NL1015547C2 - Sieve chute for feed of bulk grains has full-width curtains preventing entrapment of fine grains in coarse grains such as sand and gravel - Google Patents

Abstract

A feed of bulk grains (1) e.g. sand or gravel is sieved and graded as it descends down a plane inclined at an angle alpha, which is also a flat sieve (2). The in-fed of bulk grains has to pass one or more throttle gaps (10) which are formed by semi-rigid curtains (4) spanning the sieve (3) width and transverse to the direction of flow. The size of the vertical gap (10) is adjustable.

Description

Short designation: Strainer.

This invention relates to a device for separating by size sizing granules contained in a liquid stream, comprising a feed for the stream to be sieved, a stationary screen surface placed under a slope, the longitudinal section of which is substantially flat, wherein the flow can be transported under the sieve of the granulate over the top of the sieve surface, a discharge for the sieved flow.

Seven of the above type are known in the art. In the sand and gravel extraction, granulate (sand and gravel) extracted as a size separation step is flowed over a screen slope in a water flow. The granulate is hereby brought into contact with the screen surface, whereby the fraction to be sieved passes through the meshes of the screen with an amount of liquid and thus is separated from the coarser granulate.

By "longitudinal section" is meant the section of the screen surface along the intended flow direction of the granulate 20. There are thus no gutters extending transversely to the flow direction in such a screen surface.

However, it has been found that the granulate tends to settle in flow and sediment on the sieve surface, causing clogging of the sieve. This problem is avoided in the prior art by increasing the angle of inclination of the screen surface so that the flow rate of the granulate / water flow increases; however, this has the drawback that a considerable part of the fraction to be separated is not sieved and is discharged with the coarser fraction, so that the sieve efficiency is reduced. The tendency to sediment is also partly determined by the sieving conditions, such as the water-granulate ratio and the grain size distribution of the granulate and the feed rate.

The object of the invention is to solve the above-mentioned problem and is to that end characterized in that the device further comprises at least one spit-shaped flow throttle opening, the bottom of which is bounded by the screen surface and the top by throttling means to be placed in the flow. .

By "throttle opening" is meant a passage for the flow to be sieved, the area of which is less than the area of the cross-section of the flow, when it flows unobstructed over the sieve surface. By "throttling means" is meant means which delimit the top of the throttling opening. The throttling means can have many shapes, as long as this defines a suitable throttling opening and can for instance be designed as a bulkhead or beam-shaped body, which is remote from the screen surface. When the device is used, the throttling means are thus at least partly in the stream to form a throttling opening. Due to the presence of a throttling opening, propulsion of the granulate stream will be created at the location of the throttling opening and the flow velocity is increased there. Surprisingly, it has been found that this effectively prevents sedimentation of the granulate on the screen surface, without the granulate undergoing strong mixing and without losing contact with the screen surface, because the particles to be sieved lose contact with the screen surface due to a strong mixing. causing the strain to be disadvantageous affected. Thus, the granulate flow is maintained in a continuous flow during transport. Optimal sieving will take place when the transport of the granulate flow over the sieve surface is kept going, the granulate in the flow not losing contact with the sieve surface. The particles to be sieved can thus be optimally fed with water through the openings of the sieve surface.

Thus, gutter-shaped depressions in the screen surface are not required, which extend transversely to the direction of flow of the granulate. Such troughs are provided in the art to prevent sedimentation of the granulate. In this connection reference is made to GB-A-2 015 367 and DE-C-605 477. If desired, in the device according to the invention gutter-shaped 35 recesses may be present in the screen surface, which however extend in the longitudinal direction, i.e. in the intended direction of flow of the granulate, although such a shape of the screen surface does not entail any significant additional beneficial effect within the scope of the invention. It is therefore preferable to design the screen surface flat in both the length and width directions.

US-A-5 614 094 describes a vibrating screen installation, in which a plurality of screen surfaces placed under a slope are arranged one below the other. A size-separable granulate is poured onto the top sieve surface, after which the granulate is vibrated down the slope of the top sieve surface. Above said screen surface, a scraper extending transversely to the screen surface is placed, which complicates the further transport of the granulate over the screen surface, as a result of which accumulation of the granulate at the scraper occurs. Due to this accumulation, the small cross-sectional size granulate fraction is forced through the screen surface at this location and lands on the second, finer screen surface. The coarser granulate eventually passes the scraper and is collected downstream. Said scraper is thus a means that impedes the progress of the granulate over the screen surface, while the throttle opening according to the invention causes an acceleration of the granulate over the screen surface.

