Drying and gas or vapor contact with solids – Apparatus – For diverse operations on treated material
Patent
1986-12-16
1988-09-06
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
For diverse operations on treated material
100904, F26B 1900
Patent
active
047682922
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of drying sewage sludge and an apparatus for carrying out the method.
A known method for drying sewage sludge uses a drum drier into which the sewage sludge is introduced in liquid form. Besides the sludge, hot air is also introduced at a temperature of between 600.degree. C. and 800.degree. C. into the drum drier which rotates about its axis at a low speed of the order of magnitude of one revolution per minute. The hot air causes the liquid component of the sludge to evaporate. The evaporated liquid component is removed from the drum drier so that only the solids component of the sludge, with a given level of residual moisture content, remains behind in the drum drier.
The residual moisture content of the sludge after the drying operation is of the order of magnitude between the 10 and 20% by weight or higher, depending on the temperature of the hot air introduced into the drum drier and the rotation time of the drum drier. If the dried sludge is used for example in agriculture as a fertilizer, it is advantageous for the residual moisture content of the dried sludge to be of the order of magnitude of around 10% by weight. Such a dry sludge can be spread using the conventional fertilizer spreading equipment. If the sludge is to be deposited on a dump, it is advantageous for the residual moisture content thereof to be between 10 and 20% by weight. When composting sewage sludges, higher residual moisture contents, of the order of magnitude of between 50 and 65% by weight, are desired.
A drum drier requires a high level of energy, by virtue of its using hot air. Another disadvantage of such a drum drier is that the feed amount of hot air becomes progressively smaller with an increasing volume of the sewage sludge introduced into the drier so that it is necessary for the amount of sludge introduced to be correctly set.
The object of the present invention is to provide a method of drying sewage sludge and an apparatus for carrying out that method which requires a low level of energy and with which the residual moisture content of the dried sewage sludge can be easily adjusted.
According to the invention, that object is attained in that the liquid sewage sludge is converted into a pasty consistency by predrying, that the pasty sludge is then put into the form of particles with a relatively large surface area, and that the particles are exposed to a stream of drying gas.
By virture of the fact that the sludge which is converted into a pasty consistency is put into the form of particles with a relatively large surface area, the stream of drying gas can come into contact with the particles over a large area, thus providing a good particle drying action in an advantageous manner with a comparatively low-temperature stream of drying gas. The particles which have a relatively large surface area have a residual moisture content of .gtoreq.5% by weight after the drying operation.
The method according to the invention makes it easily possible for the residual moisture content of the sludge which is in the form of particles to be adjusted as desired, while the amount of energy required in the method according to the invention is small in comparison with the known methods of drying sewage sludge.
It has been found advantageous for the predried pasty sludge to be formed into particles resembling small sausages, the length thereof being larger than the diameter thereof by a multiple. Sausage-like particles of that kind are of a diameter of the order of magnitude of about 5 mm and a length of the order of magnitude of 40 mm. The method according to the invention makes it possible to provide for any desired residual moisture content in the dried sewage sludge. The lower the residual moisture content of the dried sludge, the lower are the costs of transporting the dried sewage sludge for example to a dump, to an agricultural site, to a composting installation or the like, because in that case there is only a small amount of liquid ballast that also has to be transported therewith.
The apparatus
REFERENCES:
patent: 3156198 (1964-11-01), Koch
patent: 3447487 (1969-06-01), Landers et al.
patent: 3707774 (1973-01-01), Eise et al.
patent: 4082532 (1978-04-01), Imhof
patent: 4657682 (1987-04-01), Uyama et al.
German Journal "Ausbereitungstechnik", Sep. 1979, pp. 490-493.
"Lehr-Und Handbuch der Abwassertechnik", Band III 2. Auflage, 1978, Verlag Wilhelm Ernst & Sohn, Berlin, pp. 302-306.
Schwartz Larry I.
Sevar Entsorgungsanlagen GmbH
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