EP1771241B1 - Dynamic mixer and its use - Google Patents

Abstract

A mixer having improved axial and radial mixing which retains good mixing time even during large viscosity changes, comprising a housing with at least one helical or anchor agitator located centrally in the housing in combination with at least one eccentrically arranged screw or blade agitator, preferably in mutual engagement, the combination of a helical agitator and a screw agitator enabling a much shorter mixing time as compared to a mixer having only a helical agitator without a screw agitator.

Description

The invention relates to a device comprising at least one housing, with at least two rotating stirrers wherein one of the stirrers is a helical or anchor stirrer arranged centrally in the housing, and at least one of the other stirrers is an eccentrically arranged screw or blade stirrer according to the preamble of Claim 1.

Helical stirrers are often used for mixing liquids and solids. The task of the stirrer is to achieve the shortest possible mixing times with the lowest possible expenditure of energy until the mixture is homogenized. Many data on the mixing behavior of spiral systems can be found in the literature [ Tatterson, GB; Fluid mixing and gas dispersion in agitated tanks; McGraw-HiII Inc .; 1991; P. 325ff ]. Spiral mixers are common mixer geometries for homogenizing higher-viscosity products.

The demands placed on the mixing behavior by chemical and other production methods are constantly increasing, since reduced mixing time with the same energy input leads to reduced overall costs in production.

To increase the space-time yield in production processes, it is also of interest to carry out as many process steps as possible in a mixing apparatus. Apparatus with stirrers must therefore be able to homogenize mixed materials despite large changes in viscosity with low mixing times. This mixing task can only be fulfilled inadequately with conventional spiral impeller arrangements with one shaft. It has often been described in the literature that the mixing times in the medium-viscosity flow range increase many times over [ Tatterson, GB; Fluid mixing and gas dispersion in agitated tanks; MeGraw-HiII Inc .; 1991; S.381 ]. This is a great disadvantage for processes with viscosity changes that require a short mixing time at all times for quality and efficiency reasons.

In the DE 10248333 A1 Mixers are described in which the mixing tools completely and reciprocally sweep each other and the container wall in order to achieve the fullest possible self-cleaning of the mixer, similar to close-meshed twin-screw extruders. This document also describes that the mixing times of such self-cleaning systems compared to conventional helical stirrers are significantly reduced.

However, the above-described mixer system has the disadvantage that it can be produced only at very high costs, because the mixing tools to achieve self-cleaning similar to gears with a precisely matched geometry must be made and driven by a precise synchromesh.

In the FR 27 16 337 A1 Another mixer is described with a centric and an eccentric stirrer, wherein the eccentric stirrer fits into a recess of the centric stirrer. However, this mixer has the disadvantages that it produces no intentional mixing in the direction parallel to the waves, since the stirrers have no axial conveying action, and that the driving torque at the central shaft always goes through a high peak value when the blade of the centric Stirrer with its recess past the blade of the eccentric stirrer. This leads to an increased cost for the drive energy of the mixer, on the other hand, the high peak torque in the mutual passage of the stirrer must be compensated by a firmer construction of the stirrer and the drive, which in turn increases the cost of the entire construction.

In GB 2076675A are described trough mixer with helical mixer geometry. They are often used for mixing bulk goods or pasty media. These horizontally arranged mixers have the disadvantage that their housings can be shaped in complex and thus expensive geometric shapes have to. Furthermore, it is disadvantageous that the mixers are to be operated with their housing only in a horizontal arrangement.

It was therefore an object to provide a mixer with a cylindrical housing, which has a good axial and radial mixing of the mix while maintaining good mixing time even during large changes in viscosity in the process and at low cost both for the production of mixing tools and the drive and for Mixing has spent energy.

Surprisingly, it has now been found that a mixer comprising at least one housing (1), at least two rotating stirrers (2) and (3) and optionally transverse bars for fixing the stirring elements of the centric rotor, wherein at least one of the stirrer (2) is centrally in the housing (1) arranged helical or anchor agitator, and at least one of the other agitator (3) is an eccentrically arranged worm or blade stirrer, the object of the invention.

The invention therefore relates to a mixer according to claim 1.

As drive means for the stirrer common motors with appropriate gear technology, an input shaft and at least two output shafts can be used. By the transmission here a fixed speed ratio between the two stirrers is realized. Depending on the selected gradient and diameter ratios, the speed ratio of the two stirrers must remain constant during operation, since collisions of the two stirrers occur without a synchronization that is almost free from play. For types of mixer where the speed ratio is independent of the geometry can be selected, also a drive technology with two or more motors in question, with which independent of each other speeds can be set. This creates at least one additional degree of freedom in the operation of the mixer.

