Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
1999-08-30
2001-06-19
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S524000
Reexamination Certificate
active
06247333
ABSTRACT:
The present invention relates to a process and for producing impure oxygen by distillation Zr.
Impure oxygen is often used for the production of synthesis gas by partial oxidation or by reforming. The synthesis gas is separated by PSA in order to produce hydrogen, which is mixed with nitrogen for the synthesis of ammonia.
Impure oxygen typically contains 1 to 5% argon. This argon accumulates in the synthesis loop and can cause ammonia production losses and possible pollution when purging.
J-B-74023997 describes the use of an air-separation device for supplying oxygen and nitrogen to an ammonia-production unit.
EP-A-0562893 describes a process using a double column for producing nitrogen containing less than 10 ppm oxygen for an ammonia-manufacturing unit and oxygen with medium to high purity, that is to say 95 to 99.5% by mole for the production of hydrogen by reacting oxygen with heavy hydrocarbons, the hydrogen being intended to feed the same ammonia-manufacturing unit.
The problem associated with the presence of argon can clearly be avoided by using oxygen with a purity in excess of 99% oxygen, containing less than 1% argon, but this increases production costs.
A process of this type is described in application FR 97 04083 in the name of the Applicant Company, which has not yet been published.
It is known to produce impure oxygen using a double column and a mixing column.
EP-A-0636845 describes a process in which oxygen pumped from a double column is sent to the head of a mixing column. The process uses an intermediate-pressure column of the type referred to as an Etienne column fed with rich liquid from the medium-pressure column, and produces oxygen at 30 bar with 95% oxygen, 2% nitrogen and 3% argon.
EP-A-0531182 discloses a process using a mixing column operating at a pressure different from that of the medium-pressure column in order to produce oxygen having a purity between 80 and 97% oxygen.
U.S. Pat. No. 5,490,391 describes a process using a double column and a mixing column with a Claude turbine to refrigerate the device.
According to one subject of the invention, a process is provided for supplying impure oxygen to a synthesis-gas production unit whose synthesis gas is separated into a hydrogen-enriched part intended for an ammonia-synthesis unit, characterized in that the impure oxygen comes from a device for separating air by cryogenic distillation and contains 70 to 98% oxygen and less than 2% argon.
The impure oxygen preferably contains 1 to 30% nitrogen.
If the impure oxygen contains between 75 and 85% oxygen, it contains 15 to 25% nitrogen and less than 2% argon.
In a process for separation of air in order to produce impure oxygen, air is sent to a medium-pressure column of a double column of the air-separation device, an oxygen-enriched liquid and a nitrogen-enriched liquid are sent from the medium-pressure column to a low-pressure column of the double column, air is sent to the base of a mixing column, an oxygen-enriched liquid is sent from the low-pressure column to the head of the mixing column and the impure oxygen is drawn off as product from the head of the mixing column.
The synthesis-gas production unit may be a reforming or partial-oxidation device.
According to another subject of the invention, a process is provided for supplying impure oxygen to a synthesis-gas production unit whose synthesis gas is separated into a hydrogen-enriched part intended for an ammonia-synthesis unit and for supplying nitrogen to the ammonia-synthesis unit, characterized in that the impure oxygen and the nitrogen come from a device for separating air by cryogenic distillation and the impure oxygen contains 70 to 98% oxygen and less than 2% argon.
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De Bussy Francois
Rieth Norbert
Doerrler William
L'Air Liquide, Societe Anonyme pour l'Etrude et l&apos
Young & Thompson
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