EP0199003B1 - Rotary air classifier with a centrifugal cage - Google Patents

Abstract

The invention relates to a rotary basket air classifier. A favorable predispersion of the material to be classified, particularly in the case of an upwardly directed spent classifying air line has always been problemmatical with such classifiers. According to the invention, the material to be classified is distributed over several stages, aided by dispersing blades and a higher drawing-off capacity of the spent classifying air is permitted by the branching of the drawing-off line.

Description

The invention relates to a rotary air centrifuge classifier according to the preamble of claim 1.

Such a classifier is known from EP 67 894 A1. Such classifiers need to separate the fine particles from the air in general dust separator, for. B. in the form of cyclones. For this purpose, it may be expedient to draw the classifying air out of the classifier as far as possible so that there is sufficient space for installing the downstream cyclones and the circulating air blower generating the classifying air. This is particularly important where the classifier is connected downstream of a mill and the classifier should be placed as close as possible above the mill in view of low investments.

However, this extraction of the visual exhaust air coaxially to the axis of rotation of the classifier and as centrally as possible on the centrifugal basket brings with it considerable problems with regard to optimal predispersion of the material to be viewed. However, particularly good predispersion is the prerequisite for excellent selectivity during the viewing process. In other words, with an optimally operating classifier, it is expected that as little oversize as possible will get into the fine material and at the same time as little undersize as possible into the coarse material if a separation grain limit is sought. The material to be viewed must therefore enter the viewing area as evenly as possible, naturally also preventing the item to be dropped into the viewing area, and in certain cases also falling into the viewing air swirl.

. However, this required predispersion is not guaranteed in the classifier known from EP 67 894 A 1, since there is an annular duct provided directly above the classifying space for supplying the classifying material or raw material around the suction line leading upwards, so that it can be assumed that in principle, the material to be viewed simply falls into the viewing area and an entry of material to be viewed against the air swirl cannot be ruled out.

In another classifier known from EP 23 320 B1, an attempt is being made to achieve a scattering effect for the classifiable material introduced, even with a coaxial upward suction line for the classifying air laden with fine material. Since only the outer, flange-shaped edge of the upper end of the centrifugal basket can be used as a mechanical scattering device in this known classifier, however, a good dispersing effect is not achieved. In addition, in this known classifier, the material to be sighted falls almost point-wise through two or more inlets arranged around the central suction line onto the flange-shaped edge rotating at a relatively high peripheral speed. The individual particles of the material to be sighted are radially accelerated immediately from each of the corresponding impact points, with only a triangular diffusion curtain that can be interrupted by neighboring diffusion curtains being formed in the event of a slight drag. In this known classifier there is also the disadvantage that the shape and spacing of the scatter curtains change with changing speeds of the centrifugal basket with regard to changed separating grain boundaries, so that a uniform distribution of the material to be viewed cannot be achieved. The lack of a central visible material feed, combined with the uneven distribution effect of the flange-shaped edge, therefore has a particularly unfavorable effect on the dispersion process which is to be aimed for optimally.

Since a good predispersion plays a major role in determining the throughput for the material to be sifted, this being particularly important in the case of previous grinding in a closed grinding material cycle, since fluctuations in quantity can have an abrupt impact on the classifying process To get predispersion.