Within the meaning of this document, helical stirrers are understood as meaning mixers which are characterized by a shaft which is arranged centrically to the stirring elements and is optionally connected to the stirring elements via at least one transverse bar. The stirring elements of the helical stirrer can be made of a simple sheet metal or of hollow or solid material with a profiled cross-section. They form a helix (helix) of the slope S, which is arranged concentrically to the shaft. Under Wendelrührers are understood here also such constructions whose slope S is due to the design changes with the circumferential length or the circumferential angle, as for example in the in DE 4117773 A1 described stirrers is the case.

Under worm stirrers in the context of this document are understood mixer, which are characterized by a preferably centrally arranged shaft and stirring elements, which are arranged helically (helically) with the slope S around the shaft, preferably no or only a small gap between the stirring elements and the Wave is to be found. With Schneckenrührer here are also such constructions meant, the slope S is not constant over the entire winding.

The terms helical stirrers and screw stirrers in the sense of this document also include the case in which the pitch of the helix or helix is infinitely large in the mathematical sense. Then the helical stirrer passes into an anchor stirrer and the screw stirrer into a blade stirrer. Anchor stirrer and blade stirrer in the sense of this document are understood to mean all technical designs according to the armature geometry, as described, for example, in: Ullmann's Encyclopedia of Industrial Chemistry; Marko Zlokarnik; stirring; DOI: 10.1002 / 14356007.b02_25; Wiley-VCH Verlag GmbH & Co. KGaA; Release 2003, 7th Editi on. Furthermore, under the terms Wendelrührer and Schneckenrührer also understood that the helical contour of the stirrer arms can also be formed by interrupted or offset elements attached. As elements, for example, rods with round or triangular or quadrangular cross-section or spiral segments can be used.

In a preferred embodiment of the invention, the housing has a substantially circular cross-section, deviations tolerated for example due to manufacturing tolerances in the ovality of containers.

The bottom of the housing may have any common shapes, such as dished bottom, basket bottom or conical tapered bottom shapes. The ground anchor shape following the helical stirrer can be adapted to the shape of the ground without mixing disadvantages. The anchor shape can have an S-shaped or straight shape when viewed in horizontal section.

In a further preferred embodiment of the invention, the mixer has at least one opening for filling and / or emptying. Embodiments with at least one respective filling and emptying opening are particularly preferred.

The mixers according to the invention are also characterized in that at least one eccentric stirrer (3) and at least one centric stirrer (2) rotate in opposite directions or in the same direction, very particularly preferably in the same direction.

In the case of the co-rotating stirrers, further preferred embodiments apply:

A mixer is preferred, which is characterized in that at least one eccentric screw mixer is in engagement with the centric helical stirrer, ie that the outside diameter of an eccentric stirrer intersects the inside diameter of the helical stirrer in a cross section perpendicular to the shafts. Under the intervention E in the sense of this writing, the relationship is the radial overlap length (e) and the coil width (b) in a section perpendicular to the waves understood. This is exemplary in Figure (2 outlined).

In a preferred embodiment, the procedure is 30 to 99%, preferably 80 to 95%.

A further relevant parameter of the mixer according to the invention is the number of flights of the stirrer.

The number of flights of a helical or Schneckenrührers is to be understood in the following the natural number, which results when dividing the angle 360 ° by the angle by which a stirrer must be rotated about its axis, so that the image of its section with a Level perpendicular to the stirrer shaft with the corresponding output sectional image coincides.

Particularly preferred are mixers in which the number of turns of the armature or helical stirrer is 2. This has the advantage that during the rotation of this stirrer symmetrical conditions prevail about its axis, so that hardly any flow forces occur perpendicular to the stirrer shaft. On the other hand, the manufacturing expense for the production of the stirrer is still relatively low due to the smaller number of operations. For the screw stirrer or blade stirrer, a geometry with the number of turns 1 or 2 is preferred.

Furthermore, the pitch of the stirrer is also a variable influencing the mixer.

The pitch of a helical or worm stirrer is here the ratio of unwound height and unwound circumferential length, when unrolling a stirrer on the outer circumference on a plane and the positions, which passes through the contact point of the stirring blade with the plane by a line. The slope of this line is then the pitch of the stirrer.

