EP0162014A1 - Device and method for separating granular goods - Google Patents

Abstract

PCT No. PCT/EP85/00209 Sec. 371 Date Dec. 23, 1985 Sec. 102(e) Date Dec. 23, 1985 PCT Filed May 8, 1985 PCT Pub. No. WO85/05050 PCT Pub. Date Nov. 21, 1985.In an apparatus for separating heavy material, more particularly stones, from cereals and other bulk goods, two superposed inclined vibrating tables (1, 2) are provided which have the same air flowing through them and a common drive (30), a product inlet (6) being provided at the top table (2). The bottom table (1) is constructed as a stone separating table and the top vibrating table is constructed throughout as a layering table and only its bottom end has a short zone (11) for the layer concentrated in heavy material to drop through and a discharge (19) to the bottom vibrating table (1). The discharge (19) is directed towards a central zone (B) of the bottom table (1). The material charged to the top vibrating table (2) via the product inlet (6) is layered thereon over its entire length and 20% to 80% of the flow of material containing the heavy material are withdrawn at its lower end and then discarded on to the middle zone (B) of the bottom table (1) in the form of a curtain to act as a material supply.

Description

The invention relates to a device for separating grain into several fractions with two oscillatingly supported and adjustable in their inclination and penetrable by a common airflow fluidized bed tables, with an inlet for the granular material is arranged above the higher end of the upper fluidized bed table, the one at the lower end there is an outlet for the lightest grain fraction and there is a stone outlet at the higher end of the lower fluidized bed table and an outlet for the heavy grain fraction at the lower end, an intermediate floor of shorter length than the fluidized bed tables being arranged between the fluid bed tables.

Underlying state of the art

For grain cleaning, all foreign matter and dirt must be removed before the grain is ground. The cleaning takes place in several stages. Large foreign bodies are usually separated out with sieve devices, the mesh size being selected in such a way that the entire grain is certainly obtained as diarrhea and all parts which are larger than the repulsion are separated off. Fine dirt and fine sand can be separated out at the same time through an appropriately finely perforated sieve. In this way, the actual grain is obtained with a foreign stock, which consists in particular of small stones, glass fragments and metal parts as well as various light stockings (such as large shell parts, fragments of straws and foreign seeds), all of which are in a certain grain size spectrum, e.g. with wheat varieties In the range of 2mm to 6mm or with maize in the range between 5mm and 20mm. Depending on their external shape and size, the light components are separated by special readout tables (such as paddy readers or light grain readers). Until about 20 years ago, a large part of the grain that had been pre-screened in this way to a certain granulation area and freed from the light constituents was passed through a water bath and the adhering dirt and stones were washed out. The stones could be collected in this way on the floor of the washing machine due to their greater weight.

The great advantage of this cleaning method, which has been widely used up to now, is its very high cleaning effect, but the disadvantage in the case of very large amounts of dirty washing water, which due to the risk of microbiological contamination could only be used once and then also had to be cleaned.

• l. eine saubere Trennung in Schwer- und Leichtkorn, sowie
• 2. eine so gut wie vollständige Steinauslese bei einem einzigen Durchlauf durch eine Maschine, jedoch unter Anwendung von zwei übereinander angeordneten, von der gleichen Luft durchströmten Schwingtischen.

DE-AS 3 148 475 proposes a new way of separating grain and similar grain in individual fractions. The three main fractions, namely the heavy grain, the light grain and the stones are extracted from the grain with a single machine. The focus is on this

• l. a clean separation into heavy and light grain, as well
• 2. a virtually complete stone selection in a single pass through a machine, but using two vibration tables arranged one above the other, through which the same air flows.

To achieve these high quality requirements, however, it is necessary to carry out each work step under optimal conditions. The upper vibrating table primarily serves for a clean separation of the light fraction and has an elongated shape for this, whereby it can be adjusted at a slight incline from the inlet end to the outlet end and is brought towards the outlet with a throwing motion so that the product over the slight inclination can be continuously promoted.

However, it has been shown in the known device that it is essential for a good function to be able to adjust the air quantity in sections along the vibrating tables. For this purpose, an extraction hood with a bulkhead-like division is used, with an individually adjustable air throttle being assigned to each intermediate space. This means that a fluidized bed that can be specially adapted to the product and the throughput can be created on the upper vibrating table. On a first section of the upper vibrating table, the heavy goods are concentrated in a layer directly above the vibrating table by means of the oscillating movement and air flow, and a second upper layer of the light goods freed from the heavy goods is formed directly above this.

