PIPE SCREENER

Description

[0001] The invention relates to a riser pipe classifier, comprising a riser pipe for the pneumatic transport of granular material suspended in conveying air, wherein the riser pipe has a vertical conveying direction component, a swirling device arranged in the riser pipe, which imparts a swirl to the conveying air, a dip pipe arranged above the swirling device, which extends the air path for the conveying air, wherein an annular gap is present between the riser pipe and the dip pipe, through which coarse-grained material, which has been thrown outwards in a radial direction with respect to the conveying direction of the conveying air by the swirl of the conveying air, separates from the conveying air flowing into the dip pipe, and a circulating grinding plant comprising such a classifier.

[0002] To separate granular material into its grain size fractions, it is known to suspend the granular material in conveying air and then divide it into at least two, sometimes even three, grain size fractions using an air classifier. Depending on the type of classifier, the classifying principle is based on exploiting the inertia principle of coarser grains, which are conveyed differently by the air in which they are suspended. A larger grain is less affected by the conveying air due to the lower air resistance relative to its volume and weight than a smaller grain, which is more strongly supported by the conveying air. The way in which the conveying air acts on the material to be separated varies depending on the type of classifier.

[0003] A very important aspect when selecting a classifier for a specific purpose is the classifier efficiency, i.e. the separation performance in a single pass, the pressure loss of the conveying air in which the material to be separated is suspended, the costs for maintaining the classifier if the classifier has moving components, the maintenance effort, the tendency to block in the event of a sudden plant shutdown, the installation height, which with each meter consumes additional energy to convey the material to be separated against gravity, and also the assembly time for the initial installation in an existing plant in which the separation of the material to be separated into its grain size fractions is to take place.

[0004] Very efficient, highly effective sifter types are known in the state of the art, such as rod cage sifters. However, these have the disadvantage of being maintenance-intensive, consuming electrical energy to drive the rod cage, and requiring a certain minimum installation height.

[0005] German patent DE 832 238 B discloses a riser separator according to the preamble of claim 1. This patent describes an air separator. A swirl element is arranged in the discharge pipe. The swirl element is thus located downstream of the separation point.

[0006] US patent US 1,724,041 discloses a separator. In this separator, conveying air with suspended material to be separated is pneumatically conveyed through a riser pipe. A swirler is arranged in the riser pipe, which imparts a swirl to the rising air. At the end of the riser pipe is a transition to an expansion chamber. A dip tube dips into the expansion chamber. This arrangement allows the material to be separated into a coarse fraction and a fine fraction.

[0007] German patent application DE 25 56 970 discloses a cyclone classifier. An impeller is immersed in the cyclone classifier to promote turbulence. There is no explicit annular gap.

[0008] European patent application EP 0 164 859 A2 discloses a separator that has an impeller positioned in the path of the rising separating air with suspended material to be separated. The impeller propels the material to be separated outward into a collecting chamber.

[0009] German patent DE 1 218 264 discloses a sifter with a spreading disc that operates like a reversed rod basket sifter. The spreading disc throws the material to be separated into a collecting chamber.

[0010] There is a need for a simple separator type with medium efficiency, but very low manufacturing and installation costs, and with a low tolerable pressure drop. The object of the invention is therefore to provide such a separator.

[0011] The object of the invention is achieved by a riser pipe classifier having the features of claim 1. Further advantageous embodiments of the riser pipe classifier are specified in the subclaims to claim 1. A circulating grinding plant comprising this type of classifier is specified in claim 5.

[0012] According to the invention, the classifier is integrated into a pneumatic conveying pipe, wherein the pneumatic conveying pipe has a vertical conveying direction component. The separation of the material to be separated into at least two grain size fractions occurs when a swirling device located in the riser pipe imparts a swirl to the conveying air. The conveying air thus moves with a linear and vertical directional component as well as with an approximately circular rotational component. These two directional components lead to a roughly helical flow. In the helical flow, the grains suspended in the conveying air experience a centrifugal force. The coarser grains experience lower air resistance in the viscous air compared to their own mass and thus to the centrifugal force acting on them than grains with a smaller grain size.This effect is based on the fact that the smaller grains are better carried due to the air viscosity. The larger grains thus collect in the outer region of the vortex, the helically flowing conveying air. At a predetermined height above the swirling device, there is an annular gap between a dip tube, which dips into the riser tube, and the riser tube itself. This annular gap separates the outer region of the vortex from the inner region of the conveying air vortex. The inner region of the vortex, which carries the smaller grain sizes, flows into the dip tube, which dips into the riser tube. In contrast, the outer region of the conveying air vortex, which carries the larger grains with the larger average diameter, flows into the annular gap.To carry out exactly this mode of operation, the riser pipe classifier is claimed, comprising a riser pipe for the pneumatic transport of granular material suspended in conveying air, wherein the riser pipe has a vertical conveying direction component, a swirling device arranged in the riser pipe, which imparts a swirl to the conveying air, a dip pipe arranged above the swirling device, which extends the air path for the conveying air, wherein between the riser pipe and the dip pipe there is an annular gap through which coarse-grained material, which has been thrown outwards in a radial direction with respect to the conveying direction of the conveying air by the swirl of the conveying air, separates from the conveying air flowing into the dip pipe.

