WO2012033440A2

WO2012033440A2 - Separation disks in a centrifugal separator

Info

Publication number: WO2012033440A2
Application number: PCT/SE2011/050987
Authority: WO
Inventors: Torgny Lagerstedt
Original assignee: Torgny Lagerstedt Ab
Priority date: 2010-09-09
Filing date: 2011-08-12
Publication date: 2012-03-15
Also published as: WO2012033440A3; EP2613886A2; SE1000920A1; SE535487C2

Abstract

The object of the present invention is to provide an improved separation disk (40) in the disk stack in a disk stack centrifuge. According to the invention the separation disks (40) in the disk stack of a centrifugalseparatorcomprise a number of flat segments (41) which are coupled (42) to each other thus forming the separation disk (40). The segments have been given such a form that after coupling the segments, afrustoconical separation disk is formed withstretchwise flat surfaces.

Description

Separation disks in a centrifugal separator

Field of the invention

The present invention relates to the form of the separation disks in a disk stack in a centrifugal separator and the object of the invention is to provide an improved separation disk. According to the invention the separation disk in the disk stack of a centrifugal separator comprise a number of flat segments which are coupled to each other thus forming the separation disk. The segments have been given such a form that after coupling the segments, a conical separation disk is formed with stretch wise flat surfaces.

Background of the invention

The invention originates from problems in the manufacturing of separation disks in a disk stack in centrifugal separator. Centrifugal technique is often used in the cleaning of fluids. The fluid can be a liquid or a gas. In the separation, particles with a density different from that of the fluid, are separated from the fluid by centrifugal forces set up by rotation of the fluid. The particles can be solid or liquid particles. One example of particle separation from a liquid is the separation of whole (raw) milk. In this process centrifuges are used for removing fat globules from the milk. The fat globules which have a density lower than that of the serum (skim milk) migrate towards the centre of the centrifuge. Also, in the same process heavy particles in the milk are removed by the centrifugal forces in the centrifuge and heavy particles with a density higher than the serum migrate outward. In the cleaning of gases particles with a density higher than that of the gas are removed from the gas by setting the gas with the entrained particles in rotation. The particles can be solid or liquid particles.

Cleaning of liquids with centrifugal forces is a well known technique and is widely used in different applications. The classical example of liquid separation is the above mentioned cleaning of whole milk. Other examples of applications are cleaning of fuel and lube oil onboard ships, cleaning of vegetable oils, cleaning of beer from yeast.

Centrifuges for the cleaning of liquids have been continuously developed during the last 140 years and the modern liquid centrifugal separator is an efficient machine. A major step in the centrifuge technology was the introduction of the disk stack which increased the efficiency of the centrifuge with a factor 10 to 100. The disk stack was invented in 1888 by Clemens Freiherr von Bechtolsheim, German patent number 48615. The dominating type of disk stack used today is a disk stack comprising a number of frusto conical separation disks. But, also axial disks have been used. Both the frusto conical and the axial disk were invented by von Bechtolsheim. However, the present invention relates to the conical disk. It is here further clarified that the cleaning efficiency of a centrifugal separator is directly proportional to the number of disks in the disk stack.

The number of separation disks in a disk stack is large and the number may be 50 to 250. The disks can be made from different material but disks made from sheet metal are dominating. Metal separation disks are made by pressure turning sheet metal into conical disks. Pressure turning is an expensive method of manufacturing. This is especially true for large disks. Also, pressure turned disks have to be supplied with spacing elements which keep the disks apart. The spacer elements (spacers) further increase the cost of the disk. The spacer elements are needed for forming the flow path for the fluid to be cleaned. Disks can also be made by injection moulding of a polymer (plastic). The cost for a disk made by injection moulding is low but the tool for the injection moulding is high. Plastic has the disadvantage of low strength of material compared to that of metal. Plastic cannot function at elevated temperatures which further reduces the number of applications for plastic disks. Injection moulding tools can only be made up to a certain size which limits the size of the disk. Also, disks made by injection moulding cannot be made in arbitrarily thin sections. This results in disks having thick sections which increases the cost for the plastic material also, this reduces the number of disk that can be fitted in a disk stack with a given height. Disk stack centrifuges are mostly used in liquid separation (liquid cleaning) but gas separation (gas cleaning) with disk stack centrifuges is increasing. Gas cleaning in disk stack centrifuges has been known for long, an example is seen in the Swedish invention 101843 (April, 1941). A later patent describing the technique is seen in US 2003097835.

