Centrifugal force air classifier and method for classifying dust-like materials

Description

[0001] The invention relates to a centrifugal force air classifier with a classifying wheel and guide vane ring according to the preamble of claim 1 and a method for separating material dispersed in a classifying fluid into a fine and a coarse fraction according to the preamble of claim 7 .

[0002] Air classifiers are used to separate a material to be classified dispersed in a fluid into a fine and a coarse fraction. The separation effect of a classifying wheel is based on the fact that the drag force of the fluid and the centrifugal force in the flow channels between the classifying wheel blades of a classifying wheel, the so-called deflector wheel, act in opposite directions on the individual particles of the solid. For small particles, the drag force predominates, so that they are carried along by the fluid and discharged as fines. For large particles, the centrifugal force predominates, so that they are thrown out of the deflector wheel against the fluid flow. The particle size for which centrifugal force and drag force are in balance, i.e. which has an equal probability of reaching either the fines or the coarse material, is referred to as the cut-off size or cut-off point.

[0003] The demands on the screening of bulk materials are becoming increasingly stringent. Ever larger quantities of bulk materials are being screened. The demands on the screening results are also becoming ever higher. The screening process must not only be economical, but also deliver high separation accuracy and high yield. Furthermore, the demands on the screeners regarding the achievable fineness are becoming ever higher.

[0004] Since these are usually bulk goods, the energy required for separation has a strong impact on production costs, so that the aim is always to achieve the desired result with the lowest possible energy expenditure and thus cost-effectively.

[0005] Centrifugal force air classifiers with deflector wheels are one of the preferred classifiers for producing very fine classified materials with relatively low energy consumption.

[0006] DE 198 40 344 A1 discloses a rigid-body vortex classifier wheel that has internals within the flow channels defined by the classifier wheel blades. These internals break up the classifying air flowing into the flow channels, creating defined classifying vortices that occur over a radius larger than the radius at which the vortices would occur without the internals, thus shifting the separation boundary to higher finenesses.

[0007] DE 10 2016 206 588 A1 discloses a separator whose separating wheel is surrounded by a guide vane ring to guide the air as evenly as possible through the separating zone and feed it to the separating wheel. The guide vanes of the guide vane ring are inclined in the same direction as the separating wheel blades, thus ensuring that the air flows toward the separating wheel in the direction of rotation.

[0008] US 505 182 A discloses a centrifugal force air classifier according to the preamble of claim 1, and a method for separating material dispersed in a fluid into a fine and a coarse fraction in a centrifugal force air classifier according to the preamble of claim 7 and a classifier with a rotor and guide vane, wherein a material distribution plate is arranged underneath, which is firmly connected to the rotor and rotates with it. The guide vanes of the guide vane ring are adjustable.

[0009] This is particularly disadvantageous for rigid body classifying wheels, as disclosed in DE 198 40 344 A1, particularly with regard to the fineness to be achieved, since the classifying fluid flowing in the direction of rotation of the classifying wheel results in a lower differential speed between the classifying fluid and the rotating classifying wheel. This is especially important for rigid body vortex classifying wheels, since here the relative speed of the classifying fluid to the classifying wheel leads to a

[0010] This leads to an increase in velocity in the forming separating vortex between the separating wheel blades. Higher relative velocities thus lead to higher flow velocities in the separating vortex and thus to higher finenesses. The increase in velocity is ultimately responsible for the achievable fineness.

[0011] The invention is therefore based on the object of providing a centrifugal force air classifier and a classifying process which extends the fineness range of existing classifiers in order to achieve an even higher fineness than before.

[0012] In a centrifugal force air classifier with a classifying wheel and guide vane ring and a method for separating material to be classified dispersed in a classifying fluid into a fine and a coarse fraction of the type described above, the object is achieved according to the invention by the characterizing part of claim 1 and claim 7.