In many cases, the pitch of spiral and worm stirrer is chosen to be constant. However, there are also designs in which, by design, there is a gradient that is variable over the circumference, such as in the case of the DE 4117773 A1 described stirrers.

wobei n₁ bzw. n₂ die Drehzahlen, D₁ bzw. D₂ die Außendurchmesser und S₁ bzw. S₂ die Steigungen des zentrischem bzw. exzentrischen Rührers bezeichnen.The slopes of the stirrers are then matched particularly favorably to one another if the following mathematical relationship (I) is fulfilled: $$\frac{S_1}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2}=\frac{{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">n</figure-callout>}}_2{D}_2}{{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">n</figure-callout>}}_1{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">D</figure-callout>}}_1}$$

where n ₁ or n ₂ denote the speeds, D ₁ and D _2, the outer diameter and S ₁ and S _2, the slopes of the centric or eccentric stirrer.

The pitches of the stirrers should therefore preferably behave inversely proportional to the peripheral speeds of the stirrers so that the vertical distances x _u and x _o between the two agitating blades remain nearly constant during engagement during movement.

For the stirrer tuned according to Equation I, a clear mixing time reduction in the Reynolds number range of 100 was observed for the same vertical distances between the stirring blades x _u = x _o compared to the configuration only with helical stirrer without screw. The measurement results are in FIG. 6 entered in the appendix.

Surprisingly, it was also found that with a vertical distance distribution x _u << x _o in the conveying direction of the spiral agitator in the container wall near down the mixing time in the Reynolds number range of 100 can be further reduced. For this shortening of the mixing time, it is advantageous if the smaller distance x _u << x _o in the conveying direction of the helix down and x _o << x _u in the conveying direction of the helix is selected upwards.

The pitch of the helical stirrer can be between 0.05 and infinite. In a preferred embodiment of the invention, the pitch of the helical stirrer is between 0.1 and 2.

The speed ratio of screw to spiral agitator is in the range between 5: 1 and 1: 1. In addition, the mixer according to the invention preferably has a speed ratio of screw to helical stirrer of 4: 1 to 2: 1, particularly preferably of 3: 1.

A particularly preferred design of the mixer is obtained by reinforcing the helical stirrer at the outer radius by means of stiffeners mounted parallel to the shaft, so that its overall construction can accommodate considerably higher forces and torques with little deformation. This design of the helical stirrer is particularly advantageous because it allows the worm stirrer to engage practically as deeply in the helical stirrer as without the stiffeners, which leads to a particularly good mixing action of the entire mixer.

If the worm stirrer does not interfere with the helical stirrer, the pitch directions, pitches, speeds, and directions of rotation of the stirrers can be independently selected.

However, if the worm stirrer engages the helical stirrer, the pitch directions and the directions of rotation of the stirrers must be the same.

In a particularly preferred embodiment of the invention, the centric and an eccentric stirrer are in mutual engagement and the pitches of these two stirrers are coordinated so that the vertical spacing between the stirrer blades remains as constant and uniform as possible during engagement of the stirrer. This has the advantage that in the manufacture of the stirrer and the construction of the transmission for the synchronous drive Both stirrer only comparatively low demands on the manufacturing tolerances must be made.

In a further embodiment of the mixer according to the invention, at least one eccentric stirrer (3) and at least one centric stirrer rotate in opposite directions.

In reverse rotation, the mixers must not be engaged.

Furthermore, the mixer preferably has a number of revolutions for the helical or anchor agitator of 2 and the number of threads for the helical or blade agitator of 1 or 2 in counter-rotating mixers.

In the case of counter-rotating stirring, the pitch can also be chosen as desired, as well as the speed ratio.

Likewise, a mixer with counter-rotating stirrers may have stiffeners. These are then possible both on the helical outer diameter and on the helical inner diameter.

The housing does not have to be completely provided with the internals according to the invention. It can e.g. for certain processes (degassing) a gas space above the stirrer installations be kept free.

The mixers according to the invention surprisingly showed that the mixing times of these mixers are considerably shortened compared with conventional, comparable stirrers (spiral stirrers), in particular when the screw stirrer engages deeply in the helical stirrer and the stirrers with a speed ratio of screw stirrer to spiral stirrer of 2: 1 to Run 4: 1, and that this good mixing effect is maintained over a wide range of viscosity.

In the vacuum distillation of a mixture of polymer and solvent, in which it comes to a strong foaming when working with a conventional mixer, it was surprisingly found that the foam Compared to the conventional mixer by the mixer according to the invention much better destroyed or retracted into the mix. The mixer according to the invention is therefore particularly suitable for processes in which a disturbing foaming occurs.