The heavy goods are then drained along a second section onto the lower vibrating table immediately below, the task of which is to read out the heavy goods and the parts with a greater specific weight (such as stones, glass, metal, etc.). For this purpose, the lower vibrating table is also equipped with a vibratory drive, which, however, generates a throwing motion against that of the upper vibrating table. The lower swing table is in inclined in the same direction as the upper swing table, but its swinging movement is oriented towards the higher outlet for the heaviest parts.

However, the structural complexity of this known device (and thus also its price) is so great that the use of this device is already limited.

In addition, it has also been shown that with this type of construction, only a limited increase in product throughput is possible, since if the throughput rates are too high, the precise guidance of the fluidized bed by controlling the local air volume is no longer sufficiently good and the desired stratification is no longer formed desired mass can be achieved.

The invention is based on the object of eliminating the disadvantages of the known device, and in particular to achieve better utilization of the given vibrating table surfaces without loss of selectivity.

The solution according to the invention is characterized in that the fluidized bed tables are arranged in a rigid and swingably mounted frame, which is assigned a common vibratory drive, the throwing motion of which is directed against the stone outlet, and that the lower fluidized bed table is preferably an air-permeable material support and parallel and at a distance below it a finely perforated plate (sandwich), which together has an approximately constant air resistance over the entire crop support result regardless of the layer thickness on the lower table.

Through the almost constant apparatus air resistance achieved according to the invention, the throughput can be increased significantly with good separation work. The sum of the hole cross sections of the finely perforated plate is preferably assumed to be less than or at most equal to the tenth part of the total area of the good support. The two vibrating tables are very particularly preferably arranged in parallel.

It is particularly advantageous if, in the upper fluidized bed table, a zone of coarse perforations is attached to a first area across the fluidized bed table.

Furthermore, it is preferred to provide a threshold across the fluidized bed table subsequent to the zone of coarse perforations, the threshold being at least one to two times the average grain size, but at most approximately half the layer thickness to be expected.

The upper fluidized bed table is preferably divided in the direction from the inlet towards the outlet for the lightest grain fraction into two consecutive areas of different perforations such that the stones and heavy grain fraction can only fall through the fluid bed table in the area of coarse perforations.

So that a clean separation of the light fraction can also be achieved, in the second area of the upper fluidized bed table, mutually adjustable side walls are provided for the working surface of the upper fluidized bed table, which with its outlet for the lightest grain fraction facing ends are pivotable against each other, for the purpose of tapering the effective surface of the upper fluidized bed table against the outlet for the lightest grain fraction.

Also very advantageously, a slide falling against the outlet for the stones and passing beneath the slot or a zone of coarse perforations is provided under the second region of the fluidized bed table, the slide being adjustable between the first region and the adjoining zone of coarse perforations or slot opening is.

The slide preferably ends approximately at a medium height between the two fluidized bed tables, and in the middle third over the length of the lower fluidized bed table.

In another particularly preferred embodiment, the intermediate area is arranged in the area following the first area, which is inclined towards the lower end of the lower fluidized bed table. The intermediate floor is arranged so that it cuts the fluidized bed tables at an angle of 25 ° to 45 °, and that the inclination of the fluidized bed tables is 5 ° to 10 ° with respect to the horizontal.

The intermediate base is preferably formed by a multiplicity of flat profiles which are mounted in the housing so as to be rotatable about their longitudinal central axis, so that a corresponding mixed fraction can be set by folding down or interconnecting.

• - eine schwere Kornfraktion
• - eine Mischfraktion sowie
• - eine Leichtfraktion

gewählt werden.This way, three fractions can be very sharp

• - a heavy grain fraction
• - a mixed fraction as well
• - a light fraction

to get voted.

The flat profiles can be set so that they touch each other when coplanar. However, they can also be graded so that an air passage opening is created between the steps.

