Agitating – With heating or cooling – Medium in stirrer or mixing chamber
Reexamination Certificate
1999-06-16
2001-04-17
Cooley, Charles E. (Department: 1723)
Agitating
With heating or cooling
Medium in stirrer or mixing chamber
C366S337000
Reexamination Certificate
active
06217208
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a static mixer apparatus for mixing viscous fluids which is constructed from an inner housing which has an inlet for material to be mixed and an outlet for material to be mixed and which comprises two or more layers of undulating or zigzag bars which are parallel to each other and which are disposed one above another rotated by an angle &agr;, preferably of 90°, to each other in an alternating manner and which are joined to each other at their upper or lower vertices. The bars are provided in particular with channels for the passage of a heat transfer fluid so that the mixer can also be employed as a heat exchanger.
Static mixers are often employed as built-in components for the mixing of liquids in pipelines. A pump pushes the liquids to be mixed through a pipe which is provided with built-in components such as these.
The two following apparatuses can be cited as examples of static mixers.
In what are termed Kenics mixers (see “Mischen beim Herstellen und Verarbeiten von Kunststoffen”, published by: VDI-Ges. Kunststofftechnik. VDI-Verlag Düsseldorf, 1986, pages 238-241) the flow of fluid is divided by a separator plate installed in the pipe. This plate is twisted about the pipe axis. A swirling flow occurs in each of the two partial flows of liquid, and results in the redistribution of the liquid over the cross-section thereof. In practice, there is a plurality of mixing elements such as this disposed in series in order to divide the liquid again and again and to achieve a good mixing effect. The stability under pressure of these mixers when employed for highly viscous fluids is comparatively low.
What are termed SMX mixers (see U.S. Pat. No. 4,062,524) consist of two mutually perpendicular grids of parallel sheet metal strips which are welded to each other at their points of intersection. On account of the many weld joints, the production cost of these mixers is relatively high.
The exchange of heat from or to highly viscous liquids during their passage through known heat exchangers typically occurs at a very low Reynolds number. If plain tubes are used for the exchange of heat, for example, the rate of exchange of heat is low at a Reynolds number which tends to zero, and on the heat exchanger side depends substantially only on the length of tube used. It is possible to achieve a significant improvement in the exchange of heat by combining a tubular heat exchanger with a static mixer device.
This combination is known in two embodiments. Firstly, static mixer elements can be inserted in the tubes of a tube bundle heat exchanger. The aforementioned Kenics mixer elements are used in particular here. Secondly, the tubes can be employed as elements of a static mixer. This is described in German Patent Specification DE 28 39 564 C2, for example.
The use of a tube bundle heat exchanger through which a product flows has to be rejected for many chemical processes, however. For example, if a polymerisation reaction has to be cooled, a higher degree of polymerisation is obtained in a tube through which slow flow occurs, due to the increased dwell time of the reactants. The liquid in the tube thereby possibly becomes more viscous than that in adjacent tubes. As a consequence, the velocity of flow of the material to be mixed is further reduced. For a given set of process parameters, the tube can therefore become blocked by polymer.
In processes such as these, a static mixer is preferred which is formed from heat exchanger tubes, such as that described in DE 28 39 564 C2. However, the production cost of these mixers is so high that this solution is frequently rejected as being uneconomic.
SUMMARY OF THE INVENTION
The object of the present invention is to identify a static mixer which exhibits a good mixing effect which is comparable with that of known mixers, which can optionally be cooled or heated, and which can be manufactured in a simple manner and therefore inexpensively.
This object is achieved according to the invention by a static mixer apparatus for mixing viscous fluids, which is constructed at least from an inner housing which has an inlet for material to be mixed and an outlet for material to be mixed and which comprises two or more layers of undulating or zigzag bars which are parallel to each other and which are disposed one above another rotated by an angle &agr;, preferably of 90°. to each other in an alternating manner and which are joined to each other at their upper or lower vertices. and which optionally comprises an outer shell.
In its highly symmetrical preferred embodiment, the bars of the static mixer are joined to each other by junction points so that four bar elements which span a tetrahedron originate from each junction point, except for the junction points which are situated at the edge of the static mixer. In this embodiment, the construction of the bar insert has a topology which resembles that of a diamond lattice. The term “bar insert” is to be understood as the totality of the layers of bars of the mixer which are joined to each other.
In one preferred embodiment of the static mixer apparatus, the bars of selected layers or of all the layers are provided with channels for the passage of a heat transfer fluid. The bars are of hollow construction, for example, and the hollow spaces then serve as channels for the heat transfer medium.
In one particularly preferred embodiment, the width of the bars in the direction of flow of the product is designed such that said heat transfer channels are each conducted along a straight line through the bars, from one side of the mixer to the opposite side.
The production of a mixer apparatus such as this is thereby simplified even further, since during the injection moulding of the mixer pattern lateral mould slides can be used in order to form the channels in the bars.
A variant of the static mixer apparatus which is particularly easy to manufacture is characterized in that the apparatus is subdivided into two or more separate segments which are stacked one above the other and in each of which two, three or more layers of bars are joined together. The segments can be produced individually by casting and any number and combination thereof can subsequently be joined to each other, optionally with individual segments even having different geometries.
In one preferred form of the invention, the bars of directly superimposed layers of bars overlap at their junction points, particularly by means of recesses which fit within one another at the vertices of the bars.
Another preferred variant of the mixer apparatus is characterised in that the parallel bars of a layer of bars are disposed laterally displaced in relation to the centre spacing of adjacent bars of the next layer of bars situated above them or below them in each case.
To achieve a further improvement of the mixing effect, particularly for highly viscous fluids, the layers of bars are set at an angle &bgr;, which is less than or greater than 90°, in relation to the main direction of flow of the material to be mixed from the inlet for material to be mixed to the outlet for material to be mixed.
The mixer is constructed in particular so that the grid planes which are formed by the junction points of the bars of a layer are placed so that none of them is at an angle of 90° to the main direction of flow through the mixer. The flow is thereby prevented from disintegrating into flow pockets (partial flows) which do not mix with each other.
The mixer can be produced in a simple manner by pre-moulding. This results in the desired low manufacturing cost, whereby the cost of the mixer can be kept low. For example, the bar insert-of the mixer can first of all be injection moulded from wax as a model. The wax model then serves as the lost pattern in a lost-wax casting process in which a ceramic hollow mould is produced from the wax model, for example. The bar insert, which is produced from metal which is cast in the hollow mould, can then be inserted and fixed in a housing a simple manner.
The aforementioned mixer variant consi
Bayer Aktiengesellschaft
Connolly Bove & Lodge & Hutz LLP
Cooley Charles E.
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