IE73241B1 - Screening apparatus - Google Patents

Description

SCREENING APPARATUS This invention relates to the screening of granular materials. In particular, the invention is directed to the screening of peat for separation of unwanted substances. The invention is especially directed to the separation of potentially deleterious particles from peat supplies for power generation.

The use of peat for power generation has been practised for a considerable number of years. A continuing problem has however been the separation of unwanted or potentially deleterious material from the peat supply. A diversity of techniques and equipment have been developed to deal with this problem. The present invention is directed to improved apparatus for such separation and screening, but also embraces the screening of other materials having like characteristics.

U.S. Patent Specification No. 2,743,813 describes an apparatus for separating coarse material from a finer material in which particle separation is accomplished by means of a set of - 2 rotatable transverse bars, each having an elliptical cross-section with the major axes of alternate bars displaced by 90°, so that, when the bars are rotated in unison, the predetermined space between bars remains constant. As the bars rotate, fine materials pass between the spaces between bars, and materials too large to pass these spaces travel longitudinally across the bars and are discharged over the end of the last bar. According to an optional feature, the bars are provided with spaced peripheral ribs to prevent large but thin particles from going through the bed. These ribs are aligned with the ribs of each adjacent bar along the length of the bed, in other words, in the direction at rightangles to the axes of the bars. The apparatus is particularly directed to the separation of oversize particles from mine run ores.

An improvement in this apparatus is disclosed in British Patent Specification No. 991,864. According to this British Patent, the rollers of the bed of parallel rollers of generally elliptical cross-section have themselves elliptical ribs extending beyond their bodies, the spacing between adjacent ribs on a roller being substantially equal to, or less than, the spacing between the bodies of successive rollers along the entire length of the bed. Again, these ribs are aligned with the ribs of adjacent rollers along the length of the bed. Again also, the apparatus of GB 991,864 is directed to the separation of oversize materials from small size materials which fall or flow through the spaces between the rollers.

The known screening apparatus provided by the above-identified patent specifications is directed to the handling of ores and like materials. It is an object of the present invention to provide screening apparatus especially suited to the treatment of granulatable materials, in particular, peat.

According to the invention, there is provided screening apparatus for separating unwanted matter from a granulatable r 35 material comprising: - 3 (a) feed means for material to be screened, (b) a screen deck comprising a plurality of driven, rotatably-mounted, axially elongate rollers of substantially elliptical cross-section, the rollers defining a substantially planar array in which the axes of rotation of the rollers are spaced apart so that a clearance is maintained between the substantially elliptical surface of each roller and the corresponding surface of the or each adjacent roller throughout rotation of the rollers, the rollers of said substantially planar array being driveably interconnected so that the major axis of each said roller is aligned at right angles to the major axis of the or each adjacent said roller of said substantially planar array for all rotational dispositions of the rollers, and each said roller having a plurality of fins extending radially and at right angles to its axis of rotation, each fin being substantially circumferentially continuous and the periphery of each fin substantially defining an ellipse uniformly spaced radially outward of the substantially elliptical surface of the roller, (c) collection means for screened material, and (d) discharge means for unwanted matter separated by said screen deck, wherein: (i) the fins of alternate rollers are axially displaced relative to the fins of the or each adjacent roller, and (ii) the fins of successive rollers are interleaved to overlap one another in end view, at least when the major axes of alternate rollers are aligned in or parallel to the plane of said substantially planar array.

In a favoured embodiment, said plurality of fins comprises an array of equally spaced fins along the axial length of the roller. The peripheral edge portion of each fin of each alternate roller is suitably in proximity to the roller surface of the or each adjacent roller at least when the major axes of said alternate rollers are aligned in or parallel to the plane of said substantially planar array.

Said feed means may comprise a conveyor for delivery of - 4 material to be screened to an input end of the screen deck. Said collection means for screened material suitably comprises a collection hopper located substantially beneath the screen deck for receiving screened material falling through the deck.

