US2737784A - Apparatus for obtaining liquid oxygen - Google Patents

Description

March 13, 1956 R. BECKER ET AL APPARATUS FOR OBTAINING LIQUID OXYGEN Filed Nov. 9, 1954 United States Patent Ofiice APPARATUS FOR OBTAINING LIQUID OXYGEN Rudolf Becker, Munich-Solln, and Wilhelm Hartmann,

Pullach, near Munich, Germany, assignors to' Gesellschaft fiir Lindes Eismaschinen Aktiengesellschaft, Hollriegelskreuth, near Munich, Germany Application November 9, 1954, Serial No. 467,816 Claims priority, application Germany December 24, 1953 3 Claims. (Cl. 62-123) The present invention relates to an apparatus for obtaining liquid oxygen.

In installations for obtaining liquid oxygen from air,

the cold loss occurring with the removal of oxygen in liquid form according to the former state of the art is compensated in that the air to be decomposed is supplied at high pressure and the cold output obtained in the ex- Pflllsion of the air is used to proceed from the fact that the cold losses are particularly slight if the total quantity of gas to be treated is small. However, it is necessary according to this method to employ relatively expensive counter-current heat exchangers, since, at high pressures, regenerators providing a better exchange cannot be used practically, owing to excessively high gas losses. It is an object of the present invention to provide an apparatus to obtain liquid oxygen by the rectification of compressed air liquefied at low temperatures, comprising a turbo-compressor to compress air to a pressure of between 3 and atmospheres excess pressure, two periodically changed-over regenerators connected at their upper end portions to the turbo-compressor, a separating column to decompose the cold air supply thereto mainly into oxygen and nitrogen, a first and second heatexchanger connected successively in series between the regenerators at the lower end portions thereof and the separating column at the upper end portion thereof, the combination of a third heat-exchanger and an expansion turbine connected successively in series between, the regenerators also at the lower end portions thereof and the separating column at a location intermediate the ends thereof, a separator for liquid oxygen'connected, at its upper end portion to the lower end portions of the regenerators and at its. lower end portion to the upper end portion of the separating column through the second heat-exchanger, and a fourth and fifth heat-exchanger located within the regenerators and connected at the top ends thereof successively through the third heat-exchanger, the bottom of the separating column and the second heatexchanger to the top of the separating column, and, at the lower end portions thereof, through the first heatexchanger to the upper end-portion of the liquid oxygen separator.

It is also an object of the present invention to provide a process for obtaining liquid oxygen by the rectification of compressed air liquefied at low temperatures, comprising the steps of succesively compressing the air to a non-uniform pressure of between 3 and 15 atmospheres excess pressure, cooling the compressed air in regenerative heat-exchange with decomposition products separated therefrom, dividing the cold, compressed air into a major and a minor fraction, partially warming the major fraction in heat-exchange with the previously warmed minor fraction, expanding the said major fraction to produce useful work, separating the expanded air mainly into oxygen and nitrogen, partially liquefying the minor fraction partly by cooling in heat-exchange with the cold, essentially nitrogen-containing gaseous mixture and partly by successive warming in parallel- 2,737,784 a Patented Mar.'13, 1955 current heat-exchange with a warm, compressed air before the division thereof into a major and a minor fraction, and in counter-current heat-exchange with the major fraction before the expansion thereof, cooling in heatexchange with liquid oxygen and with a cold, essentially nitrogen-containing gaseous mixture, separating the resulting liquid air mainly into oxygen and nitrogen, and supplying cold, essentially nitrogen-containing gaseous mixture from the air separation to cool and partially to liquefy said minor air fraction and to cool the warm, compressed air in regenerative heat-exchange.

This method of operation affords substantial advantagcs, for, at low pressure, shaking regenerators can be used, which enable particularly eflicient heat-exchange to be obtained, since they operate with remarkably small temperature differences between the entering and issuing media undergoing the heat-exchange operation. By correctly dimensioning the regenerators and by correctly adjusting the gas quantities which are exchanging heat, it is possible to ensure that, at the warm end of the regenerators, the mean temperature of the entering air is only approximately one degree or less higher than the mean temperature of the issuing nitrogen. Thus, the cold losses through incomplete heat-exchange are correspondingly small and it is no longer a decisive matter to keep to a minimum the quantity of air passed through the apparatus per unit of liquefied oxygen produced. This also permits a simpler construction and maintenance. The use of regenerators also solves the problems of water and carbon dioxide separation in a very simple way.

