Source: http://www.google.com/patents/US7156801?ie=ISO-8859-1
Timestamp: 2014-07-25 21:59:42
Document Index: 74146688

Matched Legal Cases: ['art 5', 'art 19', 'art 17', 'art 17', 'art 19', 'art 18', 'art 17', 'art 17', 'art 19', 'art 18']

Patent US7156801 - Decanter centrifuge with a screw conveyor having a varying pitch - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsThe decanter centrifuge comprises a screw conveyor having a body (4), which carries a screw comprising one or more flights (7, 7′) and having a nominal transport speed varying along the longitudinal axis. An inlet (6) is provided in the screw conveyor for the material to be separated. The screw conveyor...http://www.google.com/patents/US7156801?utm_source=gb-gplus-sharePatent US7156801 - Decanter centrifuge with a screw conveyor having a varying pitchAdvanced Patent SearchPublication numberUS7156801 B2Publication typeGrantApplication numberUS 10/509,836PCT numberPCT/DK2003/000235Publication dateJan 2, 2007Filing dateApr 9, 2003Priority dateApr 22, 2002Fee statusPaidAlso published asCA2480715A1, CA2480715C, CN1287901C, CN1646229A, DE60318833D1, DE60318833T2, EP1497033A1, EP1497033B1, US20050202950, WO2003089146A1, WO2003089146A8Publication number10509836, 509836, PCT/2003/235, PCT/DK/2003/000235, PCT/DK/2003/00235, PCT/DK/3/000235, PCT/DK/3/00235, PCT/DK2003/000235, PCT/DK2003/00235, PCT/DK2003000235, PCT/DK200300235, PCT/DK3/000235, PCT/DK3/00235, PCT/DK3000235, PCT/DK300235, US 7156801 B2, US 7156801B2, US-B2-7156801, US7156801 B2, US7156801B2InventorsKlaus Dircks, Bent MadsenOriginal AssigneeAlfa Laval Copenhagen A/SExport CitationBiBTeX, EndNote, RefManPatent Citations (22), Referenced by (3), Classifications (5), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetDecanter centrifuge with a screw conveyor having a varying pitchUS 7156801 B2Abstract The decanter centrifuge comprises a screw conveyor having a body (4), which carries a screw comprising one or more flights (7, 7′) and having a nominal transport speed varying along the longitudinal axis. An inlet (6) is provided in the screw conveyor for the material to be separated. The screw conveyor is provided with a baffle (8, 8′) dividing the separation chamber in a substantially cylindrical separation part (17) and an at least partially conical discharge part (18). Immediately upstream of the baffle (8, 8′) a transition part (19) is provided between the separation part (17) and the discharge part (18), the screw conveyor (3) having a bigger nominal transport speed in the transition part (19) than in the separation part (17) immediately before the transition part (19), the change of the nominal transport speed being established by a change (21) of the screw pitch.
3. A decanter centrifuge according to claim 2, wherein the pitch angle of the screw in the separation part is considerably smaller than 45� relative to the tangential direction and that the change of the screw pitch is an increase.
4. A decanter centrifuge according to claim 2, wherein the pitch angle of the screw in the separation part is considerably bigger than 45� relative to the tangential direction and that the change of the screw pitch is a decrease.
6. A decanter centrifuge according to claim 5, wherein the pitch angle of the screw in the separation part is considerably smaller than 45� relative to the tangential direction and that the change of the screw pitch is an increase.
7. A decanter centrifuge according to claim 5, wherein the pitch angle of the screw in the separation part is considerably bigger than 45� relative to the tangential direction and that the change of the screw pitch is a decrease.
8. A decanter centrifuge according to claim 1, wherein the pitch angle of the screw in the separation part is considerably smaller than 45� relative to the tangential direction and that the change of the screw pitch is an increase.
9. A decanter centrifuge according to claim 8, wherein said increase is 40�80%.
10. A decanter centrifuge according claim 8, wherein the screw has the bigger nominal transport speed over at least ⅓�1/n of a turn before the baffle, n being the number of flights.
11. A decanter centrifuge according to claim 1, wherein the pitch angle of the screw in the separation part is considerably bigger than 45� relative to the tangential direction and that the change of the screw pitch is a decrease.
12. A decanter centrifuge according claim 11, wherein the screw has the bigger nominal transport speed over at least ⅓�1/n of a turn before the baffle, n being the number of flights.
13. A decanter centrifuge according to claim 1, wherein the screw has the bigger nominal transport speed over at least ⅓�1/n of a turn before the baffle, n being the number of flights.
14. The decanter centrifuge of claim 13, wherein said bigger nominal transport speed is more than about ⅔�1/n of a turn.
FIELD OF THE INVENTION The present invention relates to a decanter centrifuge for separation of a supplied material in a light phase and a heavy phase, comprising an elongate bowl arranged for rotation about its longitudinal axis, said bowl having a separation chamber, a screw conveyor being provided in the separation chamber and being coaxial with the bowl, said screw conveyor comprising a body, which carries a screw comprising one or more flights and having a nominal transport speed varying along the longitudinal axis, an inlet with at least one inlet opening in the screw conveyor for supply of the material to the separated, and at least one discharge opening for the heavy phase in the bowl at one end of the screw conveyor, in which the screw conveyor is made to rotate relative to the bowl in view of conveying the heavy phase towards the discharge openings for the heavy phase, and in which the screw conveyor is provided with a baffle positioned between the inlet openings and the discharge openings, said baffle dividing the separation chamber in a substantially cylindrical separation part and an at least partially conical discharge part, the discharge openings for the heavy phase being positioned in the discharge part, the inlet openings being positioned at the opposite side of the baffle relative to said discharge openings.
