EP0983802B1 - Classifying rotor for a centrifugal pneumatic separator - Google Patents

Abstract

The blades (3) are tapered, with their outer edges defining a cylinder and their inner edges defining a cone. The broad edges of the blades are fastened to a solid disc (2) mounted on a hub (1) attached to a drive shaft. The narrow edges of the blades are attached to a ring (4) whose width is equal to the width of the narrow ends of the blades.

Description

The invention relates to a classifying wheel for a centrifugal air classifier after The preamble of claim 1 and a method for the separation of in a fluid dispersed Sichtgut in a fine and a coarse fraction according to the preamble of claim 11.

From DD 299 949 A5 is a fine-grained for fine classification of disperse Solids known. This Feinstsichter has a Sichterrad with over the circumference rotationally symmetrically distributed slots arranged on the flow channels, whose width decreases stepwise approximately in the middle of the flow channels. The slots have a larger at the outer periphery of the Feinstkorbsichters Length as on the inner circumference, and have either the shape of a trapezoid or that of a circle section bounded by two secants.

From JP 07308637-A is a generic Sichterrad with angled Flow channels known. The Sichterrad includes Sichterradschaufeln with whose outer end angled arranged auxiliary blades, wherein the Sichterradschaufeln and the auxiliary blades limit the flow channels. These However, auxiliary blades do not change the flow pattern in the Flow channels inflowing Sichtluft cause, since at the very edge of the Sichterradschaufeln, so in the field of auxiliary blades, no vortex in the Visual air can form, as it lacks a stop surface on which the incoming classifying air which has been broken at the auxiliary blades, for formation a vortex could be reflected. In the inflowing classifying air forms a vortex further inside the flow channel, in the area of the flow channels limiting classifier wheel blades.

In principle, classifiers serve to disperse them in a fluid Separate visual goods in a fine and a coarse fraction. The fluid can vary depending on the procedural requirement a gaseous or vaporous or a liquid Be visual medium. Always have the desired fractions of the final product predefined conditions with regard to the particle size distribution of the respective Fulfill fractions.

For certain application technology products, the greatest demands are made put the fineness. In addition, the particle size distributions of fine and Do not cover coarse fraction in an undesirably wide range, i. a The sharpest possible separation of the fractions should be achieved.

Since it is mostly a matter of bulk, the required for the separation affects Energy demand very much on the manufacturing costs, so that you always strive is the desired result with the least possible energy expenditure and to obtain it cost-effectively.

Centrifugal wind sifter with deflector wheel are one of the preferred classifiers for Production of very fine goods under relatively low visibility Energy expenditure. For a sharp separation of the visible material into fines and coarse material It is necessary that in all flow channels of Abweiserades a uniform flow with the same mean radial velocity of the Fluids takes place.

However, even with optimal formation of the fluid inlet, it is unavoidable that because of turbulent flow conditions and especially in a Abweiserad with relatively large axial extent only an uneven Flow through the channels between the blades sets. The result is one blurred separation and lower throughput over that of more uniform Flow possible value.

From the prior art is from the patent DD 299949-A5 a Feinstsichter known, which serves for the fine classification of disperse solids and this rotationally symmetrical distributed over the circumference of the Feinstsichters arranged Slits has. The slots have on the outer circumference of the Feinstkorbsichters a greater width than the inner circumference and have the outer circumference of the Body on a greater length than on the inner circumference. You own either the shape of a trapezium or that of a bounded by two parallel secants Circular sector. Due to the small slot width and the surface shape of the slot is caused by the decreasing from the outside inward cross-section of the slot increases the flow resistance in the slots and that sucked in air flow, which causes the Particle size reduction diameter is reduced. This will be the opportunity created, with the same Sichterdurchmesser and same Sichter speed To obtain a much finer final product and it is a wear-poorer Operation of the Feinstsichters guaranteed and the service life of the entire system increased.

From JP 07 308637-A is known a classifying wheel, which flow channels with has a bent course. These flow channels are by angled Sichterradschaufeln limited, the angled blades from the actual Sichtradschaufeln and angled arranged auxiliary blades formed become. These serve to control the pressure difference in the mill, whereby the Fine classification and the separation characteristics of the mill to be improved.

