EP0593955B1 - Device and method for cleaning a mixture of substantially granule-shape grains - Google Patents

Abstract

A device for cleaning grains (1) present essentially in the form of granules and containing particles of varying size, to remove said particles, has a housing (5) which has on its top side an inlet (11) for the grains (1) and on its underside and outlet (12) for the cleaned granules (18) and possesses a distributing plate (whizzer) (6). Cleaning gas flows through the granules falling through the device, opposite to the direction of movement of said granules. In the inlet region there is provided a guide device (19) for the inflowing grains (1) and a retaining device (2) for the larger particles (3). The distributing plate (6) is provided with a cover cowl (16) which has an opening (17) for the inlflowing grains. Between the distributing plate (6) and cover cowl (16), a gap (8) is provided which preferably has a height of approx. 8 to 15 mm. <IMAGE>

Description

The invention relates to a device for cleaning one essentially in granular form and particles grain batch containing different sizes from just these particles according to the preamble of claim 1 and a process for cleaning this grain mixture after Preamble of claim 7.

Due to the variety of possible origins in the course of different processes, such as grinding, crystallizing, Condensation - to name just a few important ones - shows particle collectives correspondingly different distribution spectra on. For example, there are particles after passing through of grinding plants in different grain sizes, whereas for example plastics, such as polyethylene terephthalate or Polyvinyl chloride after crystallization and polymerization in Granules are present with abrasion or dust particles are offset. The size of such granules varies from approx. 3 to approx. 5 mm for the diameter, and from approx. 2 up to approx. 5 mm for the length. Polyamide granules can also to be taller. In contrast, the fine dust particles are in contrast only up to a maximum of approx. 50 µm in size. Larger particles, sometimes also called angel hair or bird nests, the disc, can be ball-shaped or spherical and have a diameter of approx. 2 cm can have up to 10 cm, occur especially with pneumatic Funding on. Granules conveyed through pipelines becomes, rubs against the pipe, it heats up, forms adhering threads or foils that tear off or peel off. The length of such threads or hairs is extreme different, each can only be a fraction of a millimeter be long, but to be meter-long due to positive locking Form or assemble into balls. In the case of out Batches of particulate matter receive special value a classification with great discriminatory power, so this is in second case, which is the separation of the granules from much smaller dust particles and substantially larger ones Particles is not important.

By means of known wind classifiers, such as in DE-A1-34 25 101, DE-A1-30 24 853 or US Pat. No. 2,913,109, it is possible to get heavier from lighter particles to separate with great selectivity. This is achieved that the sifting air stream flows in a vortex shape in the separation chamber and / or divided into several partial streams of the same volume becomes. Spreading plates with wings are used to improve the separation the heavier particles are thrown outwards, the lighter through a centripetal air flow taken away. A combination is shown in EP-B1-237 641, in which brittle regrind from a roller mill first on one with Baffle-filled feed plate is crushed so that contained fine material portion and exposed at the subsequent Sighting is removed.

Such classifiers are provided for fine fractions of coarse fractions to separate, a separation of fine and substantial larger particles at the same time in order to clean purified granules received, however, is not possible. The separation into several grain size fractions with the help of multi-component classifiers (see e.g. DE-C-371 504) possible and with great selectivity, yes this is associated with considerable structural effort.

The invention is based on the object, a To provide device and a method, whereby in the course Both fine parts and coarse parts of the same viewing process Portions of one essentially in granular form Batch of grain can be separated, so that the granules free of these shares. This is achieved through realization the characterizing features of claim 1 or of claim 7.

The fact that in the inlet area for the different with the particles Size loaded, essentially in granular form present grain batch a retention device for the particles is provided which are substantially larger than that Granules are found before the spreading plate is loaded with the one then only loaded with particles of smaller size Grain batch a pre-cleaning of the batch instead. A guide for the incoming batch ensures that this passes through the restraint.

