EP2286904B1 - Static mixing device for flowable materials - Google Patents

Abstract

The device has a mixing element arranged in a flow channel (10) and comprising crosswisely arranged rods (14A, 14B) enclosing an angle of larger than 0 degree with a longitudinal axis of the flow channel. The rods are arranged in planes that lie parallel to each other. The rods are arranged between adjacent intersection points (16), and include a recess with small widths (b) under formation of large wall clearance (c) between front-sided joint edges of the rods, where the sum of the small widths of the rods amounts to 35 percentages of diameter of the mixing element.

Description

TECHNICAL AREA

The present invention relates to a static mixing device, comprising a tubular, a longitudinal axis and an inner diameter flow channel having at least one arranged in the flow channel mixing element of a length and a diameter corresponding to the inner diameter of the flow channel, each mixing element arranged a plurality of crosswise, with the longitudinal axis of the Flow channel having an angle greater 0 ° including webs, wherein the webs are arranged in two intersecting, a plurality of mutually parallel, spaced from each other by an equal distance planes levels and when projecting the two levels of crowd on a perpendicular to the longitudinal axis of the flow channel lying projection plane adjacent webs have an intermediate distance.

STATE OF THE ART

• Vermischen von pumpbaren Flüssigkeiten
• Dispergieren und Emulgieren von ineinander unlöslichen Komponenten
• Mischen von reaktiven Flüssigkeiten
• Mischen und Homogenisieren von Kunststoffschmelzen
• Gas-Flüssig-Kontaktieren
• Mischen von Gasen
• Wärmeaustausch von viskosen Stoffen

Static mixers are now used in all areas of chemical engineering. A characteristic feature of static mixers is that only the liquids or gases to be mixed are moved. In contrast to dynamic mixing systems, no stirring takes place, but pumps, blowers or compressors continuously convey the media to be mixed to the mixing tube, which is equipped with the mixing elements. Static mixers can generally be used in the following application areas:

• Mixing pumpable liquids
• Dispersing and emulsifying mutually insoluble components
• Mixing of reactive liquids
• Mixing and homogenizing of plastic melts
• Gas-liquid contacting
• Mixing gases
• Heat exchange of viscous substances

One out US Pat. No. 3,286,992 A known, known as helical mixer static mixer has helically curved, sheet-like, alternately left and right-hand plates or mixing elements, which lined up with intersecting end edges divide the flow of substances to be mixed as they enter each element. The flow channel is the same in shape and cross section in each of the elements. The spiral mixer is used in particular for mixing in the turbulent range. In the laminar field, the spiral mixer is only partially usable because of its moderate mixing performance.

A special family of static mixers are the so-called X-mixers. These consist of intersecting webs or plates. On off AT 330 135 B Known X-mixer has in a tube at least one mixing insert in the form of a webs and slots having plate pair. In each case, the webs of a plate extend through the slots of the other plate crossing therethrough. The plates are arranged inclined to one another and to the axis of the tube. The supplied stream of substances to be mixed is split by the webs as a result of the inclination of the plates in terms of time and place offset into partial streams. In this known mixer, the web approaches form strong dead zones, which increase the residence time unnecessarily and can damage critical fluids. In addition, the plates must be positioned with countless welds, which can lead to increased corrosion. The assembly of the plates is very time consuming and therefore costly. This known device is used in particular for mixing in the laminar range. In the turbulent range, it is only partially usable because of its high pressure loss.

The development of the mixer according to CH 642 564 A5 in 1979 presented an improvement in the static mixing technique for laminar flow media. Since then, this mixer has proven itself and it is successfully used in a very wide range of applications with mostly high viscosity media. He is in CH 642 564 A5 in Fig. 1 Shown as a mixer with 8 webs, also referred to as 8-bar mixer, with an L / D ratio of 1. The mixer has a very high pressure drop.

