Drying and gas or vapor contact with solids – Apparatus – Vacuum
Reexamination Certificate
1999-02-22
2001-11-06
Bennett, Henry (Department: 3744)
Drying and gas or vapor contact with solids
Apparatus
Vacuum
C034S289000
Reexamination Certificate
active
06311409
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a freeze drying method and apparatus for freeze drying a substance within a freeze drying chamber in which vapor produced by sublimation is condensed within a condensing chamber. More particularly, the present invention relates to such a freeze drying method and apparatus in which the condensing chamber is pressurized prior to the condensation of the moisture in order to help prevent the substance being freeze dried from contaminating the condensing chamber. Even more particularly the present invention relates to such a method and apparatus in which the substance is contained within a solution freeze dried in a bulk freeze drying process involving the freezing of the solution on an array of vertical plates located within the freezing chamber. Still even more particularly, the present invention relates to such a freeze drying method and apparatus that is applied to the decontamination of a solution containing radioactive materials.
Waste disposal problems involving reduction and disposal of radioactive or toxic wastes such as nuclear wastes, wastes containing heavy metals and etc. have long presented an environmental hazard. Such wastes are often processed by dissolving the waste in an acidic solution, for instance nitric acid, and then storing the resultant solution in containers that present a risk of leakage and in any event take up a great deal of storage space. Freeze drying techniques have been applied to such waste disposal problems in order to more properly contain such wastes in a safe and efficient manner. For instance, in U.K. Patent Application GB 2178588, a method and apparatus for treatment for radioactive liquid waste is disclosed in which the radioactive liquid waste is freeze dried to sublimate the solvent and thereby to produce the radioactive solute as a dried deposit.
In any freeze drying process, a substance is frozen within a freeze drying chamber. The substance is then subjected to a reduced pressure while being heated to cause frozen solids to sublimate into vapor. The vapor is condensed within a condensing chamber. In waste disposal applications of freeze drying, it is necessary that the condensing chamber be separated from the freeze drying chamber during the freeze drying process so that condensation chamber does not become contaminated. If such contamination were allowed to occur, radioactively contaminated water would then become a problem which would defeat the whole purpose of the freeze drying process. In order to overcome this problem, in the above referenced U.K. Patent Application, the condensation chamber is segregated from the freeze drying chamber by means of a filter. A filter can, however, limit the size of the freeze dryer because it will reduce the flow of vapor to the condensation chamber.
In the foregoing U.K Patent Application, the freeze drying element located within the freeze drying chamber is a set of pipes. A problem involved with such freeze drying elements is that pipes present a limited surface area and therefore, present another limitation on the size of the freeze drier. Furthermore, any freeze drying element, in addition to presenting a sufficient surface area, must be amenable to removal from the freeze drying chamber for replacement and cleaning purposes.
Although a motivating factor of the present invention is waste treatment, aspects of the present invention have broader applications involving the segregation of the freeze drying process from the environment and the bulk freeze drying of substances within solutions. As will be discussed, the present invention can be generally said to provide a freeze drying method and apparatus in which segregation of the condensation chamber from the freeze drying chamber does not primarily depend on filters. Additionally, freeze drying elements are provided that have sufficient surface area and flexibility for large scale freeze dryer setups.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a method of freeze drying a substance in which the substance is frozen in a freeze drying chamber so that a liquid component of the substance is frozen into a solid. The solid is sublimated into vapor and which is then condensed in cold condenser located within a condensation chamber in communication with the freeze drying chamber. Prior to condensing the vapor, the condensation chamber is pressurized with a gas. The pressure within the freeze drying chamber and the condensation chamber is allowed to equalize so that the gas flows from the condensation chamber to the freeze drying chamber, thereby to act to inhibit the solid from entering the condensation chamber. In this aspect of the present invention the substance could be one containing a liquid, for instance a pharmaceutical preparation to be dehydrated, or a liquid solution, which for example could be a radioactive salt dissolved in an aqueous nitric acid solution.
In another aspect, the present invention provides a bulk freeze drying method for separating a substance from a solution. The method comprises introducing the solution into a freeze drying chamber having at least one vertical plate. Part of the solution is frozen on the at least one vertical plate so that solid layers are formed on opposed surfaces of the at least one vertical plate. The remainder of the solution is removed from the freeze drying chamber and the solid layers are sublimated into a vapor so that this substance forms a deposit on the at least one plate. The vapor is condensed on a cold condenser and the deposit is removed from the at least one vertical plate. The deposit is extracted from the freeze drying chamber after having been removed from the at least one vertical plate.
In yet another aspect, the present invention provides a freeze dryer for freeze drying a substance. The freeze dryer comprises a freeze drying chamber having means for freezing the liquid component of the substance into a solid. A means is provided for heating the substance during sublimation of the solid into a vapor. A means is provided for evacuating the freeze drying chamber. A condensation chamber is provided having a cold condenser. The condensation chamber is in communication with the freeze drying chamber for condensing the vapor. An isolation valve is interposed between the cold condenser and the freeze drying chamber for isolating the cold condenser from the freeze drying chamber. A means is provided for pressurizing the condensation chamber with a gas when the condensation chamber is isolated from the freeze drying chamber so that when the isolation valve is set in a open position, pressure within the freeze drying and condensation chambers equalizes to act to inhibit the solid from entering the condensation chamber. In this aspect of the present invention, the substance could be the type of substance of the first mentioned aspect of the present invention.
In yet still another aspect of the present invention, a freeze dryer is provided for separating a substance contained within a solution. The freeze dryer comprises a freeze drying chamber for receiving the solution and at least one vertical plate located within the freeze drying chamber. The at least one vertical plate has passages for circulation of a refrigerant to freeze the solution into opposed solid layers located on the at least one vertical plate and for circulation of a diathermic fluid for heating the plate during sublimation of the solid into a vapor. The sublimation forms a deposit of the substance on the at least one vertical plate. The freeze drying chamber has an inlet for receiving the solution and an outlet for discharging from the freeze drying chamber the remainder of the solution not frozen on the at least one vertical plate. A means is provided for evacuating the freeze drying chamber during the sublimation and a condensation chamber is provided having a cold condenser. The condensation chamber is in communication with the freeze drying chamber for condensing the vapor.
As discussed above, the pressurization of the condensatio
Coppa Nicholas V.
Renzi Ernesto
Stewart Paul
Bennett Henry
Pace Salvatore P.
The BOC Group Inc.
Wilson Pamela
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