EP0638354A1 - Totally self-cleaning mixer - Google Patents

Abstract

The invention relates to a multiaxial mixer/reactor having a large free usable volume which is dynamically self-cleaning, comprising two or more parallel contrarotating axles (1, 11) on which are mounted transport paddles (2, 12), offset in a screw-like manner, which transport paddles are connected together by axially extended kneading bars (3, 13) and also comprising a surrounding housing (4) and an inlet (5) and an outlet (6) for the material to be mixed. <IMAGE>

Description

The invention relates to a multi-axis mixer / reactor with a large free usable volume, which cleans itself kinematically, consisting of two or more parallel axes rotating in opposite directions, on which are arranged in a helically offset manner, conveying blades which are connected to one another by axially extended kneading bars and a surrounding one Housing and optionally an inlet and an outlet for the mix.

The invention is directed to devices for the processing of fluids and cohesive bulk materials. The device is completely kinematically self-cleaning and has a large free usable volume.

In the production and processing of plastics, among other things, highly viscous liquids have to be treated in terms of process engineering. In particular, apparatus for mixing and evaporation are required. These must have a good mixing effect and, in the case of evaporation, a quick renewal of the free surfaces of the mixer.

Product deposits on the walls of such mixers can lead to process impairments. Undesirable side reactions in the deposits are promoted due to the significantly longer residence time in the reactor. This leads to contamination of the product. Product deposits on the walls can be avoided by kinematic self-cleaning of the mixer.

One example is the production of thermotropic, liquid-crystalline polyesters. The rate-determining factor in the final stage of polycondensation is Mass transfer of the condensate into the vacuum gas phase of the reactor. This requires the largest possible mass transfer area and the fastest possible renewal of the same. Due to the pronounced structural viscosity, the product tends to deposit on the wall in non-stirred areas. The longer dwell times here result in black cracked products which, if they get into the product stream, lead to unsaleable goods.

With a view to minimizing the manufacturing and operating costs of a reactor / mixer, a large free usable volume is also sought, i.e. the ratio of the agitator volume to the housing volume should be as low as possible.

To a certain extent, these requirements are met by the apparatus described in the published patent application DE 41 26 425 A1.

However, the apparatus described there has two serious weaknesses:
Only the shaft of the rotors serves to absorb bending forces, for example when mixing pasty fluids. However, the wave should be as thin as possible in order to obtain a large free usable volume. As a result, in the small games also sought (because of self-cleaning), due to the deflection of the shaft, a ratio between the length of the apparatus and the center distance of more than 5 at best 7 can hardly be achieved.

A heating of the blades and gears in the above-mentioned mixing device would only be possible through a complicated routing of the heating channels, with the feed and return lines having to be led through each tooth base. This is difficult to master from a manufacturing point of view or involves high costs.

The object of the invention is to provide an apparatus which is completely kinematically self-cleaning, has a large free volume, does not have the disadvantages mentioned and in which preferably heating / cooling of the stripping elements can be easily integrated.

The object is achieved in that in a multi-shaft mixer on each shaft helically offset conveyor blades are arranged, which are interconnected by axially extended kneading bars.

The invention relates to a multiaxial mixer / reactor consisting of two or more parallel, counter-rotating shafts, on which screw-shaped conveyor blades are attached, which are connected to one another by axially extended kneading bars (the entirety of the shaft, conveyor blades and kneading bars connected to one another is hereinafter referred to as Rotor)., An enclosing housing, optionally with an inlet and an outlet for the mixed material, and in particular with an additional bridge connector for degassing, characterized,
that the front and rear sides, seen in the axial direction, of each conveyor blade of a rotor, except at the ends of the mixer, are kinematically completely cleaned by the conveyor blades of another rotor,
that each kneading bar of a rotor is kinematically completely cleaned at its ends seen in the axial direction also by the conveyor blades, otherwise by the kneading bars and the shaft of another rotor,
that each shaft of one rotor is completely cleaned kinematically by the conveyor blades and the kneading bars of another rotor,
that the housing on its inner wall is completely cleaned kinematically by the kneading bars and conveyor blades,
that the cutting edges of conveying blades and kneading bars occurring in a radial section of a rotor are all either circular arcs around the center of rotation or epicycloid sections,
that the cutting edges of conveyor blades and kneading bars occurring in a radial section of a rotor are all concave if they point inwards (ie if the normal vector on the cutting edge has a component to the axis of rotation) and
that each conveyor blade except at the ends of the mixer on the front and rear sides seen in the axial direction is each connected to a kneading bar, the kneading bar located upstream in relation to the axial conveyance by the conveyor blades to the end of the conveyor blade leading in rotation and the other is connected to the end of the conveyor blade following rotation.

