AU640318B2 - Apparatus of the bend type - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 DMPLETE SPECIFICATION DR A STANDARD PATENT (Original) 1 Name of Applicant/Nominated Person: Electric Power Research Institute, Inc.

Actual Inventor(s): Address for Service: Robert G. Moorhead DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

U Invention Title: "Apparatus of the bend type" Details of Associated Provisional Application(s): No(s): The following statement is a full description of this invention, including the best method of performing it known to us: -1 92085,kayspe.i,befl-ltpe.divI la This application relates generally to the construction and mode of operation of apparatus of the bend type. It has application for the separation and sizing of solid particles dispersed in a liquid medium as a slurry. Particularly it pertains to such apparatus and methods that are applicable to the coal and mineral industry to produce two products, one comprising fine particles and the other coarse particles complying with size and quality specifications.

BACKGROUYND

Various types of separating apparatus, such as sieve bends, and methods have **.been used for the separation of fine solid particles from a liquid medium in which they are dispersed. For example, the coal industry makes use of sieve bends for the treatment of coal slurry. Particular reference may be made to simple sieve racks, hydrocyclones, sieve bends and other types of apparatus making use of hydraulic separation. For the purpose of producing products :which comply with size specifications, special techniques have been employed, such as the use of heavy or magnetic particles intermixed with the particles being subjected to separation. Such apparatus and method-, have objectionable features, having reference particularly to difficuity in meeting specifications requiring a particular particle size. Furthermore, they are unable to deal as desired with the problem of sulphur or clay which when present is attached to some of the particles, particularly the larger ones. In general, it may be said that the coal ind1ustry is in need of simple apparatus and methods which will make it possible to produce a product consisting of fine coal particles which comply with size specifications and contaminants such as sulphur.

SIUMMARIY OF TH4E !NVENTION According to a first aspect of the present invention there is provided an apparatus of the bend type for separating solid particles from a liquid medium, 920805,kayspe,00 1,bend"Apvd, 1 4 I -2comprising a structure forming a passage having an inlet end and a dischargc.

end, the structure forming the passage having a configuration such that a -sibs-tantia1 -length of the passage is arcuate, and an arcuately curved sieve disposed to receive flow from the discharge end of the passage, said sieve extending from a point between the inlet and discharge ends of the passage to a point beyond the discharge end, with a portion of the sieve being unused and being positioned behind the arcuate portion of the passage and out of the path of the flow, the sieve being adjustable to move the unused portion of the sieve incrementally out from behind the passage and into the path of the flow and thereby incrementally expose new areas of the sieve to the flow.

According to a second aspect of the present invention there is provided a bend structure defining a cured passage having an inlet end and a discharge end, a sieve screen mounted on the bend structure for receiving flow from the discharge end of the curved passage, and means for adjusting the position of the sieve screen relative to the discharge end to incrementally expose new areas of the sieve screen to the flow discharging from the passage.

According to a third aspect of the present invention there is provided a bend structure defining a curved passage having an inlet end and a discharge end, a throat of decreasing cross-sectional. area at the discharge end, means for varying the cross-sectional area of the throat, a sieve screen mounted on the bend structure for receiving flow through the throat from the discharge end of the curved passage, and means for adjusting the position of the sieve screen relative to the discharge end to incrementally expose new areas of the sieve screen to the flow discharging from the passage.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:- Figure 1 is a cross-sectional view of one embodiment of a sieve bend headbox incorporating the invention.

9MAS0,kayspe.00 "dtyp.div,2 t.

-3- Figure 2 is a cross-sectional view of a sieve bend which is provided with means for adjusting the exposed area of the sieve rack.

Figure 3 is a cross-sectional view like Figure 2 but showing the sieve rack in a different operating position.

Figure 4 is a cross-sectional view showing another embodiment of the apparatus.

Figure 5 is a schematic detail showing sieve bars such as are suitable for use with the invention.

Figure 6 is a cross-sectional view of another embodiment of a sieve bend incorporating the invention.

