Mixing device with screw drive for defibrating

Abstract

The present invention relates to a mixing device (1) for mixing highly viscous media, in particular for a biogas plant, comprising a large-volume outer container (2) and an agitator arranged therein, wherein the container (2) has a medium inlet and a discharge line (6) for discharging the mixed medium. The agitator is designed as a vertical screw mixer (8), comprising a stirring screw (12) and a sleeve (9) enclosing the stirring screw (12).

Description

[0001] The present invention relates to a mixing device for mixing highly viscous media, in particular for a biogas plant according to the features in the preamble of claim 1.

[0002] The operation of biogas plants is known from the state of the art. For this purpose, highly viscous media, i.e., particularly thick, sludgy, or pasty, are fed into a biogas tank. These media contain various biomass materials. These are usually animal excrement, such as liquid manure and solid manure, as well as energy crops as a substrate, usually corn cuttings.

[0003] Both of these highly viscous media must be mixed as homogeneously as possible, and further processes are necessary, such as filtering, cleaning or sanitizing.

[0004] A corresponding mixing device is known, for example, from DE 10 2005 022 373 A1.

[0005] Further mixing devices which disclose the preamble of claim 1 are known from AT 14 171 U1 and KR 101 015 470 B1.

[0006] The object of the present invention is to provide a mixing device which is significantly improved compared to the prior art, thus achieving better and shorter mixing times and optionally allowing the possibility of filtering and pre-tempering.

[0007] The above-mentioned object is achieved with a mixing device according to the features in claim 1.

[0008] Advantageous embodiments of the present invention are the subject of the dependent claims.

[0009] The mixing device for mixing highly viscous media, particularly for a biogas plant, comprises a large-volume outer container and an agitator arranged therein. The container itself has an inlet for the medium and a discharge line for removing, in particular pumping out, the mixed medium.

[0010] According to the invention, the mixing device is characterized in that the agitator is arranged as a vertical screw mixer in the container, wherein the screw mixer has a stirring screw and a sleeve enclosing the stirring screw.

[0011] In particular, the sleeve is suspended in the container and arranged radially spaced from the container wall. The sleeve itself has substantially the same axial length as the agitator screw itself. The sleeve itself is preferably freely suspended in the container via a suspension device or struts and suspended from a container lid. An underside of the sleeve is freely suspended in the container. This means that an underside of the sleeve is freely suspended so that the medium can be pressed downwards through the sleeve; if necessary, in conjunction with the screen described later, solids can then be separated out. At higher speeds of the screw, however, the sleeve can be supported or braced at an underside in the container. However, a fluid flow can freely exit at the underside of the sleeve. An upper side of the sleeve, in each case relative to the vertical direction, is at a distance from the container lid.This offers a significant advantage over prior art mixing devices. This is that the screw mixer, with its agitator screw within the sleeve, can circulate or mix the medium multiple times in a significantly shorter time than with prior art agitators. At the same time, the direction of rotation of the agitator screw can be changed. The agitator screw can therefore both pump or push the medium through the sleeve and simply suck the medium through the sleeve by changing the direction of rotation. This in turn offers two advantages. Firstly, the direction of rotation can be changed during mixing, allowing the medium to be passed through the mixing device vertically from top to bottom, or by changing the direction of rotation from bottom to top. This improves homogenization during mixing.A second advantage is that in the event of contamination, clumps or other foreign bodies, clogging does not occur by changing the direction of rotation and thus also the mixing direction of the medium.

[0012] In a further preferred embodiment, the feed is arranged within a projection area of ​​the sleeve's cross-section. In particular, the outlet opening of the feed is arranged in the container lid within the projection area of ​​the sleeve's cross-section. Newly added medium is thus guided directly into the suction of the screw mixer and thus mixed within the container in real time.

[0013] Furthermore, it is particularly preferred to have a minimal gap in the radial direction between the sleeve surrounding the agitator screw and the return screw itself. The gap is preferably less than 30 mm, in particular less than 20 mm, particularly preferably less than 10 mm, but most preferably greater than 5 mm.

[0014] The sleeve, as well as the agitator screw itself, are made of steel. Clumps, thickened portions, or similar materials can be forced into the sleeve due to the minimal gap between the outer surface of the agitator screw and the inner surface of the sleeve due to the centrifugal force when the agitator screw is driven. If clumps or thickened portions are present within the highly viscous medium to be mixed, they are sometimes trapped in the gap due to the movement of the agitator screw and thereby broken up, crushed, or shredded. The highly viscous medium, especially the solids content in the medium, is thus crushed or reduced. This results in more homogeneous mixing.