The limitations and the cost in the manufacturing of the disk stack limits the use of the disk stack centrifuge. This is especially limiting for the use of disk stack centrifuges in gas cleaning. The gas cleaning centrifuge can be given a very simple design and the cost of the disk stack is dominating. In gas cleaning there is a need for centrifuges that can both handle large flow rates and elevated temperatures. An example here is the cleaning of flue gas. The two main types of disk stack centrifuges are; centrifuges with a casing that co-rotates with the disk stack and centrifuges having a casing stationary relative to the rotating disk stack. The centrifuge with the co-rotating casing is normally used in liquid separation but can also be used in gas separation. A centrifuge for gas separation normally has a stationary casing. An advantage with the stationary casing is that the centrifuge is fairly simple in design which reduces the cost of the centrifuge.

Fluids to be cleaned can be led through the disk stack in the direction from the periphery to the centre of the disk stack (counter-current flow) or from the centre to the periphery (co-current flow). The present invention can be used in centrifuges with co-rotating or stationary casings and the use is not limited to any of the flow directions co-current or counter-current.

Summary of the invention

The object of the present invention is to provide an improved separation disk in the disk stack in a disk stack centrifuge. According to the invention the separation disk set forth by the introductory portion of the description is characterized by the features in claim 1 Thus, according to the principle of the invention the separation disk in the disk stack comprise a number of flat segments which are coupled to each other thus forming the separation disk. The segments have been given such a form that after coupling of the flat segments, a conical separation disk is formed with stretch wise flat surfaces. Examples of methods for coupling (joining) the flat segments are; gluing, welding riveting, folding. Other methods of joining are also possible. The flat segments that forms the conical disk can be made out of different materials. Examples are: metal, plastic, cardboard, cellulose fibre (paper). Here it shall be noted that the disks formed by flat segments in this manner are not strictly conical but are formed by stretch wise flat panels which form a conical disk.

The invention also relates to the joints between the flat segments which according to the characterizing in claim 2 are given such a height in the joining method that the joints form the wanted spacers that separates the disks. Thus, no further spacing elements are needed

The invention also concerns a centrifugal separator in which according to claim 3 the separation disks in the disk stack of the centrifugal separator are formed by part wise flat panels which form a conical disk.

The invention also relates to a way of forming the disks in the disk stack as described in claim 4. The separation disk or a continuous separation disk that forms the disk stack is formed by ,at certain intervals, folding a originally flat band in such a manner that a conical disk is obtained that have stretch wise flat sections. The folding procedure is described in the following. The flat band is folded so that the amount of material (length wise the band) that is folded in the fold increases from one edge of the band to the opposite edge. This gives at band which is shorter on one side and the band thus formed describes a circle there the outer periphery of the band is the edge there least material is folded in the fold. Consequently, the inner edge of the circle is the side with most material folded in the fold. This folded and circular band is the placed with such a radius that a continuous set of separation disks are formed that have stretch wise flat segments. In the above is the shortening of the band obtained by folding the band. Similar reduction in length can be obtained by stamping impression with different height across the band. With "across" is here meant from one edge to the opposite edge. The invention according to claim 5 relates to the height of the fold in claim 4. The fold is made with a height which is the wanted height of the spacers that keeps the distance between the separation disks. The invention also according to claim 6 relates to a method of stamping impressions on the flat segments of the separation disk described in any of the claims 1 and 4. The stamped impressions will function as spacers that keep the distance between the separation disks. The invention also according to claim 7 also relates to the form of the spacers described in claim 6. The spacers are stamped into the surface of the flat segments of the separation disk and that the spacers extend in a purely radial direction.

The invention also according to claim 8 relates to the form of the spacers described in claim 6. According to claim 8 the spacers described in claim 6 is stamped into the surface of the flat segments of the separation disk in a direction that have an angle to the pure radial direction.

The invention in claim 9 relates to the form of the spacers as described in claim 6, 7 and 8. There the spacers are stamped into the surface of the flat segments of the separation disk and that the spacers don't extend to the outer edge of the disk

The invention also according to claim 10 concerns a method of making a separation disk as described in claim 1 and 2. The flat segments are according to claim 10 joined by a suitable method of joining.

The invention will be further described below with reference to the accompanying drawings. Brief description of the drawings

Figure 1 shows a disk stack centrifuge with a rotating disk stack in a co-rotating casing. Figure 2 shows a disk stack centrifuge with a rotating disk stack in a non-rotating casing.