Figure 7 is a cross-sectional view of a portion of a sieve rack for use in a sieve bend incorporating the invention.

Figure 8 shows automatic control means for the adjustable throat in the embodiment of Figure 6.

Figure 9 is a fragmentary front elevational view of the embodiment of Figure 6.

Figure 10 is a cross-sectional detail showing the relationship between the throat, the pivoted plate and the control flap in the embodiment of Figure 6.

The embodiment of the invention illustrated in Figure 1 consists of a headbox which has its upper inlet end connected to the slurry supply conduit 11. As it appears in cross section, the headbox provides a flow passage 12 and has a throat 13 at its lower end. The side walls are laterally spaced apart (as for example, to provide a lateral dimension of between 24 and 72 inches). In 920805,kayspe.01,bendtype.div,3 normal operation, slurry or like feed material is supplied by suitable pumping or gravity flow means to the conduit 11 and sufficient slurry is introduced into the headbox to maintain a level somewhat below the level of ths,- overflow opening. The headbox: is so constructed that the passage way 12 is of gradually reduced cross sectional flow area for its lower portion. The upper portion of the headbox is shown provided with a shelf or shoulder 14, which may be shown provided with a wear resistant facing 16 of resilie t material, such as synthetic or natural rubber. Similar linings 17 and 18 may be provided for the outer and inner walls 19 and 21.

The throat 13 may be attached to or a part of the lower portion of the *...headbox. The outer convex side of the passage way 22 is defined by the fixed wall 24, and the inner side by the plate 26. A pivot 27 serves to attach the upper edge of the plate 26 with a fixed portion of the headbox, as for example, the lower edge of the headbox as shown in Figure L. Thus, the plate 26 may 5. swing between the position shown in Figure 1 and the position illustrated by dotted lines. Overlying the plate 26, there is a sheet 28 which has its upper margin secured to the lower margin of the wall 21 and its lateral margins secured to the side walls 47 to form a water-tight seal between these three margins of sheet 28 and the fixed walls of the box, 47 and 21. The lower portion extends downwardly beyond the lower end of the sheet 26 to form. a nip flap 29. This sheet likewise is made of suitable resilient material such as natural or synthetic rubber. The plate 26 is attached to means which serves to adjust its position during operation of the sieve bend. The means employed for this purpose shown in Figure 1 consists of a metal strip 31 which functions as a spring when bent laterally. A membfer 32 is pivotally attached to the lower portion of the plate 26, and its other end is secured to the member 33, which in turn is secured to the lower end of the spring strip 31. The upper end of the spring strip is shown secured to member 34 which is a part of the member 36. Both members 34 and 36 have a pivotal connection 37 with the supporting bracket 38. The arrangemvent described above makes possible movements of the plate 26 in one direction or the other and against the spring 920805,ayspe.OO01,bendrjpe-div,4 action of the strip 31.

Manually adjusting means is also provided for plate 26. Thus the wall 21 is provided with a threaded rod 41 which has its upper end attached to the bracket 42. A nut that is a part of the handwheel 43 is threaded upon the rod 41. When the handwheel is turned the member 36 moves relative to the member 42 to bend the spring strip 31 in one direction or the other. However, hydraulic, electric or pneumatic operators may also be used to make these manual adjustments. The outer wall 24 of the throat is terminated at its lower end at a level above the level of the lower end of wall 47. A sieve assembly 48 or sieve rack is schematically illustrated and has its upper portion attached to the lower end of wall 24. The arrangement and the dimensions are such that the nip flap 29 extends for a substantial distance 1-1/2 to 3 inches) alongside the sieve.

