The present invention relates to a clean-in-place decanter centrifuge. More particularly, the invention relates to a decanter centrifuge having self-cleaning components useful in the food and beverage industry, especially for dairy products.
Various centrifuges have been used to separate a crystalline or granular material from a liquid carrying the crystalline or granular material. Such centrifuges are typically used in a continuous process in which the combined liquid and solid material is continuously fed into and discharged from the centrifuge. The continuous process is distinguished from a batch process in which a batch of liquid and solid material is fed into the centrifuge. After the materials are separated, the centrifuge is stopped and the separated materials are removed before another batch is loaded into the centrifuge. Both the continuous and batch separation processes are also considered to dry the solid material. The separation process is used in a wide range of applications including the production of soap powders, coal, gypsum, plastic granules, potash, salt, food products, and dairy products.
Industrial centrifuges may be classified according to how they separate the liquid and solid materials. In screen centrifuges, the centrifugal acceleration causes the liquid to pass through a screen through which the larger solid material cannot pass. In decanter centrifuges, there is no screen to physically separate the liquid and solid materials. Instead, the liquid and solid materials are separated by the centrifugal acceleration. The clearing of the liquid typically takes place in the cylindrical portion of the bowl of a decanter centrifuge, whereas the dewatering of the solids via filtration or compression occurs in the conical portion of the bowl.
The inside of a bowl of a centrifuge must be cleaned occasionally prior to start up or after use in order to remove materials which have accumulated along the bowl wall and have not been discharged. Preferably, this clean up is performed without disassembly of the centrifuge. Centrifuges have been cleaned using various methods, such as those disclosed in U.S. Pat. Nos. 4,036,426, 4,978,331, and 5,397,471.
Decanter centrifuges used in the food processing industry require special machinery for processing food and dairy products. For example, machinery used in processing dairy products should not have metal to metal contacts exposed to the dairy products. All areas of the machine that are exposed to the dairy products, including seals, should be washable. There should be no places where product can collect and allow bacteria to grow.
To address the special requirements for centrifuges used in the food processing industry, the present invention provides for a clean-in-place decanter centrifuge. The invention is especially suited for use in the dairy industry in separating lactose (milk sugar) solids from whey.
The present invention relates to a decanter centrifuge for processing a combined liquid and solid material to separate the liquid from the solid material, the centrifuge comprising:
a drive housing having an exterior wall and an interior surface bounding a contained volume within the housing and means to drive the centrifuge, said exterior wall including an end wall;
a discharge housing mounted to the drive housing, said discharge housing having an exterior wall including a front wall, a peripheral wall disposed between the front wall and the exterior wall of the drive housing, and an interior surface bounding a contained volume within the housing;
a bowl and scroll assembly mounted in the discharge housing to rotate about an axis of rotation, said bowl and scroll assembly having an outer wall cooperating with the peripheral wall to form an enclosure therebetween, said enclosure receiving liquid that is separated from the solid material, the peripheral wall of said discharge housing cooperating with the end wall of said drive housing to form a cavity therebetween;
a first non-contacting seal means for separating said enclosure from said cavity, thereby inhibiting a flow of liquid between said enclosure and said cavity;
a second non-contacting seal means for separating said cavity from the contained volume within the drive housing, thereby inhibiting a flow of fluid between said contained volume and said cavity; and
means connected to the discharge housing for injecting a fluid into the first non-contacting seal means between said discharge housing and said bowl and scroll assembly for cleaning said non-contacting seal means;
wherein there are no metal-to-metal contact areas within the interior of the bowl and scroll assembly.
In one embodiment, the outer wall of the bowl and scroll assembly comprises a plurality of drain lines located in the rear wall section of the bowl to allow essentially all liquid to drain from the bowl and scroll assembly.
In another embodiment, the bowl hub comprises at least one drain line to allow lubrication oil to drain into said cavity and prevent ingress of lubrication oil into said bowl and scroll assembly.
In yet another embodiment, the discharge housing further comprises an enclosure bound by the interior surface of the exterior wall of the discharge housing, partitions within the discharge housing, and the outer wall of the rotating bowl, said partitions being separated from the outer wall of the rotating bowl by non-contacting seals whereby fine solid material that migrates into said enclosure is removable from the discharge housing by liquid sprayed from one or more fluid injectors inserted into said enclosure.