In continuation of these ideas, the lower fluidized bed table below the intermediate floor can be designed as a channel-like depression with an air-impermeable bottom, which depression guides the heavy grain fraction into the associated outlet. Particularly optimal and stable operating conditions are created when the clear exhaust air cross section is divided into zones with adjustable cross sections at a distance above the upper fluidized bed table. Each should have an adjustment flap for adjusting the air volume.

For an optimal functioning of the shift table, it is equipped with a large number of fine perforations, but a smooth surface. With this measure, a strong inhibiting effect is achieved for the product layer lying directly on the upper vibrating table due to the upward-promoting throwing swing movement. This creates an almost scissor-like effect on the upper table, which means that all heavy parts that have once entered the lower layer, which is prevented from flowing away quickly, cannot jump back into the upper layer either through the air or through the vibration movement. This last measure intensifies the layer effect on the upper table. This allows the be To optimally utilize the required amount of air as well as the vibration energy, so that a significantly higher throughput can now be processed on the same table surface or a clean layering over a very short table length can be completed.

In continuation of this idea, the stone reading table is designed as a good support, an air-permeable, well-impermeable mesh grid parallel and at a distance below a finely perforated plate, in between a bulkhead-like structure (sandwich), such that the lower swing table with the finely perforated plate has an approximately constant air resistance over the whole Good support results regardless of the thickness of the bed on the lower fluidized bed table. The stone reading table particularly preferably has a rough surface, such that the heavy parts are conveyed for the heavy parts due to the swinging movement after the higher outlet. The throwing swing movement used for the upper vibrating table against the flow device of the product is used here with the rough surface of the stone reading table for the actual mountain-up conveying of the lower layer, which is enriched with the heaviest components.

If you evaluate the operation of the new device, you will notice a new core idea. The particular key point now lies in the fact that the product is given the largest possible area spread both on the upper table in a first area and on the entire lower table, but in such a way that the entire work surface is uniformly exposed to the product and across an almost identical workflow occurs at every point to the direction of flow. The workflow is from Beginning of the product entry on the respective table surface progressively and consistently carried out to the point at which the corresponding work step is completed. For the upper vibrating table, this means that the product is applied evenly at the start of the table in a uniform layering over the entire width of the table and the layering is consistently perfected undisturbed until the lower layer is transferred to the stone reading table underneath. Only when the stratification has been completely reached is the entire underlayer, enriched with the heavy parts, pulled off in the very short section as diarrhea. On the lower sieve table, the product is again applied in a defined zone as uniformly as possible across the entire width of the stone reading table. From this zone, a surprisingly even stratification or fluidized bed is formed both in the direction of the higher table end and the lower table end over the entire surface. The short section of the diarrhea for the stone selection is preferably at most one fifth of the first product-impermeable area.

The use of the finely perforated plate and the sandwich-like structure of the stone reader will certainly also make a significant contribution to this good result, since this results in a uniform air speed at least on the lower table surface over the entire surface.

In a further preferred embodiment, the upper table surface in the area of the product feed is made air-permeable and a short distance at a distance above the table surface is covered to form an air flow in the direction of the incoming material current. In this way, the goods to be freshly placed on the table receive a push at the entry point, so that despite the throwing swing movement that wants to throw the goods in the opposite direction upwards, there is a clear conveyance in the area of the inlet after the lower end of the table.

The invention further relates to a method for reading out heavy goods, in particular stones from cereals, over two table surfaces inclined to the outlets, through which the same air flows and together set in motion, both of which are impressed by a throwing motion in the direction of the higher table end.

The method according to the invention is characterized in that the material on the upper vibrating table is layered over a first area (V), and from the material flow 20 to 60% with all heavy goods is discharged as a veil onto the middle area of the lower table surface. This not only precisely defines the stratification process, but also creates a clear condition for removing the lower layer enriched with the heavy admixtures. It is very important that a substantial part of the entire good, i.e. 20 to 60%, is transferred "bundled" to the lower table forming the stone reader. The fact that every vibrating table receives at least 20% or more of the material during operation and that a real fluidized bed is formed or a kind of product carpet is produced and the prerequisites for real stratification are also very particularly important.

The invention further proposes to carry out the supply of goods for the stone reader in the central region thereof, the material being thrown off in a locally veil-like manner. The focus here is on the fact that a substantial part of the goods are drawn off over a short area and transferred to the lower table in a middle area, preferably the middle third, like a veil.

