Drying and gas or vapor contact with solids – Process – With fluid current conveying or suspension of treated material
Patent
1999-03-18
2000-11-21
Wilson, Pamela
Drying and gas or vapor contact with solids
Process
With fluid current conveying or suspension of treated material
34364, 34369, 34375, 34579, 34231, 34232, 110224, 432 99, F26B 308
Patent
active
061485403
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a particulate drying method and drying
apparatus, and more particularly to a particulate drying method and drying apparatus which are used to dry particulates.
BACKGROUND ART
Flash dryers and fluidized bed dryers have been the primary devices known in the past for drying particulates using heated gas.
Here, a flash dryer is a dryer having a structure in which an ascending air current is formed by heated gas in a cylindrical straight pipe, the particulates are fed into the ascending air current, and the particulates are dried while carried aloft by the ascending air current.
Advantages of such flash dryers are that they have a simple structure, and the particulates are dried at the same time that the air is transported, resulting in high treatment capacity.
On the other hand, the ascending air current is formed only in the straight pipe in such flash dryers, resulting in less dispersion of the particulates that are supplied as the material being treated, and when wet particulates or the like which have formed into lumps are treated, a disperser or beater or the like must be provided near the opening through which the treated material is supplied. A resulting problem is that particulates end up adhering to the mechanical dispersion mechanism, such as the attached disperser or beater.
Furthermore, since the supplied particulate travels along with the ascending air current formed in the straight pipe, lengthening the straight pipe is the only way to prolong the particulate residence time in the straight pipe and to improve the drying conditions (slowing the flow rate of the ascending air current limits the amount treated and the like), leading to an increase in the size of the equipment.
In addition, since the particulates travel along with the ascending air current in the straight pipe in such devices, often the same heated gas is in contact with the particulates as they travel. There is thus some concern that the heat exchange between the particulates and the heated gas as well as the evaporation of moisture from the particulates heated by this heat exchange reach a critical state soon after contact between the particulates and heated gas, with a dramatic decrease in the subsequent heat exchange and evaporation. A method that has been adopted to increase drying efficiency is to provide a curved part in the middle of the straight drying pipe, so as to abruptly alter the direction of flow in the curved part and thus produce instantaneous changes in the rate between the particulates and the accompanying heated gas, thereby exchanging the heated gas. However, in this case as well, the particulate residence time cannot be prolonged, and it is difficult to dry the particulate to below the specified moisture. A problem is thus that wet particulates adhere to the curved part provided in the middle of the drying pipe, in the same manner as when a disperser, beater, or the like is provided as described above.
Particulates adhering inside the device as described above hinder the operating stability of the apparatus. In addition, material adhering inside the device sometimes falls off as a result of frequent heat degeneration and thermal deterioration, becoming mixed in the form of impurities with the final product. Such contamination of the final product is a major issue.
The particulate drying action in the flash dryer depends solely on the quantity of heat of the heated gas, so attaching equipment to increase the amount of hot air, elevate the hot air temperature, and the like in order to enhance the extent of drying leads to the problems of greater size and higher running costs.
Fluidized bed dryers which are widely known as apparatuses for drying particulates using heated gas in a manner similar to that of flash dryers are apparatuses having a structure in which the container is divided into two upper and lower chambers by a perforated plate such as a wire netting, the upper chamber is filled with the particulates, and the heated gas is blown from the lower ch
REFERENCES:
patent: 2292897 (1942-08-01), Nielsen
patent: 3915657 (1975-10-01), Staffin et al.
patent: 4089119 (1978-05-01), Heinze
patent: 4106892 (1978-08-01), Haga et al.
patent: 5593715 (1997-01-01), Christensen
International Search Report mailed Apr. 1, 1997 in PCT/JP96/03751.
Kato Takeshi
Ohmura Yukimasa
Omachi Atsushi
Ono Kenji
Nara Machinery Co., Ltd.
Wilson Pamela
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