The geometry known as CSE-X mixer is in CH 693 560 A5 described. This patent shows a device for static mixing, consisting of a tubular housing with at least one mixing insert arranged therein in the form of a webs and slots having plate which is bent. Preferably, the plates have projections on the web edges and have elliptical peripheral shapes. Two curved plates, each with the webs of one plate passing through the slits of the other plate, are attached to the protrusions. The mixing inserts can be positioned one behind the other in the tubular housing, wherein the mixing inserts can touch directly or can also have spacings between the inserts. The device can mix well with this simple geometry in all flow areas. The mixing quality is determined only by the number of mixing inserts and their installation position. The mixed use was known on the market especially as 4-, 6- and 8-bar construction and also has an increasing with increasing number of webs, high pressure loss.

EP 0 154 013 A1 shows a mixing device for plastic melt processing machines. The mixing element has intersecting webs whose end pieces penetrate the openings of the pipe or a sleeve. The webs have between the intersection points free spaces and reduce the pressure loss significantly. The stable welded construction can be significantly distorted at greater temperature differences, which can lead to jamming of the sleeve in the pipe.

WO 2009/000642 A1 shows a mixing device of the type mentioned, in which wie in EP 0 154 013 A1 - The webs have clear spaces between the intersections. The in WO 2009/000642 A1 in Fig. 3 illustrated 5-bar mixer has an L / D ratio of 1 on. With this geometry, the pressure loss is significantly reduced. The construction is mechanically very weak and can hardly be expertly welded. Soldered versions are very time-consuming and as a rule barely gap-free.

The trade journal Pharma und Food 2/2004 describes mikromakro ^® technology with static mixers. Micro-chromosomes are understood as the targeted use of Static mixers of different geometries and nominal widths. Basically, first a uniform pre-distribution in the macro mixer must be achieved, then in the micro mixer the best possible fine distribution is achieved. The basics typically used are the CSE-X mixers.

• das L/D-Verhältnis eine Mischelementes
• die Anzahl Steglagen
• die Dicke der Stege
• die Winkellage der Stege
• die Form der Stege
• die Breite der Stege

Summarizing the investigations of X-mixers of the last years, the following possible parameters were varied:

• the L / D ratio is a mixing element
• the number of webs
• the thickness of the bars
• the angular position of the webs
• the shape of the bars
• the width of the bars

The investigations in CH 642 564 A5 show that the number of web layers directly influences the layer formation and thus the mixing quality. The more web layers are used, the more layers are produced, which has a positive effect on the mixing quality. However, the pressure loss increases as the number of webs increases. An ideal geometry according to CH 642 564 A5 six or eight webs and an L / D ratio of 0.75 to 1.5.

Further experiments with geometries according to CH 642 564 A5 have shown that with a larger number of webs significantly higher pressure losses will be produced with only slightly improved mixing quality. As a result, static mixing elements with four web layers, which preferably have an L / D ratio of 0.5 to 1.0, are found on the market. In fact, the 4-bar mixer shows excellent properties, but also has a high pressure loss.

With the out WO 2009/000642 A1 Although known geometry in which the webs have clear spaces between the intersections, while the pressure loss of the above-described 4-bar mixer can be significantly reduced, although the mixing quality decreases. With the arrangement of interstices leaves However, already achieve a good mixing effect at an acceptable pressure drop. Out DE-A-28 22 096 and FR-A-2 807 336 Static mixing devices are known with mixing elements of crosswise webs.

PRESENTATION OF THE INVENTION

The invention has for its object to provide a static mixing device of the type mentioned with further improved mixing effect without substantial increase in pressure drop, which does not have the aforementioned disadvantages of prior art mixers. The mixing device should preferably be able to be used in the laminar flow range and ensure a largely complete mixing. The mixing elements should be simple and inexpensive to manufacture, have a significantly reduced pressure drop and mechanically stable can be assembled to mixer bars. The mixing elements should be able to be positioned as short as possible as well as long designs in the flow channel. The flow channel should have a round, rectangular, or square cross-section.

