Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
1999-11-12
2001-02-27
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S653000
Reexamination Certificate
active
06192707
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic air separation and, more particularly, to the production of enriched air.
BACKGROUND ART
Many industrial processes, such as combustion and chemical oxidation, require enriched air as a process input. Often the enriched air is required by the industrial process at a relatively high pressure, typically at a pressure much higher than that at which an air separation plant operates. This creates an inefficiency.
Accordingly it is an object of this invention to provide a system for producing enriched air, especially relatively high pressure enriched air, which employs a cryogenic air separation plant and which operates with improved efficiency over conventional systems for providing enriched air.
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 enriched air comprising:
(A) passing feed air to a multistage compressor, compressing the feed air in the multistage compressor to produce compressed feed air, and passing a first portion of the compressed feed air into a cryogenic air separation plant;
(B) separating compressed feed air in the cryogenic air separation plant by cryogenic rectification to produce oxygen fluid;
(C) passing oxygen fluid from the cryogenic air separation plant to the multistage compressor, and mixing oxygen fluid within the multistage compressor with a second portion of the compressed feed air to produce enriched air; and
(D) further compressing the enriched air within the multistage compressor and recovering further compressed enriched air from the multistage compressor.
Another aspect of the invention is:
Apparatus for producing enriched air comprising:
(A) a multistage compressor comprising an initial stage and a final stage, and means for passing feed air to the initial stage of the multistage compressor;
(B) a cryogenic air separation plant and means for passing feed air from the multistage compressor to the cryogenic air separation plant, said means communicating with the multistage compressor downstream of the initial stage;
(C) means for passing oxygen fluid from the cryogenic air separation plant to the multistage compressor at a point upstream of the final stage; and
(D) means for recovering enriched air from the final stage of the multistage compressor.
As used herein the term “oxygen fluid” means a fluid having an oxygen concentration of at least 40 mole percents preferably at least 80 mole percent, most preferably at least 95 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.
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 “enriched air” means a fluid having an oxygen concentration within the range of from 25 to 50 mole percent, with the remainder being primarily nitrogen.
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 “feed air” means a mixture comprising primarily oxygen and nitrogen, such as ambient air.
As used herein the term “cryogenic air separation plant” means a plant comprising at least one column, which processes feed air and produces oxygen fluid.
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Drnevich Raymond Francis
Shah Minish Mahendra
Doerrler William
Ktorides Stanley
Praxair Technology Inc.
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