In a specific construction, said collection means for screened material may optionally further comprise an extension conveyor extending from beneath the screen deck at a location remote from an input end of the screen deck, for return to said collection hopper of screened material falling through the screen deck at least in the region of said location. Said extension conveyor is suitably a chain conveyor. It will be appreciated that the necessity for such a further conveyor may be a function of the constructional and dimensional parameters of any particular installation.

Said discharge means for unwanted matter suitably consists of a chute extending from a location underlying the end of said screen deck remote from an input end of the deck.

The or each of said screen deck and discharge means for unwanted or waste material separated by said screen deck is preferably powered by a respective hydraulic drive, and said hydraulic drive for the screen deck suitably comprises an anti-fouling feature for automatic clearing of any blockage on the screen deck. Fouling of the rotating rollers is sensed by the drive system and the rotation of the roller drive shafts is reversed for a predetermined number of cycles. If the fouling is not cleared by this procedure, the machine is automatically withdrawn from the line, following which it again carries out a defouling cycle. If fouling is now cleared, the screen returns to the line. Otherwise it signals a fault condition and remains withdrawn from the line. At least one of said rollers at the feed end of the screen deck is suitably raised relative to the substantially planar array defined by the remainder of the rollers to prevent discharge at the input end of debris during a clearing operation in which roller drive is reversed. - 5 An embodiment of the invention will now be described having regard to the accompanying drawings, in which: Figure 1 is a pictorial diagrammatic representation of peat screening apparatus according to the invention, Figure 2 is a diagrammatic side view of the apparatus of the invention, Figure 3 is a part cutaway detail side view of the screen deck.roller arrangement in apparatus according to the invention, Figure 4 is an end view, part cutaway, of the arrangement of Figure 3, Figure 5 is a substantially idealised, diagrammatic top view of three of the rollers of the screen deck of Figures 3 and 4, showing blade interleaving, Figure 6 is a diagrammatic side view of elliptical rollers of the screen deck array of the apparatus of the invention, with the major axes of every second roller aligned in the general plane of the array, Figure 7 shows the rollers of Figure 6 in a part rotated disposition, Figure 8 is a top view of an optional chain conveyor for use in collection of waste material in an installation according to the invention, and Figure 9 is a schematic hydraulic diagram of drive arrangements in a system according to the invention.

As shown in Figures 1 and 2, apparatus according to the - 6 invention for separating waste material or unwanted matter from a granular material is designated by reference 1. As shown in these drawings, the apparatus of the invention is directed to the screening of peat for use as fuel in a power station. The apparatus thus includes peat feed means 2 in the form of a rising conveyor 11, a screen deck 3 onto which the peat delivered by the rising conveyor 11 falls at an input or feed end, screened peat collection means 4 consisting of a hopper 25 underlying the screen deck 3 and a discharge or collection conveyor 26, and a waste material discharge means 5. The peat feed means 2 consists of the rising conveyor 11 defined such as by a belt carried round a conveyor roller 12 at an upper end, roller 12 being mounted for rotation on a support frame 13. The screen deck 3 of the apparatus is mounted within an enclosure 21. As shown in Figure 2, the enclosure 21 has a pivot mounting 22 and the angle of inclination of the enclosure 21 together with the screen deck 3 may be altered by means of a hoist 23, the hoist effecting pivoting of enclosure 21 about its mounting axis 22. The collection means 4 for the screened peat is defined by the collection hopper 25 underlying the screen deck 3 and a collection conveyor 26 disposed in the lower region of the hopper 25 for advance of the screened peat to a location of storage or use. The collection means for screened peat also further comprises a conveyor 28 located at the rising or higher end of the enclosure 21, which collects screened material falling through the screen deck in the region of its discharge end (downstream end) for return to hopper 25 from that portion of the screen deck located forward or downstream of the hopper. It will be appreciated that the need for such a return conveyor is dependent upon the physical dimensions and parameters of operation of the installation, and that in an alternative configuration, the necessity for conveyor 28 may be avoided by appropriately structuring the hopper 25 so that it underlies the full length of deck 3. The requirement for conveyor 28 arises in the instance illustrated only by virtue of the length of screen deck 3 exceeding the span of the mouth of hopper 25. Since the screen deck length dimension must be sufficient to enable the required screening - 7 action to be fully effected, an additional screened material return conveyor is then required where this minimum dimension cannot be matched to the hopper size. The necessity or otherwise for the conveyor 28 is thus determined by the installation into which the screen of the invention is to be fitted. Retrofit of a screen deck according to the invention into an existing peat handling plant may necessitate an extension conveyor 28, but such a facility would not necessarily be required in a newly constructed plant.

