Drying and gas or vapor contact with solids – Process – With fluid current conveying or suspension of treated material
Patent
1994-11-21
1997-01-28
Sollecito, John M.
Drying and gas or vapor contact with solids
Process
With fluid current conveying or suspension of treated material
34191, 34583, 159 42, 159 408, 159 405, F26B 308
Patent
active
055968171
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for minimizing deposition of products on the inner surfaces of a chamber in which a liquid feed is atomized and subjected to the influence of a processing gas to form a granular or particulate product, the chamber being composed of a mainly cylindrical upper section joining an underlying mainly conical or frusto-conical lower section, both with a mainly vertical axis, an inlet for said processing gas being provided at the upper end of the cylindrical chamber section and an outlet for the processing gas being provided at the lower or upper end of the chamber.
In spray drying and spray cooling technology it is a well-known problem that the sprayed material ejected from the atomizing device may have a sticky surface, and a tendency to deposit and accumulate on wall parts of the atomizing chamber, which may be more or less pronounced according to the powder properties such as thermoplasticity, fat content, static electrical or chrystallization properties or simply moisture content.
In the past, various measures have been suggested to counteract this tendency. Electrical or pneumatic hammers or vibrators may be mounted on the chamber wall to constantly dislodge products tending to remain on the wall. The standard textbook K. Masters "Spray Drying Handbook", John Wiley & Sons. Inc., New York, 5th Edition, 1991, pp. 152-154 suggests as additional measures the introduction of a secondary air flow through slots in the lower part of the circumferential wall of the upper cylindrical section of the chamber to sweep the chamber walls or, in more severe cases, the installation of a so-called air broom device, comprising a duct member extending vertically at a short distance from the chamber walls and having a number of air outlets facing the wall. In operation, the air broom device sweeps the chamber walls by a relatively slow rotary movement.
From EP published patent application No. 0 127 031, GB patent Nos. 474 086 and 1 514 824 and U.S. Pat. Nos. 1,634,640, 2,333,333 and 3,895,994, various applications of spraying technology are known, involving the introduction of a secondary air flow in the atomizing chamber to reduce the formation of deposits on the chamber walls.
EP published patent application No. 0 127 031 discloses the use of spray drying for smoke gas cleaning by contacting the hot gas stream containing gaseous impurities with an aqueous medium containing an absorbant for the impurities to produce a gas stream of reduced impurity content and dried powder products. In order to prevent the powder products thus formed from depositing on the chamber walls as a result of insufficient drying, a minor portion of the hot gas stream is withdrawn from the main flow entering the upper part of the atomizing chamber and guided through a bypass duct to a lower portion of the chamber where it is introduced in a direction counter to the direction of swirl of the major portion of the hot gas stream.
According to GB patent No. 474 086, a rotating fluid wall or curtain is maintained around the drying zone of an atomizing chamber by providing a plurality of vertical elongate nozzles to direct a suitable fluid within the chamber.
GB patent No. 1 514 824 discloses a spray drying apparatus in which a flushing gas is introduced in the lower conical part of an atomizing chamber through tangentially directed openings in the wall of the conical part to avoid the production of a cake on the wall of the cone.
U.S. Pat. No. 1,634,640 discloses a spray processing apparatus in which objectionable contact of the treated material with the walls of the processing chamber is prevented by providing a circumferential continuous sheet of gas moving along the inner walls of the drying chamber from a number of narrow circumferential openings or slots located above each other, each slot being defined by upper and lower ends of overlapping sheet metal rings.
In U.S. Pat. No. 2,333,333 a desiccating apparatus is disclosed in which additional drying gas is introduced tangentially into the conical lower portion o
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patent: 2757956 (1956-08-01), Salminen
patent: 3895994 (1975-07-01), Saguchi et al.
patent: 4809442 (1989-03-01), Iwaya et al.
patent: 5227017 (1993-07-01), Tanaka et al.
K. Masters, "Spray Drying Handbook", 1991, pp. 152, 154.
Gravini Steve
Niro Holding A/S
Sollecito John M.
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