AU612759B2 - Process and device for separating mixed grain - Google Patents

Description

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icr DPI DATE 14/06/89 AOJP DATE 2flIO7IRq iPPLN. I D 28082 89 PCT Klijvpm QrT IllJ99 /ni n7Q iNTERNATIONALE ANMI

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INTERNATIONA[

1 E ZUSAMM1ZNAKIStzII AUI- Uiv1 UbitIei U~Z3 rAir-1Ni Vnt1-q uJ.u, 0 (51) Internationale Patentkla: B03B 4/00, B07B 9/1 Internationale Veroffentlichungsnu miner: WO 89/ 04721 (41 itern ationales $1211er6ffentlichungsdatum: 1. Juni 1989 (01.06.89) (7)Anat: O AMO- IMLTJRA FR (21) Internationales Aktenzeichen: PCT/EP88/0 1078 (22) Internationales Anmeldedatum: 28. November 1988 (28.11.88) (31) PrioritAtsaktenzeichen: (32) PrioritAtsdater.

(33) PrioritAtsland: 4626/87-6 1110/88-7 27. November 1987 (27.11.87) 24. Miirz 1988 (24.03.88)

CH

usw.; Widenmayerstr. 5, D-8000 Mtinchen 22 (DE).

(81) Bestimmungsstaaten: AU, BR, RU, JP, KR, SU, US.

Veroffentlicht Mit internationalem Recherclienbericht.

Vor A blauf derflir;inderungen der Anspriiche zugelassenen Erist. Verdffentlichung wird wiederh cit falls Anderungen eintreffen.

(71) Anmelder (fdr aile Bestimmungsstaaten ausser USJ:qG-E- BR-ER-BJ+L--R-AG-[CH/CH]; G44-9-240-L--zwil c"h 2l~ 24o (72) Erfinder; und ErfinderfAnmelder (nur fir US) MUELLER, Roman ECH/CHI; Bielhofstrasse 22, CR-9244 Niederuzwil

(CR).

(54) Title: PROCESS AND DEVICE FOR SEPARATING MIXED GRAIN (54) Bezeichnung: VERFARREN UND VORRICRTUNG ZUM TRENNEN VON KORNOEMISCH (57) Abstract A process and a device for separating mixed corn, for example for separating heavy admixtures such as stones (28) from grain, in which the grain is conducted in layers over an 13 inclined vibrating layering table surface traversed by a current 42.

of air and the layering air is conducted as a circulating air, 56 whereby the circulating air used for layering grain is conduct-

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ed through separated ducts for the incoming and outgoing air 54 and the ducts are set in vibration in synchronization with the r layering table surface.

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(57) Zusammenfassung Verfahren und Vorrichtung zum Trennen von Korgemisch, z.B. zumn Auslesen von schwerern Beimengungen wie Steinen (28) aus Korngut, bei welch~m das Gut im wesentlichen geschichtet fiber eine geneigte, luftdurchstr~mte, schwingende Schichttischfldche geleitet und die Schichtluft als Urnluft gefihrt wird, wobei die fflr die Schichtung des Gutes verwendete Umluft di'rch getr.-nnte Fulhrungen Ttir die Zu- und Abluft geleitet wird und die Fifhrungen in gemneinsame Schwingungen mit der Schichttischfldche versetzt werden.

J'4 tent Attorneys 61-82-S 88PCT/T 28th November 1988 vS/ro Applicant Gebriid Bihler AG CI 240 Uzwil Process and Device for the Separation of Grain Mixture This invention concerns a process for the separation of grain mixture, for example, for the separation of heavy admixtures, such as stones, from grain material, whereby the material is passed in essentially layered form over an inclined, air-swept and vibrating layer table surface and the layer air is supplied as recirculating air.

A grain separation device, which works with recirculating air, is known from GB-PS 1 536 905, wnich essentially consists of a vibrating table surface, as well as a stationary box, which completely encloses the table surface. The stationary box shows a fan in its lower region, by means of which the air is blown to the top from below through the table surface.

The air flowing off the top of the table surface is channeled on the sides between the vibrating table surface, as well as the walls of the stationary box, back to the entry of the fan. This is known as recirculating air operation. It has the great advantage that expensive aspiration systems with corresponding filtering equipment for the layering air can be dispensed with. It is a fact, however, that these recirculating air systems 6 RAL have until now found acceptance only to a very small extent.