The already pre-cleaned one loaded with particles of smaller size Batch then hits the spreading disc in the flow of gravity, which is preferably provided with a hood, which in particular cone-shaped with a recess for that on the Scatter plate flowing batch is formed. Such Hood causes bouncing off of the spreading disc if necessary Batch cannot emerge again against the direction of the fall. There is a on the respective peripheral edge between the hood and the granulate Gap provided, the size of the typical granule diameter depends on the grain mixture to be cleaned. So is for Polyester or polyamide granules a gap height of 8 to 15 mm is an advantage. The spreading disc itself is designed accordingly, preferably in the form of one on a truncated cone sitting cone with a larger angle of inclination against the horizontal as the angle of inclination of the truncated cone, so that ricocheting grain within the bounded by the hood Area remains and only from the gap between the spreading disc and Hood can escape. This could also have such an effect achieved that the spreading disc in the form of a cone alone is trained, but is an education in the form of on the To prefer the truncated cone, because it Problem zone, which is given by the recess in the hood, can be better controlled.

To ensure a uniform, as horizontal as possible diffuse curtain received, the extreme of the rising cleaning gas effectively flowed through and cleaned of smaller particles the edge area of the spreading plate is preferably horizontal and ring-shaped.

Since the batch loaded with the smaller particles also contains them contains bound to the granules, it is advantageous that of batch emerging from the spreading disc as a homogeneous scatter curtain to hurl against a baffle that spreads the spreading disc radially surrounds, particles adhering to the granules knocked off become. The inlet opening for the cleaning gas is preferably which are in particular in the form of an annular channel and is therefore uniform over the circumference of the device Flow possible, just below the impact device provided, particularly in terms of construction advantageous measure. A central inlet channel for the cleaning gas, which feeds the gas from below is also possible, but would be the height for such a cleaning device enlarge.

To ensure that the grain mixture flowing in from the inlet after passing the restraint through the recess in the hood on the spreading plate is above of the spreading plate provided a funnel, which if necessary has a wall raised on one side, so that the incoming batch is safely captured. This funnel can unilaterally be attached to the housing inner wall, this not only from pure fastening purposes happens, but at the same time the Possibility offers that the cleaning gas flowing upwards optionally divided into at least two sub-streams, with which the opportunity is given to both turbulent and approximate laminar (hereinafter referred to as "smoothed") flow behavior to reach. Baffles on the inner wall the housing are provided, serve to calm the after cleaning gas flowing above in the zone above the spreading disc and below the restraint. Are the baffles only arranged on one side, so only a partial flow can be targeted of the cleaning gas are smoothed. This partial flow can then optionally be directed so that it is the restraint flows through and retained larger ones Particles due to the relative to the granules relative large inflow resistance of these particles. Of the Retaining device pushed off larger expansion particles are also carried away by the calming current while the granulate-grain mixture in his case essentially is not hindered.

So that the gravity flow of the granules on the spreading disc is not hindered, the granules are not swirled or entrained is the area above the spreading disc designed so that the flow rate of the upward flowing cleaning gas is lowered. The cross section that in this area the cleaning gas flows through to.

The restraint preferably consists of one another parallel, vertical walls so that the larger particles, which are present, for example, as angel hair or bird nests, get stuck on the top edges, while the Grain batch containing particles of smaller size between them Walls can fall through. This restraint that is also referred to as a thread comb, preferably has a slant in top edges aligned with the solder so that retained, particles resting on the upper edges in the stream of Cleaning gas can slide and be carried by it.

The guide device for that entering the housing of the device Batch that skipping the restraint through the granules should prevent, in the form of swiveling Flaps be formed with their free side up to reach the top of the restraint so that restrained larger particles under these flaps as a result of other, retained particles can slip away. Alternatively, or possibly in addition to that described Flap arrangement, the guide device can be a function of from the amount of, for example, from a storage vessel into the Housing incoming product include actuatable dosing, which is arranged on the storage vessel.