So z. For example, a PSZ spiral wind sifter is known (cement-lime gypsum, year 38, No. 1/85. "New findings on sifter design", by F. Sgaslik, Fig. 7), in which a predispersion of the visible material is sought. The material to be sighted is fed in centrally in this PSZ classifier and is scattered from an inclined, rotating spreader plate into a non-rotating, conical distributor gap that widens downwards. The uniformity of the visible material distribution improves with increasing diameter. Experience has shown, however, that the angle of inclination of this distributor gap, which surrounds the visible space, depends on the coefficients of friction of the trickling material. In the case of an optimal distribution of visible material by trickling, the granular visible material must not fall, but must just slide, ie it must still be free-flowing. The trickle section must also be long enough to achieve the desired predispersion. In order to obtain a wide range of different _{'free-flowing} material to be separated in this known PSZ classifier, you go there the elaborate way to blow into the cone-shaped distribution gap purge air. In addition, this PSZ classifier has the problem that a large horizontal component has to be accepted for a sufficiently long trickling distance, the flow-correct distance from the centrifugal basket to the swirl-producing guide vanes being exceeded, and thus the annular visual space being enlarged. The resulting slight curvature of the required air spiral in the viewing space necessarily forces the user to work with higher air speeds while maintaining the same visual effect. this means however, that for larger amounts of air also larger separators, such. B. cyclone separators or filters are required, which significantly increase the investment in equipment. Starting from the above prior art, the invention has for its object to improve a rotary air centrifuge classifier with a view to a more optimal classifying, the essential disadvantages mentioned above should be avoided and good predispersion even with increased throughput rates of the classifiable material is achieved, and this should also be possible, if appropriate, even with a suction line that is led off centrally for the fine exhaust air loaded with fine material.

This object is achieved in a generic classifier by the features of the characterizing part of claim 1.

An essential idea of the invention for improving the sighting and the throughput capacity with a more favorable height of the classifier is to perform an essentially central task of the material to be sighted on a first spreading plate, at least one further spreading plate being arranged downstream of this. In addition to this spreading disc, dispersing vanes are provided especially in the area before the visible material enters the visible space, which further improve the uniformity of the spreading of the material to be sifted into the subsequent visible space. Here, the areas of the individual funnel jackets are enlarged in the direction of the visible space in comparison to the previous stage in order to achieve a thinning and uniformization of the diffusing curtain. Since flow and distribution discontinuities can occur in the dispersion process of the imported material, especially with an upward extraction line for the visual exhaust air and the fine material, the extraction line is preferably branched below the first spreading plate into several and especially two flow-symmetrical arranged exhaust air outlets. The multiple levels of spreading plates and funnel jackets compensate for any discontinuities that may occur. However, a higher suction capacity and also the connection of several cyclones is made possible by the multiple visual exhaust outlets. The concept according to the invention therefore permits an overall space-saving design of the classifier with regard to its overall height and its diameter, even with a high feed performance and high suction performance, this being achieved with largely optimal dispersion of the grain mixture to be viewed. In order to be able to control the parameters of the classifier, which influence the dispersion and classification, the spreading plates, the dispersing vanes and the centrifugal basket are preferably designed to be separately drivable. As a result, both the same and a different rotation of these devices can be achieved. The direction of rotation of these devices is such that the visible material flows into the visible air spirals circulating in the visible space in the same direction.

Even an upward discharge line is not an obstacle in the invention to provide a further, especially circular, spreading disc in this area. At this stage, the second spreading plate is combined with a tubular upwardly projecting peripheral wall coaxially surrounding the fixed suction line, this peripheral wall projecting axially upward into the mouth funnel of the first funnel jacket. With a sufficiently small distance between this peripheral wall and the suction line, an existing thin annular gap remains without impairing the suction power of the connected cyclones. However, this small annular gap can also be kept fluid-tight by a seal that enables the rotation of the spreader plate with its peripheral wall.

In order to create a classifier that is even more compact in terms of height, one can advantageously arrange the suction line from the centrifugal basket downwards where the external units allow it. As a result, the first stage of the funnel jacket can be designed to be significantly reduced axially without the dispersion of the visible material to be distributed being impaired. In the case of a suction line provided on one side, the various suction effects in the centrifugal basket which are present in some cases in the prior art can largely be eliminated by providing guide vanes which are subdivided in the axial direction and are also angle-adjustable relative to one another. This makes it possible to give the spiral-shaped inflowing viewing air a different inflow path and swirl on the suction side than in the area of an opposite plate of the centrifugal basket, which is generally largely closed.