[0013] The centrifugal air classifier for separating material to be classified into fines and coarse material comprises a housing with a classifying fluid inlet, a classifying material inlet, a fines and coarse material outlet, and a classifying fluid outlet. It comprises a rotationally driven classifying wheel and a stationary guide vane ring surrounding the classifying wheel. An annular space, the classifying space, is arranged between the guide vane ring and the classifying wheel. The guide vane ring directs the classifying fluid to the classifying wheel in a defined manner. According to the invention, the classifying fluid, which flows through the guide vane ring, flows against the classifying wheel in the opposite direction of its rotation. This pre-accelerates the classifying fluid, together with the material dispersed therein, outside the classifying wheel, thereby achieving higher relative velocities between the classifying wheel and the particle-laden fluid flow flowing toward the classifying wheel.These higher relative velocities of the incoming fluid with respect to the classifying wheel, in turn, allow for a higher velocity in the classifying vortex of the classifying wheel. This occurs particularly in rigid body vortex classifying wheels, as disclosed in DE 198 40 344 A1. The internals in the flow channels of the classifying wheel have a positive influence on the formation of classifying vortexes. This effect is intensified if the classifying vortex is bordered on both sides by internals, so that the flow channel has at least one widening delimited by two constrictions, i.e., viewed from the outside in, it first has a narrowing, then a widening, and finally a narrowing again. These are arranged in the outer radial third of the flow channel, relative to the classifying wheel radius. This allows higher finenesses to be achieved.

[0014] This allows higher finenesses to be achieved by flowing the classifying fluid against the direction of rotation of the classifying wheel, especially in rigid body vortex classifying wheels, without the classifying wheel itself having to rotate faster.

[0015] Furthermore, the opposing rotation of the classifying wheel and the incoming classifying fluid creates a highly turbulent flow in the classifying chamber. Due to the high velocity gradient, very high shear forces act on the material being classified within the classifying chamber. These shear forces, in turn, result in the material being classified being thoroughly dispersed in the immediate vicinity of the classifying wheel and thus the classifying zone. This results in very good classification quality, which is noticeable, among other things, in a very high fines extraction from the classifier. Furthermore, the good fines extraction is supported by the fact that the dispersion zone is located directly at the classifying wheel, meaning the dispersed particles do not have to travel a long distance, which could lead to re-agglomeration.

[0016] In potential vortex classifiers, the effect of the increased velocity in the flow channels between the classifier blades is not as pronounced. However, the high shear forces resulting from the opposing flow of the classifying fluid to the rotation direction of the classifier wheel also contribute to improved dispersion.

[0017] The flow channels of the guide vane ring are ideally designed almost tangentially to the enclosed classifying wheel in order to achieve the highest possible tangential velocity of the classifying fluid.

[0018] Thus, the guide vanes of the guide vane ring are aligned to the inner classifying wheel in such a way that the tangential component of the outflow direction of the classifying fluid is greater than its radial component.

[0019] In a preferred embodiment, such a targeted flow of classifying fluid is achieved by a guide vane ring that extends in a circle around the entire circumference of the classifying wheel and across the entire axial extent of the classifying wheel. In a particularly preferred embodiment, such a guide vane ring is used in combination with at least one axial transport spiral located in the classifying space between the classifying wheel and the guide vane ring. The transport spiral extends at least partially across the axial extent of the classifying space, preferably across the entire height of the classifying space. This enables targeted removal of the separated coarse material from the classifying zone, leading to a further improvement in the classifying quality.

[0020] In a further embodiment, the guide vanes of the guide vane ring have an axial flow component in addition to the radial and tangential flow components. This forces the classifying fluid flowing through the guide vane ring to exhibit an axial flow component, which supports the targeted removal of the coarse material separated and rejected by the classifying wheel from the classifying zone.

[0021] Furthermore, the guide vane ring is designed so that the cross-sectional area between the guide vanes narrows in the direction of flow. Due to the narrowing cross-sectional areas, the classifying fluid will thus flow toward the classifying wheel at an accelerated rate as it flows radially through the guide vane ring.

[0022] The guide vane ring is optionally flowed through by only the classifying fluid or by the classifying fluid and the material dispersed therein.