EP-A-0 015 633 and DE-C-674 863 also describe vibrating screens for sieving granular material, whereby partitions can be placed transversely to the sieve, which stop the material to be sieved to force the material through the sieve . There is no accelerated flow of the material to be screened through the gap between the baffles and the screen surface.

DE-A-2 329 059 describes a sieve device in which the sieve surface is arranged at a steep angle of approximately 60 ° to the horizontal. To prevent blockages, nozzles are arranged under the screen surface, through which liquid is sprayed against the bottom of the screen. At the top of the sieve, a baffle may be placed opposite such a sprinkler to retain the liquid sprayed through the sieve surface and bend to the sieve surface. However, such a baffle does not form a throttle as is present in the device according to the invention. Furthermore, such spraying means are not necessary with the device according to the invention and are preferably free of spraying means directed at the bottom of the screen.

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In the device according to the invention, the angle of inclination can also be kept substantially the same even under conditions which are not constant, that is to say when the grain size distribution of the granulate in the flow changes. Because the angle of inclination of the screen does not have to be increased, little of the fraction to be separated will be discharged with the coarser fraction, so that the screen efficiency is increased. On the contrary, the angle of inclination can be considerably reduced in order to increase the sieve efficiency, without sedimentation and clogging of the sieve surface occurring. The angle of inclination of the sieve surface with respect to the horizontal is usually between 15 ° and 40 °; in a preferred embodiment, said angle of inclination is 25 ° -30 °.

The throttling means are preferably placed substantially parallel to the screen surface. Thus, a slit of substantially rectangular shape is defined. It has been found that good propulsion can be obtained with such a slit shape without disturbing turbulence occurring downstream of the throttling means. Such a rectangular gap can be obtained by making the throttling means substantially straight. However, it is also possible to choose not to constantly select the distance between the throttling means and the screen surface, for example by making the throttling means arc-shaped, so that the limitation of the throttling opening defined by the throttling means is correspondingly arcuate. This achieves that the thrust of the granulate flow across the width of the flow is not equal. With such a measure, for instance in view of the load on the device, propulsion can be chosen lower at the edges of the screen surface than at a distance from the edges.

The throttling means are preferably placed substantially transversely of the intended flow direction of the granulate, whereby the throttle opening is also transverse to the flow direction, and the granulate thus flows at right angles through the throttling opening. Optimal propulsion and improved sieving results are hereby obtained. In such a case, the angle of the throttling means relative to the intended flow direction of the liquid flow is 90 ° or does not deviate substantially from it. However, one can also choose to place the throttling means at a different angle, for example diagonally on the screen surface, or at a smaller angle than the diagonal, so that the propulsion thus also takes place partly in the lateral direction, so that the influences the flow direction of the liquid flow over the screen.

In a further embodiment, the throttling means 5 extend substantially over the full width of the screen surface, whereby the throttling means define a spatial throttle opening extending over the entire width of the screen. Thus, the full width of the stream can be propelled across the screen and sedimentation over the full width is prevented. However, it is also possible to allow the throttle opening to extend only over a part of the width of the screen. One can then choose, for example, to define a further throttling opening downstream, which covers a different part of the width of the screen.

The distance between the screen surface and the throttling means is advantageously adjustable. When sedimentation appears to occur, this can be easily counteracted by simply reducing the distance between the throttling agents and the screen surface. By checking the screen efficiency it is easy for the skilled person to empirically check whether the optimum setting has been achieved.

The angle between the screen surface and the throttling means, viewed in the intended flow direction, is preferably up to 90 °, more preferably 20-70 °, and most preferably 40-60 °. Said angle is advantageously adjustable. When said angle is 90 ° or less, the flow is, as it were, pressed towards the screen surface, which promotes propulsion, without excessive mixing downstream of the throttling means. If sedimentation does appear to occur, it is advantageous if the angle between the screen surface and the throttling means can be adjusted to ensure a continuous flow of the granulate over the screen surface without sedimentation. Said angle also depends on the angle of inclination of the sieve surface, but usually lies in the above-mentioned range. Advantageously, the angle between the throttling means and the horizontal in the intended flow direction is also a maximum of 90 °.

