A decanter centrifuge for separating feed material

Abstract

The present invention relates to a conveyor screw for a decanter centrifuge The conveyor screw defines a cylindrical portion and a conical portion and comprises a central body. The conveyor screw defines a first flight attached to the central body. The first flight defines a first diameter and a pitch angle being less than 20°. The conveyor screw further defines a second flight attached to the central body. The second flight has the same winding direction as the first flight and being at least partially intertwined with the first flight. The second flight defines a pitch angle being greater than 30° and the second diameter being smaller than the first diameter.

Description

[0001] A decanter centrifuqe for feed material

[0002] The present invention relates to a conveyor screw for a decanter centrifuge, a decanter centrifuge and a method of operating a decanter centrifuge.

[0003] Introduction

[0004] Centrifugal based methods, and in particular decanter centrifuges, can be used for separating the oil and fat from the residual solids and liquids when extracting oil and / or fat from oil-containing plant- or animal items, such as fish oil extraction, oil from kitchen waste and vegetable oil extraction and in particular corn oil extraction from corn seeds / whole stillage, the solids of the plant- or animal items are removed in a first separation stage, leaving a residue of liquids. The liquids mainly consist of water and oil / fat. The oil / fat is separated from the water in a second separation stage after the solids have been removed.

[0005] By using the above technique, some oil / fat will inevitably be trapped in the compacted solids cake. This oil / fat is considered to be lost as it is not easily recoverable even by resuspension of the solids.

[0006] It has therefore been suggested to remove the oil already in the first separation stage using a two-phase decanter and leaving a residue of solids and liquids. In this way a higher oil yield and a cleaner oil can be obtained.

[0007] WO 2010 / 142299 A1 relates to a decanter centrifuge having a conveyor hub with a tubular steel body with an inner core made of a material such as carbon fibre reinforced epoxy.

[0008] WO 2020 / 109135 A1 relates to a method of producing a low-fat product from a starting material made of a fat and / or oil containing plant- or animal item. The method comprises extracting ta greater part of the extractable oil and / or fat originally contained in the planter animal item using a first decanter and leaving a residue of solids and liquids.

[0009] US 7156801 relates to a decanter centrifuge comprising a conveyor screw with one or more flights and having a nominal transport speed varying along the longitudinal axis. The nominal transport speed depends in a non-linear way on the screw pitch. DE 102019102623 describes a centrifugal decanter for products that are difficult to de-oil, such as olive pulp, must be mixed particularly intensively so that all or even a residual liquid / residual moisture that is still contained in the solid can be separated more easily. The screw used having two radially offset helices extending over the cylindrical region of the drum and the worm with the same or different winding directions and / or different pitches, so that a radially outer first screw thread and a radially inner second screw thread are formed, so that a part of the suspension to be processed when the drum and screw rotates through the second radially - in relation to the axis of rotation - further inward helix or in conveyed in the radially inner screw flight in a different direction and / or in the same direction and / or at a different speed than at the same time another part of the suspension that is located in the area of the radially further outer helix or the radially outer screw flight.

[0010] US 20150209804 describes an apparatus comprising an outer drum, an inner drum, an activation spiral and a heavy- mate ria I discharging spiral.

[0011] EP 0868217 discloses a decanter centrifuge having several blades arranged to convey axially in the outer drum sludge having settled on the inside of this drum.

[0012] EP 2130607 B1 relates to a decanter centrifuge having the inlet arranged at an end of the casing opposite the end in which the opening for expelling the solid phase is arranged.

[0013] DE 2651657 relates to a centrifugal decanter having a clear fluid discharge between the inlet and the solids outlet.

[0014] US 3268159 relates to a centrifugal decanter in which the feed zone is closer to large end hub than both conveyor bearings.

[0015] JP 62106856 relates to a centrifugal decanter in which the solids and liquids discharge are on the same side.

[0016] US 3494472 relates to a centrifugal separator in the form of a sieve drum.

[0017] US 7022061 describes a centrifugal separator with power recovery discharge pipes for the light phase. US 9089852 describes a centrifugal decanter mentioning that the solid discharge port may be oriented at an angle to the radial to achieve an energy-saving repulse effect

[0018] WO 2012 / 062337 A2 relates to a centrifugal separator comprising an outlet housing being rotatable around an adjustment axis.

[0019] DE 10 2020 129478 A1 relates to a conveyor screw body having web elements.

[0020] EP 0506835 B1 relates to a decanter centrifuge having at least one bearing of the conveyor supported at the free end of a trunnion.

[0021] EP 0602766 B1 relates to a decanter centrifuge having a central hub having radially projecting support ribs.

[0022] EP 2440335 A1 relates to a decanter centrifuge having conveyor screw comprising a hub with a cylindrical part and a generally conical part, the two parts being interconnected by broad mutually spaced ribs extending in the longitudinal direction.

[0023] EP 2926911 B1 relates to a decanter centrifuge having a centrifuge worm which is mounted at one of its axial end areas by means of a connecting flange.

[0024] EP 3177403 B1 relates to a decanter centrifuge having individual openings in the cylindrical section of the screw hub.

[0025] WO 2021122878A1 relates to a decanter centrifuge having, at least in the inlet area, a screw hub with an open wall structure.

[0026] WO 2021122884A1 relates to a decanter centrifuge having a transverse disk for stabilizing the worm hub construction.

[0027] WO 2022096734A1 relates to a centrifuge screw having rods between at least two winding sections. The rods are formed completely or almost completely spaced.

[0028] WO 2022096739A1 relates to a screw hub for a centrifuge screw having in the longitudinal direction having at least sections of an open wall structure. WO 2022096745A1 relates to a centrifuge screw having an open wall structure. The open wall structure extending at most over a length of 50% of the total length of the cylindrical longitudinal section.

[0029] US 8841469 relates to a method of recovering oil from corn by adding a chemical additive.

[0030] It has been noted that the normal flight configuration of the decanter conveyor screw is not optimal for oil release. It is therefore an object of the present invention to provide technologies for increasing the release of oil from the feed and in particular the oil trapped in the solids of the feed.

[0031] Summary of the invention

[0032] The object of the present invention is in a first aspect achieved by a conveyor screw for a decanter centrifuge, the conveyor screw defining a cylindrical portion and a conical portion and comprising: a central body extending in a longitudinal direction, a first flight being attached to the central body and extending in the longitudinal direction, the first flight defining a first outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the first outer perimeter defining a first diameter, the first flight defining a first pitch angle at the cylindrical portion of the conveyor screw, the first pitch angle being less than 20°, and, a second flight being attached to the central body, extending in the longitudinal direction, having the same winding direction as the first flight and being at least partially intertwined with the first flight, the second flight defining a second outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the second outer perimeter defining a second diameter, the second flight defining a second pitch angle at the cylindrical portion of the conveyor screw, the second pitch angle being greater than 30°, and the second diameter being smaller than the first diameter.

[0033] The pitch angle is here calculated by the expression: Pitch angle = ATAN(Pitch / (7t*(Bowl diameter)))

[0034] The above-described conveyor screw is intended to be used in a decanter centrifuge together with a rotatable bowl having an inner surface. The inner surface of the bowl defines a cylindrical portion and a conical portion and substantially corresponding to the outer shape of conveyor screw. The bowl has a feed inlet and light phase outlet at one end of the bowl adjacent the at the cylindrical portion and a heavy phase outlet at an opposite end of the bowl at the conical portion as seen in the longitudinal direction. The slurry is a mixture of solids and water.

[0035] The feed is introduced into the feed inlet of the bowl as a mixture of solids and liquids, whereby the liquids are mainly water and oil. By rotating the bowl, the centrifugal forces will cause a slurry being a mixture of the solids and the water to move outwards towards the inner surface of the bowl, whereas the oil will move inwards towards the central body. However, the solids contain oils and fats which do not easily release from the slurry.

[0036] The first flight of the conveyor screw has a pitch angle of less than 20° and extend substantially to the inner surface of the bowl. The first flight is intended for scraping and conveying the slurry material in the longitudinal direction from the feed inlet towards the heavy phase outlet. The second flight of the conveyor screw has a pitch angle greater than 30° and has a smaller outer diameter than the first flight. It is intended for spreading out the slurry along the inner surface of the bowl. As the second flight has a smaller diameter than the first flight there is a gap between the second flight and the inner wall of the bowl. The second flight therefore is intended to scrape and spread out the slurry in a layer of limited thickness resulting in a greater exposure of the solids to the liquid.

[0037] It has been surprisingly found out that the combination of the longitudinal conveying of the slurry by the first flight and the spreading-out effect on the slurry achieved by the second flight increases the amount of oil released from the solids. As the oil has a lower density that the slurry, the oil will accumulate near the central body and can be collected at the light phase outlet.

[0038] In the present context, a flight is understood to be a plate attached (e.g. by welding) radially to the central body of the conveyor screw to provide the conveying surface of the conveyor screw.

