Fluid sprinkling – spraying – and diffusing – Combining of separately supplied fluids – Fluid streams have angular junction
Reexamination Certificate
2000-06-27
2002-07-09
Morris, Lesley D. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Combining of separately supplied fluids
Fluid streams have angular junction
C239S498000, C239S518000
Reexamination Certificate
active
06415993
ABSTRACT:
The invention relates to an apparatus for preparing a rapidly solidifying mixture from a plurality of liquid components and subsequent atomization of the solidifying mixture.
In some areas of chemistry, the problem occurs that a mixture of low-viscosity liquids is to be used to form solids or gels as essential spherical particles.
The problems occurring, for example, in the preparation of hydrogels from water glass are discussed extensively in DE-A-2103243, for example. In general, the risk of formation of encrustation gives problems for many processes of achieving a stable mode of operation in production.
In DE-A-2103243, to prepare hydrogels, a process is used in which a rapidly solidifying mixture is first formed, in this case by gel formation, which is then, in the liquid state, directly atomized by a gaseous medium via a nozzle in a falling tower, the resulting droplets solidifying during the falling time. If, as in this case, solidification is performed chemically, it is necessary to mix the starting material streams rapidly as homogeneously as possible and to atomize them, so that the plant does not become blocked. However, the reaction in the droplets should have proceeded to approximately the same extent at a given height in the spraying tower, so that a product as uniform as possible is produced.
DE-A-2103243 discloses an apparatus for preparing hydrogels which features a mixing chamber which is preferably formed by a cylindrical tube, has, offset over its length, inlet orifices for the starting liquids, is closed at one end at its upstream end and whose downstream end ends in a nozzle outlet. In the apparatus, it is often important that back-mixing and edges are avoided in the mixing chamber. Owing to the fact that only one nozzle outlet is provided, either there can be only a very small throughput per mixing chamber or the nozzle, as in the example described in the abovementioned publication, must first produce a fan-shaped jet, for example, which then breaks down into droplets. The disadvantage of this process is either, in the first case, the low throughput of such a mixing and spraying apparatus or, in the second case, a relatively broad droplet radius distribution, which is disadvantageous for any subsequent processing steps. In addition, controlled change of the droplet size is difficult.
If, in particular, gel droplets are to be post-treated chemically, it is often of importance to obtain a narrow droplet radius distribution, since the time for diffusion into the droplets varies as the square of the droplet radius.
It is the object of the present invention, therefore, to provide an apparatus for preparing a rapidly solidifying mixture from a plurality of liquid components and subsequent atomization of the solidifying mixture which permits essentially spherical droplets having a narrow droplet radius distribution to be able to be produced on a large scale.
In addition, the apparatus is intended to produce droplets having material properties as identical as possible.
Furthermore, the apparatus is intended to be easily cleaned in the case that a blockage nevertheless occurs.
In addition, the apparatus is to readily permit change to other droplet radii.
The object is achieved by an apparatus for preparing a rapidly solidifying mixture from a plurality of liquid components and subsequent atomization of the solidifying mixture, wherein it comprises a liquid distributor and N droplet-forming nozzles which are connected to the liquid distributor, and wherein the liquid distributor is connected to the mixing chamber and distributes the mixed stream coming from the mixing chamber equally over the nozzles essentially without back-mixing or dead spaces in the flow, so that the residence times of the partial streams in the liquid distributor are essentially identical.
Mixing chamber, liquid distributor and nozzles are to be connected here in such a manner that as few edges as possible, which could give rise to encrustations, are formed. The fact that the liquid distributor has no significant back-mixing and no significant dead spaces ensures that no areas having solidified material and thus no blockages can form in the liquid distributor.
The residence times in the mixing chamber and in the liquid distributor must always correspond here to the time up to the solidification of the mixture. The dimensions of the apparatus are greatly dependent on the properties of the solidifying mixture. For each mixture component, at least one inlet orifice is provided, but a plurality of inlet orifices can also be used. The residence times in the apparatus after the addition of the last component necessary for a reaction must in any case be less than the solidification time. The size of the mixing chamber is then given by the preset: residence time in the apparatus and the required throughput. The number of nozzles is essentially a function of the throughput and the required droplet size which, at a given nozzle orifice, typically between 0.5 and 5 mm, is a function inter alia of the Reynolds number and surface a tension of the mixture at the moment of exit from the nozzle, and on the flow velocity. The nozzles must be arranged, that is their distance from one another and their direction must be selected, in such a manner that the resulting droplets after atomization do not collide and possibly form larger droplets.
In general, the apparatus is to be designed in such a manner that high flow velocities result, in order to prevent deposits on the apparatus walls.
Preferably, the nozzles produce the droplets by wavy sheet disintegration of an essentially laminar flow, since this can produce a very narrow droplet radius distribution. The conditions then to be imposed on the flow are to be taken into account during the design of the apparatus.
The advantage of the apparatus according to the invention is that, by using a liquid distributor which divides the solidifying mixture into N equal partial streams and passes them on to nozzles, and using droplet-forming nozzles, a high throughput and a narrow droplet radius distribution can be achieved simultaneously.
A further advantage is that, since the partial streams are taken off simultaneously from a relatively large mixed stream, the material properties of the droplets formed are virtually identical, so that the product formed is essentially more homogeneous than when it is produced by atomizing in a plurality of different mixing-spraying apparatuses.
A further advantage results from the fact that the residence times of the individual partial streams are identical, i.e. the residence time differences between the individual partial streams in the liquid distributor are substantially smaller than the time remaining up to a viscosity increase which is significant for the flow properties and thus the droplet formation, which leads to homogeneous product properties, i.e. identical properties of the solidifying mixtures at the individual nozzle orifices.
Preferably, the nozzles are identical; the liquid distributor is then preferably designed in such a manner that essentially identical flow properties (i.e. pressure, velocity, laminarity, etc.) prevail at the nozzles. Owing to the uniformity of flow properties at the identical nozzles, the droplet radius distributions of the individual nozzles are essentially identical, so that overall a particularly narrow droplet radius distribution can be achieved at high throughput.
The mixing chamber is preferably formed by a cylindrical tube having at least two inlet orifices displaced over its length, which tube is sealed at its upstream end. The distance between the inlet orifices in the direction of the tube axis is between 0 and 50 cm, preferably between 1 and 20 cm, particularly preferably between 2 and 5 cm.
This mixing chamber is very easy to manufacture and has virtually no back-mixing or dead spaces in the flow, which avoids areas of mixing in which the solidification is already further advanced; thus stable operation is ensured.
The mixing chamber, instead of a plurality of inlet orifices through whi
Forbert Rainald
Hartel Johannes
Schierholz Wilfried
Axiva GmbH
Connolly Bove & Lodge & Hutz LLP
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