Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-06-28
2001-08-07
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S006000, C062S912000
Reexamination Certificate
active
06269658
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to cryogenic rectification and is particularly useful for carrying out cryogenic air separation.
BACKGROUND ART
Cryogenic rectification, such as the cryogenic rectification of feed air, requires the provision of refrigeration to drive the separation. Generally such refrigeration is provided by the turboexpansion of a process stream, such as, for example, a portion of the feed air. While this conventional practice is effective, it is limiting because any change in the requisite amount of refrigeration inherently affects the operation of the overall process. It is therefor desirable to have a cryogenic rectification system 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 rectification system which is independent of the flow of internal system process streams is to provide the requisite refrigeration in the form of 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 rectification system wherein the provision of at least some of refrigeration for the separation is independent of the turboexpansion of process streams and does not require the provision of exogenous cryogenic liquid 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, one aspect of which is:
A method for carrying out cryogenic rectification comprising:
(A) passing feed into a cryogenic rectification plant comprising at least one column;
(B) applying a compressive force to a pulse tube system gas to compress the pulse tube system gas, passing the compressed pulse tube system gas to a pulse tube, and expanding the pulse tube system gas within the pulse tube to generate refrigeration;
(C) passing refrigeration generated by the pulse tube system gas into the cryogenic rectification plant; and
(D) separating the feed by cryogenic rectification within the cryogenic rectification plant using refrigeration generated by the pulse tube system gas.
Another aspect of the invention is:
Apparatus for carrying out cryogenic rectification comprising:
(A) a cryogenic rectification plant comprising at least one column and means for passing feed into the cryogenic rectification plant;
(B) a pulse tube refrigeration system comprising a precooling means, a pulse tube, means for passing pulse tube system gas from the precooling means to the pulse tube, and means for applying a compressive force to the pulse tube system gas;
(C) means for passing refrigeration from the pulse tube refrigeration system into the cryogenic rectification plant; and
(D) means for recovering product from the cryogenic rectification plant.
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 fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other. As used herein the term “product nitrogen” means a fluid having a nitrogen concentration of at least 95 mole percent.
As used herein the term “product oxygen” means a fluid having an oxygen concentration of at least 85 mole percent.
As used herein the term “product argon” means a fluid having an argon concentration of at least 90 mole percent.
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.
REFERENCES:
patent: 5711156 (1998-01-01), Matsui et al.
patent: 6053008 (2000-04-01), Arman et al.
patent: 2751060 (1998-01-01), None
Acharya Arun
Arman Bayram
Bonaquist Dante Patrick
Gottzmann Christian Friedrich
Royal John Henri
Doerrler William
Ktorides Stanley
Praxair Technology Inc.
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