[0015] Furthermore, it is particularly preferred to provide means on the agitator screw, in particular on the surface of the agitator screw and / or on the inner surface of the sleeve, which increase the friction coefficient of the surface at least in certain areas, such that the highly viscous medium or solid clumps or thickenings within the highly viscous medium are crushed, broken, and / or shredded as they pass through the means. The means can be, for example, reinforcements, teeth, cams, or the like, such that, for example, a thickening is clamped to the means and is then broken or shredded by further movement of the agitator screw.

[0016] In particular, for this purpose, the agitator screw's turns can be interrupted at certain lengths. A laterally projecting stepped shoulder can be formed at the interrupted points of the agitator screw's turns. The agitator screw can have an axially aligned stepped shoulder extending across the entire radial width at the points where the agitator screw is interrupted. In particular, the inner surface of the sleeve can also have corresponding stepped shoulders, teeth, or even a groove, so that clumps or thickened portions are trapped and shredded or broken up upon further rotation of the agitator screw.

[0017] A further advantage of the invention provides that the container itself is designed like a silo. A collecting box is arranged below the container or at a lower point of the container. The agitator screw is preferably arranged in the container at an axial distance from the collecting box. Due to the flow within the agitator screw, a portion of the medium is thus pressed into the collecting box. Solids or impurities within the medium, for example stones, are pressed into the collecting box within the flow and sink there due to gravity. However, at a transition between the lower edge of the silo-like container and the collecting box, past which the flow of the medium to be mixed flows, the stones are not carried along and sink to the bottom of the collecting box.

[0018] The container can also be used to mix food waste or other viscous media. These contain foreign matter, such as stones or glass particles. These can then be separated into the collection box by the agitator screw, where they sink into the collection box. To further enhance this effect, a screen is arranged at the end of the agitator screw. In the downward flow direction, solids hit the screen and, due to a rotational movement and the resulting centrifugal force, are propelled radially outwards, then sink to the bottom of the silo-like container. This improves the separation of solid matter from the viscous medium.

[0019] This is particularly advantageous because the high viscosity of the media being mixed makes it impossible to filter them otherwise. Any filter screen or similar device would immediately become clogged.

[0020] The effect of collecting foreign objects, especially stones, is further improved by locating the lowest point of the discharge line at least 1 cm, preferably more than 2 cm, and preferably more than 5 or 10 cm, for example, above the bottom of the collection tank. Any current generated when pumping out the mixed medium then draws the mixed medium to be pumped out as a suction effect. However, the stones lying on the bottom of the collection tank remain in place due to gravity and are not pumped out. They can then be removed via an inspection hatch.

[0021] In a further advantageous embodiment, the sleeve itself is double-walled, providing temperature control channels. This allows a temperature control medium, such as a heating medium, to pass through. The medium inside the container then passes through the sleeve wall both inside and out, and is thereby heated.

[0022] The container itself can also be double-walled, allowing a temperature control medium to flow through it. This can be used, in particular, for a so-called sanitization process. Germs and bacteria can be killed in this way. For example, at a temperature of more than 70°C, especially 72°C, for one hour. The advantage over sanitization, for example, in a pipeline, is that more surface area is available and the fact that the medium is guided over the surfaces in the agitator, thus creating forced convection and thus improving heat transfer. The medium can therefore be heated up much more quickly and the temperature can be maintained much more quickly.

[0023] A further advantage of solid separation is that the medium has better flow properties at elevated temperatures, meaning that solids move faster and more easily relative to the medium itself. This allows stones or glass fragments to slide more easily and sink more quickly in the medium. This improves the separation capacity. Bone fragments, for example, or even metal objects in general, can also be separated from food residues.

[0024] Further advantages, features, properties, and aspects are the subject of the following description. Preferred embodiments are illustrated in the figures. These serve to facilitate understanding of the invention. They show: Figure 1 shows a front view of a mixing device according to the invention, Figure 2 shows a partial longitudinal section through the mixing device according to the invention, Figure 3 shows a detailed view of the agitator screw, Figure 4 shows a detailed view of the agitator screw, Figure 5 shows a flow pattern generated by the agitator screw, Figure 6 shows a flow pattern for Figure 5 due to a change in the direction of rotation of the stirring screw, Figure 7 shows a design variant of a container according to the invention with heating in the sleeve and in the outer wall of the container and Figure 8 shows a container according to the invention with a shield arrangement at the end of the screw drive.

[0025] In the figures, the same reference symbols are used for identical or similar components, even if a repeated description is omitted for reasons of simplification.

[0026] Figure 1shows the mixing device 1 according to the invention for connection to a biogas plant (not shown in detail). The mixing device 1 has a larger silo-like container 2, preferably made of steel, in particular stainless steel, for example V2A or V4A. The container 2 further has a container lid 3 and feet 4 with which the container 2 is placed on a base (not shown in detail). A collecting container 5 is provided on a lower part of the container 2. The collecting container 5 has a square or rectangular cross-sectional configuration. A discharge line 6 is connected to the collecting container 5 for pumping out the medium mixed in the mixer. Furthermore, a shaft 7 for connection to a drive can be seen in the lid. The shaft 7 is the drive shaft of the Figure 2 described screw mixer 8.

[0027] The screw mixer 8 has an outer sleeve 9 suspended freely in the container 2. The sleeve 9 is suspended from the container lid 3 via webs 10 or positioned at a distance. Furthermore, feed openings 11 are provided through which the medium (not shown in detail) is fed. The stirring screw 12 itself has stepped interruptions 13. These are shown in cross-section along the section line III-III in Figure 3 Here, a step 14 is shown. When the medium of the agitator screw 12 is exceeded, solids are shredded. Furthermore, Figure 4 a top view of the stirring screw 12 is shown.

[0028] Here, it is shown that a lateral stepped shoulder 14 is present outwardly in the radial direction R. During the rotational movement of the agitator screw 12 within the sleeve 9, clumps are clamped and shredded between the inner surface 15 of the sleeve 9 and the agitator screw 12.

[0029] Figure 5 shows a flow pattern according to the longitudinal section of Figure 2 . Here, the agitator screw 12 is shown in a pushing operation. Medium fed through the receiving or feed openings 11 is guided into the underlying projection or cross-sectional area of ​​the sleeve 9 and the agitator screw 12 and is immediately sucked in by the agitator screw 12 from above in the vertical direction and pressed downwards by the agitator screw 12, and mixing takes place laterally past the sleeve 9. Stones located in the medium are moved downwards in the vertical direction and supported by gravity and rest on a base 16 of the collecting container 5. The discharge line 6 is spaced by at least 1 cm, preferably more than 2 cm, in particular more than 5 and in particular more than 10 cm by the distance A, in particular the lowest point 17 of the discharge line 6. InStones 19 located in the collecting container 5 are therefore not removed during the pumping movement.

[0030] Furthermore, at least a portion of the medium is pressed into the collecting container 5 during the stirring process or at least partially flows into it. At a transition of the edge 18 or undercut from the collecting container 5 to the container 2 or the bottom of the silo-like container 2, stones 19 bounce off the edge 18 and then also sink to the bottom of the collecting container 5.

[0031] Figure 6 shows the representation from Figure 5 , whereby the direction of rotation of the screw mixer 8 has been changed. The screw mixer 8 is not in pressure mode here, but in suction mode. This changes the mixing direction. This can occur, for example, at specified intervals or upon detection of a blockage.

[0032] Figure 7shows a container 2 according to the invention. It is schematically illustrated here that both the outer wall 20 of the container 2 and the sleeve 9 of the screw drive (not shown in detail) are each double-walled, allowing a fluid medium to pass through them. This is preferably also designed to be radially circumferential. A respective supply line 21 and 22 can be provided, through which a temperature control medium (not shown in detail) is supplied, as well as a corresponding discharge line 23 and 24, through which a fluid medium (not shown in detail) is discharged.

[0033] This makes it possible to carry out a hygienization process in a particularly advantageous manner. In the process, bacteria as well as other foreign bodies or germs can be killed in the medium. This is preferably carried out for a period of approximately one hour at a temperature above 70°C, preferably 72°C. The advantage is that there is a particularly large wall surface here to allow a heat input into the viscous medium. On the one hand, the inner wall 25 of the container 2, then the outer wall surface 26 of the sleeve 9 as well as the inner wall surface 27 of the sleeve 9 each serve as a heat transfer. The, for example, in Figure 5 The circulation of the medium shown in Figure 6 also enables convection and thus an even better heat transfer across the respective wall surface.

[0034] All features described above and below can also be applied to the design variant according to Figure 7be applied without departing from the scope of the invention.

[0035] Figure 8shows the present invention. Here, a screen 28 is arranged below the stirring screw 12. The screen 28 is connected to the stirring screw 12 and turns or rotates with the stirring screw 12. The medium, in particular solids or foreign particles, for example stones or glass bodies, are conveyed outwards in the radial direction due to the screen 28 and the associated rotation and then sink down the slope. The separation effect for foreign bodies in the viscous medium is thereby improved. A discharge line 6 is then arranged, in particular in the axial direction Ax, below the screen 28. The upper edge 29 of the opening of the suction line is preferably arranged well above the bottom 16 of the collecting container 5, furthermore preferably also above the edge 18 of the lower slope 30 of the container 2. This in turn ensures that separated foreign bodies fall into the collecting container 5.Furthermore, foreign bodies separated during the suction of the medium from the container 2 are precisely prevented from being reintroduced into the suction line. The screen 28 preferably has a diameter that is smaller than the diameter of the agitator screw 12. The diameter of the screen 28 is preferably 20 to 70%, in particular 30 to 60%, of the diameter of the agitator screw 12.

[0036] All features described individually in the general description and in the description of the figures can be combined with each other as desired in connection with this invention without departing from the scope of the invention. The individual features are therefore not limited to a single embodiment, but can, as already mentioned, be combined with other embodiments and the associated advantages. Reference symbol:

[0037] 1 - Mixing device 2 - Container 3 - Container lid 4 - Feet 5 - Collecting container 6 - Discharge line 7 - Shaft 8 - Screw mixer 9 - Sleeve 10 - Web 11 - Feed opening 12 - Agitator screw 13 - Interruption 14 - Step 15 - Inner surface to 9 16 - Bottom 17 - Lowest point to 6 18 - Edge 19 - Stones 20 - Outer wall 21 - Feed line 22 - Feed line 23 - Discharge line 24 - Discharge line 25 - Inner wall 26 - Outer wall surface 27 - Inner wall surface 28 - Screen 29 - Top edge 30 - Lower slope A - Distance Ax - Axial direction R - Radial direction

Claims

1. Mixing device (1) for mixing highly viscous media, in particular for a biogas plant, having a large-volume outer container (2) and an agitator arranged therein, wherein the container (2) has a supply of medium and a discharge line (6) for discharging the mixed medium, wherein the agitator is formed as a vertical screw mixer (8), having an agitator screw (12) and a sleeve (9) encasing the agitator screw (12), characterized in that a screen (28) is arranged at a lower end of the agitator screw (12), wherein the screen (28) is connected to the agitator screw (12) in a rotationally fixed manner.

2. The mixing device (1) according to claim 1, characterized in that a minimum gap in the radial direction is formed between the encasing sleeve (9) and the agitator screw (12), wherein the gap is preferably less than 30 mm, in particular less than 20 mm and most preferably less than 10 mm, but very particularly greater than 5 mm.

3. The mixing device (1) according to any one of the preceding claims, characterized in that means are provided on the agitator screw (12) and / or an inner circumferential surface 15 of the sleeve (9) which increase the coefficient of friction of the surface at least sectionwise, so that the highly viscous medium is comminuted, broken and / or defibrated as it passes the means.

4. The mixing device (1) according to any one of the preceding claims, characterized in that the turns of the agitator screw (12) are interrupted in length sections.

5. The mixing device (1) according to any one of the preceding claims, characterized in that a laterally projecting step shoulder (14) is formed at the interrupted points of the turns of the agitator screw (12).

6. The mixing device (1) according to any one of the preceding claims, characterized in that the agitator screw (12) has an axially aligned stepped shoulder (14) extending over the entire radial width at the points interrupted in length sections.

7. The mixing device (1) according to any one of the preceding claims, characterized in that the container (2) is of a silo-like design, wherein a collecting container (5) is arranged below the container (2) and the agitator screw (12) is arranged in the container (2) at an axial distance from the collecting container (5).

8. The mixing device (1) according to any one of the preceding claims, characterized in that the collecting container (5) has a cross-sectional area which substantially corresponds to the cross-sectional area of the sleeve (9) or is larger than the cross-sectional area of the sleeve (9).

9. The mixing device (1) according to any one of the preceding claims, characterized in that the discharge line (6) is coupled to the collecting container (5), wherein a lower point of the discharge line (6) is arranged at least 1 cm, preferably more than 2 cm, preferably more, above a bottom (16) of the collecting container (5).

10. The mixing device (1) according to any one of the preceding claims, characterized in that a supply of medium takes place above the sleeve (9), wherein outlet openings of the supply occur within a projection surface of the cross-section of the sleeve (9).

11. The mixing device (1) according to any one of the preceding claims, characterized in that the wall surface of the sleeve (9) is formed in a double-walled way, so that a temperature control medium can be passed through.

12. The mixing device (1) according to any one of the preceding claims, characterized in that a temperature control medium can be conducted through the wall surface of the sleeve (9) and / or through the wall surface of the container (2), wherein, for this purpose, in particular the wall surface of the container (2) and / or the wall surface of the sleeve (9) are each formed in a double-walled way.

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