[0039] According to a further embodiment of the first aspect, the conveyor screw further defining a third flight extending parallel with the second flight, the second flight extending to the second outer perimeter whereas the third flight extending to a third outer perimeter, the second flight and the third flight defining an oil channel between themselves, preferably, the oil channel defining a width between the second flight and the third flight being less than three times the distance between the central body and the second outer perimeter, more preferably, the oil channel defining a width between the second flight and the third flight being less than twice the distance between the central body and the second outer perimeter, most preferably, the oil channel defining a width between the second flight and the third flight being less than the distance between the central body and the second outer perimeter..

[0040] T o collect the oil more easily, the second flight and the third flight are formed as two parallel flights as described above. The second flight will spread out the slurry and the third flight will collect the oil. The oil will flow towards the light phase outlet in the channel between the second flight and the third flights.

[0041] A narrow channel will help keeping the solids in suspension. If the solids are allowed to form a cake, it will not be possible to extract the oil captured in the cake. A narrow channel will allow the solids separated onto the bowl wall to stay undisturbed for a shorter time period until being disturbed by the next flight.

[0042] According to a further embodiment of the first aspect, the third outer perimeter defining a third diameter, the third diameter being smaller than the second diameter.

[0043] In this way it is ensured that the oil is collected in the oil channel but not the slurry as the oil is lighter and will flow closer to the central body and the slurry will flow closer to the bowl wall due to the centrifugal forces.

[0044] According to a further embodiment of the first aspect, the second flight passes through gaps in the first flight.

[0045] In this way the first flight and the second flight can be intertwined with minimal interruption of the first flight. This will allow the conveying of the slurry to be more efficient.

[0046] According to a further embodiment of the first aspect, wherein the conveyor screw comprises a fourth flight being substantially identical to the second flight and extending in parallel with the second flight, and a fifth flight corresponding to the third flight and running parallel with the fourth flight establishing a further oil channel together with the fourth flight, the fourth flight and the fifth flight being phase shifted relative to the second flight and the third flight, respectively, preferably by 180°. In this way the spread-out effect is enhanced as the slurry will be spread out twice for every turn of the conveyor screw. A fifth flight corresponding to the third flight and running parallel with the fourth flight, establishing a further oil channel between the fourth flight and fifth flight.

[0047] According to a further embodiment of the first aspect, the second pitch angle being at least twice the first pitch angle, preferably at least thrice the first pitch angle, more preferably at least four times the first pitch angle, such as the first pitch angle is between 1° and 20°, preferably between 8° and 15° and / or the second pitch angle is between 30° and 60°, preferably between 35° and 45°.

[0048] The first pitch angle can be smaller so that the slurry move more slowly through the bowl to allow more time for the solids to release oil. The second pitch angle can be larger so as to scrape and spread out the slurry properly.

[0049] According to a further embodiment of the first aspect, the first flight extends about the cylindrical portion and the conical portion of the flight, whereas the second flight extends about the cylindrical portion only.

[0050] As the first flight is conveying the slurry, the first flight should preferably extend into the conical portion of the bowl, whereas the second flight is only intended to enhance the release of oil from the slurry, it must not necessarily extend into the conical portion of the bowl.

[0051] According to a further embodiment of the first aspect, the pitch angle of the first flight differs between the cylindrical portion and the conical portion.

[0052] In this way the conveying speed may differ between the cylindrical portion and the conical portion.

[0053] According to a further embodiment of the first aspect, the conveyor screw further comprising a baffle plate extending between the cylindrical portion and the conical portion.

[0054] The baffle plate, also known as baffle disc, is used for preventing oil flowing out via the conical end of the bowl. According to a further embodiment of the first aspect, the first flight defines a length in the longitudinal direction, the ratio between the first diameter and the length exceeding 3.9, preferably exceeding 4.2, more preferably exceeding 4.5, most preferably exceeding 4.9.

[0055] A longer first flight will allow for a longer retention time of the slurry in the bowl, which in turn will allow the solids more time to release the oil.

[0056] According to a further embodiment of the first aspect, the first diameter is exceeding 640mm, preferably exceeding 670mm, more preferably exceeding 700mm, most preferably exceeding 715mm.

[0057] According to a further embodiment of the first aspect, the central body is hollow, and fibre reinforced along the complete cylindrical portion.

[0058] A hollow and fibre reinforced central body will allow the conveyor screw to be lighter and longer while maintaining the stiffness and structural stability of the conveyor screw.

[0059] According to a further embodiment of the first aspect, the central body defines a first bearing surface and a second bearing surface, the central body being free from any openings, such as fluid openings, between the first bearing surface and the second bearing surface.

[0060] State of the art conveyor screws typically have a feed inlet opening in the central body. Having no opening in the central body will allow the conveyor screw to be lighter and longer while maintaining the stiffness and structural stability of the conveyor screw.

[0061] According to a further embodiment of the first aspect, the conveyor screw preferably comprises a cage structure extending from the central body at the first bearing surface in a direction away from the second bearing surfaces, the first screw being at least partially attached to the cage structure.

[0062] In this way the conveyor screw bearing can be moved inside the bowl while allowing the first flight to extend behind the bearing. The object of the present invention is in a second aspect achieved by a decanter centrifuge comprising a rotatable bowl and a conveyor screw according to any of the preceding embodiments accommodated inside the rotatable bowl, the rotatable bowl defining an inner surface substantially matching the first outer perimeter.

[0063] The conveyor screw according to the first aspect is preferably mounted in a bowl of a decanter centrifuge.

[0064] The object of the present invention is in a third aspect achieved by a method of operating a decanter centrifuge according to the second aspect, wherein the method comprising: continuously introducing a flowable material to be separated into the bowl at a rate higher than 75m3 / h while rotating the bowl to apply a g-force of at least 3000 G at the bowl wall.

[0065] The decanter centrifuge according to the second aspect is preferably operated at a high g-force and flow rate to allow an efficient oil release from the feed.

[0066] The object of the present invention is in a fourth aspect achieved by a circular base for a decanter centrifuge, the base being configured to be accommodated at one longitudinal end of a rotatable bowl of the decanter centrifuge, the base defining an inner surface configured to face an inner space of the bowl, a radial direction extending outwardly from a centre point of the base and a longitudinal direction extending perpendicular to the radial direction, the base defining a first outlet passage extending through the base and a first outlet housing provided at the inner surface of the base and protruding away from the inner surface in the longitudinal direction, the first outlet housing having a first outlet opening for receiving a light phase from the inner space, the first outlet housing communicating with the first outlet passage for passing the light phase from the first outlet housing to the first outlet passage, the first outlet opening comprising a first weir edge defining in normal use a level of a surface of the light phase in the inner space, wherein the first outlet housing is rotatable around a first adjustment axis.

[0067] The circular base is used for closing off the decanter centrifuge at the large end hub and provide a bearing surface for the conveyor screw of the decanter centrifuge. The bowl has one or more light phase outlet provided in the circular base at the longitudinal end of the bowl. The heavy phase outlet is located at the opposite longitudinal end of the bowl. The feed in the present case is oil containing plant- or animal items, such as fish oil extraction, oil from food waste and vegetable oil extraction and in particular corn oil extraction from corn seeds / whole stillage. The light phase in the present case is a substantially clean fat / oil in liquid phase separated from the feed, whereas the heavy phase is a residue of the feed being a mixture of other liquids and solids, mainly water and solids.

[0068] By allowing the outlet housing to protrude into the inner space of the bowl, the oil can be discharged at a distance from the base of the bowl. In that way the feed inlet can be located adjacent the base without interfering with the discharge.

[0069] By allowing the outlet housing to be rotatable around the first adjustment axis, the position of the weir edge, and thereby the level of the light phase, can be adjusted by rotating the outlet housing about the adjustment axis. Hereby is obtained that the level of the light phase in the bowl may be adjusted by simply rotating the outlet housing around the adjustment axis, as such rotation will entail an adjustment of the radial distance of the weir edge from the axis of rotation. The weir edge is defined as the point where no information can be transmitted through the discharged medium back into the separation volume inside the decanter. “Information” is anything that can affect the light phase level.

[0070] It should be understood that the centre point means the point on the base corresponding to the axis of rotation of the bowl when is use, the longitudinal direction being parallel to the axis of rotation and the radial direction being perpendicular to the longitudinal direction. The expression “level" refers to a distance in the radial direction from the centre point. In use the bowl rotates causing the feed inside the bowl to separate in a heavy phase and light liquid phase having a surface at a level, which is slightly above the level of the weir edge thereby providing a pressure head driving the light phase out of the bowl through the weir.

[0071] The outlet housing is set in a position relative to the adjustment axis so that the weir edge is positioned further from the axis of rotation than an opposite edge of the outlet opening, and the weir edge can be either the trailing or the leading edge of the outlet opening relative to the rotational movement of the bowl.

[0072] According to a further embodiment of the fourth aspect, the outlet housing comprises a first side wall offset from the first adjustment axis, the first outlet opening being present in the first side wall. Hereby is obtained that the level of the light phase in the bowl may be adjusted by simply rotating the outlet housing around the adjustment axis, as such rotation will entail an adjustment of the radial distance of the weir edge from the axis of rotation.