[0023] The feed material for classification is preferably fed directly into the annular gap, the classifying space between the guide vane ring and the classifying wheel, via a suitable metering device, especially if an axial conveying spiral is installed in this annular gap. In this case, only the classifying fluid flows through the guide vane ring.

[0024] An injector or any other suitable dosing device can be used to introduce the feed material into the annular gap.

[0025] The invention further relates to a method for separating a material to be classified dispersed in a classifying fluid into a fine fraction and a coarse fraction. The separation takes place in a centrifugal force air classifier having a classifying wheel and a guide vane ring surrounding the wheel for feeding the classifying fluid to the classifying wheel, which is preferably arranged coaxially to the classifying wheel. An annular classifying space is formed between the classifying wheel and the guide vane ring. The classifying fluid flows through the guide vane ring radially from the outside to the inside. The guide vanes of the guide vane ring are inclined such that the classifying fluid and the material to be classified dispersed therein flow against the classifying wheel in the opposite direction of rotation to its direction of rotation. Due to the narrowing cross-sectional areas between the guide vanes, the classifying fluid is accelerated as it flows radially through the blade ring and thus flows towards the classifying wheel.In the classifying space between the guide vane ring and the classifying wheel, a highly turbulent shear flow prevails to disperse the material to be classified in the classifying fluid.

[0026] In one embodiment of the invention, the turbulent shear flow encompasses the entire axial extent of the classifying wheel.

[0027] The material to be classified can be fed to the classifying zone through the guide vane ring together with the classifying fluid, e.g., classifying air. In another embodiment, the material to be classified is fed to the classifying zone separately from the classifying fluid.

[0028] By means of a classifying wheel with flow according to the invention, the fineness range of classifiers could be improved towards smaller finenesses and the dispersion of the material to be classified could be improved.

[0029] Further details, features and advantages of the subject matter of the invention emerge from the subclaims and from the following description of the associated drawings, in which a preferred embodiment of the invention is shown by way of example.

[0030] The drawings show: Figure 1 a sketch of a rigid body vortex separator wheel with surrounding guide vane ring for a centrifugal force air separator Figure 2 a sketch of a potential vortex separator wheel with surrounding guide vane ring for a centrifugal force air separator

[0031] The Figure 1 shows a classifying wheel (10) of a centrifugal force air classifier with a guide vane ring (8) surrounding the classifying wheel (10) and the flow situation of the classifying fluid.

[0032] The separating wheel (10) is coaxially surrounded by a guide vane ring (8). The guide vane ring (8) has guide vanes (9) arranged in a ring-like manner and evenly spaced around the circumference, through which the separating fluid flows from the radially outside to the inside. The guide vanes (9) have at least the same axial height as the separating wheel (10).

[0033] The classifying wheel (10) comprises a hub disc (2) supporting the classifying wheel hub (1) and a cover disc with a fines outlet. The cover disc is ring-shaped. The classifying wheel blades (3) are arranged in a ring between these discs. They are evenly distributed around the circumference of the classifying wheel (10). The classifying wheel blades (3) are essentially radially aligned and define the flow channels (6). The particle-laden classifying fluid, e.g., classifying air, flows through the classifying wheel (10) from the outside to the inside.

[0034] The classifying wheel (10) has flow channels (6) which have internals (5) in the outer radial third, relative to the classifying wheel radius.

[0035] Preferably, the classifying wheel blades (3) do not extend exactly radially in the radially outer third of the classifying wheel radius, but are arranged at an angle to the radial direction, opposite to the direction of rotation of the classifying wheel (10). In the inner two-thirds of the classifying wheel radius, the blades extend radially.

[0036] The annular space (11) between the outer diameter of the classifying wheel (10) and the inner diameter of the guide vane ring (8) forms the classifying chamber (11) over the axial height of the classifying wheel (10). In a preferred embodiment, the material to be classified flows through the classifying chamber (11) in an axial direction.

[0037] The classifying fluid flow runs radially, perpendicular to the material flow. The classifying fluid flows horizontally from the classifying fluid inlet through the stationary guide vane ring (8) into the classifying chamber (11) and flows through it perpendicular to the material flow. A portion of the classifying fluid is required for dispersing the material and thus enters the annular classifying chamber (11) with the material flow.

