This invention relates generally to cryogenic rectification of air and, more particularly, to the cryogenic rectification of air for the production of neon.
Neon is a valuable inert gas found in low concentrations of about 18 parts per million (ppm) in air. Neon is useful as a filling gas in lamps and luminous sign tubes. In addition, neon is used in airplane beacons because neon light can penetrate fog where other lights cannot. Systems which can improve the recovery of neon would be highly desirable.
One aspect of the invention is:
A method for producing crude neon comprising:
(A) separating feed air by cryogenic rectification in a higher pressure column to produce neon-containing shelf vapor, and condensing at least a portion of the neon-containing shelf vapor to produce neon-containing liquid;
(B) subcooling the neon-containing liquid, passing the resulting fluid into a separator, and separating the fluid within the separator into neon-containing vapor and remaining liquid; and
(C) passing remaining liquid from the separator into a lower pressure column, and recovering neon-containing vapor as product crude neon.
Another aspect of the invention is:
Apparatus for producing crude neon comprising:
(A) a higher pressure column, a lower pressure column having a reboiler/condenser, and means for passing feed air into the higher pressure column;
(B) a subcooler, a separator, means for passing neon-containing fluid from the higher pressure column to the reboiler/condenser, from the reboiler/condenser to the subcooler, and from the subcooler to the separator; and
(C) means for passing liquid from the separator to the lower pressure column, and means for recovering vapor from the separator as product crude neon.
As used herein the term “feed air” means a mixture comprising primarily oxygen and nitrogen, and also containing neon, such as ambient air.
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.
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 terms “reboiler” and “reboiler/condenser” mean a heat exchange device that generates column or separator vapor from liquid.
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 “crude neon” means a fluid having a neon concentration within the range of from 400 ppm to 10,000 ppm.
As used herein the term “tray” means a vapor-liquid contacting stage.
As used herein the term “phase separator” means a vessel wherein incoming 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.
The invention will be described in detail with reference to the Drawings. Referring now to
Within higher pressure column 20 the feed air is separated by cryogenic rectification into oxygen-enriched liquid and nitrogen-enriched vapor. Oxygen-enriched liquid is withdrawn from the lower portion of column 20 in stream 3, cooled by passage through heat exchanger 17 to form stream 18, and passed through valve 19 and into lower pressure column 21 as stream 22. Nitrogen-enriched vapor or shelf vapor, containing from 30 to 70 ppm neon, is withdrawn from the upper portion of higher pressure column 20 in stream 23 and passed into reboiler/condenser 24 wherein it is condensed by indirect heat exchange with lower pressure column bottom liquid. This neon-containing liquid is withdrawn from reboiler/condenser 24 in stream 25. A portion 26 of stream 25 is passed back into the upper portion of higher pressure column 20 as reflux. Another portion of the neon-containing fluid from reboiler/condenser 24 is passed in stream 27 to subcooler 28.
Within subcooler 28 the neon-containing liquid is subcooled by indirect heat exchange with nitrogen streams from the lower pressure column, and the resulting fluid is withdrawn from subcooler 28 as subcooled neon-containing liquid in stream 2. Stream 2 is passed through valve 29 and then into separator 30 in stream 31.
In the embodiment of the invention illustrated in
Lower pressure column 21 is operating at a pressure less than that of higher pressure column 20 and generally within the range of from 16 to 75 psia. Within lower pressure column 21 the various fluids passed into that column are separated by cryogenic rectification into oxygen-rich liquid and nitrogen-rich vapor. Oxygen-rich liquid is withdrawn from the lower portion of column 21 in stream 36 for recovery as product oxygen having an oxygen concentration of at least 90 mole percent. If desired, as shown in
The numerals in the embodiment of the invention illustrated in
The numerals in the embodiment of the invention illustrated in
A computer simulation of the embodiment of the invention illustrated in
Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims.