cannot exceed a certain length because otherwise it will experience vibration because the rotation speed exceeds the natural frequency of the pipe. One solution is to have a fixed portion followed by a rotating portion.)  
     [0060] As further illustrated in FIGS. 8A and 8B, a flow guide member  196  in the form of a helical fin extends the entire length of bowl  178 . Guide fin  196  constrains the suspension to move along a substantially circumferential or annular path inside bowl  178 . Guide fin  196  has a spiraling outer edge  198  which is spaced a predetermined distance from an inner surface  200  of sidewall  180  to define therewith a cake flow path  202 . Solids that are deposited in a cake layer (not shown) on inner surface  200  during rotation of bowl  178  about axis  184  flow on inner surface  200  along path  202 , from a narrow-diameter end of bowl  178  towards a large-diameter end thereof. Path  202  is oriented at a substantial angle to the flights of guide fin  196 , rather than parallel to the major surfaces (not designated) of the guide fin. In contrast to the liquid phase path, which is defined by guide fin  196  to have a substantial circumferential or annular component, the cake path  202  is mostly, if not entirely, axial or longitudinal along the cone.  
     [0061] Bowl  178  is provided with a movable bottom panel or discharge closure head  204  which is usually in a closed position as shown in FIG. 8A. Bottom panel or discharge closure head  204  is temporarily opened (FIG. 8B) at intervals to form a gap  205  discharge granular non-flowable solids in an output flow  206 . The solids accumulate in an annular storage space  208  defined proximate to bottom panel or discharge closure head  204  by guide fin  196 . Typically, the intermittent actuation of bottom panel or discharge closure head  204  is hydraulic. The frequency of opening of the bottom panel or discharge closure head  204  for cake discharge can be set for fixed time interval control or actuated by pressure (indicative the cake storage area is filled) as with disk centrifuges. Effluent liquid  210  exits bowl  178  at an upper end, proximate to bearing  182 , and is temporarily held in an effluent catcher  212  prior to final discharge.  
     [0062] Guide fin  196  may be rotatably mounted to bowl  178  for rotation relative thereto. In the illustrated embodiment, guide fin  196  is fixed relative to the bowl. Fin  196  may be mounted directly to a shaft (not shown) disposed in the bowl coaxially with rotation axis  184  and/or to inner surface  200  of bowl sidewall  180 , for instance, by studs (not shown).  
     [0063] Bowl sidewall  180  exhibits a half conical angle  214  greater than the angle of friction for a granular cake. The half angle  214  needs to be large to ensure the cake flows down the path  202  toward the large bowl diameter.  
     [0064]FIG. 9 depicts an improvement in the bowl assembly of FIG. 4. Bowl  94  is provided with a helical fin  216  extending the length of cylindrical sidewall section  96 , from conical bowl section  98  at an input end to conical bowl section  100  at an output end. Guide fin  216  guides the liquid phase or suspension fluid to move along a substantially circumferential or annular path inside bowl  94 . Guide fin  216  is preferably fixed relative to bowl  94  so as to rotate at the same angular velocity. Fin  216  may be fixed directly to bowl sidewall  96  via spaced studs (not shown) and/or to an axial shaft (not shown). Preferably, fin  216  has a spiraling outer edge (not separately designated) that is spaced a predetermined distance from inner surface  50  of bowl sidewall  96  to facilitate the removal of sediment layer  118  from bowl sidewall  96   
     [0065]FIG. 10 shows a horizontally oriented conical centrifuge bowl  218  comprising a conical sidewall  220  and a pair of disk-shaped bowl heads  222  and  224  at opposite ends of the sidewall. A slurry  226  is introduced into bowl  218  via a feed pipe  227  traversing head  224  and forms a separation pool  228  in bowl  218 . A flow guide member  230  in the form of a helical fin extends the entire length of bowl  218 . Guide fin  230  constrains the liquid phase in pool  228  to move along a substantially circumferential or annular path  232  inside bowl  218 . Guide fin  230  has a spiraling outer edge  234  which is spaced a predetermined distance from an inner surface  236  of sidewall  220  to define therewith a cake flow path  238 . Solids that are deposited in a cake layer (not shown) on inner surface  236  during rotation of bowl  218  about a horizontal axis  240  flow on inner surface  236  along path  238 , from a narrow-diameter end of bowl  218  towards a large-diameter end thereof. Path  238  is oriented at a substantial angle to the flights of guide fin  230 , rather than parallel to the major surfaces (not designated) thereof. In contrast to the liquid phase path, which is defined by guide fin  230  to have a substantial circumferential or annular component, the cake path  238  is mostly, if not entirely, axial or longitudinal. The cake exits the bowl  218  in continuous streams  242  and  244  at an intermediate axial location through a first series of circumferentially spaced outlet nozzles  246  and at a terminal axial location through a second series of circumferentially spaced outlet nozzles  248 . The liquid phase exits bowl  218  in effluent streams  250  passing over weirs  252  in head  222 .  