[0013] The swirling device of the riser pipe separator according to the invention can be designed in different ways. In a preferred embodiment, the swirling device consists of an impeller arranged approximately centrally in the riser pipe. If the impeller is static, it is fixed in the center of the riser pipe. When the conveying air passes over the impeller, it experiences a swirl that leads to a helical flow, forming a vortex with the desired effect explained above. The static, but height- and angle-adjustable impeller has the advantage of a particularly favorable design with only a low pressure loss during the formation of a vortex, whereby the magnitude of the pressure loss depends on the air resistance of the impeller.

[0014] To increase the turbulence and thus improve separation efficiency, the impeller can be driven. The impeller thus has a stimulating effect and also the effect of creating a vortex.

[0015] In addition to the quantitative separation efficiency, i.e. the ratio of the grain size quantity above a certain size in the coarse fraction to the ratio of the total coarse grain fraction above this certain size in the entire product to be separated, the qualitative separation efficiency is also an important parameter for the use of a classifier in a plant. In order to influence the qualitative separation efficiency, the height of the swirling device in relation to the annular gap can be variable and adjustable. In the simplest case, the swirling device can be suspended in the riser pipe on a ring segment or in a cage, with the ring segment or cage being adjustable via a vertical slot in the riser pipe. The cage or ring segment can be attached from the outside in various positions via the slot. The vertical slot in the riser pipe can be covered from the outside to maintain the pressure in the riser pipe.It is also possible to provide a helical slot in the riser tube and adjust the height of the swirling device by turning a control lever with the ring segment or cage extending through the slot. When the height changes, the separating effect of the annular gap, which separates the outer part of the conveying air vortex from the inner part of the vortex, acts at different points of a steady state of the grain size distribution within the vortex. This changes the grain size composition of the two fractions, one flowing into the dip tube and one flowing into the annular gap.

[0016] Finally, the impeller can be designed to be angle-adjustable. This feature helps optimize the turbulence effect when the impeller's flow is not ideal.

[0017] A specific application for the immersion tube classifier presented here is a recirculating grinding plant, in which a fraction containing larger grains is fed back into the grinding circuit. For this purpose, a recirculating grinding plant is claimed, comprising a comminution device, such as an impact hammer mill, a high-pressure roller press, or a roller mill, a downpipe through which the material to be ground is fed to the comminution device, and a riser tube classifier as described above, a housing that separates the conveying air from the atmospheric air, wherein the riser tube of the riser tube classifier and the downpipe are connected to the housing, and the annular gap is connected to the downpipe.

[0018] The invention is explained in more detail with reference to the following figures. They show: Fig. 1a riser classifier as part of a circulating grinding plant, Fig. 2an enlarged detail from Figure 1representing the riser pipe separator itself, Fig. 3 a sketch to illustrate the influence of the height of the swirling device on the qualitative separation performance

[0019] In Figure 11 shows a sketch of a circulating grinding plant in which the riser pipe classifier 1 according to the invention is integrated. The riser pipe classifier 1 consists of a riser pipe 5 for the pneumatic transport of granular material 15 suspended in conveying air 10. The riser pipe 5 always has a vertical conveying direction component. In the riser pipe classifier 1 shown here, the conveying direction is exactly vertical. Furthermore, the riser pipe classifier 1 has a swirling device 20 arranged in the riser pipe 5, which imparts a swirl to the conveying air 10. Above the swirling device 20, an immersion pipe 25 is arranged, which extends the air path for the conveying air 10. According to the invention, an annular gap 30 is present between the riser pipe 5 and the immersion pipe 10.Coarse-grained material 35 is separated from the conveying air 10 through the annular gap 30 because the coarse-grained material 35 is propelled outward in a radial direction relative to the conveying direction of the conveying air 10, i.e., toward the wall of the riser pipe 1, by the swirl of the conveying air 10. The remainder of the conveying air 10 flows into the immersion pipe 25.