If the single-stage sifting is to be improved despite predispersion, a further visual air inlet with appropriate guide vanes can expediently be provided in the area of the outlet for the coarse material adjacent to the lower area of the centrifugal basket. In order that the outdoor units can be kept as simple as possible, this second visual air inlet can be designed in the manner of a bypass or a branch from the main visual air inlet.

With a funnel-shaped design of the spreading plate with the opening surface facing upwards, an improvement in the spreading of the visible material falling thereon is achieved, since the inclination of the spreading plate and the weight of the individual particles achieve a uniform movement of the grain sizes to the edge of the spreading plate.

Since the invention has both an up and down single suction line allows constructively, in order to improve the flow conditions within the centrifuge basket, a coaxial suction line can advantageously be provided on both sides of the centrifugal basket. This has the advantage that the additional, fixed or non-rotatable sieve shells normally required inside the rotating centrifugal basket can be dispensed with. As a result, the flow vanes of the centrifugal basket, which are designed as strips or blades, can be stiffened radially to save weight and material. This enables a reduced moment of inertia due to the reduced mass, and the replaceable wear protection is also easier to handle.

• Figur 1 ein erstes Ausführungsbeispiel eines Drehluft-Schleuderkorb-Sichters im wesentlichen im Axialschnitt, bei dem die Sichtabluft zentral aus dem Schleuderkorb nach oben abgesaugt wird;
• Figur 2 einen schematischen Radialschnitt durch den Sichter nach Fig. 1, in dem einerseits die Konfiguration der Sichtabluftstutzen und andererseits das Spiralgehäuse des Sichters auf der Ebene der Sichtlufteintritte dargestellt ist;
• Figur 3 ein zweites Ausführungsbeispiel eines Drehluft-Schleuderkorb-Sichters im wesentlichen im Axialschnitt, bei dem die Sichtabluft zentral aus dem Schleuderkorb nach unten abgesaugt wird, und
• Figur 4 zwei Radialschnitte durch den Sichter nach Fig. 3 in verschiedenen Ebenen, wobei links ein Schnitt im Bereich der Leitschaufeln in Draufsicht nach unten und im rechten Teil eine Draufsicht auf die den Schleuderkorb nach oben abschließende geschlossene Platte dargestellt ist.

The invention will be explained in more detail below with the aid of schematic drawings of two exemplary embodiments; show it:

• Figure 1 shows a first embodiment of a rotary air centrifuge classifier essentially in axial section, in which the exhaust air is extracted centrally from the centrifugal basket upwards;
• FIG. 2 shows a schematic radial section through the classifier according to FIG. 1, in which, on the one hand, the configuration of the classifying air outlet connection and, on the other hand, the spiral housing of the classifier is shown on the level of the classifying air inlets;
• Figure 3 shows a second embodiment of a rotary air centrifuge classifier essentially in axial section, in which the visible exhaust air is sucked down centrally from the centrifugal basket, and
• 4 shows two radial sections through the classifier according to FIG. 3 in different planes, a section in the area of the guide vanes being shown on the left in a top view downward and in the right part a top view of the closed plate closing the centrifugal basket upward.

Since generic rotary air centrifuge classifiers and their mode of operation are well known, the main differences of the invention with respect to these known classifiers will be referred to below.

1 and 2 relate to a classifier 20, in which the classifying air is extracted upwards. In the example, the vertically operated classifier 20 has a central shaft 8 for driving an upper, first spreading plate 2 and a second spreading plate 5 arranged below it, with dispersing vanes 10 and a centrifugal basket 6 associated therewith.