In a preferred embodiment of the invention, the mixers according to the invention have heating or cooling elements on the inner wall of the housing. Otherwise, the housing may also be provided per se with the known conventional cooling or heating means, e.g. with a through-flow of heat transfer double jacket, electric heating coils etc.

The mixer according to the invention is suitable for any mixing tasks in the chemical process technology, of course, as a reactor for stirred reactions.

The mixer can also be used as a horizontal mixer, i. E. with horizontally arranged waves, operated. A horizontal arrangement of the shafts is useful, for example, for processes involving bulk goods or moist bulk materials. In addition, of course, all other angles of inclination of the waves relative to the vertical between 0 and 90 ° are possible.

The invention will be explained in more detail by way of example with reference to the figures.

Figur 1a

die Vorderansicht eines erfindungsgemäßen Mischers; das Gehäuse (1) ist geschnitten dargestellt.

Figur 1b

die Vorderansicht eines erfindungsgemäßen Mischers mit gegenüber Figur 1a vergrößerten Steigungen von Wendel- und Schneckenrührer, das Gehäuse ist wiederum geschnitten dargestellt.

Figur 1c

die Vorderansicht eines erfindungsgemäßen Mischers mit gegenüber Figur 1a erhöhten Steigungen, bei dem Verstärkungsstäbe (5) am Außendurchmesser des Wendelrührers (2) angebracht sind. Das Gehäuse (1) ist wiederum geschnitten dargestellt.

Figur 2

einen Schnitt durch einen erfindungsgemäßen Mischer mit der Gangzahl zwei für die Wendel (2) und der Gangzahl zwei für die Schnecke (3). Die Figur zeigt auch die Eingriffstiefe (e) und die Wendelbreite (b), aus denen sich der prozentuale Eingriff E errechnet.

Figur 3

einen Schnitt durch einen anderen erfindungsgemäßen Mischer, bei dem die Gangzahl des Wendelrührers (2) zwei und die Gangzahl des Schneckenrührers (3) eins beträgt.

Figur 4

einen Schnitt durch einen erfindungsgemäßen Mischer, bei dem Wendel (2) und Schnecke (3) sich nicht im Eingriff befinden.

Figur 5

einen Schnitt durch einen etfindungsgemäßen Mischer, bei dem zur Verbesserung der mechanischen Stabilität Verstärkungsstäbe (5) parallel zur Welle auf dem Außendurchmesser des Wendelrührers (2) angebracht sind.

Figur 6

eine graphische Darstellung des Zusammenhangs zwischen Re und NTm.

Show it

FIG. 1a

the front view of a mixer according to the invention; the housing (1) is shown in section.

FIG. 1b

the front view of a mixer according to the invention with opposite FIG. 1a enlarged pitches of spiral and worm stirrer, the housing is shown in section again.

Figure 1c

the front view of a mixer according to the invention with opposite FIG. 1a elevated slopes, in which reinforcing rods (5) on the outer diameter of the helical stirrer (2) are mounted. The housing (1) is shown in section again.

FIG. 2

a section through a mixer according to the invention with the number of threads two for the coil (2) and the number of gears two for the screw (3). The figure also shows the depth of engagement (e) and the helix width (b), from which the percentage engagement E is calculated.

FIG. 3

a section through another mixer according to the invention, in which the number of turns of the helical stirrer (2) is two and the number of flights of the Schneckenrührers (3) one.

FIG. 4

a section through a mixer according to the invention, wherein the helix (2) and worm (3) are not engaged.

FIG. 5

a section through a ethers according to the invention, in which for improving the mechanical stability reinforcing rods (5) are mounted parallel to the shaft on the outer diameter of the helical stirrer (2).

FIG. 6

a graphic representation of the relationship between Re and NTm.

Examples

The following examples serve to illustrate the invention without being limiting.

example 1

FIGS. 1a, 1b and 1c show inventive mixer in the side view in different embodiments.

The cylindrical housing (1), the centric helical stirrer (2) and the eccentric worm stirrer (3) are shown. The FIGS. 1a, 1b and 1c show by way of example the embodiment with a transverse bar (4) at the end of the central shaft on which the coils are mounted. Figure 1c additionally shows the reinforcing rods (5) mounted parallel to the shaft.

Since the helical and the worm stirrer are engaged, both the sense of rotation and the pitch of both stirrers must be identical. It also requires a synchronizing drive for both stirrers, which ensures that the two stirrers move at a fixed speed ratio and the stirring blades do not come into contact with each other.

