Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-11-06
2001-11-27
Doerrler, William C. (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S643000
Reexamination Certificate
active
06321568
ABSTRACT:
The present invention relates to a process and an apparatus for the separation of air by cryogenic distillation. In particular, it relates to a process and an apparatus for the separation of air by cryogenic distillation in which a stream of liquid, in particular a liquid comprising at least 85 mol % oxygen, coming from a cryogenic distillation column, is pressurized and vaporized by heat exchange with a stream of air intended to be distilled.
U.S. Pat. No. 5,901,578 describes an air separation process in which a stream of liquid oxygen is pumped, sent to a phase separator, sent from the phase separator to a heat exchanger, where it partially vaporizes, and sent back to the phase separator. A gas stream from the phase separator is warmed in the exchanger and serves as product. A stream of liquid oxygen is taken off as product between the pump and the phase separator.
EP-A-0,464,630 describes an air separation process in which a stream of liquid oxygen is pumped, sent to a phase separator, sent from the phase separator to a first heat exchanger, where it partially vaporizes, and sent back to the phase separator. A gas stream coming from the phase separator is warmed in a second exchanger and serves as product. A stream of liquid oxygen is taken off as product between the phase separator and the first exchanger.
The object of the invention is to improve the safety of the above processes and to reduce the size of the phase separator.
According to one subject of the invention, the process for the separation of air by distillation in order to produce a gaseous product, in which:
i) air is cooled in a heat exchanger and sent to a cryogenic distillation apparatus;
ii) the air is separated in the cryogenic apparatus in order to form oxygen-enriched and nitrogen-enriched fluids and at least one liquid;
iii) liquid is sent to the heat exchanger here it partially vaporizes;
iv) the partially vaporized stream is sent a phase separator;
v) a gas stream is withdrawn from the phase separator and warmed in a heat exchanger;
vi) one portion of the liquid stream is sent from the phase separator back to the exchanger and another portion of the liquid is taken off, is characterized in that, in step iii), the liquid is sent directly to the exchanger, possibly after having been pressurized, and is not sent to the phase separator before having been sent to the exchanger.
Optionally, all of the air intended to be distilled is sent to the exchanger where the liquid vaporizes and the gas stream from the phase separator warms up in this same exchanger.
The liquid stream coming from the phase separator is mixed with the liquid stream coming from the apparatus and intended for the exchanger downstream of the point at which the liquid stream is taken off.
The liquid taken off in step vi) is a liquid product.
Another object of the invention is to provide an air separation plant comprising:
i) an air separation apparatus comprising at least one column
ii) an exchanger, means for sending an air stream to the exchanger in order to cool it and means for sending the cooled air to a column of the air separation apparatus
iii) means for withdrawing a liquid from a column of the air separation apparatus
iv) means for sending the liquid to the exchanger, a phase separator and means for sending the partially vaporized liquid from the exchanger to the phase separator
v) means for sending a gas from the phase separator to a heat exchanger
vi) means for sending one portion of the liquid from the phase separator to the exchanger and for taking off another portion of the phase separator liquid
characterized in that the means for sending the liquid from the separation apparatus to the exchanger are not connected to the phase separator.
Optionally:
the plant comprises means for sending all of the air to be distilled to the exchanger;
the plant comprises means for mixing the liquid coming from the phase separator with the liquid coming from the separation apparatus upstream of the exchanger and downstream of the means for taking off the other liquid portion coming from the phase separator.
Thus it is not necessary to send all of the liquid to be vaporized from the separation apparatus to the phase separator before sending it to the exchanger.
Since the phase separator no longer receives the stream of liquid coming from the apparatus but only the partially vaporized stream coming from the exchanger, its size is reduced and its cost will be less.
REFERENCES:
patent: 5685173 (1997-11-01), De L'lsle et al.
patent: 5946942 (1999-09-01), Wong et al.
Doerrler William C.
L'Air Liquide, Societe Anonyme pour l'etude et l'
Young & Thompson
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