The material to be sighted passes almost centrally into the sifter 20 through the inlet nozzle 1. In the example, a single inlet nozzle 1 is provided which, in an inclined position, feeds the material to be sighted against the funnel opening of the spreading disc 2 into its inner cone. From the first rotating spreading plate 2, the introduced visible material is thrown against a funnel casing 3 surrounding the spreading plate 2 at a radial distance. In a special design, this funnel jacket 3 consists of two conically tapered jacket regions which are connected to an essentially vertical circumferential wall, through which on each side of the classifier 20 a view exhaust pipe 4 is guided to the outside.

This vertical casing area of the first funnel casing 3 helps to achieve a largely uniform distribution of the introduced material to be seen despite the implementation of the sight air outlet 4. If higher suction powers are considered desirable for the sighting process, instead of the two shown in the example, approximately diametrically opposite, outward-looking exhaust air nozzles also leading to the outside, several, e.g. B. three or four such nozzles are provided with the same angular distance from each other.

From the upper stage of the funnel jacket 3, the granular visible material slides downward in a spiral drag into a tapering opening which forms a mouth surface 35.

Strands of the sliding veil of the material to be sifted, which can form in the case of very small quantities of the imported material to be sifted as a result of the penetration of the air outlet nozzle, are largely compensated for and the material to be sifted is largely uniform, somewhat collected.

From the tapering opening 36 of the funnel casing 3, the grain mixture to be sifted slides into the second rotating spreader plate 5, which is essentially circular in shape, with a collar-like, tubular circumferential wall 34 at its radially inner end upwards over the mouth surface 35 of the first funnel casing 3 protrudes. This circumferential wall 34 surrounds a central open-air exhaust pipe 7 which is open at the bottom and which is branched upward in the region of the vertical peripheral wall of the funnel jacket 3 into the two view-air connecting pieces 4.

At the, a partial funnel opening upward forming spreading plate 5 are followed by approximately radially standing dispersing vanes 10, the z. B. are rotationally rigidly connected to the second spreading plate 5 and the centrifugal basket 6 arranged underneath.

The second spreading plate 5 is surrounded radially on the outside by a second funnel casing 9, which has a larger diameter than the first funnel casing 3. The second spreading plate 5 throws the material to be sifted against the second funnel casing 9, on the circumference of which there is a complete circular distribution of the visible material . The dispersing vanes 10 are provided for generating air vortices in order to allow the already largely uniformly distributed visible material to flow optimally predispersed into the viewing space 11 provided below.

Instead of the torsionally rigid link between the spreading discs 2 and 5 and the Dispersing vanes 10 and the centrifugal basket 6 can also have separate rotary drives, e.g. B. via hollow shafts, can be provided for these individual assemblies.

The largely cylindrical centrifuge basket 6 has a relatively thin, closed plate 6 ″ at the bottom. Radially outside, the centrifugal basket 6 has a ring of flow vanes 6 ′ which are arranged essentially axially parallel and which are designed, for example, as strips, blades or the like At its upper end, the centrifugal basket 6 is kept open over most of its diameter, for example over 2/3 of its diameter and more, in order to form a large suction opening in the direction of the central suction line 7. For reasons of stability, therefore this open part of the centrifugal basket 6 is equipped with a small number of radial spokes 6 "'which are fixed to the shaft 8 and below the dispersing vanes z. B. are welded. These spokes 6 '"can have a streamlined shape in cross-section, taking into account their direction of rotation, so that the suction flow acting in the centrifugal basket 6 remains largely unaffected.

Radially outward closes at least over the entire axial height of the centrifugal basket 6 and if necessary. even downwards, the viewing space 11, which is bounded radially outwards by guide vane rings 12 and 13.

In the example, the guide vanes are divided axially and divided into two individual, separately adjustable guide vane rings 12 and 13. For reasons of simplification, only two subdivisions are shown in the example. These independently adjustable guide vane rings 12 and 13 can be used to set the type of air movement circulating in the viewing space 11, with the suction acting on the fine material depending on the axial height in the viewing space and at least partially reaching into the centrifugal basket, particularly in the case of a suction line provided on one side can be.

