Drying and gas or vapor contact with solids – Process – By centrifugal force
Patent
1993-12-27
1995-06-27
Gromada, Denise L.
Drying and gas or vapor contact with solids
Process
By centrifugal force
34 58, 210609, 210771, F26B 508
Patent
active
054268664
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and to an apparatus for dewatering sludges, particularly from sewage treatment facilities, as defined in the preamble of independent claim 1 and 21. Methods and apparatus of this type are known to be in public use.
In prior art methods for dewatering sewage sludge, the sludge is dewatered mechanically by means of a solid bowl screw centrifuge, a chamber filter press or a traveling screen press to about 25 to 35 weight percent of dry substance content. In order to be able to dry the resulting wet and sticky solid matter that is baked together into lumps to, for example, 90 weight percent dry substance in a dryer, the solid matter lumps are pre-comminuted, according to DE 3,915,082.C1, are re-mixed with very large amounts of dry dust and granulated in order to overcome the so-called glue phase in the wet solid matter and to increase the dry substance content to about 60 weight percent. After coarse lumps have been screened out, the resulting solids are repeatedly intermediately stored and are fed in measured quantities into a contact dryer or convection dryer. In addition to the enormously increased amount of apparatus required, this manner of proceeding leads to the consequence that the drying system connected to the centrifuge outlet must process a quantity of material that is increased almost three to five times compared to the centrifuged quantity of wet solid matter, which results in a corresponding increase in the structural size of the drying system. Another drawback is that the increased amount of material requires the removal of all of the moisture at a very much lower moisture level and thus with a greatly reduced drying speed.
In German Patent 948,497, the still wet centrifuged solids that have been dewatered in a continuously operating screen centrifuge, for example a sliding screen centrifuge, a screw-type screen centrifuge or a solid bowl centrifuge, are dried further by employing a drying device that is operated with hot gas or hot steam and forms a structural unit with the centrifuge. In the case of the sliding centrifuge, the drying device is composed of a casing disposed between the discharge end of the centrifuge drum and the collecting chamber for the solids. At its end where it is connected to the centrifuge drum, the casing has an interior diameter that approximately corresponds to the exterior diameter of this drum and widens conically toward the end where it is connected with the collection chamber for the solids. Along its circumference, the casing is provided with a plurality of uniformly distributed, helically arranged openings that are parallel to the axis of the casing and through which hot air or hot steam is introduced by way of a distributor into the interior of the casing. The distributor is formed by an annular chamber between the conical casing and a cylindrical housing that surrounds the casing. The incoming hot air or hot steam conducts the solids expelled from the centrifuge chamber of the sliding centrifuge through the interior of the casing and thus dries them. The device according to German Patent 3,630,920 operates in a similar manner. It provides adjustable metal guide sheets within the drying device in addition to the air guidance. However, the prior art drying device is intended only for grainy, granulate-like solids which, after centrifuging, have only a slight residual moisture of about 10 to 15 weight percent. For wet solids from sludge centrifuges containing water in a proportion of 60 to 85 weight percent, the prior art drying device is neither intended nor suitable. Moreover, the diameter of the particles to be dewatered in the prior art drying device is predetermined and not a function of the apparatus parameters. In contrast thereto, the wet solids particles produced in sludge centrifuges depend in their size to a quite significant degree on the apparatus parameters, namely on the number of revolutions of the centrifuge, the exterior diameter of the discharge zone, the number and opening width of the discharge openings as
REFERENCES:
patent: 3319587 (1967-05-01), Albertson et al.
patent: 3580193 (1971-05-01), Logan
patent: 3724091 (1973-04-01), Rousselet
patent: 4330411 (1982-05-01), Florin et al.
Gromada Denise L.
Lucia Baumann-Schilp
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