Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1999-11-15
2000-10-24
Capossela, Ronald
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
62925, F25J 100
Patent
active
061349143
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process and a device for separating off one component from a gas mixture and to a process for recycling a gas mixture such as an anesthetic gas. The invention finds application, in particular, in connection with instruments for and techniques of xenon anesthesia.
The anesthetic effects of xenon have been known since the 1940s. A mixture of about 80% xenon and 20% oxygen is regarded as a virtually ideal anesthetic gas, with numerous advantages over the anesthetic gases predominantly in use today which are based on laughing gas. Owing to the high costs of xenon, xenon anesthesia is practiced hardly at all in the clinical field. In order to reduce these costs proposals have therefore been made, for example in DE 44 11 533 C1, for anesthetic machines having a xenon recovery system. In the case of the recovery system proposed in DE 44 11 533 C1, the exhaled respiratory gas is first cleaned and then compressed and passed into a pressure vessel which is taken into a cooling device. By means of the cooling device the pressure vessel is cooled to such an extent that the xenon that is to be recovered is liquefied. The gaseous constituents in the pressure vessel are let off through an outflow valve. When there is a sufficient amount of liquid xenon in the pressure vessel, it is pumped into a further vessel.
This device has the disadvantage of a highly complex apparatus for compressing the gas and for the cooling of an entire vessel. Moreover, the degree of transfer in xenon recovery is not satisfactory.
DE 35 18 283 A1 discloses a process for removing volatile purities from gases which are produced in the semiconductor industry, where the gas to be cleaned is guided, in a vacuum system, onto a cold surface of a condensor, on which condenser the gas to be purified is deposited while the more volatile impurities are drawn off continuously in gas form from the vacuum system. In this process too, the vacuum system used means that the apparatus for recovery is highly complex.
SUMMARY OF INVENTION
It is the object of the invention to provide a simple and economic process for separating off one component of an anesthetic gas from the expirational respiratory gas of an anesthetized patient, and an associated device. Another object of the invention is to provide an economic recycling process for an anesthetic gas, especially for a xenon-based anesthetic gas.
It has surprisingly been found that it is also still possible to separate off xenon with an acceptable purity with condensation under a pressure in the range from 0.6 bar to 150 bar. When the novel recycling process is used for an anesthetic gas, it is even possible to reduce the purity requirements for the xenon still further, since residual fractions of oxygen in the recovered xenon can be compensated for by an appropriately lower proportion of oxygen when the anesthetic gas is remixed.
Advantageously, through the use of a heat exchanger consisting of a tube or a tube bundle, the energy required to condense out the xenon is reduced, since it is now necessary to cool no longer the entire vessel but instead a comparatively small condensation surface to the temperature which is required for the condensation of the xenon in solid form. At the same time this opens up a possibility of controlling the layer thickness. Since the solid xenon deposited on the heat exchanger has an insulating effect, the degree of cooling of the interior of the vessel by the heat exchanger drops as the thickness of the solid xenon layer grows, so that the thickness of the xenon layer on the heat exchanger can be deduced from the temperature in the vessel.
The pressure produced when the deposited xenon is evaporated can be used, in accordance with the invention, to transfer the recovered xenon to another vessel. Pumps for conveying the recovered xenon for further processing, therefore, can be omitted or made smaller.
The novel process can be designed as a continuous process at low pressure, with the respiratory gas, after first being cleane
REFERENCES:
patent: 3853507 (1974-12-01), Monroe et al.
patent: 4668261 (1987-05-01), Chatzipros et al.
patent: 4755201 (1988-07-01), Eschwey et al.
patent: 5520169 (1996-05-01), Georgieff et al.
patent: 5626035 (1997-05-01), Pozvonkov
Eschwey Manfred
Hamm Reiner
Neu Peter
Schmidt Renate
Schroeder Georg
Capossela Ronald
Messer Griesheim GmbH
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