Static cascade classifier with downwardly widened profile

Abstract

The invention relates to a classifier (100) for classifying granular material into at least two fractions, comprising an inlet (105) for classifying gas (101), at least one outlet (170) for each fine fraction suspended in the classifying gas (101), cascade-like arranged first classifying streams (130) which are arranged downstream of the inlet (105) for classifying gas (101) in the flow direction of the suspended material, and cascade-like arranged second classifying streams (160) which are arranged upstream of at least one outlet (170) for a fine fraction, wherein the first classifying streams (130) and the second classifying streams (160) form a classifying zone (140) between them which, in intended use, extends from top to bottom and from one side wall (190) to the other side wall (190). extend to include at least one outlet (180) for a coarse fraction, which is located at the lower end of the sighting zone (140),an inlet (150) for visible material, which is located at the upper end of the viewing zone (140), , According to the invention, the side walls (190) are not arranged as two parallel planes in their entirety, but the classifier (100) has a downwardly flared profile due to the arrangement and shape of the side walls (190), wherein the side walls (190) have a downwardly bulbous profile. This results in greater visual efficiency.

Description

[0001] The invention relates to a classifier for classifying granular material to be classified into at least two fractions, comprising an inlet for classifying gas, at least one outlet for each fine fraction, cascade-like arranged first classifying flues which are arranged in the path of the suspended material to be classified downstream of the inlet in the direction of flow, cascade-like arranged second classifying flues which are arranged in front of at least one outlet for a fine fraction in the direction of flow, wherein the first classifying flues and the second classifying flues form a classifying zone running from top to bottom between them and extend from one side wall of two side walls to the other side wall, at least one outlet for a coarse fraction which is arranged at the lower end of the classifying zone and an inlet for material to be classified which is arranged at the upper end of the classifying zone.

[0002] For classifying granular material, it is known to use so-called V-classifiers or cascade classifiers. In these, the material falls down a cascade of classifying streams through which classifying gas flows, and is split into two fractions. A fine fraction is suspended in the classifying gas as it falls down the cascade and is blown out of the classifier suspended in the classifying gas through the outlet for a fine fraction. In contrast, a coarse fraction falls to the lower edge of the cascade and exits the classifier through a corresponding outlet for a coarse fraction. These cascade classifiers are also called V-classifiers because their typical outer housing shape is V-shaped. Such classifier concepts have been known for a very long time.

[0003] One problem when operating a cascade classifier is the uneven flow of classifying gas through the classifying cascade and also the fact that the material to be classified loses fines as it falls over the classifying cascade from top to bottom. As a result, there is a lot of fines in the classifying gas at the upper end of the classifying cascade, and towards the bottom the coarse material, which has been partially freed of fines, becomes coarser, which changes the flow resistance of the classifying gas through the cascade-like staircase. On the other hand, a lower classifying gas flow flows through the lower cascade stages because the pressure of the classifying gas decreases along the cascade-like staircase. This is because with each individual cascade stage, a portion of the classifying gas escapes into the classifying zone and into the fines outlet. Each cascade stage therefore operates with a different classifying gas flow velocity, while the classifying material becomes depleted of fines.Depending on the setting of the supplied classifying gas flow, it is also possible that the classifying gas flow at the lower cascade stages is too high. It is always observed that the ideal classifying gas flow parameters are not achieved in every single cascade stage; instead, the ideal classifying gas flow parameters are only achieved in a few cascade stages. The ideal parameters for classifying are relatively narrow. Fine material should be discharged, and coarse material should just not be entrained in the classifying gas flow. Thus, a cascade classifier or V-classifier only operates with ideal parameters at a few cascade stages, which reduces the classifying efficiency compared to if all cascade stages could be operated with parameters adapted to the composition of the material being classified at that stage.

[0004] German patent application DE 199 44 421 A describes a cascade separator combined with a rod cage separator, which share a common housing. The flow in this separator is determined by the ratio of the separating air flow to the rod cage capacity.