To the inventive solution of the problem results in that the webs are formed waisted between adjacent intersections and in the middle between adjacent intersections, the webs their smallest width and adjacent webs have their greatest distance, and the inner wall of the flow channel adjacent webs between the front edge edges one of Sidecut of the webs corresponding recess having the smallest width to form a largest in the middle between the front edge edges wall distance, wherein the measured over the diameter of the mixing element sum of the smallest widths of the webs is at least 35% of the diameter of the mixing element.

• Alle Stege schliessen mit der Längsachse des Strömungskanals einen Winkel von 45° ein.
• Alle Stege weisen die gleiche kleinste Breite auf.
• Alle einander benachbarten Stege weisen den gleichen grössten Zwischenabstand auf.
• Die kleinste Breite der Stege beträgt 50 % ihrer Breite an den Kreuzungsstellen der Stege.
• Die kleinste Breite der Stege ist gleich gross ist wie der grösste Zwischenabstand benachbarter Stege.
• Der grösste Wandabstand beträgt 50% der kleinsten Breite der Stege und 50% des grössten Zwischenabstandes benachbarter Stege.
• Das Mischelement weist vier Steglagen auf.
• Aufeinanderfolgende Mischelemente sind bezüglich der Längsachse des Strömungskanals um einen Winkel von 90° gegeneinander verdreht angeordnet.
• Aufeinanderfolgende Mischelemente sind von einander beabstandet.

Preferred embodiments of the static mixing device according to the invention have one or more of the following features:

• All webs form an angle of 45 ° with the longitudinal axis of the flow channel.
• All webs have the same smallest width.
• All adjacent webs have the same maximum spacing.
• The smallest width of the webs is 50% of their width at the intersection of the webs.
• The smallest width of the webs is the same size as the largest distance between adjacent webs.
• The largest wall distance is 50% of the smallest width of the webs and 50% of the greatest distance between adjacent webs.
• The mixing element has four web layers.
• Successive mixing elements are arranged rotated with respect to the longitudinal axis of the flow channel by an angle of 90 ° to each other.
• Successive mixing elements are spaced from each other.

The static mixing device according to the present invention is particularly suitable for mixing media, at least one of which is a flowable, laminar flowing medium, in particular a polymer melt or another highly viscous fluid.

In order to be able to compare the efficiency of static mixers, the energy requirement and the mixing quality must be used for comparison. The energy requirement of the static mixer is directly proportional to the pressure loss. In the laminar flow range, for a static mixer in a round hollow body: $$\mathrm{\Delta }{p}_L=32\cdot z\cdot \eta \cdot w\cdot \frac{L}{D^2}$$

The size z is called pressure loss manifold and represents the ratio of the pressure loss for a static mixer in a round hollow body to the empty tube. Η stands for the dynamic viscosity, w for the flow rate, L for the length and D for the diameter. The z-factor is a conventional laminar resistance factor in static mixing technology and is regularly used for the comparison of static mixers.

For the comparison of the mixing performance, the relative standard deviation is generally used S / S _{O on} . With this known mixture quality measure, it should be noted that only measurement results can be recorded with the same measurement analyzes. Measurements can be taken in the literature by means of conductivity measurement, decolorization, laser-induced fluorescence (LIF) or medium photometric analysis FIP (Fluitec Image Processing). Therefore, only measurements with the same method may be compared, otherwise significant deviations will occur.

In order to be able to compare the mixing performance of different static mixer geometries, one usually uses the mixing intensity M, which is determined as follows: $$M=\frac{\mathrm{\Delta }{p}_L\cdot D}{\eta \cdot w}=32\cdot z\cdot \frac{L}{D}\mathit{in\; which}\frac{L}{D}=\mathrm{<figure-callout\; id="0"\; label="f\; S\; S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">f\; </figure-callout>}\left(\frac{S}{S_{}}\right)\left(\frac{{}_0}{}\right)$$

The mixing intensity allows the comparison of static mixers with a uniform diameter D.