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2 In general, it has been found that the equipment, which worked with recirculating air, was either of very complicated construction or it was not possible to achieve adequate separation quality, for example, a sufficiently high degree of selection for the stone selection. The reason for this was that compromises had to be made for the product supply, in particular, the entry and discharge channeling of the product, as well as the ducting of the air. In order for the vibrating table to vibrate freely, either sufficient clearance must be provided between the vibrating and the stationary parts or flexible rubber bands must be wrapped around the entire table surface, which, however, influences the vibration characteristics of the table negatively. Secondary air regularly disrupts the formation of good product layering and thus the successful separation of the various material components. The actual point, which was still unsolved, was the accumulation of dust, dirt and husk parts within the stationary box. The type of devices mentioned were mainly those for the separation of foreign matter from grain and other seeds, whereby 1-2% of foreign matter is quite common. With through-put performances of, for example, 5 20 tonnes per hour, the seemingly small quantity of unwanted foreign matter results in a large quantities. Recirculating air systems place higher demands on the operator, due to the greater expenses for cleaning operation; or else, they are problematic from the hygiene point of view, From all the theoretical advantages, what was left, were huge practical disadvantages. Quite often, dust-containing air escaped into the environment with the known recirculating-air plants, because the pressure conditions could not be sufficiently controlled.

It is an objective of the invention to provide a new separating process, which works in recirculating air operation, with extensive reduction of the disadvantages of the known solutions with high through-put.

i i 3 This task has been solved in a generic process in that the recirculating air used for the layering of the material is guided through separate ducts for the supply and exhaust air, whereby the ducts are set into joint vibrations with the layer table surface.

In addition to the solution of the set task, the invention has the advantage of high separation quality, simple construction and clean operation.

The formation of a vibration unit of layer table and air ducting has the particular advantage that with a "little-more" in vibrating mass, any attachment point for the accumulation of dust, etc., is effectively avoided. It is not only the effect of the dust being carried with the air.

Due to the vibration of all wall parts, which come into contact with -the dust, they are continuously shaken clean.

As a particularly surprising advantage for the vibrating unit turned out to be the attachment of the product feeder into the region of the elevated end of the table and of the air extraction, approximately in the central region above the layer table, further, the return of the air around the lower region of the layer table. Each of these functions can be set to a maximum, as it was up to now only possible with the best machines without recirculating air. Hereby, the vibrating product feeder or material supply, which is formed cascade-like, widening from top to bottom, ensured complete spreading and loosening-up of the product from the beginning, while simultaneously functioning as an air lock. The attachment of the product feeder cascade in the region of the elevated end of the taole ensured unobstructed and thereby well controllable flow conditions, not only through, but also above the whole region of the layer table.

-y\ r 4 4-- The air return in the form of a recirculating air supply duct, which is guided around the lower end of the table and enters it in broad-faced form, also ensures optimal flow conditions. Furthermore, it is of particular importance that the recirculating air is channelled to the layer operation impulse-free and essentially free of vortices. The recirculating air can now, if required, be cleaned in stationary devices. Since the respective air remains in the circuit continuously, mechanical cleaning without filtering is sufficient. However, it is also possible, to divert only a small part of the recirculating air into a dust filter. This has the additional advantage that the whole system remains under negative pressure relative to the outside.

For the various further, advantageous forms of construction, reference is made to claims 2 to 7.

The invention concerns further a device for the separation of grain mixtures, in particular for the selection of heavy admixtures, such as stones, from the grain material with an air-swept, inclined layer table, which can be set into vibration, with air ducting for operation of the device with recirculating air, which is characterized in that the layer table, as well as the ducting for the air extraction and the air return, form a vibrating box.

It was a surprise for the experts involved, that all disadvantages were eliminated with the new separating device operating with recirculating air.

Since not only the functional parts required for the separation task were set into vibration, but in addition also the supply and exhaust duct for the air, the problem of dusting-up of the device was effectively eliminated.

5 The fine dust does not pass through the device any more. An easily controlled vibrating box can be formed, where each function has a clearly defined local placement. It is preferred that the material feeder is arranged on the side of the elevated end of the layer table. On this side, the layer tables can also be pulled out for maintenance work. The air return is preferably arranged on the other, lower end, This may be formed as a flat channel, so that the air flowing from it enters the lower table surface without any vortices. The air extraction device is arranged in the central, upper region of the box. The material and flow connection of the vibrating parts with the stationary parts occurs through round canvas or rubber sleeves, as this is clone with other ;vibrating machinery without any problems.

