Drying and gas or vapor contact with solids – Process – With fluid current conveying or suspension of treated material
Reexamination Certificate
1998-06-09
2001-05-29
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
With fluid current conveying or suspension of treated material
C034S372000, C034S374000, C034S583000, C034S068000, C034S174000
Reexamination Certificate
active
06237247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a spray dryer which is particularly suitable for the production of detergents and/or cleaners and components thereof and which comprises a drying chamber, at least one spraying element for introducing the material to be spray-dried into the chamber and means for introducing a heated gas into the chamber in co-current or countercurrent to the descending spray-dried material.
2. Discussion of Related Art
Spray dryers of the type in question are known. They are used on an industrial scale for the production of powder-form detergents or cleaners and components thereof known as “tower powders”. In these spray dryers, a coherent liquid mass or slurry is divided up by nozzles into small droplets which are then dried by a hot air stream flowing in countercurrent to the descending droplets, the liquid suddenly evaporating.
Spray drying in the production of detergents/cleaners is characterized on the one hand by the relatively high temperature of the drying gas used which can exceed 300° C. On the other hand, the material to be dried generally contains a large percentage of organic ingredients, more particularly surfactants, which are not only temperature-sensitive, they also tend to carbonize and self-ignite at the high temperatures prevailing in the spray dryer if the product remains in the drying chamber for longer than a few seconds.
Accordingly, in the production of detergents/cleaners and components thereof, it is important that the material to be spray-dried pass through the spray dryer relatively quickly and, in particular, be rapidly discharged from the dryer.
Unfortunately, some of the material to be spray-dried is inevitably deposited onto the inner walls of the drying chamber where it gradually heats up, dries out completely and, after a certain time, becomes so hard that it is extremely difficult to remove.
These deposits are formed in particular in the production of detergents/cleaners because the only partly dried-on particles, which are rich in surfactants, have a very tacky surface. In addition, black product particles are formed by carbonization and contaminate the tower powder so that it no longer meets consumer quality requirements.
To solve the problems caused by hard deposits, carbonization and the risk of fire, operation of the spray dryer for the production of detergents/cleaners and components thereof is interrupted at regular intervals for the purpose of cleaning the inner walls of the chamber.
The problems mentioned above occur to a greater extent with modern detergent formulations which contain particularly large amounts of surfactants. To prevent deposits formed on the inner walls of the spray-drying chamber from burning, not only is operation of the dryer regularly interrupted, the temperatures of the hot gas are also lowered. As a result, the performance of the spray dryer diminishes.
The deposits are formed all over the inner wall of the drying chamber, but especially in the lower region thereof which, generally, tapers conically downwards. The inclination of the inner walls in this cone leads to increased deposits which, moreover, become particularly hot in this region because the hot drying gas enters the drying chamber in the vicinity of the tower cone.
Although the deposits could conceivably be removed by externally mounted knockers, the resulting deformation of the tower cone would result in damage to the surface and in unevenness in the inner wall which in turn would result in increased deposits. Other disadvantages include the noise generated, the uncontrolled cleaning and the difficulties involved in removing particularly hard deposits.
Accordingly, the problem addressed by the present invention was significantly to ease the problems caused by deposits, carbonization and the risk of fire in a spray dryer of the type mentioned at the beginning. In addition, the operational interruptions for cleaning the inner walls of the drying chamber would only be necessary at very much longer time intervals.
DESCRIPTION OF THE INVENTION
According to the invention, the solution to this problem in a spray dryer of the type mentioned at the beginning is characterized in that at least part of the inner wall of the drying chamber is lined with an air-permeable textile at a distance from the chamber wall and at least one outlet for compressed gas, more particularly compressed air, is provided between the chamber wall and the textile. In a preferred embodiment, the lower part of the inner wall and/or the inner wall in the vicinity of the spraying elements and/or the inner wall below this region is/are lined with the textile.
The particles adhering to the inner walls of the spray dryer according to the invention are deposited onto the air-permeable textile which can be cleaned simply and effectively from the back by exposure to a pulse of the compressed gas. When cleaned in this way, the textile expands and adhering particles fly off and are blown into the interior of the drying chamber. There is no longer any need to interrupt the operation of the dryer to clean the walls.
Another advantage lies in the increased performance of the spray dryer according to the invention because the product contains fewer agglomerates which, hitherto, would have been removed as oversize particles by sieving. The absence of deposits according to the invention reduces the risk of fire and allows higher temperatures for the hot gas so that the performance of the spray dryer can be increased.
The gas used for cleaning may be compressed air. However, inert gases, for example nitrogen, combustion gases or the gas used for drying, for example hot air or superheated steam, may also be used.
Since the problems mentioned at the beginning occur to a greater extent in a downwardly tapering drying chamber, the cone is lined with the air-permeable textile in a particularly preferred embodiment of the invention.
The air-permeable textile lining according to the invention is advantageous for all regions of the inner wall of the drying chamber where the product is preferentially deposited. Thus, in another advantageous embodiment of the spray dryer according to the invention of which the spraying elements are arranged in at least two horizontal planes, the inner wall of the drying chamber is lined with the textile in the region between the planes and/or below the planes. In this region, the sprayed droplets still contain a relatively large amount of liquid, particularly water, and accordingly have a particularly pronounced tendency to adhere to the inner wall of the drying chamber.
Woven fabrics combining high heat resistance with high tensile strength are particularly suitable as the textile. The high tensile strength enables the textile to be cleaned with relatively high gas pressures. In one particular embodiment, the textile is a fabric of high-modulus fibers, more particularly polyamide and preferably aramide fibers. High-modulus fibers such as these are heat-resistant and non-inflammable. They possess very high strength and glass and decomposition temperatures of >400° C. and are therefore particularly suitable for use in spray dryers which are used for the production of detergents/cleaners and components thereof and, accordingly, operate with particularly hot drying gases. High-strength textiles of the type in question advantageously accommodate a relatively high pressure of the gas for cleaning the textile of up to 10 bar and, more particularly, from 3 to 8 bar.
The scope of the present invention encompasses various embodiments of the spray dryer which allow various modes of operation for the cleaning of the textile. Thus, the textile can be periodically freed from adhering deposits by a pulse of compressed gas. However, continuous pulsation of the textile with the compressed gas is particularly advantageous. Accordingly, the invention proposes a control unit for valves preceding the outlets by which the valves are intermittently opened and closed, the frequency and pulse duration in particular being variable.
In
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Murphy Glenn E.J.
Wilson Pamela
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