Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1999-02-26
2000-02-15
Capossela, Ronald
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
F25J 300
Patent
active
060239441
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatus for processing a sublimed material and particularly, though not exclusively, for desubliming and trapping sublimed uranium hexafluoride (UF.sub.6).
Currently, when UF.sub.6 is being manufactured or irradiated uranium fuel is being reprocessed, a common step in the processing cycle is to de-sublime UF.sub.6 gas from the vapour phase to the solid and then convert to the liquid by heating under increased pressure. The apparatus currently in use employs large heat exchanger vessels having many internal tubes and a cooling jacket through which ethylene glycol coolant, for example, is pumped and around which, by means of many baffles fixed to the tubes, UF.sub.6 is forced to take a circuitous route. The UF.sub.6 condenses on the outside of the tubes and the process stops when the internal volume of the heat exchanger becomes filled with condensed UF.sub.6 and blocks the passage of further UF.sub.6 gas. However, owing to the nature of the apparatus and process, the heat exchanger can become blocked to the passage of further UF.sub.6 gas long before the total available volume of the heat exchanger is filled with condensed gas leading to inefficiency in the process.
The condensed UF.sub.6 gas is then converted to the liquid form by sealing off the heat exchanger by valves, heating the contents using hot heat exchange fluid and allowing the subliming UF.sub.6 to create a pressure rise up above 2 Bar within the heat exchanger vessel such that the UF.sub.6 liquefies and is finally run off to storage as UF.sub.6 product or to the next process step for uranium which is being reprocessed.
A further disadvantage of the present plant is that many welded joints are required to manufacture the heat exchanger, the welds being susceptible to mechanical failure by fatigue from thermal cycling. Weld failure can lead to contamination of the coolant which then requires treatment itself and which is extremely expensive.
A yet further significant disadvantage of the present apparatus is that the glycol heat transfer fluid requires complex and expensive additional plant for its treatment and recirculation.
GB-A-1 381 892 describes a method and apparatus for the desublimation of a sublimable substance. The apparatus and method principally relate to the desublimation of materials which are normally solid at ambient temperatures and pressures and which sublime at relatively higher temperatures. This reference is mainly concerned with preventing the build-up of desublimed vapours onto the internal walls of the desubliming vessel by the provision of a porous inner wall in the vessel through which gas may be passed to prevent deposition of desublimed material thereon.
It is an object of the present invention to provide treatment plant, principally for UF.sub.6, which is significantly more economic to operate and manufacture and which does not have the operating blockage problems of known plant as described above. It is a further object of the present invention to provide apparatus, principally for the treatment of UF.sub.6, which has fewer welds liable to fatigue than are present in prior art apparatus.
According to a first aspect of the present invention there is provided apparatus for the solidification by desublimation of a sublimed gaseous substance and the subsequent trapping and liquefication of said desublimed substance, the apparatus comprising: said sublimed substance so as to reduce the temperature of said sublimed substance to below a dewpoint thereof; desublimed substance falls; portion; pressure to be established in said vessel means; tank portion such as to be immersed in liquid resulting from the liquefaction of said desublimed substance, and a second end remote from said first end outside said vessel and connected to means to receive said liquefied substance; and liquefied desublimed substance.
According to a second aspect of the present invention there is provided a method for the solidification by desublimation of a sublimed gaseous substance and the subsequent trapping and lique
REFERENCES:
patent: 4181508 (1980-01-01), Schmid et al.
patent: 4281518 (1981-08-01), Muller et al.
patent: 4546611 (1985-10-01), Eby et al.
patent: 4773923 (1988-09-01), Scharf
patent: 4867763 (1989-09-01), Scharf
British Nuclear Fuels plc
Capossela Ronald
LandOfFree
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