Refrigeration – Low pressure cold trap process and apparatus
Reexamination Certificate
2000-01-03
2001-09-11
Doerrler, William (Department: 3744)
Refrigeration
Low pressure cold trap process and apparatus
Reexamination Certificate
active
06286321
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to recovery of solvents from the effluent which evolves in a vacuum drying operation, and refers more particularly to a cold trap unit wherein condensing of the solvents is effected.
In the drying of, e.g., solvent-containing biological specimens, the drying of specimens commonly is done in a chamber maintained under a condition of vacuum. During drying, an effluent in which vaporized solvents are contained is given off from the operation. It is understood that the solvents should be recovered from the effluent for several reasons.
One is the need to reduce as much as possible carryover of solvent from the chamber to the vacuum pump used to maintain the chamber under vacuum as the solvents have corrosive properties that can cause pump damage. Another reason is to minimize entry of solvents to normal ambient atmosphere since solvents presence in the atmosphere can be harmful to humans.
The common practice for solvents recovery utilized two separate cold traps. Effluent from the chamber is directed into a first of these cold traps after the effluent leaves the drying chamber but before the location of the inlet to the vacuum pump. Solvents in the effluent condense is this first cold trap but solvent condensation therein may not be total so that the effluent outflowing the first cold trap to the inlet of the vacuum pump contains solvents carryover.
This solvents carryover passes through the vacuum pump and leaves is as gas exhaust from the pump outlet. The gas exhaust is then directed through a second cold trap to condense out the carryover solvents.
The foregoing described recovery practice has some disadvantages. Notable is the need for space for locating two separate cold traps. Space sometimes is at a premium in a laboratory where many of such practiced drying operations take place so that finding locations for two cold traps proximal the drying chamber and convenient to the scientist or technician can be a problem.
Since cold traps operate at sub-zero temperatures, it is necessary to provide a separate refrigeration source for each of the two cold traps. Additionally, use of separate cold traps does not allow convenience of immediate presence at a single location of all collected condensate thereby to facilitate disposal of same.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a condenser cold trap unit which overcomes the drawbacks of the prior art.
It is a further object of the invention to provide a condenser cold trap unit for condensing separate fractions of solvents evolved from a specimen drying operation in a vacuum chamber which uses a single refrigeration source for maintaining solvents condensing temperature levels in each of two separate condensing vessel spaces.
It is a still further object of the invention to provide a condenser cold trap unit which is of less space occupying character than the separate cold traps used for the same purpose.
Another object is to provide a condenser cold trap that is more economical to make and use than the two separate cold traps employed in the prior art for the same solvents recovery end purpose.
Briefly stated, there is provided a condenser cold trap unit for recovering as separate primary and secondary condensate fractions, solvents contained in an effluent drawn from products being dried in a vacuum chamber. The unit includes inner and outer shell vessels. The inner shell vessel is disposed coaxially with the outer shell vessel inside said outer shell vessel. A space is present in the outer shell vessel under the bottom of the inner shell vessel and in a course surrounding the exterior of the inner shell vessel. A cover closes off the open tops of the two shell vessels and the interior space of the outer shell vessel is sealed from communication with outside atmosphere. The interior space of the inner shell vessel also is sealed from any communication with the interior space of the outer shell vessel. A common refrigeration coil encircles the exterior of the inner shell vessel and extends down therefrom to provide solvents condensing temperature levels cooling in both shell vessels. Fittings on the cover allow for connection of the outer vessel condensing chamber with outlet from the drying chamber and for passing effluent subjected to primary solvent fraction condensing in the outer vessel chamber to the inlet of the vacuum pump that evacuates the chamber. Cover fittings allow return of exhaust from the vacuum pump to be directed into the inner vessel for condensing solvent secondary fraction and for venting solvent free gas to the outside atmosphere. Drain fittings at the bottom of each vessel allow draining collected recovered solvent to disposal.
In accordance with these and other objects of the invention, there is provided a condenser cold trap unit for recovering as primary and secondary condensate fractions solvents contained in an effluent drawn from products being dried in a chamber maintained under a condition of vacuum by a vacuum pump, which comprises an outer containment housing and an inner containment housing within the outer containment housing. The outer containment housing has an interior space at least a part of which provides a primary condensate collection well. The inner containment housing has an interior space providing a secondary condensate collection well. The interior space of the outer containment housing is sealed against any inflow thereto of ambient atmospheric air. It also is sealed against any inflow/outflow communication between the outer containment housing interior space and the inner containment housing interior space. Means is provided for introducing effluent flow outletting the chamber into the outer containment housing interior space for condensing solvent from the effluent therein as a primary condensate fraction collecting in the primary condensate collection well. A means for communicating the interior space of the outer containment housing interior space with an inlet of the vacuum pump is provided so that effluent in the outer containment housing interior space containing any uncondensed solvent can pass to the vacuum pump. Means for introducing exhaust effluent outletting the vacuum pump into the interior space of the inner containment housing for condensing solvent therein as a secondary condensate fraction collecting in the secondary condensate well is provided, as is means for venting the interior space of the inner containment housing to pass solvents free effluent gas to ambient atmosphere. Means is provided for introducing a refrigerating agent into the interior space of the outer containment housing in a closed flow course therein to maintain the inner containment housing interior space at a solvents condensing temperature condition. The refrigerant flow course includes a winding course part passing proximal the inner containment housing thereby to cool said inner containment housing sufficiently to maintain a solvents condensing temperature in the interior space of said inner containment housing.
According to a feature of the invention, there is further provided a condenser cold trap unit for recovering as primary and secondary condensate fractions solvents contained in an effluent drawn from products being dried in a chamber maintained under a condition of vacuum by a vacuum pump which comprises outer and inner elongated containment vessels, each containment vessel having a top opening and a bottom head. The inner containment vessel is disposed in the outer containment vessel codirectionally therewith and such that the top openings of the respective vessels are planar aligned. An outer surface of the inner containment vessel is spaced from an interior surface of the outer containment vessel, and the bottom head of the inner containment vessel is spaced from the bottom head of the outer containment vessel to define a primary condensate collection well. An interior space of the inner containment vessel provides a secondary condensate collection well. A cover is set o
Doerrler William
Drake Malik N.
Morrison Law Firm
Thermo Savant Inc.
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