The screen deck will now be further described having regard to Figures 3 to 7. The deck is defined by a set of elliptical rollers 31, each mounted in a frame 41 for rotation about a respective axis of rotation 32. The axes of rotation 32 are disposed transverse to the direction of advance of the product to be screened to thus define a roller array, the rollers 31 being driven for advance of product to be screened from right to left in the representations of Figures 1, 2 and 3, i.e. from the input or feed end of deck 3 to the unwanted matter discharge or downstream end of the apparatus. Each roller 31 is of elliptical cross-section and has a major axis 33. The rollers 31 are mounted in the frame in the manner depicted in Figures 3 and 6, so that when the major axis of every second ellipse is substantially horizontal, the major axis of each intermediate ellipse is vertical. The rollers are maintained in this same relative orientation so far as their major axes are concerned at all rotational dispositions by means of a drive arrangement to be described. The axes of rotation 32 of the rollers 31 are spaced apart along the length of the frame 41 so that in this orientation of the rollers, a space is defined between the outer elliptical peripheral surfaces 43 of adjacent rollers. The periphery of each elliptical roller 31 is also provided with a series of substantially elliptical fins or blades 34, formed from an abrasion-resistant steel, equally spaced at transverse intervals across the width of the roller, as shown in Figure 4. The blades 34 of alternate rollers 31 are laterally displaced with respect to one another, so that the blades of each successive pair of rollers 31 - 8 along the array are interleaved or interdigitated, i.e. they overlap one another in side view at least during a part of roller rotation, as can be seen in the representations of Figures 5 and 7. Figure 5 is a highly diagrammatic top view of three of the rollers 31 of the screen deck of Figures 3 and 4, showing the manner of interleaving of the blades or fins 34. Figure 7 is a similarly diagrammatic end view of this blade interleaving.

Each roller is mounted on a drive shaft 35, held at each end in bearings 36 and provided with a sprocket wheel 37 at one end for drive by means of a drive chain 38. A single drive motor, also mounted on the deck frame 41, drives the entire array of rollers 31 in unison. Thus the relative angular orientation of the major axes 33 of successive rollers 31 is preserved at all times during roller rotary drive, as previously adverted to above.

This screening arrangement is especially effective in separating deleterious particles from peat supplies for power generation. The parallel elliptical shafts or rollers 31 are bearing-mounted between heavy steel frame members 41 to form the base of a hopper, defined by enclosure 21, to which peat to be screened is delivered by the rising conveyor 11. The elliptical shafts 31 are pre-set in the alternate vertical and horizontal dispositions shown in Figure 6 and are rotated, all in the same direction, by the enclosed roller chain drive system 38 mounted on one side of the machine, as described above. Particle sizing for the screened material is determined by a combination of the pre-set spacing of the shafts along the frame 41 and the array of equally-spaced elliptical pattern abrasion-resistant steel blades 34 mounted in alternate positions across the width of the shafts 31. In other words, the fins or blades 34 of alternate elliptical rollers 31 along the length of the array in the direction of feed or advance are displaced to one side with respect to those of the or each adjacent roller or shaft 31, so that the fins 34 overlap or intermesh in side view, as shown in Figures 4 and 5, to thereby effect a macerating or fragmenting - 9 action on the material being screened. As the shafts 31 rotate, they also impart a rocking/tumbling motion to the material being screened, as indicated diagrammatically in the representation of Figure 7, which moves debris and other large particles towards the discharge chute end 42 of the deck, while the screened materials drop through the deck 3 into the peat collection hopper 25. The inclined mounting of the enclosure 21 and screen deck 3 improves screening efficiency, and the degree of inclination or tilt may be adjusted for maximum efficiency.