Throttling means are preferably designed as elongated partitions, and can be rigid, adjustable, hinged or flexible and, if desired, mounted above the screen surface together in a frame, the height and angle of which is adjustable with respect to the screen deck. A continuous adjustment is advantageous in order to keep the flow going in the event of continuous variations in the quantity and grain size distribution of the granulate supplied to be sieved. An important point is, for example, that at the downstream end of the sieve surface there must be sufficient water to discharge the "coarse" present there under all circumstances. By "coarse" is meant granulate, which has a larger diameter than the 10 meshes of the sieve and thus cannot pass through the sieve, and remains in the liquid flow. Surprisingly, it has been found that "coarse" is generally better entrained by a liquid flow than "fine". By "fine" is meant the granulate fraction, which has a smaller diameter than the mesh of the sieve, and can thus pass through the sieve during sieving. This is advantageous because a lot of water is available at the beginning of the sieve surface, where it has to be sieved "fine", and at the end of the sieve, where a large part of the water is already through the mesh of the sieve has disappeared, the remaining amount of water is still sufficient to transport it "coarsely". Sedimentation of the "coarse" can thus be prevented even with a small amount of water. There is a lot of water available at the beginning where it has to be rinsed "fine" while the "coarse" at the end where little water is left is easier to carry.

The device according to the invention very advantageously comprises a plurality of spaced-apart throttle openings to effectively prevent sedimentation over the entire screen surface.

When the device comprises several successively placed throttling means, such as baffles, the height of the throttling means resp. partitions are preferably adjusted such that they decrease in flow direction. Since some of the water flows through the screen deck, the amount of water from the granulate stream decreases downstream. In order to maintain the transport of the granulate and thus prevent sedimentation, and to maintain the speed of the flow, it is advantageous for the passage between the partitions and the screen deck, ie the dimensions of the throttle openings, in downstream direction.

The invention furthermore relates to a method for separating a granulate incorporated in a liquid with a screen at an incline at a slope, in which a flow of granulate incorporated in the liquid is allowed to flow over the screen. forces the flow through a spit-shaped throttle opening, limited in height by the sieve surface on the one hand and throttling means on the other hand, the height of the gap being smaller than the height of the liquid flow, measured perpendicular to the sieve surface.

Preferably, said height and the angle between the screen surface and the throttling means are set in the intended flow direction 10, depending on the amount of granulate, the grain size distribution of the granulate and the amount of liquid with which the granulate is transported over the screen. This setting can be done manually; in a simple manner it can be determined by the operating personnel whether the sieve efficiency increases by the setting in order to thus obtain the optimum setting.

Advantageously, the angles and height of the baffles are continuously adjustable, so that the screen efficiency is optimal under all conditions of variable granulate quantity, grain size distribution and the water: granulate ratio in the flow.

Multiple throttling means can also be coupled to one another in a suitable manner. For example, several baffles can be placed together in a frame, the angle and height of the baffles in the frame being adjustable by adjusting the position of the frame in order to maintain the optimal course of the process when changing described variations in the supplied granulate-water mixture.

There are several options for optimally setting the throttling devices in relation to the stated conditions. In an attractive embodiment, it is determined with a sensor whether coarse material which cannot pass through the screen sediments at the end of the screen deck. When this occurs, the throttling means is preferably adjusted to allow more water to pass through. This can be done, for example, by increasing the height between the partitions and the sieve surface, whereby it is necessary to check whether the desired thrust and thereby the sieve efficiency of the liquid flow remains sufficient. For example, to measure sieve efficiency, one can measure the sieved material per unit time and set the settings continuously to maintain the highest sieve efficiency.

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One or more sensors can also be placed along the screen surface, which register any sedimentation of the granulate to be sieved. When sedimentation is recorded, the distance of the baffles to the sieve surface can be reduced thereon. This can be done by, for example, bringing the baffles closer to the screen surface or by increasing the angle between the screen surface and the baffle, measured in the intended flow direction. The above settings can also be controlled computer-controlled if desired. The setting can be fully automated by applying suitable measuring and control technology.

The invention will be explained in more detail below with reference to the drawing.