In this mixer, the front and back of each of the rotor blades (except at the ends of the mixer) seen in the axial direction are separated by the conveyor blades of the adjacent rotors, and the kneading bars of a rotor at their ends (viewed in the axial direction) are also separated by the conveyor blades , otherwise by the kneading bars and the shaft of the adjacent rotors, the shafts by the conveyor blades and the kneading bars of the adjacent rotor and the housing by kneading bars and conveyor blades completely kinematically cleaned.

Kinematic cleaning is understood to mean the smallest possible approximation of the moving parts of the mixer, which can be achieved when mixing tolerance is taken into account, so that the parts mentioned can slide past one another without blocking.

As described, a complete kinematic self-cleaning of all surfaces of the mixing room can be achieved.

Each feed scoop, with the exception of the feed scoop at the ends of the mixer, is connected to a kneading bar on the front and rear. In this case, the kneading bar located upstream with respect to the axial conveyance by the conveying blades is connected to the end of the conveying blade leading during rotation and the other to the end of the conveying blade following during rotation. Each kneading bar (with the exception of the ends of the mixer) is connected to two conveyor blades. This results in consequences of conveying blades connected by kneading bars extending over the entire mixer length.

These sequences of conveyor blades connected by kneading bars essentially absorb the bending forces of the rotor that occur due to deflection.

According to their arrangement on the circumference of the rotor, a maximum area moment of inertia and thus a minimal deflection of the shafts is achieved.

Dann kann die Bewegung eines Punktes

des Rotors 1 im Koordinatensystem des Rotors 11 beschrieben werden als:

In einer bevorzugten Ausführungsform rotieren die Rotoren betragsmäßig gleichschnell. Hier gilt $\text{ω₁ = -ω₁₁}$

.The edges of the rotors appearing in a radial section can be described mathematically:
There are 1 and 11 two rotors with the angular velocities ω₁ and ω₁₁ and the center points

Then the movement of a point

of the rotor 1 in the coordinate system of the rotor 11 are described as:

In a preferred embodiment, the rotors rotate at the same rate. Applies here $\text{ω₁ = -ω₁₁}$

.

wobei

n

die Gangzahl,

m

den Grad der Rotationssymmetrie,

φ

einen Teilwinkel zwischen nächstbenachbarten Knetbarren,

π

die Zahl 3, 14159.... (π) und

ψ

den Versatz zwischen Knetbarren auf Vorder- und Rückseite einer Förderschaufel bedeutet.

A goal in kinematic cleaning is to achieve the smallest possible play of the moving parts. This can be achieved if the torsion angle of all rotors is the same over the length, ie the torques are the same. This is made possible with a preferred embodiment of the invention by equipping the rotors with the same repeating elements. If the rotation is at the same speed in opposite directions, this means that the partial angle between the next adjacent kneading bars of a rotor is determined as follows:

in which

n

the number of gears,

m

the degree of rotational symmetry,

φ

a partial angle between the next adjacent kneading bars,

π

the number 3, 14159 .... (π) and

ψ

means the offset between the kneading bars on the front and back of a conveyor scoop.

In order to avoid vibration excitation, a torque that is constant over time is also sought. In a particularly preferred embodiment, this is achieved in that the offset between the kneading bars on the front and on the back of a conveyor scoop (ψ) is not an integral multiple of the partial angle between two adjacent kneading bars (φ) in order to equalize the drive torque. The offset between the kneading bars on the front and back of a blade is the angle by which the one kneading bar must be rotated about the axis of rotation of the connected shaft so that its imaginary axial extension merges precisely into the kneading bars.

