Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2000-12-20
2001-09-18
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S474000, C034S557000, C034S080000, C034S212000, C034S165000, C034S169000
Reexamination Certificate
active
06289606
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to moisture control in a material handling system, and more particularly to an apparatus and method used to control the moisture content of solid particulate material, such as plastic pellets used for making thermoplastic molded articles and extrusions.
2. Brief Description of the Prior Art
A typical system for controlling the moisture content in a particulate bed, for example, supplies moisture-controlled air to the particulate bed and uses a dessicant to dehumidify air returning from the particulate bed.
This system causes very low dew point air to be supplied to the particulate bed. When the material in the particulate bed comprises resins such as certain homopolymer and copolymer polyamides and some polyesters (e.g., nylon 6 and 6.6), the resins may be over-dried undesirably. Some moisture content is required to maintain desired impact resistance and flexibility in finished products produced from the resins.
A prior approach to the over-drying problem proposed to sense the moisture content of air being supplied to a particulate bed and to inject moisture-containing compressed air into the particulate bed as necessary. But this approach has certain disadvantages.
Therefore, a need has continued to exist for a method and apparatus for accurately maintaining a desired level of moisture in a particulate bed by removing unwanted, excessive moisture from the particulate bed without lowering the moisture content to an undesirable level.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an apparatus and method for controlling the moisture content of a material, such as plastic pellets in a particulate bed, without lowering the moisture content to an undesirable level.
Further objects of the invention will be apparent from the description of the invention which follows.
In accordance with one of the broader aspects of the invention, an apparatus for controlling the moisture content of a material in a material handling system comprises a supply gas flow path to supply moisture-controlled gas to the material handling system; a return gas flow path to extract gas from the material handling system; a dehumidifying system having a first gas flow path including a dryer and a second gas flow path devoid of a dryer; and a selector to alternatively connect one of the first gas flow path, the second gas flow path, and both of the first and second gas flow paths between the supply and return gas flow paths to thereby provide a closed-loop circuit of moisture-controlled gas to control the moisture content of the material.
In accordance with another of the broader aspects of the invention, a method for controlling the moisture content of material in a material handling system uses a dehumidifying system having a first gas flow path including a dryer and a second gas flow path devoid of a dryer. The method comprises providing a supply gas flow path to supply moisture-controlled gas to the material handling system; providing a return gas flow path to extract gas from the material handling system; and alternatively connecting one of the first gas flow path, the second gas flow path, and both of the first and second gas flow paths between the supply and return gas flow paths to thereby provide a closed-loop circuit of moisture-controlled gas to control the moisture content of the material.
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Frank Paul M.
Gillette W. John
Miles & Stockbridge P.C.
Novatec, Inc.
Wilson Pamela
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