Continuous belt for belt-type separator devices

Abstract

An improved belt for use in a belt separation apparatus and an improved method to separate a particle mixture based on tribo-electric charging of particles is disclosed. The improved belt is particularly suitable for tribo-electric separation of particles that tend to accumulate on the edges of the belt separation apparatus and/or tend to compound, or blend, with the belt material. The improved belt comprises impermeable longitudinal edges, apertures interior to the longitudinal edges of the belt, and periodic notches formed in the longitudinal edges of the belt at periodic locations in the edge of the belt.

Claims

1. A continuous belt for use in a belt separator system for separating components of a difficult-to-fluidize material, the belt comprising: impermeable longitudinal edges of a predefined width; apertures interior to the longitudinal edges of the belt that are configured to be permeable to the components of the difficult-to-fluidize material, the apertures further being configured for conveying components of the difficult-to-fluidize material along the longitudinal direction of the belt; periodic notches formed in the longitudinal edges of the belt at periodic locations in the edge of the belt, the notches being configured for conveying the components of the difficult-to-fluidize material in a direction along the longitudinal direction of the belt and away from the edges of the belt separation system.

2. The continuous belt of claim 1, wherein the notches formed in the longitudinal edge of the belt have a beveled edge.

3. The continuous belt of claim 1, wherein the bevel edge of each notch has a radius in a range of 4-5 mm.

4. The continuous belt of claim 1, wherein the notches formed in the longitudinal edge of the belt have a triangular-shape.

5. The continuous belt of claim 1, wherein the notches have an opening length is in the range of 19 mm-400 mm.

6. The continuous belt of claim 1, wherein the notches have an opening depth is in the range of 13 mm-31 mm.

7. The continuous belt of claim 1, wherein the notches have a spacing is in the range of 63 mm-960 mm.

8. The continuous belt of claim 1, wherein a leading edge of the notch has an angle in a range from 12-45 with respect to the longitudinal edge.

9. The continuous belt of claim 1, wherein a trailing edge of the notch is perpendicular with respect to the longitudinal edge.

10. The continuous belt of claim 1, wherein the notches in the longitudinal edges have dimensions selected to maximize throughput of a belt separator system for a difficult-to-fluidize material.

11. The continuous belt of claim 1, wherein the notches in the longitudinal edges have dimensions selected to minimize frictional heating of the belt longitudinal edge strands.

12. The continuous belt of claim 1, wherein the notches in the longitudinal edges have dimensions selected to maximize an operating lifetime of the belt for a difficult-to-fluidize material.

13. The continuous belt of claim 1, wherein the belt has a width a few mm less than a width of the inside of the belt separator system.

14. A method of making a continuous belt for use in a belt separator system for separating components of a difficult-to-fluidize material, the method comprising: forming a continuous belt with impermeable longitudinal edges of a predefined width; forming apertures interior to the longitudinal edges of the belt that are configured to be permeable to the components of the difficult-to-fluidize material and for conveying components of the difficult-to-fluidize material along the longitudinal direction of the belt; forming periodic notches in the longitudinal edges of the belt at periodic locations in the edge of the belt and for conveying the components of the difficult-to-fluidize material in a direction along the longitudinal direction of the belt.

15. The method of making the continuous belt of claim 14, further comprising forming the notches formed in the longitudinal edge of the belt with a beveled edge.

16. The method of making the continuous belt of claim 15, further comprising forming the beveled edge of each notch with a radius in a range of 4-5 mm.

17. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt with a triangular-shape.

18. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt with a leading edge having an angle in a range from 12-45 with respect to the longitudinal edge.

19. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt with a trailing edge of the notch being perpendicular with respect to the longitudinal edge.

20. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt width dimensions selected to maximize throughput of a belt separator system for a difficult-to-fluidize material.

21. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt width dimensions selected to maximize an operating lifetime of the belt for a difficult-to-fluidize material.

22. The method of making the continuous belt of claim 14, further comprising forming the belt with a width that is a few mm short of a width of an inside of the belt separator system.

23. The method of making the continuous belt of claim 14, further comprising forming the apertures interior to the longitudinal edges of the belt any of extruding, molding, punching, machining, water jet cutting, and laser cutting.