The partial angle between two kneading bars is the angle by which a kneading bar must be rotated about the axis of rotation of the connected shaft so that it coincides with the other kneading bar.

wobei

φ

den Teilwinkel zwischen zwei nächstbenachbarten Knetbarren,

i

eine ganze Zahl ungleich 0 ohne gemeinsamen Teiler mit o,

l_i

den axialen Abstand zwischen zwei durch Knetbarren verbundenen Förderschaufeln,

l_Σ

die Länge des Mischers und

ψ

den Winkelversatz zwischen Knetbarren auf Vorder- und Rückseite einer Förderschaufel bedeutet.

If the mixer length is an integral multiple of the axial distance between two conveyor blades connected by kneading bars, the following should apply to the preferred embodiment of the reactor / mixer:

in which

φ

the partial angle between two neighboring kneading bars,

i

an integer not equal to 0 without a common divisor with o,

l _i

the axial distance between two conveyor blades connected by kneading bars,

l _Σ

the length of the mixer and

ψ

means the angular misalignment between the kneading bars on the front and back of a conveyor scoop.

In the case of systems rotating at different speeds, the requirement for torsion ratios that are as constant as possible leads to the approach that the degree of rotational symmetry is inversely proportional to the magnitude of the angular velocity of the waves.

A complete heating or cooling of the rotors, conveyor blades and kneading bars is possible in a preferred embodiment of the invention, if the heating / cooling medium is passed through a shaft end, in each case a partial flow of the medium through the respective first delivery blades of a sequence of interconnected kneading bars and conveyor blades to the subsequent kneading bar, following the consequences of kneading bars and conveyor blades over the entire rotor length, through the last conveyor blade back to the shaft and from there through the shaft end opposite to the inlet, with a further partial flow of the heating / cooling medium passing through a longitudinal hole in the shaft to heat or cool the shaft. In contrast to the apparatus described in DE 41 26 425 A1, there are no places where the supply and return lines of the heating medium have to be guided through a conveyor blade root or a tooth root. The manufacturing process is correspondingly simple to control.

Fig. 1

zeigt die Darstellung des prinzipiellen Aufbaus eines erfindungsgemäßen Mischers im Schnittbild in Aufsicht (Fig. 1b) Vorder- (Fig.1c) und Seitenansicht (Fig. 1a).

Fig. 2

zeigt die Darstellung eines erfindungsgemäßen Mischers.

Fig. 3

zeigt die Darstellung eines Radialschnittes durch den Mischer nach Fig. 2, wie er auch als Frontfläche des Mischers erscheint.

Fig. 4a und 4b

zeigen die Darstellung der Drehbewegung in einem Radialschnitt entsprechend Fig. 3 in 18 Momentaufnahmen.

Fig. 5

zeigt eine weitere bevorzugte Ausführungsform des erfindungsgemäßen Mischers.

The invention is explained in more detail below by way of example with reference to the accompanying drawings:

Fig. 1

shows the representation of the basic structure of a mixer according to the invention in the sectional view in top view (Fig. 1b) front (Fig.1c) and side view (Fig. 1a).

Fig. 2

shows the representation of a mixer according to the invention.

Fig. 3

shows the representation of a radial section through the mixer of FIG. 2, as it also appears as the front surface of the mixer.

FIGS. 4a and 4b

show the representation of the rotary movement in a radial section corresponding to FIG. 3 in 18 snapshots.

Fig. 5

shows a further preferred embodiment of the mixer according to the invention.

Examples

In Fig. 1 the basic structure of a mixer according to the invention is shown. There are two shafts 1, 11 in a housing 4. Conveyor blades 2, 7, 12, 17... Are connected to these in each case following a simple spiral. The illustration in FIG. 1 is simplified to such an extent that the edges occurring in a radial section are not epicycloids and the mixer shown is also not completely self-cleaning.

