Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-05-18
2001-08-28
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S652000
Reexamination Certificate
active
06279345
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic air separation and, more particularly, to cryogenic air separation wherein ultra high purity product may be produced.
BACKGROUND ART
Oxygen and nitrogen are produced commercially in large quantities and high purities by the cryogenic rectification of air. It is sometimes desired to employ oxygen or nitrogen at an ultra high purity, for example, for use in the electronics industry. While cryogenic air separation systems for producing oxygen or nitrogen at an ultra high purity are known, such system generally produce such product with a significantly reduced recovery.
Accordingly, it is an object of this invention to provide an improved cryogenic air separation system for the production of oxygen or nitrogen at an ultra high purity.
It is another object of this invention to provide an improved cryogenic air separation system which can produce oxygen or nitrogen at an ultra high purity and with high recovery.
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 carrying out cryogenic air separation comprising:
(A) passing feed air into a cryogenic rectification column and separating the feed air within the column by cryogenic rectification into nitrogen-enriched top fluid and oxygen-enriched kettle liquid;
(B) partially vaporizing the oxygen-enriched kettle liquid by indirect heat exchange with nitrogen-enriched top fluid to produce oxygen-enriched kettle vapor and remaining oxygen-enriched kettle liquid;
(C) compressing the oxygen-enriched kettle vapor and passing the resulting compressed oxygen-enriched kettle vapor into the cryogenic rectification column;
(D) vaporizing remaining oxygen-enriched kettle liquid by indirect heat exchange with nitrogen-enriched top fluid; and
(E) recovering some of the nitrogen-enriched top fluid as product nitrogen.
Another aspect of the invention is:
Apparatus for carrying out cryogenic air separation comprising:
(A) a cryogenic rectification column and means for passing feed air into the cryogenic rectification column;
(B) a split kettle top condenser, a phase separator, means for passing fluid from the lower portion of the cryogenic rectification column to the split kettle top condenser, and means for passing fluid from the split kettle top condenser to the phase separator;
(C) means for passing fluid from the phase separator to the split kettle top condenser, and means for passing fluid from the upper portion of the cryogenic rectification column to the split kettle top condenser;
(D) a compressor, means for passing vapor from the phase separator to the compressor, and means for passing fluid from the compressor to the cryogenic rectification column; and
(E) means for recovering fluid from the upper portion of the cryogenic rectification column as product nitrogen.
As used herein the term “feed air” means a mixture comprising primarily oxygen and nitrogen, such as ambient air.
As used herein the term “ultra high purity oxygen” means a fluid having an oxygen concentration of at least 99.99 mole percent with a methane impurity of less than 10
−8
mole percent.
As used herein the term “ultra high purity nitrogen” means a fluid having a nitrogen concentration of at least 99.95 mole percent with an oxygen impurity of less than 10
−8
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 counter currently 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 separation process that combines successive partial vaporizations and condensations as obtained by a counter current treatment of the vapor and liquid phases. The counter current 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 terms “turbo expansion” and “turbo expander” 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 “subcooling” and “subcooler” mean respectively method and apparatus for cooling a liquid to be at a temperature lower than the saturation temperature of that liquid for the existing pressure.
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.
As used herein the term “phase separator” means a vessel wherein incoming two phase feed is separated into individual vapor and liquid fractions. Typically, the vessel has sufficient cross-sectional area so that the vapor and liquid are separated by gravity.
As used herein the term “stripping column” means a column operated with sufficient vapor upflow relative to liquid downflow to achieve separation of a volatile component from the liquid into the vapor in which the volatile component becomes progressively richer upwardly.
As used herein the term “split kettle top condenser” means a condenser wherein two different kettle liquid streams provide refrigeration to condense nitrogen-enriched vapor without rectification.
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Arman Bayram
Bonaquist Dante Patrick
Capossela Ronald
Ktorides Stanley
Praxair Technology Inc.
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