24. The method of making the continuous belt of claim 14, further comprising forming the notches in the longitudinal edges of the belt any of extruding, molding, punching, machining, water jet cutting, and laser cutting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures and description. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

(2) FIG. 1 illustrates a diagram of one example of belt separator system (BSS);

(3) FIG. 2 illustrates a plan view of an extruded belt

(4) FIG. 3 illustrates an enlarged view of portion of current belt and BSS

(5) FIG. 4 illustrates a plan view of an extruded belt;

(6) FIG. 5A illustrates an enlarged plan view of a belt edge with a triangular edge notch that is beveled and with blanked hole adjacent to notch;

(7) FIG. 5B illustrates an side view of the belt of FIG. 5A;

(8) FIG. 6. illustrates an enlarged plan view of a belt with a semi-circular edge notch;

(9) FIG. 7. illustrates an enlarged plan view of a belt edge with a long, extended edge notch;

(10) FIG. 8. illustrates an enlarged plan view of a belt edge illustrating edge notch spacing; and

(11) FIG. 9. illustrates an enlarged plan view of a belt edge having different edge notch spacing.

DETAILED DESCRIPTION

(12) Aspects and embodiments are directed to an improved belt that may be used in a belt separation apparatus to separate a particle mixture based on tribo-electric charging of the particles, and more specifically to an improved belt having notches in each impermeable longitudinal edge. The improved belt is particularly suitable for tribo-electric separation of particles that tend to accumulate on the edges of the belt separation apparatus and/or tend to compound, or blend, with the belt material. The improved belt also results in an improved separation process, improved belt lifetime, reduced failure of the belt and less down time for the separation apparatus.

(13) It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of including, comprising, having, containing, involving, and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to or may be construed as inclusive so that any terms described using or may indicate any of a single, more than one, and all of the described terms. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to embodiments or elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality of these elements, and any references in plural to any embodiment or element or act herein may also embrace embodiments including only a single element. References to or may be construed as inclusive so that any terms described using or may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation.

(14) Referring to FIG. 4, one current design of a UHMWPE belt 45 has straight and smooth machine direction edge strands 47 that are thicker than the machine direction strands 42 or the cross direction strands 46 in the interior of the belt. These wider (20-30 mm) edge strands 47 serve to carry more of the tension load, provide dimensional stability and reduce the incidence of belt failure by edge 49 abrasion.

(15) These UHMWPE sheet belts 45 have proven to have much longer life than the aforementioned extruded belts (See FIG. 2). In certain applications, such as the separation of unburned carbon from coal combustion fly ash, these UMHWPE belts have had been tested and shown to have a maximum life of up to 1950 hours before failure.

(16) The fluidization characteristic of powders is one parameter in determining how the particles of the powder are conveyed and separated in a BSS. Section 3.5 in Pnuematic Conveying of Solids by Klinzig G. E. et al., second edition 1997, describes materials loosely as fluidizable or difficult to fluidize. This property is qualitatively assessed by the behavior of the material in a fluidized bed. The fluidization property of powders is generally accepted to be influenced by the powder particle size, specific gravity, particle shape, surface moisture, and by other less well understood properties. Coal combustion fly ash is an example of an easily fluidizable powder. Many other industrial mineral powders are more difficult to fluidize than fly ash.

(17) The embodiment of the BSS with a continuous counter current belt moving between two longitudinal, parallel planar electrodes has inside edges of the separation chamber that are not directly swept by the belt 45. It is desirable to minimize the area of the unswept zone of the edges of the separation chamber, since it represents electrode area that is not effective for particle separation. However, it is also typical to leave a gap between the edge 47 of the belt 45 and the inside edge of the separation chamber to prevent the belt from rubbing and wearing against the inside edge of the separation chamber, which could lead to early belt failure. Therefore the width w (See FIG. 4) of the belt 45 is approximately 20 mm narrower than the width of the separation chamber, in order to leave about 10 mm clearance between the inside wall of the separation chamber and the edges 47 of the belt 45.