Fig. 2 shows the spatial representation of a mixer according to the invention. The housing is only partially shown. Conveyor blades 2, 7, 12, 17 ... are arranged on each shaft following a double spiral. The front and rear sides of the conveyor blades are not, as in FIG. 1, in planes perpendicular to the axes of rotation, rather the conveyor blades are set up in such a way that they increasingly contribute to axial transport. The conveying blades are connected by kneading bars 3, 13 ... on each shaft to form 7 sequences of alternating kneading bars and conveying blades. The mixer is designed to rotate at the same speed in opposite directions.

The free usable volume is 68.5% of the interior volume.

Fig. 3 shows a radial section corresponding to A in Fig. 1c through the mixer of Fig. 2, as it also shows on the front surface of the mixer in Fig. 2. Scraper 9 from FIG. 2 thus appears as line 414, 415, 416, 417 and scraper 19 as 314, 315, 316, 317 in FIG. 3. In FIGS. 4a and 4b, the same radial section is shown in 18 phase images that follow one another in time shown during a full revolution of the shafts. Here the cleaning effect becomes clear: Edge 314 cleans the surface 445-447, Edge 414 cleans the surface 345-347, Edge 324 cleans the surface 455-457, Edge 424 cleans the surface 355-357, Edge 334 cleans the surface 465-467, Edge 434 cleans the surface 365-367, Edge 344 cleans the surface 475-477, Edge 444 cleans the surface 375-377, Edge 354 cleans the surface 416-417, Edge 454 cleans the surface 316-317, Edge 364 cleans the surface 425-427, Edge 464 cleans the surface 325-327, Edge 374 cleans the surface 435-437, Edge 474 cleans the surface 335-337, Edge 315 cleans the surface 443-447, Edge 415 cleans the surface 343-347, Edge 315 cleans the surface 442-448, Edge 415 cleans the surface 342-348, Edge 325 cleans the surface 457-462, Edge 425 cleans the surface 357-362, Edge 325 cleans the surface 463-464, Edge 425 cleans the surface 363-364, Edge 335 cleans the surface 462-472, Edge 435 cleans the surface 362-372, Edge 335 cleans the surface 463-467, Edge 435 cleans the surface 363-367, Edge 335 cleans the surface 473-474, Edge 435 cleans the surface 373-374, Edge 345 cleans the surface 414-472, Edge 445 cleans the surface 314-372, Edge 345 cleans the surface 473-474, Edge 445 cleans the surface 373-374, Edge 355 cleans the surface 422-417, Edge 455 cleans the surface 322-317, Edge 355 cleans the surface 423-424, Edge 455 cleans the surface 323-324, Edge 365 cleans the surface 423-427, Edge 465 cleans the surface 323-327, Edge 365 cleans the surface 432-442, Edge 465 cleans the surface 332-342, Edge 365 cleans the surface 433-434, Edge 465 cleans the surface 333-334, Edge 375 cleans the surface 432-442, Edge 475 cleans the surface 332-342, Edge 375 cleans the surface 433-437, Edge 475 cleans the surface 333-337, Edge 375 cleans the surface 443-444, Edge 475 cleans the surface 343-344, Edge 316 cleans the surface 451-454, Edge 416 cleans the surface 351-354, Edge 317 cleans the surface 454-455, Edge 417 cleans the surface 354-355, Edge 327 cleans the surface 464-465, Edge 427 cleans the surface 364-365, Edge 337 cleans the surface 474-475, Edge 437 cleans the surface 374-375, Edge 347 cleans the surface 414-415, Edge 447 cleans the surface 314-315, Edge 357 cleans the surface 424-425, Edge 457 cleans the surface 324-325, Edge 367 cleans the surface 434-435, Edge 467 cleans the surface 334-335, Edge 377 cleans the surface 444-445, Edge 477 cleans the surface 344-345, Surface 351-316 cleans surface 448-451, Area 451-416 cleans area 348-351.

As can be seen, all peripheral surfaces are cleaned.

It is also clear that the inside walls of the housing are cleaned by the edges 445, 435, 345, 335 ...

The end faces of the housing are e.g. completely cleaned by edges of the terminal blades 9, 19 ...

Another preferred variant of the mixer according to the invention is shown in FIG. 5. This differs from the mixer according to FIG. 2 primarily in that the conveyor blades 2, 12, 7, 9, 17, 19 ... are designed as flat disks, the front and rear of which are perpendicular to the axes of rotation 1, 11 .