As a result of the rotation of the spreading disc, this will also go up flowing cleaning gas is set in rotation. This will make the Differential speed between gas flow and granules reduced. An arrangement therefore proves to be advantageous for a swirl against the gas flowing into the housing Direction of rotation of the spreading disc is issued. To do this are preferred Guide vanes in the particularly designed as an annular channel Inlet opening for the gas arranged. These guide vanes should preferably be adjustable, especially depending on the speed of the spreading disc, so that different product or process-specific conditions can be met.

Fig.1

einen Längsschnitt durch eine erfindungsgemäße Vorrichtung;

Fig.2

einen Teil-Längsschnitt und eine Teilansicht bei entfernter Gehäusewandung einer Ausführungsvariante;

Fig.3

eine Fig.2 entsprechende Vorrichtung mit alternativer Ausbildung des Einlaß-Dosierorgans; und die

Fig. 4 und 5

je eine weitere Ausführungsvariante.

The invention is described below by way of example with reference to drawings. Show it:

Fig. 1

a longitudinal section through a device according to the invention;

Fig. 2

a partial longitudinal section and a partial view with the housing wall of a variant embodiment removed;

Fig. 3

a Fig.2 corresponding device with an alternative design of the inlet metering; and the

4 and 5

one more design variant each.

From Fig.1 is an inventive device for cleaning one essentially in granular form and particles of different sizes containing grain batch 1 from just from these particles. This device is as follows referred to as granule cleaner. The granule cleaner has a housing 5 with an inlet 11 for the batch 1, which contains coarse and fine impurities. At the bottom End of the housing 5 is an outlet 12 for the contaminants cleaned granules 18 are provided. Cleaning gas occurs flows through an inlet opening 13 into the housing 5 upwards, against which gravity flows through the housing 5 moving batch 1, and leaves the housing through the outlet opening 7. That with impurities in the form of coarse and fine particles laden grain batch 1 occurs, if necessary from a feed vessel 20, into the housing 5 and passes a restraint 2 made up of several to each other parallel, vertical walls on a chute 2 ' consists. The distance between the walls depends on the size of the granules from; in the case of a granule cleaner which is suitable for polyester or Polyamide granules is provided, it is approximately 15 mm. Such a restraint device is also referred to as a thread comb. Larger particles 3, which are in the form of "angel hair" or "bird nests" are incurred to the Top edges of the thread comb 2 get caught, whereas that with fine particles in dust form loaded granules 4 through this can fall through between the walls. On the inside wall of the The inlet area of the housing 5 has hinged flaps 15, which with their free sides on the upper edges of the Thread comb 2 rest. This prevents incoming Granules over lying on the upper edges of the thread comb 2 Impurities 3 can jump, it must through Thread comb 2 run. The coarse impurities 3 are after and after under the rotatable flaps 15 as a result of pushing other impurities pushed through by the cleaning gas, that carries the fine impurities with it of the high flow resistance compared to that of the granules taken away by the gas and carried away.

The granulate 4 loaded with the fine particles falls through the thread comb 2 through to the spreading plate 6, by a recess 17 in a seated on the spreading plate 6 Cover hood 16. Spreading plate 6 and hood 16 are over narrow Connectors (not shown) spaced from each other, so that a gap 8 of about 10 mm remains free between the granules can leak. However, this gap width is not critical.

The spreading disc is set in rotation by a motor 21 the wave of which he is directly attached, as well as the one connected to it Cover 16. As will be explained later, is the circumferential speed of this spreading plate is appropriate approximately 6 to 16 m / s, preferably 8 to 14 m / s, based on the average diameter of the spreading gap 8 Spreading plate 6 not noticeable granules spring back again can, spreading plate 6 and cover 16 have approximately the shape a double cone, so that the granules always against the gap 8 is reflected. For this purpose, the spreading plate 6 is preferably in Form of a truncated cone seated on a horizontal ring 6c 6b formed, which carries a cone 6a. The angle of inclination of the cone 6a against the horizontal is larger than that of the truncated cone 6b.