(18) Fluidizable powders, such as coal combustion fly ash, are effectively swept from the inside edges of the separation chamber by the motion of the belt 45. This occurs because the motion of the belt 45 creates a shear force which exceeds the inter-particle forces between particles of the coal combustion flyash and between particles of the combustion flyash and the edge walls of the separation chamber. However, for difficult to fluidize or more cohesive powders, such as many industrial minerals, the shear force generated by the moving belt 47 is not typically sufficient to overcome the interparticle forces in the powder, which results in a build-up of compacted, thermally insulating, abrasive powder on the inside edge of the separation chamber in the zone between the inside wall of the separation chamber and the edges 47 of the belt 45 that the belt 45 does not sweep.

(19) Such non-fluidized abrasive powder that can also become trapped, or sandwiched, between the machine direction edge strands 42 of the top section of the belt 30 and the bottom section of the belt 28 (See FIG. 2) which are moving in opposite directions at relative velocities from 20 to 100 ft/sec. The abrasion between the moving belt segments, enhanced by the non-fluidized abrasive powder, leads to small fragments of UHMWPE belt being removed from the belt and frictional heating of the edge strands 47 over their width and along their length. At these elevated temperatures, the small fragments of plastic belt material and the powder tend to fuse together to form composites of powder and plastic, which can grow to 10-200 mm in length and 5-25 mm wide. With the edge of the belt 47 now running against these plastic-powder compound deposits, they cause further frictional heating and eventually destroy the edge of the belt, sometimes even fusing the belt strands together. The composition of a typical thermoplastic-powder composite that was retrieved from a belt failure caused by the buildup of this composite residue has been measured as approximately 50% thermoplastic and 50% industrial mineral powder. This phenomenon of plastic powder composite buildup and accumulation on the unswept edges 47 of the BSS separation chamber has led to extremely short belt life in the range of tens of hours for the BSS when processing some industrial minerals (particularly non-fluidized materials).

(20) Referring to FIG. 5A, there is illustrated a plan view of an improved belt for a BSS, particularly for processing and separating some industrial materials (particularly non-fluidized materials). To improve belt life when processing difficult to fluidize particles using a BSS, the improved belt design 50 has been provided with continuous (having a width w1 of 20-30 mm wide) edge strands 47 on each side of the belt (only one side of the belt is illustrated), which have been modified by creating open notches 52 of a prescribed shape and location. These notches 52 can be obtained through various forming means such as molding, punching, machining, water jet cutting, laser cutting, and the like.

(21) The edge notches 52 provide a mechanism, pathway and conveying mechanism for powder sandwiched between edge strands 47 of oppositely moving belt segments 28, 30 to convey the particles of powder in either direction of belt motion. It is to be appreciated that the removal of stagnant powder between the edge strands 47 of oppositely moving belt segments 28, 30 significantly reduces abrasion and frictional heating. This belt 50 having such edge notches 52 has been tested in existing BSS of FIG. 1, and it has been shown that the use of belts with notched edges 52 has eliminated the formation of the plastic-powder composite build-up material that has historically resulted in short belt file. This belt 50 having such edge notches 52 has been tested in existing BSS of FIG. 1, and it has been shown that the belt life for has increased to 100's of hours when processing difficult to fluidize industrial mineral powders. This compares to belt life in the 10's of hours for prior art extruded belts having straight edge strands 47 without any notches, such as shown in FIG. 4. The trailing edge 54 of the notch 52 perpendicular to the edge of the belt 49 and the direction the belt is moving 41 provides a motive force to move powder in the direction of the belt motion. The volume of the notch 52, which is determined by depth of notch D, length of notch L, angle , and thickness t of the belt (See FIG. 5B), provides the carrying capacity of each notch 52. The spacing between notches (S) determines the carrying capacity of the belt per unit belt length of the belt. FIG. 5B illustrates a side view of the belt 50 and the notch 52, and in particular illustrates that the edges of the notch, such as the trailing edge 46, can be provided we a bevel having a bevel radius of b.

EXAMPLE 1

(22) In one example, separator belts 45 illustrated in FIG. 4 containing no notches 52 and a continuous, unbroken, straight edge geometry 47 with a width (w) of 25 mm was operated in a belt type electrostatic separator system (BSS) while processing ground calcium carbonate material, a difficult to fluidize powder. These belts failed due to edge deposit compounding after a maximum of 15 hours of total operation. Belts 50 of FIG. 5 containing triangular shaped edge notches 52 were operated on the same difficult to fluidize mineral powder. Belts containing the triangular-shaped edge notches 52 operated 20 times longer than the belt 45 without the edge notches, and very rarely failed due to edge deposits. Only 1 edge deposit failure was observed out of 21 belts 50 operated with edge notches 52. This significant increase in operating life of the separator belt 50 is advantageous for reducing costs when operating a BSS. The dimensions of the belts used in this example are listed below with dimensions referenced to FIG. 4.