A further feature of the screen deck is shown in Figures 1, and 3, in the form of a cranked-up input end portion 44 of the screen deck frame 41. This end portion is inclined upwardly at an angle of substantially 45° with respect to the general plane of the screen deck. A single elliptical roller 45 is mounted in this upwardly inclined frame portion 44 for rotational drive and cooperation with the endmost roller of the planar array at this input end, in the same manner as prevails between the successive rollers of the planar array itself. However, the raised disposition of this roller or bladed shaft 45 compared with the remainder of the rollers ensures that when the screen deck is operated in a defouling mode, to be described, in which forward drive of the rollers is reversed, unwanted material does not fall from the screen deck at the input end into the screened material receiving hopper 25. In other words, the raised roller 45 forms a barrier at the input end against return of unwanted material during reverse drive of the screen deck.

The downstream end screened material collection arrangement comprised by conveyor 28 is shown in Figure 8. Reference may also be made to Figures 1 and 2. Recovery of screened material falling though deck 3 at this downstream end is provided for by a chain conveyor 51 , extending from beneath the waste material discharge end 42 of the screen deck to a discharge end overlying hopper 25. Chain conveyor 51 has idler rollers 52, 52a, one set at each end, and a drive sprocket arrangement 53 intermediate the idler rollers for - 10 advance of the chain. Roller 52a overlies hopper 25, i.e. is located at the discharge end of the screened material return conveyor. The chain is driven by further hydraulic motor 54, mounted on a conveyor support frame 55. As previously recited, the necessity or otherwise for this return conveyor is a function of the relative longitudinal dimensions of the screen deck and those of the mouth of the hopper. In a situation such as that illustrated in the drawings where the length of the screen deck exceeds the span of the mouth of the hopper, the return conveyor 28 is required to collect material falling through the screen in the region of the screen not located over the mouth of the hopper. It will be appreciated that in an alternative installation, other screened material collection arrangements may be provided, and in particular the gravity collection of all material falling through the screen deck may be provided for, without any necessity for an additional return conveyor such as item 28 of the present configuration.

Finally, unwanted material or debris, which is advanced forwardly along the screen deck by the action of the elliptical rollers, falls from the downstream or output end 42 of the screen deck for discharge and removal by way of chute 29.

A hydraulic drive and control system especially suited to the apparatus of the invention is shown in Figure 9. Hydraulic fluid is drawn from a tank 61 by a pump 62 for screen deck drive. Pressurised hydraulic fluid passes through a valve manifold block 63, containing a pressure relief valve 64, a controllable direction valve 65 and an automatic direction control valve 66. From the manifold block 63, the hydraulic fluid is directed to a hydraulic motor 67, which drives the elliptical rollers of 31 the screen deck 3. An automatic reversing feature is provided by hydraulic cylinder and piston device 68.

Drive of the waste material discharge conveyor takes place along an alternative hydraulic line through pump 72, manifold block - 11 73 containing a direction valve 75, and a further hydraulic motor 77. Automatic reversal is not provided for this feature of the invention.

The control system allows both variation in shaft speed for the screen deck and conveyor drives and also variable torque settings. For the screen deck, the arrangement shown provides an automatic defouling feature. Fouling of the rotating shafts of the screen deck is detected by a rise in hydraulic motor pressure, at motor 67, and reversal of motor direction is effected by device 68 and automatic direction control valve 66, so that rotation of the elliptical shafts or rollers 31 is reversed through one full revolution for a predetermined number of cycles on detection of overpressure at pump 67. If fouling is not cleared by this operation, the control system then allows for the apparatus to be automatically withdrawn from the processing line, for execution of a further defouling cycle. If this further defouling cycle is successful in clearing the line, normal operation is resumed. Alternatively, if defouling is unsuccessful, the screening machine is arranged to switch out and indicate a fault condition by a further feature of the control system.