[0038] The guide vanes (9) are arranged so that the classifying fluid flows towards the classifying wheel (10) in the opposite direction to its direction of rotation.

[0039] The flow channels between the guide vanes (9) of the guide vane ring (8) are ideally designed almost tangential to the enclosed classifying wheel (10) in order to achieve the highest possible tangential velocity of the classifying fluid.

[0040] The flow cross-section between the guide vanes (8) narrows in the flow direction so that the separating fluid is accelerated.

[0041] Figure 2 shows the flow situation for a potential vortex classifying wheel (10) with guide vane ring (8), whereby the classifying wheel (10) is also subjected to flow in the opposite direction to its direction of rotation. Reference symbol

[0042] Classifying wheel hub (1) Hub disc (2) Classifying wheel blades (3) Internals (5) Flow channels (6) Guide vane ring (8) Guide vane (9) Classifying wheel (10) Classifying chamber (11)

Claims

1. Centrifugal force air classifier for separating classified material into fine material and coarse material, with a housing with classifying fluid supply, classifier material supply, fine material discharge, coarse material discharge and classifying fluid discharge - with a rotary-driven classifying wheel (10) and surrounding this, a fixed guide vane ring (8) with guide vanes (9) for supplying the classifying fluid to the classifying wheel (10), - whereby an annular-shaped classifying chamber (11) is formed between the classifying wheel (10) and the guide vane ring (8), where the classifying fluid flow pattern is radial from the outside in, whereby the guide vanes (9) of the guide vane ring (8) are inclined such that the flow of classifying fluid as well as the classifier material dispersed in the fluid can be routed through the classifying wheel (10) contrary to its direction of rotation, characterised in that the cross-section of the flow channels between the guide vanes (8) becomes narrower in the direction of flow.

2. Centrifugal-force air classifier according to Claim 1, characterised in that the flow channels between the guide vanes (9) of the vane ring (8) are aligned with the inside classifying wheel (10) in such a way that the tangential directional component is greater than its radial directional component.

3. Centrifugal-force air classifier according to Claim 1, characterised in that the flow channels of the guide vane ring (8) are aligned with the inside classifying wheel in such a way that the tangential directional component is greater than its radial directional component and its axial directional component.

4. Centrifugal-force air classifier according to one of the preceding claims, characterised in that the guide vane ring (8) extends over the axial extent of the enclosed classifying wheel (10).

5. Centrifugal-force air classifier according to one of the preceding claims, characterised in that at least one axial transport spiral is installed in the classifying chamber (11) between the guide vane ring (8) and classifying wheel (10) which extends over the axial extent of the classifying wheel (10).

6. Centrifugal-force air classifier according to one of the preceding claims, characterised in that the classifying wheel (10) has internal fittings (5) or at least one extension delimited by two bottlenecks in its flow channels (6) in the outer radial third related to the classifying wheel radius.

7. Process for separating - classified material dispersed in a fluid into a fine material and a coarse fraction, - in a centrifugal-force air classifier - with a classifying wheel (10) and surrounding this, a fixed guide vane ring (8) with guide vanes (9) for supplying the classifying fluid to the classifying wheel (10), - whereby an annular-shaped classifying chamber (11) is formed between the classifying wheel (10) and the guide vane ring (8) where the classifying fluid flow pattern is radial from the outside in, whereby the guide vanes (9) of the guide vane ring (8) are inclined such that the flow of classifying fluid as well as the classifier material dispersed in the fluid are routed through the classifying wheel (10) contrary to its direction of rotation characterised in that the classifying fluid flow is accelerated towards the classifying wheel (10) by virtue of the narrowing cross-sectional areas of the guide vane ring (8) during its radial flow.

8. Process according to Claim 7, characterised in that a highly turbulent shear flow for dispersing the classifier material is formed in the classifying chamber (11) between the guide vane ring (8) and the classifying wheel (10).

9. Process according to Claim 8, characterised in that the turbulent shear flow spans the axial extent of the classifying wheel (10).