[0020] In Figure 2 is the Figure 1 Detail enclosed by rectangle A is shown enlarged. I Figure 2 It is shown that the conveying air 10, which flows into the riser pipe 1 from below, is given a swirl by the swirling device, here a static, but optionally also height-adjustable and / or angle-adjustable impeller. The swirl in is in Figure 2represented by the wavy lines. Coarser grains of the material to be separated are carried outwards against the air resistance by the centrifugal force acting on them during the swirling movement. The track of a single grain of the material to be separated is therefore approximately that of an upwardly expanding spiral. In the upper part of the riser tube 1 there is an annular gap 30 between the immersion tube 25, which projects downwards into the riser tube 1, and the riser tube 1 itself. This annular gap 30 separates the front between a fraction of coarse-grained material and a fraction with finer material, which is discharged through the immersion tube 25. The height adjustability is indicated by the double arrow to the right of the impeller 20 and the angle adjustability by the angle symbol α.

[0021] In Figure 3is a sketch that helps to understand the effect of adjusting the height of the swirling device. The swirling device creates a vortex, with more coarse-grained material 35 being present in the outer regions of the vortex. This coarse-grained material 35 is slowly carried outwards on its journey from the swirling device 20 to the annular gap 30. This creates a cone-shaped front between the fine material and the coarse-grained material 35, which is represented here by the upside-down truncated cone that becomes darker towards the outside. If the height of the swirling device is now adjusted, as shown by the vertical double arrow to the right of the swirling device 20, the annular gap 30 encounters a front that differs depending on the height of the swirling device 20 in the darker and outer region of the grain size front represented as a truncated cone.Depending on the front position, the grain size fraction can be varied. If the swirling device 20 is pushed upwards, the coarse-grained material will contain more finer material than if the swirling device is pushed downwards.

[0022] Returning to Figure 1It shows how the riser pipe classifier 1, a housing 50 for an impact hammer mill as comminution device 40, and a downpipe 45 for feeding the ground material are connected to one another, thus separating the conveying air 10 from the atmospheric air. Ground material 55, which is fed through the downpipe 45 onto the impact hammer mill as comminution device 40, is comminuted there and conveyed by the conveying air 10 through the swirling device 20. At this point, the swirling device swirls the conveying air with the ground material suspended therein, which, as described, separates the ground material into different fractions with different grain size compositions. The fraction with coarse-grained material 35 flows back into the downpipe through the annular gap 30, which is connected to the downpipe 45, so that coarse-grained material 35 is once again fed to the impact hammer mill as comminution device 40.Fine material, however, is discharged through the dip tube 25. LIST OF REFERENCE SYMBOLS

[0023] 1 Riser pipe classifier 35 coarse-grained material 5 riser pipe 40 Shredding device 10 Conveying air 45 downpipe 15 granular material 50 Enclosure 20 swirling device 55 Ground material 25 dip tube 30 Annular gap

Claims

1. Riser pipe separator (1), having - a riser pipe (5) for the pneumatic transport of granular goods (15) suspended in conveying air (10), wherein the riser pipe (5) has a vertical conveying direction component, - a swirling device (20) which is disposed in the riser pipe (5) and imparts a swirl to the conveying air (10), - an immersion pipe (25) which is disposed above the swirling device (20) and lengthens the air path for the conveying air (10), characterized in that between the riser pipe (5) and the immersion pipe (10), above the swirling device (20), there is an annular gap (30) by way of which coarse granular goods (35) which have been spun outwards in the radial direction in terms of the conveying direction of the conveying air (10) by the swirl of the conveying air (10), are separated from the conveying air (10) that flows into the immersion pipe (25), wherein the height position of the swirling device (20) in the riser pipe (5) is variable and adjustable from the outside.

2. Riser pipe separator according to Claim 1, characterized in that the swirling device (20) is an impeller which is disposed so as to be approximately centric in the riser pipe (5).

3. Riser pipe separator according to Claim 2, characterized in that the impeller is static.

4. Riser pipe separator according to Claim 2, characterized in that the impeller is driven.

5. Recirculating grinding system, comprising - a comminution device (40) such as an impact hammer mill, a high-pressure roller press or a roller mill, - a downpipe (45) by way of which ground material (55) is fed to the comminution device (40), and a riser pipe separator (1) according to one of Claims 1 to 4, - an encapsulation (50) which separates the conveying air (5) from the atmospheric air, wherein the riser pipe (5) of the riser pipe separator (1) and the downpipe (45) are connected to the encapsulation (50), characterized in that the annular gap (30) is connected to the downpipe (45).