The granules are opposed in the form of a homogeneous diffusing curtain 9 thrown a baffle ring 10, adhering, dusty Impurities are knocked off and the granules are reflected against the outlet opening 12. The impact ring 10 has the shape of a truncated cone shell; this and the corresponding Selection of the rotational speed of the spreading plate 6 causes that the granules are not destroyed, such as this this is the case with loading plates with impact elements would be (for example, according to an embodiment such as is described in EP-B1-237 641 and that of smashing of agglomerates).

The cleaning gas passes through the annular channel-shaped inlet opening 13 just below the impact ring 10 in the housing a, flows through the granules reflected by the impact ring 10 and the scatter curtain 9, where it is the knocked-off fines, Remains of fine particles and other dust-like particles that are still carried along Impurities. The cleaning gas then flows in the area between cover 16 and housing inner wall high, the cross section of this area increasing towards the top and the flow rate decreases. As a result of Rotation of the spreading plate 6 and the cover 16 is also gives a swirl to the cleaning gas. Baffles 22 on the Housing inner wall are arranged above the spreading plate 6, serve to calm the upward flowing gas stream threads in this area, possibly through the thread comb 2 could fall through with the dust-laden granules, as well as larger impurities pushed off the thread comb. This coarse and fine impurities with it bearing, the cleaning gas leaves the housing 5 through the outlet opening 7.

Fig.2 shows an alternative to Fig.1, in which both the guidance of the grain mixture as well as the gas flow is optimized. In the right part of Fig.2 is a central longitudinal section of the granule cleaner, while the left Part of Figure 2 is a view of the granule cleaner after removal the housing outer wall illustrated. The contaminated batch 1 is introduced into the housing 5 from a feed container 20. The feed container 20 is rotatable about an axis 23 stored. With increasing filling of the feed container 20 Via a cutting edge 25, a slide 19a mounted at point 26 always open. This ensures that the thread comb 2nd is always fed from a bed, via the thread comb jumping granulate is avoided.

The dust-laden granulate runs through the thread comb 2, a one-sided attached to the inner wall of the housing 5 somewhat higher trained funnel 29 causes the granules securely through the recess 17 of the cover 16 reaches the spreading plate 6. The thrown from the spreading plate 6 Scattering curtain 9 (Fig. 1) meets the impact ring 10, dust adhering to the granules is knocked off and from entrained with the cleaning gas. The cleaning gas passes through the ring channel 13 in the housing 5, with him from guide vanes 28 an opposite to the direction of rotation of the spreading disc 6 Swirl is given. The gas flows through, as described above, granules reflected against the outlet opening 12 and the scatter curtain, knocked off and carried along by the granulate Sweeping dust with it. Since the collecting funnel 29 its raised side attached to the inner wall of the housing 5 the gas flow is there after being at the top of the Cover 16 has flowed along, on both sides of the Flow up funnel 29. The thread comb projecting into the housing 5 2 is from a gas stream smoothed by baffles 22 flows from below, which the larger particles, like angel hair and bird nests. Because the collecting funnel 29 is connected to the housing inner wall, there is the possibility the gas streams flowing up on its sides steer that they no longer go through thread comb 2, and only the partial flow that is on the free side of the collecting funnel 29, calmed by the guide plates 22, flows high, flows through the thread comb 2. It has proven to be beneficial shown, only a partial flow of the cleaning gas through the Thread comb 2 to guide only the coarse ones Contaminants are carried away. It is conceivable the size this gas flow through pivotable baffles on the inside wall of the housing and / or on the outer sides of the collecting funnel 29 and / or to make adjustable on the cover 16, depending on the degree of pollution of the batch or on the size the granules or the flow rate of the cleaning gas.

The guide vanes 28 should preferably be designed to be adjustable be so depending on the rotation speed of the Scatter plates 6 - and possibly the flow speed the gas - the gas can be given such a swirl that optimized the difference in speed between gas and granulate becomes.