Investigations of the flow fields in classifying devices with deflector wheels have already been carried out by K. Leschonski and K. Legenhausen. An article in Chemical Engineering and Processing, 31 (1992) 131-136 describes the flow conditions within the flow channels bounded by the classifier blades.

As a result, three different flow forms are distinguished. They can be traced back to three different operating states. These are essentially the ratio of the velocity of the fluid (v _φ ) flowing along the outer periphery of the deflector wheel and the peripheral speed of the rotating deflector wheel (v _s ).

An approximately uniform flow can only develop if the flow is parallel to the Sichterradschaufeln. Such a desired homogeneous flow can be achieved only if the velocity of the fluid (v _φ ) flowing along the outer periphery of the deflector wheel and the peripheral speed of the rotating deflector wheel (v _s ) are the same.

At unequal velocities flow vortices occur which cause the Discriminate clarity and affect the overall fineness negative. The separation limit for fine and coarse is namely over the radial extent the flow channels within the Sichtrades not constant. The highest, so The finest separation limit for the fine lies on the outer circumference of the deflector wheel and worsens with decreasing radius to the axis of rotation of the Deflection straight out. Normally, the coarse material is already on the outer circumference of the Rades rejected and gets into the coarse material. Only the fines can continue into the Penetrate interior of the deflector and is with the fluid flow in the fines deducted. However, by an unwanted vortex formation in the Flow channels of the deflector wheel coarse particles further inward, so they can only be rejected after the dividing line, as on the respective inner radius of the deflector wheel is present. Since this separation limit coarser is as the separation limit on the outer circumference of the deflector can be a certain part In itself coarse particles are not rejected and therefore reach the Fines. The selectivity is considered bad in such cases.

The efforts are therefore towards a uniform flow of the Abweiserades to the separation limit worsening vortex formations avoid. A first solution to achieve a uniform flow discloses DE 43 26 604 A1. The flow of the Abweiserad inflowing Fluids with the visual material dispersed therein is outside the Flow channels of the deflector wheel evenly and gradually on the Circumferential speed of the Abweisrades accelerated. To serve firmly with the Abweiserad connected, an acceleration of the fluid flow enabling components extending from the peripheral area of the deflector wheel extend radially outward.

In a further prior art according to DE 195 13 745 A1, the Flow turbulence thereby minimized that the diameter of the rotor disks the deflector wheel are chosen so large that the outer edges of the Rotor disks extend into the solids or fluid supply channel and thereby forming the lateral boundaries of this channel. It will be a strong one Abbremsung the fluid flow in the circumferential direction of the deflector avoided. Here, too, a substantial approximation of the flow velocity of Aspired fluids to the peripheral speed of the deflector wheel.

But it is not possible in some cases Speed adjustment in the peripheral region of the deflector wheels to realize. In deflector wheels according to DE 195 13 745 A1 and the publication of K. Leschonski and K. Legenhausen, the flow of the deflector through a tangential feed of the carrier fluid. When changing the Rotational speed of the deflector wheel, e.g. Increasing the separation limit to Achieving even finer extracts must also tangential Flow rate of the carrier fluid can be increased, which only by Increase of the carrier fluid flow rate is possible. However, this inevitably leads to lower fines yields.

In DE 43 26 604 A1 a Abweiserad is therefore described with arranged on the outer circumference rings, which allow by their entrainment effect a uniform flow of Abweiserades, but without having to rely on a given tangential flow. Thus, relationships in which the velocity of the fluid (v _φ ) flowing along the outer circumference of the deflector wheel and the peripheral velocity of the rotating deflector wheel (v _s ) are equal can be generated, which in turn cause uniform flow in the flow channels and to the good described above Results.

Even with this solution, it is necessary that the procedural and constructive circumstances allow it at all Beuelemente such as e.g. Ring washers to attach to the outer periphery of the deflector wheel. Also is not always a tangential inflow to the deflector wheel possible.

In the case of a totally undirected flow of the deflector wheel, as e.g. in certain classifier mills or in wind sifters with special Housing form occur, deflection wheels are not according to the prior art can be used to a uniform flow in the flow channels enable.

The object of the invention is therefore to make a Abweiserad so that a uniform flow in the interior of the flow channels is also realized when the speed of the outer circumference of the Abweiserades along flowing fluid (v _φ ) and the peripheral speed of the rotating Abweiserades (v _s ) are not the same, that is, when there is a non-directional flow at the outer periphery of the deflector wheel.