It has been shown in the method according to the invention that the stratification as such can be carried out almost completely over a relatively short distance or over a short period of time. The layering is completely completed after passing through about half of the upper table surface. This process can also be carried out continuously with a large mass flow; the stratification is even improved as the product throughput increases.

The invention enables two things: Firstly, a partial flow is simultaneously branched off from the entire crop flow and delivered to the stone reading table. In contrast to known methods, this causes the stone reading table to be relieved of part of the goods or the light fraction from the outset. This could not be achieved, for example, if a sieving process is carried out at the same time during the layer formation, in which both heavy parts and small parts fall down through the sieve. Secondly, according to the invention, however, it is also achieved that there are now clear drainage conditions at every point on the stone reading table, with stratification again taking place on the stone reading table. However, the stratification in the stone picker is countered by the throwing swing movement and the set or table upward movement carried out with only a small part of the original crop flow, since the larger amount flows directly downwards on the stone selection table. On the stone reading table there is a constant exchange of the different parts between

• - schwerste Teile tischaufwärts und
• - leichtere Fraktionen tischabwärts

werden alle verhältnismässig leichteren Teile der oberen abschwimmenden Schicht sofort nach unten dem Auslauf für das Korngut zugeführt.the lower and upper layers instead. Through the two distinct currents

• - heaviest parts up the table and
• - lighter fractions down the table

all relatively lighter parts of the upper floating layer are immediately fed down to the grain outlet.

Preferably 20 to 50% of the material flow with the heavy material is transferred to the middle area of the lower table surface. In most cases, the aim is that less than 50% of the material flow is thrown onto the stone reading table. It is also particularly advantageous if the material falling from the upper table surface to the lower table surface is blown with a strong air flow. This loosens up the falling veil of material so that almost every grain hits the fluidized bed of the stone reading table individually. At the upper end of the lower table, an air jet for delimiting the fluidized bed is preferably generated directly above the table surface. The supply of material to the lower table surface is very particularly preferably deflected and thrown off in a direction opposite to the upper table by means of a slide in relation to the flow direction. This measure loosens the material and also allows the air to pass through the two tables is sucked through surfaces, and is diverted in the area of the slide opposite to the good movement.

• Fig. 1 einen Vertikalschnitt (im Prinzip) durch eine erfindungsgemässe Vorrichtung,
• Fig. 2 einen Teilausschnitt aus einer Draufsicht auf den unteren Wirbelschichttisch, aus der Vorrichtung nach der Fig. 1,
• Fig. 3 den Schnitt III-III aus Fig. 2,
• Fig. 4 schematisch den Materialfluss in der erfindungsgemässen Vorrichtung gemäss Fig. 1,
• Fig. 5 ein Detailausschnitt der Vorrichtung aus der Fig. 1,
• Fig. 6 ein weiteres Ausführungsbeispiel einer erfindungsgemässen Vorrichtung,
• Fig. 7 eine entsprechende Darstellung der Fig. 1 eines weiteren Ausführungsbeispieles einer erfindungsgemässen Vorrichtung.
• Fig. 8a einen Grundriss des oberen Schichttisches,
• Fig. 8b eine Doppelausführung für grosse Durchsatzleistungen.

The invention will now be explained in more detail with the aid of a few exemplary embodiments. Show it

• 1 is a vertical section (in principle) through an inventive device,
• 2 shows a partial section from a top view of the lower fluidized bed table, from the device according to FIG. 1,
• 3 shows the section III-III from FIG. 2,
• 4 schematically shows the material flow in the device according to the invention according to FIG. 1,
• 5 shows a detail of the device from FIG. 1,
• 6 shows a further exemplary embodiment of a device according to the invention,
• FIG. 7 shows a corresponding representation of FIG. 1 of a further exemplary embodiment of a device according to the invention.
• 8a is a plan view of the upper layer table,
• Fig. 8b a double version for high throughputs.