(23) TABLE-US-00001 Dimensions No Edge Notches With Triangular Feature (ref. FIG. 5) (ref. FIG. 4) Edge Notches Thickness t 3-4 mm 3-4 mm Edge Width (W) D + f 25 mm 25 mm Notch Opening L N/A 33 mm Notch Spacing S N/A 100 mm Notch Depth D N/A 19 mm Solid Width f 25 mm 6 mm Notch Angle N/A 45 degrees Bevel Radius b N/A 4-5 mm Ultimate Belt 4 - Edge 20 - Not Edge Failure Mode Compounding Compounding 1 - Edge Compounding Highest Belt Life 15 hours 300 hours

EXAMPLE 2

(24) FIG. 6 illustrates another example of a improved belt 60 having beveled belt edge notches 62 cut with a semi-circular pattern into edge 49 of the separator belt edge strand 47 with a standard edge thickness of 25 mm. (FIG. 5) The semi-circular notches were cut with a smaller notch depth (D) than the notches described in example 1, but the belt and notches were still effective in preventing the edge buildup of the same difficult to fluidize powder that has been observed with belts without notches. The Belt Life of this embodiment was not as good at the belt life of the belt with the triangular-shaped notches as of Example 1. Thus, it is apparent from this Example 2 and Example 1, that a variety of edge notch configurations or shapes can be utilized to prevent edge deposit compounding, and that the shape of notch affects the improvement in the belt life. The optimum notch dimensions for a particular powder can be determined empirically by testing various belt notch designs.

(25) TABLE-US-00002 Dimensions No Edge Notches Semi-Circular Feature (ref. FIG. 6) (ref. FIG. 4) Notches Thickness t 3-4 mm 3-4 mm Edge Width (W) D + f 25 mm 25-44 mm Notch Opening L N/A 19 mm Notch Spacing S N/A 63 mm Notch Depth D N/A 13 mm Solid Width f 25 mm 12-31 mm Notch Radius r N/A 13 mm Ultimate Belt 4 - Edge 2 - Not Edge Failure Mode Compounding Compounding Highest Belt Life 15 hours 96 hours

EXAMPLE 3

(26) FIG. 7 illustrates another example of a belt 70, wherein the notch geometry was varied by cutting a large continuous notch 72 of length (L) of 700 mm, with beveled edges to avoid a damaging catch of the belt notch against a belt notch travelling in the opposing direction (FIG. 7). This belt was operated while processing ground calcium carbonate material, a difficult to fluidize powder, during which time no evidence of edge deposits or compounding was observed. From this example it is evident that notches with different lengths are effective in preventing edge deposit compounding. The optimum notch dimensions for a particular powder can be determined empirically by testing various belt notch designs.

(27) TABLE-US-00003 Dimensions No Edge Notches Extended Length Feature (ref. FIG. 7) (ref. FIG. 4) Notches Thickness t 3-4 mm 3-4 mm Notch Opening L N/A 400 mm Notch Spacing S N/A 960 mm Notch Depth D N/A 31 mm Solid Width f 25 mm 25 mm Notch Angle N/A 12 degrees Bevel Radius b N/A 4-5 mm Ultimate Belt 4 - Edge 1 - Not Edge Failure Mode Compounding Compounding Highest Belt Life 15 hours 93 hours

EXAMPLE 4

(28) FIG. 8 illustrates another example of a belt 80, for which the spacing (S) of the notches was investigated by varying the frequency and location of triangular-shaped belt notches 82 along the length of the belt. Notches with length (L) 33 mm and spacing (S) of 100 mm were cut into the side of several belts in an uninterrupted pattern. Notches of the same geometry were cut into a second set of belts in a repeating pattern of a notched section and a straight sidewall section with 4 notches of length (L) 33 mm and spacing (S) of 183 mm into a 730 mm long section, followed by an 820 mm long section of belt containing no notches (See FIG. 9). This pattern was repeated throughout the length of the entire belt. From this example it is evident belts with increased spacing between notches are effective in preventing edge deposit compounding. The optimum notch spacing for a particular powder can be determined empirically by testing various belt notch designs.

