Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-03-23
2001-07-17
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S912000
Reexamination Certificate
active
06260380
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the separation of feed air by cryogenic rectification and, more particularly, to the production of liquid oxygen and other liquid products.
BACKGROUND ART
The production of liquids, such as liquid oxygen, by the cryogenic rectification of feed air requires the provision of a significant amount of refrigeration to drive the separation because a significant amount of refrigeration is removed from the columns with the product liquid. Generally such refrigeration is provided by the turboexpansion of a process stream, such as a portion of the feed air. While this conventional practice is effective, it is limiting because an increase in the amount of refrigeration inherently affects the operation of the overall process. It is therefor desirable to have a cryogenic air separation process which can produce significant amounts of liquid product wherein the provision of the requisite refrigeration is independent of the flow of process streams for the system.
One method for providing refrigeration for a cryogenic air separation system which is independent of the flow of internal system process streams is to provide the requisite refrigeration in the form of exogenous cryogenic liquid brought into the system. Unfortunately such a procedure is very costly.
Accordingly it is an object of this invention to provide an improved cryogenic air separation process which can produce significant amounts of liquid product wherein the provision of the requisite refrigeration for the separation is independent of the flow of process streams.
It is another object of this invention to provide a cryogenic air separation process which can produce significant amounts of liquid product wherein the provision of the requisite refrigeration for the separation is independently and efficiently provided to the system.
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 which is:
A process for the production of liquid oxygen by the cryogenic rectification of feed air comprising:
(A) compressing a multicomponent refrigerant fluid, cooling the compressed multicomponent refrigerant fluid, expanding the cooled, compressed multicomponent refrigerant fluid, and warming the expanded multicomponent refrigerant fluid by indirect heat exchange with said cooling compressed multicomponent refrigerant fluid and also with feed air to produce cooled feed air;
(B) passing the cooled feed air into a higher pressure cryogenic rectification column and separating the feed air by cryogenic rectification within the higher pressure cryogenic rectification column into nitrogen-enriched fluid and oxygen-enriched fluid;
(C) passing nitrogen-enriched fluid and oxygen-enriched fluid into a lower pressure cryogenic rectification column, and separating the fluids passed into the lower pressure column by cryogenic rectification to produce nitrogen-rich fluid and oxygen-rich fluid; and
(D) withdrawing oxygen-rich fluid from the lower portion of the lower pressure column as liquid and recovering the withdrawn oxygen-rich fluid as product liquid oxygen.
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. 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 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 fluid streams into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term “expansion” means to effect a reduction in pressure.
As used herein the term “liquid nitrogen” means a liquid having a nitrogen concentration of at least 95 mole percent.
As used herein the term “liquid oxygen” means a liquid having an oxygen concentration of at least 85 mole percent.
As used herein the term “liquid argon” means a liquid having an argon concentration of at least 90 mole percent.
As used herein the term “low boiling component” means a component having an atmospheric boiling point less than 140 K.
As used herein the term “medium boiling component” means a component having an atmospheric boiling point within the range of from 140 K to 220 K.
As used herein the term “high boiling component” means a component having an atmospheric boiling point greater than 220 K.
As used herein the term “feed air” means a mixture comprising primarily oxygen, nitrogen and argon, such as ambient air.
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 “variable load refrigerant” means a multicomponent fluid, i.e. a mixture of two or more components, in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the practice of this invention the temperature differences between the bubble point and the dew point for the multicomponent refrigerant fluid is at least 10° K, preferably at least 20° K and most preferably at least 50° K.
As used here
Arman Bayram
Bonaquist Dante Patrick
Vincett Mark Edward
Weber Joseph Alfred
Doerrler William
Ktorides Stanley
Praxair Technology Inc.
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