Figure 3 shows a conical separation disk with the form commonly used in a disk stack centrifuge. Figure 4 shows a separation disk in a disk stack centrifuge formed by stretch wise flat segments according to claim 1.

Figure 5 shows a separation disk made according to claim 4. Figure 6 shows a part of a separation disk with spacers impressed in the flat part of the disk surface.

Figure 7 shows a part of a separation disk with spacers impressed in the flat part of disk surface. There the impressions are in two directions perpendicular to the disk surface.

Detailed description of preferred embodiments

Figure 1 shows a disk stack centrifuge 18 with a co-rotating casing 1. A disk stack 2 is situated inside the casing 1 which co-rotates with the disk stack. The disk stack comprises a number of individual separation disks 3. The separation disks 3 are stacked on each other thus forming the disk stack 2. The disks 3 are axially separated from each other by spacers 33 (shown in figure 3). The spacers 33 can be in a purely radial direction or having an angle from the pure radial direction, also curved spacers are possible. Purely radial spacers are seen in figure 3. The separation disk has an upper side 15 and a lower side 13. The disk stack and the casing are driven by a drive element 4. The rotating casing 1 rotates inside a non rotating shell 5. The centrifuge 18 can be used in liquid cleaning or gas cleaning. In the ensuing description the word gas will be used throughout but the centrifuge will operate in the same manner with a liquid.

The operation of the centrifuge is described in the following. Gas 9 flows into the centrifuge 18 via an inlet pipe 6 and the gas continues via a distribution channel 7 to a periphery 8 of the disk stack. The flow direction is depicted by flow direction arrows 10, 11. The gas will proceed radially inward through channels 12 in the disk stack and cleaned gas reaches a space 17. Heavy particles in the gas will by centrifugal forces migrate outward and reach the underside 13 of the disk 3. Particles will then on the underside 13 slide towards the periphery and reach a collection chamber 14. During the transport on the underside 13 particles will agglomerate to larger particles. The cleaned gas leaves the rotating casing 1 via the flow path between the inlet pipe 6 and a rim 16. The cleaned gas finally exits the centrifuge through a flow channel 19. Figure 1 shows a centrifuge with a flow direction of the gas from the periphery 8 to the centre of the centrifuge. This flow direction is called counter-current flow and the centrifuge is called a counter-current centrifuge. The centrifuge can also be configured for a flow direction from the centre of the centrifuge towards the periphery 8. A centrifuge of this type is called a co-current centrifuge. Counter-current centrifuges are common in liquid cleaning and co-current centrifuges are mostly used in gas cleaning. However, both counter-current and co-current centrifuges can be used in liquid or gas cleaning Figure 2 shows a disk stack centrifuge 20a with a non-rotating casing 24. Figure 2 shows the centrifuge 20a in a co-current operation. Co-current operation has the advantage that a disk stack 20 acts as a fan that pushes the flow of gas through the centrifuge and piping system downstream the centrifuge. The centrifuge 20a can also operate with counter- current separation but an external fan will be needed to push the flow through the centrifuge and piping. The centrifuge in figure 2 is mostly used for gas cleaning but can be used for liquid cleaning. A detailed description of the centrifuge and its operation will be presented in the following. The disk stack 20 with a lower disk 21 and an upper disk 22 is situated the non-rotating casing 24. The disk stack 20 comprises a number of individual separation disks 23. The separation disks 23 are stacked on each other thus forming the disk stack 20. The disks 3, 23 are axially separated from each other by spacers 33 (shown in figure 3). The spacers 33 can be in a purely radial direction or having an angle from the pure radial direction, also curved spacers are possible. Radial spacers are seen in figure 3. The disk stack is driven by a drive element 4. The disk stack 20 and the lower 21 and the upper disk 22 rotate in the stationary (non-rotating) casing 24. Gas to be cleaned enters the centrifuge 20a through an inlet pipe 25. The gas is distributed and flows between the disks 23 in the disk stack 20. Heavy particles are subjected to centrifugal forces set up by the rotation of the gas which co-rotates with the disk stack. The particles migrate towards the underside 13 of the disk (seen in figure 1). The particles will reach the underside 13 and slide on the underside to the periphery of the disk stack. During the transport on the underside 13, the particles will agglomerate to large particles. The agglomerates are thrown from the periphery and are collected on an inside 26 of the stationary casing 24. The cleaned gas exits the centrifuge via an outlet 27. Particles collected on the inside 26 are removed in by a cleaning process (not described in figure 2). However, particles in the form of liquid drops will coalesce and exit the centrifuge as a liquid via a liquid outlet 28. A barrier 29 hinders the liquid from being entrained in the outgoing clean gas flow. The barrier is not needed in counter-current operation. The centrifuge in figure 2 with a non-rotating casing can also operate in counter-current mode. The counter-current mode for a centrifuge with a non-rotating casing is not shown with a figure.