The comparison of the static mixer geometries is carried out at a relative standard deviation S / S ₀ of 0.05, which corresponds to a practically homogeneous mixture in the photometric analysis FIP.

I

Wendelmischer

II

CSE-X-Mischer (4-Steg-Mischer), z.B. gemäss CH 693 560 A5

III

X-Mischer (8-Steg-Mischer), z.B. gemäss CH 642 564 A5

IV

X-Mischer (6-Steg-Mischer, gekreuzte Stege seitlich beabstandet), gemäss WO 2009/000642 A1

V

X-Mischer (4-Steg-Mischer, gekreuzte Stege seitlich beabstandet), gemäss vorliegender Erfindung

Tabelle 1: Mischintensität unterschiedlicher Mischertypen Mischertyp Anzahl Steglagen L/D z Winkel a S/S₀ M % I 1 25 6.5 - 0.05 5200 100 II 4 11 23 45° 0.05 8096 166 III 8 8 37 45° 0.05 9472 182 IV 6 10 18 45° 0.05 5760 111 V 4 10 15 45° 0.05 4800 92 Table 1 compares the mixing intensities of a mixer according to the invention and four mixers according to the prior art. The mixing quality of the following mixer types were compared:

I

spiral mixer

II

CSE-X mixer (4-bar mixer), eg according to CH 693 560 A5

III

X mixer (8-bar mixer), eg according to CH 642 564 A5

IV

X-mixer (6-bar mixer, crossed bars laterally spaced), according to WO 2009/000642 A1

V

X-mixer (4-bar mixer, crossed bars laterally spaced), according to the present invention

Table 1: Mixing intensity of different mixer types mixer type Number of webs L / D z Angle a S / S ₀ M % I 1 25 6.5 - 12:05 5200 100 II 4 11 23 45 ° 12:05 8096 166 III 8th 8th 37 45 ° 12:05 9472 182 IV 6 10 18 45 ° 12:05 5760 111 V 4 10 15 45 ° 12:05 4800 92

The L / D ratio with a relative standard deviation S / S ₀ of 0.05 results for the individual mixer types from the in Fig. 5 illustrated diagram.

The mixing intensity M used as Mischgütemass referred to in the present comparative experiments on the basis of 100% set intensity of the previously applicable as a mixer with the smallest mixing intensity spiral mixer, the disadvantage, however, a high L / D ratio of 25 and consequently a large Length required. This applies to two media to be mixed for a viscosity ratio of 1: 1.

The test results in Table 1 clearly show the positive influence of free spaces between laterally adjacent webs in the projection plane perpendicular to the mixer longitudinal axis on the mixing quality at mixer type IV and the mixer type V, the arrangement of two additional spaces between the wall near webs and the inner wall of the flow channel in the case of mixer type V according to the invention, a further striking reduction of the mixing intensity results, which is even smaller than the mixing intensity of the spiral mixer. This seems to contradict the experience that wall-to-wall spaces lead to a marginality. By tailoring the webs, however, a Randgängigkeit can be prevented.

Strength calculations have also shown that a mixing element by the sidecut of the webs against a mixer element with non-waisted webs endures a higher pressure difference. By waisting the mixing element is more flexible and the loads are better distributed over the bars.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

eine Seitenansicht eines Teils eines Strömungskanals mit zwei aneinander grenzenden Mischelementen;

Fig . 2

die Sicht auf ein Mischelement im Strömungskanal von Fig. 1 in Blickrichtung der Längsachse des Strömungskanals;

Fig. 3

die Draufsicht auf eine Stegplatte eines Mischelementes mit vier Stegteilen vor dem Biegen;