As can be seen more clearly from FIG. 2, the sight air blown in through the sight air inlets 14 flows through the spiral housing 15 approximately on a narrowing spiral path. The blown-in air is introduced into the viewing space 11 via the inclined vane guide rings 12 and 13 with a corresponding flow and swirl direction. The visible material introduced through the entry gap 33 at the lower opening of the second funnel jacket 9 and dispersed into the viewing space 11 is viewed here in accordance with the grain size limit set. This grain size limit depends on a variety of parameters, such as. B. speed of the centrifugal basket 6, throughput, degree of predispersion, adjustment of the guide vane limit, blowing and extraction speed of the sifting air, etc. The sifting air laden with fine material flows through the flow vanes 6 ′ of the centrifugal basket 6 on its further path radially inward and is subsequently sucked off through the tubular suction line 7 onto the two sifting air sockets 4. The following separators and cyclones for separating the fine material from the exhaust air are not shown.

At the bottom of the classifier 20 according to FIG. 1, there is essentially the coarse material hopper 16, via which the material lying above the grain size limit is discharged. In order to be able to carry out an after-treatment, a further spiral housing 17 with a likewise adjustable guide vane ring 18 adjoins after a short funnel-shaped transition region. In this area, there is therefore an inspection of the material falling down. The secondary sight air inlet 14 'in the spiral housing 17 is therefore expediently connected to the primary sight air inlet 14, so that a controllable proportion of sight air can be blown in there for indulgence.

The flow vanes 6 'of the centrifugal basket 6 can have different profiles depending on the intended use and also differ in their radial extent. It is important to coordinate these assemblies, according to which the suction effect is largely evenly adjusted over the axial height of the centrifugal basket, even with one-sided suction line.

In the sectional view according to FIG. 2 it can be seen that a radially expanded sight air duct in the area of the sight air inlet creates a constriction in the area of 180 ° after the entry of the sight air through the spiral housing 15. In accordance with the flow direction generated in the classifier, the transition areas from the exhaust air line 7 to the visual exhaust air connection 4 are also designed. In the example, the fluidic extraction of the visual air loaded with fine material takes place in a displacement of the visual air nozzle of 90 to 180 ° with respect to the confluence of the visual air inlets 14.

3 and 4 schematize a sifter 30, the central exhaust air pipe 27 of which is provided below the centrifugal basket 56. In the case of functionally matching assemblies, the same reference numerals have been chosen as in the first exemplary embodiment according to FIGS. 1 and 2, the mode of operation of the classifier 30 also being essentially the same, apart from the direction of withdrawal.

The centrifuge basket 56 of the classifier 30 is constructed axially reversed, so that the closed plate 6 "lies at the top, while the spokes 6" 'are arranged below to stiffen the centrifugal basket 56.

The serious advantage of the sifter 30 is that a central task of the material to be sifted is provided, the axial extent of the entire sifter being able to be significantly reduced by the omission of an upper exhaust air duct and corresponding connections, in particular the first distribution of the sifter 30 good to be sifted be carried out via a conical funnel jacket 3 with a single stage. For this reason, the spreading discs 2 and 5 can be attached to the shaft almost at certain points.

A downward, tubular exhaust air line 27 connects centrally to the centrifugal basket 6, which is open at the bottom. This is slightly tapered in the after-inspection area, in order to subsequently open it in the area of the coarse material hopper 16 in two outgoing air outlet pipes which are guided outwards at an angle to the axis of the sifter 30. The extraction of the visual exhaust air downwards also has the advantage that any stringy designs of the visual material sliding curtain are excluded from the outset.

An exemplary profile of the flow vanes 6 'can be seen in the left half of FIG. 4. In this example, the flow vanes 6 'are designed approximately as isosceles rectangular angles, the tips of which point radially outwards. A symmetrical arrangement to the radius is sought. A change in the angle in the axial height is also expedient in order to ensure a suction which is as uniform as possible over the axial height of the centrifugal basket 56 when the exhaust air is sucked in from one side.