A suitable sieve screen assembly may have bars substantially as illustrated in Figure 5. In this instance, the bars are triangular shaped as viewed in cross section, and are connected together to form a sieve rack assembly. The slurry flow is directed across the end faces of the bars substantially as indicated by the arrows in Figure 5. The smaller solid particles of material are of a size that they pass through the slots between the bars. The larger particles which cannot pass through the slots, continue flowing over the sieve bars. In normal operation, a sieve of this character has what is termed a slicing action, and as the slurry passes over the bars, thin slices are removed with the smaller particles passing through the slots between the bars. Wear through usage erodes the surfaces exposed to the flow and can gradually reduce the separating size overtime as each bar slices a tLin"e- section of slurry and diverts it into the slot. Schematic Figure 5 indisztes a slice of the slurry flow being diverted through the slot and also the width of the slot. The separation is made by the thickness of the slurry slices diverted by the bars.

The method of operation of a sieve bend constructed as described above, is as 92M85SXkayspe.001,bendtype.div,5 -6follows: a slurry containing solid particles, some larger than the smaller particles which cannot pass through the slots of the sieve, is delivered into the upper part of the headbox which supplies the slurry through the throat and over the sieve rack. Adjustment of the slurry level within the upper part of the headbox serves to control the velocity of the slurry as it exits the throat and enters upon the sieve. The outer side of the flow through the throat is defined by the wall 24. Plate 26 forms the inner wall for the throat. Due to the arcuate shaping of the headbox and the flow passage through the same, some centrifugal force is developed which tends to urge the slurry against the wall 19 and the outer wall 24 of the throat. Minor changes in flow velocity of slurry through the throat, and through the flow passage between the outer wall 24 and the plate 26 are compensated for by compensating movements of the plate as permitted by the yieldable means formed by the spring 31. Such coimpensating adjustments occur automatically. The nip flap 29 plays a part in 15 this automatic compensation. The rapid flow of slurry past and in contact with the flap serves to create a reduction in pressure at the interface of the flap and the slurry which serves to cause the flap to press against the flow by atmospheric pressure. This pressure upon the flow is deemed to aid in assuring that the slurry immediately contacts the screen, thus making possible increased operating capacity.

Aside from the automatic or dynamic compensation described above, the apparatus provides a manual adjustment. Thus by turning the wheel 43, the spring strip 31 can be flexed to apply increased force against the plate 26, or to permit the plate to be retracted. Such adjustments may be desirable when there is a substantial change in the character of the slurry or its rate of delivery to the headbox, which results in a substantial change in the velocity of slurry past the nip flap.

The embodiment of the invention shown in Figure 2 makes use of a sieve rack which is adjustably mounted upon the bend structure. The bend structure 51 in this instance is indicated schematically and is presumed to have the same 92005,kayspe.1,bendtype.dv,6 -7control means as in Figure 1. Portion 52 is presumed to be the throat of the bend and the control means for the throat is shown schematically at 53. The sieve rack 54 consists of a frame which serves to mount the bars of the sieve 56. This assembly is arcuate as illustrated, and its upper portion is carried by and conforms with the curvature of the bend struc The mounting is such that, when desired, the position of the sieve rack upon the sieve structure may be changed to incrementally expose a new area of the sieve to the flux discharging from the bend as needed to counteract the change in performance resulting from the gradual dulling of the exposed bars caused by particle abrasion. In other words, the sieve rack may ultimately be shifted to a position shown in Figure 3 which exposes all of the sieve to the flow from the throat, :**seawhereby the unused portion of the sieve as illustrated in Figure 2 is now exposed for use.

15 After the sizing performance of the apparatus eventually deteriorates below an acceptable level when in the position shown in Figure 3, the sieve frame and screen must be turned. This is accomplished by rotating the screen frame until completely free of the headbox, spinning it 180 degrees on the screen's centre radius and reinserting the previous discharge end behind the headbox, to the position shown in Figure 2. This operation essentially restores the original performance of the device and positions the screen to permit the screen exposure cycle to be repeated.

The means in this instance for shifting the position of the sieve rack consists of a member 57, which together with the walls 58 serve to carry the curved sieve rack. For automatic or remote operation, an operator 59 which may be motivated either pneumatically, hydraulically, or electrically, is pivotally connected to member 57, and is carried by the structural member 61. The lower end of the structure is provided with means for collecting the finer particles which pass through the slots of the sieve bars, and the oversized material. Thus, the fine particles are collected in the hopper 62, and the larger sized particles are removed by pan 63 and deposited in receptacle 64.