[0073] According to a further embodiment of the fourth aspect, the first outlet housing being at least partially cylindrical having a cylinder axis coaxial with the first adjustment axis. This provides for a simple construction and accordingly cost-efficient production.

[0074] According to a further embodiment of the fourth aspect, the first weir edge is extending in parallel with the first adjustment axis. In this way the weir edge will be parallel to the light phase surface during use for a well-defined level of the light phase in the bowl.

[0075] According to a further embodiment of fourth first aspect, the first outlet housing is cylindroconical having the outlet opening in a conical part. By having the outflow in a conical part, the outflow may be smoother and recirculation inside the outlet housing may be avoided.

[0076] According to a further embodiment of the fourth aspect, the first outlet opening is extending over an angle of 30° to 75°, preferably 45° to 60°, around the first adjustment axis. In this way the outlet opening and especially its angular range of extension around the adjustment axis can be sufficiently large that the outlet opening does not run full during normal operation, but an air-vent can be left between the surface of the out-flowing light phase and the edge opposite the weir edge.

[0077] According to a further embodiment of the fourth aspect, the first outlet housing has an axial length in the direction of the first adjustment axis, and that the first outlet opening is extending an axial length in the direction of the first adjustment axis shorter than the axial length of the first outlet housing.

[0078] According to a further embodiment of the fourth aspect, the first adjustment axis is parallel to the longitudinal direction. In this way the position of the weir edge, and thereby the level of the light phase, can be adjusted by rotating the outlet housing about the adjustment axis.

[0079] According to a further embodiment of the fourth aspect, the base further comprising a bearing surface for a conveyor screw, the bearing surface being located at the inner surface of the base. The base preferably has the additional purpose of accommodating the bearing surface for the conveyor screw. According to a further embodiment of the fourth aspect, the base further comprising a feed inlet for introducing a flowable material into the bowl of the decanter centrifuge, the feed inlet being located at the inwardly oriented surface of the base. The base preferably has the additional purpose of accommodating the feed inlet. The heavy phase of the feed will thereby have a longer travel time through the bowl to reach the heavy phase outlet opposite the base. In this way the solids will have more time to release oil.

[0080] According to a further embodiment of the fourth aspect, the feed inlet, the bearing surface and the outlet housing are located on a cylindrical part at the inner surface of the base, the cylindrical part protruding in the longitudinal direction. There is a tendency for the conveyor screw to deflect and bend during use, in particular when running at high rotational velocities which are near the eigenfrequency of the conveyor. This problem increases for longer conveyor screw, where the distance between the conveyor bearings is long. By having the bearing surface protruding into the bowl, the distance between the conveyor bearings can be reduced and the eigenfrequency will be higher.

[0081] According to a further embodiment of the fourth aspect, the first weir edge extends further away from the inner surface than the feed inlet. In this way the feed can be introduced as close as possible to the base without interfering with the light phase outlet.

[0082] According to a further embodiment of the fourth aspect, the base defining a second outlet passage extending through the base, and a second outlet housing provided at the inner surface, the second outlet housing communicating with the second outlet passage to pass a part of the light phase from the second outlet housing to the second outlet passage, the second outlet housing having a second outlet opening for receiving a part of the light phase from the inner space together with the first outlet opening, the second outlet opening comprising a second weir edge defining in normal use the level of the surface of the light phase in the bowl together with the first weir edge, wherein the second outlet housing is rotatable around a second adjustment axis. To better distribute the outflow from the bowl more than one outlet housing preferably can be used, such as two outlet housings. Even three or more outlet housing can be used to distribute the outflow even better. The weir edges should preferably be set at the same level, i.e. angular position and have the same angular distance in between themselves for them to distribute the outflow optimally between themselves. The outlet housings are preferably identical having the same features as described above. The object of the present invention is in a fifth aspect achieved by decanter centrifuge comprising bowl rotating in use in a direction of rotation around an axis of rotation, the bowl comprising a base according to any of the preceding embodiments of the fourth aspect at one end of the bowl in the axis of rotation and a heavy phase outlet at an opposite end of the bowl in the axis of rotation, the longitudinal direction of the base coinciding with the axis of rotation.

[0083] The decanter centrifuge according to the fifth aspect can preferably be used together with the base according to the fourth aspect. The heavy phase outlet is located at an opposite end of the bowl relative to the light phase outlet and the feed inlet.

[0084] The object of the present invention is in a sixth aspect achieved by method of operating a decanter centrifuge according to the fifth aspect, wherein the method comprising: rotating the outlet housing around the first adjustment axis, continuously introducing a flowable material into the bowl while rotating the bowl about the axis of rotation, the flowable material including light phase and a heavy phase, and allowing the light phase in the bowl to flow out of the bowl via the outlet opening.

[0085] The method according to the sixth aspect can preferably be used together with the decanter centrifuge according to the fifth aspect.

[0086] The object of the present invention is according to a seventh aspect achieved by a conveyor screw for a decanter centrifuge, the conveyor screw comprising a central body extending in a longitudinal direction, the central body comprising a first bearing surface at a first end of the central body and a second bearing surface at a second end of the central body, the second end being opposite the first end, the central body further defining a cylindrical portion adjacent the first bearing surface and a conical portion adjacent the second bearing surface, the conveyor screw further comprising a screw thread being attached to the central body, the screw thread extending in the longitudinal direction and defining an outer perimeter extending circumferentially about the cylindrical portion, the central body being free from any fluid openings between the first bearing surface and the second bearing surface. The conveyor screw is used in a bowl of a decanter centrifuge to convey a slurry being a mixture of the solids and the water towards the heavy phase outlet. It rotates at a differential speed relative to the bowl for the thread to impose a conveying action on the slurry. The heavy phase outlet is located at a conical portion of the bowl. The bearing surfaces of the conveyor screw are located at opposite ends of the central body. There is typically a drive and a gearbox at one of the bearings for rotating the conveyor screw. During operation, the drive applies a torque onto the central body causing the conveyor screw to rotate.

[0087] It has been noted that the typical conveyor screws used in standard decanter centrifuges accommodates a feed passage along the axis of the central body and at least one fluid opening along the axial direction for introducing the flowable feed material to be separated into the decanter centrifuge. However, this imposes structural limitations to the conveyor screw and decreases the rigidity of the conveyor screw as the fluid opening constitutes a void which limits the stiffness of the conveyor screw. The fluid opening is typically located near the middle of the central body along the axial direction which further decreases the bending rigidity of the overall structure. Further, the feed passage inside the conveyor screw limits the use of reinforcing structures inside the conveyor screw for increasing the bending rigidity.

[0088] In addition to the length of the conveyor screw, the stiffness of the conveyor screw also depends on the diameter of the central body. An increased diameter of the central body will increase the stiffness of the conveyor screw. Consequently, the length of the central body can be increased if the diameter of the central body increases. However, an increased diameter of the central body will reduce the available process volume between the conveyor hub and the bowl wall and the retention time of the process media will be reduced and the oil extraction will be compromised.

[0089] The presence of openings in the central body lowers the stiffness of the conveyor screw which lowers the natural frequency, also known as the eigenfrequency, of the conveyor screw. Further, making the central body longer will lower the natural frequency of the conveyor screw. Operating a long conveyor screw at high rotational speeds near the natural frequency of the conveyor screw may cause harmful vibrations that may cause the conveyor screw to fail. This also limits the length of the conveyor screw when operating at high speeds. However, keeping the central body of decanter centrifuge free from openings between the first bearing surface and the second bearing surface will increase the stiffness and structural stability of the conveyor screw compared to having fluid openings in the central body. This allows the conveyor screw to be longer. The fluid inlet is then preferably moved to the large end hub of the decanter centrifuge.

[0090] According to a further embodiment of the seventh aspect, the central body being free from any openings between the first bearing surface and a second bearing surface.

[0091] Preferably, there are no openings at all between the first bearing surface and a second bearing surface as any opening will constitute a constitutes a void which limits the stiffness of the conveyor screw.

[0092] According to a further embodiment of the seventh aspect, the conveyor screw comprises a cage structure extending from the central body at the first bearing surface in a direction away from the second bearing surface, the screw thread being at least partially attached to the cage structure.

[0093] In this way the bearing surface can be moved inside the bowl while allowing the first screw to extend behind the bearing.

[0094] According to a further embodiment of the seventh aspect, the cage structure part comprises an inner ring attached to the central body, and outer ring and a plurality of ribs interconnecting the inner ring and the outer ring.

[0095] In this embodiment of the cage structure the screw thread can be attached onto the ribs while the inner and outer ring keeps the structural stability of the cage structure.

[0096] According to a further embodiment of the seventh aspect, the central body defines a cylinder at the cylindrical portion and a truncated cone at the conical portion.

[0097] The cylinder and the truncated cone extend along the longitudinal direction. The screw thread follows the outline of the central body.

[0098] According to a further embodiment of the seventh aspect, the outer perimeter of the screw thread defines a diameter and the screw thread defines a length in the longitudinal direction, the ratio between the diameter and the length exceeding 3.9, preferably exceeding 4.2, more preferably exceeding 4.5, most preferably exceeding 4.9.