[0005] German patent DE 43 29 947 C1 discloses a dust removal device for bulk material, in particular for crusher-produced gravel or chippings, comprising a substantially vertically extending shaft with an upper feed opening for dust-laden bulk material and a lower discharge opening for dedusted bulk material, an arrangement of impact bodies for cascading and fanning out the bulk material, which are distributed over the vertical height of the shaft, at least one blower air supply opening into the shaft below the arrangement of impact bodies, and at least one air extraction line leading out of the shaft, wherein air extraction openings are provided distributed over a substantial part of the vertical height of the shaft. This dust removal device has a downwardly widened profile.

[0006] The object of the invention is therefore to modify a previously described classifier in such a way as to increase the classifying efficiency. Classifying efficiency is defined by the number of cycles of coarse material required through a given classifier until a desired separation efficiency between two fractions is achieved. The separation efficiency, in turn, is a measure of the grain size distribution in each fraction, with the grain size distribution in the feed material already influencing the separation efficiency.

[0007] The object of the invention is achieved in that the side walls are not arranged as two parallel planes in their entirety, but rather the sifter has a downwardly widened profile due to the arrangement and shape of the side walls, with the side walls having a downwardly bulging profile. Further advantageous embodiments are specified in the subclaims to claim 1. The use of such a sifter is claimed in method claims 7 and 8.

[0008] According to the concept of the invention, the V-sifter or cascade sifter is not designed in a box shape. In a very simple design, two opposing side walls, which carry the sifting streams between them, are arranged at an angle. The opposing side walls are therefore not arranged parallel to each other, which corresponds to an angle of 0°, but rather the opposing side walls have an angle different from 0°. As a result, the sifter forms a downwardly widened profile, with the sifter widening from top to bottom.

[0009] According to the idea of ​​the invention, it is provided that the side walls are not arranged as a whole as two parallel planes, but the sifter has a profile that widens downwards due to the arrangement and shape of the side walls.

[0010] The downwardly widened profile results in a larger cross-section for the classifying gas flow in the lower cascade stages, thus preventing excessive velocity in these stages. This significantly reduces the discharge of coarse particles with the fines, increasing separation efficiency.

[0011] A sufficiently downwardly flared shape is achieved when the angle of the side walls is between 1° and 5°. Thus, only a slight downward flare is necessary to achieve the efficiency increase. Experiments have shown that even a downwardly flared shape with side surfaces set at an angle of 3° to each other leads to an increase in sifting efficiency compared to a sifter with parallel side walls. This reduced the required number of revolutions and improved separation efficiency.

[0012] If the flow cross-section of the separating gas supply is very narrow while the size of the separating flute arrangement, i.e., the area spanned by the width of the separator and the connecting line of the separating flutes, remains constant, the downwardly widened shape of the separator has less of an impact on the equalization of the pressure drop and the flow velocity. Equalizing the pressure drop across the separating flutes from top to bottom is particularly easy to achieve if the cross-sectional ratio between the surface area of ​​the separating gas inlet and the area spanned by the side walls and the first separating flutes is 1:3 to 1:10, preferably 1:5.

[0013] Another parameter that affects screening efficiency is the ratio of the channel length between the first screening flume cascade and the second screening flume cascade, which form the screening zone between them. Two adjacent screening flumes and the side walls each form a channel. The ratio of the average length of the channels enclosed by two adjacent first screening flumes and the side walls, as the first average channel length, and the ratio of the length of the channels enclosed by two adjacent second screening flumes and the side walls, as the second average channel length, can be between 1:2 and 1:4, preferably 1:3.

[0014] The downwardly flared shape of the separator's profile has a particularly homogenizing effect when the inlet for the separating gas opens into a flow channel that directs the separating gas at a shallow angle from top to bottom onto the connecting line of the first separating flutes. Due to the shallow angle, the free flow cross-section in the flow channel decreases with increasing depth to the individual separating flutes. The downwardly flared shape compensates for the decreasing flow cross-section or even has the opposite effect, namely, increasing the free flow cross-section to the separating flutes located further down, thereby reducing flow resistance.

[0015] The downwardly widened profile of the classifier proves to be particularly advantageous for a classifier when it is operated with the following parameters, namely, the inlet for the classifying material is fed with 2 t / h to 5 t / h of granular material and the inlet for the classifying gas is fed with 5,000 m 3 / h up to 20,000 m 3 / h clear gas, preferably with 9,000 m 3 / h up to 18,000 m 3 / h sight gas.

