Refrigeration – Processes – Circulating external gas
Patent
1987-02-06
1989-04-04
Warner, Steven E.
Refrigeration
Processes
Circulating external gas
62 30, 62 33, 62 39, F25J 304
Patent
active
048182621
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the technique of distilling air by means of a plant provided with an argon-producing column.
As is well known, air distillation plants provided with an argon-producing column usually comprise a double column formed by a medium distillation column operating at about 6 bars, a low pressure distillation column operating at a little above atmospheric pressure, and a condenser-vaporizer. The air is sent, after having been purified and cooled, to the bottom of the medium pressure column. The "rich liquid" (air enriches in oxygen) received at the bottom of the medium pressure column is fed to an intermediate point of the low pressure column, while a part of the "poor liquid," formed almost entirely by nitrogen, received at the top of the medium pressure column is refluxed to the top of the low pressure column. Below the rich liquid inlet, the low pressure column is connected to the argon-producing column through a conduit termed "argon tapping conduit" and a conduit for the return of liquid poorer in argon. The low pressure column is usually provided at the bottom with gaseous oxygen and liquid oxygen withdrawing conduits, and the medium pressure column is usually provided at the top with gaseous nitrogen and liquid nitrogen withdrawing conduits. The vapor at the top of the low pressure column ("impure nitrogen") is formed by nitrogen containing up to a few % oxygen and is usually rejected to the atmosphere.
In plants adapted mainly to produce gaseous oxygen delivered directly to a user through piping, oxygen is sometimes temporarily in excess. This is the case in particular during periods in which the factories of the user stop work. With conventional distillation plants, the gaseous oxygen is then put into communication with the atmosphere and the energy used for the separation of this oxygen is lost. FR-A-2,550,325 proposes a solution for limiting this drawback. This solution has the advantage of being simple but is of limited effectiveness.
More generally, the distillation of a given flow of air is capable of providing about 21% of this flow as oxygen and, under certain conditions, this quantity of oxygen is in excess of the real needs, whereas other productions, in particular argon, are desired.
An object of the invention is to permit in all cases the optimum valorization of the excess of oxygen so as to increase the desired productions and in particular that of argon.
The invention therefore provides a process for distilling air by means of a plant comprising a main distillation apparatus associated with an argon producing column through an argon tapping conduit, this process being characterized in that it comprises:
sending to the base of a first mixing column section gaseous nitrogen which may be impure but is substantially without argon, and to the top of a second mixing column section liquid oxygen which may possibly be impure but is substantially without argon;
sending to the base of the second section at least a part of the top vapor of the first section and to the top of the first section at least a part of the liquid produced at the base of the second section;
effecting between the base of the first section and the top of the second section at least one intermediate withdrawal which constitutes a residual gas or from which such a gas is produced, which gas is a mixture of nitrogen and oxygen comprising about 10 to 30% oxygen;
discharging from the second section, at the top of the latter, impure oxygen containing at the most a few % nitrogen; and
discharging from the first section, at the base of the latter, poor liquid constituted by nitrogen containing at the most a few % oxygen, and refluxing said poor liquid to the main distillation apparatus.
The invention also provides a plant adapted to carry out such a process. This plant, which is of the type comprising a main distillation apparatus associated with an argon producing column through an argon tapping conduit, is characterized in that it comprises:
a first mixing column section and means for feeding gaseous nitr
REFERENCES:
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patent: 4022030 (1977-05-01), Brugerolle
patent: 4137056 (1979-01-01), Golovko
patent: 4433989 (1984-02-01), Erickson
patent: 4533375 (1985-08-01), Erickson
L'Air Liquide, Societe Anonyme Pour L'Etude Et L'Exploitation de
Warner Steven E.
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