The task is solved by a Sichtrad, the internals within the Has flow channels, the unwanted vortices in the Prevent flow channels. In particular, the object is achieved by the features the claims solved.

In centrifugal force classifying wheels, the coronally arranged blades cause that the angular velocity of the flow fluid within the through Blades limited flow channel at any radial distance from the Rotation axis of the classifying wheel is constant. The thereby adjusting Festkörperwirbel has the property that the separation limit on the outer circumference of Sichterrades is the smallest. The further the fluid together with the inside dispersed particles penetrates into the wheel interior, i. the smaller the radius becomes, the greater the separation limit becomes.

This results in ideal separation conditions on the outer circumference of the Sichterrades. rough Particles are rejected on the outside of the Sichterrad and thus burden the Classifier wheel not, which can be achieved high Feiningutauszüge. Provided however, coarse particles, whatever causes, into the interior of the Sichterrades can penetrate, so applies to these particles a coarser Separation limit, which causes particles that are actually larger than the separation limit at the External circumference can not be dismissed, but in the center of the Sichterrades and can be discharged together with the fines. this leads to to a blurred separation between coarse and fines, also is the Classifier wheel loaded by coarse particles, which actually immediately on the outer circumference should have been rejected. The high load of Sichterrades leads to smaller fines yields and worsens the efficiency of the classifier.

A cause that coarse particles undesirably penetrate into the Sichterrad can be vortexes that form in the flow channels and coarse Aspirate particles and transport them to the inside of the classifier wheel.

The invention provides means that reduce vortex formation within the Flow channels influenced so that no or only a few coarse particles be sucked into the flow channels.

In one embodiment of the invention is provided in the radially central region the flow channel flow breaker on the boundary walls of the Blades to be mounted so that the penetrating into the flow channels Fluid flow already broken in the first radial third of the flow channel and vortex formation only in this third of the flow channel can occur. Because the vortex is the cause of the suction of coarse particles are, coarse particles are not sucked so far into the flow channels, if the vortices are as close as possible to the outer circumference of the classifier wheel form. When the coarse particles penetrate less far into the classifier wheel can, then it is less burdened with coarse particles and the Probability that coarse particles penetrate into the interior and thus into the Fines can be greatly minimized.

The breaking of the flow takes place at Sichterrädern whose peripheral speed (v _s ) is greater than the speed of the outer circumference of the deflector along along flowing fluid (v _φ ), on those boundary surfaces of the Sichterradschaufeln, which are located in the Roationsrichtung front.

In contrast, in the case of classifier wheels whose peripheral speed (v _s ) is less than the velocity of the fluid (v _φ ) flowing along the outer circumference of the deflector wheel, the flow is broken at those boundary surfaces of the classifier wheel blades located rearwardly in the ro- tation direction.

As flow breaker serve internals whose cross sections preferably square, rectangular or triangular in shape and extending axially over the extend the entire length of Sichterrradschaufeln. It may, however, depending on Use also find any other cross-sectional shapes application.

Decisive for the shape and position of the internals is the desired detachment the inflowing fluid from the boundary surface of the classifier blades and the desired location of the vertebrae training. Depending on the application, the spatial design of the Sichterrades and the classifier as well as the Properties of the product to be viewed may have a different optimal Location of the vortex and possibly a different size of the vortex as beneficial prove. In any case, an improvement will occur when the location of the Vortex occurs on a radius that is greater than the radius for the vortex, the would form if no internals are used.

The reduction of the vortex with respect to the vortex size, however, must inevitably mean an improvement in sighting. It even became found that a defined vortex formation in the outer peripheral region of Flow channels for a better dispersion of Sichtgut and Flow fluid leads. This has a positive effect on the fines extract, i. more Fines can be separated from the Sichtgut and the Sichterrad in the Fine fraction are spent.

The classifier wheels according to the invention with internals are preferred in classifiers used, which work with undirected Fluidzströmströmung. When using the Inventive wheels according to the invention can be directed to a pre-acceleration of the Classifier fluids are dispensed with.

The internals can be used in classifier wheels whose Clearance paddles optionally to the radial direction straight, oblique or angled are arranged running.