In general terms, the operation of a decanter centrifuge of the invention can be described as follows. The main rotating assembly in the decanter centrifuge is a solid bowl with a cylindrical/conical configuration that is supported at one end only (overhung design). Within the bowl there is a scroll assembly supported by bearings between itself and the bowl. By using some type of driver, such as an electric or hydraulic motor, the bowl and scroll assembly usually rotate in the same direction but with a difference in speed that is governed by a gear reducer. The scroll assembly rotates either slightly faster or slower depending on the application and how it is mechanically set-up. The rotational speed of the bowl determines the gravitational force developed based on the bowl's largest diameter. Such a decanter centrifuge can be used when the feed slurry is comprised of liquid and solid phases that are required to be separated and the solid phase is either too small or too light to settle on its own. The added effect of increased gravitational force helps to accelerate the settling rate of the solids from the liquids.
The feed slurry is introduced into the feed zone of the rotating scroll via a feed tube. The feed slurry passes through the rotating scroll and begins to collect inside the rotating cylindrical section of the bowl. Due to the centrifugal forces exerted by the rotating bowl, the solids settle through the liquid phase and collect and compress against the inside of the bowl wall. The liquid phase forms a pool within the rotating bowl and eventually reaches a pre-determined height and begins to decant out of the rotating bowl. This clarified liquid phase exits the decanter via a liquid discharge chute. Simultaneously, the collecting solids are transported along the cylindrical section of the bowl until they reach the conical section. As the solids are transported up the conical section, the solids eventually reach a level where they are no longer submerged in the liquid pool. In this area of the bowl, the separated solids are dewatered as they tumble in front of the rotating scroll flights and continue to be transported to the solids discharge chute. At this point, the dewatered solids leave the rotating bowl assembly and are discharged through a solids discharge chute. The decanter centrifuge is capable of receiving a continuous feed and separating, dewatering, transporting and discharging the separated solid and liquid materials at full process speed. If the physical and chemical properties of the feed slurry are held constant, a properly sized decanter can process large volumes of material over extended periods of time with little, if any, variation in separation quality.
In the centrifuge of the invention, all surfaces in contact with the material being processed may be cleaned-in-place, and all such surfaces are oriented vertically downward such that they drain freely. The construction of the centrifuge eliminates all metal-to-metal contact or joints between metallic surfaces in contact with the material being processed. Therefore, the invention has an advantage of providing a clean-in-place decanter centrifuge that may be used for processing a wide range of products in the food and dairy industries.
A bowl and scroll assembly 26 comprising a bowl 56 and a scroll assembly 27 is rotatably mounted within the discharge housing 14. The bowl 56 has an outer wall 28 comprised of a circumferential wall section 30 and a rear wall section 32. The rear wall section 32 of the bowl 56 cooperates with the interior surface 24 of the peripheral wall 22 of the discharge housing 14 to form an enclosure 34 therebetween. The end wall 20 of the drive housing 15 cooperates with the peripheral wall 22 of the discharge housing 14 to form a cavity 36 therebetween. The combined liquid and solid material is fed into the centrifuge 10 through a feed tube 38 to a feed zone 40 of the scroll assembly 27. Rotation of the bowl and scroll assembly 26 results in liquid being discharged through a plurality of openings 33 in the rear wall section 32 of the bowl 56 (for example, eight openings equally spaced around the circumference of the rear wall section of the bowl) into the enclosure 34 where it falls into liquid discharge chute 35 of discharge housing 14 and is discharged from the centrifuge. The solid material is discharged from the front end of the bowl 56 and the scroll assembly 27 into the solids discharge chute 42 of the discharge housing 14.
The centrifuge is powered by a motor 44 (see
The bowl and scroll assembly 26 comprises a bowl 56 having an integral hub 60 which is centrally located in the rear wall section 32 of the bowl 56 and is mechanically connected to the outer drive shaft 48 by bolts 62. Therefore, the bowl 56 is mounted within the discharge housing 14 to rotate about the axis of rotation 12. A scroll member 64 has a hub 66 which is centrally located within the bore 65 of the scroll member 64 and is mechanically connected to the inner drive 50 by a key (not shown) and retained by bolts 68. A cap 70 having an integral threaded stud 72 is removably connected to the inner drive shaft 50 thereby permitting access to the bolts 68 which secure retaining plate 67 to the inner drive shaft 50. As shown in
Screw flights 82 extend outwardly from a tubular side wall 83 of scroll member 64, and the screw flights extend helically relative to the axis of rotation 12 between the front and rear ends, 74, 78, respectively, of the scroll member 64. As shown in
For application in the food processing industry, the materials being processed should be contained within the machine and not exposed to foreign material. The majority of the liquid being separated passes through the openings 33 in the rear wall section 32 of the bowl 56. Therefore, the centrifuge contains a first non-contacting seal 90 for separating the enclosure 34 from the cavity 36 and inhibiting the flow of liquid therebetween. As shown in
It is also desirable to isolate the cavity 36 from the chamber 108 in which the drive mechanics and a lubricant are located. The lubricant in the chamber 108 may slip past bearings 54 and into the cavity 36. Therefore, a second non-contacting seal 110 is provided to isolate cavity 36 from chamber 108. As shown in
Referring to
Referring to
As shown in
It is necessary that the centrifuge 10, when used for processing food materials, be able to be cleaned in place. Preferably, that cleaning should be implemented without requiring the disassembly of components of the centrifuge 10. Therefore, the present invention has the additional advantage of having self-cleaning components. Referring to
The rear wall section 32 of the bowl 56 contains a plurality of openings 33 providing access to the space 126 bounded by the closed end 80 of the bowl 56 and the rear end 78 of the scroll member 64. A fluid injector 148 also provides wash liquid via passage 152 and opening 154 and into the space 126 for washing the surfaces bounding the space 126. This wash liquid enters into space 126 by passing through openings 33 in the bowl 56 and contacts the rear end wall 78 of scroll member 64. The wash liquid in space 126 is released through a plurality of drain ports 57 in the bowl 56 and is discharged via liquid discharge chute 35.