The energy required for an installation operating according to this process is approximately 10% greater than for an installation in which high-pressure is allowed to expand. However, the simpler construction of the apparatus and the simpler attention required, together with the possibility of going over to larger units (without the necessity of subdividing the compressor equipment into a plurality of units) and other advantages indicated hereinafter are more than sufiicient to balance the somewhat higher energy requirement. There are also other factors which make the use of the above-described process advantageous. In particular, the fact that, with the earlier installations, for a relatively high output it was necessary to increase appropriately the number of piston compressors providing the higher pressure. (High pressure compressors are normally built only up to outputs of approximately 1,000 m. /h.) But this not only requires space and buildings but also leads to an'increased outlay in attention and maintenance. In some circumstances, the interruptions in operation owing to trouble in the running of the plant can be a heavier item than repairs and additional running costs. In addition, turbo-compressors and turbines exhibit an improved degree of efficiency with increased output, in contrast to piston compressors, whose degree of efiiciency does not rise with increased size. It should also be borne in mind that turbo-machines (rotary compressors and, more particularly, expansion turbines) have just recently been so improved that their degree of efficiency, e. g. for expansion turbines, has risen from 70% to over This means that the energy differences will be even less than before, or will disappear completely.

In view of the above, it is obvious that the present process is substantially more eflicient than the known processes.

A particular advantage is that the liquid oxygen obtained is absolutely oil-free, since the air to be decomposed does not come into contact in the turbo-compres sors and turbines with lubricated surfaces.

For a better understanding of the invention and to shown how the same is to be carried into effect, reference will now be made to the accompanying drawing, in which:

An apparatus and process for obtaining liquid oxygen from air are illustrated schematically by a flow diagram.

The whole of the air to be treated is compressed to a pressure of approximately 6 atmospheres absolute in a turbo-compressor 1, intensively cooled by one of two regenerators 3, 4 (3 in the case shown), partially warmed in a first heat-exchanger 5 in heat-exchange with warmer air, allowed to expand and produce work in a turbine 6 and supplied to a separating column 7. A portion of the air intensively cooled in the regenerator 3 is branched off at 8, passed through a separator 9, and a second heat-exchanger 19, from which condensate can flow back to the separator 9, and partially reheated in a third and fourth heat- exchanger 10 and 11 within the regenerators 3 and 4, which are expediently filled with loose material. It is then led through the first heat-exchanger 5, liquefied by heat-exchange with a bath of liquid oxygen in a liquefier 12 at the foot of the separating column 7, led through a fifth exchanger 18 and, after combination (at 13) with ether liquid, air, delivered as wash liquid at the head of the column 7 (at 14). The valve 2 serves as a by-pass valve for a part of the air, which can be conveyed parallel to the exchangers 10, 11 and 5 for regulating the air pre-warming before the turbine.

The liquid air separated in the exchanger 19 and conveyed back or collected in the separator 9 is removed, cleaned by a filter 15 for the purpose of separating out impurities such as carbon dioxide and ice and, after being allowed to expand in a valve 17, is combined at 13 with the other liquid air from the liquefier 12, which is allowed to expand by means of the valve 16.

Nitrogen, which still contains approximately 10% of oxygen, is allowed to escape from the top of the column 7, brought into heat-exchange in the exchanger 18 with the liquid air which has been liquefied in the liquefier 12 and taken from the separator 9 and, after passing through the exchanger 19-where it liquefies further quantities of air-is conveyed out through the second of the two regenerators 3, 4 in the case shown and warmed in so doing. Oxygen which is produced in the separating column 7 is removed in the liquid state at 20.

-As usual, the regenerators 3, 4 are switched over at regular intervals, so that the air flows alternately through the regenerators 3 and 4 and the nitrogen alternately through the regenerators 4 and 3. The removal of part of the air after the regenerators, in order to heat it again in the exchangers 10 and 11, is chiefly carried out for the purpose of heating the main quantity of air before the expansion turbine 6 in order to increase its efiiciency and to prevent liquefaction therein. By this means, the branched-off part quantity of air, being removed after the regenerator, has the same purity from carbon dioxide and water as the non re-warmed quantity of air. The

4 tubular heat- exchangers 10 and 11 within the'regenerators can be dispensed with if the air used to heat the turbine air is branched off in a relatively warm region of the regenerators, and purified in a manner known per se by passage through one of two alternately operated adsorbers.