92085,kayspe.001,befldqwp.&i,7 p -8- Occasionally shifting of the sieve rack may be carried out from a remote station 65 which is indicated as having controlling connection with the operator 59. For example, assuming that the operator 9 is hydraulically operated, application or discharge of fluid from the operator may be controlled from the station 65. Figure 3 is similar to Figure 2 except that it shows the sieve rack shifted to a position where substantially all of the sieve is being supplied with slurry from the bend.

In the embodiments described above, it is desirable to provide means for applying a tapping action to the sieve. Thus as illustrated in Figure 2 and 3, a device 66 which may be pneumatically operated, is attached to member 67 which is in close proximity with sieve screen. Continuous or occasional operation of the device 66 serves to apply tapping action to the sieve bars thus 'aiding in dislodging any accumulation of material in the screen apertures which "to# *15 otherwise might cause clogging and interfere with efficient operation.

Figure 4 illustrates a modified sieve assembly for a sieve bend. This design embodies previous headbox throat features but instead of the sieve screen exposure being variable, this design has a fixed screen. Thus in this instance, vertical and inclined walls 71 and 72 define the lower part of the throat and extend upwards to the height necessary to achieve the desired static head.

The control plate 73 extends from the lower edge of the inclined walls 72 and is provided with a facing 76 of resilient material. The lower portion 77 of this 71 b %*to facing forms a nip flap. It overlaps the upper portion of the sieve. The adjusting means associated with the plate 73 includes a threaded rod 78 which is pivotally connected at 79 with the wall 72. The handwheel and nut 81 has threaded engagement with the rod 78 and the lower end of the rod is connected with the member 82. The upper end of plate 73 is pivotally connected by pivot 83 with a fixed member of the bend structure. Plate 73 is fixed with respect to member 82 and is pivotally connected at 83 with the structure of the bend. A helical spring 84 is positioned between member 82 and the nut of the handwheel 81. Thus during the course of automatic control, 920805Xkayspe.0o1,ber'dtype.div,8 -9the helical spring 84 provides yieldable means serving to urge the plate 73 toward the right as viewed in Figure 4. However, the thrust of spring 83 can be adjusted by manually turning the handwheel 81. A remote system may also be used to control this manual adjustment as well.

Also included in the modified sieve assembly shown in Figure 4 is a detail that permits adjusting the alignment of the fixed sieve screen 90 tangent to wall 71.

This is accomplished by providing flange 85 on the back of _d 71 and an inverted complementary flange 87 on the screen frame which holds the sieve scr-n. Flange 85 is fastened to flange 87 using machine bolts 88 placed in slotted holes 89. When the screen face 90 is tangent with wall 71, the machine bolts 88 are tightened, compressing the foam seal strip 91 between the upper edge of the screen 86 and the bottom edge of wall 71 and flange 89, and making a sl'3"r tight seal that prohibits large particles in the feed slurry from leaking through the joint and contaminating the undersized particle flow.

The embodiment of the invention illustrated in Figure 6 consists of a headbox 110 which has its upper inlet end communicating with the feed box 111. As it appears in cross section, the headbox provides a flow passage 112 which terminates in a throat 113 at its lower end. The width of the passage 112 is shown in Figure 8. In normal operation, slurry or like feed material is supplied by separate pumping means to the feed box 111 and sufficient slurry is introduced to maintain a level corresponding to the level of the upper edge of the spillover tank 113. Feed slurry in tank 113 is withdrawn through a hose 114 which may be connected to the lower end of the tank 113. The equipment is so constructed that the lower portion of the passageway 112 is of a gradually reduced cross-sectional flow area formed by the throat 114. The throat (Figure 7) is tapered and the sidewall 116 is concave as viewed from the exterior. The throat extends the entire width of the device and may be in sections as shown in Figure 9.