3 shows an embodiment of the granule cleaner corresponding to FIG. That from the - here firmly arranged feed container 20a - outflowing batch 1 is by the as a pendulum flap 19b trained metering element. The bigger the Filling the feed container 20a, the wider the swing flap opens 19b, which can be reset via a weight 30. In order to is achieved in accordance with the arrangement shown in FIG. 2, that the thread comb 2 is always loaded from a bed becomes.

It goes without saying that the thread comb 2 described is independent per se of which is advantageous, like the cleaning device underneath looks. However, it should be mentioned that the necessary inclination of the pouring channel supporting the walls 2 under certain circumstances for the delivery of the centrifugal or Scatter plates 6 is not always advantageous because of the falling Granules 4 possibly more or less from the center and the axis of rotation can hit it and so the granulate experiences 4 different accelerations.

It is therefore possible in the sense of FIG. 4, above the spreading plate 6 a vertical, on the axis of rotation of the spreading disc Arrange 6 directed shaft 31 from a chamber 105 in the inclined chute 2 'with the vertical on its top Thread comb walls 2 opens. The chamber 105 corresponds thus approximately the space designated 5 in FIG. 1.

The air can now either in the one hand in parallel Spreading plate 6 enclosing space and on the other hand in the in the mentioned manner, having the thread comb Flow into chamber 105. However, it preferably flows through the 4, both rooms one after the other. For this a transfer pipe 32 is provided, which over the air paths 13 and 9 inflowing air at 10 loaded with dust receives and the chamber 105, preferably in the area of Pouring channel 2 '. The pouring channel 2 'can optionally be fork-shaped at its free end, so that the prongs of this fork are formed by the vertical walls 2 and the floor in between recedes a little, so that air flows from below between the vertical walls 2 and any threads from the top of the walls 2 can tear up freely, whereupon the air (or a Inert gas) flows out again at 7.

While in the previous embodiments the one Pre-separation restraining device 2 as one 5 is a restraint device 102, which in itself is also granular for a pre-separation Suitable for fine ingredients and therefore more universally applicable is. It is advantageously a concentric to the axis of rotation of the spreading plate 6 arranged feed hopper 205 provided with a vertical axis, that with a tripod support 41 is held stationary in the jacket 10 '. Above this Feed funnel 205 is a construction with a Guide cone 102 ', which together with a conical metering valve 33 and a valve seat 33 'is similar to that shown in DE-A-29 29 672 is shown. However, the guide cone forms 102 'together with an air guide ring 102' 'a pneumatic one Restraint device 102.

For this purpose, the air guide ring 102 ″ closes at the bottom with a lower, here funnel-shaped, surface 34 with an optionally adjustable gap 35 to the feed hopper 205 in order to forward a message via the Gap 35 penetrating partial flow 36 through the inlet 13th to cause air supplied. Of course, for the Feed this flowing through the restraint device 102 Partial stream 36 also other constructions, such as, if necessary adjustable nozzles distributed over the circumference of the surface 34 or the like. be provided.

The cross-sectional ratio of the slots 35, 35 'now provides for a relatively even and flow-stable branch of air flow 36 from residual air flow 36 '. It also goes without saying that the lower surface 34 is not necessarily funnel-shaped must be, but possibly also cylindrical or can be conical. But is the guide cone 102 'after provided at the bottom with a counter cone 37, however, forms advantageously together with the surface 34 the even distribution favoring air duct between these two surfaces, the one from the slot 35 in air that has entered the relatively wide feed funnel 205 initially accelerated again and evenly over the circumference is distributed before the top, preferably approximately parallel to the guide cone 102 'extending surface 38 reached and from it is deflected over the surface of the guide cone 102 'in such a way that it sweeps across the surface of the guide cone 102 '.

Now the guide cone 102 'has a function that is capable of technology has no role model. Because on the one hand is with the conical surface is imperatively connected that the radially inside trickling down through the valve 33, 33 ' Material flow due to the increasing radially outward Tapered surface thinned more and more until only one of the edges Single grains of material veil remain. On the other hand defines the guide cone 102 'together with the surface 38 an expediently adjustable gap 39 which is formed in this way or can be set that larger balls of thread Material can be stopped. By using the area 38 with the slit nozzle 39 formed in the guide cone 102 'blows the partial flow 36 over the edge area of the guide cone, where the material veil is diluted and therefore releases any threads, so that such Threads 3 can be easily taken.