A valve 21 serves to regulate the quantity of air passing through the column.

We claim:

1. An apparatus to obtain liquid oxygen by the rectification of compressed air liquefied at low temperatures, comprising a turbo-compressor to compress air to a pressure of between 3 and 15 atmospheres excess pressure, two periodically changed-over regenerators connected at their upper end portions to the turbo-compressor, a separating column to decompose the cold air supply thereto mainly into oxygen and nitrogen, at first and second heatexchanger connected successively in series between the regenerators at the lower end portions thereof and the separating column at the upper end portion thereof, the combination of a third heat-exchanger and an expansion turbine connected successively in series between the regenerators also at the lower end portions thereof and the separating column at a location intermediate the ends thereof, a filter for liquid air connected at its upper end portion to the lower end portions of the regenerators and at its lower end portion to the upper end portion of the separating column through the second heat-exchanger, and a fourth and fifth heat-exchanger located within the regenerators and connected at the top ends thereof successively through the third heat-exchanger, the bottom of the separating column and the second heat-exchanger to the top of the separating column, and, at the lower end portions thereof, through the first heat-exchanger to the upper end-portion of the liquid oxygen separator.

2. An apparatus as claimed in claim 1, wherein a valve 21 is further provided connected between the conduit from the expansion turbine to the separating column and the conduit from the upper end portion of the separating column to the second heat-exchanger.

3. An apparatus as claimed in Claim 1, wherein there is further provided a filter for liquid oxygen connected between the lower end portion of the liquid oxygen separator and the upper end portion of the separating column.

References Cited in the file of this patent UNITED STATES PATENTS 2,619,810 Rice Dec. 2, 1952 2,650,481 Cooper Sept. 1, 1953 2,664,719 Rice Jan. 5, 1954 2,671,324 Trumpler Mar. 9, 1954

Claims (1)

1. AN APPARATUS TO OBTAIN LIQUID OXYGEN BY THE RECTIFICATION OF COMPRESSED AIR LIQUEFIED AT LOWER TEMPERATURES, COMPRISING A TURBO-COMPRESSOR TO COMPRESS AIR TO A PRESSURE OF BETWEEN 3 TO 15 ATMOSPHERES EXCESS PRESSURE, TWO PERIODICALLY CHANGED-OVER REGENERATORS CONNECTED AT THEIR UPPER END PORTIONS TO THE TURBO-COMPRESSOR, A SEPARATING COLUMN TO DECOMPOSE THE COLD AIR SUPPLY THERETO MAINLY INTO OXYGEN AND NITROGEN, A FIRST AND SECOND HEATEXCHANGER CONNECTED SUCCESSIVELY IN SERIES BETWEEN THE REGENERATORS AT THE LOWER END PORTIONS THEREOF AND THE SEPARATING COLUMN AT THE UPPER END PORTION THEREOF, THE COMBINATION OF A THIRD HEAT-EXCHANGER AND AN EXPANSION TURBINE CONNECTED SUCCESSIVELY IN SERIES BETWEEN THE REGENERATORS ALSO AT THE LOWER END PORTIONS THEREOF AND THE SEPARATING COLUMN AT A LOCATION INTERMEDIATE THE ENDS THEREOF, A FILTER FOR LIQUID AIR CONNECTED AT ITS UPPER END PORTION TO THE LOWER END PORTIONS OF THE REGENERATORS AND AT ITS LOWER END PORTION TO THE UPPER END PORITON OF THE SEPARATING COLUMN THROUGH THE SECOND HEAT-EXCHANGER, AND A FOURTH AND FIFTH HEAT-EXCHANGER LOCATED WITHIN THE REGENERATORS AND CONNECTED AT THE TOP ENDS THEREOF SUCCESSIVELY THROUGH THE THIRD HEAT-EXCHANGER, THE BOTTOM OF THE SEPARATING COLUMN AND THE SECOND HEAT-EXCHANGER TO THE TOP OF THE SEPARATING COLUMN AND, AT THE LOWER END PORTIONS THEREOF, THROUGH THE FIRST HEAT-EXCHANGE TO THE UPPER END-PORTION OF THE LIQUID OXYGEN SEPARATOR.

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