The wall 114 of the throat which appears to be concave from the exterior, is a 92M85,kayspe.0G1,bendtype.div,9 10 plate 116 attached at its upper end to the lower part of the feed box by the hinge or nivotai connection 117. The plate 116 is shown covered on its inner surface with a liner 117 of rubber or other resilient material. The lower part of the resilient material is shown extending from the plate to form a flexible flap 118. It is believed that this flap plays an important part in automatic control. Additional elements of the automatic control includes a tube 1 19 which extends for the width of each plate, and is secured to one end of an operating arm 121. T1he free end of this arm is attached to the rod 122, which extends through the stationary member 123 of the machine frame. A helical spring 124 is shown surrounding member 126 and is seated at one end on the frame member 124. The other end is seated upon a nut 126, which can be turned by hand. When the plate 114 is in a normal position for the average flow of feed material through the throat, the spring 124 is partially compressed.

However, variations through the throat will cause the plate to be moved from one position to another, as permitted by spring 124.

Referring to Figures 6 and 7, a sieve assembly 127 is incorporated in the :separator. It is carried by the sieve box 128 and its shape corresponds to the section of a cylinder. It extends tt~e entire width of the separator and it may be termned as corresponding to a bowl. A sieve of the type indicated consists of spaced bars or wires which extend across the assembly, and are attached to suitable means at their ends. As shown in Figure 7, normally each wire diverts layer of slurry through the preceding aperture. Figure 6 shows the cross secti?n of the rods or wires when they are relatively new. At that time the slot between the rods is relatively precise and determines the size of the slurry which passes through the slot. When a rack has had extensive use, a leading edge of a bar will 10 no longer be sharp but will be somewhat rounded.

When the flow has been excessive, the wire profile is worn to the point that the slurry essentially passes over the slot. As discussed above in connection with the embodiment of Figures 2-3, after one portion of the sieve assembly has been directly subjected to the discharge from, the throat, the screen assembly can be moved to present a new part to the discharging slurry, while 92M8O,kzys 1 3e.00,bendtyp.&i,10 I I 11 thrc major screening operation is taking place. This is also accomplished by the arrangement shown in Figure 6. The sieve assembly box shown in Figure 6 is so mounted that it can be moved to present different portions of the sieve assembly to the flow from the throat. As shown particularly in Figare 6, the sieve assembly is carried by a curved plate 129 which is fixed to the screen box.

For the position shown, the slurry from the throat does not impinge upon ';he upper end portion of the sieve assembly. However, it does function for the int"- portion of the sieve screen. When it is desired to move that portion or ,xeen assembly to receive the discharging slurry, the screen box, together with the screen assembly, is rotated a given amount, which directly e,,-,poses another portion of the screen assembly to the discharging slurry. To permit such movements, the screen box is carried by the bearing 131 at the extremity of the hinged member 132 of the framework.

A preferred feature of the invention is that operation of the apparatus and particularly flow of slurry through the throat may continue while such adjustments are being made. An example of the invention is as follows: The bend was constructed with a throat substantially as shown in Figure 1 or Figure 6. The feed slurry was one such as produced in the coal industry comprised 5.8% of solid particles dispersed in water. The concentration of solids in the slurry was 2.5% of total coal particles ranging in size from smaller particles about 0.006 to 0.G004 inches in diameter to large solids ranging from 0.02 to 0.006 inches in diameter. The particles also included about 35.7% of a clay associated mainly with the smaller particles. About 711 gallons of such slurry were pumped through a 2-foot wide, two-stage sieve bend system with plate 73 being adjusted to hold 30 inch static head and appeared to give best performance and capacity. Of the two fractions discharged, the product comprised solids concentrated in a range in size from 0.02 to O.u0 6 inches in diameter, with about 0.7 to 0.8% of clay particles. The other fraction ranged in size fAo about 0.006 to 0.0004 inches in diameter and contained about 58% of clay particles.