With respect to further advantages, reference is made to claims 9 to A particularly advantageous form of construction can be seen, if one or two table surfaces can be arranged in the same vibrating box, whereby the lower table takes over part of the material of the upper table and where the product transfer occurs preferably at the elevated end of the table.

The upper table may also show possibly even additionally a trough-like pit (stone or material sink) in its lower region, with passage openings in the trough bottom for the separation of the product stream into a heavy and a light fraction. In this case, the material transfer from the upper to the lower table occurs through a chute, which is arranged opposite to the main flow direction of the upper table and which ends on the lower table.

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6 The invention makes it posible, to achieve a high degree in grain separation, in particular, also for stone selection. Also, advantageously little air is used and the process and the device are simple and, in particular, are not very sensitive to through-put variations and do not dust up from the inside.

In the following, a few embodiments of the invention are explained with further details. It is shown in: Fig. 1 the simplest form of a small table selector for stones, Fig. 2 the product in-feed onto the layer table, Fig. 3 the same solution principle as in fig. 1, but with two table surfaces, in particular, for large product through-put, Fig. 4 a solution according to fig. 1, but with a recirculating air duct, Fig. 5 a solution according to fig. 3, but with a recirculating air duct, Fig. 6 fig. 5 with recirculating air separator, Fig. 7 is a solution similar to fig. 3 with the additional formation of two heavy fractions apart from 'the stone selection, Fig. 8 a variation of construction to that of fig. 7, Fig. 9 shows a stone sink on the layer table surface, Fig. 10 shows the device as in figs. 3, 7 and 8 with the duct for the recirculating air fed through the box.

In the following, reference is made to figs. 1 and 2. Fig. 1 shows a basic type for a new stone selector 1, whereby the fresh grain material is fed through an inlet opening 2 onto a layer table 3 and from there is discharged as cleaned grain material through outlet opening 4.

4 4\ ~1 i 7 A closed hood is arranged above the layer table 3, which shows a suction opening 6. The hood 5, together with the layer table 3, forms a vibration unit 7, which, with the aid of a vibration generator 8, can be set into vibration with a vibration component into the direction of the upper end of the layer table 3. The upper end of the layer table 3 is formed as a final separation zone by means of guide panel 19. The whole vibration unit 7 is supported through spring elements 9 on a frame 10, which is firmly connected to the floor. Also connected to the frame 10 is the non-vibrating header 12, to which 'the inlet 2, as well as the air extraction line 13 is attached. Further, an air quantity regulating flap 14 is installed in the air extraction line for the adjustment of the aspired air through the whole stone selector 1. The connection of the vibrating parts, or the vibrating unit 7 with the header 12, respectively, occurs through flexible sleeves which are arranged after the inlet 2.

Seen in plan view, the layer table 3 shows a preferably at least approximate rectangular shape. At the table, the layer table 3 may be work. The product transfer point The width is designated with "B" The formation of a broad-faced n veil, for the purpose of material the vibrating hood 5, the fresh box 17. The vibration enhances grain material in the distributor side of the elevated end of the layer withdrawn for the purpose of maintenance extends over the full width of the table.

in fig. 2, the layer thickness with naterial stream 20, also called material in-feed, occurs in two steps. As part of ;:din material is fed into a distributor the uniform, broad distribution of the box 17, which, in order to reinforce the effect, is widened cascade-like towards the bottom. A baffle plate 18 provided on the distributor box 17 serves the same purpose, so that the grain material is fed onto the guide panel 19, which extends over the whole width of the table, already as a broad-faced product stream and then as a uniform, wide product stream 20 onto layer table 3.

L 1; r L l 8 The broad-faced spread of the product stream 20 is further supported in that the free end of the guide panel 19 has an overflow edge 16, thus, it is formed in a trough-like manner. For the purpose of preliminary separation of heavy material from light material, the trough-shaped guide panel 19 may also show bottom openings for the passage of the heavier admixtures.

The broad, uniform spread of the product stream on the layer table 3 is made particularly clear in fig. 2. The same figure shows the layering, which has been exaggerated deliberately. Layer table 3 shows a rough mesh grating 21 as a product support and is constructed in the known form of sandwich construction, whereby the mesh grating forms the top side, which is carried by sheet metal strips 34 in honeycomb-fashion, which at the bottom are held together through a finely perforated sheet metal 22.