The valve body 33 is in one relative to its seat 33 ' Way adjustable or self-adjusting, as from the DE-C-29 29 672 has become known, the content of which by reference should be considered disclosed here, so that an in-depth Description of the associated adjustment mechanism 42 is omitted can.

The height of the guide cone 102 'is for the purpose of adjusting the gap 39 relative to the air guide ring 102 ″ with the aid of an adjusting device 49 fixed adjustable. A change in the flow cross-section the column 35 and 35 'is by raising or lowering the unit consisting of traffic cone 102 'and guide ring 112' ' possible from the outside. Similar to the adjustment device 42 a support rod 44 is provided at its upper end a screw nut supported on a fixed stop 45 46 wears.

To accommodate both adjustment devices 42, 43 in the smallest of spaces To be able to, is advantageously one of the support rods, here the rod 47 of the adjusting device 42 for the valve 33, 33 ', hollow and includes the other rod 44.

Another guide for the guide cone 102 'is on his Bottom provided where a plurality, conveniently three, guide rods 48 protrude vertically downwards and in guide bushings 50 of the stationary funnel 205 are guided. To this Way is a uniform slot width, and thus one even air distribution over the entire circumference of the guide cone 102 'and an adjustable division of the air flow secured in partial flows 36, 36 '.

An advantageous dimensioning will also be described with reference to FIG. 5, which can be used analogously for the other exemplary embodiments is. If you have a circle around the edges the spreading plate 6 pulls, there will be a maximum in this area Particle speed. In the embodiments 4 and 5 are the particles in this Edge area by a radially outwardly extending Flange 16 'out. In the middle of the resulting Slot 8 is a dash-dotted line m in Fig. 5 pulled, and it turned out to be favorable if the Motor 21 or at most between it and the spreading plate 6 arranged gear are dimensioned such that in Edge area of the spreading plate 6, and in particular in the middle Area m of slot 8, an average particle speed from 6 to 16 m / s, preferably 8 to 14 m / s, results.

Numerous variants are conceivable within the scope of the invention; for example the restraint device 2 or 102 can also be used without a turntable can be realized with the same advantages.

Claims (9)

1. Apparatus for the purification of a grain mixture (1) which occurs substantially in granule form and which contains particles of different sizes, of precisely those particles, comprising a housing (5) which has at its top side an inlet (11) for the mixture (1) and at its underside an outlet (12) for the purified granules (18), at least one intake opening (13) and at least one discharge opening (7) for a purification gas so that it flows in opposite relationship to the direction of movement of the granules falling through the apparatus, and a scatter plate (6) arranged beneath the inlet (11), wherein provided in the inlet region are a guide device (15; 19) for the incoming mixture (1) and a retention device (2) for the larger particles (3), characterised in that the retention device (2) has at least one gap (39) which is defined by two, in particular mutually parallel walls (2; 102'; 102'') and through which at least a partial air flow (36) is passed,
      and/or
      the retention device has an obliquely downwardly inclined chute (2') which in particular is provided with the vertical walls, and the retention device opens into a chamber (105) which is disposed above the scatter plate (6) and out of which leads a vertical shaft (31) which is centred on the scatter plate (Figure 4).
2. Apparatus according to claim 1 characterised in that there is provided at least one of the following features:

   a) the walls (2) are directed approximately vertically and their upper edges are oriented in particular inclinedly in relation to the perpendicular;

   b) the walls (102', 102'') are directed inclinedly upwardly and preferably one of the walls is formed by a cone (102') which is loaded in its centre with the material;