[0099] As the stiffness of the conveyor screw increases with the diameter of the central body while decreasing with the length of the central body, a ratio between the diameter and the length of the central part can be established. For simplicity, the ratio is established between the outer perimeter of the screw thread instead of the diameter of the central body. Typical limits for maintaining sufficient stiffness for decanter centrifuges having a fluid opening in the central body is about 4. However, a higher ratio exceeding 4.2 is possible provided no fluid opening is provided in the central body. Such as a ratio exceeding 4.5 or 4.9.

[0100] According to a further embodiment of the seventh aspect, the diameter is exceeding 640mm, preferably exceeding 670mm, more preferably exceeding 700mm, most preferably exceeding 715mm.

[0101] According to a further embodiment of the seventh aspect, the central body defines a hollow interior which is at least partially reinforced by a reinforcing material extending at least half the distance between the first bearing surface and the second bearing surface, the reinforcing material preferably being fibre reinforced epoxy.

[0102] A hollow and fibre reinforced central body will allow the conveyor screw to be lighter and longer while maintaining the stiffness and structural stability of the conveyor screw.

[0103] According to a further embodiment of the seventh aspect, the screw thread comprising: a first flight being attached to the central body and extending in the longitudinal direction, the first flight defining a first outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the first outer perimeter defining a first diameter, the first flight defining a first pitch angle at the cylindrical portion of the conveyor screw, the first pitch angle being less than 20°, and, a second flight being attached to the central body, extending in the longitudinal direction, having the same winding direction as the first flight and being at least partially intertwined with the first flight, the second flight defining a second outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the second outer perimeter defining a second diameter, the second flight defining a second pitch angle at the cylindrical portion of the conveyor screw, the second pitch angle being greater than 30°, and the second diameter being smaller than the first diameter. The pitch angle is here calculated by the expression: Pitch angle = ATAN(Pitch / (7t*(Bowl diameter)))

[0104] It has been surprisingly found out that the combination of the longitudinal conveying of the slurry by the first flight and the spreading-out effect on the slurry achieved by the second flight increases the amount of oil released from the solids. As the oil has a lower density than the slurry, the oil will accumulate near the central body and can be collected at the light phase outlet.

[0105] In the present context, a flight is understood to be a plate welded radially to the central body of the conveyor screw to provide the conveying surface of the conveyor screw.

[0106] According to a further embodiment of the seventh aspect, the conveyor screw further defining a third flight extending parallel with the second flight, the second flight extending to the second outer perimeter whereas the third flight extending to a third outer perimeter, the second flight and the third flight defining an oil channel between themselves, the oil channel defining a width between the second flight and the third flight being less than the distance between the central body and the second outer perimeter.

[0107] T o collect the oil more easily, the second flight and the third flight are formed as two parallel flights as described above. The second flight will spread out the solids and the third flight will collect the oil. The oil will flow towards the light phase outlet in the channel between the second flight and the third flights.

[0108] According to a further embodiment of the seventh aspect, the third outer perimeter defining a third diameter, the third diameter being smaller than the second diameter.

[0109] In this way it is ensured that the oil is collected in the oil channel but not the water as the oil is lighter and will flow closer to the central body and the water will flow between the oil and the slurry due to the centrifugal forces.

[0110] According to a further embodiment of the seventh aspect, the second flight passes through gaps in the first flight.

[0111] In this way the first flight and the second flight can be intertwined with minimal interruption of the first flight. This will allow the conveying of the solids to be more efficient. According to a further embodiment of the seventh aspect, the conveyor screw comprises a fourth flight being substantially identical to the second flight and extending in parallel with the second flight, and a fifth flight corresponding to the third flight and running parallel with the fourth flight establishing a further oil channel together with the fourth flight, the fourth flight and the fifth flight being phase shifted relative to the second flight and the third flight, respectively, preferably by 180°

[0112] In this way the spread-out effect is enhanced as the solids will be spread out twice for every turn of the conveyor screw. A fifth flight corresponding to the third flight and running parallel with the fourth flight establishing a further oil channel.

[0113] The object of the present invention is according to an eighth aspect achieved by decanter centrifuge comprising a rotatable bowl and a conveyor screw according to any of the preceding embodiments accommodated inside the rotatable bowl, the rotatable bowl defining an inner surface substantially matching the outer perimeter of the screw thread.

[0114] The conveyor screw according to the eighth aspect is preferably mounted in a bowl of a decanter centrifuge.

[0115] The object of the present invention is according to a ninth aspect achieved by method of operating a decanter centrifuge according to the eighth aspect, wherein the method comprising: continuously introducing a flowable material to be separated into the bowl at a rate higher than 75m3 / h while rotating the bowl to apply a g-force of at least 3000 G at the bowl wall.

[0116] The decanter centrifuge according to the ninth aspect is preferably operated at a high g- force and flow rate to allow an efficient oil release from the feed.

[0117] The object of the present invention is in a tenth aspect achieved by a circular base for a decanter centrifuge, the base being configured to be accommodated at one longitudinal end of a rotatable bowl of the decanter centrifuge, the base defining an inner surface configured to face an interior of the bowl, a radial direction extending outwardly from a centre point of the base and a longitudinal direction extending perpendicular to the radial direction, the base comprising: a bearing surface for a conveyor screw, the bearing surface being centrally located at the inner surface of the base and extending about the centre point of the base, a feed inlet for introducing a flowable material into the bowl of the decanter centrifuge, the flowable material comprising a light phase and a heavy phase, and a first light phase outlet for receiving the light phase from the bowl of the decanter centrifuge, the first light phase outlet comprising a first weir edge defining in normal use a level of the light phase in the bowl.

[0118] The circular base is used for closing off the decanter centrifuge at the large end hub and provide a bearing surface for the conveyor screw of the decanter centrifuge. The bowl has one or more light phase outlet provided in the circular base at the longitudinal end of the bowl. The heavy phase outlet is located at the opposite longitudinal end of the bowl. The feed in the present case is oil containing plant- or animal items, such as fish oil extraction, oil from food waste and vegetable oil extraction and in particular corn oil extraction from corn seeds / whole stillage. The light phase in the present case is a substantially clean fat / oil in liquid phase separated from the feed, whereas the heavy phase is a residue of the feed being a mixture of other liquids and solids, mainly water and solids.

[0119] In conventional decanters, the feed inlet located in the core of the conveyor screw for introducing the feed into the bowl at a location substantially in the middle between the light phase outlet and the heavy phase outlet. However, it has surprisingly been found out that by introducing the flowable material close to the large end hub, the solids will have a longer retention time in the bowl and the release of oil / fat from the solid material will be larger compared to having the feed inlet between the light phase outlet and the heavy phase outlet.

[0120] It should be understood that the centre point means the point on the base corresponding to the axis of rotation of the bowl when is use, the longitudinal direction being parallel to the axis of rotation and the radial direction being perpendicular to the longitudinal direction. The expression “level" refers to a distance in the radial direction from the centre point. In use the bowl rotates causing the feed inside the bowl to separate in a heavy phase and light liquid phase having a surface at a level, which is slightly above the level of the weir edge thereby providing a pressure head driving the light phase out of the bowl through the weir. The weir edge is defined as the point where no information can be transmitted through the discharged medium back into the separation volume inside the decanter. “Information” is anything that can affect the light phase level.

[0121] According to a further embodiment of the tenth aspect, the light phase outlet is provided in an outlet housing, the outlet housing being cylindrical and protruding in the longitudinal direction from the inner surface.

[0122] The outlet can be provided in a specific outlet housing for being able to optimally position the weir edge in the bowl.

[0123] According to a further embodiment of the tenth aspect, the outlet housing defining an adjustment axis extending parallel to the longitudinal direction, the outlet housing being rotatable around the adjustment axis.

[0124] In this way the position of the weir edge, and thereby the level of the light phase, can be adjusted by rotating the outlet housing about the adjustment axis.

[0125] According to a further embodiment of the tenth aspect, the outlet housing being spaced apart from centre point of the base.

[0126] The light phase outlet should be located at a radial distance from the axis of rotation to be able to separate the light phase from the heavy phase and define a level of the light phase in the bowl. In use the heavy phase will accumulate near the bowl wall, whereas the light phase will accumulate at a radial distance from the axis of rotation.

[0127] According to a further embodiment of the tenth aspect, the outlet housing being at least partially cylindrical and extending in the direction of the adjustment axis, the weir edge being parallel to the adjustment axis .

[0128] In this way the weir edge will be parallel to the light phase surface during use for a well- defined level of the light phase in the bowl.

[0129] According to a further embodiment of the tenth aspect, the base comprising one or more further outlet housings for receiving the light phase from the inner space together with the first outlet housing, the one or more further outlet housings being substantially identical to the first outlet housing. To better distribute the outflow from the bowl more than one outlet housing preferably can be used, such as two or three outlet housings.

[0130] According to a further embodiment of the tenth aspect, the feed inlet and the bearing surface being located on a cylindrical trunnion protruding in the longitudinal direction from the inner surface of the base.

