US3531942A

US3531942A - Cryogenic separation of fluids associated with a power cycle

Info

Publication number: US3531942A
Application number: US704824A
Authority: US
Inventors: James K La Fleur
Original assignee: JAMES K LA FLEUR
Current assignee: JAMES K LA FLEUR
Priority date: 1968-02-12
Filing date: 1968-02-12
Publication date: 1970-10-06
Anticipated expiration: 1987-10-06

Description

Oct. 6,1970 K, LA FLEUR 3,531,942

CRYOGENIC SEPARATION OF FLUIDS ASSOCIATED WITH A POWER CYCLE Filed Feb. 12, 1968 2 Sheets-Sheet 1 I 1 1 ll? GAS IN 42 l 4 4| "2' y B 4 l AFTEQCOOLEE COMPQ. 37

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CRYOGENIC SEPARATION OF FLUIDS ASSOCIATED WITH A POWER CYCLE Oct. 6, 1970 Filed Feb. 12, 1968 2 Sheets-Sheet 2 AT EXPANDEE AT HEATER AT EEGEN. 3

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ENTQOPV INVENTOR. JQMES K. 110F050? United States Patent 3,531,942 CRYOGENIC SEPARATION OF FLUIDS ASSOCI- ATED WITH A POWER CYCLE James K. La Fleur, 6342 Mulholland Hwy., Los Angeles, Calif. 90028 Filed Feb. 12, 1968, Ser. No. 704,824 Int. Cl. F25j 3/06; F01k 3/18 US. Cl. 6223 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The Linde dual-pressure liquefaction cycle is wellknown. It consists of compressing and cooling a gas to the point where a subsequent Joule-Thomson expansion causes partial liquefaction. This first expansion is to an intermediate pressure somewhere between the high pressure of the system and the compressor-input low pressure, which is usually atmospheric. From a phase separator the portion which is still gas is returned to an intermediate pressure point on the compressor and recycled. The liquid phase is then further Joule-Thomson expanded to a still lower temperature, down to the low pressure of the system (atmospheric). It is again phase separated. The liquid phase is removed as useful product, i.e., liquefied gas, such as air. The gas portion or phase is returned to the low-pressure input of the compressor.

Employment of the intermediate pressure gas by reinjecting it into the compression cycle is relatively inefficient, and it is the purpose of this invention to markedly increase the basic efficiently of this cycle.

SUMMARY OF THE INVENTION In accordance with the present invention, the basic Linde dual-pressure system is modified by taking the intermediate pressure gas, after separation and after heat exchange has raised its temperature substantially to ambient, and significantly increasing its temperature by adding heat from an external heat source not associated with the heat exchange step-s implicit in the system itself. The intermediate pressure gas may, of course, also be subjected to heat exchange, as in the basic Linde system. After this external heating, the gas is ready for very efficient use in a heat expansion engine, in which its pressure is lowered to the low pressure of the system, e.g., atmospheric. It may be then heat exchanged with the gas incoming to the expansion motor, and returned to the low pressure input of the compressor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1, consisting of FIGS. 1A and 1B, illustrates a first form of the present invention, involving liquefac "ice FIG. 1B is a temperature-entropy diagram illustrating the states and conditions through which the substance passes in its transit through the cycle of the present invention.

FIGS. 2A and 2B are corresponding figures for the non-liquefaction form of the present refrigeration cycle.

Referring to FIG. 1A, 11 designates a compressor means powered in any suitable manner, represented, for example, by the drive shaft 12. Input gas is fed to the compressor means 11 at 13. The gas may be a single gas or a mixture of gases, such as air. The gas is compressed from a relatively low pressure at 13, typically, but not necessarily, atmospheric, to a relatively high pressure at the output 14 and then cooled in an aftercooler 16. The aftercooler is typically an ambient heat exchanger in which the rise in temperature effected by the compression in 11 is dissipated to the air or through some other ambient medium, such as a water cooling system. After being cooled as close to ambient temperature as is economically feasible, the compressed gas is applied at 17 to a heat exchanger 18, where it is further cooled and delivered at 19 to a throttle valve 21. The gas is Joule- Thomson expanded across the valve 21, and in so doing, its temperature is lowered to the liquefaction temperature. Substance, now part gas and part liquid, is delivered at 22 to a separator 23.

The liquid phase settles to the bottom and flows out a lower outlet 24. The gaseous phase rises to the top of the separator 23 and flows out an upper outlet 26. The pressure in the separator 23, i.e., at the throttle output 22, is at an intermediate point, substantially below the high pressure at 14, but still substantially above the low pressure at 13.