Cleaning bodies 24 are arranged in the individual fields 23 between the sheet metal strips 34, which keep the mesh grating 21, as well as the perforated sheet metal 22, clean. Important is also, that the perforated sheet metal 22 h-s an air resistance, which is much higher than the air resistance of the mesh grating 21, ie., in the order of magnitude of 1:10.

With this measure, the air distribution can be held approximately constant independent of the layer thickness on the mesh grating 21 over the whole surface area of the layer table 3.

The layering of the material itself consists essentially of three different layers, whereby the lower, heavy layer 25, which contains the heavy admixtures, is conveyed upwards on the table through the mechanical throwing movement of the vibration. A light layer 26, which has been freed of heavy admixtures, is held, not only in the loosened state, but also in suspension at a distance above the mesh grating 21 through targetted air flow. Since the layer table 3 is slightly inclined, and the upper light layer 26 does not receive a direct feeder impulse in the upwards direction of the table, but is still under vibration, it flows towards the lower part of the table.

9 Moreover, the inclination of the layer table 3 can be set with an adjustment device 35. A third layer 27 consists of the actual heavy admixtures, mostly only individual particles, individual foreign bodies, stones 28 etc.

Good, heavy grains 29 and light particles, such as half grains, husk parts are represented in their approximately corresponding shape. The heavy material with the stones 28 sinks straight onto the vibrating table surface 7 and, due to the vibration and the rough table surface formed by the mesh grating 21, moves upwards on the table.

It is now important for the described function, that the air flow is guided correctly. The whole layer table surface is swept uniformly from bottom to top with a suction air flow, whereby the flow direction is made clear t'irough arrows 31. This air flow 31 sets the grain material into a highly fluidized state. Since only the heaviest parts, that is, the stones 28, should be separated onto the elevated end of the table and transferred from there into a stone lock 45, a corresponding reverse blast flow 33 is formed, which prevents light particles or grains from being transported upwards along with the heaviest admixtures. The reverse blast flow is formed preferably underneath the guide panel 19, If the guide panel 19 is firmly attached to the wall of the hood, then the air directed into the slot between guide panel and layer table can only escape in the direction 33.

Thus, ahead of the final separation zone, the material, with the exception of the stones 28, is prevented from migrating further up by the air flow.

The stones 28 may continue their movement towards the elevated end of the table.

N 41 1rj In practice, this reverse blast flow 33 causes a flow front, or flow front reversal 32, respectively, to be clearly established. At the point of the reversal of direction of flow 32, the grain material 29, which is freed of stones 28 is lifted from the table surface by the strong air flow 31, 33 and flows now freely downwards along the table, together with all other light material in the upper separated light layer 26. The lightest fraction is carried out straight at the outlet 4; a medium grain fraction can possibly make several circular migration movements up and down the table, which is particularly applicable to boundary grains.

In figs. 1 and 2, the product stream 20 is fed directly into the zone of the flow reversal 32. The flow reversal 32 is caused by three forces, namely the mechanical feeder effect upwards along the table, fluidic flow of the upper layer 26 downwards along the table, as well as the reverse blast flow 33.

The constructional main difference between fig. 3 and fig. 1 is, that fig.

3 shows that two layer tables are used, one layer table 3a and a lower layer table 3b. Fundamentally, both layer tables 3a and 3b are of the same construction, such as shown in fig. 2. In principle, the reverse blast flow 33 is missing in the upper layer table 3a, so that not only the heaviest admixtures, but the whole heavy layer 25 is moved upwards on the table and drops through a discharge channel 40 over a baffle 41 onto the guide panel 19, From the guide plate 19 onwards, the functioning of the layer table 3b is identical to that of the layer table 3 of fig. 1 or 2, respectively.

In order to prevent the freshly entered product stream 20 from the distributor box 17 being mixed directly with the heavy layer 25, a baffle plate 42 is arranged at the uppermost point between the distributor box 17 and the layer table 3a.

j ;"t 1- 11 The off-flowing product stream is released through a product lock 43 directly into a discharge channel 44 of the lower layer table 3b. The two material streams of the two layer tables 3a and 3b, which have been freed of the heaviest admixtures, are combined again at outlet 4. All heaviest admixtures, such as stones 28, etc., are separated first, together with the heavy layer 25. The actual separation and the diposal of the stones 28 through the stone lock 45, takes place on the lower layer table 3b. The stone selection takes place in two sequentially and spatially soparated steps. Initially, a concentrate is formed with all heavy material, for example, 30% to 60 of the whole material through-put on the upper layer table 3a and only from the reduced material through-put are the stone and other heaviest admixtures be sorted and discharged separately.