To minimize within the flow channels of Sichterrades To maintain radial velocities, the axial height of the classifier wheel should be be as large as possible. When Sichterrädern with axial high height must However, on a largely uniform distribution of the radial velocity of the Flow fluids are respected. The equal distribution of Radial speeds is exceeded by an over the axial Sichterradhöhe reached different radial blade depth. In the embodiment with Fines discharge through the annular cover disk, the blade depth is in axial Direction from the circular wheel bearing the Sichtradnabe towards the annular Cover disc smaller.

The different blade depth over the axial Sichterradhöhe causes a uniform suction of the flow fluid and thus a uniform Radial velocity of the fluid over the axial height. With separator wheels this new type, the Sichterradhöhe can be increased without increasing the visual quality deteriorate. The design of classifying wheels with different blade depths can also in classifying wheels without internals to equalize the Radial speed can be used.

Fig. 1 zeigt ein erfindungsgemäßes Sichterrad mit geraden Schaufeln und Einbauten mit quadratischem Querschnitt.

Fig. 2 zeigt ein erfindungsgemäßes Sichterrad mit schrägen, abgewinkelten Schaufeln und Einbauten mit quadratischem Querschnitt.

Fig. 3 zeigt ein erfindungsgemäßes Sichterrad mit schrägen Schaufeln und stufenförmiger Strömungskante.

Fig.4 zeigt ein erfindungsgemäßes Sichterrad mit schrägen Schaufelenden und Strömungskante im Knickbereich zwischen geraden und schrägen Schaufelabschnitten.

The invention is described below with reference to the drawings.

Fig. 1 shows an inventive Sichterrad with straight blades and internals with square cross-section.

Fig. 2 shows an inventive Sichterrad with oblique, angled blades and internals with a square cross-section.

Fig. 3 shows an inventive Sichterrad with inclined blades and stepped flow edge.

4 shows an inventive classifier wheel with oblique blade ends and flow edge in the bending region between straight and inclined blade sections.

The Sichterrad of Fig. 1 consists of a Sichterradnabe (1) bearing Circular disc (2), which has radial and annular slots, in the the Sichterradschaufeln (3) can be used. The evenly over the circumference of the Classifier wheel distributed blades (3) are through the circular disc (2) and the annular cover plate (4) held. In one embodiment, both Circular disc (2) and annular cover plate (4) and the blades (3) made Made of steel. The blades (3) are fixed by soldering or welding with the Circle (2) - and cover plate (4) connected.

Are classifier blades (3) chosen, the one from another and not weld or solderable material, e.g. ceramic or plastic, like that For example, the blades (3) can be made by gluing in the slots of the circle (2) - and cover plate (4) are attached. But there are also all others Connection techniques possible. Depending on the material and application may be to prove another lanyard as the most meaningful. In particular it is also possible with the use of steel materials, the Sichterradschaufeln (3) and circle (2) - and cover plate (4) to glue.

On the front boundary surface in the direction of rotation, each sifter bucket (3) the internals (5) are attached. The internals (5) have, for example, a square cross section and extend axially over the entire Blade height. You can e.g. by welding, soldering or gluing with the Boundary surfaces of Sichterrradschaufeln (3) are connected.

The internals are preferably located on a common radial Circular orbit, which is approximately in an area within the outer third of the radial Total width of Sichterradschaufeln (3) is located.

The separator wheel shown in FIG. 2 differs from that in FIG. 1 shown Sichterrad by the arrangement of Sichterradschaufeln (3). The Sichterradschaufeln (3) do not run exactly in the radial direction, but are in rotated at an angle to the radial direction opposite to the direction of rotation arranged. If the Sichterradschaufeln (3) close to the Extend axis of rotation, the Sichterradschaufeln (3) remain in the inner region radially aligned, where, however, the Sichterradschaufeln (3) in the outer region are arranged rotated to the radial direction at an angle. The Sichterradschaufeln (3) thereby form a flow channel with a kinked course.

It can also be used Sichterradschaufeln (3), which are not far to extend into the interior of the Sichterrades, but only on an outer extend radial portion of the wheel. Such a configuration is shown in FIG. 3 shown.