[0131] There is a tendency for the conveyor screw to deflect and bend during use. This is due to vibrations induced into the conveyor screw by the rotation of the conveyor screw and the bowl. The vibrations induced by the rotation of the conveyor has a frequency corresponding to the rotation of the conveyor screw, i.e. a higher rotational speed of the conveyor screw will induce a higher frequency vibration into the conveyor screw. To avoid resonance effects in the conveyor screw, it must be ensured that the frequency of the vibrations due to the rotation of the conveyor screw will not be at or near the eigenfrequency of the conveyor screw. Resonance effects in the conveyor screw may cause excessive bending stress on the conveyor screw. This problem increases for longer conveyor screws, where the distance between the conveyor bearings is longer, since the bending rigidity degreases when the length of the conveyor screw increases. As the bending rigidity decreases, the eigenfrequency of the conveyor screw decreases, thus the eigenfrequency decreases with increasing length of the conveyor screw. By having the bearing surface protruding into the bowl, the distance between the conveyor bearings can be reduced and the bending stress on the conveyor bearing due to the length of the decanter bowl will be reduced.

[0132] According to a further embodiment of the tenth aspect, the outlet housing is located on the cylindrical trunnion.

[0133] In this way, the outlet housing can be positioned to extend from the cylindrical trunnion without interfering with the flow around the cylindrical trunnion.

[0134] According to a further embodiment of the tenth aspect, the weir edge of the light phase outlet extends further away from the inner surface in the longitudinal direction than the feed inlet. To allow the feed inlet to be located as close as possible to the inner surface, the light phase outlet can extend further away from the inner surface in the longitudinal direction than the feed inlet. This will allow the feed to enter the bowl close to the inner surface and thereby increase the retention time of the heavy phase in the bowl.

[0135] According to a further embodiment of the tenth aspect, the feed inlet defines an inlet opening facing in the radial direction, the feed inlet further comprising deflectors for causing the feed to flow substantially in a tangential direction relative to the opening.

[0136] In this way, the feed will have a rotational momentum when entering the bowl, allowing the heavy phase to settle more quickly at the outer wall of the bowl.

[0137] According to a further embodiment of the tenth aspect, the bearing surface is located further away from the inner surface in the longitudinal direction than the feed inlet.

[0138] To allow the feed inlet to be located as close as possible to the inner surface, the bearing surface can be located further away from the inner surface in the longitudinal direction than the feed inlet. This will allow the feed to enter the bowl close to the inner surface and thereby increase the retention time of the heavy phase in the bowl.

[0139] The object of the present invention is in an eleventh aspect achieved by a decanter centrifuge comprising bowl rotating in use in a direction of rotation around an axis of rotation, the bowl comprising a base according to any of the preceding embodiments of the first aspect at one end of the bowl in the axis of rotation and a heavy phase outlet at an opposite end of the bowl in the axis of rotation, the longitudinal direction of the base coinciding with the axis of rotation.

[0140] The decanter centrifuge according to the eleventh aspect can preferably be used together with the base according to the tenth aspect. The heavy phase outlet is located at an opposite end of the bowl relative to the light phase outlet and the feed inlet.

[0141] The object of the present invention is in a twelfth aspect achieved by a method of operating a decanter centrifuge according to the second aspect, wherein the method comprising continuously introducing a flowable material into the bowl via the feed inlet while rotating the bowl about the axis of rotation thereby separating the flowable material into a light phase and a heavy phase and allowing the light phase to flow out of the bowl via the first light phase outlet and the heavy phase to flow out via the heavy phase outlet.

[0142] The method according to the twelfth aspect can preferably be used together with the decanter centrifuge according to the eleventh aspect.

[0143] According to a further embodiment of the twelfth aspect, the flowable material is introduced at a rate higher than 75m3 / h and the bowl is rotating to apply a g-force of at least 3000 G at the bowl wall.

[0144] A high rotational speed can be applied causing a high g-force to act on the flowable material. This will separate as much oil / fat from the solids of the heavy phase as possible and / or allow a high flow rate,

[0145] According to a further embodiment of the twelfth aspect, the light phase is an oil and the heavy phase is a mixture of water and solids.

[0146] The oil / fat is discharged at the light phase outlet whereas other liquids, i.e. water, is discharged together with the solids at the heavy phase outlet.

[0147] Brief description of the drawings

[0148] FIG. 1A is a side view of a first embodiment of a decanter centrifuge according to the present invention.

[0149] FIG. 1 B is a side view of a first embodiment of a decanter centrifuge according to the present invention.

[0150] FIG. 10 is a side view of a second embodiment of a decanter centrifuge according to the present invention.

[0151] FIG. 1 D is a side view of a second embodiment of a decanter centrifuge according to the present invention.

[0152] FIG. 2A is a perspective view of a circular base according to the first embodiment of the present invention.

[0153] FIG. 2B is a perspective view of the circular base according to the first embodiment of the present invention showing the discharge of the light phase.

[0154] FIG. 2C is a perspective view of the circular base according to the first embodiment of the present invention from the rear side showing the discharge. FIG. 3A is a perspective view of the circular base according to the first embodiment of the present invention showing the inflow of the flowable material.

[0155] FIG. 3B is a perspective cutaway view of the circular base according to the first embodiment of the present invention showing the trunnion interior.

[0156] FIG. 30 is a perspective view of the circular base according to the first embodiment of the present invention from the rear side showing the inflow.

[0157] FIG. 4A is a perspective view of the conveyor screw according to the first embodiment of the present invention.

[0158] FIG. 4B is a perspective view of the conveyor screw according to the first embodiment of the present invention.

[0159] FIG. 40 is a side view of the conveyor screw according to the second embodiment of the present invention.

[0160] Detailed of the

[0161] Fig. 1A is a side view of a decanter centrifuge 10 according to a first embodiment of the present invention. The decanter centrifuge 10 comprises a rotatable bowl 12 and a conveyor screw 14. The bowl 12 has a cylindrical part 12a and a conical part 12b. The conveyor screw 14 has a corresponding cylindrical part 14a and conical part 14b. The bowl 12 is rotated by a drive motor 16a and the conveyor screw 14 is rotated by a back drive motor 16b. The back drive motor 16b is typically connected via a gearbox (not shown). An inlet 18 is provided for introducing the feed into the decanter centrifuge 10. The bowl 12 comprises a heavy phase outlet 20 at a small end hub 22 at the conical part 12b of the of the bowl 12 and a light phase outlet 24 at a base 26 forming a large end hub at the cylindrical part 12a of the bowl 12.

[0162] The conveyor screw 14 comprises a central body 28 extending in a longitudinal direction between a first bearing surface 30a at the cylindrical part 14a and a second bearing surface 30b at the conical part 14b. The conveyor screw 14 comprises a first flight 32 being attached to the central body 28. The first flight 32 extends over both the cylindrical part 14a and the conical part 14b of the conveyor screw 14. The first flight 32 extending to an inner wall 12c of the bowl 12 and defines a pitch angle being less than 20°. The present embodiment further comprises a second flight 34 not extending to the inner wall 12c of the bowl 12 and defining a pitch angle being greater than 30°. The pitch angle is here calculated by the expression: Pitch angle = ATAN(Pitch / (7t*(Bowl diameter))) The second flight 34 does not extend to the inner wall 12c and extends over only the cylindrical part 14a of the conveyor screw 14. The base 26 comprising a trunnion 40 which encompasses feed inlets 42a 42b for the feed and the bearing surface 30a for the conveyor screw 14. The feed inlets 42a 42b communicating with the inlet 18. The trunnion 40 also comprises outlet housings 44a 44b extending into the bowl 12 for transporting the light phase from the bowl 12 to the light phase outlet 24.

[0163] Fig. 1 B is a side view of a decanter centrifuge 10 according to a first embodiment of the present invention showing the inlet and outlet flows. The feed is introduced via the inlet 18 as shown by the arrow. The feed can be a crushed oil-containing plant- or animal item such as crushed corn seeds. The feed enters the bowl 12 via feed inlets 42a 42b. The feed is separated into a slurry fraction and an oil fraction by centrifugal forces from the rotation of the bowl 12. The slurry fraction is a mixture of solids and water. The slurry fraction forms a heavy phase and are conveyed by the conveyor screw 14 and is discharged at the heavy phase outlet 20 as shown by the arrow. The oil fraction forms a light phase which is discharged via the outlet housings 44 and light phase outlet 24 as shown by the arrow. The slurry fraction being heavier than the oil fraction and will thus flow outwards and accumulate at the inner wall 12c of the bowl 12, the oil fraction being lighter than the slurry fraction and will thus flow inwards and accumulates near the central body 28. The first flight 32 collects the slurry fraction and conveys it towards the heavy phase outlet 20 of the bowl 12, whereas the second flight 34 being able to scrape and spread out the slurry fraction.