With regard to product guidance, fig. 4 is identical with fig. 1 and fig. corresponds to fig. 3. The solution proposal in fig. 4 and fig. 5 contains, however, a hermetically sealed box 50, which is divided by the layer table(s) into an upper extraction room 51 and a lower suction room 52. On the side at the lower end of the layer table(s), a duct for recirculating air 53 is placed, which is connected to an air return duct 55 by means of a flexible hose 54 and a air return connector 55'. An air flow restrictor 56 is arranged in the air return duct 55. In fig. 4 and fig. 5, the box itself is supported on a fixed frame 10 through spring elements 9. On the top side of the box 50, a material inlet connector which connects to the material inlet 2, is arranged on one end, an air extraction connector 13', which connects to the air extraction line 13, is arranged approximately in the centre and an air return connector 55', which connects to the air return line 55, is arranged on the opposite end.

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12 The previously mentioned connectors 13', 55' are connected, on one hand, to the non-vibrating header 12 through flexible sleeves 15, 54 and on the other hand, to the box 50, in order to take part in the movement. In the double machine in fig. 5, two outlets 4 are arranged as tubular product ducts 57 on each side (perpendicularly to the plane of the drawing), so that the remaining space between the two product ducts 57 remains available for the recirculating air duct 53. For better identification, box 50 is surrounded with a dashed line in figs. 4 and In fig. 6, as a supplement to figs. 4 and 5, a recirculating air separator with suction fan 61, c.s well as motor drive 62, is additionally shown.

Hereby, the air extraction connector 13 leads directly into the recirculating air separator 60, whereby the significant or, respectively, the interfering part of fine husks and dust is extracted from the air flow through the dust extraction line 64.

In most cases, where recirculating air is used, air cleaning is of advantage, because dust accumulation in the whole plant can be effectively avoided and reliability and hygiene can be increased. The recirculating air operation has the significant advantage that only a minimal amount of air, for example, 10% of the recirculating quantity of air, must be directed through fine dust filters. The aspiration connection 65 is provided for this. The recirculating air separator 60 can, together with the fan, be mounted directly on the room ceiling 66.

Fig. 7 shows a basic difference to fig. 3, whereby in fig. 7 only a small part of the material through-put is transferred from the upper layer table 3c at the highest point through a series of large holes 71 across the width of the entire table, downwards to the uppermost zone of the flow reversal of the lower layer table 3d.

.IEUU~EELU:kNJ i I I' i i; 13 The main bulk of the heavy material is directed in the region of the lower end of the table, over a chute 72, to approximately the centre of the lower layer table 3d, again, across the entire width of the table. Several test series have shown that with this solution, still the main part of the stones is transferred through the holes 71 directly onto the lower layer table 3d. With the solutions according to fig. 7 and 8, it is important that the upper layer table has only a less rough surface than the lower layer table 3d, as is shown in fig. 9, whereby the upper layer table 3c consists of perforated sheet metal and the lower layer table 3d is made from mesh grating.

A particularly interesting original thought is now shown in figs. 8 and 9.

This is the use of a stone sink 80 in the region of the upper layer table 3c. The functioning is as follows: The stone sink 80 consists of a troughlike pit 81, which extends over the entire width of the layer table 3c.

Similar to fig. 2, two different layers are formed in figs. 8 and 9 as well, that is, one heavy layer 25 and the light layer 26, which has been freed of heavy admixtures.

Because the surface of the upper layer table 13 shows only slight roughness, no actual upwards flow occurs; at least the whole of the heavy layer cannot be be moved upwards. It is more likely that the heavy layer moves downward along the table at a greatly reduced rate, as is indicated by the single arrow 82. In contrast, the light layer 26 moves down the table with high velocity (double arrow 83). Upon reaching the region of the pit, the heavy layer sinks of necessity into the stone sink 80. The stone sink 80 shows a number of passage openings 84 at the bottom, through which part of the material, together with the stones, is discharged continuously onto the chute 72 underneath it, or, respectively, the lower layer table 3d.