As previously described, during defouling, the raised roller 45 at the input end of the screen deck ensures that debris is not discharged in the reverse direction into hopper 25 during the blockage clearance phase of operation of the system.

It is a particular advantage of the control and drive system described that it can be integrated into and matched with existing control arrangements in a peat handling plant or peat-fired power station, thereby facilitating application of the system of the invention as a retro-fit.

Operation of the system of the invention will be apparent from the foregoing description and drawings. In summary, peat or other granular material to be screened is fed into the system by means of the rising conveyor 11, falls onto the screen deck 3, where it is subjected to the agitating action provided by the elliptical rollers 31 and the elliptical blades 34. Peat for use as power station fuel in the particular apparatus described falls through the elliptical rollers 31 to be withdrawn by way of hopper 25 and conveyor 26, with collection also by conveyor 28 where appropriate. Waste material for discharge is advanced along the screen deck to its discharge chute end 42, from where it falls into debris chute 29 for discharge by gravity.

The apparatus of the invention and its manner of operation have been described in detail with particular reference to the screening of peat to be used as a power station fuel. The system, apparatus and method of use of the invention are however, also applicable to the screening of other materials having like properties, where there is a need to separate unwanted matter.

Claims (11)

1. Screening apparatus for separating unwanted matter from a granulatable material comprising: (a) feed means for material to be screened, (b) a screen deck comprising a plurality of driven, rotatably-mounted, axially elongate rollers of substantially elliptical cross-section, the rollers defining a substantially planar array in which the axes of rotation of the rollers are spaced apart so that a clearance is maintained between the substantially elliptical surface of each roller and the corresponding surface of the or each adjacent roller throughout rotation of the rollers, the rollers of said substantially planar array being driveably interconnected so that the major axis of each said roller is aligned at right angles to the major axis of the or each adjacent said roller of said substantially planar array for all rotational dispositions of the rollers, and each said roller having a plurality of fins extending radially and at right angles to its axis of rotation, each fin being substantially circumferentially continuous and the periphery of each fin substantially defining an ellipse uniformly spaced radially outward of the substantially elliptical surface of the roller, (c) collection means for screened material, and (d) discharge means for unwanted matter separated by said screen deck, wherein: (i) the fins of alternate rollers are axially displaced relative to the fins of the or each adjacent roller, and (ii) the fins of successive rollers are interleaved to overlap one another in end view, at least when the major axes of alternate rollers are aligned in or parallel to the plane of said substantially planar array.

2. Apparatus according to Claim 1, wherein said plurality of fins comprises an array of equally spaced fins along the axial length of the roller. 14

3. Apparatus according to Claim 1 or Claim 2, wherein the peripheral edge portion of each fin of each alternate roller is in proximity to the roller surface of the or each adjacent roller at least when the major axes of said alternate rollers are aligned in or parallel to the plane of said substantially planar array.

4. Apparatus according to any preceding claim, wherein said feed means comprises a conveyor for delivery of material to be screened to an input end of the screen deck.

5. Apparatus according to any preceding claim, wherein said collection means for screened material comprises a collection hopper located substantially beneath the screen deck for receiving screened material falling through the deck.

6. Apparatus according to Claim 5, wherein said collection means for screened material further comprises an extension conveyor extending from beneath the screen deck at a location remote from an input end of the screen deck, for return to said collection hopper of screened material falling through the screen deck at least in the region of said location.

7. Apparatus according to any preceding claim, wherein said discharge means for unwanted matter comprises a chute extending from a location underlying the end of said screen deck remote from an input end of the deck.

8. Apparatus according to any preceding claim, wherein the or each of said screen deck and discharge means for material separated by said screen deck is powered by a respective hydraulic drive.

9. Apparatus according to Claim 8, wherein said hydraulic drive for the screen deck comprises an anti-fouling feature for automatic clearing of any blockage on the screen deck. - 15

10. Apparatus according to any preceding claim, comprising at least one roller at a feed end of said screen deck which is raised relative to said substantially planar array defined by said plurality of rollers.

11. Screening apparatus substantially as described herein with reference to and as shown in the accompanying drawings.