The liquid emerging at 24 is further throttled, through a throttle valve 27, from the intermediate pressure down substantially to the low pressure at 28. It is then applied to a second liquid/ gas separator 29. The Joule-Thomson expansion across 27 lowers the temperature still further. From the second separator 29 liquefied substance is taken out at 31, this being the end poduct of the system. The gaseous fraction of the substance existing in separator 29 is taken out at the top outlet 32 and applied through the heat exchanger 18 to return to the input 13 of the compressor 11. In passing through the heat exchanger 18, this low-pressure, very cold gas receives heat from the high-pressure gas flowing from 17 to 19, and thus serves to pre-cool the high pressure gas before it is applied to the throttle valve 21. The cold intermediatepressure gas at 26 is also applied to the heat exchanger 18 and it also receives heat from the high-pressure gas, thus also cooling it.

The apparatus and thermodynamic cycle described up to this point is essentialy the prior art Linde dual-pressure liquefaction system. In the Linde system, the intermediate-pressure gas from point 33 is recompressed in the compressor 11, "being introduced at an intermediate pressnre point in the compressor.

In accordance with the present invention, however, the intermediate pressure gas from 33 is applied to an expansion engine 34 after being heated substantially, by passage through an external heater 36, which represents a source of heat independent of the heat exchanges which take place between various states of the substance as it flows through the system. If desired, the gas, prior to subjection to the heat source 36, may be heated in a heat exchanger 37.

From the output 38 of the heater 36, the gas is expanded in the expansion engine 34, which derives or extracts work therefrom, at the same time lowering the pressure andtemperature. From the output 39 of the engine 34, the gas, still considerably warmer than the gas at 33, gives up heat in the heat exchanger 37. It may be further cooled in an aftercooler 41 by giving up heat to an ambient medium, such as air.

In the expansion engine 34 the gas is expanded substantially to the low pressure at 13; so from the aftercooler 41 it is ready to rejoin the low-pressure gas taken from the separator 29, and thence be applied at 13 through the input to the compressor 11. Since substance was extracted from the system 31 in the form of liquid, it must be made up a 42 by a constant supply of makeup gas which joins the re-cycled gas at the input It is usually found desirable to maintain the pressure at 13 substantially at atmospheric, although it may be either above or below atmospheric. If below atmospheric, however, there is involved operations with various types of vacuum equipment which is costly and cumbersome. If above atmospheric, the maximum use is not made of the gas, either in expansion across the valve 27 or in the engine 34. However, in certain circumstances, the makeup gas 42 comes in at a pressure above atmospheric, and under these circumstances this determines the input pressure at 13. Alternatively if the makeup gas is received at a pressure significantly above atmospheric, the system may be designed so that this pressure prevails at 33. In this case, the makeup gas is injected at 33, and 13 is maintained at substantially atmospheric. The optimum high pressure at 17/ 19 will depend upon the gas being used, but in general it is the pressure at which the isenthalpic slope is zero. The intermediate pressure at 26/33 is preferably somewhere between the low pressure at 13 (atmospheric) and the critical pressure of the gas.

The temperature of the gas at 19' must be below the Joule-Thomson inversion temperature of the gas. For some substances and under certain conditions, this may require auxiliary cooling, which may be injected in the form of auxiliary refrigeration at 43. For certain applications, this also increases the cycle efficiency. Alternatively or additionally, a portion of the gas flowing through the heat exchanger 18 may be split out at 44 and applied to an expansion engine 46, the output of which is at the low pressure of 13 and rejoins the expanded gas at 47. This is essentially the known Claude cycle and is used to provide further cooling in the heat exchanger 18 in order to lower the gas at 19 to a sufficiently low temperature. Alternatively, the input 44 to engine 46 may be taken from line 26/33, rather than line 17/19.

Mechanical power output from the expansion engine 34, represented by the shaft 48, may be directly connected to the compressor input shaft 12, or may generate power for use elsewhere. The same may be said for power output from expansion engine 46.

The system may be designed so that the work output equals the work input required by the compressor 11, in which case all of the energy injected into the system is done so at the heater 36, and external power is not required except to initially drive the compressor 11 up to steady-state operation. Alternatively, the power output may even be designed to exceed the power requirements of 11, in which case the power may be used elsewhere, or the system may be designed so that the power output from the engine 34 '(and 46 if employed) is less than that required by the compressor 11, in which case external power at 12 is constantly required. The design of the system in this regard is dependent simply upon the economy and availabiliy of power required at 11 vis a vis fuel required at 36.

The thermodynamic cycle to which the substance is subjected is illustrated in the temperature/entropy diagram of FIG. 1B. In this figure the reference points on the diagram correspond to the similarly numerated points in the apparatus of FIG. 1A.

The substance in gaseous form is injected into the compressor 11 at point 13 and at temperature T1 which is customarily, although not necessarily, the ambient temperature. As noted hereinbefore, the pressure represented by the line P1 is the low pressure of the system and is preferably, although not necessarily, atmospheric. The gas is compressed to the high pressure represented by the line P2. The aggregate effect of the compressor 11 and aftercooler 16 is to make the compression essentially iso thermal, as shown by the line 11 in FIG. 1B.