Fig. 4

die Draufsicht auf vier mit zwei Stegplatten von Fig. 4 nach dem Biegen zu einem Mischelement zu verbindenden Stegen;

Fig. 5

ein Diagramm zur Bestimmung des L/D-Verhältnisses unterschiedlicher Mischer bei gleicher relativer Standardabweichung S/S₀.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing, which is merely illustrative and not restrictive interpreted. The drawing shows schematically in

Fig. 1

a side view of a portion of a flow channel with two adjacent mixing elements;

Fig. 2

the view of a mixing element in the flow channel of Fig. 1 in the direction of the longitudinal axis of the flow channel;

Fig. 3

the top view of a web plate of a mixing element with four web parts before bending;

Fig. 4

the top view of four with two multi-wall sheets of Fig. 4 after bending to a mixing element to be connected webs;

Fig. 5

a diagram for determining the L / D ratio of different mixers with the same relative standard deviation S / S ₀ .

DESCRIPTION OF PREFERRED EMBODIMENTS

An in Fig. 1 shown, tubular flow channel 10 having a longitudinal axis x and an inner diameter D has two adjoining, a length L having identical mixing elements 12 with a substantially the inner diameter D of the flow channel 10 corresponding Umhüllungsdurchmesser. The two mixing elements 12 are with respect to the longitudinal axis x of the flow channel 10 by a Angle of 90 ° rotated against each other. The mixing element 12 consists of a plurality of intersecting webs 14A, 14B. The webs 14A, 14B are arranged in mutually parallel planes separated from each other by an equal distance and forming two intersecting planes A, B. The two level shares A, B close with the longitudinal axis x of the flow channel an angle α of 45 ° and with each other an angle of 90 °. The mixing element 12 shown by way of example in the drawing has four web layers, each with two webs 14A, 14B which intersect alternately, and thus corresponds to a 4-web mixer.

From the in Fig. 2 shown projection on a plane perpendicular to the longitudinal axis x of the flow channel 10 projection plane can be seen that the webs 14A, 14B are formed symmetrically waisted between intersections 16 and all have in the middle between adjacent intersections 16 the same smallest width b which is 50% of the width b 'at the intersections 16. All the webs 14A, 14B are waisted in the same way and have the same dimensions. In the present case corresponds to the greatest distance between a adjacent bars 14A, 14B of the smallest web width b.

All webs 14A, 14B extend within the mixing element 12 via their respective maximum length which is limited by the end faces of the mixing element 12 and by the inner wall of the flow channel 10, the contour of the webs 14A, 14B close to the wall being the circular cross-section of the wall Flow channel 10 is only partially adapted so that in the near-wall webs 14A, 14B - as in the other webs - only front end portions 22 adjoin the inner wall of the flow channel 10 with little play. The adjoining the inner wall of the flow channel 10 webs 14A, 14B are provided on the directed against the inner wall side with a recess 24 which extends between the end-side end portions or butt edges 22 with the inner wall of the flow channel 10 and corresponding to the waist of the webs largest Wall distance c have, which in the present case is 50% of the greatest distance between a adjacent bars 14A, 14B.

Like from the 3 and 4 recognizable, the webs 14A, 14B have on each provided Junction 16 a notch 18 or the notch depth of the notch 18 corresponding, a projection 20 generating cutback on.

The assembly of the mixing element 12 is carried out in a simple manner of two in Fig. 3 shown web plates 26 with four arranged alternately, the four in Fig. 4 shown webs 14A, 14B corresponding half webs 14A ', 14B' and the four in Fig. 4 illustrated webs 14A, 14B. Here, two web plates 26 are bent about an axis s at an angle of 90 ° and in the in Fig. 1 shown connected by ends 28 of the two middle web halves 14A ', 14B' by welding together. In the Fig. 4 shown four webs 14A, 14B are placed over the notches 18 and projections 20 at the intersections 16 on the curved and welded together web plates 24 and partially welded at the intersection points 16.