[0016] With such a classifier, raw meal for the production of cement clinker can be processed more efficiently in a closed-loop grinding plant, i.e. with a lower required number of circulations.

[0017] The invention is explained in more detail with reference to the following figures. They show: Fig. 1 a sifter according to the invention in a sectional view from the side, Fig. 2 a view of the classifier Fig. 1 without section with view of the inlet for sight gas, Fig. 3 different profiles of the classifier that are possible according to the subject matter of the invention.

[0018] In Fig. Figure 1 shows a sectional side view of a separator 100 according to the invention. Sifting gas 101, whose possible local flow direction is indicated by the arrows P, flows into the separator 100 from the left into the inlet 105 for sifting gas 101. For this purpose, the separator housing 110 is shaped such that a flow channel 120 for the sifting gas 101 is formed, which guides the sifting gas 101 at a shallow angle to the connecting line K1 of the individual first sifting streams 130. Since separating gas 101 flows into the separating zone 140 between each two adjacent separating flutes 130, the flat inflow with a corresponding shape of the separator housing 110 acts in such a way that the flow velocity of the separating gas 101 is maintained up to the separating flutes 130 arranged further down and is not reduced by a constant cross-sectional area of ​​the flow channel 120 with a simultaneous decrease in separating gas 101.From above, the material to be separated falls through the inlet 150 for the material to be separated onto the individual, first separating flutes 130. The separating gas 101 flowing through the separating flutes 130 blows fines away from the material to be separated and suspends them in the separating gas 101. The fines suspended in the separating gas 101 are redirected through the second separating flutes 160 and directed to the outlet 170 for a fine fraction. Coarse material that has fallen to the lowest separating flute 130 leaves the separator 100 through the outlet 180 for the coarse material. For high separating efficiency, and thus the lowest possible number of circulations for the material to be separated, the flow conditions in the separator 100 are of particular importance. It is particularly important that the flow conditions between two adjacent upper viewing floods 130 and two lower adjacent viewing floods 130 are adapted to the composition of the visible material falling over the individual viewing floods 130 in the viewing zone 140.The composition of the material to be classified ultimately changes as it passes through the individual classifying streams 130 from top to bottom. The flow of the classifying gas 101 within the classifying zone 140 also influences the classifying efficiency of the classifier 100. The flow deflection, which is predetermined by the angle β of the first classifying streams 130 and the second classifying streams 160, also plays a role. It has been shown that high classifying efficiency can be achieved if the angle β between the first classifying streams 130 and the second classifying streams 160 is between 60° and 120°. The length ratio of the channel length between two adjacent first classifying streams 130 and the channel length between two adjacent second classifying streams 160 is also a parameter that influences the classifying efficiency of the classifier 100.A classifier 100 has proven advantageous in which the ratio of the average length of the channels enclosed by two adjacent, first classifying flutes and the side walls as the first, average channel length and those enclosed by two adjacent, second classifying flutes and the side walls as the second, average channel length is between 1:2 and 1:4, preferably 1:3.

[0019] Fig. 2 shows a view of the classifier from Fig. 1 without section with a view of the inlet 105 (dotted area) for the separating gas 101. This illustration shows the angle α between the side walls 190 and the vertical, which according to the concept of the invention should be between 1° and 5°. With this downward widening of the separator housing 110, the free cross-section in the flow channel 120 upstream of the first separating flutes 130, as well as the free cross-section between the individual separating flutes 130 and separating flutes 160, and the free cross-section in the flow direction downstream of the second separating flutes 160 also increase. This view also shows a ratio between the cross-sectional area of ​​the inlet 105 for the separating gas and the cross-sectional area spanned by the side walls 190 and the first separating flutes 130. This area ratio can be seen between the dotted cross-sectional area between points A and B and the area between points C and D.

