Drying of water-containing useful materials or mixtures thereof

Details Drying of water-containing useful materials or mixtures thereof Drying of water-containing useful materials or mixtures thereof

1996-02-23

1997-04-01

Bennett, Henry A.

Drying and gas or vapor contact with solids

Apparatus

With means to treat gas or vapor

159 481, 159 163, 203 49, 203 90, 34 77, 34408, F26B 2106

Patent

active

056154925

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a process for drying water-containing useful materials or mixtures thereof, more particularly with high sensitivity to heat and preferably with a suitability as--or for use in--wetting agents, detergents and/or cleaning products, in a vertical tower using superheated steam circulating in countercurrent to the descending material to be dried as the drying gas.
2. Discussion of Related Art
The drying of aqueous preparations of useful materials and mixtures of useful materials suitable as wetting agents, detergents and/or cleaning products with superheated steam as the drying gas is known from Applicants' International patent application WO 92/5849. The advantages of this method of drying over conventional spray drying using hot air as the drying gas lie on the one hand in the absence of oxygen so that the problems involved in the drying of purely organic or substantially organic useful materials, for example corresponding surfactants based on natural materials, for example oxidative damage or the risk of fire, are avoided. Circulation of the drying gas provides for operation in the virtual absence of waste gases. Other advantages attributable inter alia to the fundamental differences in the drying gas can be found in the cited document.
Circulation of the drying gas to enable the drying process to be carried out in the absence of waste gases means that the installation has to be closed. The presence of extraneous air in conventional spray drying with hot air or hot combustion gases as the drying gas would not be possible here or at least would be inappropriate. Accordingly, the closed construction of the drying installation operated with superheated steam leads to a virtually flow-free space below the lowermost superheated steam inlets, inside which the temperature substantially corresponds to the entry temperature of the superheated steam. The walls in the lower part of the drying tower also have this temperature unless special precautions are taken.
Numerous products intended for drying, more particularly organic products, have tacky properties after drying or at least pass through an adhesive phase during the drying process. Accordingly, the completely or partly dried particles cake on the one hand together and, on the other hand, on the inner wall of the tower in the substantially flow-free space situated beneath the superheated steam inlets. This effect is intensified by the relatively long residence time of the particles in that space. Thermal damage to the particles caking on the hot walls of the tower is unavoidable.
In conventional spray drying using hot air as the drying gas, the problem is solved by rapid discharge of the product through a permanently open channel at the lower end of the drying tower. This solution is not applicable to drying with a circulated drying gas which is carried out in the substantial absence of waste gases.
The problems caused by the caking of thermoplastic materials and sugar-containing foods on the tower walls of spray dryers is known from the prior art (K. Kroll, Trocknungstechnik, Vol. 2, Trockner und Trocknungsverfahren (Dryers and Drying Processes), 2nd Edition 1978, Springer Verlag, page 294). Materials of this type remain soft and tacky towards the end of drying even at moderately high temperatures. To solve this problem, the walls of the dryers used for such materials are provided with air-permeated casings or, alternatively, cleaning jets are allowed to rotate inside the drying tower and blow away the powder with cold air. It is also known that a cool and moisture-free airstream can be introduced into the dryer in such a way that it sweeps along the inside of the walls in the form of a downwardly directed curtain of cold air. The introduction of cold air or a curtain of cold air takes place at the lower end of the cylindrical drying tower, especially for the normally conical discharge funnel. The cold air is introduced into the interior of a double jacket through a ring channel arr

REFERENCES:
patent: 2911036 (1959-11-01), Lazar et al.
patent: 3620776 (1971-11-01), Mishkin et al.
patent: 3633283 (1972-01-01), Mishkin et al.
patent: 3895994 (1975-07-01), Saguchi et al.

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