LIST OF REFERENCE NUMBERS

10

flow channel

12

mixing element

14A, 14B

Stege

16

Intersection 14A-14B

18

Notch at 14A, 14B

20

Projection at 14A, 14B

22

end-side end regions

24

recesses

26

wall sheets

28

Ends of 14A, 14B

A

Plains of 14A

B

Plains of 14B

D

Diameter of 10

L

Length of 12

x

Longitudinal axis of 10

a

largest gap 14A-14B

b / b '

smallest / largest bridge width of 14A, 14B

c

largest wall distance of 14A, 14B

Claims (11)

1. Static mixing device, having a tubular flow duct (10) which has a longitudinal axis (x) and an inner diameter (D), having a mixing element (12) which is arranged in the flow duct (10) and which has a length (L) and a diameter corresponding to the inner diameter (D) of the flow duct (10), with each mixing element (12) having a multiplicity of webs (14A, 14B) which are arranged in a crossed fashion and which enclose an angle (α) of greater than 0° with the longitudinal axis (x) of the flow duct (10), with the webs (14A, 14B) being arranged in two intersecting plane groups (A, B) which have a multiplicity of planes arranged parallel to one another and separated from one another by an equal spacing, and with mutually adjacent webs (14A, 14B) having an intermediate spacing in a projection of the two plane groups (A, B) onto a projection plane situated perpendicular to the longitudinal axis (x) of the flow duct (10),
   characterized in that
   the webs (14A, 14B) are of waisted design between adjacent crossing points (16), and in the middle between adjacent crossing points (16) the webs (14A, 14B) have their smallest width (b) and mutually adjacent webs (14A, 14B) have their greatest intermediate spacing (a), and those webs (14A, 14B) which are adjacent to the inner wall of the flow duct (10) have, between face-side abutting edges (22), a recess which corresponds to the waisting of the webs (14A, 14B) and which has the smallest width (b) so as to form a greatest wall spacing (c) in the middle between the face-side abutting edges (22), with the sum, measured over the diameter of the mixing element (12), of the smallest widths (b) of the webs (14A, 14B) amounting to at least 35% of the diameter of the mixing element (12).
2. Static mixing device according to Claim 1, characterized in that all the webs (14A, 14B) enclose an angle (α) of 45° with the longitudinal axis (x) of the flow duct (10).
3. Static mixing device according to Claim 1 or 2, characterized in that all the webs (14A, 14B) have the same smallest width (b).
4. Static mixing device according to one of Claims 1 to 3, characterized in that all the mutually adjacent webs (14A, 14B) have the same greatest intermediate spacing (a).
5. Static mixing device according to one of Claims 1 to 4, characterized in that the smallest width (b) of the webs (14A, 14B) amounts to 50% of their width (b') at the crossing points (16) of the webs (14A, 14B).
6. Static mixing device according to one of Claims 1 to 4, characterized in that the smallest width (b) of the webs (14A, 14B) is equal to the greatest intermediate spacing (a) of adjacent webs (14A, 14B).
7. Static mixing device according to one of Claims 1 to 6, characterized in that the greatest wall spacing (c) amounts to 50% of the smallest width (b) of the webs (14A, 14B) and 50% of the greatest intermediate spacing (a) of adjacent webs (14A, 14B).
8. Static mixing device according to one of Claims 1 to 7, characterized in that the mixing element (12) has four web tiers.
9. Static mixing device according to one of Claims 1 to 8, characterized in that successive mixing elements (12) in relation to the longitudinal axis (x) of the flow duct (10) are arranged so as to be rotated relative to one another by 90°.
10. Static mixing device according to one of Claims 1 to 9, characterized in that successive mixing elements (12) are spaced apart from one another.
11. Use of a static mixing device according to one of the preceding claims for mixing media, with at least one of said media being a laminarly flowing medium, in particular some highly viscous fluid.

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