   c) the space surrounding the scatter plate (6) has a communication (32) with the chamber (105) disposed thereabove to provide a serial connection for the air flow flowing through said communication.
3. Apparatus according to claim 1 or claim 2 characterised in that the guide device includes at least one pivotable flap (15) which extends with its free side to the top side of the retention device (2) and/or the guide device includes a metering member (19a; 19b) actuable in dependence on the amount of the incoming product (1).
4. Apparatus according to one of the preceding claims characterised in that a baffle arrangement (10) is disposed at the inside wall of the housing (5), surrounding the scatter plate (6) in an annular configuration - in particular directly above the intake opening (13) for the purification gas - and/or the cross-section through which the purification gas flows - in particular above the baffle arrangement (10)-becomes greater towards the gas discharge opening (7).
5. Apparatus according to one of the preceding claims characterised in that guide vanes (28) are provided in the gas intake opening (13) which in particular is in the form of an annular passage so that a spin which is in opposite relationship to the direction of rotation of the scatter plate (6) is imparted to the purification gas, the guide vanes (28) preferably being adjustable, in particular in dependence on the speed of rotation of the scatter plate (6).
6. Apparatus according to one of the preceding claims characterised in that at least one of the following features is embodied on the scatter plate:

   a) the scatter plate (6) is provided with a hood (16) which in particular is in the form of the surface of a truncated cone and which has an opening (17) for mixture (1) flowing into same from the inlet (11), the hood being arranged at a spacing from the surface of the scatter plate (6) of 3 to 50 mm - preferably about 8 to 15 mm -;

   b) the scatter plate (6) is in the form of a cone (6a) which is disposed on a truncated cone (6b) - preferably delimited by a ring (6c)-and which has a larger angle of inclination relative to the horizontal than the truncated cone (6b);

   c) the speed of rotation of the scatter plate (6) is such that the particle speed in the edge region (m) of the scatter plate is 6 to 16 m/s, preferably 8 to 14 m/s;

   d) guide plates (22) are arranged at the inside wall of the housing - in particular asymmetrically - above the scatter plate (6) and below the retention device (2) for smoothing at least a part of the purification gas flow which flows towards the discharge opening (7); and

   e) arranged above the scatter plate (6) is a hopper (29) - which in particular is fixed at one side to the inside wall of the housing - and the wall of which is of a raised configuration preferably at the side opposite to the intake (11) of the mixture (1).
7. A process for the purification of a grain mixture (1) which is substantially in granule form and which contains particles of different sizes, of precisely those particles, wherein the mixture

   is introduced into a housing (5) by way of an inlet (11) arranged at the top side thereof,

   in the inlet region the mixture (1) is subjected to a pre-purification operation in which the larger particles are retained by a retention device (2) and the mixture loaded with the smaller particles is guided in such a way that it must pass the retention device (2),

   as that happens on the path of the mixture which is substantially governed by the force of gravity to an outlet (12) for the purified granules (18), which is disposed at the underside of the housing, purification gas flows through the mixture in opposite relationship to its direction of movement, and

   radial acceleration is imparted to the mixture by virtue of impinging on a scatter plate (6) arranged beneath the inlet (11),
      characterised in that the upwardly flowing purification gas is divided into at least two partial flows of which one - in particular smoothed by guide plates (22) - flows through the region which can be associated with the retention device (2) and in particular through same.
8. A process according to claim 7 characterised in that the mixture (4) which is loaded with the smaller particles is radially accelerated by the scatter plate (6), it is flung in the form of a homogeneous haze (9) on to a baffle arrangement (10) which radially surrounds the scatter plate (6), from which it is reflected towards the granule discharge (12), wherein smaller particles adhering to the granules are detached upon impinging against the baffle arrangement (10).
9. A process according to claim 7 or claim 8 characterised in that a spin is imparted to the purification gas which passes into the housing (5) - in particular just below the baffle arrangement (10) or the scatter plate (6) - , the spin being in opposite relationship to the direction of rotation of the scatter plate (6) and the magnitude thereof preferably being variable in dependence on the speed of rotation of the scatter plate (6).

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