The device shown in Fig. 1 has an inlet 1 for the granular or the raw material, which directly on the higher end of an upper vortex shift table 2 falls. A lower fluidized bed table 3 is installed at a distance below the upper one in a common frame 4. Both tables are set in motion with the frame 4 by an oscillating drive 5, for which purpose they are mounted on a frame 8 by means of a spring 6 or a height-adjustable oscillating support 7. On the frame 8, two side wall parts 9 are also attached, on which an exhaust hood 10 connected to an intake line is placed. This is divided into individual zones 11 by transverse walls. Each zone 11 has an air adjustment flap 32, so that the size of the flow cross section can be set individually in each individual zone. The upper fluidized bed table 2 has a light material outlet 14, whereas the lower fluidized bed table 3 is assigned a stone outlet 13, and an outlet 15 each for the heavy fraction and an outlet 16 for the middle mixed fraction.

Furthermore, the upper fluidized bed table in a region (V) has a smooth surface with a large number of fine perforations, the region (V) of the upper table surface is air-permeable, but impermeable to the raw material. There is then a zone of coarse perforations 24 over the entire width, which can also be replaced by a passage slot across the entire width. In a region (A) adjoining the coarse perforations, which extends to the light material outlet 14, the table surface also has coarse, possibly medium-coarse perforations 24 'through which the various raw material fractions can fall. It is essential that the upper table does not have a sieve function, since all of the diaphragm openings are larger than the largest part of the material flow. The stratification is caused by the air flow receive. The whole lower layer falls through the rough openings. The openings can easily make up 2o to 50% of the entire table area.

The lower fluidized bed table 3 is permeable to air over the entire surface, but impermeable to the falling material. As FIGS. 2 and 3 show, it has a lower perforated plate 20 with a perforation 21, over which a parallel machined grating 23 is arranged. In the space between the perforated plate 20 and the mesh 23, cheekboard-like bulkhead walls 22 are provided, which divide the flow cross-section for the air into rectangular channels.

A base 17 is essential for the separation of a medium fraction, which allows the separation of medium-heavy grains from the material falling through the upper fluidized bed table 2. The bottom 17 consists of a number of flaps 18 which extend from one longitudinal wall of the frame 4 to the other and are pivotably mounted in these longitudinal walls about their longitudinal center. The length of the bottom 17 ending at the outlet 16 and thus the quantitative proportion of the medium-heavy fraction in the falling material is determined by the number of flaps 18 pivoted coplanarly against one another.

Another essential point is the use of a slide 19, which can be adjustable in length and inclination. The chute 19 conveys the portion of material enriched with the stones and with the heaviest grains, which then falls through the upper fluidized bed table 2 to the first product-permeable area against the stone outlet 13.

FIG. 4 shows the device again with regard to its mode of operation and the material flow occurring therein. The product enters the device at the inlet 1 and is layered in a first region of the upper fluidized bed table 2. The stones below, the light bodies (including husks, seeds and the like) above and the other grains, according to their speed of suspension in between. In the example shown, the lowermost layer is thrown through the rough perforations 24 onto the slide 19 in the central region and conveyed in the direction of arrow 25 against the stone outlet 13. The stones are discharged at stone outlet 13. The seeds float to the outlet 16 and are discharged there. A part of the rest of the goods falls on the floor 17 in the second half of the area (A). A part of the first half of the area (A) can still fall on the lower fluidized bed table 3 when the flaps 18 are open. The diarrhea of the second half is then discharged through the outlet 16, the diarrhea of the first half through the outlet 15. In contrast to FIG. 1 (outlet 14), the light material outlet 14 'is separated out directly.

The possibility of double air control of the suction air is particularly interesting for the overall function of the device. On the one hand, with the special construction of the lower fluidized bed table 3, uniform ventilation is achieved over the entire table surface, regardless of the layer thickness of the grain. The function of the upper fluidized bed table 2 requires for the areas that follow from left to right, ie for product stratification, for throwing off the stones and the heavy grain fraction, and for separating into medium-weight and light goods, each have a specifically controlled and adjusted amount of air, which can be adjusted by means of the adjusting flaps 32.

A very important point, however, in addition to the air routing and a corresponding product steering, is the possibility of directing the goods by installing the slide 19 and the floor 17. These two internals allow very precise guidance and, if necessary, fine adjustment of the product flows.