[0020] In Fig.3 shows various profiles of the sifter. Sub-figure a) shows a round, pear-shaped, or bulbous profile of a cascade sifter according to the invention. In this cascade sifter, the side walls are not arranged as a whole as two parallel planes, but rather the sifter has a downwardly widened profile due to the arrangement and shape of the side walls. Sub-figure b) shows a downwardly widened profile of another cascade sifter, in which only the lower part of the sifter is box-shaped with parallel side walls there, in the lower part of the cascade sifter. Above this, the side walls are aligned at an angle to one another. In this cascade sifter, too, the side walls are not arranged as a whole as two parallel planes, but rather the arrangement and shape of the side walls give the sifter a downwardly widened profile.Finally, sub-figure c) shows a third profile shape of a cascade sifter. Here, the lower side walls are stepped, so that the horizontal parts of the side walls are not parallel but rather in one plane. It is also possible to angle these horizontal side wall parts. This embodiment also has a downwardly widened profile due to the arrangement and shape of the side walls. In this cascade sifter, the side walls are not arranged as two parallel planes in their entirety; instead, the sifter has a downwardly widened profile due to the arrangement and shape of the side walls. LIST OF REFERENCE SYMBOLS 100 sifters 101 Sight gas 105 Inlet for sight gas 110 classifier housing 120 flow channel 130 visual floods 140 visibility zone 150 Inlet for visible goods 160 visual floods 170 Outlet for a fine fraction 180 outlet for a coarse fraction 190 side wall A point B point C point D point P Arrow K1 connecting line a angle b angle

Claims

[1] Classifier (100) for classifying granular material into at least two fractions, comprising - an inlet (105) for sight gas (101), - at least one outlet (170) for each fine fraction suspended in the classifying gas (101), - cascade-like first sifting streams (130) arranged in the path of the suspended sifting material downstream of the inlet (105) for sifting gas (101), - second sifting streams (160) arranged in a cascade-like manner, which are arranged in the flow direction upstream of at least one outlet (170) for a fine fraction, wherein the first sifting streams (130) and the second sifting streams (160) form a sifting zone (140) between them which, in normal use, runs from top to bottom and extends from one side wall (190) of two side walls (190) to the other side wall (190), - at least one outlet (180) for a coarse fraction, which is arranged at the lower end of the classifying zone (140), - an inlet (150) for material to be seen, which is arranged at the upper end of the viewing zone (140), characterized by that the side walls (190) are not arranged as a whole as two parallel planes, but the sifter (100) has a downwardly widened profile due to the arrangement and shape of the side walls (190), wherein the side walls (190) have a downwardly bulbous profile. [2] Classifier according to claim 1, characterized by that the angle (α) between the planes of the side walls (190) and the vertical is between 1° and 5°. [3] Classifier according to one of claims 1 to 2, characterized by that the cross-sectional ratio between - the cross-sectional area of ​​the inlet (105) for the classifying gas (101) and - the cross-sectional area spanned by the side walls (190) and the first viewing floods (130) has a ratio of 1:3 to 1:10, preferably 1:

5. [4] Classifier according to one of claims 1 to 3, characterized by that the ratio of the average length of the channels, - which are enclosed by two adjacent first viewing floods (130) and the side walls (190) as the first average channel length and - which are enclosed by two adjacent, second viewing floods (160) and the side walls (190) as a second, average channel length is between 1:2 and 1:4, preferably 1:

3. [5] Classifier according to one of claims 1 to 4, characterized by that the angle (β) between the first viewing floods (130) and the second viewing floods (160) is on average between 60° and 120°. [6] Classifier according to one of claims 1 to 5, characterized bythat inlet (105) for the classifying gas (101) opens into a flow channel (120) which guides the classifying gas (101) at a shallow angle to a connecting line (K1) of the first classifying streams (130). [7] Method for classifying granular material with a classifier according to one of claims 1 to 6, characterized by - Feeding the inlet for screening material with 2 t / h to 5 t / h of granular screening material, - Pressurizing the inlet for sight gas with 5,000 m 3 / h up to 20,000 m 3 / h clear gas, preferably with 9,000 m 3 / h up to 18,000 m 3 / h. [8] A process according to claim 7 for classifying raw meal for the production of cement clinker in a circulation grinding plant.

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