920805,kayspe.001,befldtypC.div, 11 I I I -12- In the above example, the sieve had a capacity of 365 gallons per minute of slurry per foot of width. In contrast, typical sieve bends being used in the coal industry function at a capacity of only about 100 gallons per minute per foot of width. Tests with the invention indicate capacity advantages of about three times 'he conventional sieve bends currently being used in the coal industry.

Various additional elements of the apparatus may be used in conjunction with the screening operation. Pneumatic, electrical or hydraulic tapping devices 141 may be used and mounted upon one wall of the screen box. An operating rod connects with device 141 which vibrates the sieve assembly. The sieve box is shown supported by cable 143 which extends over the sheave 144. By playing out this cable, the screen box may be adjusted to various positions. A structure below the apparatus provides conduits which remove the coarse and fine screen particles.

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o 920805,kayspe.001,benipc.dvJ 2

Claims (4)

1. Apparatus of the bend type for separating solid particles from a liquid medium, comprising a structure forming a passage having an inlet end and a discharge end, the structure forming the passage having a configuration such that a substantial length of the passage is arcuate, and an arcuately curved sieve disposed to receive flow from the discharge end of the passage, said sieve extending from a point between the inlet and discharge ends of the passage to a point beyond the discharge end, with a portion of the sieve being unused and being positioned behind the arcuate portion of the passage and out of the path of the flow, the sieve being adjustable to move the unused portion of the sieve incrementally out from behind the passage and into the path of the flow and thereby incrementally expose new areas of the sieve to the flow.

2. A bend structure defining a curved passage having an inlet end and a discharge end, a sieve screen mounted on the bend structure for receiving flow from the discharge end of thec curved passage, and means for adjusting the

7..:position of the sieve screen relative to the discharge end to incrementally expose new areas of the sieve screen to the flow discharging from the passage. 3. A bend structure according to claim 2 wherein the passage and the sieve screen are arcuately curved and disposed concentrically of each other, with the sieve screen being partially disposed behind the passage and being rotatable about the centre of curvature of the pasage to incrementally move new areas of the screen out from behind the passage and into the path of the flow. 4. A bend structure according to claim 3 further including means permitting the sieve screen to be rotated 180 0 about an axis generally perpendicular to the flow so that the flow can impinge upon the screen from either of two opposite directions. 9208O5,kary.,pe.O1,bndtypc.div.13 I

14- A bend structure defining a curved passage having an inlet end and a discharge end, a throat of decreasing cross-sectional area at the discharge end, means for varying the cross-sectional area of the throat, a sieve screen mounted on the bend structure for receiving flow through the throat from the discharge end of the curved passage, and means for adjusting the position of the sieve screen relative to the discharge end to incrementally expose new areas of the sieve screen to the flow discharging from the passage. 6. A bend structure according to claim 5 wherein the throat includes a movable plate which forms one wall thereof, and the means for varying the cross-sectional area of the throat includes means for adjusting the position of the plate. 7. A bend structure according to claim 5 wherein the passage and the sieve screen are arcuately curved and disposed concentrically of each other, with a portion of the sieve screen being positioned behind the passage and the .ieve being rotatable about the centre of curvature of the passage to move the S. sieve out from behind the passage in an incremental manner and to thereby incrementally expose the new areas of the screen. 8. A bend structure according to claim 5 further including means permitting the sieve screen to be rotated 180 about an axis generally perpendicular to the flow so that the flow can impinge upon the screen from either of two opposite directions. An apparatus and/or a bend structure substantially as hereinbefore described with reference to the accompanying drawings. 92080o,kayspe.001,beadtype.div,14 15 DATED this 5th day of August 1992 Electric Power Research Institute, Inc. By Its Faterit Attorneys DAVIES COLLISON CAVE S S S S. S S S. 5555 S S. S S S S S 55 .5.5 S S 5* S* S .55. S *5*S 55 SSSS S SSSS 920805,kayspe.00 1,bend"A~iv,