In the section from FIG. 1 shown in FIG. 5, the bottom 17 and the slide 19 are shown enlarged. The two fluidized bed tables 2 and 3 are preferably parallel to one another and adjustable by means of the vibration support 7 with respect to a horizontal plane (angle 26) between 5 ° and 10 °. The direction of oscillation of the oscillating drive 5 intersects the planes of the fluidized bed tables 2 and 3 at an angle of 25 ° to 45 ° (angle 27), whereas the plane of the bottom 17 or the plane of the slide 19 each with an angle of those of the fluidized bed tables 2 and 3 from 5 ° to 40 ° (angle 28) or an angle from 0 ° to 65 ° (angle 29). When the device is operating, the inclination of the lower fluidized bed table 3 is set in such a way that it is the most favorable for the separation of the stones through the outlet 13. As a rule, however, the inclination of the upper fluidized bed table 2 (since the two tables are firmly connected to one another by the frame 4) should be less optimal for separating the other fractions. With the length adjustability of the base 17, the amount of the mixed fraction to be discharged through the outlet 16 can be increased or reduced, in particular in the case of large throughput differences, at the expense of the heavy grain fraction to be discharged through the outlet 15. Due to the inclination of the bottom 17, it can fall on it lumbar flow into the outlet 16 without delay despite the opposite direction of oscillation of the oscillating drive 5.

As shown in FIG. 6, the bottom 17 can also be designed in a step-like manner, suction air being able to flow from the lower fluidized bed table 3 to the upper one in the area of the steps, which facilitates a uniform air flow through it; the lightest fraction (shells, husks, etc.) is discharged as an expulsion of the upper layer table 2 through an outlet 14 '.

The upper end of the slide 19 lies under the area (D) directly adjoining the pre-layer area of the upper fluidized bed table 2, through which almost all the stones fall in order to guide them as far as possible into the middle area of the lower table 3. The slide 19 is preferably mounted in a longitudinally displaceable manner in the frame 4, so that its upper end can be brought to a greater or smaller distance from the end of the pre-layer area of the upper fluidized bed table 2. This makes it possible to catch practically all the stones with the slide 19 and to transfer them to the lower fluidized bed table 3 for the final separation.

In the exemplary embodiment according to FIG. 7, the same reference numerals designate the same or equivalent parts as in the example according to FIG. 1; their repetitive description is therefore omitted. In this exemplary embodiment, a transversely oriented threshold 31 is arranged on the upper fluidized bed table 2 in the zone of coarse perforations 24. The threshold 31 can also be arranged in an adjustable manner depending on the product throughput and the arrangement of the upper collecting end 19 'of the slide 19. In this embodiment, the zone "V" is Pre-layering of the goods about the same length as zone "A" for the separation of the light fractions or a mixed fraction.

The lower fluidized bed table 3 also has a non-ventilated base piece 30. The base piece 30 has several functions. The portion of the heavy fraction thrown from zone "A" after the chute 19 directly onto the lower fluidized bed table no longer disturbs the layering process on the lower fluidized bed table 3, since no build-up can occur at this point.

A second function is that the total amount of air enters through the part of the lower fluidized bed table in which the air is actually used. The air only enters or through the device where it has to do work.

8a is a top view of the upper vibrating table. The table has a rectangular shape in a first area “V”. The adjoining zone "A" becomes narrower towards the outlet in order to maintain the stratification until the end, with the progressive diarrhea of the goods through the area "A".

FIG. 8b only shows a doubling of FIG. 8a.

The device described is in a special way for separating heavy parts, such as broken glass, fine metal parts, stones and the like. heavy grains, broken, withered and light grains, seeds, shells, dirt and the like. suitable from cereals. However, it has also been shown that there is an almost identical task for compost, namely Removal of heavy parts and light material from shredded, especially in the case of mature, dry waste compost, provided the material is free-flowing. In the foreground are three fractions, the heavy parts (stones, broken glass, fine metal parts), the light parts (small pieces of plastic) and the main mass of the good compost.