     [0066] Guide fin  230  is mounted to an axial shaft  254 . Preferably, shaft  254  and guide fin  230  are stationary relative to bowl  218  and thus rotate at a common velocity therewith. Alternatively, guide fin  230  may be mounted directly to bowl heads  222  and  224  or to inner surface  236  of bowl sidewall  220 , for instance, by studs (not shown).  
     [0067]FIGS. 11 and 12 show a modification of the centrifuge of FIG. 10 in which plural rake elements  256  are disposed in bowl  218  for stirring the cake and breaking up any clumps on sidewall inner surface  236  to ensure flowability of the deposited cake solids. Rake elements  256  are connected to a conveyor hub  258  via respective rigid posts  260  for moving at a different angular velocity than bowl  218 . In the developed view of FIG. 12, arrow  262  represents the bowl speed, while arrows  264  represent the speed of rake elements  256 . Arrows  266  represent the cake flow along inner surface  236  of bowl sidewall  220 . Arrow  267  is the longitudinal direction along the bowl  218  toward the large diameter end.  
     [0068]FIG. 13 depicts another modification of the centrifuge of FIG. 10 wherein a sediment conveyor  268  is provided in bowl  218  for transporting deposited cake sediments along inner surface  236  of bowl sidewall  220 . Conveyor  268  is mounted to a hub  270  for rotation at a different angular speed than bowl  218 .  
     [0069]FIG. 14 shows a pair of graphs comparing the percentage of solids recovery by centrifugation in a conventional centrifuge (graph  272 ) with the percentage of solids recovery by centrifugation in a centrifuge having a flow guide as described herein (graph  274 ). The flow guide works well with high speed and high G centrifugation, for instance, 5000-20,000 g, such as using in tubular (manual and automatic) centrifuges for biotech, pharmaceutical, and specialty chemicals. The flow guide enables superior performance as shown in FIG. 14 for the same G or same rate or same performance but with a higher rate. In fact, it is expected that high speed would only further bring out the enhancement of the flow guide in separation. Also, a flow guide as described herein may be used in some of the disk centrifuge applications such as oil-water separation, polishing, clarification and separation of solid-liquid, liquid-liquid, or solidliquid-liquid.  
     [0070]FIG. 15A shows a slanting side wall or surface  276  of a fin or flow guide  278  disposed in a bowl  280  rotating about an axis  282 . An outer edge  283  of fin  278  is spaced a predetermined distance D 1  from an inner surface  285  of bowl  280  to permit axially directed cake flow. Slanting surface  276  results in a wider channel  284  between adjacent wraps at the large radius as compared with at the small radius or when compared with a fin which has a straight sidewall (not shown) with the same pitch. The reverse is true (not shown) when the slanting surface reverses in orientation with respect to the radial direction.  
     [0071]FIG. 15B shows a slanting wall or surface  286  on one face of a fin  288  having a straight or planar surface  290  on the opposite face. Fin  288  is disposed in a bowl  292  rotating about an axis  294 . An outer edge  296  of fin  288  is spaced a predetermined distance D 2  from an inner surface  298  of bowl  292  to permit axially directed cake flow. Both designs as depicted in FIGS. 15A and 15B are used for directing flow and changing the cross sectional area opened to flow at, respectively, the small and large radius locations to obtain the most optimal result for separation.  
     [0072]FIG. 16 depicts a circumferentially extending flow guide or fin  300  in a bowl  302  shown in a developed view along the flow-stream direction. The flow guide or fin defines a substantially circumferential flow channel having an inlet  304  and a general direction of flow  310 . One or more gates  306 ,  307  are so disposed in the flow channel as to extend substantially perpendicularly to the flow path defined by the channel. Gates  306 ,  307  serve to direct the flow  308  of a suspension either radially inward or radially outward, so that the velocity of the lighter phase and suspension in the circumferential direction is optimized and the volume of sweep in the pool is more uniform. The design and location of gates  306 ,  307  are arranged to improve the separation of the suspension. These gates  306 ,  307  are part of the flow guide or fin  300  and thus rotate at the same speed as the flow guide. (Gates  306 ,  307  are different from baffles that are more circumferentially or axially oriented, parallel to the streamwise direction to direct the flow either axially or circumferentially. In contrast, gates  306 ,  307  are more radially oriented and perpendicular to the streamwise direction to redirect the flow radially in-and out as the flow moves through the flow guide channel.)  
     [0073] Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For example, one skilled in the art will appreciate that the orientation of the rotating bowl and the rotation axis is not relevant to the invention. The bowl may rotate about an axis having essentially any orientation, even though only horizontal and vertical orientations are specifically disclosed herein. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.