From the point 17, the gas is cooled at substantially constant pressure P2 in the heat exchanger 18 to the point 19. A Joule-Thomson expansion is effected at 21 to bring the substance to the point 22 within the two-phase locus 51. The liquid phase is subjected to further Joule- Thomson expansion at 27, from the point 24 to 28. The liquid phase, now still further cooled, is removed at 31. The separator 29, operating at pressure P1, now delivers the gas phase at 32 to the heat exchanger 18 where it takes on heat from the gas at pressure P2 and rises to the temperature T1, as shown at point 13. The substance in separator 23 existing at the intermediate pressure P3 is separated in gaseous phase at the point 2.6, also taking on heat in 18, to rise to the temperature T1.

The cycle of FIG. 1B described up to this point, as noted, is substantially the Linde dual-pressure system.

In accordance with the present invention, the intermediate pressure gaS at P3, instead of being merely raised to ambient temperature T1, is subjected to the heat of the heat exchanger 37 and to further heating in the external heater 36; so it is raised to temperature T2 at point 38. It is then expanded in the engine 34, which extracts useful work, drops the temperature to a point intermediate T1 and T2, and lowers the pressure to the lowpressure point P1, as shown at 39. From 39 to 13, the gas gives up heat in the heat exchanger 37 and aftercooler 41, and returns to the point 13 to be re-cycled.

As noted hereinbefore, substance extracted at 31 in liquid form is made up at 42 in gaseous phase.

Because of the significant increase in gas temperature from T1 to T2, the work extracted at 34, unlike a typical Claude cycle, represents a considerable portion of the work or power required to operate the system.

The essential attributes of the system described in FIGS. 1A and 1B are as follows:

There is an initial J oule-Thomson expansion from some optimum pressure P2 to an intermediate pressure P3, between the low pressure P1 (atmospheric) and the critical pressure of the gas; followed by division of the substance. One portion (in FIG. 1B, liquid) is further Joule- Thomson expanded to the low pressure P1, while the other portion is warmed by heat exchange with the high-pressure gas at P2 and then is further externally heated to the high-temperature T2, at which its employment in an expansion engine 34 becomes very efficient. Expansion in the engine reduces the gas substantially to the low-pressure P1, and it rejoins the first portion to be re-cycled into the compressor.

The system described is applicable not only to the liquefaction of cryogenic gases, but may be employed generally in any three-pressure refrigeration system, even though no liquefaction takes place. This is illustrated in FIG. 2A, which is the counterpart of FIG. 1A, except that the gas is not necessarily liquefied. FIG. 2A il1ustrates only those portions of the system which differ from FIG. 1A, the correlation between the two figures readily being evident.

In FIG. 2A, the high-pressure gas is throttled, as in FIG. 1A, through the restriction or valve 21. From 21, the gas enters any suitable divider, shown schematically at 23, where a portion of the gas, now at intermediate pressure P3, is taken off at 26 and applied to the heat exchanger 18, the same as in FIG. 1. The other portion of the substance, also in gaseous phase, is removed at 24 and further throttled at 27, down to the low-pressure P1 existing at 28. These two steps, while not liquefying the gas, each successively reduce its temperature. It is then used to refrigerate any medium which is to be cooled, by being applied to the heat exchanger 29'. The

medium to be cooled flows in at 61 and out at 62. The gas then returns at 32, as in the case of FIG. 1, through the heat exchanger 18 and thence back to the low-pressure input 13 of the compressor 11.

The dynamic cycle to which the gas is subjected is shown in FIG. 2B. The correspondence between FIG. 2B and FIG. 13 will be readily evident. The gas is cooled to the point 19, then throttled in 21 before being divided at 23' into a portion of intermediate pressure P3, and another portion, which is throttled from pressure P3 down to pressure P1 in the expansion valve or throttle 27. Thereafter the two portions of the substance at P3 and P1, respectively, are heated and treated the same as in the case of FIG. 1B.

Whereas the present invention has been shown and described herein in what is conceived to be the best mode contemplated, it is recognized that departures may be made therefrom within the scope of the invention which is, therefore, not to be limited to the details disclosed herein, but is to be afforded the full scope of the invention as hereinafter claimed.

What is claimed is:

1. Process for the liquefaction of a substance from gaseous to liquid phase, comprising:

compressing the substance in gaseous phase from substantially atmospheric pressure to a relatively high pressure,

cooling said substance to below its inversion temperature,

Joule-Thomson expanding said substance to an intermediate pressure to liquefy a first portion thereof, a, second portion remaining in gaseous phase,

Joule-Thomson expanding said first portion to substantially atmospheric temperature, a fraction of References Cited UNITED STATES PATENTS 1,571,461 2/1926 Van Nuys 6239 2,520,626 8/1950 De Baufre 6288 2,952,984 9/1960 Marshall 6239 2,956,410 10/1960 Palazzo 6223 3,119,677 1/1964 Moon et a1. 6223 1,379,102 5/1921 Iefferies.

NORMAN YUDKOFF, Primary Examiner A. F. PURCELL, Assistant Examiner US. Cl. X.R.