DESCRIPTION OF RELATED ART A decanter centrifuge of this kind is known from WO-A-97/22411, which discloses a decanter centrifuge having a baffle shaped as a rib extending from the upstream side of a screw turn as a part of a turn having a bigger pitch than the screw to the downstream side of a screw turn at an axial distance from its starting point.
SUMMARY OF THE INVENTION This object is according to the invention met in that immediately upstream of the baffle, seen in relation to the transport direction, a transition part is provided between the separation part and the discharge part, and that the screw conveyor has a bigger nominal transport speed in the transition part than in the separation part immediately before the transition part, the change of the nominal transport speed of the screw from the nominal transport speed in the separation part immediately before the transition part to the higher nominal transport speed in the transition part being established by a change of the screw pitch.
By nominal transport speed for the screw is to be understood the speed, at which a given part of the screw would convey the heavy phase without disturbance from the surrounding parts of the screw, like for instance downstream accumulation of heavy phase. The nominal transport speed depends in a non-linear way on the screw pitch and is highest at a pitch angle of approx. 450� relative to the tangential direction.
In a preferred embodiment the pitch angle of the screw in the separation part is considerably smaller than 45� relative to the tangential direction, and the change of the screw pitch from the separation part to the transition part is an increase. This increase is preferably 40�80%.
In another embodiment the pitch angle of the screw in the separation part is considerably bigger than 45� relative to the tangential direction, and the change of the screw pitch is a decrease from the separation part to the transition part.
To obtain full effect of the invention the heavy phase, which is conveyed towards the baffle, should be conveyed at the increased speed over the whole peripheral extension of the baffle. Therefore, the screw has the bigger nominal transport speed over at least ⅓�1/n of a turn before the baffle, preferably over approximately ⅔�1/n of a turn, n being the number of flights, corresponding to an axial length of ⅓ and preferably ⅔, respectively, of the pitch in the transition part, if there is only one flight, or the axial distance between two adjacent turns, if several flights are present.
BRIEF DESCRIPTION OF THE DRAWING The invention will now be explained in detail in the following by means of some examples of embodiments and with reference to the drawings, in which
DESCRIPTION OF THE PREFERRED EMBODIMENTS The decanter centrifuge 1 in FIG. 1 has a hollow bowl 2 with a separation chamber containing a screw conveyor 3 having a body 4 with a screw with a flight 7, which is wound in a number of turns. The body 4 is substantially cylindrical and has a conical part 5 at one end. In the screw conveyor 3 inlet openings 6 for the material to be separated are provided, and in the bowl 2 discharge openings 14 for the separated heavy phase are provided. As indicated in the figure, the light phase 12 will be positioned closest to the body of the screw conveyor 4, whereas the heavy phase 13 is positioned at the interior side of the bowl 2. The light phase is taken away via a discharge edge 10 on the bowl. The heavy phase is conveyed by the screw turn towards the discharge openings 14 in the bowl at its conical end. The figure shows a baffle 8 comprising an annular disc, which is perpendicular to the longitudinal axis or axial direction of the screw conveyor.
FIG. 3 shows another embodiment having a baffle 8 extending axially. The flight 7 of the screw conveyor 3 has in the position 21 a leap of the pitch, which is consequently bigger in the transition part 19 than in the separation part 17. In the separation part 17 the pitch is constant. On account of the axial extension of the baffle 8, the dividing line between the transition part 19 and the discharge part 18 is considered to lie at the axial centre point 23 of the baffle. As the position 21 is somewhat downstream of the starting point 24 of the baffle, the position 21 will lie slightly more than a half pitch before the centre point 23 of the baffle. The pitch of the flight 7 is, in the screw conveyors described up till now, equal to the axial dimension of the passageway 25 formed between the adjacent turns of the flight 7, and the pitch angle of the flight 7 in the separation part 17 is substantially smaller than 45� relative to the tangential direction.
FIG. 4 shows an embodiment, in which the screw of the screw conveyor 3 has three flights 7′ having a pitch angle substantially bigger than 45� relative to the tangential direction in the separation part 17. At an axial position 21′ the pitch is changed, the pitch angle being changed in direction of 45�, following which the nominal transport speed increases.
The baffle members 8′ extending from the position 21′ and having a pitch smaller than 90� (axial direction), and the dividing line between the transition part 19 and the discharge part 18 being counted to lie at the axial centre point 23 of the baffle members, the leap regarding the nominal transport speed occurs more than ⅙ (��⅓ (3=the number of flights)) of a flight upstream of the transition part corresponding to more than half of the axial extension of a passageway 25 between two adjacent flights 7′ in the transition part.
From the position 21 the sludge is accelerated on account of the change of the pitch of the flight 7 or the flights 7′. The position 21 is in the embodiment in FIG. 2 positioned approximately ⅔ turn before the intersection point 21 of the screw turn 7 with the baffle 8 corresponding to an axial distance between the position 21 and the point 22 of ⅔ of the pitch of the screw turn or the axial dimension of the passageway at this point. In the embodiments in FIGS. 3 and 4, the position 21 is positioned a little bit more than � time the axial dimension of the passageway 25 upstream of the axial centre point 23 of the baffle 8 or the baffle members 8′. In this manner the changing point of the transport speed is situated sufficiently far from the baffle 8, 8′ to convey the sludge along the periphery of the entire baffle at the increased speed.
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