Figure 1 is a longitudinal section of a prior art screen,

Figure 2 is a longitudinal section through a sieve above which bulkheads are placed,

Figure 3 is a detailed representation of Figure 2.

In figure 1 a granulate contained in a liquid 1 flows over a sieve surface 3 placed under a slope cc. The sieve surface is flat in the longitudinal section. The flow direction of the flow is indicated by an arrow. There is sedimented granulate 2 on the screen surface, which prevents proper operation of the screen.

In Figure 2, partitions 4A and 4B are placed at a distance from the sieve surface. The liquid / granulate stream will pass through a throttling opening 10 as it passes the upstream baffle 4A, propelling the granulate downstream of the baffle at 5A through the screen, the granulate to be sieved into contact with the screen surface essentials. Sedimentation is thus effectively prevented. Sedimentation formation 2 is possible upstream of baffle 4A. At the downstream baffle 4B, the current is again driven and 35 sieves with high efficiency. In order to counteract sedimentation downstream of the baffles shown, it is advantageous to arrange baffles regularly spaced over substantially the entire slope.

In Figure 3, partitions 4A and 4B of a flexible material 40 are formed and are spaced at a distance d from each other, which are denoted by 1Π1 ς c; a - 9 - benefit is adjustable. The angle β between the screen surface and the vanes in the intended flow direction is approximately 40 ° in the case shown. It is advantageously adjustable and in the case shown is approximately 20 °. The angle of inclination α 5 between the horizontal H and the sieve surface 3 is also advantageously adjustable. 6 indicates a supply flow of a granulate-liquid mixture. During the sieving over the sieve surface 3, the fraction ("fine") 7 with the desired maximum grain size is recovered. The coarser granulate ("coarse") 8 can be further processed or discharged downstream of the screen.

The distance between baffle 4A and the screen surface is greater than the distance between the downstream baffle 4B and said screen surface, thereby defining two throttle openings 10A and 10B of different sizes, respectively. Thus, downstream despite the fact that less water is available, sufficient propulsion takes place to counteract sedimentation.

It will be clear that the device according to the invention is not limited to size fractionation of sand and gravel in a water mixture. Any granulate, but also any liquid, can be used in the device according to the invention to obtain a granulate with the desired grain size.

The invention can also be applied for the prevention of sedimentation on the bottom of channels and beds, ie for displacing the granulate that would otherwise settle on the bottom in places where this is not desired.

101554?

Claims (10)

Apparatus for separating by sieving a granulate contained in a liquid flow, comprising 5. a feed for the flow to be sieved, a stationary sieve surface (3) placed under a slope (e), the longitudinal section of which is substantially flat wherein the flow can be transported over the top of the sieve surface under the sieving of the granulate, is a discharge for the sieved flow, characterized in that the device further comprises: at least one spit-type throttle opening (10) of which the bottom side is delimited by the sieve surface (3) and the top side by throttling means (4) to be placed in the flow. 2. Device according to claim 1, characterized in that the throttling means are disposed substantially transversely of the intended direction of flow of the granulate. Device according to any one of the preceding claims, characterized in that the throttling means extend substantially over the full width of the screen surface. 25 Device according to one of the preceding claims, characterized in that the distance between the screen surface and the throttling means is adjustable. Device according to one or more of the preceding claims, characterized in that the angle (β) between the sieve surface and the throttling means in the intended flow direction is a maximum of 90 ° C. Device according to any one of the preceding claims, characterized in that the angle (β) between the screen surface and the throttling means is adjustable in the intended flow direction. 1015547 - 11 - A device according to any one of the preceding claims, characterized in that the device comprises a plurality of spaced-apart throttle openings. Device as claimed in one or more of the foregoing claims, characterized in that the throttling means have a shot-shaped design. 9. A method for separating a granulate contained in a liquid in size with a stationary sieve at a slope, whereby a stream of granulate incorporated in the liquid is allowed to flow over the sieve, characterized in that the flow is passed through a spike-shaped throttle opening, limited in height by the sieve surface on the one hand and throttling means on the other hand, the height of the gap being smaller than the height of the liquid flow, measured perpendicular to the sieve surface. 10. Process according to claim 10, characterized in that said height and the angle between the screen surface and the throttling means are adjusted in the intended flow direction according to the amount of granulate, the grain size distribution of the granulate and the amount of liquid with which the granulate is the sieve is transported. 1015547