[0164] Fig. 1C is a side view of a decanter centrifuge 10’ according to a second embodiment of the present invention. The decanter centrifuge 10’ comprises a rotatable bowl 12 and a conveyor screw 14’. The bowl 12 has a cylindrical part 12a and a conical part 12b. The conveyor screw 14’ has a corresponding cylindrical part 14a’ and conical part 14b’. The bowl 12 is rotated by a drive motor 16a and the conveyor screw 14’ is rotated by a back drive motor 16b. The back drive motor 16b is typically connected via a gearbox (not shown). An inlet 18 is provided for introducing the feed into the decanter centrifuge 10. The bowl 12 comprises a heavy phase outlet 20 at a small end hub 22 at the conical part 12b of the of the bowl 12 and a light phase outlet 24 at a base 26’ forming a large end hub at the cylindrical part 12a of the bowl 12.

[0165] The conveyor screw 14’ comprises a central body 28’ extending in a longitudinal direction between a first bearing surface 30a’ at the cylindrical part 14a’ and a second bearing surface 30b’ at the conical part 14b’. The conveyor screw 14’ comprises a first flight 32’ being attached to the central body 28’. The first flight 32’ extends over both the cylindrical part 14a’ and the conical part 14b’ of the conveyor screw 14’. The first flight 32’ extending to an inner wall 12c of the bowl 12 and defines a pitch angle being less than 20°. The present embodiment further comprises a second flight 34 not extending to the inner wall 12c of the bowl 12 and defining a pitch angle being greater than 30°. The pitch angle is here calculated by the expression: Pitch angle = ATAN(Pitch / (7t*(Bowl diameter))) The second flight 34 does not extend to the inner wall 12c and extends over only the cylindrical part 14a’ of the conveyor screw 14’. The base 26’ comprising the bearing surface 30a’ for the conveyor screw 14’. The feed inlet 42 communicating with the inlet 18. The base 26’ also comprises an outlet 48’ for transporting the light phase from the bowl 12 to the light phase outlet 24.

[0166] Fig. 1 D is a side view of a decanter centrifuge 10’ according to the second embodiment of the present invention showing the inlet and outlet flows. The feed is introduced via the inlet 18 as shown by the arrow. The feed can be a crushed oil-containing plant- or animal item such as crushed corn seeds. The feed enters the bowl 12 via the feed inlet 42. The feed is separated into a slurry fraction and an oil fraction by centrifugal forces from the rotation of the bowl 12. The slurry fraction is a mixture of solids and water. The slurry fraction forms a heavy phase and are conveyed by the conveyor screw 14’ and is discharged at the heavy phase outlet 20 as shown by the arrow. The oil fraction forms a light phase which is discharged via the outlet 48’ and light phase outlet 24 as shown by the arrow. The slurry fraction being heavier than the oil fraction and will thus flow outwards and accumulate at the inner wall 12c of the bowl 12, the oil fraction being lighter than the slurry fraction and will thus flow inwards and accumulates near the central body 28’. The first flight 32’ collects the slurry fraction and conveys it towards the heavy phase outlet 20 of the bowl 12, whereas the second flight 34 being able to scrape and spread out the slurry fraction.

[0167] FIG. 2A is a perspective view of a circular base 26 according to the first embodiment of present invention. The base 26 comprises an inner surface 36a facing the interior of the bowl (not shown here) and an outer surface (not visible here) being opposite the inner surface 36a and facing the outside of the bowl. The base 26 comprising the trunnion 40 which constitutes a cylindrical element positioned about a centre point C of the base 26 protruding in a longitudinal direction L from the inner surface 36a of the base 26 into the bowl. The trunnion 40 comprising a bearing surface 30a for the conveyor screw and feed inlets 42a 42b for introducing feed (not shown) into the bowl. The bearing surface 30a being located further away in the longitudinal direction L from the inner surface 36 than the feed inlets 42a 42b and encircles the centre point C. The bearing surface 30a being spaced apart from the centre point C in a radial direction r. The radial direction r being perpendicular to the longitudinal direction L. The feed inlets 42a 42b is located more spaced apart in radial direction r from the centre point C than the bearing surface 30a. In the present embodiment, two feed inlets 42a and 42b are provided, whereby the feed inlet 42a is the main feed inlet and the feed inlet 42b is an overflow inlet used during temporary high inflows.

[0168] The trunnion 40 further comprising the outlet housings 44a 44b. The outlet housings 44a 44b being at least partially cylindrical and extending from the base 26 through the trunnion 40 in the longitudinal direction L into the bowl. The outlet housings 44a 44b are located spaced apart in radial direction r from the centre point C, typically further spaced apart from the centre point C than the bearing surface 30a. In the present embodiment, the screw flight 34 ends at the outlet housing 44. Further, in the present embodiment two outlet housings 44a and 44b are provided spaced apart by 180 degrees about the centre point C.

[0169] The light phase being oil / fat. During use, the light phase flows inwardly due to centrifugal forces and enters one of the outlet housings 44a 44b as shown by the arrows. The light phase enters the outlet housing 44b via a light phase opening 46b. (Only the light phase opening 46b of the outlet housing 44b is visible in the present view, however, the outlet housing 44a has an identically configured light phase opening). The light phase opening 46b defines a weir edge extending in parallel with the first adjustment axis of the outlet housing 44b and defining in normal use a level of the light phase within the bowl. In the present embodiment, the outlet housing 44b has a cylindroconical shape having the light phase opening 46b in a conically shaped part of the outlet housing 44b for a smoother flow.

[0170] FIG. 2B is a perspective view of the base according to the first embodiment of present invention showing the discharge of the light phase. The light phase enters the outlet housings 44a 44b at a radial distance from the centre point C. The radial distance of the opening 46b (and thereby the weir) from the centre point C can be adjusted by rotating the outlet housing 44a 44b about an adjustment axis A. In this way the level of the light phase within the bowl can be adjusted. In use the bowl (not shown) rotates causing the feed (not shown) inside the bowl to separate in a heavy phase (not shown) and light liquid phase having a surface at a level, which is slightly above the level of the weir edge thereby providing a pressure head driving the light phase out of the bowl through the opening 46b and the outlet housing 44b.

[0171] FIG. 20 is a perspective view of the base according to the first embodiment of present invention from the rear side showing the outer surface 36b and the discharge of the light phase as shown by the arrows. The outlet housing 44a extends to the outer surface 36b of the base 26 and defines an outlet 48 at the outer surface 36b of the base 26 for ejecting the light phase. The outlet housings 44a 44b can be adjusted about the adjustment axis A from the outside.

[0172] FIG. 3A is a perspective view of the base 26 according to the first embodiment of present invention showing the inflow of the flowable material. The flowable material is introduced centrally in the longitudinal direction and flows out in the radial direction into the bowl (not shown) via the feed inlets 42a 42b.

[0173] FIG. 3B is a perspective cutaway view of the base 26 according to the first embodiment of present invention showing the interior of the trunnion 40. As can be seen the flowable material is deflected by deflectors 50 from flowing in the longitudinal direction to a direction substantially corresponding to the tangential direction of the rotation of the bowl (not shown). In this way, less time within the bowl is needed to accelerate the flowable material to the bowl rotation speed, and the separation can therefore be more efficient.

[0174] FIG. 30 is a perspective view of the base according to the first embodiment of present invention from the rear side showing the inlet 18. The inlet is centrally in the longitudinal direction.

[0175] Fig. 4A is a perspective view of the conveyor screw 14 according to the first embodiment of the present invention. The conveyor screw 14 comprises the first flight 32 and the second flight 34 being attached to the central body 28. The first flight 32 extends over both the cylindrical part 14a and the conical part 14b of the conveyor screw 14 and defines a pitch angle being less than 20° for being able to collect the solid fraction and convey it towards the heavy phase outlet of the bowl. The second flight 34 extends in the longitudinal direction along the cylindrical portion of the conveyor screw 14 only. The first flight 32 and the second flight 34 being at least partially intertwined.

[0176] Both the first flight 32 and the second flight 34 has the same winding direction, however, the second flight 34 defining a pitch angle being more than 30° for scraping and spreading out the slurry at the inner surface of the bowl. The second flight 34 extends to a smaller outer perimeter than the first flight 32 for the slurry to be spread out on the inner surface of the bowl. This will allow more oil to be released from the slurry.

[0177] The conveyor screw 14 is further provided with a baffle plate 60 between the cylindrical part 14a and the conical part 14b for preventing oil from flowing towards the heavy phase outlet of the bowl. The conveyor screw 14 is further provided with a third flight 52 extending to a smaller outer perimeter than the second flight 34. The purpose of the third flight 52 is to define an oil channel 54 between the second flight 34 and the third flight 52 to allow the oil to flow towards the light phase outlet of the bowl.

[0178] The first flight 32 comprises gaps 56 for allowing the second flight 34 and the third flight

[0179] 52 to pass through. The first flight 32 is slightly offset at the gaps 56 to scrape any slurry which would otherwise be missed due to the gaps 56. The conveyor screw 14 further comprises a cage structure 58 extending from the first bearing surface 30a away from the second bearing surface 30b for carrying the first screw 32 beyond the first bearing surface 30a.

