Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-06-14
2001-12-11
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S925000
Reexamination Certificate
active
06327873
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic rectification and, more particularly, to the use of cryogenic rectification to produce ultra high purity oxygen.
BACKGROUND ART
Ultra high purity oxygen is required in manufacturing processes that are very sensitive to contaminants, such as in the production of semiconductors and other electronic components. As the demand for ultra high purity oxygen increases, there is a need for a system which can efficiently produce ultra high purity oxygen.
Accordingly, it is an object of this invention to provide an improved system for producing ultra high purity oxygen.
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 ultra high purity oxygen by cryogenic rectification comprising:
(A) providing a feed comprising oxygen, argon, krypton and xenon, and passing the feed into the upper portion of a first column;
(B) separating the feed by cryogenic rectification within the first column into a top fluid comprising oxygen and argon, and into a bottom fluid comprising krypton and xenon;
(C) passing top fluid from the upper portion of the first column into the upper portion of a second column, and separating the top fluid by cryogenic rectification within the second column into argon-enriched fluid and ultra high purity oxygen; and
(D) withdrawing ultra high purity oxygen from the lower portion of the second column and recovering the withdrawn ultra high purity oxygen as product.
Another aspect of the invention is:
Apparatus for producing ultra high purity oxygen comprising:
(A) a first column having a top condenser and a bottom reboiler, and means for passing a feed comprising oxygen, argon, krypton and xenon into the upper portion of the first column;
(B) a second column having a top condenser and a bottom reboiler, and means for passing fluid from the upper portion of the first column into the upper portion of the second column;
(C) means for passing fluid from the bottom reboiler of the first column to the top condenser of the first column, and means for passing fluid from the bottom reboiler of the second column to the top condenser of the second column; and
(D) means for recovering ultra high purity oxygen from the lower portion of the second column.
As used herein the term “ultra high purity oxygen” means a fluid having an oxygen concentration of at least 99.99 mole percent.
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.
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. Distillation is the separation process whereby heating of a liquid mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) 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 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 or nonadiabatic 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 “upper portion” and “lower portion” mean those sections of a column respectively above and below the mid point of the column.
As used herein, the term “tray” means a contacting stage, which is not necessarily an equilibrium stage, and may mean other contacting apparatus such as packing having a separation capability equivalent to one tray.
As used herein, the term “equilibrium stage” means a vapor-liquid contacting stage whereby the vapor and liquid leaving the stage are in mass transfer equilibrium, e.g. a tray having 100 percent efficiency or a packing element height equivalent to one theoretical plate (HETP).
As used herein, the term “top” when referring to a column means that section of the column above the column mass transfer internals, i.e. trays or packing.
As used herein, the term “bottom” when referring to a column means that section of the column below the column mass transfer internals, i.e. trays or packing.
As used herein, the term “bottom reboiler” means a heat exchanger for generating column upflow vapor from column liquid.
As used herein, the term “top condenser” means a heat exchanger for generating column downflow liquid from column vapor.
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Dray James Robert
Jaynes Scot Eric
Capossela Ronald
Ktorides Stanley
Praxair Technology Inc.
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