Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-08-25
2001-11-13
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S925000
Reexamination Certificate
active
06314757
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic rectification and, more particularly, to improving the recovery of the rare gases krypton and xenon.
BACKGROUND ART
The rare gases, i.e. krypton and xenon, exist in very small concentrations in the atmosphere. Xenon is found in the ambient air in a concentration of 0.087 parts per million (ppm) and krypton is found in the ambient air in a concentration of 1.14 ppm. Because of these very small concentrations, krypton and xenon can be economically produced from only very large cryogenic air separation plants. Since the demand for these rare gases is increasing, it is desirable to be able to produce economically krypton and xenon from any size cryogenic air separation plant, and not just the very large cryogenic air separation plants.
Accordingly, it is an object of this invention to provide a system which will facilitate the recovery of krypton and xenon from smaller as well as larger cryogenic air separation plants.
Cryogenic air separation plants which produce gaseous oxygen operate most efficiently at steady state conditions. Unfortunately the demand for oxygen produced from such a facility can fluctuate between periods of high demand and periods of low demand as often as every few minutes or hours. This may require that such cryogenic air separation plants operate in an inefficient manner for much of the time although a number of methods have been identified to minimize operating and capital costs to meet variable demand.
Accordingly, it is another object of this invention to provide a system whereby cryogenic air separation plants which produce gaseous oxygen, such as for delivery to a pipeline, may operate at efficient steady state conditions during both high and low demand periods.
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 processing atmospheric fluids to produce gaseous oxygen, liquid nitrogen, and a rare gas richer liquid comprising:
(A) passing a feed liquid into a cryogenic rectification column, said feed liquid comprising oxygen, krypton and xenon, and passing the feed liquid down the cryogenic rectification column against upflowing vapor;
(B) separating the feed liquid by cryogenic rectification within the cryogenic rectification column to produce oxygen vapor and a rare gas richer liquid, and recovering oxygen vapor from the upper portion of the rectification column as product gaseous oxygen;
(C) vaporizing a portion of the rare gas richer liquid by indirect heat exchange by nitrogen vapor to generate said upflowing vapor and to produce liquid nitrogen; and
(D) recovering at least some of said liquid nitrogen, and recovering rare gas richer liquid from the lower portion of the cryogenic rectification column.
Another aspect of the invention is:
Apparatus for processing atmospheric fluid to produce gaseous oxygen, liquid nitrogen, and a rare gas richer liquid comprising:
(A) a cryogenic rectification column having a bottom reboiler;
(B) means for passing a feed liquid comprising oxygen, krypton and xenon into the cryogenic rectification column;
(C) means for passing nitrogen vapor into the bottom reboiler and means for recovering liquid nitrogen from the bottom reboiler; and
(D) means for recovering gaseous oxygen from the upper portion of the cryogenic rectification column, and means for recovering rare gas richer liquid from the lower portion of the cryogenic rectification column.
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 portion in heat exchange relation with the lower portion 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 is generally 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 that generates column upflow vapor from column liquid. A bottom reboiler may be inside or outside the column.
As used herein the terms “subcooling” and “subcooler” mean respectively method and apparatus for cooling a liquid to be at a temperature lower than that liquid's saturation temperature for the existing pressure.
As used herein the term “top condenser” means a heat exchange device that generates column downflow liquid from column vapor. A top condenser may be inside or outside the column.
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.
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Dray James Robert
Fisher Theodore Fringelin
Capossela Ronald
Ktorides Stanley
Prakair Technology, Inc.
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