Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-06-01
2001-08-28
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S654000
Reexamination Certificate
active
06279344
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic air separation and, more particularly, to cryogenic air separation for producing oxygen, particularly at elevated pressure.
BACKGROUND ART
Oxygen is produced commercially in large quantities by the cryogenic separation of air, generally employing a double column arrangement having a higher pressure column in heat exchange relation with a lower pressure column. A recent significant advancement in the production of oxygen is the side column system which enables the production of oxygen with lower operating costs. Examples of side column systems may be found in U.S. Pat. No. 5,463,871—Cheung and U.S. Pat. No. 5,582,036—Drnevich et al.
When the production of elevated pressure oxygen is desired using the side column system, liquid oxygen from the side column is pumped and then vaporized against boosted feed air. The air pressure for the booster air compressor may fluctuate especially where the base load air compressor is also supplying air for another use such as the blast air for a blast furnace. Such fluctuations result in unstable operation.
Accordingly it is an object of this invention to provide a cryogenic air separation system using a side column arrangement which can produce oxygen with improved stability.
SUMMARY Of THE INVENTION
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for producing oxygen comprising:
(A) passing feed air into a higher pressure column and separating the feed air by cryogenic rectification within the higher pressure column into nitrogen-enriched vapor and oxygen-enriched fluid;
(B) passing oxygen-enriched fluid from the higher pressure column into a lower pressure column and producing oxygen-richer fluid within the lower pressure column;
(C) passing oxygen-richer fluid from the lower portion of the lower pressure column into the upper portion of a side column and producing oxygen-rich liquid within the side column;
(D) withdrawing nitrogen-enriched vapor from the higher pressure column, compressing the nitrogen-enriched vapor, and cooling the compressed nitrogen-enriched vapor by indirect heat exchange with oxygen-rich liquid to produce oxygen-rich vapor; and
(E) recovering vaporized oxygen-rich liquid as product oxygen.
Another aspect of the invention is:
Apparatus for producing oxygen comprising:
(A) a higher pressure column, a lower pressure column, means for passing feed air into the higher pressure column, and means for passing fluid from the higher pressure column to the lower pressure column;
(B) a side column and means for passing fluid from the lower portion of the lower pressure column to the upper portion of the side column;
(C) a compressor, a heat exchanger, means for passing fluid from the upper portion of the higher pressure column to the compressor and from the compressor to the heat exchanger;
(D) means for passing fluid from the lower portion of the side column to the heat exchanger; and
(E) means for recovering fluid from the heat exchanger as product oxygen.
As used herein the term “feed air” means a mixture comprising primarily nitrogen and oxygen, such as ambient air.
As used herein the term “column” means a distillation or fractionation column or zone, i.e., a contacting column or zone wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer's Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. The term, “double column” is used to mean a higher pressure column having its upper end in heat exchange relation with the lower end of a lower pressure column. A further discussion of double columns appears in Ruheman “The Separation of Gases”, Oxford University Press, 1949, Chapter VII, Commercial Air Separation.
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases can be adiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).
As used herein the term “indirect heat exchange” means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term “bottom reboiler” means a heat exchange device which generates column upflow vapor from column bottom liquid.
As used herein the terms “turboexpansion” and “turboexpander” mean respectively method and apparatus for the flow of high pressure gas through a turbine to reduce the pressure and the temperature of the gas thereby generating refrigeration.
As used herein the terms “upper portion” and “lower portion” mean those sections of a column respectively above and below the mid point of the column.
REFERENCES:
patent: 2079019 (1937-05-01), Karwat
patent: 3304074 (1967-02-01), Atherton
patent: 4022030 (1977-05-01), Brugerolle
patent: 5244489 (1993-09-01), Grenier
patent: 5265429 (1993-11-01), Dray
patent: 5355682 (1994-10-01), Agrawal et al.
patent: 5463871 (1995-11-01), Cheung
patent: 5538534 (1996-07-01), Guillard et al.
patent: 5582036 (1996-12-01), Drnevich et al.
patent: 5600970 (1997-02-01), Drnevich et al.
patent: 5682766 (1997-11-01), Bonaquist et al.
patent: 5881570 (1999-03-01), Drnevich et al.
patent: 6045602 (2000-04-01), Shah et al.
Drnevich Raymond Francis
Shah Minish Mahendra
Capossela Ronald
Ktorides Stanley
Praxair Technology Inc.
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