° In the right half of FIG. 6, the closed plate 6 ″ can be seen radially on the inside, to which the entry gap 33 or the annular-cylindrical visible space 11 adjoins it.

Claims (13)

1. Centrifuge basket rotary air classifier (20) with a centrifuge basket (6) which can be driven about a vertical rotation axis and which has radially outwardly located flow blades (6') and through which the classifying air essentially flows from the outside to the inside, with an annular classifying zone (11) surrounding the centrifuge basket (6) and to which is radially outwardly adjacent a coaxial ring of guide vanes (12, 13), in which the classifying air can be introduced pass the guide vanes (12, 13) spirally and with an angular momentum into the classifying zone (11), with an inlet (1) above the classifying zone (11) for the classifying material and an outlet (16) below the classifying zone (11) for the oversize material and with at least one substantially coaxial suction line (4, 27) provided axially with respect to the centrifuge basket (6) for the classifying outgoing air containing undersize material, characterized in that with the inlet (1) for the classifying material is associated a first whizzer (2) rotatable about the vertical rotation axis and which supplies the classifying material to an at least single- stage, first hopper jacket (3) _Apacedly surrounding the said whizzer (2), that subsequently at least with the opening of the first hopper jacket (3) is associated a further, second whizzer (5) rotatable about the vertical axis for supplying the classifying material to a second hopper jacket (9) having a larger diameter than the first hopper jacket (3) and in that in the vicinity of the intake annular clearance (33) connected to the opening of the second hopper jacket (9) dispersing blades (10) for the classifying material rotatable about the vertical rotation axis are provided in annular classifying zone (11).

2. Classifier according to claim 1, characterized in that the suction line (7, 27) in the classifier casing (40) passes into several flow-symmetrically arranged classifying outgoing air outlets (4, 24).

3. Classifier according to claims 1 or 2, characterized in that, emanating from the centrifuge basket (6), the suction line (7) is so upwardly arranged that the several classifying outgoing air outlets below the first whizzer (2) are lead out of the classifier casing (40) more particularly with the same circumferential spacing and/or substantially at right angles to the rotation axis.

4. Classifier according to one of the claims 1 to 3, characterized in that the second whizzer (5) is constructed approximately annularly and has a circumferential wall (3) coaxially surrounding the upwardly lead suction line (7) and which in particular projects axially into the bottom opening surface (35) of the first hopper jacket (3).

5. Classifier according to one of the claims 1 to 4, characterized in that, emanating from the centrifuge basket (56), the suction line (27) is located at the bottom.

6. Classifier according to one of the claims 1 to 5, characterized in that facing the individual suction line (7; 27), the centrifuge basket (6; 56) has a substantially closed plate (6").

7. Classifier according to one of the claims 1 to 6, characterized in that at least the second whizzer (5) and/or the dispersing blades (10) are connected in non- rotary manner to the centrifuge basket (6).

8. Classifier according to one of the claims 1 to 6, characterized in that the whizzers (2, 5), dispersing blades (10) and centrifuge basket (6;

56) can be driven at the same or different speeds relative to one another.

9. Classifier according to one of the claims 1 to 8, characterized in that the guide vanes (12, 13) are axially subdivided and/or are angularly adjustable, particularly relative to one another.

10. Classifier according to one of the claims 1 to 9, characterized in that in the vicinity of the oversize material outlet (16) is provided a second classifying air intake (14') for reclassification and which is in particular branched from the first classifying air intake (14).

11. Classifier according to one of the claims 1 to 10, characterized in that the whizzers (2, 5) are substantially conical with an upwardly open conical surface.

12. Classifier according to one of the claims 1 to 11, characterized in that a coaxial suction line for the classifying outgoing air containing undersize material is provided axially on either side of the centrifuge basket.

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