(29) TABLE-US-00004 Notches Spaced Notches in Alternating Dimensions No Edge Notches Every 100 mm Sections Increased Feature (ref. FIG. 8) (ref. FIG. 4) (FIG. 8) Spacing (FIG. 9) Thickness t 3-4 mm 3-4 mm 3-4 mm Edge Width (W) D + f 25 mm 22-44 mm 25 mm Notch Opening L N/A 19 mm 30 mm Effective S N/A 100 mm 388 mm Notch Spacing Notch Depth D N/A 11 mm 17 mm Solid Width f 25 mm 10-32 mm 21 mm Notch Angle N/A 45 deg 45 deg Bevel Radius b N/A 4-5 mm 4-5 mm Ultimate Belt 4 - Edge 2 - Not Edge 4 - Not Edge Failure Mode Compounding Compounding Compounding Highest Belt Life 15 hours 64 hours 124 hours

EXAMPLE 5

(30) Referring to FIG. 4, in another example, the importance of the belt edge notches was demonstrated by testing a belt containing no edge notches, but a smaller edge width (W)=(D+f) of only 11 mm as compared to 25 mm. Both belt edge geometries were operated while processing ground calcium carbonate material, a difficult to fluidize powder, and failed prematurely due to edge deposit compounding. This example illustrates the importance of edge notches to process difficult to fluidize mineral powders. Furthermore edge notches allow for thicker belt edge strands, which increase the resistance to stretching and allow for longer belt operating life prior to stretch failure.

(31) TABLE-US-00005 No Notches - No Notches - 25 mm 11 mm Feature FIG. 4 Edge Width Edge Width Thickness t 3-4 mm 3-4 mm Edge Width (W) D + f 25 mm 11 mm Solid Width f 25 mm 11 mm Ultimate Belt 4 - Edge 2 - Edge Failure Mode Compounding Compounding Belt Life Average 15 hours 20 hours

(32) Extensive work has been conducted to determine the optimum notch geometry. In all cases notched edge belts operated significantly longer than straight edge belts, and prevented edge compounding leading to premature belt failure. It should be appreciate that after many hours of operation the belt edge can wear, reducing the notch depth and length. As a result, the geometry of the belt notches can change with time. Therefore, the dimensions provided in the examples are not intended to represent all possible notch dimensions, and that other notch dimensions are possible and are within the scope of the invention.

(33) One newly observed mode of separator belt failure when operating a BSS with a notched edge belt is notch tearing. For notches with a large open area, a narrow, longitudinal strand (f) is created between the inside edge of the notch and first hole opening in the body of the belt. During operation, the edge 49 of the belt is rubbing against either the compacted, abrasive powder that has accumulated on the unswept edges of the separation chamber, or the edges of the separation chamber itself. The edge of the belt rubbing at high velocity creates a shear stress, which stress if it exceeds the yield stress of the narrow longitudinal strand (f) between the inside of the notch and the first hole opening in the body of the belt, will cause the narrow, longitudinal strand (f) to stretch and break. This breaking of the narrow longitudinal strand is facilitated by the flex fatigue of the plastic at the narrowest joint between the notch and the adjacent hole as it is repeatedly flexed up to six times per second as it moves through the tensioning and drive system. The broken longitudinal strand (f) can create catch point for the belt on its edge, which will lead to premature belt failure. The tensile strength of the strand can be increased by increasing the thickness (t) of the strand. An alternative solution is to eliminate the narrow strand by omitting or creating a blank (illustrated in FIG. 5A) of the first hole in the body of the belt nearest to the edge notch.

(34) Having thus described certain embodiments of a continuous belt, method of making the same, a separation system using such belt, and a method of separation, various alterations, modifications and improvements will be apparent to those of ordinary skill in the art. Such alterations, variations and improvements are intended to be within the spirit and scope of the application. Accordingly, the foregoing description is by way of example and is not intended to be limiting. The application is limited only as defined in the following claims and the equivalents thereto.