[0180] The present conveyor screw 14 also includes an additional fourth flight 35 and fifth flight

[0181] 53 which essentially correspond to the second flight 34 and third flight 52, respectively, albeit being 180° phase shifted. In this way there will be an additional oil channel 55 and two spread-out effects on the slurry for each turn of the conveyor screw 14.

[0182] The present view also shows the base 26 being attached to the first bearing surface 30a during use. The base 28 comprises the feed inlet 42 42’ and the outlet housing 44.

[0183] Fig. 4B is a perspective view of the conveyor screw 14 according to the first embodiment of the present invention when the base 26 is connected to the first bearing surface 30a. The central body 28 being free from any fluid openings between the first bearing surface 30a and the second bearing surface 30b for increasing the structural stability and stiffness of the conveyor screw 14. FIG. 40 is a side view of the conveyor screw 14’ according to the second embodiment of the present invention. The conveyor screw 14’ comprises the first flight 32’ and the second flight 34 being attached to the central body 28’. The central body 28’ extends between the first bearing surface 30a’ and the second bearing surface 30b’. The feed inlet 42 is located adjacent the first bearing surface 30a’. The first flight 32’ extends over both the cylindrical part 14a’ and the conical part 14b’ of the conveyor screw 14’ and defines a pitch angle being less than 20° for being able to collect the solid fraction and convey it towards the heavy phase outlet of the bowl. The second flight 34 extends in the longitudinal direction along the cylindrical portion 14a’ of the conveyor screw 14’ only. The first flight 32’ and the second flight 34 being at least partially intertwined.

[0184] Both the first flight 32’ and the second flight 34 has the same winding direction, however, the second flight 34 defining a pitch angle being more than 30° for scraping and spreading out the slurry at the inner surface of the bowl. The second flight 34 extends to a smaller outer perimeter than the first flight 32’ for the slurry to be spread out on the inner surface of the bowl. This will allow more oil to be released from the slurry.

[0185] The conveyor screw 14’ is further provided with a baffle plate 60 between the cylindrical part 14a’ and the conical part 14b’ for preventing oil from flowing towards the heavy phase outlet of the bowl. The conveyor screw 14’ is further provided with a third flight 52 extending to a smaller outer perimeter than the second flight 34. The purpose of the third flight 52 is to define an oil channel 54 between the second flight 34 and the third flight 52 to allow the oil to flow towards the light phase outlet of the bowl. All of the first flight 32’, second flight 34 and third flight 52 are connected to the central body and extend to the bearing surface 30a.’

[0186] The first flight 32 comprises gaps 56 for allowing the second flight 34 and the third flight

[0187] 52 to pass through. The first flight 32 is slightly offset at the gaps 56 to scrape any slurry which would otherwise be missed due to the gaps 56.

[0188] The present conveyor screw 14’ also includes an additional fourth flight 35 and fifth flight

[0189] 53 which essentially correspond to the second flight 34 and third flight 52, respectively, albeit being 180° phase shifted. In this way there will be an additional oil channel 55 and two spread-out effects on the slurry for each turn of the conveyor screw 14’.

Claims

Claims1. A conveyor screw for a decanter centrifuge, the conveyor screw defining a cylindrical portion and a conical portion and comprising: a central body extending in a longitudinal direction, a first flight being attached to the central body and extending in the longitudinal direction, the first flight defining a first outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the first outer perimeter defining a first diameter, the first flight defining a first pitch angle at the cylindrical portion of the conveyor screw, the first pitch angle being less than 20°, and, a second flight being attached to the central body, extending in the longitudinal direction, having the same winding direction as the first flight and being at least partially intertwined with the first flight, the second flight defining a second outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the second outer perimeter defining a second diameter, the second flight defining a second pitch angle at the cylindrical portion of the conveyor screw, the second pitch angle being greater than 30°, and the second diameter being smaller than the first diameter.

2. The conveyor screw according to claim 1 , wherein the conveyor screw further defining a third flight extending parallel with the second flight, the second flight extending to the second outer perimeter whereas the third flight extending to a third outer perimeter, the second flight and the third flight defining an oil channel between themselves, preferably, the oil channel defining a width between the second flight and the third flight being less than three times the distance between the central body and the second outer perimeter, more preferably, the oil channel defining a width between the second flight and the third flight being less than twice the distance between the central body and the second outer perimeter, most preferably, the oil channel defining a width between the second flight and the third flight being less than the distance between the central body and the second outer perimeter.

3. The conveyor screw according to claim 2, wherein the third outer perimeter defining a third diameter, the third diameter being smaller than the second diameter.

4. The conveyor screw according any of the preceding claims, wherein the second flight passes through gaps in the first flight.

5. The conveyor screw according to any of the preceding claims, the conveyor screw comprises a fourth flight being substantially identical to the second flight and extending in parallel with the second flight, and a fifth flight corresponding to the third flight and running parallel with the fourth flight establishing a further oil channel together with the fourth flight, the fourth flight and the fifth flight being phase shifted relative to the second flight and the third flight, respectively, preferably by 180°.

6. The conveyor screw according to claim 1 , wherein the second pitch angle being at least twice the first pitch angle, preferably at least thrice the first pitch angle, more preferably at least four times the first pitch angle, such as the first pitch angle is between 1° and 20°, preferably between 8° and 15° and / or the second pitch angle is between 30° and 60°, preferably between 35° and 45°.

7. The conveyor screw according to any of the preceding claims, wherein the first flight extends about the cylindrical portion and the conical portion of the flight, whereas the second flight extends about the cylindrical portion only.

8. The conveyor screw according to any of the preceding claims, wherein the pitch angle of the first flight differs between the cylindrical portion and the conical portion.

9. The conveyor screw according to any of the preceding claims, further comprising a baffle plate extending between the cylindrical portion and the conical portion.

10. The conveyor screw according to any of the preceding claims, wherein the first flight defines a length in the longitudinal direction, the ratio between the first diameter and the length exceeding 3.9, preferably exceeding 4.2, more preferably exceeding 4.5, most preferably exceeding 4.9, and / or, the first diameter is exceeding 640mm, preferably exceeding 670mm, more preferably exceeding 700mm, most preferably exceeding 715mm.

11. The conveyor screw according to any of the preceding claims, wherein the central body is hollow and fibre reinforced along the complete cylindrical portion.

12. The conveyor screw according to any of the preceding claims, wherein the central body defines a first bearing surface and a second bearing surface, the central bodybeing free from any openings, such as fluid openings, between the first bearing surface and the second bearing surface,13. The conveyor screw according to claim 12, wherein the conveyor screw preferably comprises a cage structure extending from the central body at the first bearing surface in a direction away from the second bearing surfaces, the first screw being at least partially attached to the cage structure.

14. A decanter centrifuge comprising a rotatable bowl and a conveyor screw according to any of the preceding claims accommodated inside the rotatable bowl, the rotatable bowl defining an inner surface substantially matching the first outer perimeter.

15. A method of operating a decanter centrifuge according to claim 14, wherein the method comprising: continuously introducing a flowable material to be separated into the bowl at a rate higher than 75m3 / h while rotating the bowl to apply a g-force of at least 3000 G at the bowl wall.

16. A circular base for a decanter centrifuge, the base being configured to be accommodated at one longitudinal end of a rotatable bowl of the decanter centrifuge, the base defining an inner surface configured to face an inner space of the bowl, a radial direction extending outwardly from a centre point of the base and a longitudinal direction extending perpendicular to the radial direction, the base defining a first outlet passage extending through the base and a first outlet housing provided at the inner surface of the base and protruding away from the inner surface in the longitudinal direction, the first outlet housing having a first outlet opening for receiving a light phase from the inner space, the first outlet housing communicating with the first outlet passage for passing the light phase from the first outlet housing to the first outlet passage, the first outlet opening comprising a first weir edge defining in normal use a level of a surface of the light phase in the inner space, wherein the first outlet housing is rotatable around a first adjustment axis.

17. The circular base according to claim 16, wherein the outlet housing comprises a first side wall offset from the first adjustment axis, the first outlet opening being present in the first side wall.

18. The circular base according to any of the claims 16-17, wherein the first outlet housing being at least partially cylindrical having a cylinder axis coaxial with the first adjustment axis.

19. The circular base according to claim 18, wherein the first weir edge is extending in parallel with the first adjustment axis.

20. The circular base according to any of the claims 16-19, wherein the first outlet housing is cylindroconical having the outlet opening in a conical part.

21. The circular base according to any of the claims 16-20, wherein the first outlet opening is extending over an angle of 30° to 90°, preferably 45° to 75°, around the first adjustment axis.

22. The circular base according to any of the claims 16-21 , wherein the first outlet housing has an axial length in the direction of the first adjustment axis, and that the first outlet opening is extending an axial length in the direction of the first adjustment axis shorter than the axial length of the first outlet housing.

23. The circular base according to any of the claims 16-22, wherein the first adjustment axis is parallel to the longitudinal direction.

24. The circular base according to any of the claims 16-23, wherein the base further comprising a bearing surface for a conveyor screw, the bearing surface being located at the inner surface of the base.