Claims (17)

1.Device for separating grain into several fractions with two oscillating fluid bed tables (2, 3) which can be tilted and adjusted in their inclination and which can be penetrated by a common air flow, with an inlet (1) for the granular material is arranged, at the lower end of which there is an outlet (14) for the lightest grain fraction, and further at the higher end of the lower fluidized bed table (3) is a stone outlet (13) and at the lower end an outlet (15) for the heavy grain fraction There is an intermediate floor (17) of shorter length than the fluidized bed tables (2, 3) between the fluidized bed tables (2, 3), characterized in that the fluidized bed tables (2, 3) are arranged in a rigid frame (4) which is mounted so that it can vibrate are assigned to a common vibratory drive (5), the throwing motion of which is directed against the stone outlet (13), and that the lower vortex Layer table (3) has an air-permeable good support, under which a finely perforated plate (20) is preferably arranged parallel and at a distance (sandwich construction), which together have an approximately constant air resistance over the entire lower good support, regardless of the good layer thickness on the lower table , result. 2. Device according to claim 1, characterized in that the sum of the cross sections of the hole finely perforated plate (20) is less than or at most equal to tenth part of the total area of the good support. 3. Device according to claim 1 or 2, characterized in that a slot or a zone of coarse perforations (24) is attached to the upper fluidized bed table (2) at a first area across the fluidized bed table (2). 4. Device according to claim 3, characterized in that a threshold (31) is provided across the fluidized bed table (2) subsequent to the slot or the zone of coarse perforations (24), the threshold (31) at least one height of the one - Has up to twice the average grain size. 5. Device according to claim 3 or 4, characterized in that the upper fluidized bed table (2) in the direction from the inlet (1) against the outlet (14) for the lightest grain fraction is divided into two areas of different perforations, such that the Stones and heavy grain fractions can only fall through the fluidized bed table (2) in the area of the slot or in the area of coarse perforations (24). 6. Device according to one of the claims 3 to 5, characterized in that in a second region (A) of the upper fluidized bed table (2) mutually adjustable side walls are provided for the working surface of the upper fluidized bed table (2), which with its outlet (14 ) for the lightest grain fraction facing ends are pivotable against each other, for the purpose of tapering the effective surface of the upper fluidized bed table (2) against the outlet (14) for the lightest grain fraction. 7. Device according to one of the claims 3 to 6, characterized in that under the second area of the upper fluidized bed table (2) falling towards the outlet (13) for the stones and below the slot or the zone of coarse perforations (24) leading past Slide (19) is provided. 8. The device according to claim 7, characterized in that the slide (19) between the first region and the adjoining zone of coarse perforations (24) or slot opening is adjustable in length and / or inclination. 9. The device according to claim 7 or 8, characterized in that the slide (19) ends approximately in the middle between the two fluidized bed tables (2, 3) and over the length of the lower fluidized bed table (3) in its middle third. 10. Device according to one of the claims 1 to 9, characterized in that in the area (A) following the first area (A) an intermediate floor (17) is arranged, which is inclined towards the lower end of the lower fluidized bed table (3). 11. The device according to claim 10, characterized in that the intermediate floor (17) intersects the fluidized bed tables (2, 3) at an angle of 25 ° to 40 ° (angle 28), and that the inclination (angle 26) of the fluidized bed tables (2 , 3) with respect to the horizontal is 5 ° to 10 °. 12. The device according to claim 11, characterized in that the intermediate floor (17) is formed by a plurality of flat profiles (18) which are rotatably mounted about their longitudinal central axis in the frame (4) are so that a corresponding mixed fraction can be set by folding down or by interconnecting. 13. Device according to one of the claims 11 or 12, characterized in that the flat profiles (18) are graduated so that an air passage opening (X) is formed between the steps. 14. Device according to one of claims 1 to 13, characterized in that the lower fluidized bed table (3) below the intermediate floor (17) is designed as a channel-like depression (30) with an air-impermeable bottom, the depression (30) the heavy grain fraction in the associated outlet (15) leads. 15. Device according to one of the claims 1 to 14, characterized in that with the distance above the upper fluidized bed table (2) the clear exhaust air cross section is divided into zones (11) adjustable in cross section by partition walls, each zone (11) having an adjustment flap ( 32) for setting the air volume. 16. Method for reading out heavy goods, in particular stones, from grain by means of two table surfaces inclined to the product outlets, through which the same air flows and which is set together to oscillate, wherein both are impressed by a throwing swinging movement in the direction of the higher table end that the goods are layered along a first area (V) on the upper table surface, then a portion of 20 to 60% is subtracted here with all heavy goods and grinded as a goods supply it is dropped onto a central area of the lower table surface. 17. The method according to claim 16, characterized in that the central region of the lower table surface - seen in the longitudinal direction thereof - comprises approximately the region of the middle third.

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