Example 2

• Bei einem Drehzahlverhältnis von 3:1: S₁/S₂=3*0,37/0,95=1,17
• Bei einem Drehzahlverhältnis von 2:1: S₁/S₂=2*0,37/0,95=0,78

FIG. 2 shows a cross section through a mixer according to the invention. The number of turns of the spiral agitator (2) and of the worm agitator (3) is two. The mixer can be operated with a speed ratio of screw stirrer to spiral stirrer of 3: 1 or 2: 1. For a precise tuning of the slopes for the purpose of large and safe vertical distances in engagement between the two stirrers, use relationship (I). In Example 2, the outer diameter of the helix is 95% of the container inner diameter and the outer diameter of the screw 37% of the container inner diameter. The distance between the axes of the centric and the eccentric stirrer is 28% of the Vessel inner diameter. According to relation (I), the ratio of helix and worm slopes must be as follows:

• At a speed ratio of 3: 1: S ₁ / S ₂ = 3 * 0.37 / 0.95 = 1.17
• At a speed ratio of 2: 1: S ₁ / S ₂ = 2 * 0.37 / 0.95 = 0.78

If, for example, for the centric helical stirrer, the value S ₁ = 1 is specified for the pitch, which corresponds to a pitch angle of 45 °, the pitch S ₂ = 0.85 (corresponding to a lead angle of 40.6 mm) is selected for the eccentric worm stirrer °) at a speed ratio of 3: 1 and the slope S ₂ = 1.28 (corresponding to a pitch angle of 52.1 °) at a speed ratio of 2: 1.

Example 3

FIG. 4 shows a variant of the mixer according to the invention, in which the centric helical stirrer (2) and the eccentric worm stirrer (3) are not in mutual engagement. Now both the direction of rotation and the pitch of both stirrers can be selected independently of each other. In addition, no synchronizing transmission with a fixed speed ratio is required here. It is now possible to adjust the conveying direction of both stirrers independently of each other so that either both stirrers have the same or different conveying directions axially.

Example 4

FIG. 5 shows a variant of the mixer according to the invention, in which the centric helical stirrer (2) and the eccentric worm stirrer (3) are in mutual engagement and driven synchronized. To improve the mechanical stability (in this example) four stiffening rods (4) are mounted parallel to the shafts on the outer diameter of the helical stirrer. hereby the entire construction of the helical stirrer is very efficiently stiffened against elastic and plastic deformation, without obstructing the engagement between the helical and the helical stirrer, which is important for shortening the mixing times.

Claims (10)

1. Device at least comprising a housing (1), at least two rotating agitators (2) and (3), one of the agitators (2) being a helical or anchor agitator arranged centrally in the housing (1), and at least one of the other agitators (3) being an eccentrically arranged screw or blade agitator, characterized in that the pitches, the rotary speeds and the outer diameters of the agitators satisfy the following mathematical relationship (I) : $$\frac{S_1}{S_2}=\frac{n_2{D}_2}{n_1{D}_1}$$

   

   where n₁ and n₂ are the rotary speeds, D₁ and D₂ are the outer diameters and S₁ and S₂ are the pitches, respectively, of the at least one central and eccentric agitator.
2. Device according to claim 1, characterized in that at least one eccentric agitator (3) and at least one central agitator (2) are corotating or counter rotating.
3. Device according to one of claims 1 to 2, characterized in that the eccentric screw agitator engages with the central helical agitator.
4. Device according to one of claims 1 to 3, characterized in that the engagement E is 30-99%.
5. Device according to one of claims 1 to 3, characterized in that the engagement E is 80-95%.
6. Device according to one of claims 1 to 4, characterized in that the number of flights for the helical or anchor agitator is two and the number of flights for the screw or blade agitator is one or two.
7. Device according to one of claims 1 to 6, characterized in that the pitch S of the helical agitator is between 0.05 and infinity.
8. Device according to one of claims 1 to 7, characterized in that the rotary speed ratio of screw agitator to helical agitator is in the range between 5:1 and 1:1.
9. Device according to one of claims 1 to 8, having the upper distance x_o and the lower distance x_u between a helix of an eccentric agitator and a helix of a central agitator, characterized in that with downwards pumping direction of the helix x_u << x_o and with upwards pumping direction of the helix x_o << x_u.
10. Use of a device according to one of claims 1 to 9 for producing or processing polymers.

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