Figure 3 shows a detailed picture of a separation disk 3, 23, 30 in the disk stack 2, 20. The separation disk 3, 23, 30 is in a form of frusto conical disk with an upper side 31 and an lower side 32 with spacers 33.

Figure 4 shows a separation disk 40 with stretch wise flat segments 41. The number of segments 41 may vary but the lowest possible number is 3. In the figure 4 a separation disk with 10 segments is shown. The segments are joined together with a joint 42. The joint 42 is only schematically shown in figure 4. The method of joining and the type of joint may vary. The joint can as claimed in claim 2 be given such a height that the joint function as a spacer between the individual disks 40.

Figure 5 shows a separation disk 50 according to claim 4 with stretch wise flat segments 41, 51. The disk is manufactured from originally flat band of sheet material. This flat band is turned into individual separations disks or a continuous set of separation disks by the following procedure. The originally flat band is turned into a conical disk by removing different length (amount) of material from an inner edge 52 to an opposite outer edge 53. The length reduction is in figure 5 shown as a fold 54. The view A - A shows one of the possible ways of folding the material. Another way of reduction in length is by stamping impressions shown schematically in figure 6 and 7. The impressions are stamped with amplitude which differ from the edge 52 to the edge 53. Other methods of reduction in length may also be possible.

Figure 6 schematically shows a method of making a spacer 61 on the flat part 41 of the separation disk 40 shown in figure 4. Only one spacer is shown in figure 6. The spacer 61 are made by stamping impressions in the material in a disk 62. The form of the spacer 61 may vary. The extension on the flat surface may also vary. I. e. the spacer don't have to reach from edge to edge. The spacers can be in a pure radial direction or having a angle from the pure radial direction. The spacers can also have a curved form, not shown in a figure. The spacers can also extend in different directions perpendicular from the flat surface as shown in figure 7. Figure 7 shows spacers 71, 72 which are made by stamping an impression of disk material 73 that extends perpendicular from the flat surface 41, 51 but in different directions.

Claims

1)

Separation disk (3, 23) in a disk stack (2, 20) in a centrifugal cleaner intended for cleaning of liquids or gases in which the separation disk (3, 23) has a frusto conical form, characterized in that each individual separation disk (3, 23) in the disk stack comprises sections of mainly flat segments (41).

2)

Separation disk according to claim 1, characterized in that said flat segments (41) are joined together in manner that a joint (42) between two segments obtains the height of the wanted distance between the separation disks and thus function as spacers between the disks.

3)

Centrifugal cleaner having a disk stack, characterized in that the disk stack comprises a number of separation disks according to any of the claims 1 or 2.

4)

Separation disks (3, 23) according to claim 1, characterized in that the separation disks (3, 23) is formed by stretch wise flat segments (51) which are manufactured from a originally flat band material which at certain intervals are folded in such a manner the amount of material in a fold (54) increases from one edge of the band to a given value on the opposite edge of the band by which a band is formed that can be turned into a frusto conical separation disk (50) with the above said stretch wise flat segments (51). 5)

Method according to claim 4, characterized in that the fold (54) is formed in such a manner that the fold between two flat segments (51) obtains the height of the wanted distance between the separation and disks thus function as spacers between the disks.

6)

Method according to claim 5 characterized in that spacers (61, 71, 72) are stamped impression in the flat segments (51). 7)

Method according to claim 6, characterized in that spacers (61, 71, 72) stamped in the flat segments (51) extend in a purely radial direction.

8)

Method according to claim 6, characterized in that spacers (61, 71, 72) stamped in the flat segments (51) extend in an angle which is≠ 0 from the pure radial direction.

9)

Method according to claim 6 to 8, characterized in that spacers (61, 71, 72) stamped in the flat segments (51) don't extend all the way to an outer periphery (53) of the separation disk (50).

10)

Method to manufacture a separation disk (3, 23) in a disk stack (2, 20) in a centrifugal cleaner according to any of the claims 1 or 2, Characterized in that the separation disks (3, 23) are formed by flat segments (41) joined to the form a of a frusto conical separation disk by a suitable method of joining such a gluing, welding, riveting or folding.