Referring to
A fluid injector 176 is connected to the fluid source (not shown) and by fluid lines (not shown) has an internal passage 178 terminating with a fluid nozzle 180 which is effective to spray cleaning fluid on the internal surfaces of the front side of the centrifuge 10. The third non-contacting seal 138 is at the dry end of the centrifuge; and therefore, with its construction, it should accumulate little or no liquid or solid material between its mating surfaces 140, 142. However, during the cleaning process the fluid sprays from the nozzles 174, 180 are effective to circulate cleaning fluid between the surfaces 140, 142 of the third non-contacting seal 138.
Referring to
Additional fluid injectors may be connected to the fluid source by fluid lines and extend through the peripheral wall 22, the exterior wall 16 and/or the front wall 18 of the discharge housing 14. Consequently, all of the surfaces of the bowl and scroll assembly 26 and the housing 14 in contact with the liquid and solid material may be cleaned in place without disassembling the centrifuge 10.
As shown in
In use, for example in the application of separating lactose (milk sugar) solids from whey, the motor 44 drives the bowl and scroll assembly 26 in a clockwise direction as viewed from the front of the centrifuge, as in
The angular velocity of the rotating scroll member 64 is faster than the angular velocity of the bowl 56. The difference in angular velocities between the scroll member 64 and the bowl 56 is effective to cause the lactose solid material to move along the leading front edge 88 of the screw flights 82 and across the inner surface 86 of the bowl 56 toward the open end 76 of the bowl 56. Fluid injector 176 has an internal passage 178 connecting spray nozzle 180 to a fluid source (not shown) by a fluid line (not shown). The lactose solid particles may collect on the interior surface and the front wall 18 of the discharge housing 14. Therefore, the fluid injector 176 sprays a sluicing solution such as water onto the lactose solid material moving toward the open end 76 of the bowl 56 to direct the solids down discharge chute 212.
Referring to
The components of the centrifuge 10 which are in contact with the material being processed are made of 316 L stainless steel. All product contact surfaces are polished to 150 grit finish. The metallic housing, metallic bowl and metallic scroll member are constructed and interconnected such that no metallic surface inside the centrifuge that contacts the liquid and solid material is in metal-to-metal contact with another metallic surface also in contact with the liquid and solid material. As illustrated in the drawings, the centrifuge is further constructed such that all metallic surfaces of the housing, bowl member and scroll member in contact with the liquid and solid material being processed are oriented in a vertically downward direction so that they drain freely.
After a predetermined period of use which may be measured in hours, days or weeks, the input of the mother liquor is stopped, and the machine is cleaned in place without disassembly. The cleaning process may require cleaning the centrifuge with a succession of different fluids such as an acid solution, a caustic solution and water. The fluid source contains or is connected to the sources of the required solutions, and under automatic or manual control the appropriate solutions are fed through the feed lines, through the fluid injectors and into the centrifuge 10. Consequently, the centrifuge of the present invention may be used in applications such as food processing where the clean-in-place capability is required.
While the invention has been set forth by the description of the embodiments in considerable detail, it is not intended to restrict or in any way limit the claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, the multiple shaft drive may be driven at different speeds by independent input shafts connected to multiple pulleys or gears mounted on the output drive shaft of the motor. Further, the bowl and scroll assembly is typically oriented to rotate about a horizontal axis of rotation, however, the bowl and scroll assembly may be constructed to rotate about a vertical axis of rotation. The invention, in its broadest aspects, is therefore not limited to the specific details shown and described. Accordingly, departures may be made from such details without parting from the spirit or scope of the general inventive concept.
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