25. The circular base according to any of the claims 16-24, wherein the base further comprising a feed inlet for introducing a flowable material into the bowl of the decanter centrifuge, the feed inlet being located at the inwardly oriented surface of the base.

26. The circular base according to claim 24 and 25, wherein the feed inlet, the bearing surface and the outlet housing are located on a cylindrical part at the inner surface of the base, the cylindrical part protruding in the longitudinal direction.

27. The circular base according to any of the claims 25-26, wherein the first weir edge extends further away from the inner surface than the feed inlet.

28. The circular base according to any of the claims 16-27, wherein the base defining a second outlet passage extending through the base, and a second outlet housing provided at the inner surface, the second outlet housing communicating with the second outlet passage to pass a part of the light phase from the second outlet housing to the second outlet passage, the second outlet housing having a second outlet opening for receiving a part of the light phase from the inner space together with the first outlet opening, the second outlet opening comprising a second weir edge defining in normal use the level of the surface of the light phase in the bowl together with the first weir edge, wherein the second outlet housing is rotatable around a second adjustment axis.

29. A decanter centrifuge comprising bowl rotating in use in a direction of rotation around an axis of rotation, the bowl comprising a base according to any of the claims 16- 28 at one end of the bowl in the axis of rotation and a heavy phase outlet at an opposite end of the bowl in the axis of rotation, the longitudinal direction of the base coinciding with the axis of rotation.

30. A method of operating a decanter centrifuge according to claim 29, wherein the method comprising: rotating the outlet housing around the first adjustment axis, continuously introducing a flowable material into the bowl while rotating the bowl about the axis of rotation, the flowable material including light phase and a heavy phase, and allowing the light phase in the bowl to flow out of the bowl via the outlet opening.

31. A conveyor screw for a decanter centrifuge, the conveyor screw comprising a central body extending in a longitudinal direction, the central body comprising a first bearing surface at a first end of the central body and a second bearing surface at a second end of the central body, the second end being opposite the first end, the central body further defining a cylindrical portion adjacent the first bearing surface and a conical portion adjacent the second bearing surface, the conveyor screw further comprising a screw thread being attached to the central body, the screw thread extending in the longitudinal direction and defining an outer perimeter extending circumferentially about the cylindrical portion, the central body being free from any fluid openings between the first bearing surface and the second bearing surface.

32. The conveyor screw according to claim 31 , wherein the central body being free from any openings between the first bearing surface and a second bearing surface33. The conveyor screw according to any of the claims 30-31 , wherein the conveyor screw comprises a cage structure extending from the central body at the first bearing surface in a direction away from the second bearing surface, the screw thread being at least partially attached to the cage structure.

34. The conveyor screw according to claim 33, wherein the cage structure part comprises an inner ring attached to the central body, and outer ring and a plurality of ribs interconnecting the inner ring and the outer ring.

35. The conveyor screw according to claims 30-34, wherein the central body defines a cylinder at the cylindrical portion and a truncated cone at the conical portion.

36. The conveyor screw according to claims 30-35, wherein the outer perimeter of the screw thread defines a diameter and the screw thread defines a length in the longitudinal direction, the ratio between the diameter and the length exceeding 3.9, preferably exceeding 4.2, more preferably exceeding 4.5, most preferably exceeding 4.9.

37. The conveyor screw according to claim 36, wherein the diameter is exceeding 640mm, preferably exceeding 670mm, more preferably exceeding 700mm, most preferably exceeding 715mm.

38. The conveyor screw according to any of the claims 30-37, wherein the central body defines a hollow interior which is at least partially reinforced by a reinforcing material extending at least half the distance between the first bearing surface and the second bearing surface, the reinforcing material preferably being fibre reinforced epoxy.

39. The conveyor screw according to any of the claims 30-38, wherein a first flight being attached to the central body and extending in the longitudinal direction, the first flight defining a first outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the first outer perimeter defining a first diameter, the first flight defining a first pitch angle at the cylindrical portion of the conveyor screw, the first pitch angle being less than 20°, and,a second flight being attached to the central body, extending in the longitudinal direction, having the same winding direction as the first flight and being at least partially intertwined with the first flight, the second flight defining a second outer perimeter extending circumferentially about the cylindrical portion of the conveyor screw, the second outer perimeter defining a second diameter, the second flight defining a second pitch angle at the cylindrical portion of the conveyor screw, the second pitch angle being greater than 30°, and the second diameter being smaller than the first diameter.

40. The conveyor screw according to claim 39, wherein the conveyor screw further defining a third flight extending parallel with the second flight, the second flight extending to the second outer perimeter whereas the third flight extending to a third outer perimeter, the second flight and the third flight defining an oil channel between themselves, the oil channel defining a width between the second flight and the third flight being less than the distance between the central body and the second outer perimeter.

41. The conveyor screw according to claim 40, wherein the third outer perimeter defining a third diameter, the third diameter being smaller than the second diameter.

42. The conveyor screw according to any of the claims 39-41 , wherein the second screw thread passes through gaps in the first screw thread.

43. The conveyor screw according to any of claims 39-42, wherein the conveyor screw comprises a fourth flight being substantially identical to the second flight and extending in parallel with the second flight, and a fifth flight corresponding to the third flight and running parallel with the fourth flight establishing a further oil channel together with the fourth flight, the fourth flight and the fifth flight being phase shifted relative to the second flight and the third flight, respectively, preferably by 180°.

44. A decanter centrifuge comprising a rotatable bowl and a conveyor screw according to any of the claims 31-43 accommodated inside the rotatable bowl, the rotatable bowl defining an inner surface substantially matching the outer perimeter of the screw thread.

45. A method of operating a decanter centrifuge according to claim 44, wherein the method comprising: continuously introducing a flowable material to be separated into thebowl at a rate higher than 75m3 / h while rotating the bowl to apply a g-force of at least 3000 G at the bowl wall.

46. A circular base for a decanter centrifuge, the base being configured to be accommodated at one longitudinal end of a rotatable bowl of the decanter centrifuge, the base defining an inner surface configured to face an interior of the bowl, a radial direction extending outwardly from a centre point of the base and a longitudinal direction extending perpendicular to the radial direction, the base comprising: a bearing surface for a conveyor screw, the bearing surface being centrally located at the inner surface of the base and extending about the centre point of the base, a feed inlet for introducing a flowable material into the bowl of the decanter centrifuge, the flowable material comprising a light phase and a heavy phase, and a first light phase outlet for receiving the light phase from the bowl of the decanter centrifuge, the first light phase outlet comprising a first weir edge defining in normal use a level of the light phase in the bowl.

47. The base according to claim 46, wherein the first light phase outlet is provided in an outlet housing, the outlet housing being cylindrical and protruding in the longitudinal direction from the inner surface.

48. The base according to claim 47, wherein the outlet housing defining an adjustment axis extending parallel to the longitudinal direction, the outlet housing being rotatable around the adjustment axis.

49. The base according to according to claim 48, wherein the outlet housing being spaced apart from centre point of the base.

50. The base according to any of the claims 48-49, wherein the outlet housing being at least partially cylindrical and extending in the direction of the adjustment axis, the weir edge being parallel to the adjustment axis.

51. The base according to any of the claims 47-50, wherein the base comprising one or more further outlet housings for receiving the light phase from the inner space together with the first outlet housing, the one or more further outlet housings being substantially identical to the first outlet housing.

52. The base according to any of the claims 46-51, wherein the feed inlet and the bearing surface being located on a cylindrical trunnion protruding in the longitudinal direction from the inner surface of the base.

53. The base according to claim 52 and any of the claims 47-50, wherein the outlet housing is located on the cylindrical trunnion.

54. The base according to any of the claims 46-53, wherein the weir edge of the light phase outlet extends further away from the inner surface in the longitudinal direction than the feed inlet.

55. The base according to any of the claims 46-54, wherein the feed inlet defines an inlet opening facing in the radial direction, the feed inlet further comprising deflectors for causing the feed to flow substantially in a tangential direction relative to the opening.

56. The base according to any of the claims 46-55, wherein the bearing surface is located further away from the inner surface in the longitudinal direction than the feed inlet.

57. A decanter centrifuge comprising bowl rotating in use in a direction of rotation around an axis of rotation, the bowl comprising a base according to any of the claims 46- 56 at one end of the bowl in the axis of rotation and a heavy phase outlet at an opposite end of the bowl in the axis of rotation, the longitudinal direction of the base coinciding with the axis of rotation.

58. A method of operating a decanter centrifuge according to claim 57, wherein the method comprising continuously introducing a flowable material into the bowl via the feed inlet while rotating the bowl about the axis of rotation thereby separating the flowable material into a light phase and a heavy phase and allowing the light phase to flow out of the bowl via the light phase outlet and the heavy phase to flow out via the heavy phase outlet.

59. The method according to claim 58, wherein the flowable material is introduced at a rate higher than 75m3 / h and the bowl is rotating to apply a g-force of at least 3000 gnat the bowl wall.

60. The method according to any of the claims 58-59, wherein the light phase is an oil and the heavy phase is a mixture of water and solids.

Images