An advantage of this preferred mixer is the simpler technical manufacture of the mixer due to the simpler construction.

Conveyor blades and kneading bars are prismatic and therefore light e.g. by milling.

Claims (8)

Mixer / reactor with two or more parallel, counter-rotating rotors, consisting of shafts (1, 11), on which screw-like offset conveyor blades (2, 12) are attached, which are connected to one another by axially extended kneading bars (3, 13) Housing (4) optionally with an inlet (5) and an outlet (6) for the mix, characterized in that
that seen in the axial direction front and back of each conveyor blade (2, 12) of a rotor except at the ends of the mixer, where they clean each other with the end face of the housing (4), through the conveyor blades (12, 2) of another Rotors are completely cleaned kinematically,
that the kneading bars (3, 13) of a rotor at its ends seen in the axial direction are also completely kinematically cleaned by the kneading bars (12, 2) by the kneading bars (13, 3) and the shaft (11, 1) of another rotor ,
that the shaft (1, 11) of one rotor is completely kinematically cleaned by the conveyor blades (12, 2) and the kneading bars (13, 3) of the other rotor,
that the housing (4) on its inner wall is completely kinematically cleaned by the kneading bars (3, 13) and conveyor blades (2, 12),
that the step edges of conveyor blades (2, 12) and kneading bars (3, 13) occurring in a radial section of a rotor (1, 2, 3 or 11, 13) are all either circular arcs around the center of rotation or epicycloid sections,
that the cutting edges of conveyor blades (2, 12) and kneading bars (3, 13) occurring in a radial section of a rotor (1, 2, 3 or 11, 12, 13) are all concave if they point inwards (ie if the normal vector on the cutting edge has a component to the axis of rotation) and
that each delivery scoop (2, 12) is connected to a kneading bar (3, 13) with the exception of the ends of the mixer on the front and rear sides seen in the axial direction, the kneading bar (3, 13) with respect to the axial delivery by the delivery vanes (2, 12) kneading bar located upstream is connected to the end of the conveying vane leading during rotation and the other to the end of the conveying vane following during rotation. Mixer / reactor according to claim 1, characterized in that the rotors rotate at the same rate. Mixer / reactor according to Claims 1 to 2, characterized in that the rotors (3, 13) have the same number n of the series of conveying blades (2, 12) distributed over the circumference and connected to one another by kneading bars, the partial angle between the respective next adjacent kneading bar of a rotor is determined to:

in which φ the partial angle between the next adjacent kneading bars, n the number of gears, m the degree of rotational symmetry, ψ the offset between the kneading bars on the front and back of a conveyor scoop, π is the number π (3.14159). Mixer / reactor according to claims 1 to 3, characterized in that to equalize the drive torque, the offset (ψ) between the kneading bars on the front and rear of a conveyor scoop is not an integral multiple of the partial angle (φ) between two adjacent kneading bars. Device according to claims 1 to 4, characterized in that the mixer length is an integral multiple o of the axial distance between two conveyor blades connected by kneading bars and

in which φ = the partial angle between the next adjacent kneading bars, i = an integer not equal to 0 without a common divisor with o, l _i = the axial distance between two conveyor blades connected by kneading bars, l _Σ = the length of the mixer, ψ = the angular misalignment between the kneading bars on the front and back of a conveyor scoop. Mixer / reactor according to claims 1 to 5, characterized in that its conveying blades (2) and kneading bars (3) can be completely heated or cooled. Mixer / reactor according to claim 6, in which the heating / cooling is carried out with a heating / cooling medium which is passed through a shaft end, a partial flow of the medium through the respective first delivery scoop of a sequence of interconnected delivery blades and kneading bars to the next Kneading bars guided, following the interconnected conveying blades and kneading bars led to the end of the rotor, through the respective last conveying blades back to the shaft and out of the shaft end opposite the inlet and a further partial flow of the medium is passed through a longitudinal bore of the shaft to the shaft heat. Mixer / reactor according to claims 1 to 7, characterized in that it has an additional bridge connection for degassing processes.

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