The internals can, depending on the application, various cross-sections exhibit. Thus, the internals to the Sichterradschaufeln (3) according to FIG. 3 no square cross section, but consist essentially only of a stepped shoulder (6), which in an advantageous embodiment already in the Sichterradschaufel (3) is integrated and not in addition to the Sichterradschaufeln (3) must be connected.

To allow a large inclination of the individual blades (3) and to maintain a sufficient flow channel, the blades (3) on their inner ends (7) are bevelled. Thereby remain very large even when using many and in their thickness dimensioned blades (3) get sufficiently large flow channels.

In a further embodiment of the invention, the Sichterradschaufeln are made two sections formed. The radially inner sections run thereby straight in the radial direction. The radially outer sections are according to Fig. 4 arranged obliquely. At the kink between the oblique and straight Blade sections project beyond the outer end of the inner section Kink point and thereby forms the flow edge according to the invention.

Claims (13)

1. Separating rotor for a centrifugal pneumatic separator with blades (3) which are arranged in a ring running parallel to the axis of rotation and are located between a circular disc (2) carrying the separating rotor hub (1) and a ring-shaped covering disc (4), through which flow channels are formed between the blades (3) by the faces of the blades (3) which run a distance from one another in the direction of the axis of rotation and through which the separating air flows from the outside to the inside counter to its centrifuging direction, characterised in that baffles (5) which project into the flow channels are provided on the blades (3) in the area within the outer third in order to influence the flow characteristics of the separating air there so that the vortices formed in the separating air flowing into the flow channels occur on a radius which is greater than the radius on which the vortices would occur without the baffles.
2. Separating rotor according to claim 1, characterised in that the baffles (5) extend over the entire axial height of the separating rotor.
3. Separating rotor according to claim 1 or 2, characterised in that the baffles (5) exhibit a square cross-section.
4. Separating rotor according to claims 1 to 2, characterised in that the baffles (5) exhibit a rectangular cross-section.
5. Separating rotor according to claims 1 to 2, characterised in that the baffles (5) exhibit a triangular cross-section.
6. Separating rotor according to claims 1 to 5, characterised in that the baffles (5) are embodied as step-shaped shoulders of the separating rotor blades (3).
7. Separating rotor according to claims 1 to 6, characterised in that the separating rotor blades (3) exhibit a radial blade depth which differs over the axial height of the separating rotor.
8. Separating rotor according to claim 7, characterised in that the blade depth becomes smaller in the axial direction from the circular disc (2) carrying the separating rotor hub (1) to the ring-shaped covering disc (4).
9. Separating rotor according to claim 8, characterised in that the blade depth becomes continuously smaller in the axial direction from the circular disc (2) carrying the separating rotor hub (1) to the ring-shaped covering disc (4).
10. Separating rotor according to claim 8, characterised in that the blade depth becomes continuously smaller in the axial direction from the circular disc (2) carrying the separating rotor hub (1) to the ring-shaped covering disc (4) with a constant pitch.
11. Method for separating material dispersed in a fluid into a fine and a coarse fraction with a separating rotor for a centrifugal pneumatic separator with blades (3) which are arranged in a ring running parallel to the axis of rotation and are located between a circular disc (2) carrying the separating rotor hub (1) and a ring-shaped covering disc (4), with the separating air flowing from the outside to the inside counter to the centrifuging direction of the separating rotor through flow channels which are formed between the blades (3) by the faces of the blades (3) running a distance from one another in the direction of the axis of rotation, characterised in that baffles (5) provided on the blades (3) in the area within the outer third ensure that the vortices which form in the separating air flowing into the flow channels occur on a radius which is greater than the radius on which the vortices would occur without the baffles.
12. Method according to claim 11, characterised by operation of the centrifugal pneumatic separator such that the circumferential velocity (v_s) of the separating rotor is greater than the velocity of the fluid (v_ϕ) flowing along the outside circumference of the separating rotor and in that the baffles (5) are mounted on the boundary faces of the blades (3) which are at the front in the direction of rotation.
13. Method according to claim 11, characterised by operation of the centrifugal pneumatic separator such that the circumferential velocity (v_s) of the separating rotor is smaller than the velocity of the fluid (v_ϕ) flowing along the outside circumference of the separating rotor and in that the baffles (5) are mounted on the boundary faces of the blades (3) which are at the rear in the direction of rotation.

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