L. r- 14 With correct tuning of the number of effective passage openings 84 in relation to the mass flow of the heavy layer, the light and heavy layers can be separated in such a way that the heavy layer 25 is constantly sinking completely into the stone sink 80 and carried away directly downwards. This results in two great advantages: 1. A high degree of selection for the heaviest admixtures (stones, etc.) is achieved 2. With minimal additional expenditure, the additional separation of the heaviest admixtures into a clean heavy fraction (good grain) and the rest into a light material fraction (husks, undersize and broken grains) can be achieved.

This makes it possible to carry out the separation of the various basic fractions (stones, etc., heavy, light) in a single device and with very high quality.

Finally, fig. 10 shows a device, which works along the same principles as the devices according to figs. 3, 7 and 8. For this reason, a repetition of the description of the same structural components is superfluous. The device according to fig. 10 distinguishes itself from the previously mentioned devices merely in that a recirculating air duct 53 is arranged separately in the box 50, so that the influence by it on the flow characteristics of the air in the box 50 can be avoided.

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Claims (9)

1. 2. Process according to claim 1, characterized in that S, the ducting forms a box together with the first layer table which is set into vib- raion. -16-
2. 3. Process according to claim 1 or 2, characterized in that a stationary platform is arranged above the vibrating box and a stationary fan is arranged on top of it, whereby the recirculation of air is maintained by the fan
3. 4. Process according to at least one of the preceding claims, characterized in that part of the grain mixture is transferred from a first to a further layer table which is arranged underneath the first layer S table whereby the recirculating air sweeps ~through both layer tables. Process accorcing to at least one of the claims 1 to 4, characterized in that the material is fed in as a broad-faced stream into the region of the elevated end of the first table, the exhaust air is extracted in the center and the supply air is returned in broad-faced form in the region of the lower layer table end.
4. 6. Process according to at least one of the claims 2 to 5, characerized in that the material is fed in as a uniform drop flow, which extends over the entire width of the first table and that a material feeder provided for this, is firmly connected to the vibrating box and is formed in the shape of a cascade, which widens from top to bottom. .Lt\ 'N -17
5. 7. Process according to at least one of the claims 1 to 6, characterized in that the recirculating air is cleaned of dust particles in the region of the central air extraction in stationary aranged elements.
6. 8. Device for the separation of grain mixtures, in particular for the selection of heavy admixtures, such as stones from grain material with an air-swept, inclined layer table which can be set into vibration, and with air ducting for characterized in that the layer table as well as the ducting for the air extration and the air return, form a vibrating box
7. 9. Device according to claim 8, characterized in that the inside of the box is equipped with: an air ex- S,° o traction space above layer table and a supply duct for recirculating air separate from it, which enters in the region of the lower end of th, layer table Device according to claim 8 or 9, characterized in that a material supply inlet which is widened cascade-like from top to bottom, is part of the vibrating box and is arranged in the region of the elevated end of the table. 1- j
8. 18- 11. Device according to at least one of the claims 8 to 10, characterized in that a material entry connector is arrangend on one end of the top side of the box an air extraction connector at about the center and an air return duct connector at the opposite end. 12. Device according to at least one of the claims 8 to 11, characterized in that at least two layer tables are arranged on top of each other Sinside the box whereby the recirculating air S Sl sweeps both layer tables from bottom to top and that a product transfer device is S provided for the transfer of material of the upper S.. layer table onto the lower layer table 13. Device according to at least one of the claims 8 or 12, charaterized in that the material supply device and/or the product transfer device enters over the en- tire width of the layer table and an entry of the feeder duct comprises a guide panel ar- ranged at a distance above the layer table S. S 14. Device according to at least one of the claims 8 .055*5 to 13, characterized in that the box is supported in a frame capable of vibrating, whereby the frame comprises in its upper region a stationary header ii i I.
9. 19- Device according to claim 14, characterized in that flexible sleeves are arranged between the sta- tionary header on one hand and the air extraction connecor or the air return connector re- spectively, as well as the material entry connector on the other hand. 16. Device according to claim 14 or 15, characterized in that that a recirculating air separator is arranged above the stationary header 17. Device according to claim 16, characterized in that recirculating air separator is connected to a suction fan and a dust extraction duct *o 0 18. Device according to at least one of the claims 8 to 17, characterized in that the recirculating air duct is connected with an aspiration connection for a fine-dust filter. Dated this 28th day of March 1991. Buehler AG. Patent attorneys For and on behalf of the applicant: F.B. RICE CO. 000 9 ~C